Multi-crucible vacuum descending furnace device for fluoride crystal growth and growth method thereof

Abstract

The invention relates to a multi-crucible vacuum descending furnace device for fluoride crystal growth, which comprises a furnace body with a vacuum inner cavity, the side wall, close to the top, of the furnace body is provided with an air exhaust pipeline communicated with the vacuum inner cavity, and the bottom wall of the furnace body is provided with an air inlet for filling the vacuum inner cavity with protective atmosphere; two heaters are symmetrically arranged on the two opposite side walls in the furnace body, a plurality of crucibles are arranged between the two heaters in the furnace body in a lifting mode, a plurality of driving assemblies are arranged at the bottom of the furnace body and correspond to the crucibles to drive the crucibles to ascend and descend, each driving assembly independently controls ascending and descending, and every two adjacent crucibles are separated through a carbon felt partition plate. The carbon felt partition plates divide the vacuum inner cavity into a plurality of independent hot areas with the number equal to that of the crucibles. According to the invention, multiple crucibles can realize synchronous crystal growth, the crystal growth aperture and length can be freely regulated and controlled, the crystal growth device is suitable for synchronous growth of multiple crystals with medium and small apertures, a relatively high growth speed can be maintained, and the feeding amount can be effectively increased under the condition of multiple crucibles.

Description

Technical Field

[0001] The present application relates to the technical field of fluoride crystal preparation, and in particular to a multi-crucible vacuum descending furnace device for growing fluoride crystals and a growth method thereof. Background Art

[0002] Fluoride crystals are a type of optical crystal material with excellent performance. For example, calcium fluoride, magnesium fluoride, lithium fluoride, barium fluoride, etc. have wide-band and high-transmittance optical properties from deep ultraviolet to mid- and far-infrared, and are widely used in ultraviolet lasers, semiconductor lithography, high-magnification microscopy and other fields. In particular, large-size ultraviolet-grade calcium fluoride single crystals are used as key components of the objective lens system of DUV lithography machines.

[0003] Traditional fluoride optical crystal preparation mainly includes crucible descent method and Czochralski method. Among them, the Czochralski method mainly uses platinum crucible in fluoride crystal preparation technology, which has high cost, small crystal growth diameter (generally crystal growth diameter <4 inches), fast crystal growth speed leading to large crystal stress, and open crucible leading to more volatiles in the furnace. In actual industry, the Czochralski method will not be adopted on a large scale, and is only used in some small-category and small-diameter fluoride crystal preparation industries, such as YLF crystals, or in the development process of new fluoride crystal growth, because the entire process of crystal growth by the Czochralski method can be observed, and the actual process of crystal growth can be judged more intuitively.

[0004] The traditional crucible descent method is the mainstream industrial technology for the preparation of fluoride crystals. It has a large crystal growth diameter and simple equipment operation. However, since the crystal and the crucible are in contact throughout the growth process, and the thermal expansion coefficients of the crystal and the crucible (usually a graphite crucible) are different, the crystal will be prone to cracking due to high stress. It is also prone to edge and corner breakage in subsequent processing, which affects the processing yield. Therefore, in order to eliminate the crystallization stress and thermal stress during the growth process, very slow crystal growth and secondary high-temperature annealing are required. This results in a generally long crystal growth cycle for fluoride using the crucible descent method, especially in the preparation of large-diameter fluoride crystals.

[0005] At present, there is also a method of preparing fluorides by using a porous crucible descent method. This method processes the original large-diameter crucible into a porous crucible, and multiple crystals grow synchronously during the crystal growth process. The advantage of this method is that the aperture can be designed according to the external dimensions of the product, and small-diameter crystals can be prepared at a faster crystal growth rate. However, as the overall crucible size continues to increase, there will be a large temperature difference between the crystal growth holes at the edge of the crucible and the crystal growth holes in the center of the crucible. Because the heater is generally set on the side of the cylindrical crucible, the fluoride growth rates in the crystal growth holes at different positions of the crucible will be inconsistent, and the crystals produced in the same furnace will have poor consistency, affecting the yield.

[0006] Therefore, the art is in urgent need of a growth preparation device and preparation method that has low production cost, can simultaneously perform growth preparation of multiple crystals, and can synchronously or independently control the growth rates of the multiple crystals. Summary of the invention

[0007] In order to enable multiple crucibles to achieve synchronous crystal growth, the crystal growth diameter and length can be freely adjusted, which is especially suitable for the synchronous growth of multiple crystals with small and medium diameters in the range of 4-6 inches. It can not only maintain a high growth rate, but also effectively increase the feed amount under multiple crucibles, thereby achieving low-cost and large-scale preparation of fluoride crystals.

[0008] The present application provides a multi-crucible vacuum descending furnace device for growing fluoride crystals and a growth method thereof, which adopts the following technical solutions: In the first aspect, the present invention provides a multi-crucible vacuum descending furnace device for growing fluoride crystals, comprising a furnace body, wherein a vacuum cavity is provided in the furnace body, an exhaust pipe connected to the vacuum cavity is provided on the side wall near the top of the furnace body for realizing vacuum in the furnace, and an air inlet for filling the vacuum cavity with a protective atmosphere is provided on the bottom wall of the furnace body; two heaters are symmetrically arranged on two opposite side walls of the furnace body, two electrodes corresponding to the heaters are provided on the outer wall of the furnace body, a plurality of crucibles are arranged in the furnace body for lifting and lowering between the two heaters, a plurality of driving components are provided at the bottom of the furnace body corresponding to the crucibles to drive the crucibles to lift and lower, two adjacent crucibles are separated by a carbon felt partition, and the plurality of carbon felt partitions divide the vacuum cavity into a plurality of independent hot zones equal to the number of crucibles; a control unit for independently controlling the heater, each of the driving components and the temperature of the heater is provided on the outer wall of the furnace body.

[0009] Optionally, the driving assembly includes a lifting motor, a screw, a guide rail, a displacement platform and a connector. The lifting motor is arranged at the bottom of the furnace body and directly opposite the crucible. The screw is coaxially and fixedly connected to the output shaft of the lifting motor. The displacement platform is threadedly connected to the screw and is limited by the guide rail arranged on the side wall of the lifting motor so as to slide in a direction close to or away from the bottom wall of the furnace body. One end of the connector is connected and fixed to one end of the displacement platform, and the other end of the connector penetrates the bottom wall of the furnace body and extends into the vacuum cavity for installing and fixing the crucible.

[0010] Optionally, the heater is a strip-shaped graphite heater, and a thermal insulation layer is provided on the outside of the heater.

[0011] Furthermore, the thermal insulation layer is graphite hard felt and the outer surface is coated with a pyrolytic graphite coating.

[0012] Optionally, the furnace body has an opening at the top, and a heat-insulating cover is detachably provided at the opening at the top of the furnace body.

[0013] Optionally, the heating rate of the heater is in the range of 100-150°C / h.

[0014] Optionally, a temperature measuring component electrically connected to the control unit is provided at the bottom of the furnace body, and the control unit has a program setting system associated with the temperature measuring component, which can set parameters such as the heating and cooling slope, temperature heating and cooling range, and constant temperature time of the heater.

[0015] In the second aspect, the present invention provides a method for growing and preparing fluoride crystals, which uses the above-mentioned multi-crucible vacuum descending furnace device for growing fluoride crystals to carry out growth and preparation, including the following steps: installing and loading the hot field; evacuating and filling with a protective atmosphere; steadily heating the material to an appropriate temperature by a heater to melt the raw materials; the crystal grows as the crucible descends under a stable gas pressure; and cooling and annealing the crucible after the crystal growth is completed.

[0016] Optionally, when the raw materials are subjected to chemical treatment, the heating rate of the heater is controlled within the range of 100-150° C. / h until the temperature in the crucible reaches 1480° C. and the temperature is kept constant for two hours to ensure that all the raw materials in the crucible are melted.

[0017] Optionally, when the crystal grows as the crucible descends, the descent rate of the crucible is controlled at 0.1-0.5 mm / h, the heating power of the heater remains unchanged during the descent, and the total descent stroke of the crucible is 2 / 3 of the crucible height until the crystal growth is completed.

[0018] In summary, the present application includes at least one of the following beneficial technical effects: 1. The multi-crucible vacuum descending furnace device for growing fluoride crystals of the present invention adopts a horizontally placed graphite plate heater, and the crucibles are arranged horizontally between two plates. All crucibles are heated from front to back and evenly.

[0019] 2. The multi-crucible vacuum descending furnace device for growing fluoride crystals of the present invention has crucibles separated by graphite carbon felt insulation plates, which can be used to grow the same type of fluoride crystals with different doping concentrations simultaneously. As long as the melting points are close, crystals can be grown in the same furnace without interfering with each other.

[0020] 3. In the multi-crucible vacuum descending furnace device for growing fluoride crystals of the present invention, each crucible has its own independent crucible descending mechanism, and the crystals in each crucible can descend synchronously, or each can have different descending growth rates and be independently controlled; under this scheme, multiple crucibles can achieve synchronous crystal growth, and the crystal growth diameter and length can be freely adjusted, which is especially suitable for the synchronous growth of multiple crystals of 4-6 inch small and medium diameters, which can maintain a relatively high growth rate and effectively increase the feed amount under multiple crucibles, thereby realizing low-cost and large-scale preparation of fluoride crystals. BRIEF DESCRIPTION OF THE DRAWINGS

[0021] Figure 1is a side view of a multi-crucible vacuum descending furnace device for growing fluoride crystals provided by an embodiment of the present invention; Figure 2 It is a top view of a multi-crucible vacuum descending furnace device for growing fluoride crystals provided by an embodiment of the present invention with a heat-insulating cover removed; Figure 3 It is an axial schematic diagram of a multi-crucible vacuum descending furnace device for growing fluoride crystals provided by an embodiment of the present invention with a heat-insulating cover removed; Figure 4 It is a schematic cross-sectional structure diagram of a multi-crucible vacuum descending furnace device for growing fluoride crystals provided by an embodiment of the present invention.

[0022] Figure numerals: 1. furnace body; 11. vacuum cavity; 12. exhaust pipe; 13. air inlet; 14. electrode; 2. heater; 3. crucible; 4. drive assembly; 41. lifting motor; 42. screw rod; 43. guide rail; 44. displacement table; 45. connector; 5. carbon felt partition; 6. control unit; 7. temperature measuring component; 8. insulation cover. DETAILED DESCRIPTION

[0023] In order to make the purpose, technical scheme and advantages of the embodiment of the present application clearer, the technical scheme of the embodiment of the present application will be clearly and completely described in conjunction with the drawings of the embodiment of the present application. Obviously, the described embodiment is a part of the embodiment of the present application, not all of the embodiments. Based on the described embodiment of the present application, all other embodiments obtained by ordinary technicians in this field without creative work belong to the scope of protection of this application.

[0024] Unless otherwise defined, the technical terms or scientific terms used herein shall have the common meanings understood by persons with ordinary skills in the field to which this application belongs. The words "one" or "an" and the like used in the patent application specification and claims of this application do not indicate a quantity limitation, but indicate the existence of at least one.

[0025] The following is combined with Figure 1-4 This application is described in further detail.

[0026] The embodiment of the present application discloses a multi-crucible vacuum descending furnace device for growing fluoride crystals.

[0027] Reference Figure 1 and Figure 4 A multi-crucible 3 vacuum descending furnace device for growing fluoride crystals includes a furnace body 1, a heater 2, a crucible 3 and a driving component 4.

[0028] A vacuum cavity 11 is integrally formed in the furnace body 1, and an exhaust pipe 12 connected to the vacuum cavity 11 is integrally formed on the side wall of the furnace body 1 near the top. The exhaust pipe 12 is connected to an external exhaust device, and the exhaust device can be a vacuum pump for achieving vacuum in the furnace. An air inlet 13 for filling a protective atmosphere into the vacuum cavity 11 is integrally formed on the bottom wall of the furnace body 1, so that the crystal can obtain a good crystal growth effect under the action of the protective atmosphere.

[0029] Two heaters 2 are symmetrically installed on two opposite side walls in the furnace body 1, and an insulation layer (not shown in the figure) is installed on the outer wall of the heater 2. Two electrodes 14 corresponding to the heater 2 are integrally formed on the outer wall of the furnace body 1. In this embodiment, the heater 2 is preferably a strip-shaped graphite heater 2, which is horizontally installed on the side wall of the furnace body 1 front and back. The insulation layer is preferably graphite carbon felt. The insulation layer is attached to the outer wall of the heater 2 and the surface is treated with pyrolytic graphite coating to prevent fluoride corrosion. The heating rate of the heater 2 is controlled within the range of 100-150°C / h, thereby ensuring that the fluoride has a stable melting rate and a good crystal growth environment.

[0030] Reference Figure 2-Figure 4 The crucible 3 is installed between two heaters 2 in the furnace body 1 for lifting and lowering, and multiple heaters 2 are installed at intervals. Multiple driving components 4 are installed at the bottom of the furnace body 1 corresponding to the crucibles 3 to drive the corresponding crucibles 3 to rise and fall in an opposite direction. Two adjacent crucibles 3 are separated by a carbon felt partition 5. Multiple carbon felt partitions 5 divide the vacuum cavity 11 into three independent and non-interfering hot zones equal to the number of crucibles 3. In this embodiment, taking three crucibles 3 as an example, two carbon felt partitions 5 are installed at intervals.

[0031] The driving assembly 4 includes a lifting motor 41, a screw rod 42, a guide rail 43, a displacement platform 44 and a connector 45. The lifting motor 41 is installed at the bottom of the furnace body 1 and is directly opposite to the crucible 3. The screw rod 42 is coaxially fixedly connected to the output shaft of the lifting motor 41 through a coupling. The displacement platform 44 is threadedly connected to the screw rod 42 and is limited by a guide rail 43 installed on the side wall of the lifting motor 41 to slide in a direction close to or away from the bottom wall of the furnace body 1. One end of the connector 45 is fixedly connected to one end of the displacement platform 44 by bolts, and the other end of the connector 45 penetrates the bottom wall of the furnace body 1 and extends into the vacuum cavity 11 for installing and fixing the crucible 3, and then the lifting and lowering of the crucible 3 is driven by the lifting and lowering of the connector 45. In this embodiment, the driving assembly 4 as a whole can be fixedly connected to the bottom of the furnace body 1 through the guide rail 43 by bolts and ensure that the connector 45 has a sufficient sliding distance. It can also be assumed that an external frame is used to achieve relative fixation between the driving assembly 4 and the furnace body 1. The installation of the driving assembly 4 is a prior art and will not be described in detail.

[0032] Reference Figure 1-Figure 3A control unit 6 for independently controlling the heater 2 and the opening and closing of each driving component 4 and the temperature of the heater 2 is installed on the outer wall of the furnace body 1. A temperature measuring component 7 electrically connected to the control unit 6 is installed at the bottom of the furnace body 1. The control unit 6 has a program setting system associated with the temperature measuring component 7, which can set parameters such as the heating and cooling slope, temperature heating and cooling range, and constant temperature time of the heater 2. In this embodiment, the control unit 6 can adopt an MCU control unit 6 or a PLC controller. The temperature measuring component 7 is preferably an infrared thermometer, which are all existing technologies and will not be described in detail.

[0033] Furthermore, the top of the furnace body 1 is open, and a heat-insulating cover 8 is installed on the top opening of the furnace body 1 to facilitate the loading of the crucible 3 and the removal of the crystal after preparation.

[0034] The multi-crucible 3 vacuum descending furnace device for growing fluoride crystals of this embodiment is used to prepare the growth of crystals in the following manner: Step S1: Thermal field installation and loading.

[0035] Specifically, the fluoride raw material is placed in the crucible 3, and the thermal field components are installed one by one according to the thermal field structure.

[0036] Step S2, evacuating and filling with protective atmosphere.

[0037] Start the vacuum pump and evacuate the inner cavity of the furnace body 1 through the exhaust pipe 12 until the air pressure in the furnace body 1 drops below 5×10-3Pa; Depending on the process requirements, it can be grown in a vacuum or in a protective atmosphere.

[0038] Step S3, heating the material.

[0039] Specifically, the power supply is started, and the heating rate of the heater 2 is controlled to be 100-150° C. / h, until the temperature of the temperature measuring point at the bottom of the crucible 3 rises to 1480° C., and the temperature is kept constant for 2 hours to ensure that all the raw materials in the crucible 3 are melted.

[0040] Step S4, crystal growth.

[0041] After the raw materials are melted and the gas pressure in the furnace is stable, the crucible 3 is controlled to descend by the lifting motor 41 to start crystal growth. The descent rate of the crucible 3 is controlled at 0.1-0.5 mm / h. At this time, the heating power is maintained unchanged. The total descent stroke of the crucible 3 is 2 / 3 of the height of the crucible 3 until the crystal growth is completed.

[0042] Step S5, cooling and annealing.

[0043] After the crystal growth is completed, the crucible 3 is stopped from descending, and the crucible 3 is cooled to room temperature.

[0044] The above are all preferred embodiments of the present application, and the protection scope of the present application is not limited thereto. Therefore, any equivalent changes made according to the structure, shape, and principle of the present application should be included in the protection scope of the present application.

Claims

1. A multi-crucible vacuum descending furnace device for growing fluoride crystals, comprising a furnace body, characterized in that: A vacuum cavity is provided in the furnace body, and an exhaust pipe connected to the vacuum cavity is provided on the side wall of the furnace body near the top to realize the vacuum in the furnace, and an air inlet for filling the vacuum cavity with a protective atmosphere is provided on the bottom wall of the furnace body; two heaters are symmetrically arranged on two opposite side walls of the furnace body, and two electrodes corresponding to the heaters are respectively arranged on the outer wall of the furnace body, and a plurality of crucibles are arranged in the furnace body for lifting and lowering between the two heaters, and a plurality of driving components are arranged at the bottom of the furnace body corresponding to the crucibles to drive the crucibles to lift and lower, and two adjacent crucibles are separated by a carbon felt partition, and the plurality of carbon felt partitions divide the vacuum cavity into a plurality of independent hot zones equal to the number of crucibles; a control unit for independently controlling the heaters, the opening and closing of each driving component and the temperature of the heater is provided on the outer wall of the furnace body.

2. The multi-crucible vacuum descending furnace device for growing fluoride crystals according to claim 1, characterized in that: The driving assembly includes a lifting motor, a lead screw, a guide rail, a translation platform and a connector. The lifting motor is arranged at the bottom of the furnace body and directly faces the crucible. The lead screw is coaxially and fixedly connected to the output shaft of the lifting motor. The translation platform is threadedly connected to the lead screw and is limited by the guide rail arranged on the side wall of the lifting motor to slide in a direction close to or away from the bottom wall of the furnace body. One end of the connector is connected and fixed to one end of the translation platform, and the other end of the connector penetrates the bottom wall of the furnace body and extends into the vacuum cavity for installing and fixing the crucible.

3. The multi-crucible vacuum descending furnace device for growing fluoride crystals according to claim 1, characterized in that: The heater is a strip-shaped graphite heater, and a heat-insulating layer is arranged on the outer wall of the heater.

4. The multi-crucible vacuum descending furnace device for growing fluoride crystals according to claim 3, characterized in that: The outer surface of the thermal insulation layer is coated with a pyrolytic graphite coating.

5. The multi-crucible vacuum descending furnace device for growing fluoride crystals according to claim 1, characterized in that: The furnace body has an opening at the top, and a heat-insulating cover is detachably arranged at the opening at the top of the furnace body.

6. The multi-crucible vacuum descending furnace device for growing fluoride crystals according to claim 1, characterized in that: The heating rate of the heater is in the range of 100-150°C / h.

7. The multi-crucible vacuum descending furnace device for growing fluoride crystals according to claim 1, characterized in that: A temperature measuring component electrically connected to the control unit is provided at the bottom of the furnace body, and the control unit has a timing component electrically connected to the temperature measuring component for controlling the heating time of the heater.

8. A method for growing and preparing fluoride crystals, characterized in that: The multi-crucible vacuum descending furnace device for growing fluoride crystals as described in any one of claims 1 to 7 is used for growth preparation, comprising the following steps: Thermal field installation and charging; Evacuate and fill with protective atmosphere; The heater is used to stably raise the temperature to an appropriate temperature to process the raw materials; The crystal grows as the crucible descends under a stable gas pressure; The crucible is subjected to temperature reduction annealing.

9. A fluoride crystal growth preparation method according to claim 8, characterized in that: When the raw materials are subjected to the chemical treatment, the heating rate of the heater is controlled within the range of 100-150° C. / h until the temperature in the crucible reaches 1480° C. and the temperature is kept constant for two hours to ensure that all the raw materials in the crucible are melted.

10. A fluoride crystal growth preparation method according to claim 8, characterized in that: When the crystal grows with the crucible descending, the crucible descending rate is controlled at 0.1-0.5 mm / h, the heating power of the heater remains unchanged during the descending process, and the total descending stroke of the crucible is 2 / 3 of the crucible height until the crystal growth is completed.

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