Constant temperature metal bath crystal growth apparatus and method

Abstract

The application provides a constant-temperature metal bath crystal growth device and method, relates to the field of silicon carbide crystal growth, and adopts the metal bath mode to heat the crucible, can realize uniform heating of each part on the axial direction and the radial direction of the crucible, and the growth of the crystal is no longer dependent on the temperature gradient driving, but the long crystal gas phase formed after the sublimation of the silicon carbide powder is made to flow in the whole crucible in an undirectional manner, then the surface energy of the seed crystal is made to be less than the surface energy of the silicon carbide powder, the long crystal gas phase is made to crystallize on the seed crystal preferentially, and the growth is completed. In the whole crystal growth process, the temperature gradient is small or even zero, the heating structure can be operated at constant power, and the temperature change is small, so the thermal stress of the crystal can be reduced to a great extent, and the edge collapse and cracking problems of the crystal caused by the thermal stress can be effectively reduced.

Description

Technical Field

[0001] This invention relates to the field of silicon carbide crystal growth, and more specifically, to a constant-temperature metal bath crystal growth apparatus and method. Background Technology

[0002] In related technologies, silicon carbide crystal growth devices and methods based on the PVT method generally rely on the construction of temperature gradients (including axial temperature gradients and radial temperature gradients) to achieve crystal growth.

[0003] This method of crystal growth using a temperature gradient, while enabling directional flow of the growth vapor phase and increasing the crystal growth rate to some extent, suffers from several drawbacks. Firstly, the temperature is easily affected by slight changes in the external environment. Secondly, the presence of the temperature gradient leads to temperature differences across different parts of the crystal, resulting in significant thermal stress within the crystal and causing problems such as edge chipping and cracking. Furthermore, these problems become increasingly severe as the crystal size increases from 6 inches to 8 inches and then to 12 inches. Summary of the Invention

[0004] The present invention aims to provide a constant temperature metal bath crystal growth apparatus and method, which can effectively reduce the thermal stress inside the crystal and reduce defects such as crystal chipping and cracking.

[0005] The embodiments of the present invention can be implemented as follows: In a first aspect, the present invention provides a constant-temperature metal bath crystal growth apparatus, comprising: A crucible, wherein a seed crystal is provided at the top of the crucible and the lower middle part of the crucible is used to fill silicon carbide powder; An inner protective layer, which wraps around the outer wall of the crucible; An outer protective layer is provided outside the inner protective layer and together with the inner protective layer, they form a metal bath cavity, which is filled with metal bath material. A heating structure is provided around the outer side of the outer protective layer and is used to heat the metal bath material so that the metal bath material melts and forms liquid metal with a liquid level higher than the top wall of the inner protective layer; A furnace body for housing the crucible, the inner protective layer, the outer protective layer, and the heating structure.

[0006] In an optional embodiment, the metal bath material is one of copper, platinum, gold, and a gold-palladium alloy.

[0007] In an optional embodiment, both the inner protective layer and the outer protective layer are made of high-temperature inert metals with melting points higher than the crystal growth environment temperature.

[0008] In an optional embodiment, the high-temperature resistant inert metal is tantalum.

[0009] In an optional embodiment, the heating structure includes a main heater capable of simultaneously heating the peripheral wall, top wall, and bottom wall of the outer protective layer.

[0010] In an optional embodiment, the heating structure further includes an auxiliary heater that surrounds the main heater.

[0011] In a second aspect, the present invention provides a method for growing crystals in a constant-temperature metal bath, based on the constant-temperature metal bath crystal growth apparatus described in any of the foregoing embodiments, comprising: After filling the crucible with silicon carbide powder, the crucible is placed inside the inner protective layer; The heating structure is controlled to start and operate at a constant power.

[0012] In an optional implementation, the step of controlling the activation of the heating structure further includes: Argon gas is introduced into the furnace.

[0013] In an optional embodiment, the particle size of the silicon carbide powder being filled is 0.1-1 mm.

[0014] In an optional embodiment, the distance between the top surface of the packed silicon carbide powder and the growth surface of the seed crystal is 10-50 mm.

[0015] The beneficial effects of the isothermal metal bath crystal growth apparatus and method provided in the embodiments of the present invention include: This apparatus uses a metal bath to heat the crucible, achieving uniform heating of all parts of the crucible axially and radially. Crystal growth no longer relies on a temperature gradient; instead, the crystal growth vapor formed after the sublimation of silicon carbide powder flows non-directionally to fill the entire crucible. Then, taking advantage of the characteristic that the surface energy of the seed crystal is lower than that of the silicon carbide powder (the surface energy of large-sized crystals is lower than that of small-sized crystals), the crystal growth vapor preferentially crystallizes on the seed crystal until growth is complete. Because there is no or a very small temperature gradient throughout the crystal growth process, and the heating structure can operate at a constant power, temperature changes are minimal. Therefore, thermal stress on the crystal can be significantly reduced, effectively minimizing edge chipping and cracking caused by thermal stress. These defects are particularly reduced when growing large-sized crystals, resulting in high-quality crystals. Attached Figure Description

[0016] To more clearly illustrate the technical solutions of the embodiments of the present invention, the accompanying drawings used in the embodiments will be briefly introduced below. It should be understood that the following drawings only show some embodiments of the present invention and should not be regarded as a limitation on the scope. For those skilled in the art, other related drawings can be obtained based on these drawings without creative effort.

[0017] Figure 1 This is a schematic diagram of the heating structure of the isothermal metal bath crystal growth apparatus provided in this embodiment before startup; Figure 2 This is a schematic diagram of the heating structure of the isothermal metal bath crystal growth apparatus provided in this embodiment after startup.

[0018] Icons: 100-Crucible; 110-Seed crystal; 120-Silicon carbide powder; 200-Inner protective layer; 202-Metal bath cavity; 210-Metal bath material; 220-Liquid metal; 300-Outer protective layer; 400-Heating structure; 410-Main heater; 420-Auxiliary heater; 500-Furnace body. Detailed Implementation

[0019] To make the objectives, technical solutions, and advantages of the embodiments of the present invention clearer, the technical solutions of the embodiments of the present invention will be clearly and completely described below with reference to the accompanying drawings. Obviously, the described embodiments are only some embodiments of the present invention, and not all embodiments. The components of the embodiments of the present invention described and shown in the accompanying drawings can generally be arranged and designed in various different configurations.

[0020] Therefore, the following detailed description of the embodiments of the invention provided in the accompanying drawings is not intended to limit the scope of the claimed invention, but merely to illustrate selected embodiments of the invention. All other embodiments obtained by those skilled in the art based on the embodiments of the invention without inventive effort are within the scope of protection of the invention.

[0021] It should be noted that similar labels and letters in the following figures indicate similar items. Therefore, once an item is defined in one figure, it does not need to be further defined and explained in subsequent figures.

[0022] In the description of this invention, it should be noted that if terms such as "upper," "lower," "inner," or "outer" are used to indicate the orientation or positional relationship based on the orientation or positional relationship shown in the accompanying drawings, or the orientation or positional relationship in which the product of this invention is usually placed, they are only for the convenience of describing this invention and simplifying the description, and do not indicate or imply that the device or element referred to must have a specific orientation, or be constructed and operated in a specific orientation, and therefore should not be construed as a limitation of this invention.

[0023] Furthermore, the terms "first" and "second" are used only to distinguish descriptions and should not be interpreted as indicating or implying relative importance.

[0024] It should be noted that, where there is no conflict, the features in the embodiments of the present invention can be combined with each other.

[0025] Existing PVT methods for preparing silicon carbide crystals typically rely on temperature gradients to achieve crystal growth. While this method allows for directional flow of the growth vapor phase, increasing the crystal growth rate, it also presents several drawbacks. First, the crystal growth environment temperature is easily affected by slight changes in the external environment. Second, the presence of temperature gradients leads to temperature differences across different parts of the crystal, resulting in significant internal thermal stress and causing edge chipping and cracking. Furthermore, these problems become increasingly severe as crystal sizes increase from 6 inches to 8 inches and then to 12 inches.

[0026] To address the above issues, this invention provides a isothermal metal bath crystal growth apparatus and method. Instead of using a temperature gradient to drive the directional flow of the crystal growth vapor phase to the seed crystal for crystallization, it employs a metal bath to allow the crystal growth vapor phase to flow non-directionally and fill the entire crucible. Then, taking advantage of the fact that the surface energy of the seed crystal is lower than that of the silicon carbide powder, the crystal growth vapor phase preferentially crystallizes on the seed crystal. Simultaneously, the heating structure can operate at a constant power, reducing temperature fluctuations in the crystal growth environment. This significantly reduces thermal stress on the crystal, minimizing defects such as edge chipping and cracking, and enabling the production of high-quality, large-size crystals.

[0027] The following section, with reference to the accompanying drawings, details the overall structure, working principle, and supporting crystal growth methods of this constant-temperature metal bath crystal growth apparatus.

[0028] Please refer to Figure 1 and Figure 2 This isothermal metal bath crystal growth apparatus includes a furnace body 500, a crucible 100, an inner protective layer 200, an outer protective layer 300, and a heating structure 400. A seed crystal 110 is disposed at the top of the crucible 100, and silicon carbide powder 120 is filled in the lower middle part of the crucible 100. The inner protective layer 200 surrounds the outer wall of the crucible 100, and the outer protective layer 300 surrounds the outer side of the inner protective layer 200, together forming a metal bath cavity 202, which is filled with metal bath material 210. The heating structure 400 surrounds the outer protective layer 300 and is used to heat the metal bath material 210, causing it to melt and form liquid metal 220 with a liquid level higher than the top wall of the inner protective layer 200. The furnace body 500 houses the crucible 100, the inner protective layer 200, the outer protective layer 300, and the heating structure 400.

[0029] The inner protective layer 200 is located inside the outer protective layer 300. The bottom wall of the inner protective layer 200 and the bottom wall of the outer protective layer 300 are spaced apart and supported by multiple pillars, so that the inner protective layer 200 is supported and fixed to the bottom wall of the outer protective layer 300. The peripheral wall of the inner protective layer 200 and the peripheral wall of the outer protective layer 300 are spaced apart, and the top wall of the inner protective layer 200 and the top wall of the outer protective layer 300 are also spaced apart. This allows the liquid metal 220 in the metal bath 202 to cover the top wall, bottom wall, and peripheral wall of the inner protective layer 200 and the crucible 100 in all directions, so as to achieve uniform heating of all parts of the inner protective layer 200 and the crucible 100.

[0030] Both the inner protective layer 200 and the outer protective layer 300 are made of high-temperature resistant inert metals with melting points higher than the crystal growth environment temperature, to contain the liquid metal 220, prevent leakage of the liquid metal 220, and effectively protect the crucible 100. In this embodiment, the high-temperature resistant inert metal is tantalum. Tantalum has a melting point of approximately 2996°C, which is much higher than the crystal growth environment temperature, allowing it to remain stable (not melt) during crystal growth, thus containing the liquid metal 220 and protecting the crucible 100.

[0031] Furthermore, the metal bath material 210 needs to be a metal material with a melting point lower than the crystal growth environment temperature and a boiling point higher than the crystal growth environment temperature, so that the metal bath material 210 can melt to form liquid metal 220 during the crystal growth process and remain basically in a liquid state without vaporizing.

[0032] In this embodiment, the metal bath material 210 is one of copper, platinum, gold, and a gold-palladium alloy. Copper has a melting point of approximately 1084.62°C and a boiling point of 2562-2580°C. Platinum has a melting point of approximately 1772°C and a boiling point of approximately 3825°C. Gold has a melting point of approximately 1064°C and a boiling point of approximately 2856°C. The gold-palladium alloy has a melting point of 1064-1554°C and a boiling point of 2856-2940°C. All four metals meet the requirements of metal bath material 210, i.e., their melting points are lower than the crystal growth environment temperature, and their boiling points are higher than the crystal growth environment temperature. During crystal growth, all four materials can be maintained in a liquid state to stably and reliably heat the metal bath in crucible 100.

[0033] In this embodiment, the heating structure 400 includes a main heater 410, which can simultaneously heat the peripheral wall, top wall, and bottom wall of the outer protective layer 300. That is, the main heater 410 is simultaneously disposed above, below, and around the outer protective layer 300 to achieve omnidirectional and uniform heating of the metal bath material 210, thereby achieving uniform heating of all parts of the crucible 100 in the axial and radial directions and minimizing the temperature difference between different parts of the crucible 100.

[0034] Further, the heating structure 400 further comprises an auxiliary heater 420, and the auxiliary heater 420 surrounds the main heater 410. The arrangement of the auxiliary heater 420 can reduce temperature fluctuations at the outer periphery of the main heater 410, thereby further improving the omnidirectional uniform heating of the metal bath material 210 by the main heater 410. It should be noted that in this embodiment, the auxiliary heater 420 is provided as one layer; in other embodiments, the auxiliary heater 420 may also be provided as an inner layer and an outer layer, wherein the inner auxiliary heater 420 surrounds the outer protective layer 300, and the outer auxiliary heater 420 surrounds the inner auxiliary heater 420, so as to further optimize the uniform heating effect.

[0035] The constant-temperature metal bath crystal growth method matched with the constant-temperature metal bath crystal growth apparatus specifically comprises the following steps: Step S100: after filling silicon carbide powder 120 into a crucible 100, place the crucible 100 in an inner protective layer 200.

[0036] It should be noted that in this embodiment, the particle size of the filled silicon carbide powder 120 is selected as 0.1-1 mm. Compared with conventional silicon carbide powder, the silicon carbide powder 120 with such a smaller particle size is relatively easier to sublime, which can avoid too slow sublimation that seriously affects the crystal growth rate. Moreover, the distance between the top surface of the filled silicon carbide powder 120 and the growth surface of a seed crystal 110 is 10-50 mm, and this distance range is also smaller than the distance between conventional silicon carbide powder and a seed crystal, which can further avoid an excessively low crystal growth rate.

[0037] Step S200: fill a furnace body 500 with argon. The argon filled in the furnace body 500 can enable the heating structure 400 to heat the metal bath material 210 and the crucible 100 more uniformly. Meanwhile, argon increases the air pressure in the furnace body 500, thereby inhibiting gasification of liquid metal 220, especially when the metal bath material 210 is copper metal. Since the boiling point of copper metal is close to the crystal growth environment temperature, its gasification is relatively severe, and the air pressure generated by filling argon can inhibit gasification of liquid copper, ensuring the stability and uniformity of heating the crucible 100.

[0038] Step S300: The heating structure 400 is started and operates at a constant power until crystal growth is complete. After the main heater 410 and auxiliary heater 420 are started, the metal bath material 210 in the metal bath chamber 202 gradually melts to form liquid metal 220. The liquid level of the liquid metal 220 is higher than the top surface of the inner protective layer 200, so as to achieve all-round coverage heating of the inner protective layer 200 and the crucible 100 by the liquid metal 220, thereby causing the silicon carbide powder 120 to gradually sublimate to form a crystal growth vapor phase. The crystal growth vapor phase flows non-directionally in the crucible 100 until it fills the crucible 100. Then, since the surface energy of the seed crystal 110 is lower than the surface energy of the silicon carbide powder 120, the crystal growth vapor phase will preferentially crystallize and grow on the seed crystal 110 until growth is complete. Because the entire crystal growth process has no or a very small temperature gradient, and the heating structure 400 (main heater 410 and auxiliary heater 420) can operate at a constant power with minimal temperature variation, the thermal stress on the crystal is greatly reduced, effectively minimizing edge chipping and cracking caused by thermal stress. This is especially true when growing large-sized crystals, where such defects are significantly reduced, resulting in high-quality crystals.

[0039] The above description is merely a specific embodiment of the present invention, but the scope of protection of the present invention is not limited thereto. Any variations or substitutions that can be easily conceived by those skilled in the art within the scope of the technology disclosed in the present invention should be included within the scope of protection of the present invention.

Claims

1. A constant-temperature metal bath crystal growth apparatus, characterized in that, include: A crucible (100) is provided with a seed crystal (110) at the top and the middle and lower part of the crucible (100) is used to fill silicon carbide powder (120). An inner protective layer (200) is wrapped around the outer wall of the crucible (100); An outer protective layer (300) surrounds the outer side of the inner protective layer (200) and together with the inner protective layer (200) forms a metal bath cavity (202), which is filled with metal bath material (210). A heating structure (400) is disposed outside the outer protective layer (300) and is used to heat the metal bath material (210) so that the metal bath material (210) melts to form liquid metal (220) with a liquid level higher than the top wall of the inner protective layer (200). The heating structure (400) includes a main heater (410) which can simultaneously heat the peripheral wall, top wall and bottom wall of the outer protective layer (300). The furnace body (500) is used to house the crucible (100), the inner protective layer (200), the outer protective layer (300), and the heating structure (400).

2. The isothermal metal bath crystal growth apparatus according to claim 1, characterized in that, The metal bath material (210) is one of copper, platinum, gold, and gold-palladium alloy.

3. The isothermal metal bath crystal growth apparatus according to claim 1, characterized in that, The inner protective layer (200) and the outer protective layer (300) are both made of high-temperature inert metals with melting points higher than the crystal growth environment temperature.

4. The isothermal metal bath crystal growth apparatus according to claim 3, characterized in that, The high-temperature resistant inert metal is tantalum.

5. The isothermal metal bath crystal growth apparatus according to claim 1, characterized in that, The heating structure (400) also includes an auxiliary heater (420) that surrounds the main heater (410).

6. A method for growing crystals in a constant-temperature metal bath, based on the constant-temperature metal bath crystal growth apparatus according to any one of claims 1-5, characterized in that, include: After filling the crucible (100) with silicon carbide powder (120), the crucible (100) is placed inside the inner protective layer (200); The heating structure (400) is controlled to start and operate at a constant power.

7. The isothermal metal bath crystal growth method according to claim 6, characterized in that, The procedure further includes, prior to the step of controlling the activation of the heating structure (400): Argon gas is introduced into the furnace body (500).

8. The isothermal metal bath crystal growth method according to claim 6, characterized in that, The particle size of the silicon carbide powder (120) being filled is 0.1-1 mm.

9. The isothermal metal bath crystal growth method according to claim 6, characterized in that, The distance between the top surface of the filled silicon carbide powder (120) and the growth surface of the seed crystal (110) is 10-50 mm.

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