阅读说明：本技术 蓝宝石晶体生长工艺 (Sapphire crystal growth process ) 是由 付秀辉 丁军辉 林太顺 于 2021-07-22 设计创作，主要内容包括：本发明公开了一种蓝宝石晶体生长工艺,包括化料、引晶、放肩、等径、退火阶段；所述放肩阶段的晶体生长过程按照以下三个阶段进行：第一阶段晶体重量低于0.3kg,以0.2～2.5mm/h的上升速率旋转提拉籽晶,以5～7℃/h的速率降温；第二阶段晶体重量达到0.3～3.6kg,以0.3～3mm/h的上升速率旋转提拉籽晶,以10～14℃/h的速率降温,第三阶段晶体重量达到3.6kg以上,以0.5～4.5mm/h的上升速率旋转提拉籽晶,以16～20℃/h的速率降温,直至晶体距离反应炉的坩埚内壁5～10mm时完成放肩。本申请的制备方法制得的蓝宝石质量高,内应力小,无明显裂纹等缺陷。(The invention discloses a sapphire crystal growth process, which comprises the stages of material melting, seeding, shouldering, diameter equalization and annealing; the crystal growth process of the shouldering stage is carried out according to the following three stages: in the first stage, the weight of the crystal is lower than 0.3kg, the seed crystal is rotationally pulled at the rising rate of 0.2-2.5 mm/h, and the temperature is reduced at the rate of 5-7 ℃/h; the weight of the crystal in the second stage reaches 0.3-3.6 kg, the seed crystal is rotationally pulled at the rising rate of 0.3-3 mm/h, the temperature is reduced at the rate of 10-14 ℃/h, the weight of the crystal in the third stage reaches more than 3.6kg, the seed crystal is rotationally pulled at the rising rate of 0.5-4.5 mm/h, the temperature is reduced at the rate of 16-20 ℃/h, and shouldering is completed until the distance between the crystal and the inner wall of a crucible of the reaction furnace is 5-10 mm. The sapphire prepared by the preparation method has the advantages of high quality, small internal stress, no obvious crack and other defects.)

1. A sapphire crystal growth process comprises the stages of material melting, seeding, shouldering, diameter equalization and annealing;

the method is characterized in that the shouldering stage is specifically operated by rotating and pulling seed crystals which finish a seeding stage, the seed crystals generate crystals, and the crystal growth process is carried out according to the following three stages:

in the first stage, the weight of the crystal is lower than 0.3kg, the seed crystal is rotationally pulled at the rising rate of 0.2-2.5 mm/h, and meanwhile, a cooling system in the reaction furnace is controlled to cool at the rate of 5-7 ℃/h;

the weight of the crystal in the second stage reaches 0.3-3.6 kg, the seed crystal is rotationally pulled at the rising rate of 0.3-3 mm/h, and meanwhile, a cooling system in the reaction furnace is controlled to cool at the rate of 10-14 ℃/h;

and in the third stage, the weight of the crystal reaches more than 3.6kg, the seed crystal is rotationally lifted at the rising rate of 0.5-4.5 mm/h, and meanwhile, a cooling system in the reaction furnace is controlled to cool at the rate of 16-20 ℃/h until the shoulder is placed when the crystal is 5-10 mm away from the inner wall of the crucible of the reaction furnace.

2. A sapphire crystal growth process as claimed in claim 1, wherein: the cooling system in the reaction furnace is cooled by using argon.

3. A sapphire crystal growth process as claimed in claim 1, wherein: and cooling the crystal obtained after the isometric stage in the annealing stage to 1150 ℃ at a speed of 15-20 ℃/h in a reaction furnace, and preserving the heat for 4-5 h.

4. A sapphire crystal growth process as claimed in claim 3, wherein: and in the annealing stage, the temperature in the reaction furnace is reduced from 1150 ℃ to 600 ℃ at a rate of 20-25 ℃/h.

5. A sapphire crystal growth process as claimed in claim 4, wherein: and in the annealing stage, the temperature in the reaction furnace is reduced from 600 ℃ to 300 ℃ at a speed of 25-30 ℃/h.

6. A sapphire crystal growth process as claimed in claim 5, wherein: and in the annealing stage, the temperature in the reaction furnace is reduced from 300 ℃ to 25 ℃ at a rate of 30-35 ℃/h.

7. A sapphire crystal growth process as claimed in claim 1, wherein: the concrete operation of the material melting stage is that raw materials are put into a reaction furnace, and the interior of the reaction furnace is vacuumized to 10 DEG^-3～10^-4And heating after Pa, and heating at a heating rate of 100-200 ℃/h until the raw materials are completely melted to form a melt.

8. The sapphire crystal growth process of claim 7, wherein: and in the material melting stage, the temperature in the furnace is adjusted to 2100 ℃, and the melt is subjected to heat preservation for 2-4 hours.

Technical Field

The invention relates to the technical field of crystal preparation, in particular to a sapphire crystal growth process.

Background

Sapphire is an important material variety in artificial synthetic crystals, and can be used for preparing LED semiconductor substrate materials and window materials due to excellent mechanical properties and optical properties of sapphire.

At present, the mainstream growth methods of sapphire crystals internationally include a kyropoulos method and a czochralski method. The Czochralski method, the basic process of which comprises: filling an alumina raw material into a crucible of a reaction furnace, heating and melting the material to obtain a melt, fixing seed crystals in a certain direction on a top seed crystal rod, vacuumizing the furnace, extending the seed crystals into the material surface to partially melt, improving the wettability of the seed crystals, then rotating and pulling the seed crystals, and completing the growth of the crystals through processes of necking, shouldering, isometric, pull-off and the like.

The Czochralski method realizes the growth of the crystal through the manufacturing temperature gradients of heat dissipation at the top of the melt, heat radiation and heat conduction of the crystal, heat radiation of the side wall of the crucible, heat conduction at the bottom and the like in the crystal growth process. At least one of the crystal and the crucible is required to rotate in the growth process, natural convection and forced convection exist in the melt raw materials at the same time, liquid flow is complex, and a crystallization interface is easy to destabilize, so that defects are generated.

Kyropoulos method, also known as Ky method, evolved from the czochralski method, and the basic process thereof includes: alumina raw material is filled in the crucible, and directional seed crystals are fixed on a water-cooling seed crystal rod in the middle of the top. Heating and melting the materials in a vacuum environment, and adjusting the heating power to ensure that the lowest point of the temperature of the top melt, namely the temperature of the center of the crucible, is slightly higher than the melting point. And immersing seed crystals into the melt, and melting the surface of the seed crystals to improve the wettability with the melt. The temperature of the fused mass is reduced, so that the aluminum oxide is crystallized on the seed crystal, and a crystal neck is grown by adopting the process of a pulling method. And then stopping pulling, slowly reducing the heating power, and slowly moving the isothermal line downwards to realize the growth of the crystal.

Because the crystal is basically invisible in growth, the growth condition can not be regulated according to the growth condition of the crystal, and the crystallization interface is positioned at the upper part, the defects such as bubbles, cracks and the like are easily concentrated and distributed at the top under the condition of poor liquid flow regulation, and the production quality of the sapphire crystal is reduced.

With the development of infrared technology, microelectronic technology and photoelectronic technology, higher technical requirements are put forward on the performance of sapphire single crystal materials at the present stage, namely the growth technology of sapphire crystals develops towards high production quality.

Disclosure of Invention

In order to improve the production quality of sapphire crystals, the application provides a sapphire crystal growth process.

The sapphire crystal growth process provided by the application adopts the following technical scheme:

a sapphire crystal growth process comprises the stages of material melting, seeding, shouldering, diameter equalization and annealing;

the shouldering stage is specifically operated by rotating and pulling seed crystals which finish a seeding stage, the seed crystals generate crystals, and the crystal growth process is carried out according to the following three stages:

in the first stage, the weight of the crystal is lower than 0.3kg, the seed crystal is rotationally pulled at the rising rate of 0.2-2.5 mm/h, and meanwhile, a cooling system in the reaction furnace is controlled to cool at the rate of 5-7 ℃/h;

the weight of the crystal in the second stage reaches 0.3-3.6 kg, the seed crystal is rotationally pulled at the rising rate of 0.3-3 mm/h, and meanwhile, a cooling system in the reaction furnace is controlled to cool at the rate of 10-14 ℃/h;

and in the third stage, the weight of the crystal reaches more than 3.6kg, the seed crystal is rotationally lifted at the rising rate of 0.5-4.5 mm/h, and meanwhile, a cooling system in the reaction furnace is controlled to cool at the rate of 16-20 ℃/h until the shoulder is placed when the crystal is 5-10 mm away from the inner wall of the crucible of the reaction furnace.

In the present application, alpha-Al₂O₃The method comprises the steps of filling raw materials into a crucible of a reaction furnace, heating and melting the raw materials in a material melting stage to obtain a melt, selecting sapphire seed crystals according to actual needs, fixing the seed crystals to a seed crystal rod (the seed crystal rod of the reaction furnace is generally connected with a weighing device and is weighed immediately), extending the seed crystals into the melt to be partially melted, improving the wettability of the seed crystals, completing seeding, rotating and pulling the seed crystals completing the seeding at a slow rising rate in a shouldering stage, and growing the sapphire crystals on the premise of avoiding severe disturbance in the melt.

The growth temperature of the sapphire crystal is generally about 2300 ℃, and some atoms in the sapphire crystal have enough energy to be separated from the positions of the atoms in the temperature range to generate vacancies, so that the concentration of the vacancies in the sapphire growth process is high. The allowable equilibrium concentration of the crystal is rapidly reduced along with the reduction of the temperature of the crystal, if the temperature reduction rate is too high, the vacancies in the crystal are not easily eliminated by diffusion but are agglomerated into vacancy clusters, and meanwhile, the high vacancy concentration easily causes the dislocation of the crystal. Therefore, in this shouldering stage, the diameter of the crystal increases with the increase in weight, while the slower the rising rate of the spin-draw, the smaller the growth rate of the crystal diameter. Compared with the Ky method, the growth degree of the crystal diameter in actual production is judged through the weight which can be read visually, so that the cooling rate is convenient to regulate and control, the vacancy in the crystal is diffused and disappears, the possibility of forming vacancy clusters by the aggregation of the vacancies is reduced, meanwhile, the crystal dislocation is inhibited, and the growth quality of the sapphire crystal is improved.

The crystal which finishes the growth in the shouldering stage enters an equal-diameter growth stage, and after the crystal finishes the growth in the equal-diameter stage, the crystal enters an annealing stage, and the annealing stage eliminates the thermal stress in the crystal, thereby further improving the quality of the crystal.

Preferably, the cooling system in the reaction furnace is cooled by using argon gas.

Preferably, the temperature of the crystal obtained after the isometric stage in the annealing stage is reduced to 1150 ℃ in a reaction furnace at a speed of 15-20 ℃/h, and the temperature is maintained for 4-5 h.

By adopting the technical scheme, the internal stress of the sapphire crystal can be effectively eliminated within the annealing temperature range.

Preferably, the temperature in the reaction furnace in the annealing stage is reduced from 1150 ℃ to 600 ℃ at a rate of 20-25 ℃/h.

Preferably, the temperature in the reaction furnace in the annealing stage is reduced from 600 ℃ to 300 ℃ at a rate of 25-30 ℃/h.

Preferably, the temperature in the reaction furnace in the annealing stage is reduced from 300 ℃ to 25 ℃ at a rate of 30-35 ℃/h.

Preferably, the concrete operation of the material melting stage is feeding in a reaction furnaceRaw materials are added, the reaction furnace is vacuumized to 10 DEG^-3～10^-4And heating after Pa, and heating at a heating rate of 100-200 ℃/h until the raw materials are completely melted to form a melt.

Preferably, the temperature in the furnace is adjusted to 2100 ℃ in the material melting stage, and the melt is subjected to heat preservation for 2-4 hours.

By adopting the technical scheme, the raw materials are subjected to vacuum melting to form a melt in the melting stage, the melt is subjected to heat preservation, the melt is kept in a stable state by liquid level convection, and the relative deviation between the position of a cold core in the melt and the falling position of a seed crystal (the center of the vertical direction of the reaction furnace) is within 10-20 mm.

In summary, the present application has the following features:

1. the growth degree of the crystal is judged by controlling the weight of the crystal, so that the cooling rate is conveniently regulated, the diffusion of vacancies in the crystal disappears, the possibility of forming vacancy clusters by vacancy aggregation is reduced, and meanwhile, crystal dislocation is inhibited, and the growth quality of the sapphire crystal is improved.

2. This application reduces the stress of crystal inside through improving the annealing stage, further improves the growth quality of crystal.

Detailed Description

Examples 1 to 3 each provide a process for growing a sapphire crystal, and are described by taking example 1 as an example.

Example 1

A growth process of sapphire crystals comprises the following steps:

and (3) material melting stage:

80kg of alumina powder having a purity of 99.999% was placed in a crucible of a sapphire vacuum crystal growth reactor (model KZDJ-50-16, purchased from Kuste instruments, Inc. in Henan).

Sealing the sapphire vacuum crystal growth reaction furnace, vacuumizing, and adjusting the pressure in the furnace to 10^-3Pa, heating to 2300-2350 ℃ at a heating rate of 100 ℃/h (slightly higher than the melting point of alumina), and keeping the temperature for 1h to ensure that the raw materials are completely melted to form a melt.

Cooling to 2100 ℃ at the speed of 5 ℃/h, preserving heat for 4h, ensuring that the liquid level convection of the melt is in a stable state, ensuring that the relative deviation between the position of a cold core in the melt and the falling position of the seed crystal (the center of the reaction furnace in the vertical direction) is within 10-20 mm, and entering a seeding stage.

And (3) seeding stage:

selecting A-direction seed crystals (the orientation precision of the seed crystals is +/-0.005 degrees, and the size of the seed crystals is phi 10mm multiplied by 20mm), installing the seed crystals on a seed crystal rod (the seed crystal rod can be weighed immediately), and slowly adjusting the height of the seed crystals to enable the lower ends of the seed crystals to be lowered to a position 10-15 mm away from the liquid level of the melt for preheating.

Preheating for 40min, seeding at the position deviated from the cold center, rotating the seed crystal at the speed of 5r/min, after seeding for 10 times, moving the crystallization center position of the seed crystal to the cold center, simultaneously soaking the seed crystal in the melt for 20min, controlling the weight of the soaked seed crystal not to exceed 0.3kg, and entering a shouldering stage.

A shouldering stage:

in the first stage, the weight of the soaked seed crystal is lower than 0.3kg, the seed crystal rod rotates to pull the seed crystal at the rising rate of 0.2mm/h, meanwhile, argon is filled into a cooling system in the reaction furnace, the flow rate of the argon is controlled, the temperature in the furnace is reduced at the rate of 5 ℃/h, and the melt at the solid-liquid interface is crystallized around the seed crystal;

when the weight of the crystal is continuously increased to 0.3kg, entering a second stage, adjusting the rising rate of a seed rod, rotating the seed rod to pull the seed crystal at the rising rate of 0.3mm/h, and simultaneously controlling the flow rate of argon gas to cool the furnace at the rate of 10 ℃/h so that the crystal continuously grows;

and (3) when the weight of the crystals is continuously increased to 3.6kg, entering a third stage, adjusting the rising rate of a seed rod, rotating the seed rod to lift the seed crystal at the rising rate of 0.5mm/h, simultaneously controlling the flow rate of argon gas, cooling the inside of the furnace at the rate of 16 ℃/h until the crystals are 5-10 mm away from the inner wall of the crucible of the reaction furnace, and entering an equal-diameter stage.

And (3) an equal diameter stage:

stopping rotating the seed rod, resetting the rising rate of the seed rod to enable the seed rod to rise at a constant speed of 0.3mm/h, controlling the flow speed of argon in a cooling system in the reaction furnace to enable the crystal to keep equal-diameter growth, uniformly increasing the quality of the crystal at an increasing speed of 4 +/-1 kg/h, completing the equal-diameter stage until the weight is not increased any more, and entering an annealing stage.

And (3) annealing stage:

after the equal-diameter growth of the crystal is finished, in-situ annealing is carried out, the temperature of the crystal is reduced to 1150 ℃ at the speed of 15 ℃/h in a reaction furnace, and the temperature is preserved for 4 h.

After the heat preservation is finished, the temperature is reduced to 600 ℃ at the speed of 20 ℃/h, when the temperature in the furnace reaches 600 ℃, the temperature is reduced to 300 ℃ at the speed of 25 ℃/h, when the temperature in the furnace reaches 300 ℃, the temperature is reduced to 25 ℃ at the speed of 30 ℃/h, and the internal stress of the sapphire crystal is effectively eliminated through the annealing operation.

Discharging:

and after the annealing stage is finished, opening an air inlet valve of the reaction furnace to enable the pressure in the reaction furnace to be the same as the outside, closing a cooling system of the reaction furnace, opening a furnace cover of the reaction furnace, standing for 8 hours, and taking out the sapphire crystal to finish the whole technological process.

Examples 2 to 3

A growing process of sapphire crystals, which is different from that of example 1 in the rate of temperature rise and temperature drop at each stage.

TABLE 1. different process parameters at various stages

Data detection

Sapphire produced according to the growth processes of examples 1 to 3 was subjected to the following tests, with 20 sapphire crystals of the same batch being taken as samples for each example.

1. And (3) weight test: and weighing the sample, taking the sapphire crystal as a qualified product when the weight of the sapphire crystal reaches 60kg, and recording the maximum value and the minimum value of the weight of each batch of samples and the reject ratio.

TABLE 2 maximum and minimum values of sample weight in three batches

Parameter(s)	Example 1	Example 2	Example 3
				Maximum weight/kg	67.1	70.6	73.4
Minimum weight/kg	61.3	64.2	62.1
				Percent of failure/%)	0	0	0

The measured weight of each batch of samples can reach 73.4 at most, and no unqualified sample exists, so that the sapphire crystal prepared by the method is proved to have larger weight, and the large-size requirement of the sapphire crystal growth process is met.

2. And (3) testing the density: the density of the samples of the same batch was measured by the floating weight method according to GB/T25995-2010, and the maximum and minimum values of the density of the samples of each batch were recorded.

TABLE 3 maximum and minimum Density of samples from three batches

Parameter(s)	Example 1	Example 2	Example 3
				Maximum density/kg	4.01	4.00	4.02
Minimum density/kg	3.98	3.97	4.00

The density measured by each batch of samples is not lower than 3.97g/cm³And the fluctuation range of the density is small, and is equal to the theoretical density of sapphire (4.00 g/cm)³) The values are close, demonstrating that the sapphire produced by this method is internally dense.

3. And (3) hardness testing: knoop hardness characterization was performed according to GB/T16534-2009. The principle is that a Knoop pressure head is pressed into the surface of a sample by using test force, the test force is removed after the test force is kept for a specified time, the length of the long diagonal line of the indentation on the surface of the sample is measured, and the quotient of the test force divided by the projection area of the indentation on the surface of the sample is the Knoop hardness value. The maximum and minimum knoop hardness values for each batch of samples were recorded.

TABLE 4 maximum and minimum Knoop hardness values for samples in three batches

Parameter(s)	Example 1	Example 2	Example 3
				Maximum Knoop hardness value	9	9	9
Minimum Knoop hardness value	9	9	9

The Knoop hardness values measured by all batches of samples are 9, which are equivalent to the theoretical hardness of sapphire, and the internal integrity of the prepared sapphire crystal is shown, and the conditions of cracks, stress and the like which influence the hardness do not exist.

4. And (3) testing the bending strength: according to GB/T6569-2006, three-point bending strength characterization is adopted. The maximum and minimum values of the flexural strength of the samples from each batch were recorded. The bending strength of the sample is higher than 400MPa, and the sample is qualified.

TABLE 5 maximum and minimum flexural Strength of samples from three batches

Parameter(s)	Example 1	Example 2	Example 3
				Maximum bending strength/MPa	467	483	474
Minimum flexural Strength/MPa	430	421	429

The bending strength of each batch of samples is not lower than 421MPa, which proves that the strength uniformity of the sapphire crystal is good, the prepared sapphire material is uniform, the internal stress is small, and the defects of internal cracks and the like which influence the strength of the sapphire crystal are avoided.

5. Stress birefringence test: sapphire crystals were cut into disks of size phi 40mm x 10mm and tested according to JB/T9495.4-1999 using phi 40mm x 10mm C-oriented sapphire disks. The measurement wavelength was 540 nm.

TABLE 6 maximum and minimum stress birefringence measurements for samples from three batches

Parameter(s)	Example 1	Example 2	Example 3
				Maximum stress birefringence measurement/nm	72	75	71
Minimum stress birefringence measurement/nm	65	63	66

The stress birefringence measurements for each batch of samples did not range above 75 nm. The smaller the measured value of stress birefringence, the smaller the internal stress, which proves the internal crystalline integrity of the sapphire crystal.

6. And (3) testing spectral transmittance: according to JB/T15489.1-1995, the test was carried out using a Fourier transform infrared spectrometer with a measurement range of 4000cm^-1～400cm^-1. And recording the average transmission ratio of the sample in a wave band of 3-5 mu m.

The average transmission ratio of the 3-5 mu m wave band of the sample prepared by the growth process of the embodiment 1 is not lower than 86.8 percent;

the average transmission ratio of the 3-5 mu m wave band of the sample prepared by the growth process of the embodiment 2 is not lower than 87.1 percent;

the average transmission ratio of the 3-5 mu m wave band measured by the sample prepared by the growth process of the embodiment 3 is not lower than 86.3 percent; the average transmission ratio values of 3-5 mu m wave bands of the three batches of samples are not lower than 86%, and the results prove that the intermediate infrared transmittance of the sapphire crystal is high and the service performance is excellent.

The present embodiment is only for explaining the present application, and it is not limited to the present application, and those skilled in the art can make modifications of the present embodiment without inventive contribution as needed after reading the present specification, but all of them are protected by patent law within the scope of the claims of the present application.