Temperature gradient adjustable optical floating zone method crystal growth apparatus and method

Abstract

The application discloses a temperature gradient adjustable optical floating zone method crystal growth device and method, wherein the device comprises a light source, an optical assembly, a heating assembly and a motion assembly; wherein the heating assembly comprises a heating body and an induction coil, the heating body is a tubular structure, the induction coil is used for heating the heating body when powered on, and can make different heating amounts of the heating body in different regions along the axial direction of the heating body; the material rod, the seed crystal and the inner hole of the heating body are coaxially arranged, the motion assembly comprises two sets of control devices, the two sets of control devices are respectively used for mounting the material rod and the seed crystal, and provide linear motion and rotary motion for the material rod and the seed crystal, the optical assembly is used for focusing the energy emitted by the light source to a crystal melting zone, the crystal melting zone is located outside one end of the axial direction of the heating body and close to the heating body, and is located on the extension line of the inner hole axial line of the heating body. Through power control, the heating body can match the temperature gradient required by different crystal growth, the internal thermal stress of the crystal is reduced, and the cracking risk is reduced.

Description

Technical Field

[0001] This invention relates to the field of crystal growth technology, and specifically to an optical floating zone crystal growth apparatus and method with adjustable temperature gradient. Background Technology

[0002] The floating zone method is a vertical zone melting crystal growth method that does not require a precious metal crucible. The molten material in the molten zone maintains equilibrium through surface tension and its own gravity. The optical floating zone method focuses the energy emitted by a light source onto a narrow molten zone using a spherical or ellipsoidal mirror. The raw material rod melts upon heating, and the melt grows into a single crystal material under the traction of the moving or rotating seed crystal. Growth temperatures up to approximately 2000℃ can be achieved. Because the floating zone method does not require a metal crucible, no other impurities are introduced during crystal growth, and the heating temperature is not limited by the crucible's melting point. Furthermore, the cavity can be evacuated or filled with a special atmosphere at a certain pressure as needed. Therefore, the optical floating zone method for crystal growth has advantages such as low growth cost, fast growth speed, no pollution, and easy observation. It is suitable for growing high-melting-point, volatile, and other crystal materials that are difficult to grow using other methods.

[0003] In optical floating-zone crystal growth, the temperature is highest at the molten zone. According to the principle of heat transfer, the propagation of heat radiation is inversely proportional to the square of the distance. As the distance from the molten zone gradually increases, the temperature drops sharply, with temperature gradients reaching 200-300℃ / cm. However, conventional optical floating-zone crystal growth equipment lacks heat preservation or post-heating treatment devices. This type of equipment is typically only used to grow crystals requiring a large temperature gradient and less prone to cracking. For crystals requiring a small temperature gradient and prone to cracking, such as lithium niobate, lithium tantalate, and yttrium aluminum garnet, this method is difficult to use, or it cannot grow larger or longer crystals. Summary of the Invention

[0004] In view of the shortcomings of the prior art, the technical problem to be solved by the present invention is: how to provide an optical floating zone crystal growth method with adjustable temperature gradient that can increase the types of crystals grown, reduce crystal cracking, and improve the quality of grown crystals.

[0005] To solve the above-mentioned technical problems, the present invention adopts the following technical solution:

[0006] An optical floating zone crystal growth apparatus with adjustable temperature gradient includes a light source, an optical component, a heating component, and a motion component. The heating component includes a heating element and an induction coil. The heating element is tubular, and the induction coil heats the heating element when energized, generating different amounts of heat in different regions along its axial direction, thereby adjusting the axial temperature gradient of the crystal growth region. The feed rod, seed crystal, and the inner hole of the heating element are coaxially aligned. The motion component includes two sets of control devices, which are used to mount the feed rod and seed crystal, respectively, and provide linear motion along their axial direction and rotational motion around their axial direction. The optical component focuses the energy emitted by the light source onto the crystal melting zone, which is located outside and close to one end of the heating element's axial direction, and on the extension line of the inner hole axis of the heating element.

[0007] In this invention, by setting up a heating assembly consisting of a tubular heating element and an induction coil, the induction coil enables the heating element to generate different amounts of heat in different regions along the axial direction, thereby actively adjusting the axial temperature gradient of the crystal growth region. This allows for flexible adjustment of the magnitude and distribution of the axial temperature gradient according to the crystal growth requirements, making it suitable for crystals with large required temperature gradients as well as crystals with small required temperature gradients that are prone to cracking. This significantly expands the crystal growth range of the optical floating zone method and reduces the risk of crystal cracking.

[0008] As an optimization, the induction coil includes at least two sets of coil groups arranged along the axial direction of the heating element on its periphery. Each set of coil groups is connected to a power source and its power can be adjusted independently, thereby enabling different areas of the heating element to generate different amounts of heat. By independently controlling the power of each set of coils, the temperature of each segment of the heating element along the axial direction can be precisely set, thus forming a preset, gradually varying temperature field along the crystal growth direction. This allows the grown crystal to cool down slowly after leaving the high-temperature melting zone, effectively reducing thermal stress and preventing cracking. Furthermore, the independent control of multiple sets of coils also allows for a wider temperature gradient adjustment range and faster response.

[0009] As an optimization, the induction coil is made of copper tubing, through which circulating cooling water flows. The circulating cooling water in the copper tubing can promptly remove the heat generated by the coil itself, preventing overheating and burnout, and ensuring stable operation of the equipment over a long period.

[0010] As an optimization, the optical component includes a first ellipsoidal mirror and a second ellipsoidal mirror. Both the first and second ellipsoidal mirrors have a first focal point and a second focal point. The light source is located at the first focal point of the first ellipsoidal mirror, and the crystal melting zone is located at the second focal point of the second ellipsoidal mirror. The second focal point of the first ellipsoidal mirror coincides with the first focal point of the second ellipsoidal mirror. By using the double ellipsoidal mirrors to focus the energy of the light source twice, a high-energy-density light spot is ultimately formed in the crystal melting zone, achieving efficient and stable optical heating.

[0011] As an optimization, the crystal growth apparatus also includes a transparent cavity, which is a sealed device made of transparent material, used to provide a vacuum or atmospheric environment for the crystal molten zone. The transparent material ensures that optical energy penetrates the cavity to reach the molten zone, the vacuum prevents oxidation and impurity contamination, and the filling with a protective atmosphere (such as argon or nitrogen) can suppress the loss of volatile components.

[0012] As an optimization, both the heating component and the motion component are housed within the transparent cavity, and the crystal melting zone is located within the transparent cavity. All components are within a sealed environment, simplifying the cavity structure and reducing the risk of leakage.

[0013] As an optimization, the heating assembly is disposed within the transparent cavity, the crystal melting zone is located within the transparent cavity, and the motion assembly is disposed outside the transparent cavity. The motion assembly includes a motion actuator that passes through the transparent cavity and slides and rotates in a sealed engagement with the transparent cavity. The motion actuator is used to mount the corresponding material rod and seed crystal and drive their linear and rotational movements. Placing the motion assembly outside the cavity reduces the cavity volume, while the sliding and rotational sealed engagement of the motion actuator ensures both the accuracy of the linear and rotational movements of the material rod and seed crystal and maintains the airtightness of the cavity.

[0014] An optical floating zone crystal growth method with adjustable temperature gradient is disclosed. This method employs the crystal growth apparatus described above. The optical components focus light source energy onto the crystal melting zone, melting the feed rod. By controlling the heating components, different regions along the heating element's axis generate varying amounts of heat, causing the axial temperature gradient of the heating element to gradually decrease away from the crystal melting zone. Controlling the relative linear and rotational motions of the feed rod and the seed crystal allows the grown crystal to move towards the interior of the heating element, thus promoting crystal growth. The movement of the grown crystal towards the interior of the heating element and its subsequent slow cooling reduces thermal stress and effectively prevents cracking. The temperature gradient and growth rate can be adjusted for different crystal types.

[0015] As an optimization, by independently controlling the power of at least two sets of induction coils, different regions of the heating element generate different amounts of heat, thereby forming an axial temperature gradient along the crystal growth direction. By adjusting the power of multiple independent coils, the temperature drop rate from the molten zone to the rear of the crystal can be precisely set.

[0016] As an optimization, after crystal growth is complete, the power of the induction coil is controlled to slowly cool the crystal, achieving in-situ annealing. This eliminates the need to transfer the crystal to a dedicated annealing furnace, reducing equipment investment.

[0017] Compared with existing technologies, this invention sets up multiple sets of adjustable induction coils. Through power control, the heating element can be matched with the temperature gradient required for different crystal growth. In addition to growing common crystal materials that require a large temperature gradient, it is also suitable for growing some crystals that require a small temperature gradient. This increases the types of crystals that can be grown, expands its application range, reduces internal thermal stress in the crystal, and lowers the risk of cracking. Attached Figure Description

[0018] Figure 1 This is a schematic diagram of the device structure of the present invention;

[0019] Figure 2 This is a schematic diagram of the motion component in this invention. Detailed Implementation

[0020] To make the objectives, technical solutions, and advantages of the embodiments of the present invention clearer, the technical solutions of the embodiments of the present invention will be clearly and completely described below with reference to the accompanying drawings. Obviously, the described embodiments are only some, not all, of the embodiments of the present invention. The components of the embodiments of the present invention described and shown in the accompanying drawings can generally be arranged and designed in various different configurations. Therefore, the following detailed description of the embodiments of the present invention provided in the accompanying drawings is not intended to limit the scope of the claimed invention, but merely represents selected embodiments of the invention. All other embodiments obtained by those skilled in the art based on the embodiments of the present invention without inventive effort are within the scope of protection of the present invention.

[0021] It should be noted that similar reference numerals and letters in the following figures indicate similar items. Therefore, once an item is defined in one figure, it does not need to be further defined and explained in subsequent figures. In the description of this invention, it should be noted that the terms "center," "upper," "lower," "left," "right," "vertical," "horizontal," "inner," and "outer," etc., indicate the orientation or positional relationship based on the orientation or positional relationship shown in the figures, or the orientation or positional relationship commonly used when the product is in use. They are only for the convenience of describing the invention and simplifying the description, and do not indicate or imply that the device or element referred to must have a specific orientation, or be constructed and operated in a specific orientation. Therefore, they should not be construed as limitations on the invention. Furthermore, the terms "first," "second," and "third," etc., are only used to distinguish descriptions and should not be construed as indicating or implying relative importance. In addition, the terms "horizontal," "vertical," etc., do not indicate that the component is required to be absolutely horizontal or suspended, but can be slightly tilted. For example, "horizontal" simply means that its direction is more horizontal than "vertical," and does not mean that the structure must be completely horizontal, but can be slightly tilted. In the description of this invention, it should also be noted that, unless otherwise explicitly specified and limited, the terms "set," "install," "connect," and "link" should be interpreted broadly. For example, they can refer to a fixed connection, a detachable connection, or an integral connection; they can refer to a mechanical connection or an electrical connection; they can refer to a direct connection or an indirect connection through an intermediate medium; and they can refer to the internal connection of two components. Those skilled in the art can understand the specific meaning of the above terms in this invention based on the specific circumstances.

[0022] like Figure 1 and Figure 2 As shown, the arrows emanating from the light source indicate one of the optical path directions, and the arrows corresponding to the motion actuators indicate the directions of movement and rotation. This embodiment of the temperature gradient adjustable optical floating zone crystal growth apparatus includes a light source 6, an optical component, a heating component, and a motion component. The heating component includes a heating element 1 and an induction coil 2. The heating element 1 has a tubular structure, and the induction coil 2 heats the heating element when energized, enabling different regions of the heating element 1 to generate different amounts of heat along its axial direction, thereby adjusting the axial temperature gradient of the crystal growth region. The feed rod 3, seed crystal 4, and the inner hole of the heating element 1 are coaxially arranged. The motion component includes two sets of control devices, which are used to install the feed rod 3 and seed crystal 4, respectively, and can provide linear motion along their axial direction and rotational motion around their axial direction for the feed rod 3 and seed crystal 4, respectively. The optical component focuses the energy emitted by the light source 6 onto the crystal melting zone, which is located outside and close to one end of the heating element 1's axial direction, and on the extension line of the inner hole axis of the heating element 1.

[0023] In this specific embodiment, the induction coil 2 includes at least two sets of coil groups arranged along the axial direction of the heating element 1 on the periphery of the heating element. Each set of coil groups is connected to a power source and the power of each set of coil groups can be adjusted separately, thereby enabling different areas on the heating element 1 to generate different amounts of heat.

[0024] In this specific embodiment, the induction coil 2 is made of copper tube wound with circulating cooling water inside the copper tube.

[0025] In this specific embodiment, the optical component includes a first ellipsoidal reflector 7 and a second ellipsoidal reflector 8. Both the first ellipsoidal reflector 7 and the second ellipsoidal reflector 8 include a first focal point and a second focal point. The light source 6 is located at the first focal point of the first ellipsoidal reflector 7, and the crystal melting zone 5 is located at the second focal point of the second ellipsoidal reflector 8. The second focal point of the first ellipsoidal reflector 7 coincides with the first focal point of the second ellipsoidal reflector 8.

[0026] In this specific embodiment, the crystal growth apparatus further includes a transparent cavity 9, which is a sealing device made of transparent material, used to provide a vacuum or atmospheric environment for the crystal melting zone 5.

[0027] In this specific embodiment, the heating component is disposed inside the transparent cavity 9, the crystal melting zone 5 is located inside the transparent cavity 9, and the motion component is disposed outside the transparent cavity 9. The motion component includes a motion actuator that passes through the transparent cavity 9 and slides and rotates in a sealed fit with the transparent cavity 9. The motion actuator is used to install the corresponding material rod 3 and seed crystal 4 and drive them to linear and rotational motion.

[0028] An optical floating zone crystal growth method with adjustable temperature gradient is disclosed. The method employs the crystal growth apparatus described above. The optical components focus the energy of the light source onto the crystal melting zone, melting the feed rod 3. By controlling the heating components, different regions of the heating element 1 along its axial direction generate different amounts of heat, causing the axial temperature gradient of the heating element 1 to gradually decrease towards the direction away from the crystal melting zone 5. The relative linear and rotational movements of the feed rod 3 and the seed crystal 4 are controlled, causing the grown crystal to move towards the interior of the heating element 1, thus performing crystal growth.

[0029] In this specific embodiment, by independently controlling the power of at least two sets of induction coils 2, different regions of the heating element 1 generate different amounts of heat, thereby forming an axial temperature gradient along the crystal growth direction.

[0030] In this specific embodiment, after the crystal growth is completed, the power of the induction coil 2 is controlled to slowly cool the crystal, thereby achieving in-situ annealing.

[0031] In practical implementation, the motion components include linear motion mechanisms and rotary motion mechanisms.

[0032] The linear motion mechanism includes a base plate 10. A ball screw pair is provided on one side of the base plate 10. The ball screw pair includes a lead screw 11 and a nut. The extension direction of the lead screw 11 is parallel to the axial direction of the inner hole of the heating element 1. Support seats 12 are rotatably connected to both ends of the lead screw 11. The support seats 12 are fixed on the base plate 10. A linear drive motor 13 is fixed on one of the support seats 12. The linear drive motor 13 is connected to the lead screw 11 to drive the lead screw 11 to rotate. A slide table 14 is sleeved on the lead screw 11. The slide table 14 is threadedly engaged with the lead screw 11 by a nut. A guide rail 15 extending parallel to the length direction of the lead screw 11 is also fixedly connected to the base plate 10. The slide table 14 and the guide rail 15 are slidably engaged so that they can slide along the length direction of the guide rail 15.

[0033] The rotary motion mechanism includes a rotary drive motor 16 and a support rod 17 that passes through the slide table 14 and is rotatably engaged with the slide table 14. The support rod 17 is coaxially arranged with the inner hole of the heating element 1. The rotary drive motor 16 is fixed on the slide table 14 and is connected to one end of the support rod 17 to drive the support rod 17 to rotate. The other end of the support rod 17 is equipped with a chuck 18, which is used to clamp and install the corresponding seed crystal 4 or material rod 3.

[0034] The specific operating steps of using the device of the present invention include:

[0035] (1) Install the seed crystal on the chuck of the second motion component, install the material bar on the chuck of the first motion component, and fill the cavity with the required atmosphere (nitrogen).

[0036] (2) Control the motion components to move the seed crystal and the bar to the vicinity of the second focal point (crystal melting zone) of the second ellipsoidal reflector, so that the end faces of the two are 1-2 mm apart. At the same time, start the rotation of the two sets of motion components. The rotation speed is set according to the process requirements (usually 1-5 rpm).

[0037] (3) Turn on the light source and gradually increase the power until the end of the bar begins to melt. At the same time, turn on the intermediate frequency power supply of the induction coil and independently control the power of each group of coils so that the heating element generates different amounts of heat in different regions along the axial direction. Adjust the power of each group so that the axial temperature gradient of the heating element gradually decreases in the direction away from the crystal melting zone. For example, the power is higher in the region near the crystal melting zone and lower in the region away from the melting zone, forming a gradient distribution of temperature from high to low.

[0038] (4) Control the linear movement of the seed crystal so that its upper end face contacts the melting part of the bar to form a molten zone. After stabilizing the molten zone for about 0.3 hours, start the linear movement of the two sets of motion components at the same time so that the bar and the seed crystal move downward (or upward, depending on the direction of the device). The moving speed is set according to the crystal growth process requirements (usually 1-10 mm / h). During this process, the grown crystal gradually moves toward the interior of the heating element. As the axial temperature gradient of the heating element gradually decreases, the crystal naturally and slowly cools down during the growth process, thereby reducing thermal stress and preventing cracking.

[0039] (5) After the material bar has melted, change the linear motion direction of the moving component that installs the material bar, and pull the remaining material bar away from the melting zone at a relatively fast speed (e.g., 3000 mm / h or more);

[0040] (6) After the crystal growth is completed, the power of the induction coil is controlled to make the crystal slowly cool down in the heating body according to the set cooling curve (for example, the cooling rate does not exceed 100℃ / h) to achieve in-situ annealing and further eliminate the internal stress of the crystal.

[0041] (7) After the cooling is complete, open the transparent cavity and take out the crystal.

[0042] Finally, it should be noted that the above embodiments are only used to illustrate the technical solutions of the present invention and are not intended to limit it. Although the present invention has been described with reference to preferred embodiments, those skilled in the art should understand that various changes in form and detail can be made without departing from the spirit and scope of the invention as defined in the appended claims.

Claims

1. A temperature gradient adjustable optical floating zone crystal growth apparatus, characterized in that: It includes a light source, optical components, a heating component, and a motion component. The heating component includes a heating element and an induction coil. The heating element is a tubular structure. The induction coil is used to heat the heating element when energized, and can generate different amounts of heat in different regions along its axis, thereby adjusting the axial temperature gradient of the crystal growth region. The material rod, seed crystal, and the inner hole of the heating element are arranged coaxially. The motion component includes two sets of control devices, which are used to install the material rod and the seed crystal, and can respectively provide linear motion along its axis and rotational motion around its axis for the material rod and the seed crystal. The optical component is used to focus the energy emitted by the light source onto the crystal melting zone, which is located outside one end of the heating element's axis and close to the heating element, and is located on the extension line of the inner hole axis of the heating element.

2. The temperature gradient adjustable optical floating zone crystal growth apparatus according to claim 1, characterized in that: The induction coil includes at least two sets of coil groups arranged along the axial direction of the heating element on the periphery of the heating element. Each set of coil groups is connected to a power source and the power of each set of coil groups can be adjusted separately, thereby enabling different areas of the heating element to generate different amounts of heat.

3. The temperature gradient adjustable optical floating zone crystal growth apparatus according to claim 1, characterized in that: The induction coil is made of copper tubes wound together, and circulating cooling water flows through the copper tubes.

4. The temperature gradient adjustable optical floating zone crystal growth apparatus according to claim 1, characterized in that: The optical component includes a first ellipsoidal mirror and a second ellipsoidal mirror. Both the first and second ellipsoidal mirrors include a first focal point and a second focal point. The light source is located at the first focal point of the first ellipsoidal mirror, and the crystal melting zone is located at the second focal point of the second ellipsoidal mirror. The second focal point of the first ellipsoidal mirror coincides with the first focal point of the second ellipsoidal mirror.

5. The temperature gradient adjustable optical floating zone crystal growth apparatus according to claim 1, characterized in that: The crystal growth apparatus also includes a transparent cavity, which is a sealed device made of transparent material, used to provide a vacuum or atmospheric environment for the crystal melting zone.

6. The temperature gradient adjustable optical floating zone crystal growth apparatus according to claim 5, characterized in that: Both the heating component and the motion component are disposed within the transparent cavity, and the crystal melting zone is located within the transparent cavity.

7. The temperature gradient adjustable optical floating zone crystal growth apparatus according to claim 5, characterized in that: The heating component is disposed inside the transparent cavity, the crystal melting zone is located inside the transparent cavity, and the motion component is disposed outside the transparent cavity. The motion component includes a motion actuator that passes through the transparent cavity and slides and rotates in a sealed fit with the transparent cavity. The motion actuator is used to install the corresponding material bar and seed crystal and drive them to linear and rotational motion.

8. A temperature gradient adjustable optical floating zone crystal growth method, characterized in that: Using the crystal growth apparatus as described in claim 1, the light source energy is focused onto the crystal melting zone by the optical component, causing the material rod to melt. By controlling the heating component, different regions of the heating element along its axial direction generate different amounts of heat, causing the axial temperature gradient of the heating element to gradually decrease in the direction away from the crystal melting zone. The relative linear and rotational motions of the material rod and the seed crystal are controlled, causing the grown crystal to move toward the interior of the heating element, thus performing crystal growth.

9. The temperature gradient adjustable optical floating zone crystal growth method according to claim 8, characterized in that: By independently controlling the power of at least two sets of induction coils, different regions of the heating element generate different amounts of heat, thereby forming an axial temperature gradient along the crystal growth direction.

10. The temperature gradient adjustable optical floating zone crystal growth method according to claim 8, characterized in that: After crystal growth is complete, the power of the induction coil is controlled to slowly cool the crystal, achieving in-situ annealing.

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