Crystal preparation method

Abstract

A crystal preparation method. The method comprises: obtaining a first crystal wafer that has undergone first treatment; using the first crystal wafer that has undergone the first treatment as a first seed crystal, and growing a prefabricated crystal on the basis of a top-seeded solution growth method; carrying out second treatment on the prefabricated crystal; and using the prefabricated crystal that has undergone the second treatment as a second seed crystal, and growing a target crystal on the basis of a physical vapor transport method.

Description

A crystal preparation method Technical Field

[0001] This specification relates to the technical field of crystal preparation, and in particular to a crystal preparation method. Background Art

[0002] Silicon carbide single crystals have excellent physical and chemical properties, making them an important material for manufacturing high-frequency and high-power devices. Physical vapor transport (PVT) is a method used to grow semiconductor crystals. However, due to the lack of high-quality seed crystals, inherent defects in the seed crystals during PVT growth can extend into the epitaxial layer, resulting in a high defect density in the produced crystals.

[0003] The top seeded solution growth (TSSG) method can be used to grow high-quality silicon carbide crystals due to its low growth temperature and proximity to thermodynamic equilibrium. However, the thickness of crystals grown using the TSSG method is limited, making it unsuitable for industrial production.

[0004] Therefore, it is necessary to provide a crystal preparation method to prepare large-sized, high-quality crystals.

[0005] Summary of the Invention

[0006] One or more embodiments of the present specification provide a crystal preparation method, the method comprising: obtaining a first wafer after a first treatment; using the first wafer after the first treatment as a first seed crystal, and growing a prefabricated crystal based on a top seed crystal solution growth method; performing a second treatment on the prefabricated crystal; using the prefabricated crystal after the second treatment as a second seed crystal, and growing a target crystal based on a physical vapor transport method.

[0007] One or more embodiments of the present specification provide a method for preparing a seed crystal, the method comprising: radially cutting an off-axis seed crystal to obtain at least two seed crystals; splicing the at least two seed crystals so that the step directions of the at least two seed crystals after splicing are opposite to each other, to obtain a target seed crystal. BRIEF DESCRIPTION OF THE DRAWINGS

[0008] This specification will be further described in the form of exemplary embodiments, which will be described in detail with reference to the accompanying drawings. These embodiments are not limiting, and in these embodiments, like numbers represent like structures, wherein:

[0009] FIG1 is an exemplary flow chart of a crystal preparation method according to some embodiments of the present specification.

[0010] FIG2 is an exemplary schematic diagram of a crystal preparation method according to some embodiments of the present specification.

[0011] FIG. 3A is an exemplary schematic diagram of a first process performed on an off-axis wafer according to some embodiments of the present disclosure.

[0012] FIG. 3B is an exemplary top view of the first wafer 2 after being cut in FIG. 3A .

[0013] FIG. 3C is an exemplary schematic diagram showing that the step direction of the first seed crystal is opposite to the solution flow direction according to some embodiments of the present specification.

[0014] FIG. 4A is an exemplary cross-sectional view of a second wafer according to some embodiments of the present disclosure.

[0015] FIG. 4B is an exemplary cross-sectional view of a second wafer according to other embodiments of the present disclosure.

[0016] FIG. 4C is an exemplary cross-sectional view of a second wafer according to other embodiments of the present disclosure.

[0017] FIG. 5 is an exemplary schematic diagram of an immersion angle according to some embodiments of the present specification.

[0018] In the figure, 210 is the first wafer after the first treatment; 220 is the crystal growth layer; 230 is the crystal growth layer after the second treatment; 240 is the target crystal growth layer; 310 is the off-axis wafer; 320 is the first wafer after cutting; 321, 321-1 are the first wafer one after cutting; 322, 322-1, 322-2, 322-3 are the first wafer two after cutting; 330 is the first seed crystal; 400 is the second wafer, and 410 is the groove. DETAILED DESCRIPTION

[0019] To more clearly illustrate the technical solutions of the embodiments of this specification, the following briefly describes the drawings required for describing the embodiments. Obviously, the drawings described below are merely examples or embodiments of this specification. Those skilled in the art can apply this specification to other similar scenarios based on these drawings without inventive effort. Unless otherwise apparent from the context or otherwise noted, the same reference numerals in the figures represent the same structure or operation.

[0020] As used in this specification and claims, unless the context clearly indicates otherwise, the words "a," "an," "an," and / or "the" are not intended to refer to the singular but may include the plural. Generally speaking, the terms "comprise" and "include" only indicate the inclusion of the steps and elements specifically identified, and these steps and elements do not constitute an exclusive list. A method or apparatus may also include additional steps or elements.

[0021] Flowcharts are used throughout this specification to illustrate the operations performed by systems according to embodiments of this specification. It should be understood that preceding or following operations do not necessarily need to be performed in exact order. Instead, the steps may be processed in reverse order or simultaneously. Furthermore, other operations may be added to these processes, or one or more operations may be removed from these processes.

[0022] Some embodiments of the present specification provide a crystal preparation method, in which a first wafer after a first treatment is used as a first seed crystal, and a high-quality prefabricated crystal is grown based on a top seed crystal solution growth method; and a prefabricated crystal after a second treatment is used as a second seed crystal, and a large-sized, high-quality target crystal is grown based on a physical vapor transport method.

[0023] FIG1 is an exemplary flow chart of a crystal preparation method according to some embodiments of this specification. In some embodiments, process 100 can be performed by one or more components. In some embodiments, process 100 can be automatically performed by a control system. For example, process 100 can be implemented by a control instruction, and the control system controls each component to complete each operation of process 100 based on the control instruction. In some embodiments, process 100 can be performed semi-automatically. For example, one or more operations of process 100 can be manually performed by an operator. In some embodiments, when completing process 100, one or more additional operations not described above can be added, and / or one or more operations discussed herein can be deleted. As shown in FIG1 , process 100 can include the following steps.

[0024] Step 110: Obtain a first wafer after the first processing.

[0025] In some embodiments, the first treatment may include, but is not limited to, grinding and / or polishing the first wafer. In some embodiments, grinding may refer to processing the surface of the first wafer by relative motion between a grinding tool and the first wafer under a preset pressure. In some embodiments, the surface of the grinding tool may be coated with or embedded with abrasive particles. In some embodiments, polishing may refer to processing the surface of the first wafer using a polishing medium to reduce its roughness and make its surface smooth. In some embodiments, the polishing medium may be polishing powder.

[0026] In some embodiments, before grinding and / or polishing the first wafer, the first processing may further include cutting, etc. In some embodiments, the first wafer may be grown by a PVT method.

[0027] In some embodiments, the first wafer may include, but is not limited to, a silicon carbide wafer, an aluminum nitride wafer, or the like.

[0028] It should be understood that the defect density of the first wafer prepared by the PVT method is relatively high, so the first wafer needs to be subjected to a first treatment to make the surface of the first wafer obtained after the first treatment smoother and reduce the defect density of the first wafer.

[0029] In some embodiments, the material of the seed crystal holder may include but is not limited to graphite, etc. When the first wafer after the first treatment is used as the first seed crystal and the prefabricated crystal is grown based on the top seed crystal solution growth method, in order to avoid the solution climbing to the back of the first seed crystal due to the effect of surface tension during the crystal growth process and reacting with the seed crystal holder, resulting in a decrease in the quality of the prepared prefabricated crystal, the thickness of the first wafer after the first treatment needs to be greater than the first thickness threshold. However, if the thickness of the first seed crystal is too large, it may cause the first seed crystal to fall off from the seed crystal holder due to bonding strength problems during the preparation of the prefabricated crystal by the TSSG method due to the excessive weight of the first seed crystal. Therefore, the thickness of the first wafer after the first treatment needs to be less than the second thickness threshold. Among them, the first thickness threshold and the second thickness threshold can be empirical values ​​or preset values.

[0030] In some embodiments, the thickness of the first wafer after the first treatment may be 0.35 mm to 10 mm. In some embodiments, the thickness of the first wafer after the first treatment may be 0.5 mm to 9.5 mm. In some embodiments, the thickness of the first wafer after the first treatment may be 1 mm to 9 mm. In some embodiments, the thickness of the first wafer after the first treatment may be 1.5 mm to 8.5 mm. In some embodiments, the thickness of the first wafer after the first treatment may be 2 mm to 8 mm. In some embodiments, the thickness of the first wafer after the first treatment may be 2.5 mm to 7.5 mm. In some embodiments, the thickness of the first wafer after the first treatment may be 3 mm to 7 mm. In some embodiments, the thickness of the first wafer after the first treatment may be 3.5 mm to 6.5 mm. In some embodiments, the thickness of the first wafer after the first treatment may be 4 mm to 6 mm. In some embodiments, the thickness of the first wafer after the first treatment may be 4.5 mm to 5.5 mm.

[0031] In some embodiments of the present specification, by controlling the thickness of the first wafer after the first treatment, it is not only ensured that when used as the first seed crystal in the process of preparing prefabricated crystals by the TSSG method, there is a certain thickness for the first seed crystal to be dissolved back, but also the solution can be prevented from climbing to the back of the first seed crystal and reacting with the seed crystal holder, and it can be ensured that the first seed crystal will not fall off the seed crystal holder due to its heavy weight.

[0032] When the first wafer after the first treatment is used as the first seed crystal for preparing a prefabricated crystal by the TSSG method, since the solution will diffuse from the center to the surroundings under the action of centrifugal force, if the first wafer is an off-axis wafer, the direction of some steps of the off-axis wafer will be the same as the flow direction of the solution, resulting in more defects in the crystal grown in this part. In some embodiments, when the first wafer is an off-axis wafer, the first treatment may also include radially cutting the first wafer to obtain at least two cut first wafers; and splicing the at least two cut first wafers so that the steps of the at least two spliced ​​first wafers are in opposite directions. In this way, when the at least two spliced ​​cut first wafers are used as the first seed crystal for preparing a prefabricated crystal by the TSSG method, the solution flow direction is opposite to the step direction of the first seed crystal.

[0033] Figure 2 is an exemplary schematic diagram of a crystal preparation method according to some embodiments of the present specification. Figure 3A is an exemplary schematic diagram of a first process for an off-axis wafer according to some embodiments of the present specification. Figure 3B is an exemplary top view of the first wafer 2 after cutting in Figure 3A. Figure 3C is an exemplary schematic diagram of a first seed crystal with a step direction opposite to the solution flow direction according to some embodiments of the present specification.

[0034] In some embodiments, as shown in FIG3A , when the first wafer is an off-axis wafer 310, the off-axis wafer 310 can be radially cut to obtain two cut first wafers 320. In some embodiments, radial cutting can refer to cutting along the diameter direction or the direction perpendicular to the axis. As shown in FIG2 , radial cutting can be represented by double arrows ab. An off-axis wafer refers to a wafer in which the crystallographic c-axis (longest axis) is deflected by a preset angle toward the crystal direction. In some embodiments, the off-axis wafer can be obtained by machining the wafer (for example, cutting or beveling). It should be understood that due to the limitations of machining, the step direction of the off-axis wafer is always along a single direction. As shown in FIG3A , the step directions of the off-axis wafer 310 are consistent and all point to one side. Therefore, in order to achieve a solution flow direction opposite to all the step directions of the first seed crystal, at least two cut first wafers 320 need to be spliced.

[0035] At least two cut first wafers 320 can be spliced ​​together in various ways so that the steps of the at least two spliced ​​cut first wafers 320 are in opposite directions. For example, when splicing two cut first wafers 320, one of the cut first wafers (e.g., cut first wafer 1 321 as shown in FIG3A ) can be kept stationary, while the other cut first wafer (e.g., cut first wafer 2 322 as shown in FIG3A ) is subjected to at least one mirror transformation. The mirror-transformed cut first wafer 2 322 is then spliced ​​together with the stationary cut first wafer 1 321 so that the steps of the two spliced ​​cut first wafers are in opposite directions. The mirror transformation can include a 180° rotation about a certain axis (e.g., a sideline, a vertical center axis, or a horizontal center axis of the cut first wafer 2).

[0036] In some embodiments, the first process may further include rotating and / or flipping at least one of the at least two cut first wafers 320. The rotation and / or flipping may include rotating at a preset angle about a certain axis (e.g., a certain edge line, a vertical center axis, or a horizontal center axis of the cut first wafer). For example only, as shown in FIG3A , when the first wafer is an off-axis wafer 310, the off-axis wafer 310 may be radially cut to obtain a cut first wafer 1 321 and a cut first wafer 2 322. The cut first wafer 1 321 is kept stationary, and the cut first wafer 2 322 is rotated 180° clockwise (in the direction indicated by arrow b in FIG. 3A ) with its edge (the edge indicated by m in FIG. 3B ) as the rotation axis to obtain the cut first wafer 2 322-1 as shown in FIG. 3A . The cut first wafer 2 322-1 is then rotated 180° with its edge (the edge indicated by n in FIG. 3A ) as the rotation axis to obtain the cut first wafer 2 322-2. The cut first wafer 2 322-2 is then spliced ​​with the cut first wafer 1 321, as shown in FIG. 3A , to obtain two spliced ​​cut first wafers (also referred to as first seed crystals 330). As shown in FIG. 3A and FIG. 3C , the steps of the cut first wafer 1 321 and the cut first wafer 2 322 in the spliced ​​two cut first wafers (also referred to as first seed crystals 330) are in opposite directions. As shown in FIG3C , when two spliced, cut first wafers are used as first seed crystal 330 for preparing a prefabricated crystal by the TSSG method, the direction of the step is opposite to the direction of solution flow (it can be understood that step B blocks the solution flow or the solution flow collides with step B). Step B can be understood as a cut parallel to the axis of first seed crystal 330.

[0037] The embodiments of this specification do not limit the shape of the eccentric wafer 310. For example, it can be a rectangular parallelepiped, a cube, a cylinder, etc. For example, as shown in Figures 3A-3B, the eccentric wafer 310 can be a rectangular parallelepiped. In some embodiments, the cross-section of the eccentric wafer 310 can be a regular or irregular shape such as a polygon (for example, a rectangle, a square), a circle, an ellipse, etc. In some embodiments, its shape can also be changed by cutting the edges of at least two cut first wafers after splicing. For example, the rectangular parallelepiped first seed crystal 330 shown in Figure 3A can be cut to obtain a cylindrical seed crystal.

[0038] In some embodiments, when the first chip (also referred to herein as the eccentric chip 310) is a cylinder, the two cylindrical first chips with opposite step directions can be radially cut separately, and then the two cut first chips with opposite step directions are spliced ​​together to obtain two cut first chips with opposite step directions, and the two spliced ​​cut first chips are cylinders.

[0039] In some embodiments of the present specification, the first wafer is radially cut and at least two cut first wafers obtained by cutting are spliced ​​together so that the steps of the at least two spliced ​​first wafers are in opposite directions. When the first wafer is used as the first seed crystal to grow a prefabricated crystal based on the TSSG method, the step direction of the first seed crystal is opposite to the flow direction of the solution, and the step aggregation behavior can be significantly suppressed, which is beneficial to reduce microscopic defects and macroscopic defects, improve the quality of the prepared prefabricated crystal, and make the overall morphology of the crystal more flat and smooth.

[0040] It should be understood that since the first wafer is radially cut and spliced, if the at least two spliced ​​first wafers are directly bonded to the seed crystal holder and used as the first seed crystal to prepare a prefabricated crystal based on the TSSG method, during the crystal growth process, at the splicing gap of the at least two spliced ​​first wafers, the solution will rise along the splicing gap under the action of capillary force until it contacts the seed crystal holder and reacts, resulting in a low quality of the prepared prefabricated crystal. In some embodiments, in order to avoid the above situation, the at least two cut first wafers can be spliced ​​by bonding them to the second wafer. For example only, as shown in Figures 3A and 3C, the cut first wafer 1 321 and the cut first wafer 2 322 are spliced ​​to obtain two spliced ​​first wafers (also referred to as first seed crystals 330). The first seed crystal 330 can be bonded to one side of the second wafer 400, and the other side of the second wafer 400 can be bonded to the seed crystal holder A.

[0041] As shown in Figures 3A and 3C, the second wafer 400 can be positioned between the first seed crystal 330 and the seed crystal holder A to bond the first seed crystal 330 and the seed crystal holder A. In some embodiments, the second wafer 400 can include an equiaxial wafer or an eccentric wafer. In some embodiments, the material of the second wafer 400 can be the same as or different from that of the first seed crystal 330. In some embodiments, the shape of the second wafer 400 can be the same as or different from that of the first seed crystal 330.

[0042] The at least two cut first wafers after splicing can be bonded to the second wafer by thermal bonding. Other bonding methods can also be used, such as adhesive bonding. The bonding method between the second wafer and the seed crystal holder can be the same as or different from the bonding method between the at least two cut first wafers (also referred to as first seed crystals) after splicing and the second wafer.

[0043] In some embodiments of the present specification, by bonding at least two cut first wafers (also referred to as first seed crystals) after splicing to one side of a second wafer, and then bonding the other side of the second wafer to a seed crystal holder, it is possible to avoid direct contact and reaction between the solution and the seed crystal holder through the splicing gap during the process of preparing a prefabricated crystal based on the TSSG method from the first seed crystal, which is beneficial to improving the quality of the prepared prefabricated crystal.

[0044] In some embodiments, a groove may be provided at a preset height on the second wafer to further reduce the amount of solution climbing onto the surface of the seed crystal holder. In some embodiments, the preset height may refer to the distance between the lowest end of the groove of the second wafer and the lower bottom surface of the second wafer. The preset height may be a preset value or a default value, etc. In some embodiments, the groove may include a variety of structures, for example, an annular structure. In some embodiments, the longitudinal section of the groove may be of any shape, for example, a regular or irregular shape such as a polygon or a circle. In some embodiments, the groove depth may refer to the distance between the farthest end of the groove and the side of the second wafer. In some embodiments, the groove inclination may refer to the angle between the inclined edge of the groove and the horizontal plane.

[0045] As shown in Figure 4A, an annular groove 410 with a rectangular longitudinal section is provided at a preset height of the second wafer 400 (as shown in h1 in Figure 4A). The depth of the groove 410 (which can be understood as the length of the rectangle) can be represented as L1 in Figure 4A. As shown in Figure 4B, an annular groove 410 with a parallelogram longitudinal section is provided at a preset height of the second wafer 400 (as shown in h2 in Figure 4B). The depth of the groove 410 can be represented as L2 in Figure 4B, and the inclination of the groove 410 is α. As shown in Figure 4C, an annular groove 410 with a semicircular longitudinal section is provided at a preset height of the second wafer 400 (as shown in h3 in Figure 4C). The depth of the groove 410 (which can also be understood as the radius of the semicircle) can be represented as L3 in Figure 4C.

[0046] When preparing a prefabricated crystal using the spliced ​​at least two cut first wafers as first seed crystals based on the TSSG method, in order to allow the solution to better infiltrate the entire splicing gap under the action of surface tension, the solution causes crystal growth at the splicing gap to close the entire splicing gap. In some embodiments, the first treatment may further include performing a third treatment on the spliced ​​at least two cut first wafers to form an immersion angle near one end of the at least two cut first wafers near the splicing gap.

[0047] The third process may include cutting at least two cut first wafers at one end (e.g., the growth end) near the joint gap to form an immersion angle. By way of example only, as shown in FIG5 , cut first wafer 1 321 and cut first wafer 2 322 may be cut at one end (e.g., the growth end) near the joint gap to obtain cut first wafer 1 321-1 and cut first wafer 2 322-3 after the third process, which may then be joined to form first seed crystal 330. As shown in FIG5 , an immersion angle θ may be formed at the joint gap of first seed crystal 330.

[0048] It should be understood that the immersion angle is to allow the solution of the first seed crystal to better penetrate into the splicing gap during the TSSG method of growing crystals, so that the splicing gap grows and closes. The immersion angle can be a variety of structures. For example, a cylinder, a cone, a polyhedron, etc. Correspondingly, the longitudinal section of the immersion angle can be a polygon, a triangle (as shown in Figure 5), etc. In some embodiments, the longitudinal section of the immersion angle can also be any other shape that can increase the capillary force of the solution at the splicing gap. As an example, as shown in Figure 5, the splicing gap can be a cone, and the bottom circle of the cone is close to one end of the step. The radius of the splicing gap can be understood as the radius of the bottom circle of the cone, and the immersion angle can be understood as the top angle of the cone. The length of the solution immersed in the splicing gap can be calculated by the formula Calculated. Where H is the length of the joint gap (i.e., the thickness of the first wafer after the first treatment); γ is the surface tension of the liquid (which can be understood as the raw material melt) in the TSSG method; ρ is the density of the liquid; g is the acceleration due to gravity; r is the radius of the joint gap; and θ is the wetting angle between the liquid and the seed crystal (e.g., the first seed crystal).

[0049] In some embodiments, an immersion angle that is too large may cause cracks in the growing crystal. Therefore, the immersion angle needs to be less than a preset threshold. In some embodiments, the immersion angle θ may be greater than 0° and less than 20°. In some embodiments, the immersion angle θ may be greater than 2° and less than 18°. In some embodiments, the immersion angle θ may be greater than 4° and less than 16°. In some embodiments, the immersion angle θ may be greater than 6° and less than 14°. In some embodiments, the immersion angle θ may be greater than 8° and less than 12°. In some embodiments, the immersion angle θ may be greater than 9° and less than 10°.

[0050] In some embodiments of the present specification, by performing a third treatment on at least two cut first wafers, an immersion angle is formed at one end of the at least two cut first wafers after splicing close to the splicing gap, which is beneficial to enhancing the capillary force of the solution, allowing the solution to better penetrate the splicing gap and close the splicing gap through crystal growth.

[0051] In step 120 , the first wafer after the first treatment is used as a first seed crystal, and a prefabricated crystal is grown based on a top seed crystal solution growth method.

[0052] The top seed solution growth method refers to a method in which the raw material for preparing the crystal (for example, silicon carbide powder) is dissolved in a low-melting-point flux at high temperature to form a uniform saturated solution, and then a supersaturated melt is formed by slowly cooling the solution, so that the solution is precipitated on the seed crystal to prepare the crystal.

[0053] Preformed crystal refers to an intermediate crystal prepared by the TSSG method.

[0054] After bonding the first seed crystal to one side of the second wafer, the other side of the second wafer is bonded to the seed crystal holder, and a prefabricated crystal is grown using a top seed solution growth method. As an example, as shown in FIG2 , a first wafer 210 after the first treatment is used as the first seed crystal, and a crystal growth layer 220 having a predetermined thickness is grown using the TSSG method. The first wafer 210 after the first treatment and the crystal growth layer 220 can be referred to as a prefabricated crystal.

[0055] It should be understood that when a prefabricated crystal is grown by a top seed solution growth method based on the first seed crystal, due to the limitations of the TSSG method, when the thickness of the prepared crystal growth layer is too large, a large number of macro defects (for example, solvent inclusions) will appear in the crystal growth layer. Therefore, the thickness of the crystal growth layer prepared by the TSSG method needs to meet the preset conditions. In some embodiments, during the growth process of the crystal growth layer of the prefabricated crystal, it is necessary to control the thickness of the crystal growth layer 220 grown based on the top seed solution growth method to be within the range of 1 mm to 1.5 mm. In some embodiments, during the growth process of the prefabricated crystal, the thickness of the crystal growth layer 220 grown based on the top seed solution growth method can be controlled to be within the range of 1.1 mm to 1.4 mm. In some embodiments, during the growth process of the prefabricated crystal, the thickness of the crystal growth layer 220 grown based on the top seed solution growth method can be controlled to be within the range of 1.2 mm to 1.3 mm.

[0056] In some embodiments of the present specification, by controlling the thickness of the crystal growth layer prepared by the TSSG method, not only can various defects of the prepared prefabricated crystal caused by excessive growth thickness be reduced, but the prefabricated crystal with a preset thickness can also ensure that the prefabricated crystal can be subsequently subjected to a second treatment.

[0057] Step 130 : performing a second treatment on the prefabricated crystal.

[0058] The second treatment may include, but is not limited to, grinding and / or polishing the prefabricated crystal or its crystal growth layer.

[0059] It should be understood that since a certain amount of solvent and / or crystalline particles will adhere to the surface of the crystal growth layer of the prefabricated crystal prepared by the TSSG method, the prefabricated crystal or its crystal growth layer needs to be subjected to a second treatment. In some embodiments, the prefabricated crystal or its crystal growth layer can be subjected to a second treatment in a variety of ways. As an example only, as shown in FIG2 , the surface of the crystal growth layer 220 can be processed by relative movement of the grinding tool and the crystal growth layer 220 under a preset pressure to improve its surface smoothness and flatness, reduce surface defects, and obtain a crystal growth layer 230 after the second treatment. In some embodiments, the second treatment method may be the same as or different from the first treatment method. As shown in FIG2 , the first wafer 210 after the first treatment and the crystal growth layer 230 after the second treatment can be referred to as a prefabricated crystal after the second treatment.

[0060] In order to be able to prepare high-quality target crystals, when the prefabricated crystal after the second treatment is used as the second seed crystal, it is necessary to ensure that the surface of the second seed crystal is sufficiently smooth and flat, and as free of defects as possible. In some embodiments, the surface roughness of the second seed crystal may be no greater than 0.2nm. In some embodiments, the surface roughness of the second seed crystal may be no greater than 0.15nm. In some embodiments, the surface roughness of the second seed crystal may be no greater than 0.1nm. In some embodiments, the surface roughness of the second seed crystal may be no greater than 0.05nm.

[0061] In some embodiments of the present specification, by performing a second treatment on the prefabricated crystal so that its surface roughness when used as the second seed crystal in the PVT method is no more than 0.2 nm, the smoothness and flatness of the surface of the second seed crystal can be ensured, the quality of the second seed crystal can be improved, and it is beneficial to further improve the quality of the target crystal prepared subsequently by the PVT method.

[0062] Step 140 , using the prefabricated crystal after the second treatment as a second seed crystal, and growing the target crystal based on physical vapor transport method.

[0063] The physical vapor transport method refers to a method in which the material decomposes and sublimates into gaseous components under high temperature conditions. The gaseous components are transported to the seed crystal in the low temperature zone driven by the axial temperature gradient and deposited on the surface of the seed crystal to form crystals.

[0064] The target crystal can be grown based on the second seed crystal by physical vapor transport. As an example only, as shown in FIG2 , the first wafer 210 after the first treatment and the crystal growth layer 230 after the second treatment can be used as a whole as the second seed crystal (which can be called a prefabricated crystal after the second treatment). The target crystal growth layer 240 can be prepared based on the second seed crystal by PVT. The target crystal can include the first wafer 210 after the first treatment, the crystal growth layer 230 after the second treatment, and the target crystal growth layer 240.

[0065] In some embodiments of this specification, high-quality prefabricated crystals are prepared by the TSSG method, and are subjected to a second treatment to obtain high-quality second seed crystals, which are used to prepare target crystals by the PVT method. This not only obtains large-sized target crystals, but also ensures the high quality of the target crystals and reduces micro- and macro-defects in the target crystals.

[0066] It should be noted that the above description of process 100 is for illustration and purpose only and does not limit the scope of application of this specification. Those skilled in the art may make various modifications and alterations to process 100 under the guidance of this specification. However, such modifications and alterations are still within the scope of this specification.

[0067] The embodiments of this specification also provide a method for preparing a seed crystal, the method comprising: radially cutting an off-axis seed crystal to obtain at least two seed crystals; splicing the at least two seed crystals so that the step directions of the at least two seed crystals after splicing are opposite to obtain a target seed crystal. In some embodiments, the method may further comprise rotating and / or flipping at least one of the at least two seed crystals. In the embodiments of this specification, the off-axis seed crystal and the off-axis crystal can be used interchangeably. In some embodiments, splicing may comprise splicing at least two seed crystals by bonding them to a wafer. For relevant descriptions of radial cutting and splicing, please refer to the relevant descriptions in other parts of this specification (for example, Figures 3A-3C), which will not be repeated here.

[0068] In some embodiments, a groove may be provided at a predetermined height on the wafer. For a description of the groove, please refer to the descriptions in other parts of this specification (eg, FIG. 4A to FIG. 4C ), which will not be repeated here.

[0069] In some embodiments, the method further includes processing the at least two seed wafers after splicing so that an immersion angle is formed at one end of the at least two seed wafers near the splicing gap. For a description of the immersion angle, please refer to the relevant description in other parts of this specification (e.g., Figure 5), which will not be repeated here.

[0070] In some embodiments of the present specification, a target seed crystal is obtained by radially slicing an off-axis seed crystal and splicing at least two seed crystals obtained by the slicing, so that the steps of the at least two spliced ​​seed crystals are in opposite directions. When the target seed crystal is used to grow a crystal using the TSSG method, because the steps of the target seed crystal are in the opposite direction of the solution flow, step aggregation behavior can be significantly suppressed, which is beneficial for reducing micro- and macro-defects, improving the quality of the prepared crystal, and making the overall crystal morphology flatter and smoother.

[0071] While the basic concepts have been described above, it will be apparent to those skilled in the art that the detailed disclosure is merely illustrative and does not limit this specification. Although not explicitly stated herein, various modifications, improvements, and revisions to this specification may be made by those skilled in the art. Such modifications, improvements, and revisions are suggested in this specification and remain within the spirit and scope of the exemplary embodiments of this specification.

[0072] This specification also uses specific terms to describe the embodiments of this specification. For example, "one embodiment," "an embodiment," and / or "some embodiments" refer to a feature, structure, or characteristic associated with at least one embodiment of this specification. Therefore, it should be emphasized and noted that references to "one embodiment," "an embodiment," or "an alternative embodiment" two or more times in different locations in this specification do not necessarily refer to the same embodiment. Furthermore, certain features, structures, or characteristics of one or more embodiments of this specification may be appropriately combined.

[0073] In addition, unless expressly stated in the claims, the order of the processing elements and sequences, the use of alphanumeric characters, or the use of other names described in this specification are not intended to limit the order of the processes and methods of this specification. Although the above disclosure discusses some of the invention embodiments currently considered useful through various examples, it should be understood that such details are for illustrative purposes only, and the appended claims are not limited to the disclosed embodiments. On the contrary, the claims are intended to cover all modifications and equivalent combinations that are consistent with the spirit and scope of the embodiments of this specification. For example, although the system components described above can be implemented by hardware devices, they can also be implemented only by software solutions, such as installing the described system on an existing server or mobile device.

[0074] Similarly, it should be noted that, in order to simplify the presentation of this specification and thus facilitate understanding of one or more embodiments of the invention, the foregoing descriptions of the embodiments of this specification sometimes combine multiple features into a single embodiment, figure, or description thereof. However, this disclosure method does not imply that the subject matter of this specification requires more features than those recited in the claims. In fact, an embodiment may have fewer features than all of the features of a single disclosed embodiment.

[0075] In some embodiments, numbers are used to describe the quantity of components and attributes. It should be understood that such numbers used in the description of the embodiments are modified by the modifiers "about", "approximately" or "substantially" in some examples. Unless otherwise stated, "about", "approximately" or "substantially" indicate that the numbers are allowed to vary by ±20%. Accordingly, in some embodiments, the numerical parameters used in the description and claims are approximate values, which may change according to the required characteristics of individual embodiments. In some embodiments, the numerical parameters should take into account the specified significant digits and adopt the general method of retaining digits. Although the numerical domains and parameters used to confirm the breadth of their range in some embodiments of this specification are approximate values, in specific embodiments, the settings of such numerical values ​​are as accurate as possible within the feasible range.

[0076] Each patent, patent application, patent application publication, and other materials, such as articles, books, specifications, publications, and documents, cited in this specification is hereby incorporated by reference in its entirety. This includes application history documents that are inconsistent with or conflict with the content of this specification, as well as documents (currently or subsequently attached to this specification) that limit the broadest scope of the claims of this specification. It should be noted that if the descriptions, definitions, and / or terminology used in the accompanying materials are inconsistent or conflicting with the content of this specification, the descriptions, definitions, and / or terminology used in this specification will control.

[0077] Finally, it should be understood that the embodiments described in this specification are intended only to illustrate the principles of the embodiments of this specification. Other variations may also fall within the scope of this specification. Therefore, by way of example and not limitation, alternative configurations of the embodiments of this specification may be considered consistent with the teachings of this specification. Accordingly, the embodiments of this specification are not limited to the embodiments explicitly described and illustrated in this specification.

Claims

1. A method for preparing a crystal, characterized in that: The method comprises: Obtaining a first wafer after a first process; Using the first wafer after the first treatment as a first seed crystal, and growing a prefabricated crystal based on a top seed crystal solution growth method; performing a second treatment on the prefabricated crystal; The prefabricated crystal after the second treatment is used as a second seed crystal, and a target crystal is grown based on a physical vapor transport method.

2. The crystal preparation method according to claim 1, characterized in that: The thickness of the first wafer after the first treatment is 0.35 mm-10 mm.

3. The crystal preparation method according to claim 1, characterized in that: The method further comprises: During the growth of the prefabricated crystal, the thickness of the crystal growth layer grown based on the top seed solution growth method is controlled to be within the range of 1 mm to 1.5 mm.

4. The crystal preparation method according to claim 1, characterized in that: The surface roughness of the second seed crystal is no greater than 0.2 nm.

5. The crystal preparation method according to claim 1, characterized in that: The first treatment and / or the second treatment include grinding and / or polishing.

6. The crystal preparation method according to claim 1, characterized in that: When the first wafer is an off-axis wafer, the first process further includes: radially cutting the first wafer to obtain at least two cut first wafers; The at least two cut first wafers are spliced ​​together so that the step directions of the at least two cut first wafers after splicing are opposite.

7. The crystal preparation method according to claim 6, characterized in that: The first processing further includes: rotating and / or flipping at least one of the at least two cut first wafers.

8. The crystal preparation method according to claim 6, characterized in that: The step of splicing the at least two cut first wafers comprises: splicing the at least two cut first wafers by bonding them to a second wafer.

9. The crystal preparation method according to claim 8, characterized in that: A groove is provided on the second wafer at a preset height.

10. The crystal preparation method according to claim 6, characterized in that: The first process further includes: The at least two cut first wafers after splicing are subjected to a third treatment, so that an end of the at least two cut first wafers close to the splicing gap forms an immersion angle.

11. A method for preparing a seed crystal, characterized in that: The method comprises: radially cutting the off-axis seed crystal to obtain at least two seed crystals; The at least two seed crystals are spliced ​​together so that the step directions of the at least two seed crystals after splicing are opposite to each other, thereby obtaining a target seed crystal.

12. The method for preparing a seed crystal according to claim 11, characterized in that: The method further includes: rotating and / or flipping at least one of the at least two seed wafers.

13. The method for preparing a seed crystal according to claim 11, characterized in that: The step of splicing the at least two seed chips comprises: splicing the at least two seed chips by bonding them on a chip.

14. The method for preparing a seed crystal according to claim 13, characterized in that: A groove is arranged at a preset height on the wafer.

15. The method for preparing a seed crystal according to claim 11, characterized in that: The method further comprises: The at least two spliced ​​seed sheets are processed so that an end of the at least two seed sheets close to the splicing gap forms an immersion angle.

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