Single crystal fiber manufacturing apparatus and method

Abstract

To provide an apparatus and method for manufacturing a single crystal fiber, capable of extremely and easily maintaining a stable stationary state for a long time without entirely requiring highly accurate controllability required in the conventional apparatus for manufacturing a single crystal and stably manufacturing a single crystal fiber having a length of a several hundred meters.SOLUTION: An apparatus for manufacturing a single crystal fiber, capable of irradiating the upper surface of a raw material rod with a laser beam in a chamber to form a melt, dipping a seed single crystal in the melt and pulling it upward to manufacture a single crystal fiber includes: a laser beam source emitting the laser beam as a parallel light; a pulling device vertically and movably constituted in the vertical direction in the state of holding the seed single crystal; and a planar reflector for reflecting the laser beam so as to be perpendicularly incident on the upper surface of the raw material rod. The upper surface of the raw material rod is irradiated with the laser beam so that the temperature of the melt has a doughnut-shaped temperature distribution.SELECTED DRAWING: Figure 1

Description

[Technical field]

[0001] The present invention relates to an apparatus and method for producing single crystals, and more particularly to an apparatus and method for producing single crystal fibers having an extremely fine diameter of several tens of μm and a length of at least several hundred meters, preferably several kilometers. [Background technology]

[0002] Conventionally, efforts have been made to develop methods for manufacturing high-quality ultrafine single crystal fibers in order to develop new electronic devices and to miniaturize and improve the performance of electronic components. In the 1980s, a method for manufacturing single crystal fibers with diameters of several tens of μm was developed, mainly at Stanford University in the United States, using laser light, and named the Laser Heated Pedestal Growth (LHPG) method (Non-Patent Document 1, etc.). However, as will be described later, this LHPG method requires extremely high-precision control, and thus has not yet been put to practical use.

[0003] As a result, methods with greater control have been developed, such as the pull-down method and μ-PD method, which use a container such as a crucible and drip the raw material molten liquid little by little from a nozzle to solidify it below, thereby producing single crystal fiber.

[0004] However, in the methods using these containers, there are many cases where it is difficult to find a suitable container material for some materials, or where contamination of the raw material melt from the container cannot be ignored, causing problems in practical use. For this reason, there is a need for the development of a new manufacturing method that does not require the use of a container and can stably and inexpensively produce high-purity, high-quality single crystal fiber. [Prior art documents] [Non-patent literature]

[0005] [Non-Patent Document 1] RS Feigelson, "Pulling optical fibers", Journal of Crystal Growth 79 (1986) 669-680 Summary of the Invention [Problem to be solved by the invention]

[0006] FIG. 5 is a schematic diagram of a single crystal fiber manufacturing apparatus using a conventional LHPG method. As shown in FIG. 5, in a single crystal fiber manufacturing apparatus 100, laser light irradiated from a laser light source 102 is focused by a parabolic mirror 104 onto an upper surface 106a of a raw material rod 106 to melt it, and a target thin-diameter seed single crystal 108 is immersed in the resulting melt and then pulled upward using a pulling device 110.

[0007] The heat of the melt is absorbed by the seed single crystal 108, and the melt in contact with the seed single crystal 108 solidifies, making it possible to pull it up. This allows the production of a single crystal fiber 112 having a desired diameter. At this time, in order to continue stable production, it is necessary to set the radius r of the single crystal fiber 112 to be produced as shown in FIG. f and the radius R of the raw material rod 106 s It has been reported that the ratio of about 1:3 is preferable.

[0008] When a single crystal fiber 112 is produced using a single crystal fiber production apparatus 100 that uses a conventional LHPG method, in order to stably grow the single crystal fiber 112, it is necessary to control all of the factors related to the melting and solidification of the raw material rod, i.e., (1) Laser light irradiation intensity (2) Laser light distribution (3) Laser light irradiation position (4) Vertical position of the tip of the feed rod (5) Position of the tip of the feed rod in the horizontal plane (6) The speed at which the tip of the feed rod is moved upward in conjunction with the pulling up of the single crystal fiber. (7) Position of the single crystal fiber in the horizontal plane (8) The speed at which the single crystal fiber is pulled upward All of these factors must be controlled accurately and precisely.

[0009] For example, when manufacturing a single crystal fiber with a diameter of 20 μm, the above-mentioned position control accuracy needs to be at least ±2 μm, and preferably ±0.2 μm. However, it is extremely difficult to meet this requirement, which has been a factor in pushing up the price of single crystal fiber manufacturing equipment.

[0010] In view of the current situation, an object of the present invention is to provide a single crystal fiber production apparatus and a single crystal fiber production method that do not require high precision control of the above-mentioned control factors, which was necessary in single crystal fiber production apparatuses using the conventional LHPG method, and that make it extremely easy to maintain a stable steady state for a long period of time, thereby enabling the stable production of single crystal fibers that are several hundred meters or longer. [Means for solving the problem]

[0011] The present invention has been invented to solve the problem that there is a need for extremely accurate position control in the LHPG method, which is a conventional technique as described above. The single crystal fiber production apparatus of the present invention comprises: In the chamber 1. A single crystal fiber manufacturing apparatus for manufacturing a single crystal fiber by irradiating a top surface of a raw material rod with a laser beam to form a melt, immersing a seed single crystal in the melt and pulling it upward to manufacture a single crystal fiber, comprising: a laser light source that irradiates the laser light as parallel light; a pulling device configured to be movable up and down in the vertical direction while holding the seed single crystal; A flat reflecting mirror that reflects the laser light so that the laser light is perpendicularly incident on the upper surface of the raw material rod, The laser beam is irradiated onto the upper surface of the raw material rod so that the temperature of the melt has a doughnut-shaped temperature distribution.

[0012] In such a single crystal fiber manufacturing apparatus, the laser light preferably has a doughnut-shaped intensity distribution. It is also preferable that the radius of the raw material rod is at least 10 times the radius of the single crystal fiber to be produced. Furthermore, when the radius of the single crystal fiber to be manufactured is 100 μm or less, the radius of the raw material rod is more preferably in the range of 2 mm to 5 mm.

[0013] The laser device may further include a light guide device that houses the laser light introduction window of the chamber and the flat reflecting mirror.

[0014] In this case, the light guide device From the above The chamber may be configured to introduce an atmospheric gas into the chamber.

[0015] The optical fiber may further include a position control means for controlling the position of the single crystal fiber in a horizontal plane within a predetermined limited range.

[0016] The method for producing a single crystal fiber of the present invention further comprises the steps of: A method for producing a single crystal fiber, comprising the steps of irradiating an upper surface of a raw material rod with a parallel laser beam to form a melt, immersing a seed single crystal in the melt and pulling it upward to produce a single crystal fiber, the method comprising the steps of: The laser light is irradiated onto the upper surface of the raw material rod so that the temperature of the melt has a doughnut-shaped temperature distribution.

[0017] In such a method for producing a single crystal fiber, the laser light preferably has a doughnut-shaped intensity distribution. It is also preferable that the radius of the raw material rod is at least 10 times the radius of the single crystal fiber to be produced.

[0018] Furthermore, when the radius of the single crystal fiber to be manufactured is 100 μm or less, the radius of the raw material rod is more preferably in the range of 2 mm to 5 mm. Effect of the Invention

[0019] According to the present invention, even if the production of single crystal fiber progresses and the raw material rod is consumed, the fluctuation in the vertical position of the tip of the raw material rod is small. For example, even when a raw material rod with a radius of 3 mm is used to produce a single crystal fiber with a radius of 10 μm and a length of 100 m, the length of the raw material rod consumed is only about 1.1 mm.

[0020] Furthermore, because the laser light is irradiated vertically from above onto the top surface of the feedstock rod while maintaining a constant shape, even if the vertical position of the tip of the feedstock rod becomes slightly lower, the shape and intensity of the irradiated laser light are kept constant. Therefore, even if the vertical position of the tip of the feedstock rod becomes lower as the production of single crystal fiber progresses, there is no need to control the position of the feedstock rod (the vertical position and horizontal position of the tip of the feedstock rod), and it can remain fixed.

[0021] This makes it extremely easy to maintain a stable steady state for a long period of time, and makes it possible to stably produce single crystal fibers as long as several hundred meters or more. [Brief description of the drawings]

[0022] [Figure 1] FIG. 1 is a schematic diagram illustrating the configuration of a single crystal fiber manufacturing apparatus in this embodiment. [Diagram 2] FIG. 2 is a graph showing the intensity distribution of a laser beam. [Diagram 3] FIG. 3 is a schematic diagram showing the configuration of the position control means. [Figure 4] FIG. 4 is a graph showing the temperature distribution of the melt. [Diagram 5] FIG. 5 is a schematic diagram of a single crystal fiber manufacturing apparatus using a conventional LHPG method. [Figure 6] FIG. 6 is a schematic diagram for explaining the relationship between the radius of a single crystal fiber and the radius of a raw material rod when a single crystal fiber is produced by the single crystal fiber production apparatus shown in FIG. DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENTS

[0023] BEST MODE FOR CARRYING OUT THE DISCLOSURE Hereinafter, embodiments (examples) of the present invention will be described in more detail with reference to the drawings, taking as an example the manufacture of lithium fluoride single crystal fibers. FIG. 1 is a schematic diagram illustrating the configuration of a single crystal fiber manufacturing apparatus in this embodiment.

[0024] As shown in Figure 1, the single crystal fiber manufacturing apparatus 10 of this embodiment includes a carbon dioxide laser light source 12 that irradiates laser light, an optical system 13 for shaping the laser light to an optimal diameter and donut-shaped intensity distribution, a flat reflector 14 that reflects the horizontally incident laser light at a right angle so that the laser light is irradiated onto the top surface 16a of the raw material rod 16, and a winding device 20 that immerses a seed single crystal 18 in a molten liquid formed by melting the top surface 16a of the raw material rod 16, and then pulls it upward and winds it up on a drum.

[0025] The raw material rod 16, the seed single crystal 18, etc. are placed in a chamber 26, and a gas suitable for the target material, for example, an atmospheric gas such as tetrafluoromethane in the case of producing lithium fluoride single crystal fiber, is introduced into the chamber 26 by an atmospheric gas introduction device 30. In this chamber 26, the production of the single crystal fiber 22 is carried out.

[0026] The chamber is provided with a laser light introduction window (window a) for introducing a laser light, which is a parallel light irradiated from an external laser light source 12, into the chamber .

[0027] In this embodiment, the laser light source 12 is configured to be able to irradiate laser light, which is parallel light having a doughnut-shaped intensity distribution as shown in FIG. In this embodiment, the optical system 13 includes a beam expander 13a and an axicon lens 13b.

[0028] In addition, as shown in Figure 1, the plane reflecting mirror 14 is arranged to surround the seed single crystal 18 and is configured to reflect the laser light, which is parallel light irradiated horizontally from the laser light source 12, at a right angle and make it enter vertically onto the upper surface 16a of the raw material rod 16.

[0029] The winding device 20 is configured to connect the seed single crystal 18 to a gold wire having a diameter of, for example, 15 μm, and to move the seed single crystal 18 up and down in the vertical direction while holding this gold wire.The winding device 20 is configured to immerse the seed single crystal in the molten liquid (raw material melt) formed on the upper surface 16a of the raw material rod 16 that has been melted by irradiation with laser light, and then to pull it upward at a predetermined speed and wind the produced single crystal fiber 22 onto a drum.

[0030] In this embodiment, the plane reflecting mirror 14 and the window 26a provided in the chamber 26 are preferably housed within the light-guiding device 24. By disposing the plane reflecting mirror 14 and the window 26a within the light-guiding device 24 in this manner and introducing the atmospheric gas into the light-guiding device 24, it is possible to prevent the plane reflecting mirror 14 and the window 26a from becoming dirty due to the adhesion of evaporated matter from the melt (raw material melt).

[0031] The material for forming the light guide device 24 is not particularly limited, but may be transparent quartz, stainless steel, or the like.

[0032] In addition, when configured in this manner, it is preferable to introduce atmospheric gas from an atmospheric gas introduction device 30 provided near the window 26a of the chamber 26 into the light-guiding device 24 through the introduction hole 24a, and to release the atmospheric gas from the light-guiding device 24 into the chamber 26 at a position approximately 10 mm to 20 mm above the molten liquid of the raw material rod 16.

[0033] The chamber 26 is provided with an exhaust hole 24b near the side of the melt of the raw material rod 16, and is configured so that the atmospheric gas is exhausted from this exhaust hole 24b to the outside of the chamber 26. This makes it possible to maintain the chamber 26 filled with the atmospheric gas suitable for manufacturing the single crystal fiber 22 to be manufactured.

[0034] Furthermore, in this embodiment, a position control means 17 is provided to suppress fluctuation in the horizontal position of the manufactured single crystal fiber 22. There are no particular limitations on the position control means 17, so long as it is configured to control the fluctuation in the horizontal position of the single crystal fiber 22 within a predetermined limited range.

[0035] The position control means 17 is configured, for example, by a circular ring 17a as shown in Fig. 3(a) or four thin threads 17b as shown in Fig. 3(b) arranged perpendicularly at a predetermined interval. By passing the single crystal fiber 22 inside such a circular ring 17a or in a region surrounded by the threads 17b, the swinging of the single crystal fiber 22 can be suppressed by the circular ring 17a and the threads 17b.

[0036] When manufacturing single crystal fibers 22 having a diameter of about several tens of μm, the diameter of the circular rings 17a and the intervals between the arranged threads 17b are preferably about 100 μm.

[0037] In the single crystal fiber manufacturing apparatus 10 of this embodiment configured as described above, a feedstock rod 16 having a radius of at least 10 times the radius of the single crystal fiber 22 to be manufactured is used. In particular, when the radius of the single crystal fiber 22 to be manufactured is 100 μm or less, the radius of the feedstock rod is preferably in the range of 2 mm to 5 mm. By irradiating the upper surface 16a of such a feedstock rod 16 with a laser beam, the irradiated portion of the feedstock rod 16 melts and liquefies. The outer diameter of the laser beam is preferably approximately equal to or slightly larger than the diameter of the feedstock rod 16. By optimizing the outer diameter of the laser beam in this manner, the entire upper surface 16a of the feedstock rod 16 can be stably melted to obtain a melt.

[0038] At this time, the temperature distribution of the melt formed on the upper surface 16a of the raw material rod 16 is such that the temperature at the outer periphery is slightly higher than at the center, as shown in FIG. 4 (in this specification, such a temperature distribution is referred to as a "doughnut-shaped temperature distribution"). This is because the laser light having a doughnut-shaped intensity distribution as shown in FIG. 2 is irradiated, and the intensity distribution of the laser light is stronger at the periphery than near the center. Therefore, the amount of laser light irradiated near the center of the melt (raw material melt) formed by irradiating the upper surface 16a of the raw material rod 16 with the laser light is small, and the melt is also heated less. In addition, the melt (raw material melt) near the center is heated by thermal conduction from the melt at the periphery, which has become hot due to irradiation with the high-intensity laser light, and therefore its temperature is lower than that of the periphery.

[0039] Furthermore, even if the irradiation intensity of the laser light fluctuates slightly, the influence of the temperature of the melt near the center of the upper surface of the raw material rod 16 configured in this manner can be reduced, and the temperature of the raw material melt can be stably maintained.

[0040] In this state, when the seed single crystal 18 is attached to the melt of the feed rod 16, heat is absorbed by the seed single crystal 18 by thermal conduction, so that the melt in contact with the seed single crystal 18 solidifies and can be pulled up. At this time, the manufactured single crystal fiber 22 is immersed in a feed melt having a diameter sufficiently larger than the diameter of the single crystal fiber 22 to be manufactured, but the temperature of the interface between the single crystal fiber 22 and the feed melt decreases due to thermal conduction to the manufactured single crystal fiber 22, so single crystallization continues.

[0041] Furthermore, the heat transferred to the single crystal fiber 22 is dissipated as radiant heat from the surroundings, and the single crystallization continues. As a result, if the material of the single crystal fiber 22 has high thermal conductivity, it is possible to increase the pulling speed, and even if the material has low thermal conductivity, in the case of a small-diameter single crystal fiber 22, since the surface area ratio is high, it is possible to pull the fiber at a speed that is orders of magnitude faster than conventional bulk single crystal manufacturing methods, such as the pulling method that is widely used in industry, due to the radiation of heat from the surface, making it possible to manufacture high-quality single crystal fiber 22 at low cost.

[0042] In addition, when the temperature of the melt has a doughnut-shaped temperature distribution in this manner, even if the positional accuracy of the seed single crystal 18 is not precise, the temperature of the part of the raw material rod 16 in contact with the melt remains almost unchanged, so there is almost no effect on the growth of the single crystal.

[0043] Furthermore, in the present invention, the laser light is not focused but is instead irradiated vertically onto the top surface 16a of the feedstock rod 16 as parallel light, so that even if the production of the single crystal fiber 22 progresses and the feedstock rod 16 is consumed and shortened, the shortened length of the feedstock rod 16 is limited because the radius of the feedstock rod 16 is sufficiently larger than the radius of the single crystal fiber 22. Therefore, the intensity of the laser light irradiated onto the top surface 16a of the feedstock rod 16 is always constant, and there is no fluctuation in the amount of melt formed on the top surface 16a of the feedstock rod 16. Therefore, even if the production of the single crystal fiber 22 progresses, so long as the shortened length (variation) of the feedstock rod 16 due to consumption is up to about 20 mm, there is no need to change the vertical position of the tip of the feedstock rod 16.

[0044] Therefore, with the single crystal fiber manufacturing apparatus 10 of the present invention, there is no need to control the irradiation position of the laser light or the vertical and horizontal positions of the tip of the feedstock rod, and the irradiation intensity of the laser light and the horizontal position of the seed single crystal do not require high precision control compared to the conventional LHPG method.

[0045] Furthermore, according to the single crystal fiber manufacturing apparatus 10 of the present invention, even when a decomposed melt substance or a solid solution substance is used as the single crystal material, highly accurate controllability is not required, and it is possible to continue stable production for a long period of time.

[0046] When a decomposed melt substance or a solid solution substance is used as the single crystal material, the melt is adjusted to a liquid phase (hereinafter referred to as "solvent") composition in which a solid having the composition of the single crystal fiber 22 to be manufactured coexists in equilibrium. In this case, the melting point of the solvent is generally several tens of degrees lower than the melting point of the material of the single crystal fiber 22 to be manufactured.

[0047] Even in such a case, by producing the single crystal fiber 22 from a raw material rod 16 having a radius sufficiently large relative to the radius of the single crystal fiber 22 to be produced, i.e., from a solvent with a large diameter, even if the position of the single crystal fiber 22, i.e., the position of the seed single crystal 18, fluctuates by several tens of μm, the temperature of the solvent hardly fluctuates, and therefore the effect on the growth of the single crystal is negligible.

[0048] When a decomposed melt substance or solid solution substance is used as the single crystal material, the radius of the feed rod 16 is preferably 100 times or more the radius of the single crystal fiber 22 to be manufactured, and more preferably about 2 mm to 5 mm. This is because it is advantageous for stably maintaining the range in which the concentrated composition portion (boundary region) of the solvent expelled from the solid-liquid interface as the single crystal grows is homogenized by solution diffusion, and it is possible to stabilize the single crystal growth.

[0049] As the single crystal fiber 22 grows, the composition and amount of the solvent change, but the composition changes toward a lower melting point, and as the amount of solvent decreases, the amount of laser light that passes through the solvent and reaches the interface between the solvent and the feed rod increases, which acts to promote the dissolution of the feed rod into the solvent. Therefore, the composition and amount of the solvent are always maintained constant. As a result, the composition and diameter of the growing single crystal fiber 22 are always constant, and a single crystal fiber 22 with a constant diameter and a specified composition can be manufactured.

[0050] Although the preferred embodiment of the present invention has been described above, the present invention is not limited thereto. For example, in the above embodiment, a laser beam having a doughnut-shaped intensity distribution is used to make the temperature of the melt of the raw material rod 16 have a doughnut-shaped temperature distribution. However, the laser beam may have, for example, a Gaussian-shaped intensity distribution. When using a laser beam having a Gaussian-shaped intensity distribution, a light shielding plate or the like may be placed on the optical path of the laser beam to lower the temperature near the center. In this way, various modifications are possible within the scope of the present invention. [Explanation of symbols]

[0051] 10. Single crystal fiber manufacturing equipment 12 Laser light source 13 Optical system 13a Beam Expander 13b Axicon Lens 14 Plane reflector 16 Raw material rod 16a Top side 17 Position control means 17a Circular Ring 17b Thread 18 Seed single crystal 20 Winding device 22 Single crystal fiber 24 Light guiding equipment 24a Introduction hole 24b Discharge hole 26 Chambers 26a Window 30 Atmospheric gas introduction device 100 Single crystal fiber manufacturing equipment 102 Laser light source 104 Parabolic Mirror 106 Raw material rod 106a Top side 108 Seed single crystal 110 Lifting device 112 Single Crystal Fiber

Claims

1. A single crystal fiber manufacturing apparatus for manufacturing a single crystal fiber by irradiating a top surface of a raw material rod in a chamber with a laser beam to form a melt, immersing a seed single crystal in the melt and pulling it upward to manufacture a single crystal fiber, comprising: a laser light source that irradiates the laser light as parallel light and has a donut-shaped intensity distribution in which the intensity of the laser light at the periphery is stronger than the intensity of the laser light near the center; a pulling device configured to be movable up and down in the vertical direction while holding the seed single crystal; A flat reflecting mirror that reflects the laser light so that the laser light is perpendicularly incident on the upper surface of the raw material rod; Equipped with a laser beam irradiated onto the upper surface of the raw material rod so as to form a donut-shaped temperature distribution in which the temperature of the outer periphery of the melt is slightly higher than the temperature of the center of the melt.

2. 2. The apparatus for producing a single crystal fiber according to claim 1, wherein the radius of said raw material rod is at least 10 times the radius of the single crystal fiber to be produced.

3. 3. The single crystal fiber manufacturing apparatus according to claim 2, wherein when the radius of the single crystal fiber to be manufactured is 100 μm or less, the radius of said raw material rod is set in the range of 2 mm to 5 mm.

4. 4. The single crystal fiber production apparatus according to claim 1, further comprising a light guide device that houses a laser light introduction window of the chamber and the flat reflecting mirror.

5. 5. The single crystal fiber manufacturing apparatus according to claim 4, wherein an atmospheric gas is introduced into the chamber from the light guide device.

6. 6. An apparatus for producing a single crystal fiber according to claim 1, further comprising position control means for controlling the position of the single crystal fiber in a horizontal plane within a predetermined limit range.

7. A method for producing a single crystal fiber, comprising the steps of irradiating a parallel laser beam onto an upper surface of a raw material rod in a chamber to form a melt, immersing a seed single crystal in the melt and pulling it upward to produce a single crystal fiber, the method comprising the steps of: The laser light is the laser light has a doughnut-shaped intensity distribution in which the intensity of the peripheral portion of the laser light is stronger than the intensity of the central portion of the laser light, A method for producing a single crystal fiber, comprising irradiating the upper surface of the raw material rod with the laser light so as to form a donut-shaped temperature distribution in which the temperature of the outer periphery of the melt is slightly higher than the temperature of the center of the melt.

8. 8. The method for producing a single crystal fiber according to claim 7, wherein the radius of the raw material rod is at least 10 times the radius of the single crystal fiber to be produced.

9. 9. The method for producing a single crystal fiber according to claim 8, wherein when the radius of the single crystal fiber to be produced is 100 μm or less, the radius of the raw material rod is set in the range of 2 mm to 5 mm.

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