Czochralski method fluoride crystal growth control method and control device

Abstract

The invention discloses a Czochralski method fluoride crystal growth control method and device, and the method comprises the following steps: S1, adding a fluorinating agent into a fluoride raw material, and drying to form a pretreated raw material; relates to the technical field of fluoride crystal growth. Seed crystals are heated at a first heating rate, the initial processing stress of the seed crystals is released firstly, and the thermal expansion difference between the surface layer and the core part of the seed crystals is constructed through the two-stage heating rate difference of segmented annealing; forming a fine grain strengthening layer on the surface of the seed crystal in a gas quenching manner of spraying inert gas to the surface of the seed crystal and maintaining the temperature difference between the surface of the seed crystal and the core part of the seed crystal, so that the surface of the seed crystal generates pressure stress and the core part of the seed crystal forms a uniform stress field; and the pretreated seed crystal with small axial stress gradient, low axial elongation and improved surface hardness is obtained after stepped cooling, so that the problems of high-temperature deformation, tensile failure and cracking of the seed crystal caused by concentrated internal stress or insufficient surface strength in the traditional process are solved.

Description

Technical Field

[0001] The present invention relates to the technical field of fluoride crystal growth, and in particular to a Czochralski fluoride crystal growth control method and a control device. Background Art

[0002] The Czochralski method is a technology for preparing single crystals by solidifying a melt. The seed crystal is immersed in the molten raw material, and the melt is directionally solidified and grown into a single crystal on the seed crystal through rotation and slow pulling. Fluoride crystals refer to ionic crystals or covalent crystals with fluoride as the main component.

[0003] Publication No. CN118374872A discloses a method for growing large-sized calcium fluoride crystals using a Czochralski method, and the resulting calcium fluoride crystals. The method comprises the following steps: a three-stage shouldering process: in the first shouldering process, the seed crystal is pulled upward at a rate of 3-5 mm / h until the crystal diameter reaches 50 mm, with the first shouldering length being 50-100 mm; in the second shouldering process, the seed crystal is pulled upward at a rate of 1-4 mm / h until the crystal diameter reaches 150 mm, with the second shouldering length being 30-60 mm; and in the third shouldering process, the seed crystal is pulled upward at a rate of 0.5-3 mm / h until the crystal diameter reaches 250-350 mm, with the third shouldering length being 20-40 mm. This process reduces seed crystal deformation and effectively prevents seed crystal breakage.

[0004] However, the above application still has the following problems: the above application only releases processing stress through a single temperature annealing treatment, but does not perform segmented regulation of the heating rate. The thermal expansion difference between the surface and the core of the seed crystal cannot be controlled, resulting in a large residual stress inside the seed crystal. When pulled at high temperature, it is easy to superimpose with the thermal stress to form a stress concentration area. The axial elongation of the seed crystal after pulling is still at a high risk of high axial elongation. Although the three-stage shoulder release accelerates heat dissipation by increasing the surface area of ​​the shoulder, it does not change the stress state of the seed crystal surface. The surface is still in a tensile stress environment and cannot withstand external mechanical shocks, which makes the seed crystal prone to high-temperature deformation, breakage and cracking. Summary of the Invention

[0005] In order to solve the technical problems existing in the background technology, the present invention proposes a Czochralski fluoride crystal growth control method and control device.

[0006] The present invention provides a method for controlling the growth of fluoride crystals using a Czochralski method, comprising the following steps: S1. Adding a fluorinating agent to a fluoride raw material and drying the raw material to form a pretreated raw material, and subjecting the seed crystal to a coordinated treatment of segmented annealing and surface gas quenching to form a pretreated seed crystal; S2, placing the pretreated raw materials into a crucible and heating them to above the melting point to form a melt, and starting a circumferential pulse pre-disturbance uniform flow mechanism before the pretreated seed crystal is immersed in the melt; S3, lowering the pretreated seed crystal to 5-10 mm from the melt surface at a rate of 0.5-1.5 mm / min, holding for 3-5 minutes to allow the pretreated seed crystal to reach thermal equilibrium with the thermal field, and then immersing the pretreated seed crystal into the melt at an immersion rate of 0.1-0.3 mm / min, forming a solid-liquid interface at the interface between the melt and the pretreated seed crystal, and then initially growing the pretreated seed crystal at a pulling rate of 1-5 mm / h to form a crystal; S4. Use the Czochralski method to grow the crystal to the desired size. After the crystal growth is completed, the crystal is cooled to room temperature at a rate of 5-10℃ / min along with the furnace to reduce thermal stress accumulation.

[0007] Preferably, in S1, a fluorinating agent is added to the fluoride raw material and dried as follows: Add 2-5wt% PbF2 as a fluorinating agent to the fluoride raw material, heat it to 350℃ at a heating rate of 10-35℃ / h, and keep it at 350℃ for 2 hours to remove moisture.

[0008] Preferably, in S1, the seed crystal is subjected to a coordinated treatment of segmented annealing and surface gas quenching to form a pretreated seed crystal, as follows: The seed crystal is heated to 600-800°C at a first heating rate and kept at this temperature for 1-2 hours in order to release the processing stress accumulated in the seed crystal during the previous processing. The seed crystal is heated to 900-1200°C at a second heating rate, which is lower than the first heating rate. At the same time, an inert gas is sprayed onto the surface of the seed crystal to form a fine-grained strengthening layer on the surface of the seed crystal, thereby increasing the surface hardness of the seed crystal. The temperature difference between the surface of the seed crystal and the core of the seed crystal is maintained at 50-100°C. A three-stage step cooling method is used. After the third stage of cooling, the seed crystal is naturally cooled with the furnace to room temperature to obtain a pretreated seed crystal.

[0009] Preferably, in S1, when the inert gas is sprayed onto the surface of the seed crystal, the distance between the nozzle and the surface of the seed crystal is 10-15 mm, the gas spray direction of the nozzle forms an angle of 45° with the axis of the seed crystal, the inert gas spray pressure at the nozzle outlet is 0.2-0.3 MPa, the inert gas spray flow rate of the nozzle is 5-10 L / min, the purity of the inert gas is ≥99.99%, and the inert gas includes argon or nitrogen; The axis of the seed crystal is the central axis along the direction of crystal growth; The 45° angle between the gas injection direction of the nozzle and the axis of the seed crystal can ensure that the inert gas evenly covers the surface of the seed crystal and avoid local overcooling or airflow dead corners caused by vertical injection.

[0010] Preferably, in S1, when three-stage step cooling is adopted, the three-stage step cooling includes first-stage cooling, second-stage cooling, and third-stage cooling, wherein, during the first-stage cooling, the temperature of the seed crystal drops by 200-300°C and is kept warm for 30 minutes, during the second-stage cooling, the temperature of the seed crystal drops by 200-300°C and is kept warm for 30 minutes, during the third-stage cooling, the temperature of the seed crystal drops by 200-300°C, and after the third-stage cooling, the seed crystal cools naturally with the furnace to room temperature.

[0011] Preferably, in S2, the circumferential pulse pre-disturbance uniform flow mechanism includes: At least X groups of pulse heating units are evenly distributed around the periphery of the crucible, and the X groups of pulse heating units periodically heat the crucible wall at a frequency of 0.1-0.5 Hz and a basic power amplitude of 20%-50%; X is a positive integer, and X ≥ 3; The purpose of applying periodic temperature disturbance is to pre-establish a controllable temperature disturbance field in the melt to avoid stress concentration caused by thermal field mutation when the pre-treated seed crystal is immersed; Rotating the crucible at a speed of 5-10 revolutions per minute will stir the melt, making the temperature and composition of the melt uniform, laying the foundation for the stable formation of the solid-liquid interface when the pretreated seed crystal is immersed in the melt.

[0012] Preferably, in the circumferential pulse pre-disturbance uniform flow mechanism of S2, each group of pulse heating units is equipped with an independent current controller, and the phase difference of the pulse currents of adjacent units is The purpose is to use pseudo-random phase difference between the pulse signals of adjacent pulse heating units to form an asymmetric periodic temperature disturbance.

[0013] Preferably, in S4, when the crystal is grown to a desired size by the Czochralski method, a steady magnetic field perpendicular to the growth direction of the crystal is applied, and the magnetic induction intensity of the steady magnetic field is 0.1-0.3 Tesla.

[0014] A Czochralski fluoride crystal growth control device, comprising: Raw material and seed crystal pretreatment module: adding fluorinating agent to fluoride raw material and drying to form pretreated raw material, heating seed crystal to 600-800℃ at a first heating rate and keeping the temperature for 1-2 hours; The seed crystal is heated to 900-1200°C at a second heating rate, which is lower than the first heating rate; at the same time, an inert gas is sprayed onto the surface of the seed crystal to form a fine-grained strengthening layer on the surface of the seed crystal, and the temperature difference between the surface of the seed crystal and the core of the seed crystal is maintained at 50-100°C; A three-step cooling method is used, and after the third step cooling, the seed crystal is naturally cooled with the furnace to room temperature to obtain a pretreated seed crystal; The melt forming module comprises: loading the pretreated raw material into a crucible and heating to above the melting point to form a melt, and starting a circumferential pulse pre-disturbance flow uniformization mechanism before the pretreated seed crystal is immersed in the melt; The circumferential pulse pre-disturbance flow uniformization mechanism comprises: At least X groups of pulse heating units are uniformly distributed in the circumferential direction of the outer periphery of the crucible, and the X groups of pulse heating units periodically heat the crucible wall at a frequency of 0.1-0.5 Hz and an amplitude of 20%-50% of the base power; X is a positive integer, and X is greater than or equal to 3; The crucible is rotated at a speed of 5-10 revolutions per minute; Each group of pulse heating units is equipped with an independent current controller, and the phase difference of the pulse current of adjacent units is randomly changed in the range of 0-90 degrees; The crystal forming module comprises: lowering the pretreated seed crystal to a position 5-10 mm above the surface of the melt at a speed of 0.5-1.5 mm / min, maintaining for 3-5 minutes, and then immersing the pretreated seed crystal into the melt at an immersion speed of 0.1-0.3 mm / min, so that the interface between the melt and the pretreated seed crystal forms a solid-liquid interface, and then the pretreated seed crystal is preliminarily grown by a pulling speed of 1-5 mm / h to form a crystal; The crystal growth module comprises: growing the crystal to a desired size by the pulling method, and when the crystal is grown to a desired size by the pulling method, a steady magnetic field perpendicular to the growth direction of the crystal is applied, the magnetic induction intensity of the steady magnetic field is 0.1-0.3 Tesla, and after the crystal growth is completed, the crystal is cooled to room temperature at a rate of 5-10 ℃ / min.

[0015] In the present application, the pulling method fluoride crystal growth control method and control device have the following beneficial technical effects: 1. The seed crystal is heated at a first heating rate to release the initial processing stress of the seed crystal, the two-stage heating rate difference of the segmented annealing is used to construct the thermal expansion difference between the surface layer and the core of the seed crystal, and the inert gas jet quenching method is used to form a fine-grained strengthening layer on the surface of the seed crystal and maintain the temperature difference between the surface of the seed crystal and the core of the seed crystal, so that the surface of the seed crystal produces compressive stress and the core of the seed crystal forms a uniform stress field, and after stepwise cooling, a pretreated seed crystal with small axial stress gradient, low axial elongation and improved surface hardness is obtained, which greatly alleviates the problems of high-temperature deformation, breakage and cracking of the seed crystal caused by internal stress concentration or insufficient surface strength in the traditional process, and provides a seed crystal with stable stress state for subsequent crystal growth.

[0016] ​2. By setting the circumferential pulse pre-disturbance uniform flow mechanism, at least 3 groups of pulse heating units are uniformly distributed circumferentially outside the crucible, and the crucible wall is periodically heated at a frequency of 0.1-0.5 Hz and a basic power amplitude of 20%-50%, to pre-establish a temperature disturbance field in the melt. Compared with the static temperature control mode of the traditional temperature control system, the circumferential pulse pre-disturbance uniform flow mechanism can actively offset the random temperature fluctuations on the surface of the melt, reduce the amplitude of the temperature gradient fluctuations on the surface of the melt, and improve the stability of the solid-liquid interface temperature, thereby greatly alleviating the problem of periodic changes in crystal diameter caused by temperature gradient fluctuations on the surface of the melt, and reducing the frequency of periodic changes in crystal diameter; the crucible is rotated at a speed of 5-10 revolutions per minute, and the periodic disturbance of the pulse heating unit forms a rotating stirring and temperature disturbance composite uniform flow effect. On the one hand, the rotation of the crucible can force the temperature and composition distribution of the melt to be uniform; on the other hand, the temperature disturbance shell offsets the nonlinear influence of natural convection, so that the uniformity of the melt flow rate is improved, especially when growing large-size crystals, the amplitude of the convection intensity fluctuations can be reduced, and the problem of asymmetric vortex caused by rotation deviation in the traditional process can be solved.

[0017] 3. By equipping each group of pulse heating units with an independent current controller, the phase difference of the pulse current of adjacent units is randomly changed to form an asymmetric periodic temperature disturbance, thereby suppressing the local stress concentration caused by the sudden change of the heat field when the pretreated seed crystal is immersed in the melt, reducing the amplitude of the temperature gradient fluctuations at the solid-liquid interface, and improving the stability of the solid-liquid interface at the initial stage of crystal growth.

[0018] 4. When growing the crystal to the required size by the Czochralski method, a steady magnetic field perpendicular to the crystal growth direction is applied during the crystal growth stage, which has a value of 0.1-0.3 Tesla. The Lorentz force damping effect of the electromagnetic force on the conductive fluid in the melt effectively suppresses the strong convection vortex caused by natural convection and stirring, reduces the maximum flow rate of the melt, especially when growing large-size crystals, the diameter control error caused by convection lag can be reduced, thereby improving the accuracy of crystal size control. The steady magnetic field cooperates with the circumferential pulse pre-disturbance uniform flow mechanism to further reduce the amplitude of the solid-liquid interface fluctuations and the frequency of the periodic changes in the crystal diameter, thereby facilitating the increase of the pulling speed when growing the crystal to the required size by the Czochralski method. BRIEF DESCRIPTION OF DRAWINGS

[0019] Figure 1 A flowchart of a Czochralski method for controlling the growth of a fluoride crystal; Figure 2 A principle block diagram of a device for controlling the growth of a fluoride crystal by the Czochralski method. DETAILED DESCRIPTION

[0020] The following describes embodiments of the present invention in detail. Examples of the embodiments are shown in the accompanying drawings, wherein the same or similar symbols throughout represent the same or similar elements or elements having the same or similar functions. The embodiments described below with reference to the accompanying drawings are exemplary and are intended only to explain the present invention, and are not to be construed as limiting the present invention.

[0021] like Figure 1 A Czochralski method for controlling fluoride crystal growth is shown, comprising the following steps: S1. Adding a fluorinating agent to a fluoride raw material and drying the raw material to form a pretreated raw material, and subjecting the seed crystal to a coordinated treatment of segmented annealing and surface gas quenching to form a pretreated seed crystal; In an optional embodiment, in S1, a fluorinating agent is added to the fluoride raw material and dried as follows: Add 2-5wt% PbF2 as a fluorinating agent to the fluoride raw material, heat it to 350℃ at a heating rate of 10-35℃ / h, and keep it at 350℃ for 2 hours to remove moisture; 2-5wt% PbF2 means that the added mass of PbF2 accounts for 2%-5% of the total mass of the fluoride raw material; In an optional embodiment, in S1, the seed crystal is subjected to a coordinated treatment of segmented annealing and surface gas quenching to form a pretreated seed crystal, as follows: The seed crystal is heated to 600-800°C at a first heating rate and kept at this temperature for 1-2 hours in order to release the processing stress accumulated in the seed crystal during the previous processing. The seed crystal is heated to 900-1200°C at a second heating rate, which is lower than the first heating rate. At the same time, an inert gas is sprayed onto the surface of the seed crystal to form a fine-grained strengthening layer on the surface of the seed crystal, thereby increasing the surface hardness of the seed crystal. The temperature difference between the surface of the seed crystal and the core of the seed crystal is maintained at 50-100°C. A three-step cooling method is used, and after the third step cooling, the seed crystal is naturally cooled with the furnace to room temperature to obtain a pretreated seed crystal; In an optional embodiment, in S1, when the inert gas is sprayed onto the surface of the seed crystal, the distance between the nozzle and the surface of the seed crystal is 10-15 mm, the gas spray direction of the nozzle forms an angle of 45° with the axis of the seed crystal, the inert gas spray pressure at the nozzle outlet is 0.2-0.3 MPa, the inert gas spray flow rate of the nozzle is 5-10 L / min, the purity of the inert gas is ≥99.99%, and the inert gas includes argon or nitrogen; The axis of the seed crystal is the central axis along the direction of crystal growth; The 45° angle between the nozzle's gas jet direction and the axis of the seed crystal ensures that the inert gas evenly covers the seed crystal surface, avoiding local overcooling or airflow dead corners caused by vertical jetting; When three-step cooling is adopted, the three-step cooling includes the first step cooling, the second step cooling, and the third step cooling. In the first step cooling, the temperature of the seed crystal drops by 200-300°C and is kept warm for 30 minutes. In the second step cooling, the temperature of the seed crystal drops by 200-300°C and is kept warm for 30 minutes. In the third step cooling, the temperature of the seed crystal drops by 200-300°C. After the third step cooling, the seed crystal is naturally cooled with the furnace to room temperature. In an optional embodiment, in S1, the first heating rate is 5-10°C / min, the second heating rate is 3-5°C / min, and when the inert gas is sprayed onto the surface of the seed crystal, the thickness of the fine-grained strengthening layer is 0.1-0.3 mm; By heating the seed crystal at a first heating rate, the initial processing stress of the seed crystal is first released, and the thermal expansion difference between the surface and the core of the seed crystal is constructed by the difference in the two-stage heating rate of the staged annealing. Then, a fine-grained strengthening layer is formed on the surface of the seed crystal by spraying inert gas on the surface of the seed crystal and the temperature difference between the surface and the core of the seed crystal is maintained, so that compressive stress is generated on the surface of the seed crystal and a uniform stress field is formed in the core of the seed crystal. After step cooling, a pretreated seed crystal with a small axial stress gradient, low axial elongation and improved surface hardness is obtained. This solves the problems of high-temperature deformation, breakage and cracking of the seed crystal caused by internal stress concentration or insufficient surface strength in the traditional process, provides a seed crystal foundation with a stable stress state for subsequent crystal growth, and effectively reduces the risk of crystal cracking.

[0022] It should be noted that the surface hardness of the seed crystal is improved by the fine-grained strengthening layer; By heating the seed crystal at a first heating rate, the initial processing stress of the seed crystal is first released, so that the stress distribution inside the seed crystal is uniform. The seed crystal is heated to 900-1200°C at a second heating rate. At this stage, gas quenching is simultaneously used to form a fine-grained strengthening layer on the surface of the seed crystal and maintain a temperature difference between the surface and the core of the seed crystal, so that compressive stress is generated on the surface of the seed crystal and a uniform stress field is formed in the core of the seed crystal. Then, three-step cooling avoids the thermal stress mutation caused by traditional rapid cooling, maintains the stress equilibrium state from the surface to the core of the seed crystal, and ultimately makes the axial elongation of the seed crystal at high temperature lower than that of the traditional process, fundamentally suppresses the deformation caused by thermal stress, and makes the pretreated seed crystal of the present application have a lower axial elongation than that of the traditional process; By spraying an inert gas onto the surface of the seed crystal, a fine-grained strengthening layer is formed on the surface of the seed crystal and a temperature difference between the surface of the seed crystal and the core of the seed crystal is maintained. At this time, the core of the seed crystal has a higher temperature than the surface of the seed crystal and a strong plastic deformation ability of the material, so a tensile stress is formed in the core of the seed crystal. The compressive stress on the surface of the seed crystal and the tensile stress in the core of the seed crystal, combined with the temperature difference between the surface of the seed crystal and the core of the seed crystal, form an axial stress gradient from the surface to the core. The three-stage step cooling causes the stress on the surface of the seed crystal and the core of the seed crystal to be slowly released and solidified as the temperature drops, ultimately forming a stable axial stress gradient distribution, thereby solving the deformation and cracking problems caused by stress concentration caused by rapid cooling in traditional processes, so that the pretreated seed crystal of the present application has a smaller axial stress gradient than that of the traditional process. S2, placing the pretreated raw materials into a crucible and heating them to above the melting point to form a melt, and starting a circumferential pulse pre-disturbance uniform flow mechanism before the pretreated seed crystal is immersed in the melt; In an optional embodiment, in S2, the circumferential pulse pre-disturbance flow uniformity mechanism includes: The crucible is located in the furnace, and at least X groups of pulse heating units are evenly distributed around the crucible, and the X groups of pulse heating units periodically heat the crucible wall at a frequency of 0.1-0.5 Hz and a basic power amplitude of 20%-50%; X is a positive integer, and X ≥ 3; The pulse heating unit includes a resistance wire or an induction coil; The purpose of applying periodic temperature disturbance is to pre-establish a controllable temperature disturbance field in the melt to avoid stress concentration caused by thermal field mutation when the pre-treated seed crystal is immersed; Rotate the crucible at a speed of 5-10 revolutions per minute; this will stir the melt, making the temperature and composition of the melt uniform, laying the foundation for the stable formation of the solid-liquid interface when the pre-treated seed crystal is immersed in the melt; By setting up a circumferential pulse pre-disturbance uniform flow mechanism, at least three groups of pulse heating units are evenly distributed around the periphery of the crucible, and the crucible wall is periodically heated at a frequency of 0.1-0.5Hz and a basic power amplitude of 20%-50%. A temperature disturbance field is pre-established in the melt. Compared with the static temperature control mode of the traditional temperature control system, the circumferential pulse pre-disturbance uniform flow mechanism can actively offset the random temperature fluctuations on the melt surface, reduce the temperature gradient fluctuation amplitude of the melt surface, and improve the stability of the solid-liquid interface temperature, thereby greatly alleviating the temperature gradient fluctuations on the melt surface. The problem of periodic changes in crystal diameter is caused, and the frequency of periodic changes in crystal diameter is reduced; the crucible is rotated at a speed of 5-10 revolutions per minute, and the periodic disturbance of the pulse heating unit is combined to form a composite uniform flow effect of rotation stirring and temperature disturbance. On the one hand, the rotation of the crucible can force the temperature and composition distribution of the melt to be uniform; on the other hand, the temperature disturbance shell offsets the nonlinear effect of natural convection, thereby improving the uniformity of the melt flow rate, especially when large-size crystals are grown, which can reduce the fluctuation amplitude of convection intensity and solve the problem of asymmetric eddy current caused by rotation deviation in traditional processes.

[0023] In the circumferential pulse pre-disturbance uniform flow mechanism of S2, each group of pulse heating units is equipped with an independent current controller, and the phase difference of the pulse current of adjacent units is The purpose is to use pseudo-random phase difference between the pulse signals of adjacent pulse heating units to form asymmetric periodic temperature disturbances, and suppress the melt vortex through dynamic asymmetric temperature disturbances.

[0024] By equipping each group of pulse heating units with an independent current controller, the phase difference of the pulse current of adjacent units changes randomly, forming an asymmetric periodic temperature disturbance, thereby suppressing the local stress concentration caused by the sudden change of the thermal field when the pretreated seed crystal is immersed in the melt, reducing the temperature gradient fluctuation amplitude at the solid-liquid interface, and improving the stability of the solid-liquid interface in the early stage of crystal growth.

[0025] S3, lowering the pretreated seed crystal to 5-10 mm from the melt surface at a rate of 0.5-1.5 mm / min, holding for 3-5 minutes to allow the pretreated seed crystal to reach thermal equilibrium with the thermal field, and then immersing the pretreated seed crystal into the melt at an immersion rate of 0.1-0.3 mm / min, forming a solid-liquid interface at the interface between the melt and the pretreated seed crystal, and then initially growing the pretreated seed crystal at a pulling rate of 1-5 mm / h to form a crystal; S4. Use the Czochralski method to grow the crystal to the desired size. After the crystal growth is completed, the crystal is cooled to room temperature at a rate of 5-10℃ / min along with the furnace to reduce the accumulation of thermal stress; In an optional embodiment, in S4, when the crystal is grown to a desired size by the Czochralski method, a constant magnetic field perpendicular to the growth direction of the crystal is applied, and the magnetic induction intensity of the constant magnetic field is 0.1-0.3 Tesla.

[0026] When the Czochralski method is used to grow crystals to the desired size, a steady magnetic field of 0.1-0.3 Tesla perpendicular to the crystal growth direction is applied during the crystal growth stage, and electromagnetic force is used to produce a Lorentz force damping effect on the conductive fluid in the melt, effectively suppressing the strong convection vortex caused by natural convection and stirring, and reducing the maximum flow rate of the melt. Especially when large-sized crystals are grown, the diameter control error caused by convection lag can be reduced, thereby improving the accuracy of crystal size control. The steady magnetic field is combined with the setting of a circumferential pulse pre-disturbance uniform flow mechanism to further reduce the solid-liquid interface fluctuation amplitude and the frequency of periodic changes in crystal diameter, which is conducive to increasing the pulling speed when the crystal is grown to the desired size using the Czochralski method.

[0027] like Figure 2 A Czochralski fluoride crystal growth control device is shown, comprising: Raw material and seed crystal pretreatment module: adding fluorinating agent to fluoride raw material and drying to form pretreated raw material, heating seed crystal to 600-800℃ at a first heating rate and keeping the temperature for 1-2 hours; The seed crystal is heated to 900-1200°C at a second heating rate, which is lower than the first heating rate; at the same time, an inert gas is sprayed onto the surface of the seed crystal to form a fine-grained strengthening layer on the surface of the seed crystal, and the temperature difference between the surface of the seed crystal and the core of the seed crystal is maintained at 50-100°C; A three-step cooling method is used, and after the third step cooling, the seed crystal is naturally cooled with the furnace to room temperature to obtain a pretreated seed crystal; Melt formation module: The pre-treated raw materials are placed in a crucible and heated to above the melting point to form a melt. Before the pre-treated seed crystal is immersed in the melt, the circumferential pulse pre-disturbance uniform flow mechanism is activated; The circumferential pulse pre-disturbance uniform flow mechanism includes: At least X groups of pulse heating units are evenly distributed around the periphery of the crucible, and the X groups of pulse heating units periodically heat the crucible wall at a frequency of 0.1-0.5 Hz and a basic power amplitude of 20%-50%; X is a positive integer, and X ≥ 3; The crucible was rotated at a speed of 5-10 revolutions per minute; Each group of pulse heating units is equipped with an independent current controller, and the phase difference of the pulse current of adjacent units is Random changes within the range; Crystal formation module: The pretreated seed crystal is lowered to 5-10 mm from the melt surface at a rate of 0.5-1.5 mm / min and held for 3-5 minutes. It is then immersed in the melt at an immersion rate of 0.1-0.3 mm / min. A solid-liquid interface is formed at the interface between the melt and the pretreated seed crystal. The pretreated seed crystal is then initially grown at a pulling rate of 1-5 mm / h to form a crystal. Crystal growth module: The Czochralski method is used to grow the crystal to the desired size. When the Czochralski method is used to grow the crystal to the desired size, a steady magnetic field perpendicular to the crystal growth direction is applied. The magnetic induction intensity of the steady magnetic field is 0.1-0.3 Tesla. After the crystal growth is completed, the crystal is cooled to room temperature at a rate of 5-10℃ / min along with the furnace.

[0028] At the same time, the contents not described in detail in this specification belong to the existing technology well known to those skilled in the art. In the embodiments provided by the present invention, it should be understood that the disclosed systems or methods can be implemented in other ways. For example, the embodiments of the invention described above are merely illustrative. For example, the division of modules is only a logical function division, and other division methods may be used in actual implementation.

[0029] Modules described as separate components may or may not be physically separate, and components shown as modules may or may not be physical modules, and may be located in one place or distributed across multiple network modules. Some or all of these modules may be selected to achieve the objectives of this embodiment based on actual needs.

[0030] In addition, the functional modules in various embodiments of the present invention may be integrated into a single processing module, each module may exist physically separately, or two or more modules may be integrated into a single module. The aforementioned integrated modules may be implemented in the form of hardware or hardware plus software functional modules.

[0031] It is obvious to those skilled in the art that the present invention is not limited to the details of the above exemplary embodiments, and that the present invention can be implemented in other specific forms without departing from the basic characteristics of the present invention.

[0032] The above description is only a preferred specific embodiment of the present invention, but the scope of protection of the present invention is not limited thereto. Any technician familiar with the technical field, within the technical scope disclosed by the present invention, who makes equivalent replacements or changes based on the technical solution and inventive concept of the present invention, should be covered by the scope of protection of the present invention.

Claims

1. A method for controlling the growth of fluoride crystals by a Czochralski method, characterized in that: The following steps are involved: S1. Adding a fluorinating agent to a fluoride raw material and drying the raw material to form a pretreated raw material, and subjecting the seed crystal to a coordinated treatment of segmented annealing and surface gas quenching to form a pretreated seed crystal; S2, placing the pretreated raw materials into a crucible and heating them to above the melting point to form a melt, and starting a circumferential pulse pre-disturbance uniform flow mechanism before the pretreated seed crystal is immersed in the melt; S3, lowering the pretreated seed crystal to 5-10 mm from the melt surface at a rate of 0.5-1.5 mm / min, holding for 3-5 minutes, and then immersing it in the melt at an immersion rate of 0.1-0.3 mm / min, so that the interface between the melt and the pretreated seed crystal forms a solid-liquid interface, and then the pretreated seed crystal is initially grown at a pulling rate of 1-5 mm / h to form a crystal; S4. Use the Czochralski method to grow the crystal to the desired size. After the crystal growth is completed, the crystal is cooled to room temperature at a rate of 5-10℃ / min along with the furnace.

2. The Czochralski fluoride crystal growth control method according to claim 1, characterized in that: In S1, a fluorinating agent is added to the fluoride raw material and dried as follows: Add 2-5wt% PbF2 as a fluorinating agent to the fluoride raw material, heat it to 350℃ at a heating rate of 10-35℃ / h, and keep it at 350℃ for 2 hours to remove moisture.

3. The Czochralski fluoride crystal growth control method according to claim 2, characterized in that: In S1, the seed crystal is subjected to a coordinated treatment of segmented annealing and surface gas quenching to form a pretreated seed crystal as follows: Heating the seed crystal to 600-800°C at a first heating rate and keeping the temperature for 1-2 hours; The seed crystal is heated to 900-1200°C at a second heating rate, which is lower than the first heating rate; at the same time, an inert gas is sprayed onto the surface of the seed crystal to form a fine-grained strengthening layer on the surface of the seed crystal, and the temperature difference between the surface of the seed crystal and the core of the seed crystal is maintained at 50-100°C; A three-stage step cooling method is used. After the third stage of cooling, the seed crystal is naturally cooled with the furnace to room temperature to obtain a pretreated seed crystal.

4. The Czochralski fluoride crystal growth control method according to claim 3, characterized in that: In S1, when the inert gas is sprayed onto the surface of the seed crystal, the distance between the nozzle and the surface of the seed crystal is 10-15 mm, the gas spray direction of the nozzle forms an angle of 45° with the axis of the seed crystal, the inert gas spray pressure at the nozzle outlet is 0.2-0.3 MPa, the inert gas spray flow rate of the nozzle is 5-10 L / min, the purity of the inert gas is ≥99.99%, and the inert gas includes argon or nitrogen.

5. The Czochralski fluoride crystal growth control method according to claim 3 or 4, characterized in that: In S1, when three-stage step cooling is adopted, the three-stage step cooling includes first-stage cooling, second-stage cooling, and third-stage cooling. Among them, during the first-stage cooling, the temperature of the seed crystal drops by 200-300°C and is kept warm for 30 minutes. During the second-stage cooling, the temperature of the seed crystal drops by 200-300°C and is kept warm for 30 minutes. During the third-stage cooling, the temperature of the seed crystal drops by 200-300°C. After the third-stage cooling, the seed crystal is naturally cooled with the furnace to room temperature.

6. The Czochralski fluoride crystal growth control method according to claim 5, characterized in that: In S2, the circumferential pulse pre-disturbance uniform flow mechanism includes: At least X groups of pulse heating units are evenly distributed around the periphery of the crucible, and the X groups of pulse heating units periodically heat the crucible wall at a frequency of 0.1-0.5 Hz and a basic power amplitude of 20%-50%; X is a positive integer, and X ≥ 3; The crucible was rotated at a speed of 5-10 revolutions per minute.

7. The Czochralski fluoride crystal growth control method according to claim 6, characterized in that: In the circumferential pulse pre-disturbance uniform flow mechanism of S2, each group of pulse heating units is equipped with an independent current controller, and the phase difference of the pulse current of adjacent units is Randomly changes within the range.

8. The Czochralski fluoride crystal growth control method according to claim 1 or 7, characterized in that: In S4, when the crystal is grown to a desired size by the Czochralski method, a steady magnetic field perpendicular to the growth direction of the crystal is applied, and the magnetic induction intensity of the steady magnetic field is 0.1-0.3 Tesla.

9. A Czochralski fluoride crystal growth control device, used for using the Czochralski fluoride crystal growth control method according to any one of claims 1 to 8, characterized in that: include: Raw material and seed crystal pretreatment module: adding fluorinating agent to fluoride raw material and drying to form pretreated raw material, performing segmented annealing and surface gas quenching on seed crystal to form pretreated seed crystal; Melt formation module: The pre-treated raw materials are placed in a crucible and heated to above the melting point to form a melt. Before the pre-treated seed crystal is immersed in the melt, the circumferential pulse pre-disturbance uniform flow mechanism is activated; Crystal formation module: The pretreated seed crystal is lowered to 5-10 mm from the melt surface at a rate of 0.5-1.5 mm / min and held for 3-5 minutes. It is then immersed in the melt at an immersion rate of 0.1-0.3 mm / min. A solid-liquid interface is formed at the interface between the melt and the pretreated seed crystal. The pretreated seed crystal is then initially grown at a pulling rate of 1-5 mm / h to form a crystal. Crystal growth module: The pulling method is used to grow the crystal to the required size. After the crystal growth is completed, the crystal is cooled to room temperature at a rate of 5-10℃ / min along with the furnace.

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