Method for growing gallium oxide crystal by cone-die czochralski method

Abstract

The invention provides a method for growing gallium oxide crystals by a cone die czochralski method. The method comprises the following steps: melting gallium oxide powder in an iridium crucible to form a gallium oxide melt, and lowering seed crystals through a lifting rod to carry out the steps of seeding, seeding, shouldering, isomerizing and ending, before the step of seeding, the method also comprises the following steps: connecting an inverted conical funnel below the lifting rod; the tip of the funnel faces downwards, and the diameter of an opening of the tip is slightly smaller than that of the seed crystal; descending the lifting rod until the tip end of the funnel is in contact with the surface of the gallium oxide melt, and pushing impurities on the surface of the gallium oxide melt to the outer side of the funnel from the center; and continuously descending the lifting rod, so that the seed crystal is in contact with the surface of the gallium oxide melt in the funnel. Impurities on the surface of the melt are effectively cleaned in the seeding stage, so that the seed crystal can be in contact with the clean melt, and the success rate of the gallium oxide czochralski method process is effectively improved.

Description

Technical Field

[0001] This application belongs to the field of functional crystal material preparation technology, and in particular relates to a method for growing gallium oxide crystals using the cone-mold Czochralski method. Background Technology

[0002] The Czochralski (CZ) method is a widely used technique for growing functional and semiconductor crystals. It involves heating and melting the raw material in a crucible, introducing a seed crystal onto the melt surface, and then, under controlled temperature, pulling speed, and rotational speed, allowing the atoms or ions to rearrange continuously at the interface between the seed crystal and the melt, gradually solidifying to form a single crystal. Compared to other methods, crystals obtained by the Czochralski method have advantages such as high transparency, low dislocation density, and excellent surface integrity. Therefore, it is widely used in the research and industrialization of functional crystals (such as LiTaO3 and LiNbO3) and ultra-wide bandgap semiconductors (such as β-Ga2O3).

[0003] When growing gallium oxide (Ga₂O₃) single crystals using the Czochralski method, a high-melting-point metal crucible, such as an iridium (Ir) crucible, is typically required for melting due to Ga₂O₃'s high melting point of approximately 1800°C. However, in a high-temperature, oxygen-containing atmosphere, the Ir crucible is prone to oxidation, forming IrO₂. The solid IrO₂ floats on the melt surface, forming an impurity layer. Furthermore, metallic gallium decomposed from the melt reacts with the Ir crucible, generating Ir-Ga alloy impurities, which also float on the melt surface. These impurities severely affect the stable contact between the seed crystal and the melt, leading to seeding failure or unstable nucleation. For example, discontinuous nucleation can result in a multi-domain structure in the crystal; surface impurities can adhere to the crystal's outer wall, affecting its appearance and cleanliness; or they can increase the density of defects such as dislocations and voids, ultimately reducing the crystal's electrical and optical properties.

[0004] Therefore, the key issue is how to effectively clean the impurities on the surface of the melt in the next stage so that the seed crystal can come into contact with the clean melt, thereby improving the success rate of the gallium oxide Czochralski process. Summary of the Invention

[0005] The technical problem to be solved by this application is to provide a method for growing gallium oxide crystals using the conical die Czochralski method, so as to effectively clean impurities on the surface of the melt in the next seeding stage, so that the seed crystal can come into contact with the clean melt, thereby improving the success rate of the gallium oxide Czochralski process.

[0006] To achieve the aforementioned beneficial effects, this application provides a method for growing gallium oxide crystals using the Czochralski method with a cone mold, comprising: melting gallium oxide powder in an iridium crucible to form a gallium oxide melt, and lowering a seed crystal using a lifting rod for seeding, crystal pulling, shoulder formation, equal diameter setting, and finishing; characterized in that, before the seeding step, the method further comprises: A cone-shaped funnel is connected below the lifting rod; the tip of the funnel points downward and the diameter of the tip opening is slightly smaller than the diameter of the seed crystal; Lower the lifting rod until the tip of the funnel contacts the surface of the gallium oxide melt, pushing the impurities on its surface from the center to the outside of the funnel; Continue to lower the lifting rod so that the seed crystal comes into contact with the surface of the gallium oxide melt in the funnel.

[0007] This solution adds a step of using an inverted conical funnel to push away impurities before the seeding step. By having the tip of the inverted conical funnel contact the surface of the melt first, the floating impurities are pushed from the center to the outside, thereby forming a clean area free of impurities below the funnel. This allows the seed crystal to contact the clean melt, ensuring that the seed crystal achieves stable nucleation in the clean melt. This solves the problem of seeding failure or unstable nucleation caused by impurity interference and improves crystal quality.

[0008] As an improvement to the technical solution of this application, the funnel is made of platinum-rhodium alloy.

[0009] As an improvement to the technical solution of this application, the tip of the funnel is located 2-5 mm from the front end of the seed crystal.

[0010] As an improvement to the technical solution of this application, the lowering of the lifting rod includes: lowering the lifting rod at a speed of 1.5-2 mm / min.

[0011] Furthermore, lowering the lifting rod includes lowering the lifting rod at a speed of 2 mm / min.

[0012] As an improvement to the technical solution of this application, the purity of the gallium oxide powder is not less than 5N.

[0013] As an improvement to the technical solution of this application, the step of melting gallium oxide powder in an iridium crucible to form gallium oxide melt is carried out in a mixed atmosphere of oxygen and argon.

[0014] The technical advantages of this application are as follows: This application adds a step of using an inverted conical funnel to push away impurities before the seeding step. By having the tip of the inverted conical funnel contact the surface of the melt first, the floating impurities are pushed from the center to the outside, thereby forming a clean area free of impurities below the funnel. This allows the seed crystal to contact the clean melt, ensuring that the seed crystal achieves stable nucleation in the clean melt. This solves the problem of seeding failure or unstable nucleation caused by impurity interference and improves crystal quality.

[0015] This application achieves a balance between efficiently isolating impurities and maintaining melt stability by limiting the descent speed to 1.5-2 mm / min, particularly preferably 2 mm / min. This is a result of kinetic optimization, which can generate sufficient hydrodynamic force to effectively push away impurities without violently disturbing the melt surface due to excessive speed and destroying the stability of the solid-liquid interface. This improves the structural integrity and appearance quality of the crystal. Attached Figure Description

[0016] Figure 1 This is a schematic diagram of the apparatus used in a method for growing gallium oxide crystals using the Czochralski method according to an embodiment of this application.

[0017] Explanation of reference numerals in the attached figures: 1. Iridium crucible; 2. Gallium oxide melt; 3. Funnel; 4. Seed crystal; 5. Lifting rod; 6. Impurities. Detailed Implementation

[0018] The following detailed description, in conjunction with specific embodiments, illustrates a method for growing gallium oxide crystals using the Czochralski method with a tapered mold, to enable those skilled in the art to more clearly understand the technical solution and implementation effects of this application. The following embodiments are merely illustrative of the technical solution of this application and are therefore intended to limit the scope of protection of this application.

[0019] This application provides a method for growing gallium oxide crystals using the cone-mold Czochralski method, comprising: Gallium oxide powder is melted in an iridium crucible to form gallium oxide melt. A seed crystal is then lowered using a lifting rod to perform seeding, crystal pulling, shoulder formation, equal diameter setting, and finishing steps. Those skilled in the art will understand that in the process of growing gallium oxide crystals using the Czochralski method, the following steps are: The seeding step involves lowering the pull rod to allow the seed crystal to slowly contact and immerse itself in the melt surface, establishing a stable solid-liquid interface and allowing the melt to solidify and nucleate on the seed crystal; the crystal-growing step involves rapidly pulling the crystal or reducing its diameter after successful contact with the melt to grow a narrow-necked crystal, eliminating any dislocations and defects that may exist in the seed crystal and preventing their downward propagation; the shoulder-forming step involves gradually adjusting the pulling speed and temperature field after crystal-growing to gradually expand the crystal diameter from the narrow neck of the seed crystal to the predetermined target diameter; the constant-diameter step involves controlling the pulling speed, crucible rotation speed, and furnace temperature after the crystal diameter reaches the target size to allow the crystal to grow continuously with a constant diameter, obtaining the main crystal segment; and the finishing step involves gradually reducing the crystal diameter until it separates from the melt after the constant-diameter growth reaches the predetermined length, to reduce thermal stress and prevent crystal cracking.

[0020] Preferably, the gallium oxide powder has a purity of not less than 5N. Using high-purity raw materials can reduce impurity elements introduced by the raw materials themselves at the source. Commonly used high-purity gallium oxide powder purity grades include 5N (99.999%) and above.

[0021] In one implementation, the step of melting gallium oxide powder in an iridium crucible to form a gallium oxide melt is carried out in a mixed atmosphere of oxygen and argon. Specifically, at high temperatures, gallium oxide decomposes and releases oxygen, causing the melt composition to deviate from the stoichiometric ratio and producing metallic gallium. Supplementing the atmosphere with an appropriate amount of oxygen can effectively suppress the decomposition of gallium oxide, thereby reducing Ir-Ga alloy impurities generated by the reaction of metallic gallium with the iridium crucible. Simultaneously, the inert gas argon, as the base atmosphere, can maintain stable pressure within the furnace and control the oxygen partial pressure, preventing excessively high oxygen concentrations from exacerbating the oxidation of the iridium crucible.

[0022] Before the next step mentioned above, the following steps are also included: S1. Connect an inverted conical funnel below the lifting rod; Specifically, the funnel's tip points downwards, and the diameter of its opening is slightly smaller than the diameter of the seed crystal. (Refer to...) Figure 1 As shown, the inverted conical funnel is connected to the lower end of the lifting rod via a connecting part, and its installation position is directly below the seed crystal. This connecting part can be a support rod or wire made of the same / similar material as the funnel. The tip of the funnel faces the gallium oxide melt inside the crucible, and the conical structure of the funnel facilitates the generation of effective radial thrust against impurities on the surface of the melt during its descent.

[0023] Preferably, the funnel is made of a platinum-rhodium alloy. Since the funnel needs to directly contact the gallium oxide melt at approximately 1800°C, and the working environment is an oxygen-containing atmosphere, the high-temperature stability and corrosion resistance of its material are extremely important. Platinum-rhodium alloys possess excellent chemical inertness, oxidation resistance, and high-temperature strength at high temperatures. Unlike iridium crucibles, they will not oxidize themselves or react with the melt to generate new contamination, thus ensuring the cleanliness and durability of the cleaning tool and avoiding secondary contamination of the melt. More preferably, the platinum-rhodium alloy contains 30% rhodium by mass.

[0024] Preferably, the thickness of the funnel is 1-2 mm.

[0025] S2. Lower the lifting rod until the tip of the funnel contacts the surface of the gallium oxide melt and pushes the impurities on its surface from the center to the outside of the funnel. Specifically, after the melt is melted and held at a certain temperature, the lifting rod is lowered at a preset speed. When the tip of the funnel first contacts the surface of the melt, its conical outer wall begins to push away impurities such as IrO2 solid particles and Ir-Ga alloys floating in the central region of the melt, towards the outside, i.e., towards the crucible wall. As the funnel continues to immerse in the melt, a clean, circular melt surface area free of floating debris is formed inside the funnel, creating an ideal contact environment for the subsequent descent of the seed crystal.

[0026] In one implementation, the tip of the funnel is located 2-5 mm from the front end of the seed crystal. This distance ensures that during the descent of the lifting rod, the tip of the funnel has sufficient lead time to contact the melt before the seed crystal, allowing necessary time and space to push away impurities. Simultaneously, this distance is also close enough to prevent impurities that have been pushed away from flowing back to the central clean area due to melt surface tension or thermal convection after the funnel has completed its cleaning process but before the seed crystal contacts the melt, thus ensuring that the seed crystal can accurately land on the clean melt surface.

[0027] In one implementation, lowering the lifting rod includes lowering it at a speed of 1.5-2 mm / min. This speed range is an optimized balance point that efficiently pushes away impurities while maximizing the stability of the melt surface. Preferably, the lifting rod is lowered at a speed of 2 mm / min.

[0028] S3. Continue to lower the lifting rod so that the seed crystal comes into contact with the surface of the gallium oxide melt in the funnel.

[0029] Specifically, after a clean melt surface is formed in the funnel 3 in step S2, the lifting rod 5 continues to descend, allowing the seed crystal 4 located above the funnel to smoothly contact the clean gallium oxide melt 2 surface inside the funnel. Because there are no impurities interfering in the contact area, stable and uniform nucleation can be achieved, laying a solid foundation for the subsequent growth of high-quality single crystals.

[0030] The present invention will be described below with reference to specific embodiments and comparative examples. In the following embodiments, the heating equipment used is a standard Czochralski crystal growth furnace, and the seed crystal has a diameter of 20 mm. <010> For the β-Ga2O3 seed crystal with specific crystal orientation, the steps of lowering the seed crystal using a lifting rod for seeding, crystal pulling, shoulder formation, equal diameter setting, and finishing can be performed sequentially according to the conventional Czochralski process. The following is merely an example of a conventional Czochralski process. It should be noted that the following embodiments are only used to illustrate the present invention in detail and do not limit the scope of protection of the invention in any way.

[0031] Example 1 Gallium oxide powder with a purity of 5N was placed in an iridium crucible and heated to 1820°C in an oxygen / argon mixed atmosphere (where the partial pressure ratio of oxygen and argon was 1:5). The temperature was held until it was completely melted to form a uniform gallium oxide melt. At this time, IrO2 solid particles and Ir-Ga alloy impurities were observed floating on the surface of the melt. An inverted conical funnel made of Pt-30%Rh alloy (platinum-rhodium alloy) is fixed to the lower end of the lifting rod, with the tip of the funnel facing down and located 3mm from the front end of the seed crystal; the funnel is 1mm thick and has a bottom diameter of 18mm. The lifting rod is lowered at a speed of 2 mm / min. After the tip of the funnel contacts the surface of the melt, it continues to descend, using its conical structure to push the IrO2 solid particles and Ir-Ga alloy impurities in the center of the melt to the outside of the funnel. After a clean melt region with a diameter of about 18 mm is formed below the funnel, the descent continues, allowing the seed crystal to smoothly enter the clean region and contact the melt surface, thus completing the seeding process.

[0032] Subsequently, the necking crystal growth process was initiated using conventional Czochralski (CZ) technology. The seed crystal rotation speed was controlled at 3 rpm. When the seed crystal surface began to slightly melt and the necking narrowed to 1-2 mm, shoulder growth was initiated at a pulling speed of 2 mm / h. After entering the constant diameter growth stage, the pulling speed was adjusted to 2 mm / h and the rotation speed to 10 rpm. Once the crystal reached 70 mm, the furnace temperature was lowered to room temperature to complete the growth, yielding a β-Ga₂O₃ single crystal. The crystal surface was smooth and transparent, with no obvious impurities or grain boundaries observed.

[0033] Comparative Example 1 In this embodiment, the process is basically the same as in Example 1, but the descent speed is adjusted to 1 mm / min. A β-Ga₂O₃ crystal with a uniform diameter of 70 mm is obtained. The crystal transparency is similar to that of Example 1, but a small number of particles are found adhering to the crystal sidewalls in some areas, and the grain boundaries are relatively clear in certain regions.

[0034] Comparative Example 2 In this embodiment, the process is basically the same as in Embodiment 1, but the descent speed is adjusted to 3 mm / min. A β-Ga2O3 crystal with a length of 70 mm is obtained. The transparency of this crystal is significantly reduced, obvious impurities are visible on the surface, spiral growth traces are also present in the constant diameter region, and the growth interface has a concave shape, resulting in crystal distortion and stress accumulation.

[0035] Experimental conclusions Comparing the results of Example 1 and Comparative Examples 1-2, it can be seen that this application can effectively improve the success rate of seed nucleation and reduce the probability of nucleation failure and grain boundary formation caused by impurities. Furthermore, by introducing an inverted conical funnel to clean the melt surface before seeding, as shown in Example 1, this invention can obtain high-quality β-Ga2O3 single crystals with a smooth, transparent surface, no obvious impurities, and no grain boundaries.

[0036] A comparison of Example 1 with Comparative Examples 1 and 2 clearly shows that the descent speed has a decisive influence on the final crystal quality. Controlling the funnel descent speed within the preferred range of 1.5-2 mm / min (such as 2 mm / min in Example 1) yields the best technical effect, namely, efficiently removing impurities from the seed region without disturbing the melt stability, thereby obtaining a high-quality gallium oxide single crystal with a smooth surface and low internal defect density. When the descent speed is too slow or too fast, the desired technical effect cannot be achieved. This fully demonstrates that the technical solution and parameter range defined in this invention are necessary and effective in solving the background technical problems.

[0037] In Example 1, a descent speed of 2 mm / min yielded the most ideal results. This speed effectively pushed impurities away from the central region, forming a stable clean window, without causing excessive disturbance to the melt surface, ensuring a stable solid-liquid interface and ultimately obtaining a high-quality single crystal. In Comparative Example 1, a descent speed of 1 mm / min, while achieving a cleaning effect, resulted in a small amount of particle adhesion and localized grain boundaries on the crystal sidewalls. This indicates that the excessively slow speed leads to insufficient impurity removal efficiency. During the funnel descent, the surface tension or thermal convection effect of the melt itself may allow some of the pushed-away impurities sufficient time to flow back to the edge of the clean zone and be entrained in the crystal during subsequent growth, thus affecting crystal quality. In Comparative Example 2, an excessively fast descent speed of 3 mm / min severely damaged the crystal quality. The crystal transparency was significantly reduced, with obvious impurity adhesion on the surface, and spiral growth marks and interface depressions appeared. This clearly demonstrates that an excessively fast descent speed causes severe disturbance to the melt surface, disrupting the stable thermal and concentration fields required for growth. This disturbance can not only entrain impurities deep into the melt, affecting the entire growth process, but more seriously, it disrupts the smoothness of the solid-liquid interface, leading to serious crystal defects such as spiral growth, and ultimately causing a decline in crystal quality.

[0038] In summary, this invention solves the key technical bottleneck in the Czochralski method of gallium oxide growth by introducing an inverted conical funnel and supplementing it with optimized process parameters, with significant results.

[0039] Finally, it should be noted that: unless otherwise defined, all technical and scientific terms used herein have the same meaning as commonly understood by one of ordinary skill in the art to which this application belongs; the terminology used herein is for the purpose of describing particular embodiments only and is not intended to limit this application; the terms "comprising" and "having," and any variations thereof, in the specification, claims, and foregoing description of the drawings of this application are intended to cover non-exclusive inclusion; in the description of embodiments of this application, "a plurality of" means two or more, unless otherwise expressly and specifically defined. The reference to "embodiment" herein means that a particular feature, structure, or characteristic described in connection with an embodiment may be included in at least one embodiment of this application. The appearance of this phrase in various places in the specification does not necessarily refer to the same embodiment, nor is it a separate or alternative embodiment mutually exclusive with other embodiments.

[0040] The above embodiments are only used to illustrate the technical solutions of this application, and are not intended to limit them. Although this application has been described in detail with reference to the foregoing embodiments, those skilled in the art should understand that modifications can still be made to the technical solutions described in the foregoing embodiments, or equivalent substitutions can be made to some or all of the technical features therein. Such modifications or substitutions do not cause the essence of the corresponding technical solutions to deviate from the scope of the technical solutions of the embodiments of this application.

Claims

1. A method for growing gallium oxide crystals using the cone-mold Czochralski method, comprising: The process involves melting gallium oxide powder in an iridium crucible to form a gallium oxide melt, and then lowering a seed crystal using a lifting rod to perform seeding, crystal pulling, shoulder formation, equal diameter setting, and finishing steps; characterized in that, prior to the seeding step, the process further includes: A cone-shaped funnel is connected below the lifting rod; the tip of the funnel points downward and the diameter of the tip opening is slightly smaller than the diameter of the seed crystal; Lower the lifting rod until the tip of the funnel contacts the surface of the gallium oxide melt, pushing the impurities on its surface from the center to the outside of the funnel; Continue to lower the lifting rod so that the seed crystal comes into contact with the surface of the gallium oxide melt in the funnel.

2. The method as described in claim 1, characterized in that, The funnel is made of platinum-rhodium alloy.

3. The method as described in claim 1, characterized in that, The tip of the funnel is located 2-5 mm from the front end of the seed crystal.

4. The method as described in claim 1, characterized in that, The lowering of the lifting rod includes lowering the lifting rod at a speed of 1.5-2 mm / min.

5. The method as described in claim 1 or 4, characterized in that, The descent of the lifting rod includes lowering the lifting rod at a speed of 2 mm / min.

6. The method as described in claim 1, characterized in that, The purity of the gallium oxide powder is not less than 5N.

7. The method as described in claim 1, characterized in that, The step of melting gallium oxide powder in an iridium crucible to form gallium oxide melt is carried out in a mixed atmosphere of oxygen and argon.

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