Apparatus and method for producing silicon carbide crystals

Abstract

To provide a device and method for preparing a silicon carbide crystal, capable of preparing a large-sized and high-quality ingot.SOLUTION: A device for preparing a silicon carbide crystal includes a crucible 110 and a crystal expansion guide assembly 120. The crucible includes: a crucible body 112 having an interior space 116 housing a raw material; and a crucible cover 114 fixing a seed crystal 60 and covering the crucible body. The crystal expansion guide assembly includes: a frame member 122 fixed to the crucible body, located between the crucible cover and a raw material 50, and provided with a through hole 126 with a diameter greater than a diameter of a crystal growth surface of the seed crystal; and a tubular core member 124 made of a high-purity graphite material with flexibility, mechanically connected to an inner wall of the through hole, and having inside diameter equal to or less than a diameter of the crystal growth surface of the seed crystal and a length smaller than a distance between a bottom and the raw material. During a crystal growth process, the tubular core member falls off due to contact with a crystal growth front edge, and the frame member does not react with the crystal.SELECTED DRAWING: Figure 1

Description

Technical Field

[0001] This application relates to a manufacturing technology of silicon carbide ingots, and particularly relates to an apparatus and method for manufacturing silicon carbide crystals capable of producing ingots with low-defect edges.

Background Art

[0002] Conventional apparatuses for manufacturing silicon carbide crystals generally obtain crystals with gradually larger dimensions by a crystal expansion method, and particularly use a guiding member (i.e., a guiding member having a through-hole) with a fixed structure made of a graphite material that still has a certain strength at a high temperature exceeding 2300 degrees Celsius (i.e., resistant to high temperatures). By planning the sublimation path of the raw material according to the inner diameter of the guiding member, newly generated crystals grow according to the shape of the guiding member in the crystal growth process using the physical vapor transport method (PVT).

[0003] In the crystal expansion process of silicon carbide crystals, since the crystal edge contacts and then reacts with the heterogeneous material of the guiding member, the crystal edge after the crystal expansion process is connected to the graphite material. In the cooling or guiding member removal process, due to the difference in thermal expansion characteristics between the silicon carbide crystal and the material of the guiding member, tensile stress or compressive stress generated in the crystal causes the crystal to crack.

[0004] Moreover, the larger the crystal grown by the crystal expansion process, the greater the internal stress. If crystal growth is carried out according to the thickness growth rate of the original equal-diameter crystal, it is more likely to crack during quenching. Therefore, the general crystal expansion process of silicon carbide crystals needs to take a longer time than the general crystal manufacturing process of growing in an equal diameter. At a slower growth rate, the crystals in the crystal expansion region have sufficient kinetic energy required to arrange and adjust to the crystal growth position with the minimum activation energy in the crystal growth process. In addition to reducing the occurrence of defects to obtain good crystal quality, the internal stress of the crystal can also be adjusted to reduce the probability of cracks in the crystal after cooling.

[0005] However, when guide members with a fixed structure use graphite material, crystals produced by crystal fabrication equipment are prone to developing crystal defects such as polycrystalline structure, high carbon coating concentration, and polytype at the edges. Since these defects, such as polycrystalline structure, high carbon coating concentration, and polytype, are always stress concentration regions, they can cause cracking during subsequent processing of crystals or chips. Therefore, when guide members with a fixed structure use graphite material, it may be impossible to obtain usable crystals or wafers, or the utilization rate may be low, leading to increased material and time costs and reduced effectiveness and profitability.

[0006] Therefore, the industry offers guide members with a fixed structure made of graphite material equipped with a tantalum carbide or tungsten carbide coating (or plating) layer, which can produce crystals with low etching pit density (EPD). However, these methods are costly, brittle, difficult to process, difficult to adjust resistivity, difficult to produce N-type crystals, do not conform to the coefficient of thermal expansion, stress concentrates, and the effect becomes more pronounced when the crystal size increases. Furthermore, the presence of high-temperature metal impurities in the crystal can be detected, leading to failure or unexpected effects on subsequent applications. [Overview of the project] [Problems that the invention aims to solve]

[0007] The embodiments of this application provide an apparatus and method for producing silicon carbide crystals, which solve the problems of conventional silicon carbide crystal production apparatuses that use guide members with fixed structures made of graphite material, resulting in the inability to obtain usable ingots or wafers or a low utilization rate, and the problems of high cost and detection of high-temperature metal impurities in the crystals, which can render subsequent applications useless or have unexpected effects, when using guide members with fixed structures made of graphite material equipped with a tantalum carbide or tungsten carbide coating (or plating) layer. [Means for solving the problem]

[0008] To solve the above technical problems, the present invention is realized as follows.

[0009] The present invention provides an apparatus for producing silicon carbide crystals, comprising a crucible and a crystal expansion guide assembly, the crucible comprising a crucible body having an internal space for containing raw materials and a crucible lid for fixing a seed crystal and covering the crucible body, the crystal expansion guide assembly comprising an outer edge member fixed between the crucible body or the crucible body and the crucible lid and located between the crucible lid and the raw materials (i.e., located between the seed crystal and the raw materials) and having a through hole, the diameter of which is greater than the diameter of the crystal growth surface of the seed crystal and the outer edge member having a through hole, the diameter of which is greater than the diameter of the crystal growth surface of the seed crystal, and a flexible tubular core member made of graphite material with a purity greater than 99.9%, mechanically connected to the inner wall of the through hole, the inner diameter being less than or equal to the diameter of the crystal growth surface of the seed crystal and the length being less than the distance between the bottom and the raw materials. During the crystal growth process, the tubular core component falls onto the surface of the raw material due to contact with the leading edge of the crystal growth, and the outer edge component does not react with the crystal.

[0010] The present invention further provides a method for producing silicon carbide crystals and a system for producing silicon carbide crystals, the system comprising a silicon carbide crystal production apparatus, a seed crystal and a heater, the silicon carbide crystal production apparatus comprising a crucible and a crystal expansion guide assembly, the crucible comprising a crucible body and a crucible lid, the crucible body having an internal space for containing raw materials, a heater being installed around the crucible, the crucible lid being for fixing the seed crystal and covering the crucible body, the crystal expansion guide assembly comprising an outer edge member and a tubular core member, the outer edge member being fixed between the crucible body or between the crucible body and the crucible lid and positioned between the crucible lid and the raw materials (i.e., between the seed crystal and the raw materials and The method includes the steps of: positioning a tubular core member (located between) and having a through hole, the diameter of which is greater than the diameter of the crystal growth surface of the seed crystal, the tubular core member being flexible and having a purity greater than 99.9%, being mechanically connected to the inner wall of the through hole, having an inner diameter less than or equal to the diameter of the crystal growth surface of the seed crystal, and having a length less than the distance to the raw material; and setting the growth pressure of the silicon carbide crystal production apparatus and setting the growth temperature of the silicon carbide crystal production apparatus with a heater, growing a crystal from a seed crystal, and during the crystal growth process the outer edge member does not react with the crystal, and when the crystal growth leading edge of the crystal comes into contact with the tubular core member, the tubular core member falls onto the surface of the raw material. [Effects of the Invention]

[0011] In the embodiments of the present invention, the design of the outer edge member and the tubular core member (i.e., the diameter of the through-hole in the outer edge member is larger than the diameter of the crystal growth surface of the seed crystal, the tubular core member is made of a flexible graphite material with a purity greater than 99.9%, is mechanically connected to the inner wall of the through-hole, has an inner diameter less than or equal to the diameter of the crystal growth surface of the seed crystal, and a length smaller than the distance between the bottom end away from the seed crystal and the raw material) causes the raw material to fall when the tubular core member comes into contact with the leading edge of the crystal growth during the crystal growth process, thereby preventing the crystal from reacting with the outer edge member, and thus the crystal produced by the silicon carbide crystal production apparatus according to the present invention has a low-defect edge. Furthermore, the outer edge member in this application is merely a structural member, is reusable without participating in the reaction, and uses a tubular core member made of high-purity graphite material (the tubular core member will fall off during the crystal growth process). Compared to using a guide member with a fixed structure made of graphite material equipped with a tantalum carbide or tungsten carbide coating (or plating) layer, the cost is lower and no impurities that may affect subsequent processes are generated. [Brief explanation of the drawing]

[0012] The drawings described herein are provided to further understand the present application and constitute part of the present application. The schematic embodiments and descriptions thereof are for interpretive purposes and do not unfairly limit the present application. In the drawings, [Figure 1] Figure 1 is a schematic diagram of the structure of one embodiment of the silicon carbide crystal production apparatus according to the present invention. [Figure 2] Figure 2 is a schematic perspective view of the crystal expansion guide assembly in Figure 1. [Figure 3] Figure 3 is a schematic diagram showing how the tubular core member in Figure 1 falls. [Figure 4] Figure 4 is a schematic diagram of the structure of another embodiment of the silicon carbide crystal production apparatus according to the present invention. [Figure 5] Figure 5 is a schematic perspective view of the crystal expansion guide assembly shown in Figure 4. [Figure 6] Figure 6 is a schematic diagram illustrating the detachment of the graphite material layer in Figure 5. [Figure 7] Figure 7 is a structural schematic diagram of another embodiment of the silicon carbide crystal manufacturing apparatus according to the present application. [Figure 8] Figure 8 is a perspective schematic diagram of the crystal expansion guide assembly in Figure 6. [Figure 9] Figure 9 is a schematic diagram of the graphite material layer falling in Figure 8. [Figure 10] Figure 10 is a structural schematic diagram of a silicon carbide crystal manufacturing system to which the silicon carbide crystal manufacturing apparatus in Figure 1 is applied. [Figure 11] Figure 11 is a method flowchart of an embodiment of a method for manufacturing a silicon carbide crystal applied to the silicon carbide crystal manufacturing system in Figure 7. [Figure 12] Figure 12 is a defect diagram of an embodiment of a 6-inch wafer grown by applying a guide member having a fixed structure made of a graphite material in a conventional silicon carbide crystal manufacturing apparatus. [Figure 13] Figure 13 is a defect diagram of an embodiment of a 6-inch wafer grown by the silicon carbide crystal manufacturing apparatus according to the present application. [Figure 14] Figure 14 is a polarization graph of an embodiment of an 8-inch wafer grown by applying a guide member having a fixed structure made of a graphite material in a conventional silicon carbide crystal manufacturing apparatus. [Figure 15] Figure 15 is a polarization graph of an embodiment of an 8-inch wafer grown by the silicon carbide crystal manufacturing apparatus according to the present application.

Embodiments for Carrying Out the Invention

[0013] Hereinafter, embodiments of the present invention will be described in combination with the related drawings. In these drawings, the same numbers indicate the same or similar elements or method processes.

[0014] It should be understood that terms such as "comprising" and "including" used in this specification are for indicating the presence of specific technical features, numerical values, method steps, operations, and / or elements, but do not exclude the addition of more technical features, numerical values, method steps, operations, elements, or any combination thereof.

[0015] It should be understood that when an element is described as being "connected" or "coupled" to another element, it may be directly connected or coupled to the other element, and there may be intermediate elements. Conversely, when an element is described as being "directly connected" or "directly coupled" to another element, there are no intermediate elements.

[0016] Referring to FIGS. 1 to 3, FIG. 1 is a structural schematic diagram of an embodiment of an apparatus for manufacturing a silicon carbide crystal according to the present application, FIG. 2 is a perspective schematic diagram of a crystal expansion guide assembly in FIG. 1, and FIG. 3 is a schematic diagram of a tubular core member falling in FIG. 1. As shown in FIGS. 1 to 3, the apparatus 100 for manufacturing a silicon carbide crystal includes a crucible 110 and a crystal expansion guide assembly 120.

[0017] The crucible 110 includes a crucible body 112 and a crucible lid 114. The crucible body 112 has an internal space 116 for accommodating the raw material 50, and the crucible lid 114 is for fixing the seed crystal 60 and covers the crucible body 112.

[0018] The crucible 110 is used to grow a seed crystal 60 using raw material 50, and a fixing and holding device (not shown) may be placed on the crucible lid 114, and the fixing and holding device may be for fixing the seed crystal 60 and for limiting the diameter D2 of the crystal growth surface 62 of the seed crystal 60 (i.e., limiting the exposed diameter D2 of the crystal growth surface 62). The crucible 110 may be a graphite crucible, but is not limited to that, and silicon carbide may be used as the seed crystal 60. The diameter of the seed crystal 60 may be 6 inches (150 millimeters) or more, but is not limited thereto. The raw material 50 may contain silicon and / or silicon carbide, as well as carbon, but is not limited thereto. The form of the raw material 50 may be powder, granular, or lump, but is not limited thereto. The purity of the raw material 50 may be greater than 99.99%, and the crystalline phase of the raw material 50 may be the α phase or the β phase, but is not limited thereto. This embodiment is not intended to limit the present invention.

[0019] The crystal expansion guide assembly 120 includes an outer edge member 122 and a tubular core member 124, the outer edge member 122 being fixed to the crucible body 112 and positioned between the crucible lid 114 and the raw material 50 (i.e., positioned between the seed crystal 60 and the raw material 50). The outer edge member 122 may be embedded in the crucible body 112. In another embodiment, stepped edges may be provided on the crucible body 112 and the crucible lid 114, respectively, so that the outer edge member 122 can be sandwiched between the crucible body 112 and the bottom of the stepped edges of the crucible lid 114 (i.e., the outer edge member 122 is fixed between the crucible body 112 and the crucible lid 114, as shown in Figure 4, which is a schematic diagram of the structure of another embodiment of the silicon carbide crystal production apparatus according to the present invention).

[0020] The outer edge member 122 has a through hole 126, and the diameter D1 of the through hole 126 is larger than the diameter D2 of the crystal growth surface 62 of the seed crystal 60. Therefore, it can be maintained so that it does not react with the outer edge member 122 during the crystal growth process, and the outer edge member 122 is merely a structural member and is therefore reusable. The material of the outer edge member 122 may be graphite, metal carbide, or refractory compound, but is not limited to these. The purity of the graphite, high-temperature metal carbide, or refractory compound may be greater than 99.9%, and the high-temperature metal carbide material may be tungsten carbide, tantalum carbide, niobium carbide, or titanium carbide, but is not limited to these, and possesses high temperature resistance (e.g., 2500 degrees Celsius or higher) and corrosion resistance properties. Furthermore, during the crystal growth process, the outer edge member 122 does not come into contact with the crystal, is merely a structural member, does not participate in the reaction, and is reusable.

[0021] The inner diameter D3 of the tubular core member 124 is less than or equal to the diameter D2 of the crystal growth surface 62 of the seed crystal 60, so that the raw material 50 is heated, sublimes and vaporizes, and passes through the tubular core member 124 in the form of gaseous molecules and deposits on the crystal growth surface 62 of the seed crystal 60 (i.e., the tubular core member 124 is positioned in the path of crystal growth and crystal expansion).

[0022] The tubular core member 124 is made of a flexible graphite material with a purity greater than 99.9% and is mechanically connected to the inner wall of the through hole 126 so that it falls out upon contact with the leading edge of the crystal growth during the crystal growth process (as shown in Figure 3). Furthermore, its length L1 (i.e., the distance from the top end of the tubular core member 124 facing the seed crystal 60 to the bottom end away from the seed crystal 60) is smaller than the distance L2 to the raw material 50 (i.e., the distance from the bottom end of the tubular core member 124 away from the seed crystal 60 to the surface of the raw material 50), so that it can eventually fall onto the surface of the raw material 50, without affecting the crystal expansion growth, and a larger crystal growth diameter is exposed from the crystal expansion guide assembly 120, eliminating defects and stresses that may occur as the crystal expands and grows and comes into contact with the outer edge member 122.

[0023] Furthermore, by installing the crystal expansion guide assembly 120, the internal stress of the crystal can be improved, allowing for the growth of spherical crystals larger than 10 millimeters in thickness, and preventing the spherical crystals from cracking during heating (in the crystal growth process of silicon carbide, if the internal stress of the crystal is too high, it is not possible to grow spherical crystals larger than 10 millimeters in thickness). It should be noted that in this embodiment, the bottom end of the tubular core member 124 away from the seed crystal 60 and the bottom end of the outer edge member 122 away from the seed crystal 60 are installed parallel to each other, so the distance L2 between the tubular core member 124 and the raw material 50 is equal to the distance between the outer edge member 122 and the raw material 50, but this embodiment is not intended to limit the present invention.

[0024] In one embodiment, the outer diameter of the tubular core member 124 may be essentially equal to the diameter D1 of the through hole 126, and the tubular core member 124 may be engaged and connected to the inner wall of the through hole 126. For example, because the tubular core member 124 is flexible, it can be connected to the inner wall of the through hole 126 by an intermediate fit method, so that when the crystal growth leading edge of the crystal comes into contact with the tubular core member 124, the tubular core member 124 slides due to the contact thrust and falls onto the surface of the raw material 50.

[0025] In one embodiment, the diameter D1 of the through-hole 126 is essentially equal to the largest crystal growth diameter. Specifically, since the tubular core member 124 can eventually fall onto the surface of the raw material 50, the space formed between the crystal growth leading edge and the outer edge member 122 is used as the crystal expansion region for crystal growth, and therefore the diameter D1 of the through-hole 126 is essentially equal to the largest crystal growth diameter.

[0026] In one embodiment, the tubular core member 124 may be formed by winding a single flexible graphite material layer 70 into a tubular shape, and the graphite material layer 70 may be engaged and connected to the inner wall of the through hole 126 (as shown in Figures 1 to 3). The graphite material layer 70 may be graphite paper, graphite foil, or graphite blanket, but is not limited to these, as it has the advantage of being easy to process into the required shape, and the thickness of the graphite material layer 70 may be 3 millimeters, but is not limited to this.

[0027] After the graphite material layer 70 falls onto the raw material 50, a carbon coating passage can be formed on the surface of the raw material 50, separating the inner wall of the crucible 110 from the crystal. This reduces the concentration of carbon coating in the crystal, thereby decreasing the causes of crystal defect formation (e.g., microtubules and dislocations).

[0028] In one embodiment, the tubular core member 124 may be formed by winding and laminating a plurality of flexible graphite material layers 70 into a tubular shape, with the top ends of these graphite material layers 70 facing the seed crystal 60 arranged parallel to the thickness direction F of the tubular core member 124 (i.e., the direction from the inner diameter to the outer diameter of the tubular core member 124) (i.e., the lengths of each graphite material layer 70 are the same, as shown in Figures 4 to 6, where Figure 5 is a schematic perspective view of the crystal expansion guide assembly in Figure 4, and Figure 6 is a schematic diagram of the graphite material layer falling in Figure 5), or arranged in a descending step-like manner (as shown in Figures 7 to 9, where Figure 7 is a schematic structural diagram of yet another embodiment of the silicon carbide crystal manufacturing apparatus according to the present invention, Figure 8 is a schematic perspective view of the crystal expansion guide assembly in Figure 6, and Figure 9 is a schematic diagram of the graphite material layer falling in Figure 8), and the thicknesses of these graphite material layers 70 may be the same or different.

[0029] Each graphite material layer 70 may have a thickness of 1 millimeter, but is not limited to that. The number of graphite material layers 70 may be 3, but is not limited to that. The number of graphite material layers 70 can be adjusted as needed.

[0030] As shown in Figures 4 to 6, when the top ends of these graphite material layers 70 facing the seed crystal 60 are arranged parallel to the thickness direction F of the tubular core member 124, the crystal growth leading edges of the crystals may come into contact with these graphite material layers 70 simultaneously during the crystal growth process, thereby allowing these graphite material layers 70 to fall onto the surface of the raw material 50 at the same time. Specifically, the design in which these graphite material layers 70 are stacked and combined in parallel allows these graphite material layers 70 to fall onto the surface of the raw material 50 at the same time when the crystal growth leading edges of the crystals come into contact with these graphite material layers 70 at the same time.

[0031] As shown in Figures 7 to 9, when the top ends of these graphite material layers 70 facing the seed crystal 60 are arranged in a downward step-like manner along the thickness direction F of the tubular core member 124, during the crystal growth process, the crystal growth leading edges of the crystals successively come into contact with these graphite material layers 70, causing these contacted graphite material layers 70 to fall sequentially onto the surface of the raw material 50.

[0032] In Figure 9, these graphite material layers 70 are arranged in a descending staircase pattern (i.e., there is a difference in height between these graphite material layers 70), and the second graphite material layer 70 is made to contact the crystal growth leading edge of the crystal preferentially over the outermost graphite material layer 70 and falls down, after which the outermost graphite material layer 70 comes into contact with the crystal growth leading edge of the crystal and falls down.

[0033] Each graphite material layer 70 may be graphite paper, graphite foil, or graphite blanket, but is not limited to these, as it has the advantage of being easily processed into the required shape, and the maximum length L3 of the three graphite material layers 70 (i.e., the length L3 of the innermost graphite material layer 70) is smaller than the distance L2 between the bottom end of the tubular core member 124 away from the seed crystal 60 and the surface of the raw material 50, thereby allowing the tubular core member 124 to eventually fall onto the surface of the raw material 50 without affecting the crystal expansion growth of the crystal.

[0034] It should be explained that in this embodiment, the bottom end of the tubular core member 124 away from the seed crystal 60 and the bottom end of the outer edge member 122 away from the seed crystal 60 are set parallel to each other, so the distance L2 between the tubular core member 124 and the raw material 50 is equal to the distance between the outer edge member 122 and the raw material 50, but this embodiment is not intended to limit the present invention. Furthermore, after each graphite material layer 70 falls onto the raw material 50, a carbon coating passage can be formed on the surface of the raw material 50, separating the inner wall of the crucible 110 from the crystal, thereby reducing the carbon coating concentration in the crystal and thereby reducing the causes of crystal defects (e.g., microtubules and dislocations).

[0035] Figure 10 is a schematic diagram of the structure of a silicon carbide crystal production system to which the silicon carbide crystal production apparatus in Figure 1 is applied. The silicon carbide crystal production system 200 comprises a silicon carbide crystal production apparatus 100, a seed crystal 60, and a heater 80. The heater 80 is for supplying a heat source and is installed around the crucible 110. There are multiple heaters 80 as shown in the figure, and one may be installed depending on the system configuration. The number shown is for illustrative purposes only and does not limit the actual number of heaters 80 that may be installed.

[0036] The heater 80 may be a high-frequency heater or a resistance heater, and in a more specific embodiment, the heater 80 may be a heating coil or a heating resistance wire (mesh). The silicon carbide crystal production system 200 may further include a heat-insulating material 90, which may be installed outside the crucible body 112 and the crucible lid 114. The heat-insulating material 90 may be a porous insulating carbon material, but is not limited to that, as this will achieve the effect of maintaining temperature. Furthermore, the silicon carbide crystal production apparatus 100 shown in Figure 4 or Figure 7 may be applied to the silicon carbide crystal production system 200.

[0037] Figure 11 is a flowchart of one embodiment of a silicon carbide crystal production method applied to the silicon carbide crystal production system in Figure 7. As shown in Figure 11, the silicon carbide crystal production method 300 includes the steps of providing a silicon carbide crystal production system 200 (step 310), setting the growth pressure of the silicon carbide crystal production apparatus 100 and setting the growth temperature of the silicon carbide crystal production apparatus 100 with a heater 80, growing a crystal from a seed crystal 60, and during the crystal growth process the outer edge member 122 does not react with the crystal, and when the crystal growth leading edge of the crystal comes into contact with the tubular core member 124, the tubular core member 124 falls onto the surface of the raw material 50 (step 320).

[0038] The growth pressure and growth temperature may be adjusted according to actual needs. For example, the growth pressure may be 200 Pascals (Pa) to 500 Pa or 400 Pa to 1100 Pa, but is not limited to these. The growth temperature may include a temperature gradient, which may include the upper temperature and lower temperature of the crucible 110. The lower temperature of the crucible 110 must be higher than the upper temperature of the crucible 110 to form a temperature gradient, thereby generating the driving force for crystal growth. The upper temperature of the crucible 110 may be 1950°C to 2150°C or 2100°C to 2200°C, but is not limited to these. The lower temperature of the crucible 110 only needs to be higher than the upper temperature of the crucible 110, and the upper and lower temperatures of the crucible 110 can be adjusted according to actual needs.

[0039] In one embodiment, step 320 may further include, after the tubular core member 124 has fallen onto the surface of the raw material 50, defining the space formed between the crystal growth leading edge of the crystal and the outer edge member 122 as a crystal expansion region, and growing the crystal within the crystal expansion region. When the crystal expands and grows within the crystal expansion region, it is not obstructed by the outer edge member 122 and does not react with the outer edge member 122, and therefore, low-defect, low-stress edges can be generated in the crystal grown by applying the silicon carbide crystal production method 300.

[0040] Stress at the crystal edges causes low-angle grain boundaries (LAGBs), and stress concentration points exist at the tips of LAGBs. This makes spherical crystals prone to cracking during heating and during crystal processing. By improving the stress at the crystal edges, the straight-through rate when processing the crystals into ingots and ultimately wafers (chips) can be improved, thereby reducing production costs.

[0041] If the silicon carbide crystal production system 200 can use the silicon carbide crystal production apparatus 100 shown in Figure 1 (i.e., the tubular core member 124 may be made by winding a single flexible graphite material layer 70 into a tube, and the graphite material layer 70 is engaged and connected to the inner wall of the through hole 126), or if the silicon carbide crystal production apparatus 100 shown in Figure 4 can be used (i.e., the tubular core member 124 may be made by winding a plurality of flexible graphite material layers 70 into a tube, and these graphite material layers 70 are stacked in parallel and engaged and connected to the inner wall of the through hole 126), then step 320 may include, during the crystal growth process, when the crystal growth leading edge of the crystal comes into contact with the single-layer graphite material layer 70 / multi-layer graphite material layer 70, the single-layer graphite material layer 70 / multi-layer graphite material layer 70 falls from the outer edge member 122 to the surface of the raw material 50.

[0042] Step 320 may further include the fact that the unfallen graphite material layer 70 prevents free carbon generated when the outer edge member 122 is heated from entering the crystal (i.e., in the early stages of crystal growth, the tubular core member 124 prevents free carbon generated when the outer edge member 122 is heated from entering the crystal). Specifically, since free carbon generated when the outer edge member 122 is heated affects the growth of two-dimensional silicon carbide seed crystals, the installation of the unfallen graphite material layer 70 can prevent this situation from occurring.

[0043] Furthermore, when guide members with a fixed structure made of conventional graphite material are subjected to heat, they inevitably introduce impurities (e.g., aluminum, nitrogen, boron) into the growth atmosphere, leading to heterogeneous nucleation at the growth interface in the early stages of growth. This inhibits the growth of two-dimensional silicon carbide seed crystals, forming polytype inclusions and clearly disrupting the stability of the heat and flow fields at the leading edge of the growth interface. Therefore, the occurrence of the above situation can be avoided by installing an outer edge member 122 that does not participate in the reaction and a high-purity graphite material layer 70 that does not fall off unless it is in contact with the material, as described in this application.

[0044] If the silicon carbide crystal production system 200 can use the silicon carbide crystal production apparatus 100 shown in Figure 7 (i.e., the tubular core member 124 is made by winding a plurality of flexible graphite material layers 70 into a tube, and the top ends of these graphite material layers 70 toward the seed crystal 60 are arranged in a descending step-like manner along the thickness direction F of the tubular core member 124 and stacked and engaged with the inner wall of the through hole 126), then step 320 may include, during the crystal growth process, when the crystal growth leading edges of the crystal successively come into contact with these graphite material layers 70, the contacted graphite material layers 70 successively fall onto the surface of the raw material 50. Step 320 may further include, the graphite material layers 70 that have not fallen prevent free carbon generated when the outer edge member 122 is heated from entering the crystal.

[0045] In one embodiment, the crystal may be selected from the group consisting of 4H silicon carbide, 6H silicon carbide, and 15R silicon carbide, but this embodiment is not intended to limit the present invention. For example, the crystal may be other polytype silicon carbide.

[0046] In one embodiment, the crystal may contain semi-insulating silicon carbide.

[0047] In one embodiment, the crystal may contain n-type silicon carbide.

[0048] In one embodiment, the crystal may contain p-type silicon carbide.

[0049] In one embodiment, the diameter of the seed crystal 60 may be 6 inches or more, but is not limited thereto. The diameter of the crystal after crystal expansion growth by applying the silicon carbide crystal production method 300 may be 145 to 205 millimeters, but is not limited thereto. What needs to be explained is that when the fixing and holding device fixes the seed crystal 60, the diameter D2 of the exposed crystal growth surface 62 is limited (the diameter D2 of the exposed crystal growth surface 62 is smaller than the diameter of the seed crystal 60). Therefore, the diameter of the crystal after crystal expansion growth may be smaller than the diameter of the seed crystal 60. The diameter of the crystal after crystal expansion growth may be determined according to the diameter D1 of the through hole 126 of the outer edge member 122.

[0050] In one embodiment, the crystal after crystal expansion growth may be a silicon carbide single crystal ingot with a protruding or flat surface.

[0051] Refer to Table 1, which is a table showing the relationship between the diameter of the through-hole in the outer edge member, the number of graphite material layers in the tubular core member, the diameter of the crystal growth surface of the seed crystal (i.e., the diameter of the exposed crystal growth surface of the seed crystal when the fixing and holding device fixes the seed crystal), the crystal expansion diameter, the growth pressure, and the growth temperature in different embodiments. Each graphite material layer may be 1 millimeter thick, the final crystal diameter (i.e., the largest crystal growth diameter) may be essentially equal to the diameter of the through-hole in the outer edge member, the crystal expansion diameter is the difference between the final crystal diameter and the diameter of the crystal growth surface of the seed crystal, the growth temperature may include the temperature above the crucible and the temperature below the crucible, the temperature below the crucible may be higher than the temperature above, and the thickness of the outer edge member (i.e., the distance from the top end of the outer edge member facing the seed crystal to the bottom end away from the seed crystal) may be 30 millimeters, but is not limited to these.

[0052] [Table 1]

[0053] As can be seen from Table 1, by setting appropriate growth pressure and growth temperature in the silicon carbide crystal fabrication apparatus, crystals can be grown from seed crystals, the final crystal diameter (i.e., the largest crystal growth diameter) can be limited by the diameter of the through-holes in the outer edge members, and the number of graphite material layers can be adjusted according to actual needs (e.g., the diameter of the through-holes in different outer edge members).

[0054] Referring to Figures 12 and 13, Figure 12 is a defect diagram of an embodiment of a 6-inch wafer grown using a conventional silicon carbide crystal production apparatus that applies a guide member having a fixed structure made of graphite material, and Figure 13 is a defect diagram of an embodiment of a 6-inch wafer grown using the silicon carbide crystal production apparatus according to the present invention.

[0055] For the wafer shown in Figure 12, a crystal with a final crystal diameter of 153 mm was produced using a conventional silicon carbide crystal manufacturing apparatus, with a seed crystal growth surface diameter of 145 mm, a through-hole diameter of the guide member with a fixed structure of 152 mm, a growth pressure of 400 Pa, and an upper temperature of 2120 °C. This crystal was then processed and molded into a 150 mm ingot, and further processed into a 150 mm wafer sheet through cutting, polishing, and buffing steps. Finally, a surface cleaning process was performed to detect surface defects in the wafer, resulting in the defect diagram shown in Figure 12.

[0056] For the wafer shown in Figure 13, the silicon carbide crystal production apparatus according to the present invention is used to produce a crystal with a final crystal diameter of 154.5 mm, where the diameter of the crystal growth surface of the seed crystal is 145 mm, the diameter of the through-hole of the outer edge member is 155 mm, the number of graphite material layers of the tubular core member is 5 (each graphite material layer may have a thickness of 1 mm), the growth pressure is 400 Pa, and the temperature above the crucible is 2115 °C. This crystal is then processed and molded to produce a 150 mm ingot, which is then further processed into a 150 mm wafer sheet through cutting, polishing, buffing, and other processing steps. Finally, a surface cleaning process is performed to detect surface defects in the wafer and obtain the defect diagram shown in Figure 13.

[0057] The black dots in Figures 12 and 13 represent wafer defects. In Figure 12, the total number of defects on the wafer is 1279, and the total defect density (TDD) of the wafer is approximately 7.89 / cm³. 2 The microtubule count is 606, and the microtubule density (MPD) is approximately 3.74 / cm³. 2 Furthermore, most defects are distributed along the wafer edges, and the total number of defects on the wafer in Figure 13 is 41 (the actual total number of defects may be even lower because some defects are located in large flat-edge laser-etched areas and the detection table may misidentify them as defects), and the total defect density of the wafer is approximately 0.25 / cm³. 2 The microtubule count is 3, and the microtubule density is approximately 0.02 / cm³. 2 Furthermore, it has clean edges and few defects.

[0058] Therefore, as can be seen from Figures 12 and 13, wafers grown using the silicon carbide crystal production apparatus according to the present invention have low defect and low stress edges compared to wafers grown using a conventional silicon carbide crystal production apparatus, and the total defect density in wafers obtained by applying the silicon carbide crystal production apparatus according to the present invention is significantly reduced due to impurities or silicon vapor in the crystal expansion guide assembly eroding the crucible wall or the generation of carbon coatings on the crystal expansion guide assembly.

[0059] In the embodiments shown in Figures 12 and 13 above, the 150 mm (i.e., 6 inch) ingots produced by the above processing are each manufactured into 12 6-inch silicon carbide wafers.

[0060] In the example shown in Figure 12, of the 12 wafers obtained, 5 were cracked during processing, and 7 were completed. Of these 7 wafers, only one had an MPD of 1 / cm². 2It is smaller than the standard, meets commercial grade standards, has a yield of 8.3%, and of the 12 wafers obtained in the example shown in Figure 13, all 12 were successfully processed (no cracks due to processing), and all 12 wafers had an MPD of 1 / cm². 2 The yield of product-grade wafers is smaller than that, and 100%. Therefore, it can be seen that improving crystal edge stress, reducing stress-induced crystal defects, and reducing the total defect density of the crystal improves the yield of product-grade wafers.

[0061] Referring to Figures 14 and 15, Figure 14 is a polarization graph of an 8-inch wafer grown using a conventional silicon carbide crystal production apparatus that applies a guide member having a fixed structure made of graphite material, and Figure 15 is a polarization graph of an 8-inch wafer grown using the silicon carbide crystal production apparatus according to the present invention.

[0062] For the wafer in Figure 14, a silicon carbide wafer with a final crystal diameter of 203 mm is obtained by processing, slicing, and polishing a crystal produced using a conventional silicon carbide crystal production apparatus, where the diameter of the crystal growth surface of the seed crystal is 193 mm, the inner diameter of the guide member having a fixed structure is 200 mm, the growth pressure is 200 Pa, and the upper temperature of the crucible is 1980 °C. For the wafer in Figure 15, a silicon carbide wafer with a final crystal diameter of 203 to 204 mm is obtained by processing, slicing, and polishing a crystal produced using the silicon carbide crystal production apparatus according to the present invention, where the diameter of the crystal growth surface of the seed crystal is 195 mm, the diameter of the through hole of the outer edge member is 205 mm, the number of graphite material layers of the tubular core member is 5 (each graphite material layer may have a thickness of 1 mm), the growth pressure is 200 Pa, and the upper temperature of the crucible is 2000 °C.

[0063] As shown in Figures 14 and 15, wafers grown using the silicon carbide crystal production apparatus according to the present invention have low-defect and low-stress edges compared to wafers grown using a conventional silicon carbide crystal production apparatus. Furthermore, defects in polycrystalline inserts caused by impurities or silicon vapor in the crystal expansion guide assembly eroding the crucible wall or the formation of carbon coatings on the crystal expansion guide assembly are reduced in wafers obtained by applying the silicon carbide crystal production apparatus according to the present invention.

[0064] In short, the design of the outer edge member and the tubular core member (i.e., the diameter of the through-hole in the outer edge member is larger than the diameter of the crystal growth surface of the seed crystal, the tubular core member is made of a flexible graphite material with a purity greater than 99.9%, is mechanically connected to the inner wall of the through-hole, has an inner diameter less than or equal to the diameter of the crystal growth surface of the seed crystal, and a length smaller than the distance between the bottom end away from the seed crystal and the raw material) causes the raw material to fall when the tubular core member comes into contact with the leading edge of the crystal growth during the crystal growth process, preventing the crystal from reacting with the outer edge member, thereby resulting in crystals produced by the silicon carbide crystal production apparatus according to the present invention having low-defect edges.

[0065] Furthermore, the outer edge member in this application is merely a structural member, is reusable without participating in the reaction, and uses a tubular core member made of high-purity graphite material (the tubular core member will fall off during the crystal growth process). Compared to using a guide member with a fixed structure made of graphite material equipped with a tantalum carbide or tungsten carbide coating (or plating) layer, the cost is lower and no impurities that may affect subsequent processes are generated.

[0066] Furthermore, by improving the internal and edge stresses of the crystals, the growth thickness of spherical crystals and the product thickness of the ingots can be increased. By improving low-angle grain boundaries and microtubules caused by edge stress, the probability of cracking during wafer processing or manufacturing can be reduced, thereby increasing the overall production volume of product-grade wafers with the same number of furnace inputs, furnace input materials, and labor costs.

[0067] Although the present invention has been described by the embodiments described above, it should be noted that these descriptions are not intended to limit the invention. On the contrary, this invention includes modifications and similar settings that would be obvious to those skilled in the art. Therefore, the scope of the application should be interpreted in the broadest way to include all obvious modifications and similar settings. [Explanation of symbols]

[0068] 50 Ingredients 60 seed crystals 62 Crystal growth surface 70 Graphite material layer 80 Heater 90 Heat insulation material 100 Apparatus for producing silicon carbide crystals 110 Crucible 112 Crucible Body 114 Crucible lid 116 Interior space 120 Crystal Expansion Guide Assembly 122 Outer edge member 124 Tubular core member 126 Through hole 200 Silicon Carbide Crystal Fabrication System 300 Method for preparing silicon carbide crystals 310, 320 steps D1, D2, D3 diameter F thickness direction L1, L3 Length L2 distance

Claims

1. A apparatus for producing silicon carbide crystals, comprising a crucible and a crystal expansion guide assembly, The crucible includes a crucible body having an internal space for containing raw materials, and a crucible lid for fixing seed crystals and covering the crucible body. The aforementioned crystal expansion guide assembly is An outer edge member fixed between the crucible body or between the crucible body and the crucible lid, positioned between the seed crystal and the raw material, and having a through hole, wherein the diameter of the through hole is greater than the diameter of the crystal growth surface of the seed crystal, The invention comprises a tubular core member which is a flexible graphite material with a purity greater than 99.9%, is mechanically connected to the inner wall of the through hole, has an inner diameter less than or equal to the diameter of the crystal growth surface of the seed crystal, and a length less than the distance to the raw material, The outer diameter of the tubular core member is equal to the diameter of the through hole in the outer edge member, and the tubular core member is engaged and connected to the inner wall of the through hole in the outer edge member. During the crystal growth process, the outer edge member does not react with the crystal, and when the leading edge of the crystal growth comes into contact with it, the tubular core member falls onto the surface of the raw material. Apparatus for producing silicon carbide crystals.

2. The tubular core member is flexible and connected to the inner wall of the through hole by an intermediate fitting method, The apparatus for producing silicon carbide crystals according to claim 1.

3. The tubular core member is formed by winding a single flexible graphite material layer into a tubular shape, and the graphite material layer is engaged and connected to the inner wall of the through hole. The apparatus for producing silicon carbide crystals according to claim 1.

4. The tubular core member is formed by winding and laminating multiple flexible graphite material layers into a tubular shape, with the top ends of these graphite material layers toward the seed crystal arranged in a downward step-like manner along the thickness direction of the tubular core member, or arranged parallel to each other, and the thicknesses of these graphite material layers are the same or different. The apparatus for producing silicon carbide crystals according to claim 1.

5. When the top ends of these graphite material layers toward the seed crystal are arranged in a descending step-like manner along the thickness direction of the tubular core member, during the crystal growth process, the leading edges of the crystal growth of the crystals sequentially come into contact with these graphite material layers, causing the contacted graphite material layers to fall sequentially onto the surface of the raw material. Apparatus for producing silicon carbide crystals as described in claim 4.

6. The graphite material layer is graphite paper, graphite foil, or graphite blanket. Apparatus for producing silicon carbide crystals according to claim 3 or 4.

7. The material of the outer edge member is graphite, metal carbide, or melt-resistant compound. The apparatus for producing silicon carbide crystals according to claim 1.

8. The diameter of the through hole is essentially equal to the largest crystal growth diameter. The apparatus for producing silicon carbide crystals according to claim 1.

9. A method for producing silicon carbide crystals, A silicon carbide crystal production system is provided, the silicon carbide crystal production system comprising a silicon carbide crystal production apparatus, a seed crystal, and a heater, the silicon carbide crystal production apparatus comprising a crucible and a crystal expansion guide assembly, the crucible comprising a crucible body and a crucible lid, the crucible body having an internal space for containing raw materials, the heater being installed around the crucible, the crucible lid for fixing the seed crystal and covering the crucible body, and the crystal expansion guide assembly comprising an outer edge member and a tubular Step (a) includes a core member, the outer edge member is fixed to the crucible body or between the crucible body and the crucible lid, is located between the seed crystal and the raw material, and has a through hole, the diameter of which is greater than the diameter of the crystal growth surface of the seed crystal, the tubular core member is flexible and made of a graphite material with a purity greater than 99.9%, is mechanically connected to the inner wall of the through hole, has an inner diameter less than or equal to the diameter of the crystal growth surface of the seed crystal, and has a length less than the distance to the raw material, The step (b) includes setting the growth pressure of the silicon carbide crystal production apparatus and setting the growth temperature of the silicon carbide crystal production apparatus using the heater, and growing the crystal from the seed crystal, The outer diameter of the tubular core member is equal to the diameter of the through hole in the outer edge member, and the tubular core member is engaged and connected to the inner wall of the through hole in the outer edge member. During the crystal growth process, the outer edge member does not react with the crystal, and when the crystal growth leading edge of the crystal comes into contact with the tubular core member, the tubular core member falls onto the surface of the raw material. Method for producing silicon carbide crystals.

10. The tubular core member is formed by winding a single flexible graphite material layer into a tube, and the graphite material layer is engaged and connected to the inner wall of the through hole, or by winding a plurality of flexible graphite material layers into a tube, and these graphite material layers are stacked in parallel and engaged and connected to the inner wall of the through hole, and step (b) includes, in the crystal growth process, when the crystal growth leading edge of the crystal comes into contact with the graphite material layer / these graphite material layers, the graphite material layer / these graphite material layers fall from the outer edge member to the surface of the raw material, A method for producing silicon carbide crystals according to claim 9.

11. The tubular core member is formed by winding a plurality of flexible graphite material layers into a tube, the top ends of these graphite material layers toward the seed crystal are arranged in a descending step-like manner along the thickness direction of the tubular core member and are stacked and engaged with the inner wall of the through hole, and step (b) includes, in the crystal growth process, when the crystal growth leading edges of the crystal successively come into contact with these graphite material layers, the contacted graphite material layers successively fall onto the surface of the raw material, A method for producing silicon carbide crystals according to claim 9.

12. Step (b) further includes preventing the unfallen graphite material layer from allowing free carbon generated by the heating of the outer edge member to enter the crystal. A method for producing silicon carbide crystals according to claim 10 or 11.

13. Step (b) further involves, after the tubular core member has fallen onto the surface of the raw material, defining the space formed between the crystal growth leading edge of the crystal and the outer edge member as a crystal expansion region, and growing the crystal within the crystal expansion region. A method for producing silicon carbide crystals as described in claim 9.

14. The crystal is selected from the group consisting of 4H silicon carbide, 6H silicon carbide, and 15R silicon carbide, and the crystal includes p-type silicon carbide, n-type silicon carbide, or semi-insulating silicon carbide. A method for producing silicon carbide crystals according to claim 9.

15. The seed crystal has a diameter of 6 inches or more, and the crystal after crystal expansion growth has a diameter of 145 to 205 millimeters. A method for producing silicon carbide crystals according to claim 9.

Images