CN113622018A

CN113622018A - Method for growing aluminum nitride single crystal by physical vapor transport method

Info

Publication number: CN113622018A
Application number: CN202110906303.XA
Authority: CN
Inventors: 吴亮; 赵寅廷; 王琦琨; 雷丹; 李哲; 黄嘉丽; 张刚
Original assignee: Aoti Photoelectric Technology Hangzhou Co ltd
Current assignee: Aoti Photoelectric Technology Hangzhou Co ltd
Priority date: 2021-08-09
Filing date: 2021-08-09
Publication date: 2021-11-09
Anticipated expiration: 2041-08-09
Also published as: CN113622018B

Abstract

The invention discloses a method for growing aluminum nitride single crystal by a physical vapor transport method, which comprises the following steps: s1, fixing the aluminum nitride raw material on the periphery of the inner wall of the crucible; s2, fixing seed crystals in the middle of the crystal growth cavity in the crucible; and S3, placing the crucible into a high-temperature furnace, introducing high-purity nitrogen, heating to a preset temperature, adjusting to a small temperature gradient formed around the seed crystal to grow the aluminum nitride single crystal, and keeping the temperature for a period of time. Under the action of the temperature gradient, the surrounding gas phase substances are conveyed towards the seed crystal, and low supersaturation degree of Al pressure is formed around the seed crystal, so that high-speed growth of the seed crystal in a high-quality laminar flow growth mode is formed. The physical vapor transport method for preparing the aluminum nitride single crystal changes the arrangement mode of raw materials and seed crystals and the distribution of a thermal field in the traditional physical vapor transport method at present, forms a good laminar flow crystal growth environment around the seed crystals, and finally obtains the high-quality crystallized AlN single crystal.

Description

Method for growing aluminum nitride single crystal by physical vapor transport method

Technical Field

The invention relates to the technical field of semiconductor material preparation, in particular to a method for preparing crystals by a physical vapor transport method.

Background

Aluminum nitride (AlN) as a third-generation wide bandgap semiconductor material has excellent performances such as high bandgap width (6.2 eV), high thermal conductivity (340W/(m ∙ K)), high breakdown field strength (11.7 MV/cm), good ultraviolet transmittance, chemical and thermal stability and the like, and can be widely applied to manufacturing devices such as laser diodes, light receivers, ultra-high integrated circuits, microwave devices, lasers, photoelectricity, radiation resistance, high temperature resistance and the like. Although devices based on aluminum nitride single crystals have a wide application prospect, the preparation of single crystals has great difficulty and challenge, and high quality and mass production are difficult to realize.

At present, physical vapor transport has proven to be the most rational and promising method for growing large-size, high-quality bulk AlN single crystals. However, in the current physical vapor transport method, a large amount of dislocations are formed and spread in an AlN interface and a crystal in the growth process of a semiconductor, so that the quality and the performance of the crystal and a device are reduced; meanwhile, the mechanical properties and mechanical characteristics of AlN crystals are affected by dislocation behavior and ideal properties cannot be obtained.

The aluminum nitride single crystal is grown by using a physical vapor transport method, wherein the thermal environment and the atmosphere for growing the aluminum nitride crystal are crucial, and the growth mode of the crystal is directly determined, and the crystal appearance and the growth quality are influenced. For example, the conventional physical vapor transport method tends to cause large crystal surface saturation due to excessive temperature gradient and low pressure at the periphery of the crystal growth surface, resulting in deviation of multiple growth centers and crystal growth orientation, and causing crystal quality reduction. The proper temperature field distribution needs the implementation and optimization of an accurate analog simulation technology, and a high-quality thermal field structure can be designed to create a proper crystal growth environment. Low supersaturation is advantageous for growing high quality single crystals, but tends to result in low growth rates and production efficiencies. Therefore, there is an urgent need to develop a superior structural design and thermal field, to grow crystals with high quality and to realize high-speed growth or production under the condition of low supersaturation.

Disclosure of Invention

Based on the problems in the prior art, the invention provides a method for growing aluminum nitride single crystals by a physical vapor transport method, which aims to realize excellent structural design and thermal field, grow high-quality aluminum nitride single crystals under the condition of low supersaturation degree and realize high-speed crystal growth.

In order to achieve the above purpose, the invention adopts the following technical scheme.

A method for growing aluminum nitride single crystal by physical vapor transport method comprises the following steps.

S1: fixing high-purity aluminum nitride raw materials around the inner wall of the crucible.

The crucible is of a closed structure, for example, in an embodiment of the present invention, the crucible is composed of a crucible body with an upward opening and a crucible cover, and when the crucible cover is fastened to the crucible body, a closed reaction chamber, i.e., a crystal growth chamber, is formed in the crucible. Thus, in this embodiment, the inner wall of the crucible includes the bottom and side walls in the crucible body and the surface of the crucible cover facing the inside of the crucible body, and the aluminum nitride material is fixed around the inner wall of the crucible, which means that the bottom, side walls and the surface of the crucible cover facing the inside of the crucible body fix the aluminum nitride material in the crucible body.

Wherein, the aluminum nitride raw material can be powder, sintered ceramic material, crystallized porous material or crystal block material; the aluminum nitride raw material can be fixed on the inner wall of the crucible in one or more of a laying mode, a thermal bonding mode, a chemical bonding mode, a vapor deposition mode and a mechanical fixing mode.

Wherein the crucible can be prepared from one or more high-temperature resistant materials such as tantalum, tungsten, tantalum carbide, tungsten carbide, graphite, boron nitride and the like; for example, the tungsten crucible body and the tungsten crucible cover are adopted in the embodiment of the invention.

S2, fixing the aluminum nitride seed crystal in the middle of the reaction cavity in the crucible. The seed crystal fixing mode can be a hanging mode, a laying mode, a thermal bonding mode, a chemical bonding mode and a mechanical fixing mode; such as the mechanical fastening used in one embodiment of the present invention.

S3, placing the crucible assembled with the aluminum nitride raw material and the aluminum nitride seed crystal into a high-temperature furnace, introducing high-purity nitrogen into the high-temperature furnace, heating until the temperature in the crucible reaches a preset temperature, adjusting the temperature until a small temperature gradient is formed around the seed crystal for crystal growth, and preserving the temperature for a period of time; the temperature gradient of the small temperature gradient fingers formed around the seed crystal in the axial direction and the radial direction is less than or equal to 10K/cm.

The arrangement of the aluminum nitride raw material and the seed crystal in the crucible is matched, a small temperature gradient crystal growth environment is formed around the seed crystal, and the high-temperature furnace adopts three resistance type heating, namely an upper heater, a lower heater and a side heater which are distributed around the crucible, namely three groups of heaters. More specifically, the process execution process comprises the steps of firstly introducing high-purity nitrogen serving as protective gas into a furnace, and keeping the pressure constant, wherein the preferred range of the pressure constant is 30-150 kPa; and simultaneously raising the temperature to a preset temperature, wherein the preset temperature is preferably in the range of 2100-2350 ℃. Three high-temperature regions of the upper part, the lower part and the side part in the crucible are formed by adjusting the power output of the three groups of heaters, the temperature gradient faces to the seed crystal positioned in the middle of the reaction cavity, the surrounding raw materials are sublimated at high temperature, and the surrounding gas-phase substances are transmitted to the seed crystal under the action of the temperature gradient; meanwhile, higher Al pressure is formed around the seed crystal, sufficient substances are provided for growing the crystal at high speed, and the growth rate of the crystal is adjustable within 0.2-0.5 mm/h. Meanwhile, under the temperature field design, a low temperature gradient and low supersaturation crystal growth environment around the seed crystal is created, a high-quality laminar growth mode of the seed crystal is formed, and finally the high-quality crystallized AlN single crystal is obtained; in the embodiment of the invention, the temperature gradient around the seed crystal is as low as 0.5-2K/cm, and the supersaturation degree is as low as 2 x 10^-4。

S4, after the growth of the aluminum nitride single crystal is finished, cooling to room temperature, opening the crucible, and taking out the grown aluminum nitride single crystal ingot.

The physical vapor transport method for preparing the aluminum nitride single crystal changes the arrangement mode of raw materials and seed crystals and the distribution of a thermal field in the traditional physical vapor transport method at present, and forms a good laminar flow crystal growth environment around the seed crystals. At present, in the traditional physical vapor transport method AlN single crystal growing technology, seed crystals and raw materials are usually respectively arranged at the top end and the bottom two sides of a growth chamber, in the process, the material source is single, and the sublimed AlN gas source is insufficient; and because of single thermal field distribution, the temperature gradient between the growth surface of the seed crystal and the AlN raw material is large; and the low pressure around the crystal growth surface easily causes larger crystal surface saturation, leads to a plurality of growth centers and crystal growth orientations, reduces the quality of the grown crystal, and finally forms a crystal ingot with poorer quality. According to the invention, high-purity AlN crystallized raw materials are arranged on the periphery of the inner wall of the crucible, the seed crystal is fixed in the middle of the reaction cavity of the crucible, the raw materials on the periphery are sublimated under the driving of high temperature outside a designed thermal field, and gas phase substances are transmitted to the seed crystal in the middle, so that sufficient substance concentration is provided for crystal growth, and the crystal growth rate is improved. Meanwhile, by designing the lower temperature gradient around the seed crystal in the axial direction and the radial direction, a low supersaturation crystal growth environment is created, thereby being beneficial to growing high-quality aluminum nitride single crystal. By the technical means of the invention, the crystal growth rate is adjustable at 0.2-0.5mm/h, AlN single crystal ingots with high crystallization quality are prepared, the half height width of a high-resolution X-ray diffraction rocking curve 002 of the sliced aluminum nitride substrate slice is less than 80 arcsec, and the half height width 102 of the sliced aluminum nitride substrate slice is less than 100 arcsec, which indicates that the crystal quality is high. Compared with the traditional physical vapor transport crystal growth method, the technical scheme of the invention has more excellent crystal growth quality and high-speed crystal growth capacity.

Drawings

In order to more clearly illustrate the embodiments of the present invention or the technical solutions in the prior art, the drawings needed to be used in the description of the embodiments or the prior art are briefly introduced below, it is obvious that the drawings in the following description are only some embodiments described in the present invention, and for those skilled in the art, other drawings can be obtained according to the drawings without creative efforts.

FIGS. 1-3 are schematic diagrams illustrating the distribution of aluminum nitride raw material and the fixation of aluminum nitride seed crystal in the crucible according to the embodiment of the present invention.

Wherein:

FIG. 1 is a schematic view of an aluminum nitride seed crystal employing side attachment.

FIG. 2 is a schematic view of an aluminum nitride seed crystal employing bottom fixation.

FIG. 3 is a schematic representation of an aluminum nitride seed crystal employing top attachment.

Wherein in fig. 1-3: 1 is a crucible cover, 2 is a tungsten fixing bar, 3 is an aluminum nitride seed crystal, 4 is a crystal growth cavity, 5 is a crucible body, and 6 is an aluminum nitride raw material.

FIG. 4 is a temperature field distribution pattern in the crucible in example 1 of the present invention.

FIG. 5 is a graph showing the distribution of the aluminum gas pressure around the seed crystal in example 1 of the present invention.

FIG. 6 is a graph showing the temperature gradient around the seed crystal in example 1 of the present invention.

FIG. 7 is a distribution diagram of the saturation around the seed crystal in example 1 of the present invention.

FIG. 8 is a physical diagram of an aluminum nitride single crystal ingot produced in example 1 of the present invention.

FIG. 9 is a graph showing a rocking curve of a high-resolution X-ray 002 diffraction plane and a full width at half maximum value thereof of a sliced sheet of an aluminum nitride single crystal ingot produced in example 1 of the present invention.

FIG. 10 is a graph showing a rocking curve of a diffraction plane of a high resolution X-ray 102 and a full width at half maximum value thereof of a sliced crystal of a single crystal ingot of aluminum nitride obtained in example 1 of the present invention.

Detailed Description

The invention will be described in detail with reference to the accompanying drawings and specific embodiments. These embodiments are not intended to limit the present invention, and structural, methodological, or functional changes made by those skilled in the art according to these embodiments are included in the scope of the present invention.

Further, reference numerals or designations may be used in the various embodiments. These iterations are merely for simplicity and clarity of describing the present invention, and are not intended to represent any correlation between the various embodiments and/or structures discussed.

Example 1:

in this example, a high quality aluminum nitride single crystal was grown by the physical vapor transport method of the present invention, as follows.

Step 1: fixing high-purity aluminum nitride raw materials around the inner wall of the crucible.

As shown in FIGS. 1-3, the aluminum nitride raw material is fixed on the inner wall of the crucible and fixed with the seed crystal. As shown in the figure, the crucible in this embodiment is composed of a crucible body and a crucible cover, forming a closed chamber, wherein the crucible is made of high temperature resistant tungsten, the crucible is made of materials which are not limited to tungsten, and other high temperature resistant materials such as tantalum, tantalum carbide, tungsten carbide, graphite, boron nitride and the like can be used for achieving the purpose of the invention. The AlN raw material of this example includes a crystallized crushed AlN material and a polycrystalline aluminum nitride ingot. Wherein the high-purity AlN crystallized crushed aggregates are filled to the bottom of the crucible body and the side wall of the crucible body; and depositing on one surface of the crucible cover facing the growth cavity by a vapor phase method to obtain a polycrystalline aluminum nitride crystal block. And finally, enclosing the raw materials arranged around the inner wall of the crucible to form a natural cavity, namely a crystal growth cavity.

Step 2: and fixing the aluminum nitride seed crystal in the middle of the crystal growth cavity.

In this embodiment, the method of mechanically fixing the seed crystal is adopted, and three fixing modes can be adopted, as shown in fig. 1-3. The first fixing mode is shown in figure 1, the lateral part of the seed crystal is fixed, three metal tungsten rods are used as tungsten fixing bars and are positioned on a horizontal plane, and the included angle between every two metal tungsten rods is about 120^oOne end of the seed crystal is fixed on the side part of the seed crystal, and the other end of the seed crystal is fixed in the raw material on the side wall of the crucible body, so that the seed crystal is suspended in the middle of the crystal growth cavity. As shown in figure 2, the bottom of the seed crystal is fixed, one end of the tungsten fixing rod is connected with the bottom of the seed crystal, and the other end of the tungsten fixing rod is connected with the bottom of the crucible body. As shown in figure 3, the top of the seed crystal is fixed, one end of the seed crystal is connected with the top of the seed crystal, and the other end of the seed crystal is connected with the crucible cover. The three fixing modes aim at the growth of different crystal faces, the fixing mode in figure 1 is mainly beneficial to the growth of the upper and lower c faces of the seed crystal, the fixing mode in figure 2 is mainly beneficial to the growth of the upper c face and the m face at the side part of the seed crystal, and the fixing mode in figure 3 is mainly beneficial to the growth of the lower c face and the m face at the side part of the seed crystal. The seed crystal is fixed by a method not limited to the method of this embodiment, and may be suspended or placed in addition to mechanical fixationThermal bonding, chemical bonding, and the like.

And step 3: and growing the aluminum nitride single crystal.

The single crystal growth in the step is completed in a high-temperature furnace, and the high-temperature furnace adopts three resistance heaters which are respectively arranged at the upper part of a crucible cover, the lower part of a crucible body and the side part of the crucible body. Putting the assembled crucible into a high-temperature furnace, introducing high-purity nitrogen into the furnace as protective gas, and controlling the constant pressure to be 60-70 KPa; and the three resistance heaters are simultaneously heated until the crucible reaches a preset temperature, and heat preservation is carried out to carry out crystal growth. The preset temperature of the embodiment is 2200-2250 ℃. When the crucible reaches the preset temperature, the temperature field around the aluminum nitride seed crystal is adjusted simultaneously to form a small temperature gradient. Specifically, three high temperature regions of the upper part, the lower part and the side part of the crucible are formed by adjusting the power output of three heaters, as shown in fig. 4, a temperature field simulation diagram of the process execution process of the embodiment is shown, in the diagram, the temperature is represented by K, as can be seen from the diagram, the temperature is distributed from the high to low in a gradient manner from a raw material region toward the seed crystal located in the middle of the growth cavity, the raw material around the inner wall of the crucible is sublimated at high temperature, the gas phase substances around the inner wall of the crucible are transmitted toward the seed crystal under the action of the temperature gradient, higher Al gas pressure is formed around the seed crystal, as shown in fig. 5, a distribution diagram of the core substance Al gas pressure is represented by Pa, higher Al gas pressure around the seed crystal can be seen, sufficient substances are provided for growing the crystal at high speed, the purpose of growing the crystal at high speed is achieved, and the crystal growth rate in the embodiment reaches 240-. As can also be seen from FIG. 4, the temperature gradient formed around the seed crystal by adjusting the output power of the three resistance heaters is fitted to a temperature gradient profile as shown in FIG. 6, in which the temperature is expressed in K and the temperature gradient is as low as 0.5-2K/cm. The low temperature gradient forms a low supersaturation crystal growth environment, and as shown in FIG. 7, the supersaturation distribution pattern around the seed crystal is as low as 2 x 10^-4. Obviously, the temperature field design of the embodiment forms a low temperature gradient and low supersaturation crystal growth environment around the seed crystal, and the seed crystal performs high-speed growth of the aluminum nitride single crystal in a high-quality laminar flow mode.

And 4, step 4: after the crystal growth is finished, the temperature is reduced to the room temperature, the crucible is opened, and the grown aluminum nitride single crystal ingot is taken out, as shown in fig. 8, the aluminum nitride single crystal ingot of the embodiment shows a hexagonal high-crystalline-quality appearance, and the periphery of the aluminum nitride single crystal ingot has no parasitic mixed crystal.

By performing a high-resolution X-ray rocking curve test on the sliced piece of the AlN single crystal ingot obtained in example 1, the test results are shown in fig. 9 and fig. 10, which are respectively a 002 diffraction plane rocking curve and a full width at half maximum value thereof, a 102 diffraction plane rocking curve and a full width at half maximum value thereof, (002) full width at half maximum reaches 0.022 ° (79.2 arcsec), (102) full width at half maximum reaches 0.027 ° (97.2 arcsec), which indicates that the crystal has extremely high crystallization quality and low defect density, thereby indicating the effectiveness of the technical scheme of the present invention and laying a foundation for efficiently obtaining aluminum nitride single crystals and substrates thereof with larger size, high crystallization quality and low dislocation density.

On the basis of the embodiment, the technical scheme of the invention can adjust the process parameters in a certain range, such as adjusting the constant pressure of the protective gas nitrogen in the high-temperature furnace in the step 3 preferably within the range of 30-150kPa, and the preset temperature preferably within the range of 2100-2350 ℃, so that the crystal growth rate of 200-500 mu m/h can be obtained, the parameters are adjusted within the range, the growth environment with the small temperature gradient of less than or equal to 10K/cm and the low saturation in the axial direction and the radial direction around the seed crystal can be formed around the seed crystal, and the invention purpose of the technical scheme of the invention can be realized.

The technical scheme of the invention is not limited to the growth of the aluminum nitride crystal, and can also be applied to other crystal growth, such as an aluminum nitride-based crystal, and more specifically, an AlScN crystal. The above description of the embodiments is only intended to facilitate the understanding of the method of the invention and its core idea. It should be noted that, for those skilled in the art, it is possible to make various improvements and modifications to the present invention without departing from the principle of the present invention, and those improvements and modifications also fall within the scope of the claims of the present invention.

Claims

1. A method for growing an aluminum nitride single crystal by a physical vapor transport method, comprising the steps of:

s1: fixing aluminum nitride raw materials around the inner wall of the crucible, wherein the aluminum nitride raw materials enclose a cavity, namely a crystal growth cavity;

s2: fixing an aluminum nitride seed crystal in the middle of a crystal growth cavity in a crucible;

s3: placing the crucible assembled with the aluminum nitride raw material and the aluminum nitride seed crystal into a high-temperature furnace, introducing high-purity nitrogen into the high-temperature furnace, heating until the temperature in the crucible reaches a preset temperature, adjusting the temperature to be small temperature gradient from the raw material to the seed crystal in the direction from high to low around the seed crystal, growing an aluminum nitride single crystal, and preserving the temperature for a period of time; the temperature gradient of the small temperature gradient in the axial direction and the radial direction is less than or equal to 10K/cm, and low supersaturation degree of Al gas pressure is formed around the seed crystal;

2. A method for growing an aluminum nitride single crystal according to claim 1, wherein: the crucible is a closed structure formed by buckling a crucible body and a crucible cover; step S1 the inner wall of the crucible includes the bottom and the side walls of the crucible body and the surface of the crucible cover facing the crucible body, and the aluminum nitride material is fixed around the inner wall of the crucible, that is, the bottom and the side walls of the crucible body and the surface of the crucible cover facing the crucible body.

3. A method for growing an aluminum nitride single crystal according to claim 1, wherein: the aluminum nitride raw material in the step S1 is selected from one or more of powder, sintered ceramic material, crystallized porous material or crystal block material.

4. A method for growing an aluminum nitride single crystal according to claim 1, wherein: the aluminum nitride raw material fixed on the inner wall of the crucible in the step S1 is one or more of a laying method, a thermal bonding method, a chemical bonding method, a vapor deposition method and a mechanical fixing method.

5. A method for growing an aluminum nitride single crystal according to claim 1, wherein: s2, the seed crystal is fixed in any one or more of hanging mode, laying mode, thermal bonding mode, chemical bonding mode and mechanical fixing mode.

6. A method for growing an aluminum nitride single crystal according to claim 1, wherein: the high temperature furnace in step S3 adopts three resistance type heating, namely, three groups of heaters, namely an upper heater, a lower heater and a side heater, which are distributed around the crucible.

7. A method for growing an aluminum nitride single crystal according to claim 1, wherein: introducing high-purity nitrogen as protective gas in the step S3, and keeping constant pressure at 30-150 kPa; the preset temperature range is 2100-2350 ℃.

8. A method for growing an aluminum nitride single crystal according to claim 1, wherein: step S3, the temperature gradient around the seed crystal is as low as 0.5-2k/cm, and the low supersaturation degree of Al gas pressure is as low as 2 x 10^-4。

9. A method for growing an aluminum nitride single crystal according to claim 1, wherein: the crystal growth rate of the step S3 reaches 0.2-0.5 mm/h.

10. An aluminum nitride single crystal ingot produced by the method as set forth in any one of claims 1 to 9 wherein: the crystal ingot presents a regular hexagonal shape, parasitic mixed crystal is avoided, the full width at half maximum of a 002 diffraction surface of a high-resolution X-ray diffraction rocking curve is less than 80 arcseconds, and the full width at half maximum of a 102 diffraction surface is less than 100 arcseconds.