Zone melting method crystal automatic growth device

Abstract

A zone melting method crystal automatic growth device mainly includes a furnace, a force detection system, a fiber laser heating system, a temperature gradient adjustment system, a motion control system and a computer control system. During the crystal growth process, the crystal growth diameter can be automatically controlled through the feedback of the source rod force information, and the crystal growth quality can be monitored in real time; the fiber laser heating can obtain a uniform and stable melting zone; the crystal after crystallization enters the temperature gradient adjustment system with the seed crystal rod to avoid defects caused by sudden cooling.

Description

Technical Field

[0001] The invention relates to crystal growth, in particular to an automatic crystal growth device using a zone melting method. Background Art

[0002] The zone melting method (abbreviated as "zone melting method") belongs to the method of growing single crystals from the melt. In 1952, Pfannz used the zone refining method to purify the material, laying the foundation for the development of the zone melting method crystal growth technology. The following year, the zone melting method was used for single crystal growth for the first time, and many researchers subsequently proposed and improved the zone melting method single crystal growth technology. The zone melting growth process is to first heat and melt the solid material, and then control the temperature, rotation speed, growth rate and other conditions, and through the cooling process, the melt is gradually solidified and crystallized into crystals. Its basic principle is to use the light emitted by the light source as the heat source, which is reflected and focused on the material rod and the seed crystal, thereby forming a tiny melting zone between the seed crystal and the material rod. The crystal crystallizes from the melting zone and grows on the seed crystal. The melting zone moves from top to bottom or from bottom to top, away from the focusing position, thereby effectively avoiding the introduction of external impurities. At the same time, the melting zone of the crystal is uniform and the growth rate is faster.

[0003] The stability of the molten zone is the key to the smooth growth of single crystals by the zone melting method. In the optical zone melting method, the raw materials for crystal growth are heated and melted to form a molten zone, and the surface tension of the melt maintains the shape of the molten zone. Since the surface tension is determined by temperature, the stability of temperature becomes a decisive factor affecting the stability of the molten zone. The temperature of the molten zone in the optical zone melting method can be adjusted by changing the output power of the heating light source or the speed of the source rod delivery / exit. At present, the optical zone melting method crystal growth furnaces on the market all use direct visual or CCD observation of the molten zone state, and manually analyze and judge the observation results to achieve adjustment. Since the growth of crystals by the zone melting method takes more than ten to twenty hours, the manual observation and adjustment method is time-consuming and labor-intensive, and is affected by the experience and level of the crystal growth personnel, which is not conducive to large-scale continuous industrial production.

[0004] The core of the optical zone melting method crystal growth equipment is the heating light source. The currently commonly used optical zone melting method usually uses a xenon lamp as the heating light source. However, xenon lamps have many defects such as short service life, easy explosion, easy cracking, and difficult maintenance, which bring great safety hazards in actual production. In addition, the power density of xenon lamps is low, making it difficult to grow high-melting-point crystals such as sesqui-crystals. In response to this series of problems, Crystal Inc. of Japan proposed a heating device using a laser diode (patent JP5181396B2), but the laser diode still has the problem of low power. If a higher growth temperature is to be achieved, the number of lasers must be increased, which poses new challenges in cost and equipment space design. In addition, the divergence angle at the output end of the laser diode is too large, which is not conducive to subsequent shaping and focusing, and it is difficult to achieve a general-purpose laser heating zone furnace.

[0005] Temperature gradient is the core driving force of crystal growth and one of the most critical growth parameters. The temperature gradient of the optical zone melting method is generated by the temperature difference between the molten zone irradiated by the heating light source and the raw material or atmosphere. It is mainly divided into two types: one is the axial vertical gradient between the vertically distributed molten zone and the raw material rod, and the other is the radial horizontal temperature gradient between the inside and outside of the molten zone. The former is the driving force of crystallization. The traditional optical zone melting method does not have a means to regulate the growth temperature gradient. There is a huge temperature difference between the area irradiated by the heating light source and the unirradiated area. The axial temperature gradient is usually 50 to 200 ° C / mm. As the crystal moves out of the heating zone after growth, the crystal will be subject to huge temperature changes, which leads to a variety of defects such as crystal cracking, polycrystalline, and large residual thermal stress. Summary of the invention

[0006] In response to the above-mentioned problems, the present invention proposes an automated crystal growth device using the zone melting method, which adds a force feedback adjustment system and cooperates with a high-efficiency fiber laser heating system and a temperature gradient adjustment system to obtain a stable melting zone, beneficially adjust the longitudinal temperature gradient, and realize the automation of crystal growth.

[0007] The technical solution of the present invention is as follows:

[0008] A zone melting method crystal automatic growth device, characterized in that the device comprises: a furnace, a force detection system, a fiber laser heating system, a temperature gradient adjustment system, a motion control system and a computer control system, wherein the force detection system is arranged at the top of the furnace, the detection end of the force detection system is connected to the upper source rod, the fiber laser heating system is arranged at the side of the middle part of the furnace, and is composed of a plurality of groups of sub-devices with the same configuration, each group of sub-devices comprises a fiber laser output device, a light spot shaping device and a light trap device, the output end of the fiber laser output device is connected to the light spot shaping device, the light trap device is arranged on the opposite side of the melting zone along the direction of laser transmission, the sub-devices are spatially symmetrically surrounded on the side of the crystal growth melting zone, the temperature gradient adjustment device comprises a heating device and a heat preservation material, and is surrounded at the position where the lower source rod moves out of the melting zone, the motion control system comprises an upper source rod motion control device and a lower source rod motion control device, which are respectively arranged at the upper part and the lower part of the furnace, and the control ends thereof are respectively connected to the ends of the upper source rod and the lower source rod, and the above-mentioned systems are connected to the control computer control system to realize common control.

[0009] The force detection system adopts a weighing sensor, whose measuring end is connected to the upper source rod, and can monitor the stress state of the upper source rod in real time during the crystal growth process, and convert it into an analog signal or a digital signal to input into the computer control system.

[0010] The fiber laser heating system includes sub-devices of the same configuration symmetrically arranged in the array space, each group of sub-devices includes a fiber laser output device, a spot shaping device and a light trap device; the preferred number of sub-devices is 3 to 7 groups; the fiber laser output device includes a fiber laser and a corresponding fiber laser coupling output device; the spot shaping device uses two groups of cylindrical lenses placed perpendicular to each other, which are placed in a slide rail that can move back and forth and are protected by a sleeve, and can shape the Gaussian spot output by the fiber laser into a circular or elliptical spot of the required size. The spot shaping system can adjust the overall inclination angle through a spiral adjustment device; the light trap device is a high-temperature resistant material with a high laser absorption rate inside, which can effectively absorb the remaining heating laser.

[0011] The detection end of the force detection system is connected to the upper source rod to monitor the force signal in the crystal growth process in real time, transmit it to the computer control system for analysis and recording, and then adjust the power of the heating light source according to the preset program, thereby realizing feedback automatic adjustment; the fiber laser heating system is evenly distributed around the crystal growth area, and the parameters such as the shape, size, and horizontal inclination of the heating spot output are adjustable, which can adapt to source rods with different sizes and material properties; the temperature gradient adjustment system is fixed at the bottom of the crystal growth area, which effectively reduces the temperature gradient that the crystal is subjected to after growth and improves the growth quality.

[0012] Force feedback control system, the working principle is:

[0013] The measuring end of the force detection system is connected to the upper source rod, and the measurement signal is transmitted to the computer control system. During the crystal growth process, the upper source rod is subjected to the pulling force F of the upper pull rod, the buoyancy f of the melt, the surface tension σ and its own gravity G. The combined effect of these four forces puts the upper source rod in a state of force balance. As the crystallization process progresses, the gravity G of the upper source rod continues to decrease. When the decrease shows a linear change, it can be considered that the crystal is in a stable growth state, and the growth amount is the change slope. When there are external factors disturbing, the temperature of the melt zone changes, which directly changes the surface tension σ. Generally, the lower the temperature of the melt zone, the greater σ. At this time, the force feedback control system detects that the force state of the upper source rod has changed, and the power can be appropriately adjusted according to the pre-set program to return the melt zone to a stable state. Therefore, the force feedback control system can realize real-time monitoring of the state of the melt zone of the zone melting method, and can realize closed-loop automatic control.

[0014] The fiber laser heating system comprises sub-devices with the same configuration which are symmetrically arranged in the array space, and each group of sub-devices comprises a fiber laser output device, a light spot shaping device and a light trap device.

[0015] The fiber laser output device includes a fiber laser and a corresponding fiber laser coupling output device. The fiber laser provides the heat required for laser heating, and the output end is a pigtail with an SMA or other standard interface, which is connected to the overall device through a fiber laser coupling output device with spatial adjustment. The coupling output system has the advantages of plug-and-play, high reliability and easy maintenance, and can adapt to the access of various types of fiber lasers.

[0016] The light spot shaping device is composed of two groups of cylindrical lenses and other optical lenses placed perpendicular to each other, which can shape a Gaussian light spot with a certain divergence angle into a circular or elliptical light spot required for growing crystals. The above optical lenses are all set on a metal sleeve with a built-in slide rail, which can be fine-tuned within a certain range to meet the needs of different crystal growth. The optical lens is fixed to the light spot shaping system using a spiral tightening device, and can be precisely adjusted using a centimeter ruler. The entire optical system is equipped with a spiral adjustment device, which can adjust the overall tilt angle to avoid damage to the optical system and laser by reflected light.

[0017] The optical trap device is placed in a spatially symmetrical position at the output end of the fiber laser, and can absorb excess heating laser light. The interior of the optical trap device is made of a material with a high laser absorption rate, combined with an irregular reflective surface, which can absorb the incident laser light. The optical trap device has a circulating water cooling device, which can promptly transport away the heat generated by absorbing the laser light, and can achieve long-term continuous operation.

[0018] The temperature gradient adjustment system is composed of a built-in heating device and a heat-insulating material cylinder. The temperature gradient adjustment device is located at the position where the lower source rod crystal moves out of the melting zone. The heating device and the heat-insulating material can heat the crystal, thereby effectively reducing the temperature gradient to which the grown crystal is subjected, and reducing defects such as crystal breakage and polycrystalline caused by thermal shock.

[0019] The motion control system can cooperate with the force feedback control system to realize real-time and precise control of the axial speed and rotation speed of the upper and lower source rods according to the set computer program, thereby controlling the diameter of the crystal and the growth amount per unit time.

[0020] Technical advantages of the present invention:

[0021] 1. The force detection system can realize real-time monitoring of the stress state of the molten zone. After the data is transmitted to the computer control system, the feedback-type fully automatic closed-loop control of the heating light source power can be realized without manual intervention, saving time and manpower and improving the quality of crystal growth;

[0022] 2. The fiber laser heating system can obtain a high power density heating source, and can adjust the spot size and shape at any time according to parameters such as the type of crystal growth and source rod diameter;

[0023] 3. The temperature gradient control system can effectively reduce the drastic temperature changes that the crystal is subjected to after growth, reduce the risk of crystal cracking and polycrystalline, and improve crystal quality. BRIEF DESCRIPTION OF THE DRAWINGS

[0024] Figure 1 It is a schematic diagram of the automated crystal growth device using the zone melting method of the present invention.

[0025] Figure 2 Schematic diagram of the vertical force on the melt. DETAILED DESCRIPTION

[0026] In order to make the purpose, technical solution and advantages of the present invention clearer, the present invention is specifically described below in conjunction with the accompanying drawings and embodiments. The embodiments herein are only used to explain the present invention and are not used to limit the present invention.

[0027] like Figure 1 As shown, Figure 1 This is a schematic diagram of the automated crystal growth device using the zone melting method of the present invention. As can be seen from the figure, the automated crystal growth device using the zone melting method of the present invention includes: a furnace 1, a force detection system 2, a fiber laser output device 31, a spot shaping device 32 and a light trap device 33, a heating device 41, a heat preservation material 42, an upper source rod motion control device 51, a lower source rod motion control device 52 and a computer control system (not shown in the figure).

[0028] The force detection system 2 uses a capacitive weight sensor, which is placed on the top of the furnace 1. The detection end is connected to the seed crystal rod holding the upper source rod, and monitors the change of the force state of the upper source rod in real time, and transmits the digital signal to the computer control system.

[0029] The fiber laser heating system 3 adopts five groups of symmetrical sub-devices, each group of sub-devices includes: a fiber laser output device 31, a spot shaping device 32 and a light trap device 33, and the five groups of sub-devices are arranged in a five-pointed star space symmetrically on the side of the melting zone where the crystal grows; the fiber laser output device 31 adopts a laser with a rated maximum output power of 500W, and its output end is an SMA standard interface, and a circular Gaussian beam with a diameter of 500μm is output after coupling with the output device; the spot shaping device includes two groups of mutually perpendicular cylindrical lenses and other end The five-beam focusing position is the center of the melting zone in the crystal growth. The optical trap device is placed at a spatially symmetrical position at the output end of the optical fiber laser along the direction of the beam. The interior of the optical trap device is a zirconia ceramic with a rough and irregular reflecting surface. An external circulating water cooling device is connected to the optical trap device, which can timely transport away the heat generated by absorbing the laser, and can achieve long-term continuous operation.

[0030] The temperature gradient adjustment system 4 includes a heating device 41 and a heat-insulating material 42, which surrounds the position where the lower source rod moves out of the melting zone; the heating device 41 uses a resistance wire, which is nested in the heat-insulating material 42 made of zirconia ceramic circles, and is arranged with more on the top and less on the bottom to create a gradual temperature gradient.

[0031] The motion control system 5 includes an upper source rod motion control device 51 and a lower source rod motion control device 52, which are respectively arranged at the upper and lower parts of the furnace 1, and their control ends are respectively connected to the ends of the upper and lower source rods; each motion control device is composed of a lead screw, a slider and a motor, and can simultaneously control the up and down displacement and rotation speed of the source rod according to the instructions of the computer control system.

[0032] The crystal growth process is:

[0033] After solid phase synthesis, the YAG powder is pressed into a round rod with a diameter of 5mm and a length of 40mm, which is used as the upper and lower source rods for crystal growth and installed in the crystal growth furnace 1. Adjust the laser heating power of the fiber laser until the source rod temperature reaches 2000℃, so that the YAG powder is melted to form a molten zone. Adjust the rotation speed of the upper and lower source rods to 8-12r / min in opposite directions. The source rod delivery and withdrawal speed to the molten zone is 0.6-0.8mm / h. The heating temperature of the temperature gradient adjustment device is set to 1200℃;

[0034] During the automatic growth process, a force detection system is used to detect the changes in the force state of the source rod during the growth process, and a computer control system is used to record and adjust it. Figure 2 As shown in the figure, when the molten zone is disturbed by external factors and the temperature is slightly lower than the set value, the downward surface tension σ increases, which is manifested as an increase in the downward pulling force on the force detection system. The force detection system detects this change and transmits the signal to the computer control system, which appropriately increases the laser output power to restore the temperature of the molten zone to normal.

[0035] Experiments show that the present invention can achieve uniform linear changes in the amount of crystallization during the entire crystal growth process through automated feedback control. The temperature gradient adjustment system ensures that the crystal is subjected to less thermal shock when it moves out of the melting zone, significantly improving the quality of crystal growth, and ultimately obtaining high-quality YAG single crystals.

Claims

1. A zone melting method crystal automatic growth device, characterized in that The device comprises: a furnace (1), a force detection system (2), a fiber laser heating system (3), a temperature gradient adjustment system (4), a motion control system (5) and a computer control system. The force detection system (2) is arranged on the top of the furnace (1), and the detection end of the force detection system (2) is connected to the upper source rod. The fiber laser heating system (3) is arranged on the side of the middle part of the furnace (1) and is composed of a plurality of groups of sub-devices with the same configuration. Each group of sub-devices comprises a fiber laser output device (31), a light spot shaping device (32) and a light trap device (33). The output end of the fiber laser output device (31) is connected to the light spot shaping device (32). The light trap device (33) is connected to the furnace (1), and an optical trap device (33) is arranged on the opposite side of the melting zone along the direction of laser transmission. The sub-devices are spatially symmetrically surrounded on the side of the crystal growth melting zone. The temperature gradient adjustment system (4) includes a heating device (41) and a heat preservation material (42), which surround the position where the lower source rod moves out of the melting zone. The motion control system (5) includes an upper source rod motion control device (51) and a lower source rod motion control device (52), which are respectively arranged at the upper part and the lower part of the furnace (1), and the control ends thereof are respectively connected to the ends of the upper source rod and the lower source rod. The above-mentioned systems are connected to the control computer control system to realize common control; The force detection system (2) adopts a weighing sensor, whose measuring end is connected to the upper source rod, and can monitor the force state of the upper source rod in real time during the crystal growth process, and convert it into an analog signal or a digital signal to input into the computer control system.

2. The automated zone melting method crystal growth device according to claim 1, characterized in that The fiber laser heating system (3) comprises sub-devices of the same configuration which are symmetrically arranged in an array space, and each group of sub-devices comprises a fiber laser output device (31), a light spot shaping device (32) and a light trap device (33); the fiber laser output device (31) comprises a fiber laser and a corresponding fiber laser coupling output device; the light spot shaping device (32) adopts two groups of cylindrical lenses which are placed perpendicular to each other, are arranged in a slide rail which can move forward and backward, and are protected by a sleeve, so that the Gaussian light spot output by the fiber laser can be shaped into a circular or elliptical light spot of a required size; the light spot shaping system can adjust the overall inclination angle through a spiral adjustment device; the light trap device (33) is a high-temperature resistant material with a high laser absorption rate inside, which can effectively absorb the residual heating laser.

3. The automated zone melting method crystal growth device according to claim 2, characterized in that The number of the sub-devices is 3 to 7 groups.

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