Gallium oxide single crystal preparation method

Abstract

The invention is applicable to the technical field of semiconductor materials, and provides a gallium oxide single crystal preparation method which comprises the following steps: cutting a gallium oxide seed crystal into a cuboid, and processing the bottom of the cuboid gallium oxide seed crystal into a wedge shape to obtain a first gallium oxide seed crystal; sequentially carrying out annealing and surface treatment on the first gallium oxide seed crystal to obtain a second gallium oxide seed crystal; and during seeding, lowering the lower part of the second gallium oxide seed crystal to be in contact with the melt, and then sequentially carrying out lifting, shouldering, diameter equalizing, ending and cooling procedures to obtain the gallium oxide single crystal. The quality of gallium oxide crystals is improved, the defect concentration is reduced, and the risk of polycrystal is reduced.

Description

Technical Field

[0001] The present application belongs to the field of semiconductor material technology, and in particular to a method for preparing a gallium oxide single crystal. Background Art

[0002] As the size of gallium oxide single crystals increases, the size of gallium oxide seed crystals also increases, which makes the influence of gallium oxide seed crystal inheritance on crystal quality and defect concentration more prominent. In order to obtain high-quality and low-defect gallium oxide single crystals, high-quality gallium oxide seed crystals must be obtained first. In addition, as the size of gallium oxide single crystals increases, the volatilization problem of gallium oxide raw materials becomes more and more serious. The volatilization rate of growing 4-inch gallium oxide is more than 10 times that of growing 2-inch gallium oxide. The volatilization rate will continue to increase with the increase of temperature, which means that in the necking process, the problem of volatile adhesion will become more and more serious. These volatiles not only affect observation, but are also very likely to become polycrystalline nucleation points, greatly reducing the single crystal rate. Summary of the invention

[0003] The embodiments of the present application provide a method for preparing a gallium oxide single crystal to improve the quality of gallium oxide crystals, reduce defect concentration, and reduce the risk of polycrystalline.

[0004] This application is implemented through the following technical solutions: In a first aspect, an embodiment of the present application provides a method for preparing a gallium oxide single crystal, comprising: cutting the gallium oxide seed crystal into a rectangular parallelepiped, and processing the bottom of the rectangular parallelepiped gallium oxide seed crystal into a wedge shape to obtain a first gallium oxide seed crystal; annealing and surface treating the first gallium oxide seed crystal in sequence to obtain a second gallium oxide seed crystal; During seeding, the lower part of the second gallium oxide seed crystal is lowered to contact with the melt, and then the pulling, shouldering, equalizing, finishing and cooling processes are carried out in sequence to obtain a gallium oxide single crystal.

[0005] In combination with the first aspect, in some possible implementations, the ratio of the area of ​​the lower end surface of the wedge to the area of ​​the upper end surface ranges from 30% to 80%; and the angle between the two inclined surfaces of the wedge and the upper end surface ranges from 20° to 60°.

[0006] In combination with the first aspect, in some possible implementations, lowering the lower portion of the second gallium oxide seed crystal to contact with the melt includes: The lower portion of the second gallium oxide seed crystal is lowered to contact the melt and melted back to the first preset length.

[0007] In combination with the first aspect, in some possible implementations, annealing and surface treating the first gallium oxide seed crystal in sequence to obtain the second gallium oxide seed crystal includes: Placing the first gallium oxide seed crystal flat on the sapphire sheet, and placing the sapphire sheet and the first gallium oxide seed crystal as a whole into an annealing furnace for annealing; The annealed first gallium oxide seed crystal is placed in an acidic solution or an alkaline solution for surface etching to obtain a second gallium oxide seed crystal.

[0008] In combination with the first aspect, in some possible implementations, the annealing atmosphere in the annealing furnace is argon, nitrogen or other inert gases, the annealing temperature is 1200° C. to 1600° C., and the annealing time is 0.5 h to 5 h.

[0009] In combination with the first aspect, in some possible implementations, the mass concentration of the acidic solution is 20% to 80%, and the acidic solution is a phosphoric acid solution, a sulfuric acid solution or aqua regia.

[0010] In combination with the first aspect, in some possible implementations, the mass concentration of the alkaline solution is 20% to 80%, and the acidic solution is sodium hydroxide or potassium hydroxide.

[0011] In combination with the first aspect, in some possible implementations, the surface roughness of each face of the rectangular parallelepiped gallium oxide seed crystal is less than or equal to 1 nm.

[0012] In combination with the first aspect, in some possible implementations, the steps of pulling, shoulder release, equal diameter, finishing and cooling are sequentially performed to obtain a gallium oxide single crystal, including: During the pulling process, a constant temperature condition is maintained so that the grown gallium oxide does not shrink or expand and then stops the pulling process after reaching a second preset length; After that, the shoulder release, diameter equalization, finishing and cooling processes are carried out in sequence to obtain a gallium oxide single crystal.

[0013] In combination with the first aspect, in some possible implementations, cutting a gallium oxide seed crystal into a rectangular parallelepiped, and processing the bottom of the rectangular parallelepiped gallium oxide seed crystal into a wedge shape to obtain a first gallium oxide seed crystal includes: The gallium oxide seed crystal is cut into a rectangular parallelepiped by a laser cutting machine, and the bottom of the rectangular parallelepiped gallium oxide seed crystal is processed into a wedge shape to obtain a first gallium oxide seed crystal.

[0014] Compared with the prior art, the embodiments of the present invention have the following beneficial effects: The present application processes the bottom of the seed crystal into a wedge shape, thereby replacing the necking process to reduce defect inheritance and improving the single crystal rate. Since the necking process is not required, the applicability of this solution is also wider, and it can be applied to various growth methods such as the guided mold method, the Czochralski method, and the Bridgman method. The seed crystal prepared by this method is used to grow gallium oxide single crystals, and the defect density of the grown gallium oxide single crystals can be reduced by 1 to 2 orders of magnitude.

[0015] It is to be understood that the foregoing general description and the following detailed description are exemplary and explanatory only and are not restrictive of the present specification. BRIEF DESCRIPTION OF THE DRAWINGS

[0016] In order to more clearly illustrate the technical solutions in the embodiments of the present application, the drawings required for use in the embodiments or the description of the prior art will be briefly introduced below. Obviously, the drawings described below are only some embodiments of the present application. For ordinary technicians in this field, other drawings can be obtained based on these drawings without paying creative labor.

[0017] Figure 1 It is a schematic diagram of a process for preparing a gallium oxide single crystal provided in one embodiment of the present application; Figure 2 This is a schematic diagram of a rectangular gallium oxide seed crystal provided in an embodiment of the present application; Figure 3 It is a schematic diagram of a first gallium oxide seed crystal provided in an embodiment of the present application. DETAILED DESCRIPTION

[0018] In the following description, specific details such as specific system structures, technologies, etc. are provided for the purpose of illustration rather than limitation, so as to provide a thorough understanding of the embodiments of the present application. However, it should be clear to those skilled in the art that the present application may also be implemented in other embodiments without these specific details. In other cases, detailed descriptions of well-known systems, devices, circuits, and methods are omitted to prevent unnecessary details from obstructing the description of the present application.

[0019] It should be understood that when used in the present specification and the appended claims, the term "comprising" indicates the presence of described features, wholes, steps, operations, elements and / or components, but does not exclude the presence or addition of one or more other features, wholes, steps, operations, elements, components and / or combinations thereof.

[0020] It should also be understood that the term “and / or” used in the specification and appended claims refers to any and all possible combinations of one or more of the associated listed items, and includes these combinations.

[0021] As used in the specification and appended claims of this application, the term "if" can be interpreted as "when" or "uponce" or "in response to determining" or "in response to detecting", depending on the context. Similarly, the phrase "if it is determined" or "if [described condition or event] is detected" can be interpreted as meaning "uponce it is determined" or "in response to determining" or "uponce [described condition or event] is detected" or "in response to detecting [described condition or event]", depending on the context.

[0022] In addition, in the description of the present application specification and the appended claims, the terms "first", "second", "third", etc. are only used to distinguish the descriptions and cannot be understood as indicating or implying relative importance.

[0023] References to "one embodiment" or "some embodiments" etc. described in the specification of this application mean that one or more embodiments of the present application include specific features, structures or characteristics described in conjunction with the embodiment. Therefore, the statements "in one embodiment", "in some embodiments", "in some other embodiments", "in some other embodiments", etc. that appear in different places in this specification do not necessarily refer to the same embodiment, but mean "one or more but not all embodiments", unless otherwise specifically emphasized in other ways. The terms "including", "comprising", "having" and their variations all mean "including but not limited to", unless otherwise specifically emphasized in other ways.

[0024] Gallium oxide single crystal is a new type of ultra-wide bandgap semiconductor material, with a theoretical breakdown field strength of up to 8MV / cm, and a Baliga figure of merit that is more than ten times that of SiC and GaN. In addition, gallium oxide materials are resistant to high temperatures and have stable chemical properties. They have great application advantages in the field of high-voltage and high-power power electronic devices, because gallium oxide-based power devices can not only withstand high voltages but also have higher power conversion efficiency and lower conduction losses. In addition, gallium oxide single crystals can be grown using melt methods, including guided mode method, Czochralski method, Bridgman method, etc., with the advantages of fast growth rate and low cost, and are suitable for engineering. Therefore, gallium oxide single crystals have become a hot material leading the renewal of electronic information engineering.

[0025] The main application direction of gallium oxide single crystals is high-voltage and high-power power electronic devices, which puts high demands on crystal quality and defect density. The crystal quality and defect density of gallium oxide single crystals are mainly affected by two aspects: one is seed crystal inheritance, and the other is growth process and thermal stress. At present, the seed crystal inheritance problem is mainly solved by necking process, which is mainly achieved by increasing temperature and pulling speed. However, gallium oxide raw materials have serious volatile decomposition at high temperature, which will cause volatiles to adhere to the surface of seed crystals, which is very easy to cause polycrystalline in the subsequent growth process. Therefore, although the necking process can improve the crystal quality and reduce the defect concentration, it also increases the risk of polycrystalline.

[0026] The present application provides a method for preparing a gallium oxide single crystal. Figure 1 is a schematic diagram of a process for preparing a gallium oxide single crystal provided in an embodiment of the present application, with reference to Figure 1 , the method is described in detail as follows: Step 101 : cutting a gallium oxide seed crystal into a rectangular parallelepiped, and processing the bottom of the rectangular parallelepiped gallium oxide seed crystal into a wedge shape to obtain a first gallium oxide seed crystal.

[0027] For example, Figure 2 As shown, the surface roughness of each face of the rectangular gallium oxide seed crystal is less than or equal to 1 nm.

[0028] In some specific embodiments, after the gallium oxide seed crystal is cut into a cuboid, chemical mechanical polishing is performed to make the surface roughness of each face of the cuboid gallium oxide seed crystal less than or equal to 1 nm. Chemical mechanical polishing can remove cutting damage and improve the surface quality of the seed crystal.

[0029] For example, Figure 3 As shown, the ratio of the area of ​​the lower end surface of the wedge to the area of ​​the upper end surface ranges from 30% to 80%; and the angle between the two inclined surfaces of the wedge and the upper end surface ranges from 20° to 60°.

[0030] In some specific embodiments, the bottom of the seed crystal is processed into a wedge shape for the following reasons: (1) By controlling the area of ​​the lower end face, the mechanical strength of the seed crystal is maintained to ensure that it will not break during the pulling process. (2) The contact area between the seed crystal and the melt is reduced during seeding to reduce thermal shock. (3) The wedge shape can allow defects such as dislocations in the seed crystal to terminate on the inclined surface, thereby reducing the inheritance of defects in the seed crystal. (4) By controlling the angle of the wedge inclined surface and coordinating with the equal-diameter growth process during seeding, defects such as dislocations in the seed crystal can be further discharged and terminated on the surface.

[0031] Exemplarily, cutting a gallium oxide seed crystal into a cuboid and processing the bottom of the cuboid gallium oxide seed crystal into a wedge shape to obtain a first gallium oxide seed crystal includes: The gallium oxide seed crystal is cut into a rectangular parallelepiped by a laser cutting machine, and the bottom of the rectangular parallelepiped gallium oxide seed crystal is processed into a wedge shape to obtain a first gallium oxide seed crystal.

[0032] Step 102: annealing and surface treating the first gallium oxide seed crystal in sequence to obtain a second gallium oxide seed crystal.

[0033] Exemplarily, step 102 may include: Placing the first gallium oxide seed crystal flat on the sapphire sheet, and placing the sapphire sheet and the first gallium oxide seed crystal as a whole into an annealing furnace for annealing; The annealed first gallium oxide seed crystal is placed in an acidic solution or an alkaline solution for surface etching to obtain a second gallium oxide seed crystal.

[0034] Exemplarily, the annealing atmosphere in the annealing furnace is argon, nitrogen or other inert gases, the annealing temperature is 1200° C. to 1600° C., and the annealing time is 0.5 h to 5 h.

[0035] Specifically, the seed crystal annealing is to decompose the surface of the gallium oxide seed crystal and remove the processing damage layer. The decomposition temperature of gallium oxide is 1200° C., and to remove processing stress, eliminate lattice distortion, and improve the quality of the seed crystal.

[0036] Exemplarily, the mass concentration of the acidic solution is 20% to 80%, and the acidic solution is a phosphoric acid solution, a sulfuric acid solution or aqua regia.

[0037] Exemplarily, the mass concentration of the alkaline solution is 20% to 80%, and the acidic solution is sodium hydroxide or potassium hydroxide.

[0038] Specifically, the surface treatment of the seed crystal is mainly because the gallium oxide seed crystal will have surface or sub-surface damage after processing. These damages will also cause defects during the growth process. The above damages are removed by reacting the seed crystal with acid or alkali, thereby improving the quality of the seed crystal. The surface treatment of the seed crystal can not only remove the damage, but also screen the seed crystal. After corrosion, the concentration of defects such as dislocations in the upper and lower end faces of the seed crystal can be observed through a differential interference microscope, and the change in the number of defects can be intuitively detected without crystal growth.

[0039] Step 103, during seeding, the lower portion of the second gallium oxide seed crystal is lowered to contact with the melt, and then the pulling, shouldering, equalizing, finishing and cooling processes are sequentially performed to obtain a gallium oxide single crystal.

[0040] Exemplarily, lowering the lower portion of the second gallium oxide seed crystal to contact the melt may include: The lower portion of the second gallium oxide seed crystal is lowered to contact the melt and melted back to the first preset length.

[0041] Exemplarily, the steps of pulling, shouldering, equalizing diameter, finishing and cooling are sequentially performed to obtain a gallium oxide single crystal, including: During the pulling process, a constant temperature condition is maintained so that the grown gallium oxide does not shrink or expand and then stops the pulling process after reaching a second preset length; After that, the shoulder release, diameter equalization, finishing and cooling processes are carried out in sequence to obtain a gallium oxide single crystal.

[0042] The above-mentioned method for preparing gallium oxide single crystals, by processing the bottom of the seed crystal into a wedge shape, replaces the necking process to reduce defect inheritance and improves the single crystal rate. Since the necking process is not required, the applicability of this scheme is also wider, and it can be applied to various growth methods such as the guided mold method, the Czochralski method, and the Bridgman method. By using the seed crystal prepared by this method to grow gallium oxide single crystals, the defect density of the grown gallium oxide single crystals can be reduced by 1 to 2 orders of magnitude.

[0043] To facilitate understanding of the solution, two specific embodiments are shown below. Specific embodiment one: Step 1: Seed crystal processing. First, a rectangular seed crystal with a length of 40 mm, a width of 5 mm, and a thickness of 5 mm is obtained by cutting, and then the surface roughness of the six faces is reduced to 0.5 nm by chemical mechanical polishing. Then, the bottom of the seed crystal is processed into a wedge shape by cutting, with the ratio of the lower end surface area to the upper end surface area being 50%, the angle of the two inclined surfaces being 40°, and the height of the wedge being 1.56 mm.

[0045] Step 2: annealing the seed crystal. The processed seed crystal is placed flat on a flat sapphire sheet, and then placed in an annealing furnace as a whole. The annealing atmosphere is argon, the annealing temperature is 1300°C, and the annealing time is 2 hours.

[0046] Step 3: Surface treatment of seed crystal: The annealed seed crystal is placed in a phosphoric acid solution with a mass concentration of 40% for surface corrosion at a temperature of 110°C for 30 minutes.

[0047] Step 4: After corrosion, the number of dislocations (the number of corrosion pits) on the upper and lower surfaces is observed to be 2.2×10 4 and 9.7×10 3 The number has been significantly reduced.

[0048] Step 5: Use the seed crystal treated as above to grow gallium oxide single crystal. When seeding, slowly lower the seed crystal to the melt contact, melt back 0.5mm, and then start pulling, keep the temperature constant, and keep the seed crystal without shrinking or expanding for 30mm, so that the defects in the seed crystal are further discharged. Compared with necking, the biggest difference of this operation is that it does not need to overheat the solid-liquid interface, so the volatilization and decomposition of gallium oxide raw materials will not become serious due to overheating of the solid-liquid interface, and the volatiles will not accumulate at the bottom of the seed crystal, which can improve the single crystal rate and achieve the purpose of reducing the defect density.

[0049] Step 6: After shoulder placement, equal diameter, finishing, and cooling, the dislocation density of the grown gallium oxide crystal is 2×103cm -2 The dislocation density of crystals grown by traditional methods is generally 5×104cm -2 . Specific embodiment 2: Step 1, seed crystal processing, firstly, a rectangular seed crystal with a length of 70 mm, a width of 10 mm, and a thickness of 10 mm is obtained by cutting, and then the surface roughness of the six faces is reduced to 0.5 nm by chemical mechanical polishing. Then, the bottom of the seed crystal is processed into a wedge shape by cutting, and the ratio of the lower end surface area to the upper end surface area is 40%, the angle of the two inclined surfaces is 30°, and the height of the wedge is 6.5 mm.

[0051] Step 2: annealing the seed crystal. Place the processed seed crystal on a flat sapphire sheet and then put the whole into an annealing furnace. The annealing atmosphere is nitrogen, the annealing temperature is 1500°C, and the annealing time is 1 hour.

[0052] Step three, surface treatment of the seed crystal, placing the annealed seed crystal in a potassium hydroxide alkaline solution with a mass concentration of 30% for surface corrosion at a temperature of 90°C for 90 minutes.

[0053] Step 4: After corrosion, the number of dislocations on the upper and lower surfaces is 8.1×10 4 and 4.2×10 3 The number has been significantly reduced.

[0054] Step 5: Use the seed crystal treated as above to grow gallium oxide single crystal. When seeding, slowly lower the seed crystal to contact the melt, melt back 1.5 mm, and then start pulling, keep the temperature constant, and keep the seed crystal from shrinking or expanding by 50 mm.

[0055] Step 6: After shoulder placement, equal diameter, finishing, and cooling, the dislocation density of the grown gallium oxide crystal is 4×103cm -2 The dislocation density of crystals grown by traditional methods is generally 5×104cm -2 .

[0056] It should be understood that the size of the serial numbers of the steps in the above embodiments does not mean the order of execution. The execution order of each process should be determined by its function and internal logic, and should not constitute any limitation on the implementation process of the embodiments of the present application.

[0057] The embodiments described above are only used to illustrate the technical solutions of the present application, rather than to limit them. Although the present application has been described in detail with reference to the aforementioned embodiments, a person skilled in the art should understand that the technical solutions described in the aforementioned embodiments may still be modified, or some of the technical features may be replaced by equivalents. Such modifications or replacements do not deviate the essence of the corresponding technical solutions from the spirit and scope of the technical solutions of the embodiments of the present application, and should all be included in the protection scope of the present application.

Claims

1. A method for preparing a gallium oxide single crystal, characterized in that: include: cutting the gallium oxide seed crystal into a rectangular parallelepiped, and processing the bottom of the rectangular parallelepiped gallium oxide seed crystal into a wedge shape to obtain a first gallium oxide seed crystal; annealing and surface treating the first gallium oxide seed crystal in sequence to obtain a second gallium oxide seed crystal; During seeding, the lower portion of the second gallium oxide seed crystal is lowered to contact the melt, and then the pulling, shouldering, equalizing, finishing and cooling processes are performed in sequence to obtain a gallium oxide single crystal.

2. The method for preparing a gallium oxide single crystal according to claim 1, characterized in that: The ratio of the area of ​​the lower end surface of the wedge to the area of ​​the upper end surface is in the range of 30% to 80%; the angle between the two inclined surfaces of the wedge and the upper end surface is in the range of 20° to 60°.

3. The method for preparing a gallium oxide single crystal according to claim 1, characterized in that: The step of lowering the lower portion of the second gallium oxide seed crystal to contact with the melt comprises: The lower portion of the second gallium oxide seed crystal is lowered to contact with the melt and is melted back to a first preset length.

4. The method for preparing a gallium oxide single crystal according to claim 1, characterized in that: The step of sequentially annealing and surface treating the first gallium oxide seed crystal to obtain a second gallium oxide seed crystal comprises: Placing the first gallium oxide seed crystal flat on the top of the sapphire sheet, and placing the sapphire sheet and the first gallium oxide seed crystal as a whole into an annealing furnace for annealing; The annealed first gallium oxide seed crystal is placed in an acidic solution or an alkaline solution for surface etching to obtain the second gallium oxide seed crystal.

5. The method for preparing a gallium oxide single crystal according to claim 4, characterized in that: The annealing atmosphere in the annealing furnace is argon, nitrogen or other inert gases, the annealing temperature is 1200° C. to 1600° C., and the annealing time is 0.5 h to 5 h.

6. The method for preparing a gallium oxide single crystal according to claim 4, characterized in that: The mass concentration of the acidic solution is 20% to 80%, and the acidic solution is a phosphoric acid solution, a sulfuric acid solution or aqua regia.

7. The method for preparing a gallium oxide single crystal according to claim 4, characterized in that: The mass concentration of the alkaline solution is 20% to 80%, and the acidic solution is sodium hydroxide or potassium hydroxide.

8. The method for preparing a gallium oxide single crystal according to claim 1, characterized in that: The surface roughness of each face of the rectangular parallelepiped gallium oxide seed crystal is less than or equal to 1 nm.

9. The method for preparing a gallium oxide single crystal according to claim 1, characterized in that: The steps of pulling, shouldering, equalizing diameter, finishing and cooling are sequentially performed to obtain a gallium oxide single crystal, including: During the pulling process, a constant temperature condition is maintained so that the grown gallium oxide does not shrink or expand and then stops the pulling process after reaching a second preset length; Then, shoulder release, equal diameter, finishing and cooling processes are carried out in sequence to obtain the gallium oxide single crystal.

10. The method for preparing a gallium oxide single crystal according to claim 1, characterized in that: The gallium oxide seed crystal is cut into a rectangular parallelepiped, and the bottom of the rectangular parallelepiped gallium oxide seed crystal is processed into a wedge shape to obtain a first gallium oxide seed crystal, comprising: The gallium oxide seed crystal is cut into a rectangular parallelepiped by a laser cutting machine, and the bottom of the rectangular parallelepiped gallium oxide seed crystal is processed into a wedge shape to obtain a first gallium oxide seed crystal.

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