阅读说明：本技术 一种用于AlN单晶扩径生长的PVT装置 (PVT device for diameter-expanding growth of AlN single crystal ) 是由 于彤军 赵起悦 吴洁君 王泽人 韩彤 沈波 于 2021-07-23 设计创作，主要内容包括：本发明专利公开了一种用于AlN单晶生长扩径的PVT装置,属于晶体生长技术领域。该装置包括一坩埚,为生长提供腔室,坩埚放置到炉体并封闭炉体,抽真空和充高纯氮气,坩埚盖上表面边缘承载两段式气氛空腔结构,同时坩埚盖下表面固定籽晶托和籽晶,两段式气氛空腔结构将坩埚盖上表面边缘的传热方式转变,从而利用气氛较低的热导率增大坩埚盖边缘处的温度梯度,使籽晶处的径向温梯增大至适合其侧向扩径生长。本发明可以实现AlN单晶的高效扩径,获得高质量的AlN籽晶或衬底。(The invention discloses a PVT device for growth and diameter expansion of an AlN single crystal, and belongs to the technical field of crystal growth. The device includes a crucible, provides the cavity for growing, and the furnace body and closed furnace body are placed to the crucible, evacuation and filling high-purity nitrogen gas, and crucible lid upper surface edge bears two segmentation atmosphere cavity structures, and fixed seed crystal of crucible lid lower surface holds in the palm and the seed crystal simultaneously, and two segmentation atmosphere cavity structures change the heat transfer mode at crucible lid upper surface edge to utilize the lower thermal conductivity of atmosphere to increase the temperature gradient at crucible lid edge, make the radial temperature gradient of seed crystal department increase to be fit for its side direction hole enlargement growth. The invention can realize the high-efficiency diameter expansion of the AlN single crystal and obtain high-quality AlN seed crystals or substrates.)

1. A PVT device for growth and diameter expansion of AlN single crystals comprises a crucible and a furnace body, wherein the crucible is placed in the furnace body and seals the furnace body, and a heater and a heat insulation layer are arranged in the furnace body, the PVT device is characterized in that the crucible comprises a crucible cover and a crucible body, source powder is placed in the crucible body, an annular source powder cover is placed on the surface of the source powder, the crucible cover comprises a cover body, a seed crystal support and a two-section cavity structure, the size of the cover body is matched with the outer diameter of the crucible body, the seed crystal support is fixed on the lower surface of the cover body, an annular two-section cavity structure is arranged on the upper surface of the cover body, the two-section cavity structure consists of an upper half-section cavity part and a lower half-section cavity part, the lower half-section cavity part is directly placed on the upper surface of the cover body in a limiting way through a clamping groove, the upper half-section cavity part is fixed on the lower half-section cavity structure part, and the outer edge of the upper half-section cavity part and the outer edge of the lower half-section cavity part are mutually matched with the outer edge of the cover body, the inner diameter of the upper half cavity part is larger than that of the lower half cavity part, gas in the furnace body can freely fill in the cavities of the upper half cavity part and the lower half cavity part, and an upper annular cavity and a lower annular cavity containing atmosphere are formed above the edge of the cover body.

2. The PVT apparatus for expanding growth diameter of an AlN single crystal according to claim 1, wherein the heater is resistance-type heating and is suspended between the inside of the insulating layer and the outside of the crucible by means of electrodes.

3. The PVT apparatus for growing and expanding an AlN single crystal according to claim 1, wherein the annular source powder cover has an outer diameter equal to the inner diameter of the crucible, an inner diameter of 20-40mm and a thickness of 2-3mm, and is made of metal tungsten.

4. The PVT apparatus for growing and expanding an AlN single crystal according to claim 1, wherein the crucible body is a cylinder having a lower end closed and an upper end opened, and the material is metal tungsten or TaC.

5. The PVT device for growing and expanding an AlN single crystal according to claim 1, wherein the cover body and the seed crystal holder are made of metal tungsten, TaC or ceramic.

6. The PVT device for growing and expanding the diameter of the AlN single crystal according to claim 1, wherein the two-section type atmosphere cavity structure material is metal tungsten or TaC.

7. The PVT apparatus for growing and expanding an AlN single crystal according to claim 1, wherein the atmosphere is a high-purity nitrogen gas or a mixed gas of a nitrogen gas and an argon gas.

8. The PVT device for growth and diameter expansion of AlN single crystals according to claim 1, wherein the inner diameter of the cavity part of the upper half section is 20-60mm, the inner diameter of the cavity part of the lower half section is 10-40mm, and the heights of the cavity parts of the upper half section and the lower half section are both 5-10 mm.

9. The PVT apparatus for growing and expanding an AlN single crystal according to claim 1, wherein a thermo-couple is additionally provided above the crucible for monitoring the condition of the temperature field.

Technical Field

The invention relates to the technical field of crystal growth, in particular to a physical vapor transport method (PVT method) device for the diameter-expanding growth of AlN single crystals.

Background

The lattice constant and the thermal expansion coefficient of AlN (aluminum nitride) are very close to those of AlGaN (aluminum gallium nitride) with high Al component, and AlN single crystal is a homoepitaxial substrate of nitride, can obviously reduce dislocation density of an epitaxial layer so as to improve the lattice quality, and becomes the best substrate of an AlGaN-based deep ultraviolet device for epitaxial growth, comprising a deep ultraviolet light-emitting diode, a laser diode and a deep ultraviolet detector. Meanwhile, the thermal mismatch between the AlN single crystal and the GaN is only 2.4%, the heat dissipation performance is excellent, and the AlN single crystal has the excellent characteristics of high breakdown field strength, high hardness, excellent electrical performance and the like, and is an important material basis of high-temperature, high-frequency and high-power density electronic devices. At present, the method for internationally and successfully realizing the growth of the large-size AlN single crystal substrate is a physical vapor transport method (namely, a PVT method, and the basic principle is that AlN source powder is sublimated at a high temperature at the bottom of a crucible to obtain Al atoms, and the Al atoms are transported to a low temperature at the top of the crucible to be crystallized in a nitrogen environment). Because of lack of large-size AlN seed crystals, the growth of the AlN single crystal by PVT needs to use the AlN single crystal with smaller size as the seed crystals to carry out PVT growth of diameter expansion of the crystal, and the large-size AlN single crystal is gradually obtained. Therefore, PVT growth, which expands the crystal size, is a core technique for obtaining a large-sized single crystal.

At present, international research groups can obtain a 2-inch high-quality AlN single crystal substrate with low dislocation density by a PVT method, but the problems of difficult seed crystal cultivation, low diameter expansion efficiency, poor repeatability and the like are faced, and the 2-inch AlN single crystal is not industrialized yet and is very expensive.

Disclosure of Invention

In view of the above problems, the present invention provides a PVT apparatus for diameter expansion growth of an AlN single crystal, which can realize efficient diameter expansion and iterative growth of an AlN single crystal, and obtain a high-quality large-size AlN crystal.

The technical scheme provided by the invention is as follows:

a PVT device for the diameter-expanding growth of AlN single crystals is integrally of a rotational axis symmetrical structure and comprises two parts: (1) the crucible part is used for containing growth source powder and providing a growth chamber, and the crucible is placed on a cylindrical support base connected with the support rod in the furnace body; (2) the furnace body part provides a closed vacuum environment, a required gas environment and a high-temperature environment in growth, a heater and an insulating layer are arranged in the furnace body, the heater can be resistance-type heating, the shape and the number of the heater are not limited, but the simplest single straight-cylinder-shaped heater can meet the requirement of expanding growth of the invention and is suspended between the inner side of the insulating layer and the outer side of the crucible through an electrode.

The crucible as the core component comprises a crucible cover and a crucible body. The crucible cover comprises a cover body, a seed crystal support and a two-section cavity structure, wherein the size of the cover body is matched with the outer diameter of the crucible body, the seed crystal support is fixed on the lower surface of the cover body, the upper surface of the cover body is provided with an annular two-section cavity structure, the two-section cavity structure consists of an upper half section cavity part and a lower half section cavity part, the inner diameter size of the upper half section cavity part is larger than that of the lower half section cavity part, and the material can be metal tungsten or TaC. The lower half-section cavity part is directly placed on the upper surface of the cover body in a limiting mode through the clamping groove, the upper half-section cavity part is placed on the upper surface of the lower half-section cavity part in a limiting mode, the outer edge of the upper half-section cavity part and the outer edge of the lower half-section cavity part are matched with the outer edge of the cover body in a limiting mode through the limiting device, gas in the furnace body can enter and fill cavities, sealed by cavity walls, of the upper half-section cavity part and the lower half-section cavity part, the upper portion and the lower portion of the edge of the cover body form an annular cavity containing atmosphere, and therefore the special diameter-expanding thermal field design with radial temperature gradient changes is achieved. The cover body and the seed crystal support can be made of easily-processed materials suitable for AlN growth, such as metal tungsten, TaC, ceramics and the like, the inner diameter of the lower half section cavity component is larger than the diameter of the seed crystal, the inner diameter of the upper half section cavity component is 20-60mm, the inner diameter of the lower half section cavity component is 10-40mm, and the heights of the upper and lower half section cavity components are both 5-10 mm. The principle of the design is that the cavity has the same pressure and atmosphere as the furnace body, the original heat transfer mode mainly based on heat radiation at the position of the cavity is converted into heat conduction mainly, and then the large temperature gradient at the edge of the crucible cover is realized by utilizing the heat conduction characteristic difference between the gas in the cavity and the material of the crucible cover, a curved temperature field is created, and the radial temperature field distribution requirement of the diameter expansion growth of the crystal is met. The specific size of the two-section cavity structure can be adjusted according to the condition of growing crystal.

The crucible body is a cylinder with the lower end closed and the upper end opened, and can adopt metal materials which are suitable for AlN growth and easy to process, such as metal tungsten, TaC and the like, and form a growth chamber together with the crucible cover. The source powder is arranged in the crucible body, the flat annular source powder cover with a certain size is placed on the upper surface of the powder body, the flow field of the source powder cover is changed, the transportation of the Al source is changed from edge to middle, the influence of the transportation on the growth is reduced, the temperature field becomes a main factor for modulating the growth rate distribution, and the Al source can be concentrated in the seed crystal area in the center of the top. The annular source powder cover is placed on the upper surface of the source powder, the outer diameter of the annular source powder cover is the same as the inner diameter of the crucible, the inner diameter of the annular source powder cover is 20-40mm, the thickness of the annular source powder cover is 2-3mm, and the annular source powder cover is made of metal tungsten.

Adhering a small-size seed crystal to a seed crystal support, placing source powder and a source powder cover, fixing the crucible cover and the crucible body, placing the whole crucible in a growth furnace, sealing, vacuumizing, heating to 2000-plus-material 2400 ℃, simultaneously inflating and maintaining pressure (400-plus-material 700Torr), stabilizing the pressure, and carrying out growth and diameter expansion of AlN in the atmosphere of high-purity nitrogen or mixed gas of nitrogen and argon for 10-300 hours in each generation of growth.

In addition, a temperature thermocouple is arranged above the crucible and used for monitoring the temperature field condition.

The method for growing the AlN single crystal by adopting the invention specifically comprises the following steps:

1) seed crystal and crucible preparation:

bonding a small-size seed crystal (with the diameter of 5-40mm) at the central position of a seed crystal support by using a high-temperature-resistant adhesive, placing source powder and a source powder cover well, placing the seed crystal support and the seed crystal downwards concentrically with a crucible body, covering a cover body of the crucible cover, and finally placing a two-section cavity structure on the cover body in a limiting manner through a clamping groove;

2) filling and exhausting the furnace body:

placing the crucible into a furnace body, sealing the furnace body, vacuumizing and filling high-purity nitrogen, and filling, vacuumizing and replacing the atmosphere in the cavity for 3-5 times to keep the system at a certain vacuum degree after the completion;

3) and (3) inflating and maintaining the pressure of the furnace body:

after the furnace body is stopped to be vacuumized, introducing high-purity nitrogen or a mixed gas of high-purity nitrogen and high-purity argon in a certain proportion (the range is 0.1-0.9) into the furnace body to form an environmental atmosphere and keep the total pressure of the cavity stable;

4) heating the furnace body:

selecting a proper heating rate (1-100 ℃/min) to heat, and keeping the pressure stable;

5) and (3) crystal growth stage:

raising and stabilizing the temperature to a set value, wherein the temperature is 2000-2400 ℃, and the growth time can be generally 10-300 hours;

6) and (3) cooling:

after the growth is finished, starting to select a proper cooling rate (1-100 ℃/min) for cooling;

7) opening the furnace for sampling:

after the furnace body is cooled to room temperature, opening the furnace and taking out the crucible, taking down the two-section cavity structural component and the cover body, and further taking down the seed crystal holder and the crystal to obtain a block body consisting of the expanded AlN single crystal and the surrounding polycrystalline part;

8) cutting, grinding and polishing:

cutting the whole AlN block by using a multi-wire cutting machine to obtain an expanded AlN wafer, and grinding and polishing;

9) and (3) iterative growth:

and (4) performing repeated iterative growth for multiple times by using the expanded wafer as a seed crystal for next generation of expanded growth.

And (3) carrying out repeated iteration expanding growth through the steps, so that the expanding of the small size to two inches or more can be realized, and the large-size AlN single crystal is obtained.

Compared with the prior art, the invention has the beneficial effects that:

aiming at the expanding PVT growth requirement of AlN seed crystals, the invention provides a scheme of a physical vapor transport method (PVT method) growth furnace by combining the design of a temperature field and a flow field, namely, a large temperature gradient at the edge of the upper surface of a crucible cover is manufactured by utilizing a two-section type internal inflatable cavity structure at the edge of the upper surface of the crucible cover, so that the temperature field with the large radial temperature gradient is realized, and the method is suitable for the lateral expanding growth of AlN crystals; meanwhile, the flow field is changed by using the source powder cover, so that the temperature field becomes a main factor for modulating growth rate distribution, and the Al source can be concentrated in the seed crystal region at the center of the top. The crucible has a simple geometric structure, is easy to process and realize, and can be suitable for multi-generation expanding growth by changing the structural size. Therefore, the invention has another important characteristic that the diameter expanding process can be repeated and the effects are superposed, thereby realizing the continuous enlargement of the size and the gradual improvement of the crystal quality; the primary seed crystal can be a small seed crystal which is self-nucleated, and can also be an AlN wafer with a certain size; by iterative growth, the high-efficiency diameter expansion of the AlN single crystal can be realized, and high-quality AlN seed crystals or substrates can be obtained; furthermore, the design can realize the expanding temperature field without a complex heater design, and a simple single-resistance heater can generally meet the requirement.

The invention has the advantages that: firstly, the expanding efficiency is high, and each expanding growth can have an expanding angle close to 90 degrees; secondly, dislocation density and impurity concentration in the crystal are gradually reduced in the diameter-expanding iterative growth, and the effects of multiple iterative growth are superposed, so that the effects of further increasing the size and gradually improving the quality of the crystal can be simultaneously realized; thirdly, the two-section cavity structure is positioned outside the crucible and is not in contact with the crystal, so that the two-section cavity structure is favorable for repeated use and reduces the growth cost, and meanwhile, the structure is simple and easy to manufacture and can be applied to the industrialization of crystal preparation; fourthly, the crucible with the two-section type cavity structure can be combined with a single heater to construct a radial thermal field structure required by expanding, so that the heater of the equipment has the advantages of simple structure, reduction of the complexity of a heat insulation structure, and obvious reduction of cost and implementation difficulty compared with a multi-heater thermal field.

Drawings

FIG. 1 is a basic configuration diagram of a PVT apparatus for growing and expanding an AlN single crystal according to an embodiment of the present invention, the apparatus having an axisymmetric structure;

among them, 1-straight cylinder type resistance heater; 2-crucible main body; 3-cylindrical crucible support base and rod; 4-temperature thermocouple; 5, an upper half section cavity component of the two-section cavity structure; 6-a lower half section cavity component of the two-section cavity structure; 7-a cover body; 8, a seed crystal support; 9-AlN seed crystals bonded on the seed crystal holders; 10-annular source powder cover; 11-AlN source powder; 12-atmosphere, which is high purity nitrogen or a mixture of high purity nitrogen/high purity argon in a certain ratio (in the range of 0.1-0.9), and atmosphere outside the crucible, inside the crucible and inside the annular cavity member.

FIG. 2 is a simulation of temperature field, flow field distribution and crystal growth in the first embodiment, in which the two-stage cavity structure has an outer diameter of 74mm, the upper half-stage cavity component has an inner diameter of 54mm, and the lower half-stage cavity component has an inner diameter of 36 mm;

FIG. 3 is a simulation of temperature field, flow field distribution and crystal growth in the second embodiment, in which the two-stage cavity structure has an outer diameter of 74mm, the upper half-stage cavity component has an inner diameter of 48mm, and the lower half-stage cavity component has an inner diameter of 26 mm;

the fluid mechanics simulation result of the expanding growth of the embodiment comprises the simulation of a temperature field, flow field distribution and crystal growth condition (20 hours), and is obtained through finite element simulation calculation; the solid line with numbers represents isotherms, and the numbers represent temperatures; the solid line with arrows represents the transport path of the Al source; the dotted line with an arrow at the boundary of the single crystal and the polycrystal represents the diameter expansion direction, and the included angle between the dotted line and the vertical direction is the diameter expansion angle; from the comparison of simulation results of the two embodiments, the two-section type cavity structural component can play an obvious thermal field bending effect under two sizes, and both can obtain a hole expansion angle close to 90 degrees, but the polycrystal of the latter has a better supporting effect on a single crystal region, and the lateral hole expansion growth of the latter is expected to be more efficient in growth after 20 hours; and under the effect of the source powder cover, the transportation mainly depends on a temperature field, and the transportation of the Al source under two sizes is more concentrated on the transportation of the Al source under two sizes.

Detailed Description

The invention will be further described by way of examples, without in any way limiting the scope of the invention, with reference to the accompanying drawings.

The invention provides a PVT device for expanding and growing AlN single crystals. Fig. 1 is a schematic diagram of a basic structure of a PVT apparatus for growth and diameter expansion of AlN single crystal according to an embodiment of the present invention, in which a cavity of a two-stage cavity structure is filled with an atmosphere, and is placed in an edge region above a cover to create a curved thermal field and provide a larger radial temperature gradient, so that seed crystal can realize efficient diameter expansion growth. The crucible is provided with a reaction zone, the interior and the vicinity of the crucible can reach the high temperature of more than 2400 ℃, the crucible is not sealed, and gas flow can pass through the gap. The dry pump and the molecular pump can be used for vacuumizing and keeping a certain vacuum degree, and meanwhile, when nitrogen and argon are introduced, the vacuum pump works, so that gas in the furnace can be replaced, and the pressure stability is ensured. The high-purity AlN source powder is decomposed and sublimated at a relatively high temperature, Al atoms are generated and conveyed upwards to a relatively low temperature for crystallization, and the conveying and crystallization shape is directly related to the shape of a temperature field under the action of a source powder cover, so that the expanding growth characteristic is presented.

EXAMPLE one diameter enlargement growth (two-stage cavity structure outer diameter 74mm, upper half cavity part inner diameter 54mm, lower half cavity part inner diameter 36mm)

1) Seed crystal and crucible preparation:

bonding a small-size seed crystal (with the diameter of 5-40mm) at the central position of a seed crystal support by using a high-temperature-resistant adhesive, placing source powder and a source powder cover well, placing the seed crystal support and the seed crystal downwards concentrically with a crucible body, covering a cover body of the crucible cover, and finally fixing a two-section cavity structure on the cover body through a clamping groove; the outer diameter of the two-section cavity structure is 74mm, the inner diameter of the upper half section cavity component is 54mm, and the inner diameter of the lower half section cavity component is 36 mm;

2) filling and exhausting the furnace body:

placing the crucible into a furnace body, sealing the furnace body, vacuumizing and filling high-purity nitrogen, and filling, vacuumizing and replacing the atmosphere in the cavity for 3-5 times to keep the system at a certain vacuum degree after the completion;

3) and (3) inflating and maintaining the pressure of the furnace body:

after the furnace body is stopped to be vacuumized, introducing high-purity nitrogen or a mixed gas of high-purity nitrogen and high-purity argon in a certain proportion (the range is 0.1-0.9) into the furnace body to form an environmental atmosphere and keep the total pressure of the cavity stable;

4) heating the furnace body:

selecting a proper heating rate (1-100 ℃/min) to heat, and keeping the pressure stable;

5) and (3) crystal growth stage:

raising and stabilizing the temperature to a set value, wherein the temperature is 2000-2400 ℃, and the growth time can be generally 10-300 hours;

6) and (3) cooling:

after the growth is finished, starting to select a proper cooling rate (1-100 ℃/min) for cooling;

7) opening the furnace for sampling:

after the furnace body is cooled to room temperature, opening the furnace and taking out the crucible, taking down the two-section cavity structural component and the cover body, and further taking down the seed crystal holder and the crystal to obtain a block body consisting of the expanded AlN single crystal and the surrounding polycrystalline part;

8) cutting, grinding and polishing:

cutting the whole AlN block by using a multi-wire cutting machine to obtain an expanded AlN wafer, and grinding and polishing;

9) and (3) iterative growth:

and (4) performing repeated iterative growth for multiple times by using the expanded wafer as a seed crystal for next generation of expanded growth.

EXAMPLE two diameter expansion growth (two-stage cavity structure outer diameter 74mm, upper half cavity part inner diameter 48mm, lower half cavity part inner diameter 26mm)

1) Seed crystal and crucible preparation:

bonding a small-size seed crystal (with the diameter of 5-40mm) at the central position of a seed crystal support by using a high-temperature-resistant adhesive, placing source powder and a source powder cover well, placing the seed crystal support and the seed crystal downwards concentrically with a crucible body, covering a cover body of the crucible cover, and finally fixing a two-section cavity structure on the cover body through a clamping groove; the outer diameter of the two-section cavity structure is 74mm, the inner diameter of the upper half section cavity component is 48mm, and the inner diameter of the lower half section cavity component is 26 mm;

2) filling and exhausting the furnace body:

placing the crucible into a furnace body, sealing the furnace body, vacuumizing and filling high-purity nitrogen, and filling, vacuumizing and replacing the atmosphere in the cavity for 3-5 times to keep the system at a certain vacuum degree after the completion;

3) and (3) inflating and maintaining the pressure of the furnace body:

after the furnace body is stopped to be vacuumized, introducing high-purity nitrogen or a mixed gas of high-purity nitrogen and high-purity argon in a certain proportion (the range is 0.1-0.9) into the furnace body to form an environmental atmosphere and keep the total pressure of the cavity stable;

4) heating the furnace body:

selecting a proper heating rate (1-100 ℃/min) to heat, and keeping the pressure stable;

5) and (3) crystal growth stage:

raising and stabilizing the temperature to a set value, wherein the temperature is 2000-2400 ℃, and the growth time can be generally 10-300 hours;

6) and (3) cooling:

after the growth is finished, starting to select a proper cooling rate (1-100 ℃/min) for cooling;

7) opening the furnace for sampling:

after the furnace body is cooled to room temperature, opening the furnace and taking out the crucible, taking down the two-section cavity structural component and the cover body, and further taking down the seed crystal holder and the crystal to obtain a block body consisting of the expanded AlN single crystal and the surrounding polycrystalline part;

8) cutting, grinding and polishing:

cutting the whole AlN block by using a multi-wire cutting machine to obtain an expanded AlN wafer, and grinding and polishing;

9) and (3) iterative growth:

and (4) performing repeated iterative growth for multiple times by using the expanded wafer as a seed crystal for next generation of expanded growth.

It is noted that the disclosed embodiments are intended to aid in further understanding of the invention, but those skilled in the art will appreciate that: various substitutions and modifications are possible without departing from the spirit and scope of the invention and appended claims. Therefore, the invention should not be limited to the embodiments disclosed, but the scope of the invention is defined by the appended claims.