A method for eliminating the generation of small-angle grain boundary defects in the growth of tellurium dioxide single crystals

Abstract

The present invention discloses a method for eliminating the generation of small-angle grain boundary defects in the growth of tellurium dioxide single crystals, including the processing of seed crystals, the commutation treatment of seed crystals, and the growth of tellurium dioxide single crystals by the crucible descent method. Among them, the commutation treatment operation of the seed crystal refers to using the (1-10) crystal plane as the crystal growth plane instead of the traditional (110) crystal plane. The present invention uses the commutation treatment of the seed crystal to grow single crystals, replacing the method of eliminating defects through multiple iterations, improving the overall utilization rate of the crystal rod and the quality of the seed crystal, thereby further improving the yield of TeO2 single crystal products and reducing quality fluctuations.

Description

Technical Field

[0001] The invention relates to the field of artificial crystal growth equipment, and in particular to a method for eliminating small-angle grain boundary defects in the growth of tellurium dioxide single crystals. Background Art

[0002] Tellurium dioxide (TeO 2 ) crystal is an acousto-optic material with excellent acousto-optic properties and is widely used in pulsed fiber laser modulation and laser radar. In the existing industrial growth technology, TeO 2 There are two conventional methods for single crystal growth: the Czochralski method and the crucible descent method. The Czochralski method eliminates most of the dislocation defects and small-angle grain boundaries in the seed crystal by necking and shouldering the seed crystal, and grows high-quality TeO 2 Single crystal. The crucible descent method is quite different from the Czochralski method. It is not possible to eliminate dislocations and defects by effectively shrinking the neck. In addition, the crucible descent method is prone to dislocation proliferation during the shoulder growth process, which aggregates into defects such as small-angle grain boundaries. Generally, small-angle grain boundaries refer to the grain boundaries of adjacent grains with a phase difference of less than 10°.

[0003] In the prior art, high-quality TeO 2 Single crystals are usually grown using equal-diameter seed crystals. There are two options for high-quality equal-diameter seed crystals: 1. Select the defect-free part of the entire crystal (product grade) for crystal growth; 2. Select the part with slight defects for iteration to eliminate the defects. The cost of these two options is relatively high. In addition, multiple iterations are also prone to fluctuations in yield, because multiple iterations can gradually eliminate the small-angle grain boundaries near the outer layer, while the small-angle grain boundaries in the middle are difficult to completely eliminate.

[0004] In order to solve the above problems, the present invention provides a method for growing high-quality TeO when there are small-angle grain boundaries inside the seed crystal. 2 Single crystal method. Summary of the invention

[0005] In view of the above-mentioned deficiencies in the prior art, one of the purposes of the present invention is to provide a method for eliminating the generation of small-angle grain boundary defects in the growth of tellurium dioxide single crystals, thereby improving the quality of seed crystals and the utilization rate of crystal rods. In particular, when there are small-angle grain boundaries inside the crystal rod, the defects are completely eliminated by adopting a "reversing" growth method, thereby replacing the multiple iterations in the prior art, improving the overall utilization rate of the crystal rod and the quality of the seed crystal, and further improving the utilization rate of the TeO 2 Single crystal yield rate, reducing quality fluctuations.

[0006] A method for eliminating small-angle grain boundary defects in the growth of tellurium dioxide single crystals comprises the following steps:

[0007] A. Processing of seed crystals: cutting the crystal rod into crystal blocks, controlling the crystal orientation deviation of the crystal blocks within 0.5°, and then rough grinding, fine grinding, and polishing; at the same time, controlling the temperature of the cutting fluid, grinding fluid, and polishing fluid during the rough grinding, fine grinding, and polishing process, and using an infrared thermometer to regularly measure the temperature difference between the inside and outside of the seed crystal; after polishing, the required seed crystals are obtained, and the internal quality screening is performed in a dark room using a laser, and the distribution position and quantity of the corresponding small-angle grain boundaries are marked on the seed crystals with a marker pen;

[0008] B. The seed crystal is subjected to a reversing operation, that is, the (1-10) plane is used as the growth plane, and the internal small-angle grain boundary is perpendicular to the [1-10] crystal direction or parallel to the

[110] crystal direction;

[0009] C. placing the obtained seed crystal into a crucible with the growth surface facing upward, placing the tellurium dioxide raw material on top of the seed crystal, and sealing the crucible, and then placing it in a crystal growth furnace, heating and melting the tellurium dioxide raw material and the top of the seed crystal to achieve seeding growth;

[0010] D. growing a tellurium dioxide single crystal by a crucible descent method, controlling the temperature gradient of the solid-liquid interface and the descent rate of the crucible; after the growth stage is stable, using a system temperature compensation method to reduce the acceleration during the crystal growth process; and performing an in-situ annealing treatment to obtain the tellurium dioxide single crystal.

[0011] Furthermore, the number of small-angle grain boundaries inside the seed crystal does not exceed 3, and the cross-sectional dimension is 0.5-1 mm smaller than the cross-sectional dimension of the crucible, the chamfer dimensions of the four sides are R2-R3, and the height is above 30 mm.

[0012] Furthermore, the long crystal face is the end face with fewer defects on the (1-10) face, the face with more defects is marked as the bottom face, and the small-angle grain boundary is within 15 mm from the long crystal face.

[0013] Furthermore, the crystal orientation of the (110) plane of the seed crystal is 13°06′±30′, the crystal orientation of the (001) plane is 23°53′±30′, and the crystal orientation of the (1-10) plane is 13°06′±30′.

[0014] Furthermore, in step A, the temperature difference between the inside of the seed crystal and the outside is no more than 5°C.

[0015] Preferably, the seed crystals in step A are moved into a beaker containing 95% anhydrous ethanol and ultrasonically cleaned for 20 minutes. After cleaning, the seed crystals are placed on a pad to dry, marked and set aside.

[0016] Furthermore, the crystal orientation deviation control in step A adopts a combination of an orientation instrument and manual fine grinding to grind the surface with a large orientation angle in steps, and gradually control the crystal orientation deviation within 0.5°.

[0017] Preferably, the specific process of step A grinding and polishing is: using W360 silicon carbide sand on a single-axis table, using 80-100rpm to level each plane, so that the crystal orientation angle of the crystal block is within 1° and there is no step on the surface; each edge of the crystal block is chamfered (R2-R3) for protection; using W10 fine silicon carbide sand on a single-axis table, using 80-100rpm to finely grind the surface roughness within PV0.01, the crystal orientation angle is controlled within 0.5 degrees, and the dimensional tolerance is ±0.01mm; then using cerium oxide polishing liquid at a speed of 80-120rpm to polish, so that the surface roughness reaches within PV0.001, and the optical index is 40-20.

[0018] Preferably, the temperature gradient of the solid-liquid interface in step D is set within the range of 20 to 50° C. / cm, and the descent rate of the crucible is controlled between 0.1 and 1.0 mm / h.

[0019] Beneficial effects: 1. Replacing multiple iterations by switching the growth mode can further improve the yield rate and reduce quality fluctuations;

[0020] Second, the processing allowance and utilization rate of the square crystal rod are significantly related to the crystal orientation deviation of the seed crystal. The present invention controls the crystal orientation deviation during the seed crystal processing within 0.5 degrees, effectively improving the overall utilization rate of the crystal rod. In the prior art, the crystal orientation deviation of the square seed crystal processing is usually controlled within 2 degrees, and the processing loss is large.

[0021] 3. Solve the problem of TeO by regular temperature measurement and temperature control. 2 The cleavage problem caused by temperature difference during seed crystal processing can be solved, and the quality of seed crystal can be further improved. 2 Single crystal growth reversal technology, TeO 2 Anti-cleavage technology during seed crystal processing. BRIEF DESCRIPTION OF THE DRAWINGS

[0022] Figure 1 It is a square TeO 2 Schematic diagram of seed crystal processing.

[0023] Figure 2 This is a schematic diagram of the seed crystal after processing. The reversal treatment uses the (1-10) plane as the crystal growth plane.

[0024] Figure 3 This is a photo of the surface morphology of the seed crystal before processing.

[0025] Figure 4 This is the situation of the seed crystal in the dark room after reversal growth.

[0026] Explanation of reference numerals: 1, crystal rod; 10, seed crystal; 20, low-angle grain boundary; 30, (110) plane; 40, (1-10) plane; 50, padding DETAILED DESCRIPTION

[0027] In order to better understand the technical solution of the present invention, the following is a detailed description in conjunction with specific embodiments. It should be clear that the described embodiments are only part of the embodiments of the present invention, rather than all of the embodiments. Based on the embodiments of the present invention, all other embodiments obtained by ordinary technicians in this field without creative work are within the scope of protection of the present invention.

[0028] High quality TeO 2 The acquisition of single crystals is closely related to the quality of seed crystals. When there are slight defects in the seed crystals or defects generated during the processing, on the other hand, the single crystals grown by the crucible descent method are prone to dislocation multiplication during the shoulder growth process, and defects such as aggregation into small-angle grain boundaries will affect the production efficiency of tellurium dioxide single crystals.

[0029] TeO 2 The crystal is a typical tetragonal crystal, in which the (110) face 30 is a light-transmitting face, which is usually the main growth direction of the crystal, and the orientation accuracy is required to be controlled at 13°06'±30', while the (001) face is a bonding face with the LN crystal, and the orientation accuracy is required to be controlled at 23°53'±30'. The other face is the (1-10) face 40. Due to the special physical properties of the tetragonal crystal system, the (110) face 30 and the (1-10) face 40 are equivalent faces, and theoretically, the directions can be interchanged, and the equivalent reversing growth of the crystal can be achieved on the (1-10) face 40. This is also the source of the technical concept of the present invention.

[0030] The existing process generally uses the (110) plane 30 as the growth plane of the seed crystal 10. When there are defects in the seed crystal 10, the slightly defective part is selected for iteration to eliminate the defects. For example, the small angle grain boundary 20 on the outer layer of the seed crystal 10 can be gradually eliminated through multiple iterations of growth, but the small angle grain boundary 20 in the middle is difficult to be completely eliminated. If such a seed crystal 10 is used to inoculate the growth of tellurium dioxide single crystals, the small angle grain boundary 20 will be inherited to the new crystal, so the industry will not select the crystal rod 1 with a small angle grain boundary 20 in the middle as the seed crystal 10.

[0031] In this regard, the present invention provides a method for eliminating the generation of small-angle grain boundary defects in the growth of tellurium dioxide single crystals, comprising the following steps:

[0032] A. Processing of the seed crystal 10: cutting the crystal rod 1 into crystal blocks, selecting a suitable crystal block, controlling its crystal orientation deviation within 0.5 degrees, and performing rough grinding, fine grinding, and polishing; at the same time, controlling the temperature of the cutting liquid, grinding liquid, and polishing liquid during the rough grinding, fine grinding, and polishing process, and using an infrared thermometer to regularly measure the temperature difference between the inside and the outside of the seed crystal 10; after polishing, the desired seed crystal 10 is obtained, and internal quality screening is performed in a dark room using a laser, and the distribution position and quantity of the corresponding low-angle grain boundaries 20 are marked on the seed crystal 10 using a marker.

[0033] B. The seed crystal 10 is subjected to a reversing operation, that is, the (1-10) plane 40 is used as the growth plane, and the internal low-angle grain boundary 20 is perpendicular or nearly perpendicular to the [1-10] crystal direction or parallel to the

[110] crystal direction.

[0034] C. Load the obtained seed crystal 10 into a crucible with the growth surface facing upward, place the tellurium dioxide raw material above the seed crystal 10, and seal the crucible. Then put it into a crystal growth furnace, heat and melt the tellurium dioxide raw material and the top of the seed crystal 10 to achieve seeding growth.

[0035] D. growing a tellurium dioxide single crystal by a crucible descent method, controlling the temperature gradient of the solid-liquid interface and the descent rate of the crucible; after the growth stage is stable, using a system temperature compensation method to reduce the acceleration during the crystal growth process; and performing an in-situ annealing treatment to obtain the tellurium dioxide single crystal.

[0036] Among them, the selection principles of the crystal block as the seed crystal 10 are as follows: 1. The crystal block is required to have no internal cracks and cloud layers on a macro scale; 2. The number of small-angle grain boundaries 20 is ≤3; 3. The cross-sectional size is controlled to be 0.5-1mm smaller than the crucible cross-sectional size, the four-sided chamfer size is R2-R3, and the height is controlled to be above 30mm.

[0037] The more specific steps of processing the seed crystal 10 are to use a conventional

[110] oriented crystal rod to cut into the required size of the seed crystal 10 blank, grind the three groups of directions of length, width and height to the specified size and crystal orientation range respectively, and then perform a rough grinding process. After the rough grinding, enter the fine grinding process. After the fine grinding is completed, add a certain particle size of cerium oxide polishing powder on the polishing machine to perform four-sided detection polishing, including two sides of the (1-10) face 40 and two sides of the (001) face. During the grinding and polishing process, the temperature difference between the crystal block and the external environment temperature must be controlled, and the requirement is ≤5°C to avoid

[010] direction cleavage caused by the ambient temperature difference inside and outside the crystal block. If the temperature difference exceeds 5°C, the crystal block needs to be left still for a period of time, and the processing can continue after the internal and external temperatures of the crystal are stable and balanced.

[0038] Preferably, after the seed crystal 10 is processed, in order to eliminate the pollution caused by the organic materials and metal grinding disc used in the processing steps, the seed crystal 10 is ultrasonically cleaned for 20 minutes, wherein the solution used to soak the seed crystal 10 during the ultrasonic treatment is a 95% anhydrous ethanol solution, thereby further improving the internal quality of the crystal growth.

[0039] Furthermore, the end face of the (1-10) plane 40 with fewer defects is marked as the long crystal face, and the end face with more defects is marked as the bottom face, and the small-angle grain boundary is within 15 mm from the long crystal face.

[0040] It should be noted that when using the (1-10) plane 40 as the crystal growth plane, the selection and processing of the seed crystal 10 is one of the key steps, because tellurium dioxide is a covalent bond crystal, slightly soluble in water, and will decompose when encountering strong acids and alkalis. It has low hardness and is relatively soft, and is easily scratched during polishing; its thermal conductivity is also low, and it is easy to crack during processing. On the other hand, the processing allowance and utilization rate of the square crystal rod are significantly correlated with the crystal orientation deviation of the seed crystal 10. As shown in Table 1, the present invention can control the crystal orientation deviation within 0.5 degrees, greatly improving the utilization rate of the crystal rod. In the prior art, the crystal orientation deviation of the square seed crystal processing is usually controlled within 2 degrees, and the processing loss is relatively large.

[0041] Another key factor in using the (1-10) plane 40 as the crystal growth plane is to control the seeding growth of the seed crystal 10, especially to control the growth at the solid-liquid interface. No small-angle grain boundaries 20 or other defects can exist near the solid-liquid interface.

[0042] Example: The specific implementation method is as follows: 35*25*50-55mm square high-quality TeO 2 Taking the processing of seed crystal 10 as an example, several 35*25*200mm type B crystal rods 1 grown in the

[110] direction are selected. The type B crystal rod 1 refers to a crystal rod with 1-3 internal small-angle grain boundaries 20. Figure 1 As shown, the crystal rod 1 is processed in sections, and each can be cut into 5-6 crystal blocks of 35*25*36mm. After cutting, the size and direction of the crystal blocks are roughly ground, finely ground, and polished. In the process of cutting, grinding and polishing, the temperature of the cutting liquid, grinding liquid and polishing liquid is strictly controlled. An infrared handheld thermometer is used to regularly measure the temperature difference between the inside and outside of the seed crystal 10 and control it at 2-5°C. For example, the mixing ratio of hot water and cold water can be controlled by a water heater to achieve relatively accurate temperature control.

[0043] The specific process of grinding and polishing: Use W360 silicon carbide sand on a single-axis table, use 80-100rpm to level each plane, so that the crystal orientation angle of the crystal block is within 1° and there is no step on the surface. Chamfer each edge of the crystal block (R2-R3) for protection. Use W10 fine silicon carbide sand on a single-axis table, use 80-100rpm to finely grind the surface roughness within PV0.01, the crystal orientation angle within 0.5 degrees, and the dimensional tolerance is ±0.01mm. Then use cerium oxide polishing liquid at a speed of 80-120rpm to polish, so that the surface roughness reaches within PV0.001, and the optical index is 40-20.

[0044] According to the principle of seed crystal 10 selection, after polishing, a 400mW 532nm laser is used to perform internal quality screening in a dark room, and a marker is used to mark the distribution position and number of the corresponding low-angle grain boundaries 20 on the polished crystal block. After the selection is completed, the reversing processing operation is performed, such as Figures 1 to 3 As shown, Figure 2 It is a schematic diagram of the crystal plane of the seed crystal 10. The reversal process is to use the (1-10) plane 40 as the crystal growth plane instead of the (110) plane 30. Figure 3 The image shows the morphology of the processed seed crystal (110) surface, where the low-angle grain boundary 20 can be clearly seen. The end face of the (1-10) surface 40 with fewer defects is marked as the T face (i.e., the long crystal face), and the end face with more defects is marked as the B face (i.e., the bottom face). After the seed crystal 10 reversing step is completed, it is moved into a large beaker filled with 95% anhydrous ethanol and ultrasonically cleaned in an ultrasonic machine for 20 minutes. After the cleaning is completed, the seed crystal 10 and the pad are combined and dried. After the treatment is completed, the corresponding markings and distinctions are made and transferred to a moisture-proof cabinet for standby use.

[0045] Comparative example: Taking the processing of 35*25*50-55mm seed crystal 10 as an example, several 35*25*200mm Class B

[110] direction grown crystal rods 1 are selected for segmented processing. Each of them can be cut into 3-4 35*25*55mm blocks. After cutting, the size and direction of the seed crystal 10 blocks are coarsely ground, finely ground and polished. The small-angle grain boundaries 20 near the edge of the crystal rod 1 that does not change direction along the

[110] growth direction gradually terminate at the outer surface of the crystal rod during the growth process. It takes 2-3 rounds of iterative growth to gradually eliminate the small-angle grain boundaries 20 near the outer layer, and it is difficult to completely eliminate the small-angle grain boundaries 20 in the middle.

[0046] Table 1 Utilization rate of

[110] orientation of crystal ingot with different orientation deviation angles

[0047]

[0048] The seed crystals 10 prepared in the embodiment and the comparative example are placed on the pads 50 in the crucible, respectively, and single crystal growth is prepared according to the process parameters of the crucible descent method. The specific steps are to load the obtained seed crystal 10 into the crucible with the growth surface facing up, place the tellurium dioxide raw material above the seed crystal 10, and seal the crucible, then put it into the crystal growth furnace, heat and melt the tellurium dioxide raw material and the top of the seed crystal 10 to achieve inoculation growth; control the temperature gradient of the solid-liquid interface and the descent rate of the crucible; after the growth stage is stable, use the system temperature compensation method to reduce the acceleration during the crystal growth process; in-situ annealing treatment to obtain the tellurium dioxide single crystal. Preferably, the temperature gradient of the solid-liquid interface is set in the range of 20 to 50°C / cm, and the crucible descent rate is controlled between 0.1 and 1.0 mm / h.

[0049] Figure 3 The figure shows the morphology of the seed crystal after processing, and the existence of the small-angle grain boundary 20 can be clearly seen. Figure 4 This is the situation of the seed crystal 10 after the reversal growth in the dark room, using a 400mW 532nm laser. Where the small-angle grain boundary 20 exists, there will be a bright line area inside the optical path due to the refraction of light, and the uniformity of the optical path will be different. Figure 4 It can be seen that there are not so many small-angle grain boundaries 20, and the refraction of light is not very obvious.

[0050] The above description is only a preferred embodiment of the present invention and does not limit the technical scope of the present invention. Therefore, any slight modification, equivalent changes and modifications made to the above embodiments based on the technical essence of the present invention still fall within the protection scope of the present invention.

Claims

1. A method for eliminating small-angle grain boundary defects in the growth of tellurium dioxide single crystals, characterized in that: The following steps are involved: A. Processing of seed crystal: cutting the crystal rod into crystal blocks, controlling the crystal orientation deviation of the crystal blocks within 0.5°, and then rough grinding, fine grinding and polishing; at the same time, controlling the temperature of the cutting liquid, grinding liquid and polishing liquid during the rough grinding, fine grinding and polishing process, and using an infrared thermometer to regularly measure the temperature difference between the inside and outside of the seed crystal; After polishing, the desired seed crystal is obtained, and the internal quality screening is performed in a dark room using a laser, and the distribution position and number of the corresponding small-angle grain boundaries are marked on the seed crystal using a marker pen; wherein the number of the small-angle grain boundaries inside the seed crystal does not exceed 3, and the cross-sectional size is 0.5-1 mm smaller than the cross-sectional size of the crucible, the four-sided chamfer size is R2-R3, and the height is above 30 mm; B. The seed crystal is subjected to a reversing operation, that is, the (1-10) plane is used as the growth plane, and the internal small-angle grain boundary is perpendicular to the [1-10] crystal direction or parallel to the [110] crystal direction; C. placing the obtained seed crystal into a crucible with the growth surface facing upward, placing the tellurium dioxide raw material on top of the seed crystal, and sealing the crucible, and then placing it in a crystal growth furnace, heating and melting the tellurium dioxide raw material and the top of the seed crystal to achieve seeding growth; D. growing a tellurium dioxide single crystal by a crucible descent method, controlling the temperature gradient of the solid-liquid interface and the descent rate of the crucible; after the growth stage is stable, using a system temperature compensation method to reduce the acceleration during the crystal growth process; and performing an in-situ annealing treatment to obtain the tellurium dioxide single crystal.

2. A method for eliminating small-angle grain boundary defects in the growth of tellurium dioxide single crystals according to claim 1, characterized in that: The long crystal face is the end face with fewer defects on the (1-10) face, the face with more defects is marked as the bottom face, and the small-angle grain boundary is within 15 mm from the long crystal face.

3. The method for eliminating small-angle grain boundary defects in the growth of tellurium dioxide single crystal according to claim 1, characterized in that: The crystal orientation of the (110) plane of the seed crystal is 13°06′±30′, the crystal orientation of the (001) plane is 23°53′±30′, and the crystal orientation of the (1-10) plane is 13°06′±30′.

4. The method for eliminating small-angle grain boundary defects in the growth of tellurium dioxide single crystal according to claim 1, characterized in that: In step A, the temperature difference between the inside of the seed crystal and the outside is no more than 5°C.

5. The method for eliminating small-angle grain boundary defects in the growth of tellurium dioxide single crystal according to claim 1, characterized in that: The seed crystals in step A are moved into a beaker containing 95% anhydrous ethanol and ultrasonically cleaned for 20 minutes. After cleaning, the seed crystals are placed on a pad to dry, marked and set aside.

6. The method for eliminating small-angle grain boundary defects in the growth of tellurium dioxide single crystal according to claim 1, characterized in that: In step A, the crystal orientation deviation is controlled by combining an orientation instrument with manual fine grinding, and the surface with a large orientation angle is ground step by step to gradually control the crystal orientation deviation within 0.5°.

7. The method for eliminating small-angle grain boundary defects in the growth of tellurium dioxide single crystal according to claim 1, characterized in that: The specific process of step A grinding and polishing is as follows: using W360 silicon carbide sand on a single-axis table, using 80-100rpm to level each plane, so that the crystal orientation angle of the crystal block is within 1° and there is no step on the surface; each edge of the crystal block is chamfered (R2-R3) for protection; using W10 fine silicon carbide sand on a single-axis table, using 80-100rpm to finely grind the surface roughness within PV0.01, the crystal orientation angle within 0.5 degrees, and the dimensional tolerance is ±0.01mm; then using cerium oxide polishing liquid at a speed of 80-120rpm to polish, so that the surface roughness reaches within PV0.001, and the optical index is 40-20.

8. The method for eliminating small-angle grain boundary defects in the growth of tellurium dioxide single crystal according to claim 1, characterized in that: In step D, the temperature gradient of the solid-liquid interface is set in the range of 20 to 50° C. / cm, and the descent rate of the crucible is controlled between 0.1 and 1.0 mm / h.

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