Aln single crystal and method for growing the same

Abstract

This invention discloses an AlN single crystal and its growth method. The method includes: connecting an AlN seed crystal to the inner wall of a crucible so that the AlN seed crystal is suspended inside the crucible and positioned opposite to the AlN raw material; placing the crucible in a growth furnace and maintaining a vacuum; raising the temperature of the growth furnace from room temperature to a preset holding temperature and holding it for a first preset time, while simultaneously continuously introducing a first protective gas into the growth furnace to protect the AlN seed crystal and remove impurities from the crucible; the temperature rise from room temperature to the preset holding temperature is a stepwise temperature rise, and / or the volume percentage of reducing gas in the first protective gas decreases stepwise; raising the temperature inside the growth furnace from the preset holding temperature to a preset growth temperature, while simultaneously continuously introducing the first protective gas into the growth furnace to grow the AlN single crystal; cooling the temperature inside the growth furnace from the preset growth temperature to room temperature, and removing the grown AlN single crystal after breaking the vacuum at room temperature. This growth method can obtain high-quality, large-size, and highly uniform AlN single crystals.

Description

Technical Field

[0001] This invention relates to the field of semiconductor materials technology, and in particular to a method for growing AlN single crystals. Background Technology

[0002] Aluminum nitride (ANH3), a typical representative of ultra-wide bandgap semiconductor materials, possesses an ultra-wide bandgap of 6.2 eV, high thermal conductivity, high breakdown field strength, excellent piezoelectric properties, and crystal structure and chemical properties compatible with gallium nitride (GaN) and aluminum gallium nitride (AlGaN). It is an ideal substrate material for fabricating deep ultraviolet LEDs, high-power microwave devices, and high-temperature electronic devices. However, the commercial application of AlN single crystals is limited by the challenge of fabricating high-quality, large-size single crystals, and existing growth techniques still have many shortcomings.

[0003] Currently, the mainstream growth method for AlN single crystals is physical vapor transport (PVT), but it has the following key problems: First, direct contact between the seed crystal and the crucible wall easily generates mechanical stress, leading to an increase in crystal defect density and affecting crystallization quality; second, uneven temperature field distribution and unstable temperature gradient on the seed crystal surface result in large fluctuations in crystal growth rate, making it difficult to achieve effective diameter expansion and restricting the preparation of large-size single crystals; third, impurities in the growth system are easily mixed into the crystal, reducing the purity of the single crystal and affecting device performance; fourth, the controllability of crystal orientation in existing processes is poor, resulting in insufficient consistency in mass production.

[0004] In addition, other growth methods such as metal-organic chemical vapor deposition (MOCVD) have problems such as long growth cycle, high cost, and limited substrate selection due to excessively high preset growth temperature; magnetron sputtering is limited by the low mobility of Al atoms, which easily forms columnar growth mode and generates a large number of dislocations and defects.

[0005] The present invention solves at least one of the above problems. Summary of the Invention

[0006] The purpose of this invention is to solve at least one of the problems in the background art by providing a method for growing AlN single crystals. By ensuring that each step of single crystal growth, from the initial preparation to the later cooling, is mutually compatible, defects such as dislocations and stacking faults in the crystal are effectively reduced, resulting in AlN single crystals with high crystal quality, large size, and high consistency, thus meeting the requirements of device-level substrates.

[0007] The objective of this invention is achieved through the following technical solution:

[0008] A first aspect of the present invention provides a method for growing AlN single crystals, applied to a growth apparatus, the growth apparatus including a growth furnace and a crucible disposed within the growth furnace, the growth method comprising:

[0009] Provides AlN seed crystals and crucibles filled with AlN raw materials;

[0010] The AlN seed crystal is connected to the inner wall of the crucible so that the AlN seed crystal is suspended in the crucible and positioned opposite to the AlN raw material;

[0011] The crucible is placed inside the growth furnace and the growth furnace is kept under vacuum.

[0012] The temperature of the growth furnace is raised from room temperature to a preset holding temperature and held for a first set time, while a first protective gas is continuously introduced into the growth furnace to protect the AlN seed crystal and remove impurities from the crucible; wherein, the temperature rise from room temperature to the preset holding temperature is a step-wise temperature rise, and / or, the volume ratio of reducing gas in the first protective gas decreases stepwise.

[0013] The temperature inside the growth furnace is raised from the preset holding temperature to the preset growth temperature, and a first protective gas is continuously introduced into the growth furnace at the same time to grow AlN single crystals.

[0014] The temperature inside the growth furnace is lowered from the preset growth temperature to the room temperature, and the grown AlN single crystal is removed after the vacuum is broken at the room temperature.

[0015] In some possible embodiments of the first aspect, the reducing gas is hydrogen, and the first protective gas further includes nitrogen; the step of raising the temperature inside the growth furnace from room temperature to a preset holding temperature and then holding it for a first set time includes:

[0016] The temperature inside the growth furnace is increased from room temperature to a third set temperature at a first preset heating rate.

[0017] The temperature inside the growth furnace is increased from the third set temperature to the fourth set temperature at a second preset heating rate.

[0018] The temperature inside the growth furnace is increased from the fourth set temperature to the preset holding temperature at a third preset heating rate.

[0019] Wherein, the first preset heating rate is less than the second preset heating rate, and the second preset heating rate is less than the third preset heating rate;

[0020] Preferably, the first preset heating rate is 3℃ / min to 5℃ / min, the second preset heating rate is 5℃ / min to 6℃ / min, and the third preset heating rate is 6℃ / min to 8℃ / min.

[0021] In some possible implementations of the first aspect, during the process of raising the temperature in the growth furnace from room temperature to a fifth set temperature, the volume percentage of hydrogen in the first protective gas is a first set percentage; during the process of raising the temperature in the growth furnace from the fifth set temperature to the preset holding temperature, the volume percentage of hydrogen in the first protective gas is a second set percentage, the second set percentage being less than the first set percentage.

[0022] And / or, during the process of raising the temperature in the growth furnace from room temperature to the sixth set temperature, the gas flow rate of the first protective gas is the second set flow rate; during the process of raising the temperature in the growth furnace from the sixth set temperature to the preset holding temperature, the gas flow rate of the first protective gas is the third set flow rate, and the third set flow rate is less than the second set flow rate.

[0023] In some possible embodiments of the first aspect, the crucible has a raw material region and a seed crystal region arranged vertically opposite each other, the AlN seed crystal is located in the seed crystal region, and the AlN raw material is located in the raw material region. The step of raising the temperature inside the growth furnace from the preset holding temperature to a preset growth temperature, and growing AlN single crystals at the preset growth temperature, includes:

[0024] The temperature inside the growth furnace is increased from the preset holding temperature to the preset growth temperature at a heating rate of 3℃ / min to 5℃ / min, and AlN single crystals are grown at the preset growth temperature and under a growth pressure of 50mbar to 200mbar within a second preset time period.

[0025] The preset growth temperature includes the temperature of the raw material zone and the temperature of the seed crystal zone. The temperature of the raw material zone is 2200℃~2400℃, and the temperature of the seed crystal zone is 2100℃~2300℃. The second preset time period is 80h~150h.

[0026] And / or, the temperature gradient of the raw material zone is 100℃ / cm~120℃ / cm;

[0027] And / or, the temperature gradient of the seed crystal region is 80℃ / cm~100℃ / cm;

[0028] And / or, the temperature gradient of the gas phase transport zone between the raw material zone and the seed crystal zone is 60℃ / cm~80℃ / cm.

[0029] The beneficial effects of this implementation method are as follows: by precisely controlling the temperature gradient and growth pressure during the growth stage, the growth process of AlN single crystals can be further ensured to be stable, the size deviation of AlN single crystals produced in batches is ≤5%, the crystallization quality is excellent and consistent, and it is suitable for industrial promotion.

[0030] In some possible embodiments of the first aspect, the temperature gradient between the raw material region and the seed crystal region is 90℃ / cm to 120℃ / cm during the period from 0 to 50 h; the temperature gradient between the raw material region and the seed crystal region is 80℃ / cm to 100℃ / cm during the period from 50 h to 100 h; and the temperature gradient between the raw material region and the seed crystal region is 80℃ / cm to 90℃ / cm during the period from 100 to 150 h.

[0031] In some possible embodiments of the first aspect, the AlN seed crystal comprises a stacked seed crystal body and a flexible buffer film; providing the AlN seed crystal includes:

[0032] Under sputtering power of 150W to 200W, magnetron sputtering is performed on the surface of the seed crystal body for 30 to 60 minutes to form a flexible buffer film with a thickness of 50nm to 100nm.

[0033] The beneficial effects of this implementation method are: by utilizing the buffering effect of the flexible buffer film, defects such as dislocations and stacking faults in the crystal can be effectively reduced, and AlN single crystals with high crystal quality can be obtained to meet the requirements of device-level substrates.

[0034] In some possible embodiments of the first aspect, the AlN seed crystal includes a stacked seed crystal body and a flexible buffer film, the flexible buffer film including a stacked first buffer layer and a second buffer layer, and providing the AlN seed crystal includes:

[0035] Under the condition of sputtering power of 150W to 200W, magnetron sputtering is performed on the surface of the seed crystal body for 30min to 60min to form an initial buffer layer with a thickness of 30nm to 50nm.

[0036] The initial buffer layer is patterned to obtain a first buffer layer with several protrusions and several pits;

[0037] Under a sputtering power of 150W to 200W, magnetron sputtering is performed on the surface of the first buffer layer for 30 to 60 minutes to form a second buffer layer with a thickness of 20nm to 50nm that covers the plurality of protrusions and the plurality of pits.

[0038] In some possible implementations of the first aspect, at least one of the following is included:

[0039] The diameter of the protrusion is 50nm to 100nm; the height of the protrusion is 20nm to 50nm; and the diameter of the recess is 100nm to 200nm.

[0040] In some possible embodiments of the first aspect, the crucible includes a narrow section and a wide section along the height direction, the AlN seed crystal is located in the narrow section, and the AlN raw material is located in the wide section;

[0041] And / or, during the process of cooling from the preset growth temperature to the room temperature, the cooling rate first decreases and then increases.

[0042] In a second aspect, the present invention provides an AlN single crystal prepared by the above-described growth method.

[0043] Compared with the prior art, the beneficial effects of the present invention include at least the following:

[0044] 1. By adopting a near-suspended AlN seed crystal fixing method, the AlN seed crystal is not in direct contact with the crucible wall, which significantly reduces the concentration of mechanical stress. Combined with the buffering effect of the flexible buffer film, it effectively reduces defects such as dislocations and stacking faults in the crystal, and obtains AlN single crystals with high crystal quality, which meets the requirements of device-level substrates.

[0045] 2. During the heating and holding stage, under vacuum conditions inside the growth furnace, the room temperature is raised to the preset holding temperature and then held. Simultaneously, a first protective gas is introduced into the furnace. The gas flows continuously to form a stable inert atmosphere, ensuring that the entire heating and holding process is enveloped in this inert atmosphere. This avoids the occurrence of vacuum or residual air in the furnace during the heating and holding stage, and allows the atmosphere and temperature to be synchronized. It also gradually removes residual impurities from the crucible, preventing oxidation of the AlN seed crystal surface, thus protecting the AlN seed crystal and promoting the subsequent growth of AlN single crystals.

[0046] 3. During the process of heating from room temperature to the preset holding temperature, adopting a stepped heating scheme and / or a scheme of gradually decreasing volume ratio of reducing gas helps to improve the impurity removal effect and strengthen the protection of AlN seed crystals. Through impurity removal during the heating and holding stages, the temperature field in the growth furnace reaches an initial uniform state, allowing for a smooth transition from the preset holding temperature to the growth temperature. This avoids temperature gradient fluctuations in the seed crystal region caused by sudden temperature field changes, ensuring the stability of the crystal growth rate. Furthermore, the first protective gas atmosphere system in the heating and holding stages is continuously used throughout the heating stage, ensuring that the furnace remains in a stable inert atmosphere during the growth stage, preventing impurities from being introduced during atmosphere switching. The impurity removal effect directly determines the purity of the growth gas source during the AlN single crystal growth stage. The introduction of the first protective gas atmosphere provides a basis for pressure regulation during the AlN single crystal growth stage, directly addressing pressure fluctuations caused by high vacuum pressurization, thus making the growth pressure of the AlN single crystal more stable.

[0047] 4. Since the growth pressure during the AlN single crystal growth stage is positive pressure, the positive pressure inside the growth furnace is maintained throughout the cooling stage (until the vacuum is broken) to prevent outside air from seeping in during the cooling stage. At the same time, the AlN single crystal is cooled under positive pressure, reducing the porosity defects inside the AlN single crystal. Attached Figure Description

[0048] Figure 1 This is a schematic diagram of the structure where AlN seed crystals are suspended inside the crucible. Figure 1 ;

[0049] Figure 2 This is a schematic diagram of the structure where AlN seed crystals are suspended inside the crucible. Figure 2 ;

[0050] Figure 3 This is a flowchart of the AlN single crystal growth method of the present invention.

[0051] In the figure: 1. Crucible; 11. Inclined pot body; 111. Narrow section; 112. Wide section; 12. Seed crystal holder; 2. AlN seed crystal; 21. Seed crystal body; 22. Flexible buffer film; 3. AlN raw material; 5. Tungsten pillar; 6. Tungsten strip; 7. Tungsten film edging; 8. Tungsten protrusion. Detailed Implementation

[0052] Exemplary embodiments will now be described more fully with reference to the accompanying drawings. However, these exemplary embodiments can be implemented in many forms and should not be construed as limited to the embodiments set forth herein; rather, they are provided to make the invention more comprehensive and complete, and to fully convey the concept of the exemplary embodiments to those skilled in the art.

[0053] An embodiment of the present invention provides a growth apparatus, which includes a growth furnace (not shown in the figure) and a crucible 1 disposed within the growth furnace, which may be a PVT device. Optionally, the crucible 1 is made of tungsten.

[0054] In one specific implementation, in conjunction with the appendix Figure 1-2 As shown, the crucible 1 includes an inclined pot body 11 with an opening and a seed crystal holder 12 that can be fitted into the opening. The inclined pot body 11 includes a narrow section 111 and a wide section 112 along the height direction. The AlN seed crystal 2 is located in the narrow section 111, and the AlN raw material 3 is located in the wide section 112.

[0055] Optionally, when the crucible 1 is placed in the growth furnace, the wide section 112 of the inclined pot body 11 is close to the bottom of the growth furnace, and the narrow section 111 of the inclined pot body 11 is close to the top of the growth furnace.

[0056] Optionally, the inclined pot body 11 has a frustum structure, wherein the inclination angle of the side wall of the inclined pot body 11 is 5° to 15°, for example, it can be 5°, 6°, 7°, 8°, 9°, 10°, 11°, 12°, 13°, 14° or 15°.

[0057] It should be noted that the tilt angle of the sidewall of the tilted pot body 11 is determined by temperature field simulation and can be adjusted according to the target diameter expansion ratio. For example, for every 10% increase in the diameter expansion ratio of AlN single crystal, the tilt angle of the sidewall of the tilted pot body 11 increases by 2° to 3°.

[0058] Preferably, a tungsten-molybdenum insulation layer is laid inside the growth furnace to ensure the uniformity of the temperature field inside the furnace.

[0059] Embodiments of the present invention also provide a method for growing AlN single crystals, which is applied to the above-described growth equipment and combined with the attached... Figure 3 As shown, the growth method includes the following steps S1-S6.

[0060] Step S1: Provide AlN seed crystal 2 and crucible 1 filled with AlN raw material 3.

[0061] AlN seed crystal 2 can be c-face aluminum nitride seed crystal, with a size of 1 inch to 4 inches, for example, it can be 1 inch, 2 inches, 3 inches or 4 inches.

[0062] AlN raw material 3 is a high-purity aluminum nitride sintered body raw material (purity ≥99.999%), with a particle size of 200μm to 500μm, and a filling amount of 60% to 70% of the volume of the inclined pot 11; for example, the particle size of AlN raw material 3 can be 200μm, 250μm, 300μm, 350μm, 400μm, 450μm or 500μm; the filling amount of AlN raw material 3 can be 60%, 65% or 70% of the volume of the inclined pot 11.

[0063] Preferably, the AlN seed crystal 2 includes a stacked seed crystal body 21 and a flexible buffer film 22.

[0064] In one embodiment, tungsten metal is used as a flexible buffer film 22, which can quickly release the stress caused by thermal expansion mismatch through micro-deformation. It acts as a "flexible buffer pad" to offset the mechanical stress and thermal stress caused by temperature field fluctuations generated when the seed crystal body 21 is suspended in the crucible 1, and will not transmit the stress to the inside of the seed crystal body 21, thereby reducing dislocation sources.

[0065] In another embodiment, molybdenum metal is used as the flexible buffer film 22, whose coefficient of thermal expansion is more compatible with AlN. It has a better stress buffering effect than tungsten, can further reduce interface dislocations, has better sputtering film formation properties, a smoother film surface, and a better effect in suppressing impurity crystal nucleation.

[0066] In another embodiment, tantalum metal is used as a flexible buffer film 22, whose lattice constant is highly matched with AlN (Ta: 3.306 Å, AlN: 3.112 Å), which can form an epitaxial matching interface and reduce heterogeneous nucleation defects; it has stronger high-temperature oxidation resistance, and when trace oxygen is present, it will form a dense Ta2O5 passivation layer, which will not introduce oxygen impurities into AlN single crystals and improve the purity of single crystals.

[0067] In other embodiments, tungsten carbide is used as the flexible buffer film 22. It is hexagonal in crystal system as AlN, and its crystal structure is closer. It has no metal / ceramic heterogeneous stress in interface compatibility, and its high temperature stability is far superior to that of pure metal films. It does not evaporate or undergo crystal transformation at 2300℃, and the film has high hardness, which can protect the surface of the seed crystal body 21 from slight etching by gas phase atoms.

[0068] As an embodiment of step S1, the AlN seed crystal 2 is provided by step S11a: under the condition of sputtering power of 150W to 200W, magnetron sputtering is used to magnetron sputter the surface of the seed crystal body 21 for 30min to 60min to form a flexible buffer film 22 with uniform and dense film layer and thickness of 50nm to 100nm.

[0069] For example, the sputtering power is 150W, 160W, 170W, 180W, 190W or 200W; the sputtering time is 30min, 35min, 40min, 45min, 50min, 55min or 60min; and the thickness of the flexible buffer film is 50nm, 60nm, 70nm, 80nm, 90nm or 100nm.

[0070] By controlling the thickness of the flexible buffer film 22 to 50nm–100nm, a strong bond between the flexible buffer film 22 and the seed crystal body 21 can be ensured while reducing dislocation sources. If the thickness of the flexible buffer film 22 is large (e.g., 2μm–100μm), its rigidity is high and it cannot undergo micro-deformation, stress will continuously accumulate within the flexible buffer film 22. This will not only cause interface cracking / peeling between the flexible buffer film 22 and the seed crystal body 21, but will also propagate into the seed crystal body 21, forming a large number of dislocations and significantly increasing the crystal defect density.

[0071] As another embodiment of step S1, the flexible buffer film 22 includes a first buffer layer and a second buffer layer stacked together, and the AlN seed crystal is provided in steps S11b-S13b.

[0072] Step S11b: Under the condition of sputtering power of 150W to 200W, magnetron sputtering is performed on the surface of the seed crystal body 21 for 30min to 60min to form an initial buffer layer with a thickness of 30nm to 50nm.

[0073] For example, the sputtering power is 150W, 160W, 170W, 180W, 190W or 200W; the sputtering time is 30min, 35min, 40min, 45min, 50min, 55min or 6min; and the thickness of the initial buffer layer is 30nm, 35nm, 40nm, 45nm or 50nm.

[0074] Step S12b: Pattern the initial buffer layer to obtain a first buffer layer with several protrusions and several pits.

[0075] The initial buffer layer can be patterned using photolithography and ion etching methods, which are existing technologies and will not be elaborated here.

[0076] Optionally, the diameter of the boss is 50nm to 100nm, for example, 50nm, 60nm, 70nm, 80nm, 90nm or 100nm; the height of the boss is 10nm to 20nm, for example, 10nm, 15nm or 20nm; and the diameter of the pit is 100nm to 200nm, for example, 100nm, 120nm, 140nm, 160nm, 180nm or 200nm.

[0077] Step S13b: Under the condition of sputtering power of 150W to 200W, magnetron sputtering is performed on the surface of the first buffer layer for 30min to 60min to form a second buffer layer with a thickness of 20nm to 50nm and covering several protrusions and several pits.

[0078] For example, the sputtering power is 150W, 160W, 170W, 180W, 190W or 200W; the sputtering time is 30min, 35min, 40min, 45min, 50min, 55min or 6min; and the thickness of the second buffer layer is 20nm, 30nm, 40nm or 50nm.

[0079] It should be noted that several protrusions and pits can cooperate to form an ordered hexagonal concave-convex structure to match the hexagonal crystal system of AlN. Compared with replacing the original flat flexible buffer film 22 with an ordered concave-convex structure that matches the AlN crystal lattice, it can guide Al and N atoms to migrate along the sidewalls of the protrusions to the edge of the seed crystal body 21, avoiding excessive aggregation in the center to form "convex crystals" and improving the uniformity of lateral diameter expansion of large-size AlN single crystals; it can also increase the specific surface area by 3 to 5 times, increase the atomic adsorption sites, and increase the growth rate by 10% to 20% without increasing defects. Furthermore, the ordered structure allows atoms to nucleate only at the lattice matching points, further suppressing the impurity phase.

[0080] As an optional implementation, the above growth method further includes steps S101-S102 before filling the crucible 1 with AlN raw material 3.

[0081] Step S101: Anneal crucible 1 for 1.8h to 2h under vacuum conditions at a temperature of 1750℃~1850℃.

[0082] For example, the temperature can be 1750℃, 1780℃, 1810℃, 1830℃, 1850℃ or any value between the two; the annealing time can be 1.8h, 1.9h, 2h or any value between the two.

[0083] By subjecting crucible 1 to high-temperature annealing, surface impurities on the inner wall of crucible 1 can be effectively removed.

[0084] Step S102: Purge nitrogen gas into crucible 1 and cool to room temperature for later use. The purity of the nitrogen gas must be ≥99.9999%.

[0085] By introducing nitrogen gas into crucible 1, a protective atmosphere can be formed, effectively preventing oxidation inside crucible 1; by controlling the flow rate of nitrogen gas, the cooling rate of crucible 1 can be regulated, thereby effectively preventing crucible 1 from being damaged by thermal shock.

[0086] As an optional implementation, after providing the AlN seed crystal 2, the above growth method further includes steps S103-S104.

[0087] Step S103: The AlN seed crystal 2 is ultrasonically cleaned sequentially with acetone and ethanol for 8 min to 12 min each.

[0088] For example, the cleaning time can be 8 min, 9 min, 10 min, 11 min, 12 min, or any value between the two.

[0089] Ultrasonic cleaning of AlN seed crystals 2 can effectively remove surface oil stains.

[0090] Step S104: Anneal the AlN seed crystal 2 at a temperature of 1150℃~1250℃ and under a nitrogen atmosphere for 0.8h~1.2h.

[0091] For example, the temperature can be 1150℃, 1180℃, 1210℃, 1230℃, 1250℃ or any value between the two; the annealing time can be 0.8h, 0.9h, 1h, 1.1h, 1.2h or any value between the two.

[0092] High-temperature annealing of AlN seed crystals 2 can effectively eliminate internal residual stress.

[0093] It is understandable that when the AlN seed crystal 2 includes a stacked seed crystal body 21 and a flexible buffer film 22, the seed crystal body 21 is first ultrasonically cleaned with acetone and ethanol in sequence; then the seed crystal body 21 is annealed; finally, a flexible buffer film is magnetron sputtered on the surface of the seed crystal body to obtain the AlN seed crystal; the process conditions can be kept consistent with those described above, and will not be repeated here.

[0094] Step S2: Connect the AlN seed crystal 2 to the inner wall of the crucible 1 so that the AlN seed crystal 2 is suspended in the crucible 1 and positioned opposite to the AlN raw material 3.

[0095] Optionally, the vertical distance between the AlN seed crystal 2 and the AlN raw material 3 is maintained at 20mm to 30mm, for example, it can be 20mm, 22mm, 24mm, 26mm, 28mm or 30mm.

[0096] As an optional implementation of step S2, in conjunction with the appendix Figure 1 As shown, when the crucible 1 is placed in the growth furnace, the narrow section 111 of the inclined pot body 11 is close to the bottom of the growth furnace, and the wide section 112 of the inclined pot body 11 is close to the top of the growth furnace, that is, the crucible 1 is placed upside down in the growth furnace. The AlN raw material 3 is still located in the wide section 112, and the AlN seed crystal 2 is still located in the narrow section 111. The AlN seed crystal 2 is connected by the tungsten pillar 5 and the seed crystal holder 12, so that it is suspended in the crucible 1 and positioned opposite to the AlN raw material 3 under the support of the tungsten pillar 5.

[0097] The purpose of placing crucible 1 upside down in the growth furnace is to: allow gas phase atoms to be transported downwards during the growth process, aligning with the direction of gravity, thus solving the problem of A atom sedimentation due to gravity in the original process, improving the atom utilization rate by 20%-30%, and shortening the growth cycle; allow trace impurity particles in the growth furnace to settle to the outside of the seed crystal area due to gravity, preventing them from mixing into the gas phase, thereby improving the purity of AlN single crystals; and ensure that large-sized crystals grow downwards, with gravity aligned with the growth direction, preventing AlN seed crystal 2 from bending due to its weight, thus guaranteeing the flatness of the single crystal.

[0098] As an alternative implementation of step S2, combined with the appendix Figure 2 As shown, AlN seed crystal 2 is connected to the inner wall of crucible 1 so that AlN seed crystal 2 is suspended in crucible 1 and positioned opposite to AlN raw material 3, including steps S21b-S22b.

[0099] Step S21b: Form a tungsten film edging 7 on the side of the AlN seed crystal 2.

[0100] Optionally, a tungsten film with a thickness of 1μm to 2μm can be sputtered on the circumferential side of the AlN seed crystal 2 using a magnetron sputtering process.

[0101] For example, the thickness of the tungsten film edge 7 can be 1 μm, 1.5 μm or 2 μm; the width of the tungsten film edge 7 can be 5 mm.

[0102] Step S22b: Provide multiple tungsten protrusions 8 on the inner wall of the inclined pot body 11.

[0103] To ensure the stability of the AlN seed crystal 2 suspended within the tilted pot 11, all tungsten protrusions 8 are arranged in a ring array on the inner wall of the tilted pot 11.

[0104] For example, the number of tungsten protrusions 8 can be 4 to 6, such as 4, 5 or 6; the height of the tungsten protrusions 8 can be 5 mm.

[0105] Step S23b: Connect the multiple tungsten protrusions 8 to the tungsten film edge 7 one-to-one using multiple tungsten strips 6.

[0106] Optionally, high-purity tungsten wires with a diameter of 0.1 mm to 0.2 mm are woven into micro-stretchable tungsten strips 6 (flexible mesh film strips) with a thickness of 5 μm to 10 μm. One end of each tungsten strip 6 is fixedly connected to the tungsten film edge 7 by high-temperature sintering at 1000°C under a nitrogen atmosphere. The other end of each tungsten strip 6 is correspondingly connected and fixed with a tungsten protrusion 8, thereby realizing the one-to-one connection of multiple tungsten protrusions 8 and tungsten film edge 7 through multiple tungsten strips 6.

[0107] For example, the diameter of the high-purity tungsten wire can be 0.1 mm, 0.15 mm or 0.2 mm; the thickness of the tungsten strip 6 can be 5 μm, 6, 7, 8, 9 or 10 μm.

[0108] It should be noted that when the seed crystal holder 12 is assembled at the opening, the AlN seed crystal 2 can be suspended inside the inclined pot 11 under the support of multiple tungsten strips 6 (i.e., the AlN seed crystal 2 maintains a gap of 5mm to 8mm with the inner wall of the inclined pot 11, achieving a suspended state), and the AlN seed crystal 2 is positioned opposite the AlN raw material 3 along the height direction of the inclined pot 11. The narrow section 111 of the inclined pot 11 is close to the bottom of the growth furnace, and the wide section 112 of the inclined pot 11 is close to the top of the growth furnace, i.e., the crucible 1 is placed upside down inside the growth furnace. The AlN raw material 3 is still located in the wide section 112, and the AlN seed crystal 2 is still located in the narrow section 111.

[0109] This method can precisely fix the spatial position of AlN seed crystal 2, avoid AlN seed crystal 2 displacement caused by high temperature airflow disturbance, and ensure uniform temperature field; the flexible buffer film 22 realizes the gentle thermal coupling between seed crystal body 21 and crucible 1, reduces the temperature difference from the center to the edge of seed crystal, and improves radial growth uniformity; the stress is borne by tungsten strip 6, tungsten protrusion 8 and tungsten film edge 7, avoiding local stress concentration.

[0110] Step S3: Place crucible 1 inside the growth furnace and maintain a vacuum inside the growth furnace.

[0111] Optionally, after placing crucible 1 inside the growth furnace, the furnace chamber is sealed, and a combination of mechanical and molecular pumps is used to create a vacuum, achieving a vacuum level within the furnace. .

[0112] Step S4: Raise the temperature of the growth furnace from room temperature to the preset holding temperature and hold it for a first set time, while continuously introducing the first protective gas into the growth furnace to protect the AlN seed crystal 2 and remove impurities from the crucible 1.

[0113] Optionally, the first protective gas can be nitrogen or a mixture of nitrogen and a reducing gas.

[0114] It should be noted that when the growth furnace starts heating up, a first protective gas is simultaneously introduced into the furnace. The continuous flow of gas forms a stable inert atmosphere, ensuring that the entire heating process is enveloped in this inert atmosphere. This prevents the furnace from experiencing a vacuum or residual air during the heating phase and allows the atmosphere and temperature to be synchronized, gradually removing residual impurities from crucible 1 and preventing oxidation of the AlN seed crystal 2 surface. This protects the AlN seed crystal 2 and promotes the subsequent growth of AlN single crystals.

[0115] If the first protective gas is introduced before raising the temperature of the growth furnace, it will result in the waste of gas in the early low-temperature stage. Moreover, the static atmosphere at low temperature in the furnace is prone to adsorbing trace impurities. After raising the temperature, the desorption of impurities will increase the difficulty of removal, resulting in no process gain and increased costs. If the temperature of the growth furnace is raised before introducing the first protective gas, the furnace will be in a high vacuum or residual air state in the early stage of heating. At high temperature, AlN seed crystal 2 and tungsten crucible 1 are prone to react with residual oxygen and carbon, causing oxidation of the surface of AlN seed crystal 2 and micro-corrosion of crucible 1, introducing impurity defects. At the same time, the heat conduction efficiency of heating under vacuum is low, and the temperature field distribution is prone to unevenness, which will affect the subsequent AlN single crystal growth.

[0116] As an optional implementation of step S4, the first protective gas includes nitrogen and a reducing gas, wherein the reducing gas is hydrogen.

[0117] The process of raising the room temperature to the preset holding temperature is a step heating process, which involves raising the temperature inside the growth furnace from room temperature to the preset holding temperature and then holding it for a first set time, including steps S41a-S43a.

[0118] Step S41a: Increase the temperature inside the growth furnace from room temperature to a third set temperature at a first preset heating rate of 3℃ / min to 5℃ / min, wherein the room temperature is 22℃ to 25℃; and the third set temperature is 500℃ ± 5℃.

[0119] For example, the room temperature can be 22°C, 23°C, 24°C or 25°C; the first preset heating rate can be 3°C / min, 4.5°C / min or 5°C / min; the third set temperature can be 495°C, 500°C or 505°C.

[0120] The low-temperature heating range from room temperature to the third set temperature is gradually accelerated at a heating rate of 3℃ / min to 5℃ / min, which can improve process efficiency. At the same time, it allows the trace amounts of water vapor and organic impurities adsorbed in the crucible to slowly desorb, avoiding the instantaneous release of large amounts of impurities that are difficult to remove due to rapid heating.

[0121] Step S42a: Increase the temperature inside the growth furnace from the third set temperature to the fourth set temperature at a second preset heating rate of 5℃ / min to 6℃ / min, wherein the fourth set temperature is 900℃±5℃.

[0122] For example, the second preset heating rate can be 5℃ / min, 5.5℃ / min or 6℃ / min; the fourth set temperature can be 895℃, 900℃ or 905℃.

[0123] The medium-temperature heating range from the third to the fourth set temperature is heated at a low rate of 5℃ / min to 6℃ / min, which allows the tungsten-molybdenum insulation layer, crucible 1, and AlN seed crystal 2 in the furnace to be heated evenly, avoiding micro-deformation of crucible 1 and recurrence of residual stress in AlN seed crystal 2 caused by local thermal stress.

[0124] Step S43a: The temperature inside the growth furnace is increased from the fourth set temperature to the preset holding temperature at a third preset heating rate of 6℃ / min to 8℃ / min, wherein the preset holding temperature is 1200℃±5℃.

[0125] For example, the third preset heating rate can be 6℃ / min, 7℃ / min or 8℃ / min; the preset holding temperature can be 1195℃, 1200℃ or 1205℃.

[0126] The fourth set temperature to the high temperature rise range from the preset holding temperature is heated at a heating rate of 6℃ / min to 8℃ / min. Combined with the holding range at the preset holding temperature, carbon and oxygen impurities inside the crucible 1 can be further removed under the atmosphere of the first protective gas, preventing oxidation of the AlN seed crystal 2 surface and promoting the subsequent growth of AlN single crystal.

[0127] Optionally, the volume percentage of reducing gas in the first protective gas decreases in a stepwise manner.

[0128] Specifically, during the process of raising the temperature in the growth furnace from room temperature to the fifth set temperature, the volume ratio of hydrogen in the first protective gas is the first set ratio.

[0129] Optionally, the first setting percentage is 8% to 10%, for example, it can be 8%, 9% or 10%; the fifth setting temperature is 800℃±5℃, for example, it can be 795℃, 800℃ or 805℃.

[0130] The heating temperature range from room temperature to the fifth set temperature uses a high hydrogen content of 8% to 10% to quickly remove the trace oxide layer on the surface of AlN seed crystal 2 and crucible 1 by utilizing the reducing properties of hydrogen.

[0131] During the process of raising the temperature in the growth furnace from the fifth set temperature to the preset holding temperature, the volume ratio of hydrogen in the first protective gas is the second set ratio, which is less than the first set ratio.

[0132] Optionally, the second setting percentage is 5% to 8%, for example, it can be 5%, 6%, 7% or 8%.

[0133] The fifth temperature rise range to the preset holding temperature uses a hydrogen ratio of 5% to 8% to reduce the surface etching of AlN seed crystal 2 caused by excessive hydrogen, while maintaining the impurity removal capability of the first protective gas atmosphere.

[0134] Optionally, during the process of raising the temperature in the growth furnace from room temperature to the sixth set temperature, the gas flow rate of the first protective gas is the second set flow rate.

[0135] Optionally, the second set flow rate is 80sccm to 100sccm, for example, it can be 80sccm, 85sccm, 90sccm, 95sccm or 100sccm; the sixth set temperature is 600℃±5℃, for example, it can be 595℃, 600℃ or 605℃.

[0136] The heating range from room temperature to the sixth set temperature uses a high gas flow rate of 80 sccm to 100 sccm, which can quickly replace the residual air in the furnace and form a stable protective atmosphere.

[0137] During the process of raising the temperature in the growth furnace from the sixth set temperature to the preset holding temperature, the gas flow rate of the first protective gas is the third set flow rate, which is less than the second set flow rate.

[0138] Optionally, the third setting is a flow rate of 50 sccm to 80 sccm, for example, it can be 80 sccm, 85 sccm, 90 sccm, 95 sccm or 100 sccm.

[0139] The sixth setting is to raise the temperature to the preset holding temperature range using a gas flow rate of 50 sccm to 80 sccm. This ensures that impurities are discharged from the growth furnace while reducing the interference of gas turbulence on the temperature field inside the growth furnace, making the temperature field more uniform.

[0140] By adopting the above scheme, the adaptability of temperature field and atmosphere can be further optimized, the risk of thermal stress and impurity introduction during the heating stage can be reduced, the impurity removal effect during the heat preservation stage can be more thorough, and a more stable process foundation can be laid for the subsequent AlN single crystal growth.

[0141] Step S4 involves continuously introducing the first protective gas during the heating process of the growth furnace, utilizing the synergistic effect of heating and gas introduction to perform multiple functions of pretreatment protection, impurity removal, and state activation on the AlN raw material 3 and AlN seed crystal 2 in the growth furnace.

[0142] Specifically, the effects on AlN seed crystal 2 are as follows: Hydrogen in the first protective gas has reducing properties, and during the heating process, it gradually desorbs and reduces the trace oxide layer and residual oil on the surface of AlN seed crystal 2 (such as trace residues after cleaning with acetone and ethanol). This can prevent impurities from nucleating on the surface of AlN seed crystal 2 during the growth stage, thus affecting crystal epitaxy. The uniform heating under the first protective gas atmosphere during the entire heating process can not only prevent AlN seed crystal 2 from generating new thermal stress due to sudden temperature changes or contact with air, but also maintain the low stress state of AlN seed crystal 2 in conjunction with the nitrogen annealing effect of AlN seed crystal 2 at 1200℃ in the early stage. The high temperature of 1200℃ combined with the nitrogen-hydrogen mixed first protective gas atmosphere can also make the atomic arrangement of the c-face of AlN seed crystal 2 more regular, improve the crystal epitaxial matching degree in the subsequent growth stage, and reduce dislocation defects.

[0143] Specifically, the effects on AlN raw material 3 are as follows: During the heating process, trace amounts of water vapor, nitrogen, hydrogen, and other impurities adsorbed on the surface and inside of AlN raw material 3 are gradually desorbed and discharged from the growth furnace under the atmosphere of the flowing first protective gas. This prevents impurities from being transported along with Al and N atoms during the pyrolysis of AlN raw material 3 in the growth stage and mixed into the grown AlN single crystal. The inert protective atmosphere of the first protective gas can prevent AlN raw material 3 from being oxidized at high temperatures, preventing the formation of impurity phases such as Al2O3. This ensures that only high-purity Al and N gas phase atoms are produced after the pyrolysis of AlN raw material 3, providing a pure gas phase source for the growth of AlN single crystals. The high temperature of 1200℃ preheats AlN raw material 3, making the pyrolysis rate more stable when the raw material zone in the subsequent growth stage is heated to 2200-2400℃, avoiding growth rate fluctuations caused by sudden increases and decreases in gas phase atom concentration.

[0144] Precise enhancement can be achieved through gradient control during the heating process. For example, by using a higher hydrogen ratio in the lower heating range, the oxide layer on the surface of AlN seed crystal 2 and AlN raw material 3 can be reduced more gently, avoiding direct etching with a high hydrogen ratio in the higher heating range. By using a lower heating rate in the lower heating range, impurities in AlN raw material 3 can be slowly desorbed, improving impurity removal efficiency. By using a lower hydrogen ratio in the higher heating range, the surface of AlN seed crystal 2 can be activated while avoiding etching of AlN seed crystal 2. It is understandable that gradient control during the heating process can further enhance the protection and impurity removal of AlN raw material 3 and AlN seed crystal 2, with effects far superior to operations with a single heating rate and a fixed hydrogen ratio.

[0145] Step S5: Raise the temperature inside the growth furnace from the preset holding temperature to the preset growth temperature, and at the same time continuously introduce the first protective gas into the growth furnace to grow AlN single crystals.

[0146] It should be noted that the AlN single crystal grows on the surface of the AlN seed crystal 2 on the side close to the AlN raw material 3.

[0147] As a specific implementation of step S5, the crucible 1 has a raw material area and a seed crystal area arranged opposite to each other, with AlN seed crystal 2 located in the seed crystal area and AlN raw material 3 located in the raw material area.

[0148] Optionally, an infrared thermometer and a mass flow controller are installed in crucible 1. During the AlN single crystal growth process, the infrared thermometer is used to monitor the temperature of the raw material zone and the seed crystal zone in real time, and the temperature fluctuation is controlled within ±5℃. The mass flow controller is used to precisely control the gas flow rates of the first protective gas and the second protective gas, and the flow rate fluctuation is controlled within ±2sccm.

[0149] The process involves raising the temperature inside the growth furnace from a preset holding temperature to a preset growth temperature, while simultaneously continuously introducing a first protective gas into the furnace to grow AlN single crystals. This includes: raising the temperature inside the growth furnace from the preset holding temperature to the preset growth temperature at a rate of 3°C / min to 5°C / min, and growing AlN single crystals at the preset growth temperature and a growth pressure of 50 mbar to 200 mbar within a second preset time period. The preset growth temperature includes the temperature of the raw material zone and the temperature of the seed crystal zone; the temperature of the raw material zone is 2200°C to 2400°C, and the temperature of the seed crystal zone is 2100°C to 2300°C. The second preset time period is 80 h to 150 h.

[0150] For example, the heating rate can be 3℃ / min, 3.5℃ / min, 4℃ / min, 4.5℃ / min or 5℃ / min; the growth pressure can be 50mbar, 80mbar, 110mbar, 150mbar, 170mbar or 200mbar; the temperature of the raw material zone is 2200℃, 2250℃, 2300℃, 2350℃ or 2400℃; the temperature of the seed crystal zone is 2100℃, 2150℃, 2200℃, 2250℃ or 2300℃; and the length of the second preset time period is 80h, 90h, 100h, 110h, 120h, 130h, 140h or 150h.

[0151] Step S4, through heat preservation and impurity removal, ensures an initial uniform temperature field within the growth furnace, facilitating a smooth transition from the pretreatment temperature to the growth temperature. This avoids temperature gradient fluctuations in the seed crystal region caused by abrupt temperature changes, guaranteeing the stability of the crystal growth rate. Temperature monitoring throughout Step S4 provides a baseline reference for precise infrared thermometry in Step S5, making it easier to control the temperature gradient (80℃ / cm~120℃ / cm) between the raw material zone and the seed crystal zone. The nitrogen-hydrogen mixed atmosphere system formed in Step S4 is continuously used in Step S5 (maintaining only parameter stability), ensuring a stable inert atmosphere within the furnace during the growth stage and preventing impurities from being introduced during atmosphere switching. Furthermore, the impurity removal effect in Step S4 directly determines the purity of the gas source in Step S5. If the impurity removal in Step S4 is incomplete, impurities in Step S5 will be transported to the seed crystal surface with the gas atoms, forming defects. The growth furnace has been evacuated to a temperature of [missing information - likely a temperature value] before Step S4. The high vacuum in step S4 provides a basis for pressure regulation in step S5, avoiding pressure fluctuations caused by directly increasing the pressure from high vacuum in step S5, and making the growth pressure of AlN single crystal more stable.

[0152] Optionally, the temperature gradient in the raw material region is 100℃ / cm to 120℃ / cm, for example, 100℃ / cm, 105℃ / cm, 110℃ / cm, 115℃ / cm or 120℃ / cm; the temperature gradient in the seed crystal region is 80℃ / cm to 100℃ / cm, for example, 80℃ / cm, 85℃ / cm, 90℃ / cm, 95℃ / cm or 100℃ / cm; the temperature gradient in the gas phase transport region between the raw material region and the seed crystal region is 60℃ / cm to 80℃ / cm, for example, 60℃ / cm, 65℃ / cm, 70℃ / cm, 75℃ / cm or 80℃ / cm.

[0153] The temperature gradient in the raw material zone is designed to be 100℃ / cm~120℃ / cm (relatively steep) to ensure rapid and uniform pyrolysis of AlN raw material into high-purity Al and N gaseous atoms, thereby improving the generation efficiency of the gaseous source and avoiding fluctuations in gaseous atom concentration caused by incomplete local pyrolysis of the raw material. The temperature gradient in the gaseous transport zone is designed to be 60℃ / cm~80℃ / cm (relatively gentle) to reduce thermal convection disturbances of gaseous atoms during transport, allowing Al and N atoms to be smoothly transported upwards along the axial direction to the surface of the AlN seed crystal. To reduce random collisions of gas phase atoms and avoid the formation of polycrystalline nuclei, the temperature gradient of the seed crystal region (generally the surface of the AlN seed crystal and the area 5mm to 10mm below it) is designed to be 80℃ / cm to 100℃ / cm (a moderate temperature gradient compared to the raw material region and the gas phase transport region). This can precisely match the epitaxial growth rate of the AlN single crystal c-face, ensuring rapid adsorption, migration and nucleation of gas phase atoms on the AlN seed crystal 2 surface, while avoiding excessively steep gradients that lead to excessively fast growth rates and reducing defects such as dislocations and stacking faults.

[0154] Optionally, the temperature gradient between the bottom center and the bottom edge of crucible 1 is 5℃ / cm to 10℃ / cm, for example, it can be 5℃ / cm, 6℃ / cm, 7℃ / cm, 8℃ / cm, 9℃ / cm or 10℃ / cm.

[0155] To address the problem of slow single crystal edge growth and difficulty in diameter expansion caused by the large temperature difference between the bottom center and edge of the crucible in the traditional PVT method, a radial temperature gradient control is added on the basis of the axial gradient. This creates a small positive gradient (5℃ / cm~10℃ / cm) between the bottom center and edge of crucible 1 / growth furnace, meaning that the temperature at the center of crucible 1 is slightly higher than that at the edge (temperature difference ≤20℃). This allows gas phase atoms to achieve uniform adsorption and growth in both the central and edge regions of the AlN seed crystal 2 surface, avoiding "convex crystals" and "edge defects" caused by excessively rapid growth at the center and lagging growth at the edge of AlN seed crystal 2. This enables uniform growth of large single crystals from 2 inches to 6 inches with equal diameter, improving the dimensional regularity of AlN single crystals.

[0156] Optionally, the temperature gradient on the surface of AlN seed crystal 2 is ±3℃ / cm, and the temperature gradient between the center and the edge of the surface of AlN seed crystal 2 is 3℃ / cm to 5℃ / cm, for example, it can be 3℃ / cm, 3.5℃ / cm, 4℃ / cm, 4.5℃ / cm or 5℃ / cm.

[0157] To address the crystal orientation deviation caused by minute fluctuations in the local temperature field on the AlN seed crystal 2 surface, micro-gradient control is implemented on the AlN seed crystal 2 surface. Through local temperature field compensation of the seed crystal holder 12, the overall gradient fluctuation on the AlN seed crystal 2 surface is controlled within ±3℃ / cm, and the temperature gradient between the center and edge of the AlN seed crystal 2 surface is 3℃~5℃ / cm. This ensures the directional epitaxial growth of AlN single crystals along the c-plane, reduces crystal orientation deviation caused by uneven local temperature field on the AlN seed crystal 2 surface, improves the orientation consistency of single crystals in mass production, and solves the problem of poor orientation controllability in traditional processes.

[0158] Optionally, the second preset time period is 150 hours long.

[0159] During the AlN single crystal growth period from 0h to 50h, the temperature gradient between the raw material region and the seed crystal region is 90℃ / cm to 120℃ / cm, for example, it can be 90℃ / cm, 100℃ / cm, 110℃ / cm or 120℃ / cm; during the AlN single crystal growth period from 50h to 100h, the temperature gradient between the raw material region and the seed crystal region is 80℃ / cm to 100℃ / cm, for example, it can be 80℃ / cm, 85℃ / cm, 90℃ / cm, 95℃ / cm or 100℃ / cm; during the AlN single crystal growth period from 100h to 150h, the temperature gradient between the raw material region and the seed crystal region is 80℃ / cm to 90℃ / cm, for example, it can be 80℃ / cm, 82℃ / cm, 84℃ / cm, 86℃ / cm, 88℃ / cm or 90℃ / cm.

[0160] During the entire AlN single crystal growth process within the second preset time period of 150 hours, the amount of AlN raw material gradually decreases with pyrolysis, and the concentration of gas phase atoms also changes slowly. Therefore, dynamic fine-tuning of the gradient can be achieved within this second preset time period. That is, in the early stage of AlN single crystal growth (0h to 50h, when AlN raw material is sufficient), a temperature gradient closer to the upper limit (90℃ / cm to 120℃ / cm) is used to increase the growth rate of AlN single crystal and achieve rapid diameter expansion of AlN single crystal; in the middle stage of AlN single crystal growth (50h to 100h)... During the initial growth phase (after AlN single crystal diameter expansion is complete and constant diameter growth is achieved), a moderate temperature gradient (80℃ / cm~100℃ / cm) is used to stabilize the growth rate of AlN single crystals and ensure their crystal quality. In the later stages of AlN single crystal growth (100h~150h, when AlN raw material is reduced), a lower-limit temperature gradient (80℃ / cm~90℃ / cm) is used to reduce the growth rate of AlN single crystals, avoid a sharp drop in gas phase atom concentration due to insufficient AlN raw material, and prevent defects such as depressions and spots from appearing on the surface of AlN single crystals.

[0161] Step S6: Cool the temperature inside the growth furnace from the preset growth temperature to room temperature, and remove the grown AlN single crystal after breaking the vacuum at room temperature. During the cooling process from the preset growth temperature to room temperature, the cooling rate first decreases and then increases.

[0162] The room temperature can be 22℃ to 25℃, for example: 22℃, 23℃, 24℃ or 25℃.

[0163] The temperature gradient between the raw material region and the seed crystal region in step S5 is coordinated with the cooling rate in step S6. By strictly controlling the temperature gradient between the raw material region and the seed crystal region, step S5 can ensure the directional growth of AlN single crystal along the c-plane. Step S6 adopts "variable cooling", which can be adapted to the temperature gradient between the raw material region and the seed crystal region in the growth stage of step S5, allowing the thermal stress inside the AlN single crystal to be released gradually, avoiding crystal cracking and dislocation proliferation caused by rapid cooling.

[0164] As a specific implementation of step S6, cooling the temperature inside the growth furnace from a preset growth temperature to room temperature includes: cooling the temperature inside the growth furnace from the preset growth temperature to room temperature sequentially through a first cooling stage, a heat preservation stage, a second cooling stage, and a third cooling stage.

[0165] It should be noted that the cooling rate of the third cooling stage is greater than the cooling rate of the first cooling stage and greater than the cooling rate of the second cooling stage.

[0166] Furthermore, during the second cooling phase, the first protective gas is replaced with the second protective gas, and the gas flow rate of the first protective gas gradually decreases while the gas flow rate of the second protective gas gradually increases.

[0167] Optionally, the second protective gas is nitrogen.

[0168] Specifically, the temperature inside the growth furnace is lowered from the preset growth temperature to room temperature through a first cooling stage, a heat preservation stage, a second cooling stage, and a third cooling stage, including steps S61-S63.

[0169] Step S61 (First Cooling Stage): Introduce a first protective gas into the growth furnace to cool the temperature inside the growth furnace from the preset growth temperature to the first set temperature at a cooling rate of 2℃ / min to 3℃ / min.

[0170] Optionally, the cooling rate can be 2℃ / min, 2.2℃ / min, 2.4℃ / min, 2.6℃ / min, 2.8℃ / min or 3℃ / min; the first set temperature is 1500℃±5℃, for example, it can be 1495℃, 1500℃ or 1500℃.

[0171] The inventors discovered in their research that 1500℃±5℃ is the abrupt change point of thermal stress in AlN single crystals at medium and high temperatures. Therefore, they set 1500℃±5℃ as the first set temperature. Outside this temperature, the atomic thermal motion inside the single crystal is still relatively intense. The lattice distortion stress and thermal gradient stress generated during the crystal growth stage have not been completely fixed. Moreover, the single crystal is brittle at high temperatures, and rapid cooling can easily lead to instantaneous stress concentration and cause grain boundary cracking.

[0172] Furthermore, slow cooling at a rate of 2℃ / min to 3℃ / min can match the heat conduction rate of AlN single crystal from high growth temperature (i.e., the temperature of the seed crystal region is 2100℃ to 2300℃) to medium-high temperature (i.e., the first set temperature is 1500℃±5℃). This allows the temperature difference between the core and the surface of the AlN single crystal to be controlled within a very small range, avoiding the generation of new thermal stress due to inconsistent cooling rates inside and outside. At the same time, it allows the internal stress accumulated during the growth stage to be released slowly and uniformly, reducing dislocation multiplication.

[0173] Step S62 (Heating Stage): Introduce the first protective gas into the growth furnace and heat it for a second set time when the temperature inside the growth furnace is the first set temperature.

[0174] Optionally, the second set time is 0.8h to 1.2h, for example, it can be 0.8h, 0.9h, 1.0h, 1.1h or 1.2h.

[0175] The inventors discovered in their research that holding the temperature at 1500℃±5℃ for 0.8h to 1.2h allows the overall temperature of AlN single crystals to reach thermal equilibrium, eliminating local temperature gradients generated during cooling, further releasing lattice distortion stress, and allowing the atomic arrangement of AlN single crystals to complete preliminary lattice rearrangement at this temperature, making the crystal structure of AlN single crystals more stable and laying the foundation for subsequent low-temperature cooling.

[0176] Step S63 (Second Cooling Stage): The gas introduced into the growth furnace is gradually switched from the first protective gas to the second protective gas, and the temperature in the growth furnace is cooled from the first set temperature to the second set temperature at a cooling rate of 1℃ / min to 2℃ / min.

[0177] Optionally, the cooling rate can be 1℃ / min, 1.2℃ / min, 1.4℃ / min, 1.6℃ / min or 1.8℃ / min; the second set temperature is 800℃±5℃, for example, it can be 795℃, 800℃ or 805℃.

[0178] The inventors discovered in their research that 800℃±5℃ is a critical low-temperature thermal stress node for AlN single crystals, and also the critical temperature for hydrogen reducing power and crystal adsorption. Therefore, 800℃±5℃ was set as the second set temperature. Within this temperature range, the thermal expansion coefficient of aluminum nitride will fluctuate slightly, and the stress inside the single crystal will change from "thermal motion type" to "structural type". If the cooling rate is too fast, the stress will be permanently fixed in the crystal, forming irreversible defects. At the same time, outside 800℃±5℃, the reducing power of hydrogen is greatly reduced, and it is easily physically adsorbed by the surface of the single crystal, making it difficult to expel.

[0179] Furthermore, a cooling rate of 1℃ / min to 2℃ / min is used as the slowest cooling rate throughout the process, precisely adapting to the changes in the coefficient of thermal expansion within this temperature range. This allows the structural stress inside the single crystal to be completely and fully released, avoiding stress solidification and the formation of defects such as microcracks and stacking faults. Moreover, this cooling rate ensures the synchronization of cooling between the surface layer and the core of the AlN single crystal, preventing surface cracking caused by excessively rapid surface contraction while the core remains in a high-temperature expansion state. Especially for large-size single crystals of 2 inches to 6 inches, this cooling rate can effectively solve the problem of "internal and external temperature difference cracking" in large-size crystals.

[0180] It should be noted that during the switching process, while the gas flow rate of the first protective gas is gradually reduced to 0, the gas flow rate of the second protective gas is gradually increased to the first set flow rate.

[0181] During the switching process, the flow rate of the first protective gas, a mixture of hydrogen and nitrogen, is gradually reduced while the flow rate of the second protective gas, a mixture of high-purity nitrogen, is gradually increased until the flow rate of the first protective gas drops to 0 and the flow rate of the second protective gas reaches the first set flow rate. Throughout the process, the total gas flow rate in the growth furnace remains stable, without any interruption of gas flow or sudden surges in flow rate. This avoids sudden changes in gas pressure and turbulence in the furnace caused by sudden stops / starts, preventing pressure fluctuations from causing uneven deposition of gaseous atoms on the single crystal surface or localized temperature field disturbances caused by turbulence. Consequently, defects such as spots and depressions on the crystal surface are avoided. At the same time, the stable total flow rate ensures a continuous inert atmosphere in the furnace without any gaps where air may seep in.

[0182] Optionally, the first set flow rate is 50 sccm to 100 sccm, for example, it can be 50 sccm, 60 sccm, 70 sccm, 80 sccm, 90 sccm or 100 sccm.

[0183] By controlling the flow rate of the second protective gas after switching to 50 sccm to 100 sccm, which is in the same range as the flow rate of the first protective gas (hydrogen-nitrogen mixture) in steps S4 (heating and atmosphere conditioning) and S5 (single crystal growth), the growth system can be kept in the optimal stable gas flow rate range. This gas flow rate can ensure that the residual hydrogen in the furnace is quickly replaced and discharged, and can form a stable laminar flow, avoiding temperature field interference caused by large gas flow. At the same time, it matches the furnace volume and the capacity of the extraction system to ensure stable pressure (positive pressure state) in the furnace and prevent outside air from seeping in.

[0184] The core of atmosphere switching in step S63 is "stable pressure, stable airflow, and stable atmosphere". By switching smoothly and controlling the constant flow, the change in atmosphere does not affect the cooling process of the crystal, while maximizing the protective and cooling auxiliary role of high-purity nitrogen.

[0185] Step S64 (Third Cooling Stage): The temperature inside the growth furnace is cooled from the second set temperature to room temperature at a cooling rate of 4℃ / min to 6℃ / min.

[0186] Optionally, the cooling rate can be 4℃ / min, 4.5℃ / min, 5℃ / min, 5.5℃ / min or 6℃ / min.

[0187] It should be noted that the flow rate of the second protective gas remains constant throughout the third cooling stage, without any gradient changes.

[0188] Below the second set temperature, the thermal expansion coefficient of AlN single crystal tends to stabilize, atomic thermal motion is greatly reduced, the crystal structure is completely fixed, the internal residual stress is basically released, and the mechanical strength of the single crystal gradually increases with the decrease of temperature, and the tolerance to the cooling rate is significantly improved. Therefore, the cooling rate of the third cooling stage can be increased.

[0189] A relatively high cooling rate of 4℃ / min to 6℃ / min can significantly shorten the process time in the low-temperature section without introducing new defects or causing stress concentration, thereby improving the overall growth efficiency and balancing the crystallization quality of large-size single crystals with the efficiency requirements of industrial production. At this cooling rate, the continuous introduction of high-purity nitrogen gas can ensure uniform cooling of the crystal, avoid surface oxidation caused by air contact, and quickly complete the transition from high temperature to room temperature, reducing the placement time of the crystal in the medium and low temperature section and reducing the probability of external impurity adsorption.

[0190] Throughout the cooling process of step S6, a stepped design of "high-speed cooling → low-speed cooling → accelerated cooling" is used, along with key heat preservation at the first set temperature, to achieve "gradual release - complete release - no new stress generation" of internal stress in AlN single crystals. At the same time, the crystal structure completes "lattice rearrangement - structural fixation - morphological stability", solving the industry problem of easy cracking and residual stress defects during the cooling process of large-size AlN single crystals.

[0191] Step 6 employs a stepped gradient cooling design and a key heat preservation design at 1500℃±5℃. This is not simply a change in cooling rate, but a precise process design based on the changes in the thermal expansion coefficient of AlN single crystal in different temperature ranges, the internal stress release law, and the stability of crystal atomic arrangement. The cooling rate and temperature node of each cooling step correspond to the above-mentioned technical objectives. The three cooling designs are progressive and mutually supportive, ultimately achieving a cooling effect of "no cracking, no defects, and stable morphology" for AlN single crystal.

[0192] It should be noted that since the growth pressure in step S5 is positive pressure, the cooling process in step S6 maintains positive pressure inside the growth furnace (until the vacuum is broken) to prevent outside air from seeping in during the cooling stage. At the same time, the AlN single crystal is cooled under positive pressure to reduce the porosity defects inside the AlN single crystal.

[0193] Step S4 completes the initial impurity removal in the growth furnace system. Step S6 uses an inert atmosphere throughout the process to ensure the impurity removal effect continues until the crystal cools down, avoiding the introduction of new impurities during the cooling stage and achieving high purity of the single crystal throughout the growth and cooling process. Step S4 reduces the initial thermal stress of AlN seed crystal 2 and crucible 1 by uniformly heating up, and Step S6 releases the internal stress generated during crystal growth by variable-speed cooling. The two form a closed loop of "stress control in the early stage and stress release in the later stage", reducing the defect density of the crystal from the source to the end.

[0194] By coordinating steps S4 to S6, a closed-loop process is formed, ensuring consistent high-quality single crystal growth. Step S4 is the pretreatment stage, achieving "impurity removal, temperature stabilization, and substrate protection"; step S5 is the core growth stage, achieving "orientation, diameter expansion, and stable growth rate"; and step S6 is the post-treatment stage, achieving "stress relief, oxidation prevention, and morphology preservation". These three stages form an inseparable closed-loop process through continuous, stable, and precise control of three core parameters: temperature, atmosphere, and pressure. This ensures that every step of single crystal growth, from initial preparation to subsequent cooling, is mutually compatible, ultimately achieving high-quality growth of AlN single crystals.

[0195] It should be further explained that before the second cooling stage (cooling down to 800℃±5℃), a nitrogen-hydrogen mixed protective gas atmosphere is continuously introduced to maintain the same protective atmosphere as in step S5, so as to avoid the AlN single crystal being oxidized during the high-temperature cooling stage. After the second cooling stage, the hydrogen gas is stopped, and only high-purity nitrogen gas is introduced as the second protective gas atmosphere. By utilizing the inertness and thermal conductivity of nitrogen gas, the AlN single crystal is cooled down uniformly, while reducing the adsorption residue of hydrogen gas at low temperature and improving the purity of AlN single crystal.

[0196] Specifically, below 800℃±5℃, the molecular thermal motion of hydrogen weakens, making it easier for it to be physically adsorbed on the surface of AlN single crystals. If a hydrogen-nitrogen mixture continues to be introduced, the adsorbed hydrogen is difficult to expel during subsequent cooling and will remain on the surface or at the grain boundaries of the single crystal. On the one hand, residual hydrogen will increase the carbon and hydrogen impurity content of the single crystal, affecting the electrical performance of the device; on the other hand, residual hydrogen will form micropores at the grain boundaries, reducing the density of the single crystal. After the hydrogen supply is stopped, the continuous flow of high-purity nitrogen will quickly replace and expel the residual hydrogen in the furnace, avoiding the hydrogen residue problem at its source.

[0197] During the growth stage and the cooling stage above 800℃±5℃, the reducing properties of hydrogen can effectively remove trace oxygen impurities in the growth furnace system. At high temperatures, the etching effect of hydrogen is weak and will not damage the single crystal surface. However, below 800℃±5℃, the reducing properties of hydrogen decrease significantly, the impurity removal effect basically disappears, and the relative etching effect is enhanced. Continuing to introduce hydrogen will cause meaningless slight etching on the surface of the AlN single crystal, resulting in increased surface roughness and affecting the device fabrication compatibility of the substrate. Stopping the introduction of hydrogen can completely eliminate this etching effect and ensure the flatness of the single crystal surface.

[0198] Although 800℃±5℃ is considered a medium-low temperature, AlN single crystals will still react with oxygen in the air if they come into contact with air at this temperature, forming an Al2O3 oxide layer. The oxide layer will reduce the thermal conductivity and piezoelectricity of the single crystal and affect the interface matching of subsequent epitaxial growth. Continuing to introduce high-purity nitrogen as a second protective gas can keep the furnace atmosphere high-purity and inert until the crystal cools to room temperature, achieving oxygen-free contact throughout the entire process "from growth to cooling" and completely preventing crystal oxidation.

[0199] Furthermore, nitrogen has a moderate thermal conductivity and its flow stability in the furnace is better than that of hydrogen-nitrogen mixture. During the cooling stage below 800℃±5℃, the continuous flow of high-purity nitrogen can form a uniform thermal conduction atmosphere, allowing all parts of the single crystal to cool down synchronously, avoiding temperature gradients caused by excessively rapid local cooling, further ensuring the cooling uniformity of large-size single crystals and reducing surface defects.

[0200] In one embodiment, after the AlN crystal is removed, the flexible buffer film 22 is peeled off. For example, the flexible buffer film is peeled off using ultrasonic peeling technology.

[0201] An embodiment of the present invention also provides an AlN single crystal, which is prepared by the above-described growth method.

[0202] The technical solution of this application will be described in more detail below. However, it should be understood that the following embodiments are merely for explaining and illustrating the technical solution, and do not limit the scope of this application. Moreover, unless otherwise specified, the various raw materials, reaction equipment, detection equipment, and methods used in the following embodiments are all known in the art.

[0203] Example 1

[0204] This embodiment provides a growth apparatus, which includes a growth furnace and a crucible disposed within the growth furnace. Optionally, the crucible is made of tungsten. The crucible includes an inclined pot body with an opening and a seed crystal holder that can be fitted into the opening. The inclined pot body has a frustum structure, wherein the inclination angle of the side wall of the inclined pot body is 5°; the crucible has a raw material area and a seed crystal area arranged vertically opposite each other, with an AlN seed crystal located in the seed crystal area and an AlN raw material located in the raw material area.

[0205] This embodiment also provides a method for growing AlN single crystals. The growth method is applied to the above-mentioned growth equipment and includes the following steps S101-S112.

[0206] Step S101: Provide a crucible filled with AlN raw material; anneal the crucible for 1.8 hours under vacuum at 1750°C; purge nitrogen into the crucible and cool it to room temperature for later use.

[0207] The AlN raw material is a high-purity aluminum nitride sintered body raw material (purity ≥99.999%) with a particle size of 200μm and a filling amount of 60% of the tilting pot volume.

[0208] Step S102: The seed crystal body is ultrasonically cleaned with acetone and ethanol for 8 minutes each; the seed crystal body is annealed at 1150℃ and under a nitrogen atmosphere for 0.8 hours.

[0209] The seed crystal body is made of c-face aluminum nitride seed crystal, and its size is 1 inch.

[0210] Step S103: Under the condition of sputtering power of 150W, magnetron sputtering is performed on the surface of the seed crystal body for 30 minutes to form a flexible buffer film with a thickness of 50nm and tungsten material, thus obtaining AlN seed crystal.

[0211] Step S104: Open a connection hole at the center of the AlN seed crystal (flexible buffer film side).

[0212] Step S105: Connect the seed crystal holder to the connecting hole through a tungsten pillar so that the AlN seed crystal is suspended in the crucible and positioned opposite to the AlN raw material.

[0213] The tungsten pillar is bolted at both ends along its height direction to connect to the seed crystal holder and the connecting hole bolt, respectively.

[0214] The vertical distance between the AlN seed crystal and the AlN raw material is maintained at 20mm.

[0215] When the seed crystal holder is assembled at the opening, the AlN seed crystal can be suspended in the tilted pot body under the support of the tungsten pillar (that is, the AlN seed crystal maintains a 5mm gap with the inner wall of the tilted pot body to achieve a suspended state).

[0216] Step S106: Place the crucible inside the growth furnace and maintain a vacuum inside the growth furnace. When placing the crucible inside the growth furnace, the narrow section of the crucible should be close to the bottom of the growth furnace, and the wide section of the crucible should be close to the top of the growth furnace.

[0217] Step S107: Raise the temperature of the growth furnace from room temperature to the preset holding temperature and hold it for a first set time, while continuously introducing the first protective gas into the growth furnace, including steps S1071-S1073.

[0218] Step S1071: Increase the temperature inside the growth furnace from 22°C to 500°C at a first preset heating rate of 3°C / min, while simultaneously continuously introducing the first protective gas into the growth furnace.

[0219] Step S1072: Increase the temperature inside the growth furnace from 500°C to 900°C at a second preset heating rate of 5°C / min, while simultaneously continuously introducing the first protective gas into the growth furnace.

[0220] Step S1073: Increase the temperature inside the growth furnace from 900°C to 1200°C at a third preset heating rate of 6°C / min, while simultaneously continuously introducing the first protective gas into the growth furnace.

[0221] In steps S1071-S1073, the first protective gas includes nitrogen and hydrogen, with hydrogen accounting for 5% of the volume of the first protective gas and the gas flow rate of the first protective gas being 50 sccm.

[0222] Step S108: The temperature in the growth furnace is increased from 1200℃ to the preset growth temperature at a heating rate of 3℃ / min, and the growth is carried out for 80h at the preset growth temperature and a growth pressure of 50mbar to obtain AlN single crystal.

[0223] The preset growth temperature includes the temperature of the raw material zone and the temperature of the seed crystal zone. The temperature of the raw material zone is 2200℃, and the temperature of the seed crystal zone is 2100℃.

[0224] Step S109: Introduce nitrogen into the growth furnace to cool the temperature inside the furnace from the preset growth temperature to 22℃ at a cooling rate of 2℃ / min.

[0225] Example 2

[0226] The difference from Example 1 is that step S109 includes the following steps:

[0227] Step S1091: Introduce the first protective gas into the growth furnace to cool the temperature inside the growth furnace from the preset growth temperature to 1500℃ at a cooling rate of 2℃ / min.

[0228] Step S1092: Introduce the first protective gas into the growth furnace and maintain the temperature in the growth furnace at 1500℃ for 0.8h.

[0229] Step S1093: Gradually switch the gas introduced into the growth furnace from the first protective gas to nitrogen, and reduce the temperature inside the growth furnace from 1500℃ to 800℃ at a cooling rate of 1℃ / min. During the switching process, the gas flow rate of the first protective gas is gradually reduced to 0 while the gas flow rate of nitrogen is gradually increased to 50 sccm.

[0230] Step S1094: The temperature inside the growth furnace is reduced from 800℃ to 22℃ at a cooling rate of 4℃ / min.

[0231] Example 3

[0232] This embodiment provides a growth apparatus, which includes a growth furnace and a crucible disposed within the growth furnace. Optionally, the crucible is made of tungsten. The crucible includes an inclined pot body with an opening and a seed crystal holder that can be fitted into the opening. The inclined pot body has a frustum structure, wherein the inclination angle of the side wall of the inclined pot body is 10°; the crucible has a raw material area and a seed crystal area arranged vertically opposite each other, with an AlN seed crystal located in the seed crystal area and an AlN raw material located in the raw material area.

[0233] This embodiment also provides a method for growing AlN single crystals. The growth method is applied to the above-mentioned growth equipment and includes the following steps S101-S112.

[0234] Step S101: Provide an AlN seed crystal and a crucible filled with AlN raw material; anneal the crucible for 1.9 h under vacuum at 1800℃; purge nitrogen into the crucible and cool it to room temperature for later use.

[0235] The AlN raw material is a high-purity aluminum nitride sintered body raw material (purity ≥99.999%) with a particle size of 350μm and a filling amount of 65% of the tilting pot volume.

[0236] Step S102: The seed crystal body is ultrasonically cleaned with acetone and ethanol for 10 minutes each; the seed crystal body is annealed at 1200℃ in a nitrogen atmosphere for 1 hour.

[0237] The seed crystal body is made of c-face aluminum nitride seed crystal, and its size is 2 inches.

[0238] Step S103: Under the condition of sputtering power of 180W, magnetron sputtering is performed on the surface of the seed crystal body for 45 minutes to form a flexible buffer film with a thickness of 70nm and tungsten, thus obtaining an AlN seed crystal.

[0239] Step S104: Open a connection hole at the center of the AlN seed crystal (flexible buffer film side).

[0240] Step S105: Connect the seed crystal holder to the connecting hole through a tungsten pillar so that the AlN seed crystal is suspended in the crucible and positioned opposite to the AlN raw material.

[0241] The tungsten pillar is bolted at both ends along its height direction to connect to the seed crystal holder and the connecting hole bolt, respectively.

[0242] The vertical distance between the AlN seed crystal and the AlN raw material is maintained at 25mm.

[0243] When the seed crystal holder is assembled at the opening, the AlN seed crystal can be suspended in the tilted pot body under the support of the tungsten pillar (that is, the AlN seed crystal maintains a 6.5mm gap with the inner wall of the tilted pot body to achieve a suspended state).

[0244] Step S106: Place the crucible inside the growth furnace and maintain a vacuum inside the growth furnace. When placing the crucible inside the growth furnace, the narrow section of the crucible should be close to the bottom of the growth furnace, and the wide section of the crucible should be close to the top of the growth furnace.

[0245] Step S107: Raise the temperature of the growth furnace from room temperature to the preset holding temperature and hold it for a first set time, while continuously introducing the first protective gas into the growth furnace, including steps S1071-S1073.

[0246] Step S1071: Increase the temperature inside the growth furnace from 23°C to 500°C at a first preset heating rate of 4°C / min, while simultaneously continuously introducing the first protective gas into the growth furnace.

[0247] Step S1072: Increase the temperature inside the growth furnace from 500°C to 900°C at a second preset heating rate of 5.5°C / min, while simultaneously continuously introducing the first protective gas into the growth furnace.

[0248] Step S1073: Increase the temperature inside the growth furnace from 900°C to 1200°C at a third preset heating rate of 7°C / min, while continuously introducing the first protective gas into the growth furnace.

[0249] The first protective gas consists of nitrogen and hydrogen, with hydrogen accounting for 8% of the volume of the first protective gas, and the gas flow rate of the first protective gas is 75 sccm.

[0250] Step S108: The temperature in the growth furnace is increased from 1200℃ to the preset growth temperature at a heating rate of 4℃ / min, and the growth is carried out for 120h at the preset growth temperature and a growth pressure of 100mbar to obtain AlN single crystal.

[0251] The preset growth temperature includes the temperature of the raw material zone and the temperature of the seed crystal zone. The temperature of the raw material zone is 2300℃, and the temperature of the seed crystal zone is 2200℃.

[0252] Step S109: Introduce the first protective gas into the growth furnace to cool the temperature inside the growth furnace from the preset growth temperature to 1500℃ at a cooling rate of 2.5℃ / min.

[0253] Step S110: Introduce the first protective gas into the growth furnace and keep it at 1500℃ for 1 hour.

[0254] Step S111: Gradually switch the gas introduced into the growth furnace from the first protective gas to nitrogen, and reduce the temperature inside the growth furnace from 1500℃ to 800℃ at a cooling rate of 1.5℃ / min. During the switching process, the gas flow rate of the first protective gas is gradually reduced to 0 while the gas flow rate of nitrogen is gradually increased to 75 sccm.

[0255] Step S112: The temperature inside the growth furnace is reduced from 800℃ to 23℃ at a cooling rate of 5℃ / min.

[0256] Example 4

[0257] This embodiment provides a growth apparatus, which includes a growth furnace and a crucible disposed within the growth furnace. Optionally, the crucible is made of tungsten. The crucible includes an inclined pot body with an opening and a seed crystal holder that can be fitted into the opening. The inclined pot body has a frustum structure, wherein the inclination angle of the side wall of the inclined pot body is 15°; the crucible has a raw material area and a seed crystal area arranged vertically opposite each other, with an AlN seed crystal located in the seed crystal area and AlN raw material located in the raw material area.

[0258] This embodiment also provides a method for growing AlN single crystals. The growth method is applied to the above-mentioned growth equipment and includes the following steps S101-S112.

[0259] Step S101: Provide an AlN seed crystal and a crucible filled with AlN raw material; anneal the crucible for 2 hours under vacuum at 1850℃; purge nitrogen into the crucible and cool it to room temperature for later use.

[0260] The AlN raw material is a high-purity aluminum nitride sintered body raw material (purity ≥99.999%) with a particle size of 500μm and a filling amount of 70% of the tilting pot volume.

[0261] Step S102: The seed crystal body is ultrasonically cleaned with acetone and ethanol for 12 min each; the seed crystal body is annealed at 1250℃ and under a nitrogen atmosphere for 1.2 h.

[0262] The seed crystal body is made of c-face aluminum nitride seed crystal, and its size is 4 inches.

[0263] Step S103: Under the condition of sputtering power of 200W, magnetron sputtering is performed on the surface of the seed crystal body for 60 minutes to form a flexible buffer film with tungsten material and a thickness of 100nm, thus obtaining AlN seed crystal.

[0264] Step S104: Open a connection hole at the center of the AlN seed crystal (flexible buffer film side).

[0265] Step S105: Connect the seed crystal holder to the connecting hole through a tungsten pillar so that the AlN seed crystal is suspended in the crucible and positioned opposite to the AlN raw material.

[0266] The tungsten pillar is bolted at both ends along its height direction to connect to the seed crystal holder and the connecting hole bolt, respectively.

[0267] The vertical distance between the AlN seed crystal and the AlN raw material is maintained at 30mm.

[0268] When the seed crystal holder is assembled at the opening, the AlN seed crystal can be suspended in the tilted pot body under the support of the tungsten pillar (that is, the AlN seed crystal maintains an 8mm gap with the inner wall of the tilted pot body to achieve a suspended state).

[0269] Step S106: Place the crucible inside the growth furnace and maintain a vacuum inside the growth furnace. When placing the crucible inside the growth furnace, the narrow section of the crucible should be close to the bottom of the growth furnace, and the wide section of the crucible should be close to the top of the growth furnace.

[0270] Step S107: Raise the temperature of the growth furnace from room temperature to the preset holding temperature and hold it for a first set time, while continuously introducing the first protective gas into the growth furnace, including steps S1071-S1073.

[0271] Step S1071: Increase the temperature inside the growth furnace from 25°C to 500°C at a first preset heating rate of 5°C / min, while simultaneously continuously introducing a first protective gas into the growth furnace.

[0272] Step S1072: Increase the temperature inside the growth furnace from 500°C to 900°C at a second preset heating rate of 6°C / min, while simultaneously continuously introducing the first protective gas into the growth furnace.

[0273] Step S1073: Increase the temperature inside the growth furnace from 900°C to 1200°C at a third preset heating rate of 8°C / min, while simultaneously continuously introducing the first protective gas into the growth furnace.

[0274] The first protective gas consists of nitrogen and hydrogen, with hydrogen accounting for 10% of the volume and a flow rate of 100 sccm.

[0275] Step S108: The temperature in the growth furnace is increased from 1200℃ to the preset growth temperature at a heating rate of 5℃ / min, and the growth is carried out for 150h at the preset growth temperature and a growth pressure of 200mbar to obtain AlN single crystal.

[0276] The preset growth temperature includes the temperature of the raw material zone and the temperature of the seed crystal zone. The temperature of the raw material zone is 2400℃, and the temperature of the seed crystal zone is 2300℃.

[0277] Step S109: Introduce the first protective gas into the growth furnace to cool the temperature inside the growth furnace from the preset growth temperature to 1500℃ at a cooling rate of 3℃ / min.

[0278] Step S110: Introduce the first protective gas into the growth furnace and maintain the temperature at 1500℃ for 1.2 hours.

[0279] Step S111: Gradually switch the gas introduced into the growth furnace from the first protective gas to nitrogen, and reduce the temperature inside the growth furnace from 1500℃ to 800℃ at a cooling rate of 2℃ / min. During the switching process, the gas flow rate of the first protective gas is gradually reduced to 0 while the gas flow rate of nitrogen is gradually increased to 100 sccm.

[0280] Step S112: The temperature inside the growth furnace is reduced from 800℃ to 25℃ at a cooling rate of 6℃ / min.

[0281] Example 5

[0282] The difference from Example 2 is that the volume percentage of hydrogen in the first protective gas decreases stepwise in step S107. That is, during the process of raising the temperature in the growth furnace from 22°C to 800°C, the volume percentage of hydrogen in the first protective gas is 8%; during the process of raising the temperature in the growth furnace from 800°C to 1200°C, the volume percentage of hydrogen in the first protective gas is 5%.

[0283] The rest are the same and will not be repeated.

[0284] Example 6

[0285] The difference from Example 3 is that the volume percentage of hydrogen in the first protective gas decreases stepwise in step S107. That is, during the process of raising the temperature in the growth furnace from 22°C to 800°C, the volume percentage of hydrogen in the first protective gas is 9%; during the process of raising the temperature in the growth furnace from 800°C to 1200°C, the volume percentage of hydrogen in the first protective gas is 6.5%.

[0286] The rest are the same and will not be repeated.

[0287] Example 7

[0288] The difference from Example 4 is that the volume percentage of hydrogen in the first protective gas decreases stepwise in step S107. That is, during the process of raising the temperature in the growth furnace from 22°C to 800°C, the volume percentage of hydrogen in the first protective gas is 10%; during the process of raising the temperature in the growth furnace from 800°C to 1200°C, the volume percentage of hydrogen in the first protective gas is 8%.

[0289] The rest are the same and will not be repeated.

[0290] Example 8

[0291] The difference from Example 2 is that the gas flow rate of the first protective gas in step S107 is different. Specifically, the gas flow rate of the first protective gas is 80 sccm during the process of raising the temperature in the growth furnace from 22°C to 600°C, and the gas flow rate of the first protective gas is 50 sccm during the process of raising the temperature in the growth furnace from 600°C to 1200°C.

[0292] The rest are the same and will not be repeated.

[0293] Example 9

[0294] The difference from Example 3 is that the gas flow rate of the first protective gas in step S107 is different. Specifically, the gas flow rate of the first protective gas is 90 sccm during the process of raising the temperature in the growth furnace from 22°C to 600°C, and the gas flow rate of the first protective gas is 65 sccm during the process of raising the temperature in the growth furnace from 600°C to 1200°C.

[0295] The rest are the same and will not be repeated.

[0296] Example 10

[0297] The difference from Example 4 is that the gas flow rate of the first protective gas in step S107 is different. Specifically, the gas flow rate of the first protective gas is 100 sccm during the process of raising the temperature in the growth furnace from 22°C to 600°C, and the gas flow rate of the first protective gas is 80 sccm during the process of raising the temperature in the growth furnace from 600°C to 1200°C.

[0298] The rest are the same and will not be repeated.

[0299] Example 11

[0300] The difference from Example 2 is that in step S108, the temperature gradient in the raw material zone is 100℃ / cm;

[0301] The temperature gradient in the seed crystal region is 80℃ / cm; the temperature gradient in the gas phase transport region between the raw material region and the seed crystal region is 60℃ / cm.

[0302] The rest are the same and will not be repeated.

[0303] Example 12

[0304] The difference from Example 3 is that in step S108, the temperature gradient of the raw material zone is 110℃ / cm; the temperature gradient of the seed crystal zone is 90℃ / cm; and the temperature gradient of the gas phase transport zone between the raw material zone and the seed crystal zone is 70℃ / cm.

[0305] The rest are the same and will not be repeated.

[0306] Example 13

[0307] The difference from Example 4 is that in step S108, the temperature gradient of the raw material zone is 120℃ / cm; the temperature gradient of the seed crystal zone is 100℃ / cm; and the temperature gradient of the gas phase transport zone between the raw material zone and the seed crystal zone is 80℃ / cm.

[0308] The rest are the same and will not be repeated.

[0309] Example 14

[0310] The difference from Example 4 is that in step S108, the temperature gradient between the raw material region and the seed crystal region is 90℃ / cm when growing AlN single crystal for 0-50h; the temperature gradient between the raw material region and the seed crystal region is 80℃ / cm when growing AlN single crystal for 50h-100h; and the temperature gradient between the raw material region and the seed crystal region is 80℃ / cm when growing AlN single crystal for 100-150h.

[0311] The rest are the same and will not be repeated.

[0312] Example 15

[0313] The difference from Example 4 is that in step S108, the temperature gradient between the raw material region and the seed crystal region is 105℃ / cm when growing AlN single crystal for 0-50h; the temperature gradient between the raw material region and the seed crystal region is 90℃ / cm when growing AlN single crystal for 50h-100h; and the temperature gradient between the raw material region and the seed crystal region is 85℃ / cm when growing AlN single crystal for 100-150h.

[0314] The rest are the same and will not be repeated.

[0315] Example 16

[0316] The difference from Example 4 is that in step S108, the temperature gradient between the raw material region and the seed crystal region is 120℃ / cm when growing AlN single crystal for 0-50h; the temperature gradient between the raw material region and the seed crystal region is 100℃ / cm when growing AlN single crystal for 50h-100h; and the temperature gradient between the raw material region and the seed crystal region is 90℃ / cm when growing AlN single crystal for 100-150h.

[0317] The rest are the same and will not be repeated.

[0318] Example 17

[0319] The difference from Example 2 is that step S103 is different. The flexible buffer film includes a first buffer layer and a second buffer layer stacked together. Step S103 includes steps S1031-S1033.

[0320] Step S1031: Under the condition of sputtering power of 150W, magnetron sputtering is performed on the surface of the seed crystal body for 30 minutes to form an initial buffer layer with tungsten material and a thickness of 30nm.

[0321] Step S1032: The initial buffer layer is patterned by photolithography etching to obtain a first buffer layer with several protrusions and several pits.

[0322] The diameter of the boss is 50nm, the height of the boss is 20nm, and the diameter of the pit is 100nm.

[0323] Step S1033: Under the condition of sputtering power of 150W, magnetron sputtering is performed on the surface of the first buffer layer for 30 minutes to form a second buffer layer with a thickness of 20nm and covering several protrusions and several pits.

[0324] The rest are the same and will not be repeated.

[0325] Example 18

[0326] The difference from Example 3 is that step S103 is different. The flexible buffer film includes a first buffer layer and a second buffer layer stacked together. Step S103 includes steps S1031-S1033.

[0327] Step S1031: Under the condition of sputtering power of 180W, magnetron sputtering is performed on the surface of the seed crystal body for 45 minutes to form an initial buffer layer with a thickness of 40nm and tungsten.

[0328] Step S1032: The initial buffer layer is patterned by photolithography etching to obtain a first buffer layer with several protrusions and several pits.

[0329] The diameter of the boss is 75nm, the height of the boss is 20nm, and the diameter of the pit is 150nm.

[0330] Step S1033: Under the condition of sputtering power of 180W, magnetron sputtering is performed on the surface of the first buffer layer for 45 minutes to form a second buffer layer with a thickness of 35nm and covering several protrusions and several pits.

[0331] The rest are the same and will not be repeated.

[0332] Example 19

[0333] The difference from Example 4 is that step S103 is different. The flexible buffer film includes a first buffer layer and a second buffer layer stacked together. Step S103 includes steps S1031-S1033.

[0334] Step S1031: Under the condition of sputtering power of 200W, magnetron sputtering is performed on the surface of the seed crystal body for 60 minutes to form an initial buffer layer with tungsten material and a thickness of 50nm.

[0335] Step S1032: The initial buffer layer is patterned by photolithography etching to obtain a first buffer layer with several protrusions and several pits.

[0336] The diameter of the boss is 100nm, the height of the boss is 50nm, and the diameter of the pit is 200nm.

[0337] Step S1033: Under the condition of sputtering power of 200W, magnetron sputtering is performed on the surface of the first buffer layer for 60 minutes to form a second buffer layer with a thickness of 50nm and covering several protrusions and several pits.

[0338] The rest are the same and will not be repeated.

[0339] Comparative Example 1

[0340] The difference from Example 2 lies in step S107, which includes the following steps:

[0341] The temperature inside the growth furnace is increased from 22°C to 1200°C at a rate of 5°C / min, while the first protective gas is continuously introduced into the growth furnace.

[0342] The rest are the same and will not be repeated.

[0343] Comparative Example 2

[0344] The difference from Example 2 is that: Step S2: The traditional PVT method is used, a flat-bottomed tungsten crucible is selected, and the seed crystal body is directly fixed to the top of the crucible.

[0345] The rest are the same and will not be repeated.

[0346] The AlN single crystals of Examples 1-19 and Comparative Examples 1-2 were treated and tested, including XRD tests, Raman spectroscopy tests, and corrosion pit density tests. The test results are shown in Table 1 below.

[0347] Table 1: Test Results

[0348]

[0349]

[0350] Referring to Table 1, and from the analyses of Examples 1-19 and Comparative Examples 1-2, it can be seen that the AlN single crystals obtained in the Examples have more uniform crystal size and more stable crystal quality compared to the Comparative Examples. In the process of raising the temperature of the growth furnace from room temperature to the preset holding temperature, the present invention controls the use of a step-by-step heating method and / or a step-by-step decrease in the volume ratio of the reducing gas in the first protective gas, which can improve the quality of AlN single crystals. The scheme provided by the Comparative Examples has obvious dislocation defects and poor crystal quality.

[0351] This invention forms a closed-loop process through the overall coordination of the heating and holding stage, the heating and growth stage, and the cooling stage, ensuring the consistent growth of high-quality single crystals. The heating and holding stage is a pretreatment stage, achieving "impurity removal, temperature stabilization, and substrate protection"; the heating and growth stage is the core, achieving "orientation, diameter expansion, and stable growth rate"; and the cooling stage is a post-treatment stage, achieving "stress relief, oxidation prevention, and morphology preservation". The three stages form an inseparable closed-loop process through continuous, stable, and precise control of parameters such as temperature, atmosphere, and growth pressure, ensuring that every step of single crystal growth from the initial preparation to the final cooling is mutually compatible, ultimately achieving high-quality growth of AlN single crystals.

[0352] Although embodiments of the present invention have been shown and described above, it is understood that the above embodiments are exemplary and should not be construed as limiting the present invention. Those skilled in the art can make changes, modifications, substitutions and variations to the above embodiments within the scope of the invention without departing from the principles and spirit of the invention, and all such changes should fall within the protection scope of the claims of the present invention.

Claims

1. A method for growing AlN single crystals, characterized in that, The method is applied to a growth apparatus, the growth apparatus including a growth furnace and a crucible disposed within the growth furnace, and the growth method includes: Provides AlN seed crystals and crucibles filled with AlN raw materials; The AlN seed crystal is connected to the inner wall of the crucible so that the AlN seed crystal is suspended in the crucible and positioned opposite to the AlN raw material; The crucible is placed inside the growth furnace and the growth furnace is kept under vacuum. The temperature of the growth furnace is raised from room temperature to a preset holding temperature and held for a first set time, while a first protective gas is continuously introduced into the growth furnace to protect the AlN seed crystal and remove impurities from the crucible; wherein, the temperature rise from room temperature to the preset holding temperature is a step-wise temperature rise, and / or, the volume ratio of reducing gas in the first protective gas decreases stepwise. The temperature inside the growth furnace is raised from the preset holding temperature to the preset growth temperature, and a first protective gas is continuously introduced into the growth furnace at the same time to grow AlN single crystals. The temperature inside the growth furnace is lowered from the preset growth temperature to the room temperature, and the grown AlN single crystal is removed after the vacuum is broken at the room temperature.

2. The growth method according to claim 1, characterized in that, The reducing gas is hydrogen, and the first protective gas also includes nitrogen; the step of raising the temperature inside the growth furnace from room temperature to a preset holding temperature and then holding it for a first set time includes: The temperature inside the growth furnace is increased from room temperature to a third set temperature at a first preset heating rate. The temperature inside the growth furnace is increased from the third set temperature to the fourth set temperature at a second preset heating rate. The temperature inside the growth furnace is increased from the fourth set temperature to the preset holding temperature at a third preset heating rate. Wherein, the first preset heating rate is less than the second preset heating rate, and the second preset heating rate is less than the third preset heating rate; Preferably, the first preset heating rate is 3℃ / min to 5℃ / min, the second preset heating rate is 5℃ / min to 6℃ / min, and the third preset heating rate is 6℃ / min to 8℃ / min.

3. The growth method according to claim 2, characterized in that, During the process of raising the temperature in the growth furnace from room temperature to the fifth set temperature, the volume ratio of hydrogen in the first protective gas is the first set ratio; during the process of raising the temperature in the growth furnace from the fifth set temperature to the preset holding temperature, the volume ratio of hydrogen in the first protective gas is the second set ratio, which is less than the first set ratio. And / or, during the process of raising the temperature in the growth furnace from room temperature to the sixth set temperature, the gas flow rate of the first protective gas is the second set flow rate; during the process of raising the temperature in the growth furnace from the sixth set temperature to the preset holding temperature, the gas flow rate of the first protective gas is the third set flow rate, and the third set flow rate is less than the second set flow rate.

4. The growth method according to claim 1, characterized in that, The crucible has a raw material zone and a seed crystal zone arranged vertically opposite each other. The AlN seed crystal is located in the seed crystal zone, and the AlN raw material is located in the raw material zone. The step of raising the temperature in the growth furnace from the preset holding temperature to the preset growth temperature, and growing AlN single crystals at the preset growth temperature, includes: raising the temperature in the growth furnace from the preset holding temperature to the preset growth temperature at a heating rate of 3℃ / min to 5℃ / min; and growing AlN single crystals at the preset growth temperature and a growth pressure of 50mbar to 200mbar for a second preset time period. The preset growth temperature includes the temperature of the raw material zone and the temperature of the seed crystal zone; the temperature of the raw material zone is 2200℃ to 2400℃, and the temperature of the seed crystal zone is 2100℃ to 2300℃. The second preset time period is 80h to 150h. And / or, the temperature gradient of the raw material zone is 100℃ / cm~120℃ / cm; And / or, the temperature gradient of the seed crystal region is 80℃ / cm~100℃ / cm; And / or, the temperature gradient of the gas phase transport zone between the raw material zone and the seed crystal zone is 60℃ / cm~80℃ / cm.

5. The growth method according to claim 1, characterized in that, During the period from 0 to 50 hours, the temperature gradient between the raw material zone and the seed crystal zone is 90℃ / cm to 120℃ / cm. During the period of 50h to 100h, the temperature gradient between the raw material zone and the seed crystal zone is 80℃ / cm to 100℃ / cm. During the period of 100 to 150 hours, the temperature gradient between the raw material zone and the seed crystal zone is 80℃ / cm to 90℃ / cm.

6. The growth method according to claim 1, characterized in that, The AlN seed crystal comprises a stacked seed crystal body and a flexible buffer film; providing the AlN seed crystal includes: Under sputtering power of 150W to 200W, magnetron sputtering is performed on the surface of the seed crystal body for 30 to 60 minutes to form a flexible buffer film with a thickness of 50nm to 100nm.

7. The growth method according to claim 1, characterized in that, The AlN seed crystal comprises a stacked seed crystal body and a flexible buffer film; the flexible buffer film comprises a stacked first buffer layer and a second buffer layer, providing the AlN seed crystal with: Under the condition of sputtering power of 150W to 200W, magnetron sputtering is performed on the surface of the seed crystal body for 30min to 60min to form an initial buffer layer with a thickness of 30nm to 50nm. The initial buffer layer is patterned to obtain a first buffer layer with several protrusions and several pits; Under a sputtering power of 150W to 200W, magnetron sputtering is performed on the surface of the first buffer layer for 30 to 60 minutes to form a second buffer layer with a thickness of 20nm to 50nm that covers the plurality of protrusions and the plurality of pits.

8. The growth method according to claim 7, characterized in that, Include at least one of the following: The diameter of the protrusion is 50nm to 100nm; the height of the protrusion is 20nm to 50nm; and the diameter of the recess is 100nm to 200nm.

9. The growth method according to any one of claims 1-7, characterized in that, The crucible includes a narrow section and a wide section along the height direction of the crucible, the AlN seed crystal is located in the narrow section, and the AlN raw material is located in the wide section; And / or, during the process of cooling from the preset growth temperature to the room temperature, the cooling rate first decreases and then increases.

10. An AlN single crystal, characterized in that, It is prepared by the growth method described in any one of claims 1-9.

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