CN109112631B

CN109112631B - Sapphire C-direction crystal growth method

Info

Publication number: CN109112631B
Application number: CN201811267589.6A
Authority: CN
Inventors: 徐永亮; 冯微; 汪海波; 于海群; 张国华; 邱超
Original assignee: Zhejiang Yunfeng New Energy Technology Co ltd
Current assignee: Zhejiang Yunfeng New Energy Technology Co ltd
Priority date: 2018-10-29
Filing date: 2018-10-29
Publication date: 2021-01-01
Anticipated expiration: 2038-10-29
Also published as: CN109112631A

Abstract

The application provides a sapphire C is to growing crystal method, the method adopts "pagoda" seeding and "sitting pot" mode to grow crystal, can reduce the bubble scope at sapphire crystal top and can cut off defects such as crystal dislocation, can reduce moreover and give the cracked risk of pulling speed seed crystal or chuck when the bottom glues the pot to improve crystal quality, improve the utilization ratio of crystal.

Description

Sapphire C-direction crystal growth method

Technical Field

The invention belongs to the technical field of sapphire single crystal growth, and particularly relates to a C-direction crystal growth method for large-size sapphire in a single crystal furnace.

Background

Sapphire (alpha-Al)₂O₃) The preparation method has the characteristics of high hardness, high strength, corrosion resistance, high light transmittance and the like, and since the first preparation of the sapphire crystal by Viner, a French scientist in 1890, the preparation technology of the artificial sapphire crystal is rapidly developed, the crystal quality is continuously improved, and the application field is greatly widened. At present, sapphire is widely used in various fields such as civil use and military affairs. In the civil field, sapphire is used for wear-resistant structural parts, medical materials, high-temperature windows, substrate materials in the microelectronic industry, laser matrix materials, optical prisms, mobile phone windows and the like; in the military field, the sapphire is used as a wave-transparent window of a high-speed airplane and a missile, a photoelectric pod, a photoelectric mast of a submarine and the like. The continuously expanding application fields continuously put forward new requirements on sapphire materials, and besides high hardness, high strength and wear resistance, the sapphire materials are also required to have the properties of low stress, high optical integrity, large diameter and the like. Therefore, growing low cost, large size, high quality sapphire is a trend for artificially synthesizing sapphire.

Methods for artificially synthesizing sapphire, that is, growing sapphire crystals, mainly include czochralski method (cz), Heat Exchange Method (HEM), temperature gradient method (TGT), Kyropoulos method (Kyropoulos), and the like. Wherein, the Czochralski method and the temperature gradient method are mainly used for growing the sapphire crystal below 100 kg; in the heat exchange method, because the thermal expansion coefficients of the molybdenum crucible and the sapphire single crystal are different, thermal stress is easily generated at the contact part of the crystal and the crucible edge, and further the external crack of the single crystal is easily caused. Therefore, the kyropoulos method is mainly used for growing large-size sapphire at present, and the method has the advantages of few crystal defects and low dislocation density.

The rapid development of the sapphire substrate-based LED technology occupies more than 90% of the LED substrate market, and the demand for sapphire substrate sheets of 6 inches or more is increasing. Since C-plane sapphire crystals have a small lattice mismatch with iii/v and ii/vi compound thin films (e.g., GaN thin films), for example, the lattice mismatch between C-plane sapphire and GaN thin films is only 17%, C-plane sapphire is often used as a GaN thin film epitaxial growth layer in the LED field.

For sapphire, C-direction crystal growth has great difficulty in obtaining large-size and high-quality sapphire, and generally, C-direction grown sapphire crystals are small in weight, generally below 80 kg. Specifically, the degree of deformation of the C-direction growth lattice is greater than that of other directions, and any heterogeneous nucleation is liable to generate parasitic defects due to the anisotropy of the sapphire crystal. In addition, dislocation defects existing in the seed crystal itself are also propagated to the grown crystal. According to the Burger's vector conservation theory, if the dislocation intersects with the growth interface, the dislocation extends along with the interface in the growth process, the dislocation line has special topological property, the dislocation in the C axis direction can extend to the surface of the C crystal, the C-direction crystal growth can be continuously accumulated along with more and more interface dislocation lines, the crystal dislocation is higher and higher, and the C-direction crystal growth is easy to have the problems of small-angle crystal boundaries and large-angle crystal boundaries.

Compared with the crystal growth in the C direction, the crystal growth in the A direction is easier, so that the sapphire for growing the LED substrate at home and abroad at present mostly adopts the mode of crystal growth in the A direction and bar drawing in the C direction. However, since the top of the crystal growth crystal in the direction a is prone to generate conical bubble columns, the bottom of the crystal growth crystal in the direction a is prone to generate inverted bowl-shaped bubble clouds, and the transverse bar digging leads to low material utilization rate, as shown in fig. 1 and fig. 2, the utilization rate of the crystal growth in the direction a is low, and is only 37.5%. If sapphire crystals with the same size and the same weight are subjected to C-direction crystal growth, the crystal utilization rate can be increased to 56.5%, namely the C-direction crystal growth rod picking amount is 1.5 times of the A-direction crystal growth rod picking amount, so that the crystal utilization rate obtained by C-direction crystal growth is greatly increased.

As the C-direction growth process in the current market is mainly crystals below 80kg, the growth of large-size crystals is not mature, and the C-direction crystal growth is easy to have the problems of small-angle crystal boundaries and large-angle crystal boundaries, so that the utilization rate of the crystals is influenced. Therefore, it is highly desirable to develop a method for C-direction growth of sapphire that can reduce the problems of small angle grain boundaries and large angle grain boundaries.

Disclosure of Invention

The method provided by the application comprises the following steps:

step 1, putting a crucible filled with alumina raw materials into a furnace chamber, vacuumizing the furnace chamber, and melting the materials to obtain alumina dissolving soup;

step 2, putting the seed crystals into the alumina solution, and instantly extracting the seed crystals by a first preset height at intervals of a first preset time interval until the diameter of the crystals is a preset diameter;

step 3, reducing the pulling speed to 0, when the weight of the crystal is the first preset weight ratio of the charging amount, instantly extracting the second preset height of the crystal, increasing the heating power, gradually reducing the heating power after increasing the heating power, and controlling the crystal growth speed of the crystal to be smaller than the preset growth speed;

step 4, when the weight of the crystal is larger than a second preset weight proportion, calculating the average length speed v of the crystal within the last 24 hours, calculating the residual growth time h by using the following formula I according to the average length speed v, and continuously reducing the temperature h at the current amplitude reduction rate for h hours:

h ═ Δ w/v formula I

Wherein h represents the remaining growth time,

aw represents the weight of the remaining alumina sol,

v represents the average growth rate of the crystals over the last 24 hours;

and 5, adjusting the position of the crystal according to the weight of the crystal until the weight of the crystal is stabilized to a preset weight range within a preset time.

In an achievable mode, in the step 1, the purity of the alumina raw material is more than 5N, and the vacuum degree after the furnace chamber is vacuumized is lower than 1e-4 Pa.

In an implementable manner, in step 1, the material melting comprises the following sub-steps:

substep 1, increasing power to target power according to a preset power increasing speed, and keeping the temperature at the target power until the alumina raw material is in a molten state;

and step 2, preserving the temperature of the system obtained in the step 1, monitoring the state of the alumina raw material during the heat preservation period, continuously increasing the power if crystals are precipitated in the alumina dissolving soup, and preserving the temperature of the system again after increasing the power.

In an achievable mode, in the substep 1, the ramp-up power is increased by 500w/h to 1000w/h based on the existing ramp-up power.

In a realizable manner, in step 1, before placing the crucible containing the alumina feedstock into the furnace chamber, the method further comprises verifying the presence of defects in the seed crystal, said defects comprising: bubbles, twins and cracks.

In an achievable mode, in the step 2, the states of the alumina dissolving soup and the seed crystal are monitored during the process of putting the seed crystal into the alumina dissolving soup, and if the lower end of the seed crystal is rounded, the seed crystal is pulled; and/or increasing the power if crystals precipitate in the alumina sol.

In a realizable manner, in step 2, the first preset time interval is 0.5-15 min, preferably 1-10 min, and/or the first preset height is 0.1-5 mm, preferably 0.5-2 mm; and/or the preset diameter is 30-150 mm, preferably 60-100 mm.

In an achievable manner, in step 3, the predetermined weight ratio is 8 wt% to 15 wt%; and/or the second preset height is 2-5 mm.

In an achievable manner, in step 4, the predetermined weight proportion is 70 wt% to 80 wt% of the charge.

In a realizable mode, in the step 5, the preset time is 8-12 h; and/or the predetermined weight range is plus or minus 0.5-2 kg, such as plus or minus 1kg, of the charged alumina raw material.

The method provided by the application adopts a tower-type seeding mode, can effectively reduce the range of bubbles at the top, and simultaneously cuts off the defects of sapphire crystal dislocation and the like through instantaneous extraction, thereby improving the quality and the utilization rate of the sapphire crystal. Meanwhile, the pulling speed of the seed crystal is reduced to 0 at the shoulder expanding stage by the scheme provided by the application, natural convection is presented in the crystal growing furnace, so that the transverse temperature gradient and the longitudinal temperature gradient are stable during the growth of the sapphire crystal, the thermal stress in the sapphire crystal caused by temperature disturbance is reduced, the generation of dislocation, small-angle crystal boundary and large-angle crystal boundary in the sapphire crystal is reduced, the risk of cracking is reduced, the crystal growing quality is improved, the residual stress in the crystal is reduced through the reasonable design of radial temperature gradient and transverse temperature gradient, and the C-direction crystal growing of large-size sapphire is realized. In addition, this application adopts "sitting pot" mode growth sapphire crystal to reduce the formation of later stage final phase bottom back-off bowl form bubble, compare for the speed of drawing to take off the final phase, the method that this application provided has reduced because the seed crystal fracture or the cracked risk of chuck that the pot caused is glued to the crystal bottom at the in-process of growing jumbo size sapphire crystal. Further, the pulling speed is automatically adjusted according to the change of weighing during annealing in the annealing stage, so that the automatic control of the annealing stage is realized, and the risk of breakage of the seed crystal or the seed chuck caused by overweight due to improper manual monitoring is reduced.

Drawings

FIG. 1 is a schematic view showing a bar drawing manner for growing a sapphire crystal in the A direction;

fig. 2 shows a schematic drawing of a bar drawing manner of a C-direction grown sapphire crystal.

Detailed Description

The technical solutions in the embodiments of the present invention will be described clearly and completely with reference to the following embodiments of the present invention, and it is obvious that the described embodiments are only a part of the embodiments of the present invention, and not all of the embodiments. All other embodiments, which can be derived by a person skilled in the art from the embodiments given herein without making any creative effort, shall fall within the protection scope of the present invention.

The technical solution of the present application is described in detail below.

The invention provides a novel sapphire C-direction crystal growth process aiming at the defect of sapphire C-direction crystal growth process by using a kyropoulos method, and the C-direction crystal growth of large-size (such as 200kg or more) sapphire can be realized. The sapphire C-direction crystal growth method provided by the application comprises the following steps:

step 1, putting a crucible filled with alumina raw materials into a furnace chamber, vacuumizing the furnace chamber, and melting the materials to obtain alumina dissolving soup.

In this embodiment, before placing the crucible containing the alumina source material into the furnace chamber, the method further comprises inspecting the seed crystal for defects, the defects comprising: bubbles, twins and cracks. Specifically, a polarizer and a strong photoelectric inspection can be used for observing whether bubbles, twin crystals, cracks and the like exist in the seed crystal, if the seed crystal is found to be unqualified, the qualified seed crystal is replaced in time, and the phenomenon that excessive defects exist in the seed crystal and are transmitted to the growing crystal to influence the crystal quality is avoided.

In this embodiment, the purity of the alumina raw material is 5N (i.e., 99.999%) or more, and the use of such a high-purity alumina raw material can fundamentally reduce defects of the produced sapphire crystal.

The crucible filled with the high-purity alumina raw material is filled into a sapphire furnace cavity, the sapphire furnace can be any one of sapphire furnaces in the prior art, whether a thermal field, a heat preservation screen, a temperature sensor and the like of the sapphire furnace are normal or not is checked before the sapphire furnace is used, and the problem that the growth of sapphire crystals fails due to the fact that the temperature is insufficient or suddenly cooled and the like happen in the growth process of the sapphire crystals is avoided. And when the sapphire furnace is checked, closing the furnace chamber and vacuumizing.

In this embodiment, after the furnace chamber is evacuated to a degree of vacuum of less than 1e to 4Pa, evacuation is considered to be completed. Then the material melting procedure is started.

In one implementable manner, the material melting comprises the following substeps:

and substep 1, increasing the power to a target power according to a preset power increasing speed, and keeping the temperature at the target power until the alumina raw material is in a molten state.

In the embodiment, the preset power increasing rate can be determined according to the charging amount of the alumina, and specifically can be 3-10 kw/h, and preferably 5-7 kw/h, for example, for a charging amount of 400kg, the preset power can be 5.33kw/h, and for a small charging amount, the power increasing rate can be reduced appropriately.

The applicant finds that, because the expansion rates of the alumina raw material and the crucible are different, specifically, the expansion rate of the alumina is large, and the expansion rate of the crucible is small, if the preset power is increased too much, the alumina is expanded too fast, and the crucible is cracked, so that the preset power is increased at 3-10 kw/h in the embodiment.

In the embodiment, the target power can also be determined according to the alumina charge, and specifically can be 100-150 kw, for example, the charge can be 120kw for 400kg, and the target power can be reduced appropriately for a small charge.

In this example, after the system is raised to the target temperature and the solution is formed, the system is kept warm, and the state of the system is observed at intervals (e.g., 1 hour), and if the phenomenon that crystals are precipitated from the alumina solution, for example, the crystals are crystallized or cake is formed on the surface of the solution, the heating power of the system is increased, so that the solution is returned to the molten state. And continuously monitoring for 5-10 hours, and releasing seed crystals into the dissolved soup when the dissolved alumina soup is continuously kept in a molten state.

And 2, putting the seed crystal into the alumina solution, and instantly extracting the seed crystal by a first preset height at intervals of a first preset time interval until the diameter of the crystal is the preset diameter.

In this embodiment, the states of the alumina dissolving soup and the seed crystal are monitored during the process of placing the seed crystal into the alumina dissolving soup, and if the lower end of the seed crystal is rounded, it indicates that the dissolving soup temperature is too high, the seed crystal is melted in the dissolving soup and loses the function of the seed crystal as a seed crystal for growing sapphire, so that the seed crystal needs to be pulled to be separated from the alumina dissolving soup, and the alumina dissolving soup is cooled. The applicant finds that when the seed crystal is pulled to a position where the bottom end of the seed crystal is 20-30 mm away from the surface of the molten soup, the seed crystal is not influenced by the temperature of the molten soup. In this case, the operator can reduce the heating power according to the seed crystal baking position, the seed crystal end condition, the liquid flow form and other conditions, so that the dissolved soup can keep the molten state and can not bake the seed crystal.

Because the temperature of the seed crystal is far lower than that of the alumina dissolving soup, and the seed crystal is usually kept at a lower temperature by adopting cooling modes such as water cooling and the like, if crystals are separated out from the alumina dissolving soup in the process of putting down the seed crystal, for example, the surface of the alumina has crystal floating or cake formation, the heating power needs to be increased to keep the alumina solution in a molten state, thereby ensuring that the quality of the sapphire crystal is excellent.

And after continuously and repeatedly adjusting to a proper temperature, putting the seed crystal and melting the solution. When the seed crystal and the solution are welded, the system reduces the heating power according to a specific reduction amplitude, and the specific reduction amplitude can be adjusted according to the growth speed of the crystal.

In this embodiment, the first predetermined time interval is 0.5 to 15min, preferably 1 to 10 min; the first preset height is 0.1-5 mm, and preferably 0.5-2 mm.

The applicant finds that the seed crystal is beneficial to pulling out a high-quality crystal tray when growing in the alumina solution for 0.5-15 min, and the seed crystal is easy to bake if the growth time is too long; and if the growth time is too short, the defects of hollowness, deviation and the like of the finally obtained sapphire crystal can be caused because the seed crystal cannot be cleaned completely. When the seed crystal grows in the alumina solution for 0.5-15 min, the seed crystal is pulled upwards, so that the seed crystal can be cleaned, dislocation extending from the seed crystal can be reduced by using instant pulling, and a high-quality crystal junction is obtained.

The applicant also finds that each time the sapphire crystal is pulled by 0.1-5 mm, especially 0.5-2 mm, the part of the sapphire crystal which is separated from the molten liquid is subjected to quenching, so that the defects such as crystal dislocation and the like which possibly exist in the sapphire crystal are cut off along with the quenching, and the quality of the sapphire crystal is improved.

The preset diameter is 30-150 mm, preferably 60-100 mm, and when the sapphire crystal grows to the diameter, the operator can observe the form of the sapphire crystal conveniently, so that the growth process can be monitored, and the later growth of the sapphire crystal can be continued conveniently.

The applicant finds that if a universal seed crystal is used, the diameter of the sapphire crystal can reach about 60-100 mm by repeating the process for 20-50 times.

The seeding method provided by the application can effectively reduce the range of bubbles at the top, can cut off defects such as crystal dislocation and the like, and improves the product quality of the sapphire crystal.

And 3, reducing the pulling speed to 0, when the weight of the crystal is the first preset weight ratio of the charging amount, instantly extracting the second preset height of the crystal, increasing the heating power, gradually reducing the heating power after increasing the heating power, and controlling the crystal growth speed of the crystal to be smaller than the preset growth speed.

And when the diameter of the sapphire crystal reaches the preset diameter, reducing the pulling speed to 0, namely, not pulling the seed crystal any more, reducing the heating power at a specific amplitude reduction to enable the sapphire crystal to grow in a shoulder expanding manner, wherein the specific amplitude reduction can be adjusted according to the speed of the sapphire crystal growing in the shoulder expanding manner.

In the shoulder-expanding growth process, the sapphire crystal grows upwards automatically, in the process, the weight of the sapphire crystal is monitored, and according to the charging amount and the diameter of the crucible, when the weight of the sapphire crystal is 8-15 wt% of the charging amount, shoulder expanding can be finished.

In the embodiment, after the shoulder expanding is completed, the seed crystal is lifted instantly by 2-5 mm, the shoulder rotating is completed, and the phenomenon that the shoulder rotates to stick to the pot is avoided.

Further, after the instant lifting, the heating power is increased, optionally, the heating power is increased by 400-800W to prevent the crystal part from sticking to the pot during shoulder expanding, and the heating power is increased to melt the pot.

After the heating power is increased, the pulling speed of the sapphire crystal is kept to be 0, namely, the sapphire crystal is not pulled, so that the sapphire crystal is subjected to constant-diameter growth, and the amplitude reduction of the heating power is maintained to be the specific amplitude reduction in the shoulder-expanding growth stage.

In the embodiment, in the process of the constant diameter growth of the sapphire crystal, the heating power is gradually reduced to control the growth speed of the sapphire crystal to be between 1.5kg/h and 3 kg/h.

The applicant finds that when the growth speed of the sapphire crystal is more than 3kg/h, bubbles of the grown sapphire crystal are increased, the cracking risk is increased, and the crystal utilization rate is influenced; when the growth speed is less than 1.5kg/h, the growth return melting lines are increased, the crystal material taking rate is influenced, meanwhile, the growth period is increased, and the energy consumption is larger. Therefore, the present example controls the growth rate of the sapphire crystal to be between 1.5kg/h and 3 kg/h.

In this embodiment, the temperature reduction amplitude in the growth furnace is controlled by controlling the heating power reduction amplitude, optionally, the heating power reduction amplitude is 10-80 w/h, so as to control the temperature reduction amplitude in the growth furnace

h ═ Δ w/v formula I

Wherein h represents the remaining growth time,

Δ w represents the weight of the remaining alumina sol, which may be the difference between the amount of alumina raw material charge minus the weight of sapphire crystal;

v represents the average growth rate of the crystals over the last 24 hours.

In this embodiment, the second predetermined weight proportion is 70 wt% to 80 wt% of the charge amount. For example, if the charged amount is 400kg, when the weight of the sapphire crystal is 350kg, it is considered that the long speed calculated by weighing is inaccurate, and it is necessary to calculate the remaining growth time by the above formula I.

The applicant finds that the growth speed of the sapphire crystal in the equal-diameter growth stage, particularly the later stage of the equal-diameter growth is almost stable and unchanged in the last 24 hours, so that the residual growth speed can be estimated according to the average speed of the last 24 hours, the residual growth time is calculated by utilizing the residual amount of the alumina raw material, the residual growth time can be estimated more accurately, the pot-sitting growth time can be better mastered, and the quality of the sapphire crystal is improved.

In step 4 of this embodiment, after the growth time of the sapphire crystal reaches the estimated time h, the heating power of the sapphire is reduced, and the annealing stage, i.e., step 5, is performed.

In this embodiment, the position of the crystal refers to the relative position of the sapphire crystal and the alumina sol, i.e., whether the sapphire crystal is pulled up or down.

In this embodiment, the annealing time is controlled to be 150 h-200 h in the annealing stage, i.e., the total time from the current power to the power of 0 is 150 h-200 h,

because the method of 'sitting pot' growth is adopted in the application, the weight of the sapphire crystal possibly exceeds the charging amount due to the crucible sticking at the bottom in the annealing stage, and when the weight of the sapphire crystal exceeds 5 wt% of the charging amount, the sapphire crystal needs to be put down; and there is a possibility that the weight of the sapphire crystal shows to be lower than the charged amount due to the contact of the bottom of the crystal with the crucible during the lowering, and the lowering of the sapphire crystal needs to be stopped when the weight of the sapphire crystal is lower than 5 wt% of the charged amount.

In this embodiment, the preset time is 8-12 hours, such as 10 hours; the preset weight range is +/-0.5-2 kg of the charging amount of the alumina raw material, such as +/-1 kg. Namely, whether the annealing is finished or not, as long as the weight of the sapphire crystal is stabilized within 8-12 h to be +/-0.5-2 kg of the charging amount, the sapphire crystal can be considered to be taken out of the pot, and the crystal can be taken out after the annealing is finished.

The method provided by the application reduces the residual stress in the crystal through the reasonable design of the radial temperature gradient and the transverse temperature gradient, and realizes the C-direction crystal growth of the large-size sapphire through the design of the C-direction crystal growth process.

Examples

Example 1

Seed crystal detection: and after the seed crystal is taken, using a polarizer and a strong photoelectric inspection to observe whether bubbles, twin crystals, cracks and the like exist in the seed crystal, and if the seed crystal is found to be unqualified, replacing the qualified seed crystal in time so as to avoid that excessive defects exist in the seed crystal and are transmitted to the growing crystal to influence the crystal quality.

Charging: 450kg of high-purity alumina raw material with the purity of 5N is placed in a crucible, the crucible is placed in a sapphire growth furnace cavity, whether a thermal field, a heat preservation screen, a temperature sensor and the like of the growth furnace are normal or not is checked, and the furnace cavity is closed and vacuumized.

Melting materials: when the vacuum degree of the growth furnace reaches 1e-4pa, the vacuum pumping is finished, and an automatic material melting program is started, wherein the material melting power is increased to 120kw at the speed of 5.33 kw/h.

Seeding: observing the liquid flow state of the alumina dissolving soup in the growth furnace, putting the seed crystal at 2050 ℃ at the upper part of the dissolving soup, wherein the lower end of the seed crystal is not baked to be round in the descending process of the seed crystal, and the liquid surface of the alumina dissolving soup does not have crystal floating. The diameter of the prepared sapphire crystal is about 60mm by instantly extracting the seed crystal for about 40 times every 10 min.

Shoulder expanding growth: the pulling rate on the seed crystal was reduced to 0 and shoulder-widening was completed when the sapphire crystal weight was 8 wt% of the charge. At the moment, the seed crystal is extracted instantly by 2mm, and the heating power is increased by 400 w.

Sixthly, equal-diameter growth: the power reduction amplitude is controlled to be 10-80 w/h, so that the length speed is controlled to be 1.5 kg/h.

The ending stage: keeping the pulling speed of the seed crystal to be 0, and growing the sapphire crystal by adopting a 'sitting pot' mode. After the crystal weighed to 350kg, the average growth rate v was calculated to be 2.4kg/h within the previous 24h, and the estimated remaining growth time h was calculated to be 50/2.4 h to 20.8 h.

And the annealing stage: automatically lowering the crystal when the weight of the crystal exceeds 5% of the loading amount; when the weight of the display is less than 5% of the charged amount, the lowering is stopped. Until the displayed weight of the crystal is stabilized to the charging amount of +/-1 kg within 10 hours, the crystal is considered to be taken out of the pot, the total annealing time is controlled to be 150-200 hours, and the crystal is taken out.

Comparative example

Comparative example 1 preparation of sapphire crystal according to conventional protocol C

The alumina raw material and the amount of the alumina raw material used in the comparative example are the same as those in the example, and the seed crystal is also equivalent to that in the example 1.

The procedure used in this comparative example is specifically as follows:

Charging: 200kg of high-purity alumina raw material with the purity of 5N is placed in a crucible, the crucible is placed in a sapphire growth furnace cavity, whether a thermal field, a heat preservation screen, a temperature sensor and the like of the growth furnace are normal or not is checked, and the furnace cavity is closed and vacuumized.

Melting materials: when the vacuum degree of the growth furnace reaches 1e-4pa, the vacuum pumping is finished, and an automatic material melting program is started, wherein the material melting power is increased to 95kw at the speed of 4.4 kw/h.

Seeding: observing the liquid flow state of the alumina dissolving soup in the growth furnace, putting the seed crystal at 2050 ℃ at the upper part of the dissolving soup, wherein the lower end of the seed crystal is not baked to be round in the descending process of the seed crystal, and the liquid surface of the alumina dissolving soup does not have crystal floating. And (4) putting seed crystals downwards, washing the crystal seeds, inserting the seed crystals below 15mm of the liquid level, and finishing seeding at a pulling speed of 0.1 mm/h.

Shoulder expanding growth: the pulling speed of the seed crystal is 0.15mm/h, and the shoulder expanding is completed when the weight of the sapphire crystal is 18.5 kg.

Sixthly, equal-diameter growth: the power reduction amplitude is controlled to be 10-80 w/h, so that the length speed is controlled to be 1.3 kg/h.

The ending stage: the pulling rate is changed to 0.3mm/h, and when the weight of the crystal is not changed within 5h, the crystal is considered to be taken out of the pot at the moment.

And the annealing stage: the amplitude reduction is increased, and the crystal annealing is completed within 150 h.

The properties of the sapphire crystals prepared in example 1 and comparative example 1 of the present application were measured, respectively, and the results are shown in table 1 below:

TABLE 1 comparison of sapphire crystal properties obtained by different preparation methods

As can be seen from table 1 above, compared to the conventional method, the sapphire crystal produced by C-direction growth using the method provided by the present application has significantly reduced crystal defects, significantly reduced dislocation density, and significantly increased crystal utilization.

The present application has been described in detail with reference to specific embodiments and illustrative examples, but the description is not intended to limit the application. Those skilled in the art will appreciate that various equivalent substitutions, modifications or improvements may be made to the presently disclosed embodiments and implementations thereof without departing from the spirit and scope of the present disclosure, and these fall within the scope of the present disclosure. The protection scope of this application is subject to the appended claims.

Claims

1. A sapphire C-direction crystal growth method is characterized by comprising the following steps:

step 2, putting seed crystals into the alumina solution, and instantly extracting the seed crystals by a first preset height at intervals of a first preset time interval until the diameter of the crystals is a preset diameter, wherein the first preset time interval is 0.5-15 min, the first preset height is 0.1-5 mm, and the preset diameter is 30-150 mm;

step 3, reducing the pulling speed to 0, when the weight of the crystal is a first preset weight ratio of the charging amount, instantly extracting a second preset height of the crystal, increasing the heating power, gradually reducing the heating power after increasing the heating power, and controlling the crystal growth speed of the crystal to be smaller than a preset growth speed, wherein the first preset weight ratio is 8 wt% -15 wt%, the second preset height is 2-5 mm, and the preset growth speed is 1.5 kg/h-3 kg/h;

step 4, when the weight of the crystal is larger than a second preset weight proportion, calculating the average length speed v of the crystal in the last 24 hours, calculating the remaining growth time h by using the following formula I according to the average length speed v, and continuously reducing the temperature h at the current amplitude reduction rate, wherein the second preset weight proportion is 70 wt% -80 wt% of the charge amount:

h ═ Δ w/v formula I

Wherein h represents the remaining growth time,

aw represents the weight of the remaining alumina sol,

v represents the average growth rate of the crystals over the last 24 hours;

and 5, adjusting the position of the crystal according to the weight of the crystal until the weight of the crystal is stabilized to a preset weight range within a preset time, wherein the preset time is 8-12 hours, and the preset weight range is +/-0.5-2 kg of the charging amount of the alumina raw material.

2. The method according to claim 1, wherein, in step 1,

the purity of the alumina raw material is more than 5N,

and vacuumizing the furnace chamber to a vacuum degree lower than 1e-4 Pa.

3. The method according to claim 1 or 2, characterized in that in step 1, the material melting comprises the following sub-steps:

substep 1, increasing power to target power according to the rising speed of 3-10 kw/h, and keeping the temperature under the target power until the alumina raw material is in a molten state;

and a substep 2, keeping the temperature of the system obtained in the substep 1, monitoring the state of the alumina raw material during the heat preservation period, continuously increasing the power at the increasing speed of 500 w/h-1000 w/h if crystals are precipitated in the alumina dissolving soup, and keeping the temperature of the system again after increasing the power.

4. The method of claim 1 or 2, wherein in step 1, prior to placing the crucible containing the alumina feedstock into the furnace chamber, further comprising verifying the seed crystal for defects, the defects comprising: bubbles, twins and cracks.

5. The method according to claim 1 or 2, wherein, in step 2,

monitoring the states of the alumina dissolving soup and the seed crystal in the process of putting the seed crystal into the alumina dissolving soup, and if the lower end of the seed crystal is rounded, pulling the seed crystal; if crystals are precipitated in the alumina sol, the power is increased.

6. The method according to claim 1 or 2, characterized in that, in step 2,

the first preset time interval is 1-10 min; and/or

The first preset height is 0.5-2 mm; and/or

The preset diameter is 60-100 mm.