Flaky aluminum nitride seed crystal growth method and flaky aluminum nitride seed crystal

Abstract

The invention provides a growth method of a flaky aluminum nitride seed crystal and the flaky aluminum nitride seed crystal. The growth method of the flaky aluminum nitride seed crystal comprises the following steps: putting an aluminum nitride raw material into the bottom of a tungsten crucible; sequentially placing a breathable growth adjusting piece, a tungsten ring and a tungsten sheet above the tungsten crucible; wherein a growth gap is formed between the breathable growth adjusting part and the tungsten sheet, and the tungsten sheet and the aluminum nitride raw material are isolated through the breathable growth adjusting part; the tungsten crucible is heated; wherein the temperature of the lower surface of the tungsten crucible is higher than that of the upper surface of the tungsten crucible, and a gas-phase substance generated by sublimation of the aluminum nitride raw material reaches the long crystal face of the tungsten sheet through the breathable growth adjusting piece under the action of thermal motion and grows crystal on the long crystal face in the horizontal direction to obtain the flaky aluminum nitride seed crystal; and stripping the flaky aluminum nitride seed crystal from the tungsten sheet. By adopting the growth method of the flaky aluminum nitride seed crystal provided by the invention, the flaky aluminum nitride seed crystal with controllable thickness is formed.

Description

TECHNICAL FIELD

[0001] The present application relates to the technical field of crystal preparation, in particular to a growth method of a sheet-shaped aluminum nitride seed crystal and a sheet-shaped aluminum nitride seed crystal. BACKGROUND

[0002] Aluminum nitride (AlN) is a potential new generation of ultra-wide bandgap semiconductor and a key strategic new material due to its excellent performance. At present, the method for growing AlN single crystals is mostly physical vapor transport process (PVT).

[0003] However, there are still many technical difficulties in preparing AlN single crystals by the PVT method in the prior art, and how to obtain high-quality AlN seed crystals is one of the important issues in the growth technology of AlN crystals. One way is to directly purchase AlN single crystal wafers as seed crystals, but the high-quality AlN single crystal wafers available on the market are extremely limited. Another way is self-made, that is, through extensive PVT growth, a larger grain is cut from the obtained polycrystalline AlN ingot and processed as a seed crystal. The disadvantage of this method is that the obtained seed crystal is too small, and the crystal orientation is difficult to control. In addition, the gas phase material in the traditional PVT method has a large diffusion range in the vertical direction, and the diffusion is uneven, resulting in that the thickness of the aluminum nitride crystal increases too fast in the vertical direction, and it is difficult to form a sheet-shaped structure with controllable thickness.

[0004] It should be noted that the above introduction to the background art is only for the convenience of clearly and completely describing the technical solutions of the present application, and for the convenience of understanding by those skilled in the art. The above technical solutions cannot be considered as known to those skilled in the art merely because they are described in the background art section of the present application. SUMMARY

[0005] The present application aims to disclose a growth method of a sheet-shaped aluminum nitride seed crystal and a sheet-shaped aluminum nitride seed crystal, to solve the above technical problems, and in particular to realize the formation of a sheet-shaped aluminum nitride seed crystal with controllable thickness.

[0006] To achieve the above-mentioned purpose, in a first aspect, the present application provides a growth method of a sheet-shaped aluminum nitride seed crystal, comprising:

[0007] putting aluminum nitride raw materials into the bottom of a tungsten crucible;

[0008] placing a gas-permeable growth adjusting piece, a tungsten ring and a tungsten sheet in sequence above the tungsten crucible; wherein a growth gap is formed between the gas-permeable growth adjusting piece and the tungsten sheet, and the tungsten sheet and the aluminum nitride raw materials are spatially isolated by the gas-permeable growth adjusting piece;

[0009] heating the tungsten crucible; wherein the lower surface temperature of the tungsten crucible is higher than the upper surface temperature of the tungsten crucible, and the gaseous phase material generated by sublimation of the aluminum nitride raw material diffuses to the growth surface of the tungsten sheet through the gas-phase growth adjustment member and grows in the horizontal direction on the growth surface to obtain the sheet-shaped aluminum nitride seed crystal;

[0010] peeling the sheet-shaped aluminum nitride seed crystal from the tungsten sheet.

[0011] As a further improvement of the present application, the growth gap between the gas-phase growth adjustment member and the tungsten sheet is equal to the thickness of the tungsten ring.

[0012] And / or, the temperature of the tungsten crucible changes in the vertical direction.

[0013] During the heating of the tungsten crucible, the lower surface temperature of the tungsten crucible is controlled to be higher than the upper surface temperature of the tungsten crucible, forming a temperature gradient in the vertical direction. The gaseous phase material generated by sublimation of the aluminum nitride raw material enters the growth gap through the gas-phase growth adjustment member under the driving of the temperature gradient, and the gaseous phase material uniformly diffuses in the horizontal direction in the growth gap to uniformly cover the growth surface of the tungsten sheet.

[0014] As a further improvement of the present application, the heating of the tungsten crucible comprises:

[0015] placing the tungsten crucible into a heating furnace, and vacuumizing the heating furnace, and introducing high-purity nitrogen gas into the heating furnace;

[0016] controlling the upper surface temperature of the tungsten crucible to be between 2250-2280℃, the lower surface temperature of the tungsten crucible to be between 2270-2300℃, and the pressure to be between 700-800mbar, and using the heating furnace to maintain the temperature of the tungsten crucible for 5-50 hours;

[0017] wherein the lower surface temperature of the tungsten crucible is higher than the upper surface temperature of the tungsten sheet.

[0018] As a further improvement of the present application, the growth method of the sheet-shaped aluminum nitride seed crystal further comprises:

[0019] before peeling the sheet-shaped aluminum nitride seed crystal from the tungsten sheet, reducing the temperature of the heating furnace at a cooling rate of 50-100℃ / hour until the temperature of the heating furnace is reduced to room temperature;

[0020] taking out the tungsten sheet from the tungsten crucible.

[0021] As a further improvement of the present application, the sheet-shaped aluminum nitride seed crystal deposited on the growth surface of the tungsten sheet is a single crystal, and the method further comprises:

[0022] providing a first tungsten sheet;

[0023] performing heat treatment on the first tungsten sheet to obtain a tungsten sheet with ordered grain arrangement.

[0024] As a further improvement of the present application, the heat treatment on the first tungsten sheet comprises:

[0025] placing the first tungsten sheet in a heating furnace under the conditions of temperature 2200-2300℃, nitrogen atmosphere and pressure 500-900mbar for heat treatment for 0.5-6 hours to obtain the tungsten sheet with ordered grain arrangement.

[0026] As a further improvement of the present application, the heat treatment on the first tungsten sheet further comprises:

[0027] performing pretreatment on the first tungsten sheet to obtain a pretreated first tungsten sheet, wherein the roughness of the pretreated first tungsten sheet is less than that of the first tungsten sheet.

[0028] As a further improvement of the present application, the pretreatment on the first tungsten sheet comprises:

[0029] grinding and polishing the first tungsten sheet to obtain a second tungsten sheet, wherein the roughness of the second tungsten sheet is less than that of the first tungsten sheet;

[0030] immersing the second tungsten sheet in a hydrochloric acid solution and immersing for 10-60 minutes under boiling state of the hydrochloric acid solution to obtain a third tungsten sheet;

[0031] cooling the third tungsten sheet and performing rinsing and blow-drying to obtain the pretreated first tungsten sheet.

[0032] As a further improvement of the present application, the purity of the gas-permeable growth adjusting member is ≥99.9%;

[0033] and / or, the purity of the tungsten ring is ≥99.9%;

[0034] and / or, the gas-permeable growth adjusting member is a tungsten foil, and the density of the tungsten foil is in the range of 10-19.35g / cm 3 ; or, the gas-permeable growth adjusting member is a porous tungsten sheet, the porous tungsten sheet has uniformly distributed holes, the thickness of the porous tungsten sheet is 0.1mm-5mm, the ratio of the total area of all the holes to the area of the porous tungsten sheet is 1%-10%, and the diameter of the holes is less than 0.1mm;

[0035] and / or, the thickness of the tungsten ring is in the range of 0.5-2mm.

[0036] In a second aspect, the present application also provides a sheet-shaped aluminum nitride seed crystal, comprising: the sheet-shaped aluminum nitride seed crystal is prepared by the growth method of the sheet-shaped aluminum nitride seed crystal according to any one of the first aspect.

[0037] Compared with the prior art, the beneficial effects of the present application are: in the process of heating the tungsten crucible, the lower surface temperature of the tungsten crucible is controlled to be higher than the upper surface temperature of the tungsten crucible, the gaseous substances generated by sublimation of the aluminum nitride raw material pass through the gas permeable growth adjusting member into the growth gap between the gas permeable growth adjusting member and the tungsten sheet under the action of the temperature difference, the gaseous substances uniformly diffuse in the horizontal direction in the growth gap to uniformly cover the crystal growth surface of the tungsten sheet; the diffusion range of the gaseous substances in the vertical direction can be inhibited through the growth gap, so as to ensure that the gaseous substances preferentially deposit on the crystal growth surface of the tungsten sheet in the horizontal direction and slowly expand, and the thickness increase in the vertical direction is inhibited, and finally a large-size sheet-shaped aluminum nitride seed crystal with controllable thickness is formed. Compared with the prior art, the growth method of the sheet-shaped aluminum nitride seed crystal disclosed in the present application realizes the uniform deposition of the gaseous substances on the crystal growth surface of the tungsten sheet in the horizontal direction, and forms a sheet-shaped aluminum nitride seed crystal with controllable thickness; at the same time, the tungsten sheet is isolated from the aluminum nitride raw material by the gas permeable growth adjusting member, so as to reduce the possibility of impurities migrating to the crystal growth surface of the tungsten sheet with the gaseous substances, improve the purity of the sheet-shaped aluminum nitride seed crystal, and help to improve the quality of the sheet-shaped aluminum nitride seed crystal. BRIEF DESCRIPTION OF DRAWINGS

[0038] Figure 1 Flow chart of the growth method of the sheet-shaped aluminum nitride seed crystal disclosed in the present application;

[0039] Figure 2 Cross-sectional view of the connection of the gas permeable growth adjusting member, the tungsten ring, the tungsten sheet and the tungsten crucible. DETAILED DESCRIPTION

[0040] The present application will be described in detail below in conjunction with the embodiments shown in the drawings, but it should be noted that these embodiments are not a limitation on the present application, and equivalent transformations or substitutions of function, method or structure made by those skilled in the art according to these embodiments are all within the protection scope of the present application.

[0041] The drawings in the present application are not strictly drawn according to the actual proportions, and the specific dimensions of each structure can be determined according to actual needs. The drawings described in the present application are only structural schematic diagrams. The lines shown in the drawings of the present application can be understood as members with a certain actual thickness.

[0042] Please refer to Figure 1 Compared with the prior art, the beneficial effects of the present application are: in the process of heating the tungsten crucible, the lower surface temperature of the tungsten crucible is controlled to be higher than the upper surface temperature of the tungsten crucible, the gaseous substances generated by sublimation of the aluminum nitride raw material pass through the gas permeable growth adjusting member into the growth gap between the gas permeable growth adjusting member and the tungsten sheet under the action of the temperature difference, the gaseous substances uniformly diffuse in the horizontal direction in the growth gap to uniformly cover the crystal growth surface of the tungsten sheet; the diffusion range of the gaseous substances in the vertical direction can be inhibited through the growth gap, so as to ensure that the gaseous substances preferentially deposit on the crystal growth surface of the tungsten sheet in the horizontal direction and slowly expand, and the thickness increase in the vertical direction is inhibited, and finally a large-size sheet-shaped aluminum nitride seed crystal with controllable thickness is formed. Compared with the prior art, the growth method of the sheet-shaped aluminum nitride seed crystal disclosed in the present application realizes the uniform deposition of the gaseous substances on the crystal growth surface of the tungsten sheet in the horizontal direction, and forms a sheet-shaped aluminum nitride seed crystal with controllable thickness; at the same time, the tungsten sheet is isolated from the aluminum nitride raw material by the gas permeable growth adjusting member, so as to reduce the possibility of impurities migrating to the crystal growth surface of the tungsten sheet with the gaseous substances, improve the purity of the sheet-shaped aluminum nitride seed crystal, and help to improve the quality of the sheet-shaped aluminum nitride seed crystal. Figure 2 , Figure 1 Flow chart of the growth method of the sheet-shaped aluminum nitride seed crystal disclosed in the present application, Figure 2This is a cross-sectional view showing the connection between the gas-permeable growth regulator, tungsten ring, tungsten sheet, and tungsten crucible. The growth method for this sheet-like aluminum nitride seed crystal includes:

[0043] S1. Place aluminum nitride raw material 50 into the bottom of tungsten crucible 40.

[0044] S2. Place the permeable growth regulator 20, tungsten ring 30, and tungsten sheet 10 sequentially above the tungsten crucible 40; wherein, a growth gap 60 is formed between the permeable growth regulator 20 and the tungsten sheet 10, and the tungsten sheet 10 and the aluminum nitride raw material 50 are spatially isolated by the permeable growth regulator 20.

[0045] The growth gap 60 is used to accommodate the sheet-like aluminum nitride seed crystal; through the gas-permeable growth regulator 20, while ensuring the passage of gaseous substances generated by the sublimation of aluminum nitride raw material 50, the tungsten sheet 10 is isolated from the aluminum nitride raw material 50 to prevent the aluminum nitride raw material 50 from affecting it.

[0046] S3. The tungsten crucible 40 is heated; wherein the temperature of the lower surface of the tungsten crucible 40 is higher than the temperature of the upper surface of the tungsten crucible 40, and the gaseous material generated by the sublimation of aluminum nitride raw material 50 diffuses to the crystal growth surface 11 of the tungsten sheet 10 through the gas permeable growth regulating device and grows crystals in the horizontal direction on the crystal growth surface 11 to obtain sheet-shaped aluminum nitride seed crystals.

[0047] S4. Remove the sheet-like aluminum nitride seed crystal from the tungsten sheet 10.

[0048] The method for growing sheet-like aluminum nitride seed crystals disclosed in this invention involves controlling the temperature of the lower surface of the tungsten crucible 40 to be higher than the temperature of its upper surface during the heating process. This allows the gaseous substances (i.e., Al vapor and N2 gas) generated by the sublimation of the aluminum nitride raw material 50 to pass through the permeable growth regulating member 20 and enter the growth gap 60 between the permeable growth regulating member 20 and the tungsten sheet 10 under the influence of the temperature difference. The gaseous substances move horizontally (i.e., ...) within the growth gap 60. Figure 2 The gaseous material diffuses uniformly along the X-axis to evenly cover the long crystal facet 11 of the tungsten sheet 10. The growth gap 60 suppresses the vertical diffusion range of the gaseous material, ensuring that it preferentially deposits and slowly expands along the horizontal direction on the long crystal facet 11 of the tungsten sheet 10, while suppressing vertical thickness increases, ultimately forming a sheet-like aluminum nitride seed crystal with controllable thickness. Simultaneously, the permeable growth regulator 20 isolates the tungsten sheet 10 from the aluminum nitride raw material 50, reducing the possibility of impurities migrating to the long crystal facet 11 of the tungsten sheet 10 with the gaseous material, thus improving the purity of the sheet-like aluminum nitride seed crystal.

[0049] Compared with the prior art, the growth method of the sheet-shaped aluminum nitride seed crystal disclosed in the application realizes uniform deposition of gas-phase substances on the crystal growth surface 11 of the tungsten sheet 10 in the horizontal direction, and due to the low growth speed, the crystal gradually expands in diameter after single-point nucleation on the tungsten sheet 10 (or the crystal expands in diameter and converges after nucleation at a limited number of points on the tungsten sheet 10), finally forming a large-size sheet-shaped aluminum nitride seed crystal with controllable thickness and high quality.

[0050] In an embodiment, the diameter of the sheet-shaped aluminum nitride seed crystal is in the range of 10 mm to 100 mm, for example, 10 mm, 20 mm, 30 mm, 40 mm, 50 mm, 60 mm, 70 mm, 80 mm, 90 mm, or 100 mm.

[0051] In an embodiment, the temperature of the tungsten crucible 40 changes in the vertical direction, for example, the temperature of the tungsten crucible 40 gradually decreases in the upward vertical direction (i.e., from the aluminum nitride raw material to the tungsten sheet).

[0052] The growth method of the sheet-shaped aluminum nitride seed crystal disclosed in the application further comprises the following steps before placing the tungsten sheet 10 above the tungsten crucible 40:

[0053] (1) providing a first tungsten sheet.

[0054] (2) pretreating the first tungsten sheet to obtain a pretreated first tungsten sheet.

[0055] The surface roughness of the pretreated first tungsten sheet is less than that of the first tungsten sheet.

[0056] (3) heat-treating the pretreated first tungsten sheet to obtain a tungsten sheet with large grain size and ordered arrangement.

[0057] The growth method of the sheet-shaped aluminum nitride seed crystal disclosed in the application reduces the surface roughness of the first tungsten sheet by pretreating the first tungsten sheet, thereby providing a high-flatness crystal growth surface for subsequent growth of aluminum nitride crystals. The tungsten sheet 10 obtained by heat-treating the pretreated first tungsten sheet has large grain size (a few millimeters to one centimeter) and ordered arrangement, and the high matching degree between the lattice orientation of the single-crystal tungsten grain and the C face of aluminum nitride provides a more matched crystal growth surface for the growth of aluminum nitride crystals, promotes the C face directional growth of aluminum nitride, forms a single-crystal layer with high orientation consistency and suppresses polycrystal nucleation (i.e., the grown sheet-shaped aluminum nitride seed crystal is a single crystal), and finally obtains a high-quality, large-size sheet-shaped aluminum nitride seed crystal that can be used as an aluminum nitride seed crystal for subsequent growth of aluminum nitride single crystals, solves the limitation of the scarcity of aluminum nitride single crystal sheets on the market, realizes self-sufficient preparation of aluminum nitride seed crystals, and avoids the problems of small size and uncontrollable orientation caused by cutting seed crystals from polycrystalline aluminum nitride ingots.

[0058] In some examples, the grain size of the tungsten sheet 10 after the heat treatment is increased, for example, the average grain size of the tungsten sheet 10 can be 2.0 mm.

[0059] In the present application, the aluminum nitride raw material 50 is made of high-purity aluminum nitride, and the purity of the aluminum nitride raw material 50 is ≥99.9%. The aluminum nitride raw material 50 can be in the form of powder, granules or aggregates. In some examples, the aluminum nitride raw material 50 is in the form of powder and is placed at the bottom of the tungsten crucible 40.

[0060] In the present application, the first tungsten sheet is made of high-purity material, and the purity of the first tungsten sheet is ≥99.9%. In some examples, the purity of the first tungsten sheet can be 99.9%, 99.91%, 99.92% or 99.93%. The thickness of the first tungsten sheet can be 1 mm, 2 mm, 3 mm, 4 mm or 5 mm.

[0061] In some examples, the first tungsten sheet is pretreated, including:

[0062] Step S11, grinding and polishing the first tungsten sheet to obtain a second tungsten sheet.

[0063] The surface roughness of the second tungsten sheet is smaller than that of the first tungsten sheet.

[0064] Further, the surface of the first tungsten sheet can be ground by mechanical grinding and other processes to remove uneven areas on the surface of the first tungsten sheet, and the surface of the first tungsten sheet can be further polished to obtain a second tungsten sheet with low surface roughness.

[0065] Step S12, soaking the second tungsten sheet in a hydrochloric acid solution and soaking for 10-60 minutes under boiling hydrochloric acid solution to obtain a third tungsten sheet.

[0066] The soaking time of the second tungsten sheet in the boiling hydrochloric acid solution can be 10 minutes, 20 minutes, 30 minutes, 40 minutes, 50 minutes or 60 minutes.

[0067] By soaking the second tungsten sheet in the hydrochloric acid solution, impurity elements and particles embedded in the surface and shallow layer of the second tungsten sheet can be removed.

[0068] Step S13, cooling the third tungsten sheet and rinsing and blowing dry to obtain the pretreated first tungsten sheet.

[0069] In some examples, the second tungsten sheet is soaked in the boiling hydrochloric acid solution for 15 minutes to remove the surface of the second tungsten sheet and the impurity elements and particles embedded in the shallow layer of the second tungsten sheet. After cooling the third tungsten sheet, it is rinsed with deionized water to remove residual hydrochloric acid solution, and then blown dry with high-purity nitrogen or high-purity compressed air to obtain the pretreated first tungsten sheet.

[0070] The surface roughness of the first tungsten sheet obtained after the above steps S11, S12 and S13 is less than the surface roughness of the first tungsten sheet before the pretreatment, so that the surface cleanliness of the pretreated first tungsten sheet meets the demand of aluminum nitride single crystal growth, and a long crystal surface with high flatness is provided for subsequent aluminum nitride crystal growth.

[0071] In some examples, the first tungsten sheet is subjected to heat treatment, including: placing the first tungsten sheet in a heating furnace under the condition that the temperature is 2200-2300°C, the atmosphere is nitrogen, and the pressure is 500-900 mbar, and performing heat treatment for 0.5-6 hours, to obtain the tungsten sheet 10 with increased grain size and ordered arrangement.

[0072] Further, the temperature can be 2200°C, 2210°C, 2220°C, 2230°C, 2240°C, 2250°C, 2260°C, 2270°C, 2280°C, 2290°C or 2300°C.

[0073] Further, the pressure can be 500 mba, 600 mba, 700 mba, 800 mba or 900 mba.

[0074] Further, the heat treatment time can be 0.5 hours, 1 hour, 2 hours, 3 hours, 4 hours, 5 hours or 6 hours.

[0075] In some examples, the first tungsten sheet is placed in a heating furnace under the condition that the temperature is 2250°C, the atmosphere is high-purity nitrogen, and the pressure is 600 mbar, and heat treatment is performed for 1 hour, to obtain the tungsten sheet 10 with increased grain size and ordered arrangement.

[0076] After high-temperature heat treatment of the first tungsten sheet, the tungsten sheet has increased grain size and ordered arrangement, the lattice orientation of the single-crystal tungsten grain matches the C face of aluminum nitride with high degree of matching, which can promote the C face directional growth of aluminum nitride and inhibit polycrystal nucleation.

[0077] In some examples, the growth gap 60 between the gas-permeable growth adjustment member 20 and the tungsten sheet 10 is equal to the thickness of the tungsten ring 30. Specifically, the thickness of the tungsten ring 30 is in the range of 0.5-2 mm, for example, the thickness of the tungsten ring 30 can be 0.5 mm, 1 mm, 1.5 mm or 2 mm.

[0078] In some examples, the gas-permeable growth adjustment member 20 is a tungsten foil, and the density of the tungsten foil is in the range of 10-19.35 g / cm 3 Since the density of the tungsten foil is low, it has nanoscale pores, and the gas-phase substances generated by sublimation of the aluminum nitride raw material reach the crystal growth surface of the tungsten sheet through the nanoscale pores. For example, the density of the tungsten foil 20 can be 10 g / cm 3 , 11 g / cm3 , 12 g / cm 3 , 13, g / cm 3 , 14 g / cm 3 , 15 g / cm 3 , 16, g / cm 3 , 17 g / cm 3 , 18 g / cm 3 , 19 g / cm 3 or 19.35 g / cm 3 .

[0079] It should be noted that if the density of the tungsten foil 20 is too low (e.g., less than 10 g / cm 3 ), the tungsten foil 20 can have too many nanoscale pores, the diffusion rate of the gas phase material through the nanoscale pores can be high, and the gas concentration in the growth gap 60 can be too high, which can easily cause polycrystal nucleation and reduce the crystal quality. If the density of the tungsten foil 20 is too high (e.g., greater than 19.35 g / cm 3 ), the tungsten foil 20 can have too few nanoscale pores, the efficiency of the gas phase material transported into the growth gap 60 can be low, the distribution uniformity can be poor, the stable crystal growth environment can be destroyed, and the crystal quality can be affected.

[0080] In some examples, the thickness of the tungsten foil 20 is ≤ 0.1 mm.

[0081] Further, the thickness of the tungsten foil 20 can be 0.01 mm, 0.02 mm, 0.03 mm, 0.04 mm, 0.05 mm, 0.06 mm, 0.07 mm, 0.08 mm, 0.09 mm, or 0.1 mm.

[0082] It should be noted that if the thickness of the tungsten foil 20 is too large (e.g., greater than 0.1 mm), the path length of the gas phase material through the nanoscale pores can be increased, the diffusion rate of the gas phase material can be reduced, the gas concentration in the growth gap 60 can be insufficient, and the crystal growth rate can be too slow or the crystal can not be grown. If the thickness of the tungsten foil 20 is too small, the diffusion path of the gas phase material through the nanoscale pores can be shortened, the diffusion rate of the gas phase material through the nanoscale pores can be increased, and the gas concentration in the growth gap 60 can be too high, which can easily cause polycrystal nucleation and reduce the crystal quality.

[0083] In some examples, the gas permeable growth adjustment member 20 is a porous tungsten sheet having a plurality of uniformly distributed holes (not shown), the thickness of the porous tungsten sheet is 0.1 mm-5 mm, the ratio of the total area of all the holes to the area of the porous tungsten sheet is 1%-10%, and the diameter of the holes is less than 0.1 mm.

[0084] By replacing the porous tungsten sheet with different thickness, and / or adjusting the ratio of the total area of all holes to the area of the porous tungsten sheet, the diffusion rate of the gas phase material can be adjusted, and the deposition rate can be controlled.

[0085] The holes are uniformly distributed in the horizontal direction on the porous tungsten sheet, which can ensure that the gas phase material uniformly covers the entire growth surface 11 of the tungsten sheet 10 when diffusing to the growth gap 60. By controlling the hole diameter to be less than 0.1 mm, the diffusion rate of the gas phase material through the holes can be limited, so that the gas phase material can uniformly diffuse in the growth gap 60, reduce the local concentration of the seed crystal, and make the gas phase material diffuse along the horizontal direction to the growth surface 11 of the tungsten sheet 10, inhibit the vertical thickening, and promote the formation of a sheet-shaped aluminum nitride seed crystal.

[0086] Further, the diameter of the holes can be 0.01 mm, 0.02 mm, 0.03 mm, 0.04 mm, 0.05 mm, 0.06 mm, 0.07 mm, 0.08 mm, or 0.09 mm.

[0087] Further, the thickness of the porous tungsten sheet can be 0.1 mm, 0.5 mm, 1 mm, 2 mm, 3 mm, 4 mm, or 5 mm.

[0088] Further, the ratio of the total area of all holes to the area of the porous tungsten sheet can be 1%, 2%, 3%, 4%, 5%, 6%, 7%, 8%, 9%, or 10%.

[0089] In some examples, the thickness of the tungsten ring 30 is 1 mm, the thickness of the tungsten foil 20 is 0.05 mm, and the growth gap 60 between the tungsten foil 20 and the tungsten sheet 10 is equal to the thickness of the tungsten ring 30, i.e., the growth gap 60 between the tungsten foil 20 and the tungsten sheet 10 is 1 mm.

[0090] The fixed growth gap 60 is formed between the gas-permeable growth adjusting member 20 and the tungsten sheet 10 through the tungsten ring 30, and the gas phase material uniformly diffuses in the growth gap 60 after passing through the nanoscale pores, so as to ensure that the gas phase material is uniformly distributed on the growth surface 11 of the tungsten sheet 10. By setting the thickness of the growth gap 60, the diffusion range of the gas phase material in the vertical direction can be adjusted, so as to ensure that the gas phase material preferentially deposits along the horizontal direction on the growth surface 11 of the tungsten sheet 10 and slowly expands, adjust the thickness of the sheet-shaped aluminum nitride seed crystal in the vertical direction, and finally form a sheet-shaped aluminum nitride seed crystal with high orientation consistency.

[0091] The lower surface temperature of the tungsten crucible 40 is higher than the upper surface temperature of the tungsten crucible 40 to form a vertical temperature gradient. The gaseous phase material generated by sublimation of the aluminum nitride raw material 50 is driven by the temperature gradient to diffuse to the growth surface 11 of the tungsten sheet 10 through the nanoscale pores on the tungsten foil 20 into the growth gap 60 between the tungsten foil 20 and the tungsten sheet 10. The gaseous phase material preferentially diffuses to the growth surface 11 along the temperature gradient direction (i.e., the vertical direction Y-axis), reduces the local concentration of the gaseous phase material in the vertical direction, and promotes the uniform diffusion of the gaseous phase material along the horizontal direction on the growth surface 11, and inhibits the increase in thickness in the vertical direction through the growth gap 60, ultimately forming a sheet-shaped aluminum nitride seed crystal.

[0092] In some examples, the heating of the tungsten crucible 40 includes: placing the tungsten crucible 40 into a heating furnace, and vacuumizing the heating furnace, and introducing high-purity nitrogen into the heating furnace; controlling the upper surface temperature of the tungsten crucible 40 to be between 2250-2280℃, the lower surface temperature of the tungsten crucible 40 to be between 2270-2300℃, and the pressure to be between 700-800mbar, and using the heating furnace to maintain the temperature of the tungsten crucible 40 for 5-50 hours; wherein the lower surface temperature of the tungsten crucible 40 is higher than the upper surface temperature of the tungsten sheet 10.

[0093] Further, the upper surface temperature of the tungsten crucible 40 can be 2250℃, 2260℃, 2270℃, or 2280℃.

[0094] Further, the lower surface temperature of the tungsten crucible 40 can be 2270℃, 2280℃, 2290℃, or 2300℃.

[0095] Further, the pressure can be 700mbar, 720mbar, 740mbar, 760mbar, 780mbar, or 800mbar.

[0096] Further, the time for the heating furnace to maintain the temperature of the tungsten crucible 40 can be 5 hours, 10 hours, 20 hours, 30 hours, 40 hours, or 50 hours.

[0097] In some examples, the lower surface temperature of the tungsten crucible 40 is 2300℃, the upper surface temperature of the tungsten crucible 40 is 2280℃, the upper surface temperature of the tungsten sheet 10 is 2280℃, the pressure is 750mbar, and the heating furnace maintains the temperature of the tungsten crucible 40 for 20 hours.

[0098] By the temperature of the lower surface of the tungsten crucible 40 being higher than the temperature of the upper surface of the tungsten sheet 10, the gas phase material preferentially diffuses to the growth surface 11 of the tungsten sheet 10 along the temperature gradient, the rapid deposition of the gas phase material in the vertical direction is inhibited, and the gas phase material is uniformly diffused along the horizontal direction on the growth surface 11, promoting lateral epitaxial growth. Moreover, the grain size of the tungsten sheet 10 after heat treatment is large and arranged in order, which can promote the C-plane directional growth of aluminum nitride, form a single crystal grain of aluminum nitride with high orientation consistency, and converge into a single crystal.

[0099] In some examples, the growth method of the sheet-shaped aluminum nitride seed crystal further comprises: before the sheet-shaped aluminum nitride seed crystal is peeled off from the tungsten sheet 10, reducing the temperature of the heating furnace at a cooling rate of 50-100°C / hour until the temperature of the heating furnace is reduced to room temperature; and taking out the tungsten crucible 40 from the heating furnace and taking out the tungsten sheet 10 from the tungsten crucible 40.

[0100] Further, the cooling rate can be 50°C / hour, 60°C / hour, 70°C / hour, 80°C / hour, 90°C / hour or 100°C / hour.

[0101] After high-temperature growth, there is a significant difference in the thermal expansion coefficient between the sheet-shaped aluminum nitride seed crystal and the tungsten crucible 40 and the tungsten sheet 10. If the cooling rate is too fast (for example, greater than 100°C / hour), thermal stress concentration can cause cracks in the sheet-shaped aluminum nitride seed crystal or deformation of the tungsten crucible 40. Moreover, during the cooling process, if the temperature gradient is too steep, the residual gas phase material can be deposited again on the surface of the seed crystal, causing polycrystalline nucleation or surface roughness.

[0102] For example, the temperature of the heating furnace is reduced at a cooling rate of 70°C / hour, the thermal expansion difference is uniformly released at a cooling rate of 70°C / hour, stress concentration is avoided, the structural stability of the sheet-shaped aluminum nitride seed crystal during cooling can be ensured, and thermal stress can be avoided to cause cracks and other defects in the sheet-shaped aluminum nitride seed crystal. Moreover, the gas phase concentration field is maintained stable at a cooling rate of 70°C / hour, the fluctuation of supersaturation caused by sudden temperature drop is avoided, the sheet-shaped aluminum nitride seed crystal after cooling is crack-free and has a smooth surface.

[0103] After the heating furnace is cooled to room temperature, all components (sheet-shaped aluminum nitride seed crystal, tungsten sheet 10) in the tungsten crucible 40 are in a state of thermal equilibrium, and mechanical stress caused by temperature difference is avoided.

[0104] Then, a special tool (such as a crucible tongs) is used to take out the tungsten crucible 40, and the sheet-shaped aluminum nitride seed crystal is peeled off from the tungsten sheet 10 by using the thermal expansion difference or physical peeling.

[0105] In order to make the purpose, technical scheme and advantages of the present application more clear, the present application is further described in detail with examples. It should be understood that the specific examples described herein are only used to explain the present application and not to limit the present application.

[0106] Embodiment 1

[0107] Step S1, providing a first tungsten sheet, grinding and polishing the first tungsten sheet to obtain a second tungsten sheet.

[0108] The thickness of the first tungsten sheet is 5mm.

[0109] The surface roughness of the second tungsten sheet is less than that of the first tungsten sheet. The surface of the first tungsten sheet can be ground by mechanical grinding process, etc. to remove the uneven area of the surface of the first tungsten sheet, and further polish the surface of the first tungsten sheet to obtain a second tungsten sheet with low surface roughness.

[0110] Step S2, soaking the second tungsten sheet in a hydrochloric acid solution and soaking for 15 minutes under boiling hydrochloric acid solution to obtain a third tungsten sheet.

[0111] Step S3, after cooling the third tungsten sheet, rinsing with deionized water to remove residual hydrochloric acid solution, and then blowing dry with high-purity nitrogen or high-purity compressed air to obtain a pretreated first tungsten sheet.

[0112] The surface roughness of the pretreated first tungsten sheet is less than that of the first tungsten sheet before pretreatment, and the surface cleanliness meets the demand of aluminum nitride single crystal growth, providing a high flatness growth surface for subsequent aluminum nitride crystal growth.

[0113] Step S4, placing the pretreated first tungsten sheet in a heating furnace for heat treatment at a temperature of 2250℃, an atmosphere of high-purity nitrogen and a pressure of 600mbar for 1 hour to obtain a tungsten sheet with increased grain size and ordered arrangement.

[0114] After high-temperature heat treatment of the pretreated first tungsten sheet, the tungsten sheet has large grain size and uniform arrangement, the lattice orientation of the single crystal tungsten grain has high matching degree with the C face of aluminum nitride, which can promote the C face directional growth of aluminum nitride and inhibit polycrystal nucleation.

[0115] Step S5, placing the aluminum nitride raw material at the bottom of the tungsten crucible.

[0116] Step S6, placing the tungsten foil, tungsten ring and tungsten sheet successively above the tungsten crucible.

[0117] The purity of the tungsten crucible is 99.9%.

[0118] The purity of the aluminum nitride raw material is 99.9%, which is in powder form.

[0119] The purity of the tungsten foil is 99.9%, the thickness of the tungsten foil is 0.05mm, and the density of the tungsten foil is 15g / cm 3 .

[0120] The purity of the tungsten ring is 99.9%, and the thickness of the tungsten ring is 1mm;

[0121] The purity of the tungsten sheet is 99.9%, and the thickness of the tungsten sheet is 5mm.

[0122] The tungsten ring is arranged between the tungsten foil and the tungsten sheet to form a fixed growth gap, and the gas-phase substance diffuses uniformly in the growth gap after passing through the nanoscale pores in the tungsten foil, so as to ensure that the gas-phase substance is uniformly distributed on the crystal growth surface of the tungsten sheet. By setting the thickness of the growth gap, the diffusion range of the gas-phase substance in the vertical direction can be adjusted, so as to ensure that the gas-phase substance is preferentially deposited and slowly expanded along the horizontal direction on the crystal growth surface of the tungsten sheet, and the thickness of the sheet-shaped aluminum nitride seed crystal in the vertical direction is adjusted.

[0123] In step S7, the tungsten crucible is placed in the heating furnace, the heating furnace is vacuumized, high-purity nitrogen gas is introduced into the heating furnace, the lower surface temperature of the tungsten crucible is controlled to be 2300°C, the upper surface temperature of the tungsten crucible is controlled to be 2280°C, the upper surface temperature of the tungsten sheet is controlled to be 2280°C, and the pressure is 750mbar. The tungsten crucible is heated for 20 hours by using the heating furnace.

[0124] The lower surface temperature of the tungsten crucible is higher than the upper surface temperature of the tungsten crucible, the gas-phase substance generated by sublimation of the aluminum nitride raw material passes through the nanoscale pores in the tungsten foil to reach the crystal growth surface of the tungsten sheet, and the crystal growth along the horizontal direction on the crystal growth surface obtains the sheet-shaped aluminum nitride seed crystal.

[0125] During the heating process of the tungsten crucible, the lower surface temperature of the tungsten crucible is controlled to be higher than the upper surface temperature of the tungsten sheet to form a temperature gradient in the vertical direction. The gas-phase substance generated by sublimation of the aluminum nitride raw material enters the growth gap between the tungsten foil and the tungsten sheet through the nanoscale pores on the tungsten foil under the driving of the temperature gradient. The gas-phase substance uniformly diffuses along the horizontal direction in the growth gap to uniformly cover the crystal growth surface of the tungsten sheet. The diffusion range of the gas-phase substance in the vertical direction is inhibited by the growth gap, so as to ensure that the gas-phase substance is preferentially deposited and slowly expanded along the horizontal direction on the crystal growth surface of the tungsten sheet, and the thickness in the vertical direction is inhibited from increasing, and finally the sheet-shaped aluminum nitride seed crystal is formed.

[0126] In step S8, the temperature of the heating furnace is reduced at a cooling rate of 70°C / hour until the temperature of the heating furnace is reduced to room temperature.

[0127] In step S9, the tungsten crucible is taken out from the heating furnace, the tungsten sheet is taken out from the tungsten crucible, and then the sheet-shaped aluminum nitride seed crystal is peeled off from the tungsten sheet.

[0128] In summary, the sheet-shaped aluminum nitride seed crystal with high quality and large size can be prepared by using the growth method of the sheet-shaped aluminum nitride seed crystal.

[0129] In another aspect, based on the detailed description of the growth method of the sheet-shaped aluminum nitride seed crystal disclosed in the foregoing embodiments, the present application also discloses a sheet-shaped aluminum nitride seed crystal, which is prepared by the growth method of the sheet-shaped aluminum nitride seed crystal in the foregoing embodiments.

[0130] The growth method of the sheet-shaped aluminum nitride seed crystal disclosed in the present embodiment is described above, and will not be repeated here. The sheet-shaped aluminum nitride seed crystal has high quality and large size.

[0131] The above series of detailed descriptions are only specific descriptions of the feasible embodiments of the present application, and are not intended to limit the protection scope of the present application. Any equivalent embodiments or changes made without departing from the spirit of the present application should be included in the protection scope of the present application.

[0132] It is obvious for those skilled in the art that the present application is not limited to the details of the above exemplary embodiments, and can be implemented in other specific forms without departing from the spirit or essential characteristics of the present application. Therefore, the embodiments should be regarded as exemplary and non-limiting, and the scope of the present application is defined by the appended claims rather than the above description, and all changes falling within the meaning and scope of the equivalent elements of the claims should be included in the present application. Any reference signs in the claims should not be regarded as limiting the claims involved.

[0133] In addition, it should be understood that although the present specification is described in terms of embodiments, not every embodiment contains only one independent technical solution, and the description manner of the specification is only for the sake of clarity, and those skilled in the art should regard the specification as a whole, and the technical solutions in each embodiment can also be properly combined to form other embodiments that can be understood by those skilled in the art.

Claims

1. A method for growing a sheet-shaped aluminum nitride seed crystal, characterized by, The method comprises the following steps: putting aluminum nitride raw material into the bottom of a tungsten crucible; placing a gas-permeable growth adjustment piece, a tungsten ring and a tungsten sheet successively above the tungsten crucible; wherein a growth gap is formed between the gas-permeable growth adjustment piece and the tungsten sheet, and the tungsten sheet and the aluminum nitride raw material are spatially isolated by the gas-permeable growth adjustment piece; heating the tungsten crucible; wherein the lower surface temperature of the tungsten crucible is higher than the upper surface temperature of the tungsten crucible, and the gaseous substances generated by sublimation of the aluminum nitride raw material diffuse to the crystal growth surface of the tungsten sheet through the gas-permeable growth adjustment piece and grow in the horizontal direction on the crystal growth surface to obtain a sheet-shaped aluminum nitride seed crystal; peeling the sheet-shaped aluminum nitride seed crystal from the tungsten sheet.

2. The method for growing a sheet-shaped aluminum nitride seed crystal according to claim 1, wherein The growth gap between the gas-permeable growth adjustment piece and the tungsten sheet is equal to the thickness of the tungsten ring; And / or, the temperature of the tungsten crucible changes in a gradient along the vertical direction.

3. The method for growing a sheet-shaped aluminum nitride seed crystal according to claim 1, wherein The heating of the tungsten crucible comprises: placing the tungsten crucible into a heating furnace, vacuumizing the heating furnace, and introducing high-purity nitrogen into the heating furnace; controlling the upper surface temperature of the tungsten crucible to be between 2250-2280℃, the lower surface temperature of the tungsten crucible to be between 2270-2300℃, and the pressure to be between 700-800mbar, and using the heating furnace to keep the temperature of the tungsten crucible constant for 5-50 hours; wherein the lower surface temperature of the tungsten crucible is higher than the upper surface temperature of the tungsten sheet.

4. The method for growing a sheet-shaped aluminum nitride seed crystal according to claim 1, wherein The method for growing the sheet-shaped aluminum nitride seed crystal further comprises: before peeling the sheet-shaped aluminum nitride seed crystal from the tungsten sheet, reducing the temperature of the heating furnace at a cooling rate of 50-100℃ / hour until the temperature of the heating furnace is reduced to room temperature; taking the tungsten sheet out of the tungsten crucible.

5. The method for growing sheet-shaped aluminum nitride seed crystals according to claim 1, characterized by, The sheet-shaped aluminum nitride seed crystal deposited on the crystal growth surface of the tungsten sheet is a single crystal, and the method further comprises: providing a first tungsten sheet; heat-treating the first tungsten sheet to obtain a tungsten sheet with ordered grain arrangement.

6. The method for growing a sheet-shaped aluminum nitride seed crystal according to claim 5, wherein The heat-treating of the first tungsten sheet comprises: placing the first tungsten sheet in a heating furnace under the conditions of a temperature of 2200-2300℃, a nitrogen atmosphere, and a pressure of 500-900mbar for heat treatment for 0.5-6 hours to obtain the tungsten sheet with ordered grain arrangement.

7. The method for growing a sheet-shaped aluminum nitride seed crystal according to claim 5, wherein Before the heat-treating of the first tungsten sheet, the method further comprises: pre-treating the first tungsten sheet to obtain a pre-treated first tungsten sheet, wherein the surface roughness of the pre-treated first tungsten sheet is less than that of the first tungsten sheet.

8. The method for growing a sheet-shaped aluminum nitride seed crystal according to claim 7, wherein The pre-treating of the first tungsten sheet comprises: grinding and polishing the first tungsten sheet to obtain a second tungsten sheet, wherein the surface roughness of the second tungsten sheet is less than that of the first tungsten sheet; immersing the second tungsten sheet in a hydrochloric acid solution and immersing it in the boiling hydrochloric acid solution for 10-60 minutes to obtain a third tungsten sheet; cooling the third tungsten sheet and rinsing and blowing dry it to obtain the pre-treated first tungsten sheet.

9. The method of claim 1-8, wherein, The purity of the gas-permeable growth adjustment piece is ≥99.9%; And / or, the purity of the tungsten ring is ≥99.9%. And / or, the air-permeable growth adjustment member is tungsten foil, the density of the tungsten foil is in the range of 10-19.35 g / cm 3 Or, the air-permeable growth adjustment member is porous tungsten sheet, the porous tungsten sheet has uniformly distributed holes, the thickness of the porous tungsten sheet is 0.1 mm-5 mm, the ratio of the total area of all the holes to the area of the porous tungsten sheet is 1%-10%, and the diameter of the holes is less than 0.1 mm. And / or, the thickness of the tungsten ring is in the range of 0.5-2 mm.

10. A sheet-shaped aluminum nitride seed crystal, characterized by, The flaky aluminum nitride seed crystal is prepared by the growth method of the flaky aluminum nitride seed crystal according to any one of claims 1-9.

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