Device and method for preparing silicon carbide crystal

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] The present application relates to a technology for producing silicon carbide ingots, and more particularly to an apparatus and method for producing silicon carbide crystals that can produce ingots having edges with low defects. [Background technology]

[0002] Conventional silicon carbide crystal manufacturing equipment generally uses a crystal expansion method to gradually obtain crystals of larger dimensions, and in particular uses a guide member (i.e., a guide member with a through hole) with a fixed structure made of a graphite material that still has a certain strength even at high temperatures (i.e., can withstand high temperatures) exceeding 2,300 degrees Celsius. The path for the sublimation of the raw material is planned according to the inner diameter of the guide member, and the newly generated crystal grows according to the shape of the guide member during the crystal growth process using physical vapor transport (PVT).

[0003] During the crystal expansion process of the silicon carbide crystal, the crystal edge will come into contact with and react with the foreign material of the guide member, so that the crystal edge will be connected to the graphite material after the crystal expansion process. During the cooling or removal of the guide member, due to the difference in thermal expansion properties between the silicon carbide crystal and the material of the guide member, tensile or compressive stress will be generated in the crystal, causing the crystal to crack.

[0004] In addition, the larger the crystals grown by the crystal expansion process, the greater the internal stress, and if the crystals are grown according to the thickness growth rate of the original equal diameter crystals, they are more likely to crack when fired. Therefore, the crystal expansion process of a general silicon carbide crystal requires a longer time than the general crystal manufacturing process that grows with equal diameters, and at a slower growth rate, the crystals in the crystal expansion region have enough kinetic energy to be aligned and adjusted to the crystal growth position with the minimum activation energy during the crystal growth process, which not only reduces the occurrence of defects and achieves good crystal quality, but also adjusts the internal stress of the crystal to reduce the probability of cracks occurring in the crystal after cooling.

[0005] However, when the guide member having a fixed structure is made of graphite material, the crystal produced by the crystal production device is prone to have crystal defects such as polycrystal, high carbon coating concentration, and polytype at the edge, and the defects such as polycrystal, high carbon coating concentration, and polytype of the crystal are always stress concentration areas, which will cause cracks during the subsequent processing of the crystal or chip. Therefore, when the guide member having a fixed structure is made of graphite material, usable crystals or wafers cannot be obtained or the utilization rate is low, which increases material costs and time costs, and reduces the effect and profit.

[0006] For this reason, the industry has provided a guide member having a fixed structure made of a graphite material with a tantalum carbide or tungsten carbide coating (or plating) layer, which can produce a crystal with a low etching pits density (EPD). However, this method has problems such as high cost, fragility and difficulty in processing, difficulty in adjusting resistivity, difficulty in producing N-type crystal, incompatibility with expansion coefficient, stress concentration, and more pronounced effect when the crystal size increases. In addition, the presence of high-temperature metal impurities in the crystal can be detected, which will cause failure or unexpected impact on subsequent applications. Summary of the Invention [Problem to be solved by the invention]

[0007] The embodiments of the present application provide an apparatus and method for producing silicon carbide crystals, which can solve the problems of conventional silicon carbide crystal production apparatuses using guide members having a fixed structure made of graphite material, resulting in failure to obtain usable ingots or wafers or a low utilization rate, and the problems of high cost and failure or unexpected impact on subsequent applications due to the use of guide members having a fixed structure made of graphite material with a tantalum carbide or tungsten carbide coating (or plating) layer. [Means for solving the problem]

[0008] In order to solve the above technical problems, the present application is realized as follows.

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

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

[0011] In an embodiment of the present application, the design of the outer edge member and the tubular core member (i.e., the diameter of the through hole of the outer edge member is larger than the diameter of the crystal growth surface of the seed crystal, the tubular core member is a flexible graphite material with a purity of greater than 99.9%, is mechanically connected to the inner wall of the through hole, has an inner diameter less than the diameter of the crystal growth surface of the seed crystal, and has a length less 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 crystal growth front edge of the crystal during the crystal growth process, and keeps the crystal from reacting with the outer edge member, so that the crystal produced by the silicon carbide crystal production apparatus of the present application has an edge with low defects. In addition, the outer edge member of the present application is merely a structural member and is reusable without participating in the reaction. Furthermore, the cost is lower and no impurities that would affect subsequent processes are generated compared to the case where a tubular core member made of high-purity graphite material (the tubular core member will fall off during the crystal growth process) is used, and a guide member having a fixed structure made of a graphite material having a tantalum carbide or tungsten carbide coating (or plating) layer is used. [Brief description of the drawings]

[0012] The drawings described herein are intended to provide further understanding of the present application, constitute a part of the present application, and the schematic embodiments and the description thereof are intended to serve to interpret the present application, and are not intended to unduly limit the present application. [Figure 1] FIG. 1 is a structural schematic diagram of one embodiment of an apparatus for producing silicon carbide crystals according to the present application. [Diagram 2] FIG. 2 is a perspective schematic view of the crystal expansion guide assembly in FIG. [Diagram 3] FIG. 3 is a schematic diagram of the tubular core member in FIG. 1 falling. [Figure 4] FIG. 4 is a structural schematic diagram of another embodiment of the silicon carbide crystal producing apparatus according to the present application. [Diagram 5] FIG. 5 is a perspective schematic view of the crystal expansion guide assembly in FIG. [Figure 6] FIG. 6 is a schematic diagram of the graphite material layer in FIG. 5 falling off. [Figure 7] FIG. 7 is a structural schematic diagram of yet another embodiment of the silicon carbide crystal producing apparatus according to the present application. [Figure 8] FIG. 8 is a perspective schematic view of the crystal expansion guide assembly in FIG. [Figure 9] FIG. 9 is a schematic diagram of the graphite material layer in FIG. 8 falling off. [Figure 10] FIG. 10 is a structural schematic diagram of a silicon carbide crystal production system to which the silicon carbide crystal production apparatus in FIG. 1 is applied. [Figure 11] FIG. 11 is a flow chart of one embodiment of a method for producing silicon carbide crystals which is applied to the silicon carbide crystal producing system in FIG. [Figure 12] FIG. 12 is a diagram showing defects in an example of a 6-inch wafer grown using a conventional silicon carbide crystal manufacturing apparatus that employs a guide member having a fixed structure made of graphite material. [Figure 13] FIG. 13 is a diagram showing defects in one embodiment of a 6-inch wafer grown by the silicon carbide crystal production apparatus according to the present application. [Figure 14] FIG. 14 is a polarization graph of an example of an 8-inch wafer grown using a conventional silicon carbide crystal production apparatus that employs a guide member having a fixed structure made of graphite material. [Figure 15] FIG. 15 is a polarization graph of an example of an 8-inch wafer grown by the silicon carbide crystal production apparatus according to the present application. DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENTS

[0013] Embodiments of the present invention are described below in conjunction with the associated drawings, in which like numbers indicate like or similar elements or method steps.

[0014] It should be understood that terms such as "comprise", "include", and the like are used in this specification to indicate the presence of certain technical features, values, method steps, operation processes and / or elements, but do not exclude that more technical features, values, method steps, operation processes, elements, or any combination of the above may be added.

[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 intermediate elements may be present. Conversely, when an element is described as being "directly connected" or "directly coupled" to another element, no intermediate elements are present.

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

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

[0018] The crucible 110 is for growing the seed crystal 60 from the raw material 50, and a fixing and holding device (not shown) may be arranged on the crucible cover 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., for limiting the exposed diameter D2 of the crystal growth surface 62). The crucible 110 may be a graphite crucible, but is not limited thereto. The seed crystal 60 may be made of silicon carbide, Without being limited thereto, the seed crystal 60 may have a diameter of 6 inches (150 millimeters) or more, the raw material 50 may include, but is not limited to, silicon and / or silicon carbide, and carbon, the raw material 50 may be in the form of, but is not limited to, powder, granular, or chunky form, the purity of the raw material 50 may be greater than 99.99%, and the crystal phase of the raw material 50 may be, but is not limited to, alpha phase or beta phase, and this embodiment is not intended to limit the present application.

[0019] The crystal expansion guide assembly 120 includes an outer edge member 122 and a tubular core member 124, and the outer edge member 122 is fixed to the crucible body 112 and is located between the crucible lid 114 and the raw material 50 (i.e., 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, the crucible body 112 and the crucible lid 114 may be provided with stepped edges, respectively, so that the outer edge member 122 can be sandwiched between the bottom of the stepped edges of the crucible body 112 and 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 FIG. 4, which is a structural schematic diagram of another embodiment of the apparatus for producing silicon carbide crystals according to the present application).

[0020] The outer peripheral 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, so that the outer peripheral member 122 can be maintained not to react with the outer peripheral member 122 during the crystal growth process, and the outer peripheral member 122 is merely a structural member and can be reused. The material of the outer peripheral member 122 can be, but is not limited to, a graphite material, a metal carbide material, or a refractory compound, and the purity of the graphite material, the high-temperature metal carbide material, or the refractory compound can be greater than 99.9%, and the high-temperature metal carbide material can be, but is not limited to, tungsten carbide, tantalum carbide, niobium carbide, or titanium carbide, and has high-temperature resistance (for example, above 2500 degrees Celsius) and corrosion resistance properties. In addition, during the crystal growth process, the outer peripheral member 122 basically does not come into contact with the crystal, and is merely a structural member, does not participate in the reaction, and can be reused.

[0021] The inner diameter D3 of the tubular core member 124 is equal to or smaller than the diameter D2 of the crystal growth surface 62 of the seed crystal 60, so that the raw material 50 is subjected to heat and then sublimated and vaporized, passing through the tubular core member 124 in the form of gas phase molecules and being deposited on the crystal growth surface 62 of the seed crystal 60 (i.e., the tubular core member 124 is located in the path of crystal growth and crystal expansion).

[0022] The tubular core member 124 is a flexible graphite material with a purity of greater than 99.9%, and is mechanically connected to the inner wall of the through hole 126 so that it falls due to contact with the crystal growth front edge of the crystal during the crystal growth process (shown in FIG. 3). The length L1 (i.e., the distance from the top end of the tubular core member 124 toward the seed crystal 60 to the bottom end leaving the seed crystal 60) is smaller than the distance L2 from the raw material 50 (i.e., the distance between the bottom end of the tubular core member 124 leaving the seed crystal 60 and 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 of the crystal, and a larger crystal growth diameter is exposed from the crystal expansion guide assembly 120, eliminating defects and stress that may occur due to the crystal expanding and growing and coming into contact with the outer edge member 122.

[0023] In addition, the installation of the crystal expansion guide assembly 120 can improve the internal stress of the crystal, and can grow a spherical crystal with a thickness of more than 10 mm, and the spherical crystal will not break during firing (if the internal stress of the crystal is too large during the silicon carbide crystal growth process, it is impossible to grow a spherical crystal with a thickness of more than 10 mm). 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 peripheral member 122 away from the seed crystal 60 are installed in parallel, so the distance L2 between the tubular core member 124 and the raw material 50 is equal to the distance between the outer peripheral 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, since the tubular core member 124 is flexible, it may be connected to the inner wall of the through hole 126 by a transition fit manner, so that when the crystal growth front edge of the crystal contacts the tubular core member 124, the tubular core member 124 slides and falls onto the surface of the raw material 50 due to the contact thrust.

[0025] In one embodiment, the diameter D1 of the through hole 126 is essentially equal to the largest crystal growth diameter. Specifically, the tubular core member 124 can finally fall onto the surface of the raw material 50, so that the space formed between the crystal growth front edge of the crystal and the outer edge member 122 becomes a crystal expansion area 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, tubular core member 124 may be formed by winding a single flexible graphite material layer 70 into a tubular shape, and graphite material layer 70 may be engaged and connected to the inner wall of through hole 126 (as shown in FIGS. 1 to 3). Graphite material layer 70 may be, but is not limited to, graphite paper, graphite foil, or graphite blanket, which has the advantage of being easily processed into a required shape, and graphite material layer 70 may have a thickness of, but is not limited to, 3 millimeters.

[0027] After the graphite material layer 70 falls onto the raw material 50, carbon coating passages can be formed on the surface of the raw material 50 to separate the inner wall of the crucible 110 from the crystal, thereby reducing the carbon coating concentration in the crystal, thereby reducing the cause of the formation of crystal defects (e.g., microtubules and dislocations).

[0028] In one embodiment, the tubular core member 124 may be formed by winding and stacking a plurality of flexible graphite material layers 70 into a tubular shape, and 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 (i.e., the direction from the inner diameter to the outer diameter of the tubular core member 124) (i.e., the lengths of the graphite material layers 70 are the same, as shown in Figures 4 to 6, where Figure 5 is a perspective schematic view of the crystal expansion guide assembly in Figure 4, and Figure 6 is a schematic view of the graphite material layers falling in Figure 5), or arranged in a descending staircase shape (as shown in Figures 7 to 9, Figure 7 is a structural schematic view of yet another embodiment of the silicon carbide crystal production apparatus according to the present application, Figure 8 is a perspective schematic view of the crystal expansion guide assembly in Figure 6, and Figure 9 is a schematic view of the graphite material layers falling in Figure 8), and the thicknesses of these graphite material layers 70 may be the same or different.

[0029] The thickness of each graphite material layer 70 may be, but is not limited to, 1 millimeter, and the number of graphite material layers 70 may be, but is not limited to, three layers, and the number of graphite material layers 70 can be adjusted as needed.

[0030] 4 to 6 , when the apex ends of these graphite material layers 70 facing seed crystal 60 are arranged in parallel along the thickness direction F of tubular core member 124, during the crystal growth process, the crystal growth front edges of the crystals may contact these graphite material layers 70 simultaneously, so that these graphite material layers 70 can drop onto the surface of raw material 50 simultaneously. Specifically, due to a design in which these graphite material layers 70 are stacked and combined in parallel, when the crystal growth front edges of the crystals contact these graphite material layers 70 simultaneously, these graphite material layers 70 can drop onto the surface of raw material 50 simultaneously.

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

[0032] In FIG. 9 , these graphite material layers 70 are arranged in a descending staircase pattern (i.e., there is a height difference between these graphite material layers 70), and the second graphite material layer 70 comes into contact with the crystal growth front of the crystal and falls preferentially over the outermost graphite material layer 70, and then the outermost graphite material layer 70 comes into contact with the crystal growth front of the crystal and falls.

[0033] Each graphite material layer 70 may be, but is not limited to, graphite paper, graphite foil or graphite blanket, and has the advantage of being easily processed into a 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 finally fall onto the surface of the raw material 50 and not affecting the crystal expansion growth of the crystal.

[0034] 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 peripheral member 122 away from the seed crystal 60 are set parallel to each other, so that the distance L2 between the tubular core member 124 and the raw material 50 is equal to the distance between the outer peripheral member 122 and the raw material 50, but this embodiment is not intended to limit the present invention. In addition, 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 to separate the inner wall of the crucible 110 and the crystal, and the carbon coating concentration in the crystal can also be reduced, thereby reducing the cause of the formation of crystal defects (such as microtubules and dislocations).

[0035] Figure 10 is a structural schematic diagram 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 includes the silicon carbide crystal production apparatus 100, a seed crystal 60, and a heater 80, the heater 80 is for supplying a heat source, the heater 80 is installed around the crucible 110, there are multiple heaters 80 shown, one may be installed depending on the system layout, the number shown is for schematic explanation and does not limit the actual number of heaters 80 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, and the heat-insulating material 90 may be, but is not limited to, a porous insulating carbon material, thereby realizing the effect of maintaining the temperature. The silicon carbide crystal production system 200 may be applied to the silicon carbide crystal production apparatus 100 in FIG. 4 or FIG. 7.

[0037] Fig. 11 is a method flow chart of an embodiment of a method for producing silicon carbide crystals applied to the silicon carbide crystal production system in Fig. 7. As shown in Fig. 11, the method for producing silicon carbide crystals 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 by the 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 front edge of the crystal contacts 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 the growth temperature may be adjusted according to actual needs. For example, the growth pressure may be, but is not limited to, 200 Pascals (Pa) to 500 Pa or 400 Pa to 1100 Pa. The growth temperature may include a temperature gradient, and the temperature gradient may include an upper temperature of the crucible 110 and a lower temperature of the crucible 110. The lower temperature of the crucible 110 needs to be higher than the upper temperature of the crucible 110 to form a temperature gradient, thereby generating a driving force for crystal growth. The upper temperature of the crucible 110 may be, but is not limited to, 1950°C to 2150°C or 2100°C to 2200°C. The lower temperature of the crucible 110 only needs to be higher than the upper temperature of the crucible 110. The upper temperature of the crucible 110 and the lower temperature of the crucible 110 may be adjusted according to actual needs.

[0039] In one embodiment, step 320 may further include, after the tubular core member 124 falls onto the surface of the raw material 50, defining a space formed between the crystal growth front edge of the crystal and the outer edge member 122 as a crystal expansion region, and growing the crystal in the crystal expansion region. When the crystal expands and grows in the crystal expansion region, it is not blocked by the outer edge member 122 and does not react with the outer edge member 122, so that the crystal grown by applying the silicon carbide crystal manufacturing method 300 can have an edge with low defects and low stress.

[0040] Stress at the crystal edges generates low angle grain boundaries (LAGBs), and since stress concentration points exist at the tips of the LAGBs, they are prone to cause cracking problems when firing the spherical crystals and when processing the crystals. After improving the stress at the crystal edges, the straight-through rate when processing the crystals into ingots and then 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 in FIG. 1 (i.e., 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 is engaged and connected to the inner wall of the through hole 126), or the silicon carbide crystal production apparatus 100 in FIG. 4 can be used (i.e., the tubular core member 124 may be formed by winding a plurality of flexible graphite material layers 70 into a tubular shape, and these graphite material layers 70 are stacked in parallel and engaged and connected to the inner wall of the through hole 126), step 320 may include that during the crystal growth process, when the crystal growth front edge of the crystal contacts the single-layer graphite material layer 70 / multiple graphite material layers 70, the single-layer graphite material layer 70 / multiple graphite material layers 70 fall from the outer edge member 122 onto the surface of the raw material 50.

[0042] Step 320 may further include that the unshed graphite material layer 70 prevents free carbon generated when the outer peripheral member 122 is heated from entering the crystal (i.e., at the beginning of crystal growth, the tubular core member 124 prevents free carbon generated when the outer peripheral member 122 is heated from entering the crystal). Specifically, free carbon generated when the outer peripheral member 122 is heated affects the growth of the two-dimensional silicon carbide seed crystal, so the provision of the unshed graphite material layer 70 can prevent this situation from occurring.

[0043] In addition, when a guide member having a fixed structure made of conventional graphite material is subjected to heat, it inevitably introduces impurities (e.g., aluminum, nitrogen, boron) into the growth atmosphere, which leads to heterogeneous nucleation at the growth interface in the early stage of growth, thereby blocking the growth of two-dimensional silicon carbide seed crystals and forming polytype inclusions, and obviously destroying the stability of the thermal field and flow field at the leading edge of the growth interface. Therefore, the occurrence of the above situation can be avoided by installing the outer edge member 122 in the present application, which does not participate in the reaction, and the high-purity graphite material layer 70, which will not fall off unless it is touched.

[0044] 7 (i.e., the tubular core member 124 is formed by winding a plurality of flexible graphite material layers 70 into a tubular shape, and the top ends of the graphite material layers 70 facing the seed crystal 60 are arranged in a descending step shape along the thickness direction F of the tubular core member 124, stacked, and engaged with the inner wall of the through hole 126), step 320 may include that, during the crystal growth process, when the crystal growth front edge of the crystal contacts these graphite material layers 70 in order, the contacted graphite material layers 70 fall in order onto the surface of the raw material 50. Step 320 may further include that the graphite material layers 70 that have not fallen off prevent free carbon generated when the outer edge member 122 receives heat from entering the crystal.

[0045] In one embodiment, the crystals 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 be limiting, for example, the crystals may be other polytypes of silicon carbide.

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

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

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

[0049] In one embodiment, the diameter of the seed crystal 60 may be, but is not limited to, 6 inches or more, and the diameter of the crystal after crystal expansion growth by applying the silicon carbide crystal production method 300 may be, but is not limited to, 145 to 205 millimeters. It should be noted that the fixing and holding device limits the exposed diameter D2 of the crystal growth surface 62 when fixing the seed crystal 60 (the exposed diameter D2 of the crystal growth surface 62 is smaller than the diameter of the seed crystal 60), and therefore the diameter of the crystal after crystal expansion growth may be smaller than the diameter of the seed crystal 60, and 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, after crystal expansion growth, the crystal may be a silicon carbide single crystal ingot with a surface that exhibits a protruding or flat shape.

[0051] Refer to Table 1, which is a relationship table of the diameter of the through hole of the outer peripheral member, the number of graphite material layers of the tubular core member, the diameter of the crystal growth surface of the seed crystal (i.e., the diameter of the crystal growth surface exposed by 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, wherein the thickness of each graphite material layer may be 1 millimeter, the final crystal diameter (i.e., the largest crystal growth diameter) may be essentially equal to the diameter of the through hole of the outer peripheral 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 upper temperature of the crucible and the lower temperature of the crucible, the lower temperature of the crucible is higher than the upper temperature, and the thickness of the outer peripheral member (i.e., the distance from the top end of the outer peripheral member toward the seed crystal to the bottom end away from the seed crystal) may be 30 millimeters, but is not limited thereto.

[0052] [Table 1]

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

[0054] Referring to Figures 12 and 13, Figure 12 is a diagram of defects in one example of a 6-inch wafer grown by a conventional silicon carbide crystal production apparatus using a guide member having a fixed structure made of graphite material, and Figure 13 is a diagram of defects in one example of a 6-inch wafer grown by the silicon carbide crystal production apparatus of the present application.

[0055] As for the wafer in Figure 12, the diameter of the crystal growth surface of the seed crystal is 145 mm, the diameter of the through hole of the guide member having a fixed structure is 152 mm, the growth pressure is 400 Pa, and the upper temperature of the crucible is 2120°C. Using a conventional silicon carbide crystal production device, the crystal with a final crystal diameter of 153 mm is produced. The crystal is then processed and shaped into a 150 mm ingot, which is then further processed into a 150 mm wafer sheet through processing steps such as cutting, polishing, and buffing. The wafer undergoes a surface cleaning process to detect surface defects, and the defect diagram in Figure 12 is obtained.

[0056] For the wafer in Figure 13, 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 (the thickness of each graphite material layer may be 1 mm), the growth pressure is 400 Pa, and the upper temperature of the crucible is 2115°C. The crystal produced by the silicon carbide crystal production apparatus of the present application has a final crystal diameter of 154.5 mm. The crystal is processed and shaped into an ingot of 150 mm, and further processed into a wafer sheet of 150 mm by processing steps such as cutting, polishing, and buffing. The wafer is then subjected to a surface cleaning process to detect surface defects, and the defect diagram of Figure 13 is obtained.

[0057] The black dots in Figures 12 and 13 are the defective locations on the wafer. The total number of defects on the wafer in Figure 12 is 1279, and the total defect density (TDD) of the wafer is approximately 7.89 / cm 2 The number of microtubules was 606, and the micro-pipe density (MPD) was approximately 3.74 / cm 2 Most of the defects are distributed on the edge of the wafer, and the total number of defects on the wafer in FIG. 13 is 41 (the actual total number of defects is even smaller because some defects are located at the laser etching part of the large flat edge, which may be misjudged as defects by the detection table), and the total defect density on the wafer is about 0.25 / cm 2 , 3 microtubules, microtubule density of approximately 0.02 / cm 2 and has clean edges and few defects.

[0058] Therefore, as can be seen from Figures 12 and 13, compared with wafers grown by conventional silicon carbide crystal production apparatus, the wafers grown by the silicon carbide crystal production apparatus of the present application have edges with fewer defects and less stress, and the total defect density in the wafers obtained by applying the silicon carbide crystal production apparatus of the present application, caused by impurities in the crystal expansion and guide assembly or silicon vapor corroding the crucible wall or the occurrence of carbon coating on the crystal expansion and guide assembly, is significantly reduced.

[0059] Each 150 millimeter (or 6 inch) ingot produced by the process in the examples of Figures 12 and 13 above is fabricated into twelve 6 inch silicon carbide wafers.

[0060] Of the 12 wafers obtained in the embodiment of FIG. 12, 5 were broken during processing, and 7 completed final processing. Only one of the 7 wafers had an MPD of 1 / cm 2The MPD of all 12 wafers was smaller than 1 / cm, which is in line with the commercial grade. The yield was 8.3%. Of the 12 wafers obtained in the embodiment of FIG. 13, 12 were processed (no cracks due to processing). 2 and the yield of production-grade wafers is 100%. Therefore, it can be seen that the yield of production-grade wafers can be improved by improving the stress on the crystal edge, improving the crystal defects caused by stress, and reducing the total defect density of the crystal.

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

[0062] For the wafer in FIG. 14, 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., and a crystal having a final crystal diameter of 203 mm is produced using a conventional silicon carbide crystal production apparatus, which is then processed, sliced, and polished to obtain a silicon carbide wafer with a diameter of 200 mm. For the wafer in FIG. 15, the diameter of the crystal growth surface of the seed crystal is 195 mm, the diameter of the through hole of the outer peripheral member is 205 mm, the number of graphite material layers of the tubular core member is 5 (each graphite material layer may be 1 mm thick), the growth pressure is 200 Pa, and the upper temperature of the crucible is 2000° C., and a crystal having a final crystal diameter of 203 to 204 mm is produced using the silicon carbide crystal production apparatus of the present application, which is then processed, sliced, and polished to obtain a silicon carbide wafer with a diameter of 200 mm.

[0063] As shown in Figures 14 and 15, compared with wafers grown by conventional silicon carbide crystal production apparatus, wafers grown by the silicon carbide crystal production apparatus of the present application have edges with fewer defects and less stress, and in the wafers obtained by applying the silicon carbide crystal production apparatus of the present application, defects in the polycrystalline insert caused by impurities or silicon vapor of the crystal expansion and guide assembly corroding the crucible wall or the generation of carbon coating on the crystal expansion and guide assembly are reduced.

[0064] In short, due to the design of the outer edge member and the tubular core member (i.e., the diameter of the through hole of the outer edge member is larger than the diameter of the crystal growth surface of the seed crystal, the tubular core member is a flexible graphite material with a purity of greater than 99.9%, is mechanically connected to the inner wall of the through hole, has an inner diameter equal to or smaller than the diameter of the crystal growth surface of the seed crystal, and has a length smaller than the distance between the bottom end away from the seed crystal and the raw material), when the tubular core member comes into contact with the crystal growth front edge of the crystal during the crystal growth process, it causes the raw material to fall and keeps the crystal from reacting with the outer edge member, so that the crystal produced by the silicon carbide crystal production apparatus of the present application has an edge with low defects.

[0065] In addition, the outer edge member of the present application is merely a structural member and is reusable without participating in the reaction. Furthermore, the cost is lower and no impurities that would affect subsequent processes are generated compared to the case where a tubular core member made of high-purity graphite material (the tubular core member will fall off during the crystal growth process) is used, and a guide member having a fixed structure made of a graphite material having a tantalum carbide or tungsten carbide coating (or plating) layer is used.

[0066] In addition, by improving the internal stress and edge stress of the crystal, the growth thickness of the spherical crystal and the product thickness of the ingot can be increased, and by improving low-angle grain boundaries and microtubules caused by edge stress, the probability of cracking during wafer processing or processing can be reduced, and the overall production volume of product-grade wafers can be increased with the same number of inputs into the furnace and the same materials and labor costs input into the furnace.

[0067] Although the present invention has been described with reference to the above embodiments, it should be noted that these descriptions are not intended to limit the present invention. On the contrary, the present invention encompasses modifications and similar arrangements that are obvious to those skilled in the art. Therefore, the scope of the patent application should be interpreted in the broadest manner to include all obvious modifications and similar arrangements. [Explanation of symbols]

[0068] 50 Raw materials 60 seed crystals 62 Crystal Growth Surface 70 graphite material layers 80 Heater 90 Heat insulation material 100 Silicon carbide crystal production equipment 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 production system 300 How to make silicon carbide crystals 310, 320 steps D1, D2, D3 diameter F Thickness direction L1, L3 length L2 distance

Claims

1. An 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 accommodating a raw material, and a crucible lid for fixing a seed crystal and covering the crucible body; The crystal expansion guide assembly includes: An outer peripheral member that 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 the through hole being larger than the diameter of the crystal growth surface of the seed crystal; a tubular core member that is made of a flexible graphite material with a purity of more than 99.9%, is mechanically connected to the inner wall of the through hole, has an inner diameter equal to or smaller than the diameter of the crystal growth surface of the seed crystal, has a length smaller than the distance to the raw material, and the outer peripheral member does not react with the crystal during the crystal growth process, and falls onto the surface of the raw material when the crystal growth front edge of the crystal comes into contact with the outer peripheral member; Equipment for producing silicon carbide crystals.

2. an outer diameter of the tubular core member essentially equal to the diameter of the throughbore, the tubular core member engagingly connected to the inner wall of the throughbore; 2. An apparatus for producing silicon carbide crystals according to claim 1.

3. the tubular core member is formed by winding a single layer of flexible graphite material into a tubular shape, the layer of graphite material being engaged and connected to the inner wall of the through hole; 2. An apparatus for producing silicon carbide crystals according to claim 1.

4. the tubular core member is formed by winding and stacking a plurality of flexible graphite material layers into a tubular shape, the top ends of the graphite material layers facing the seed crystal are arranged in a descending step shape or in parallel along the thickness direction of the tubular core member, and the thicknesses of the graphite material layers are the same or different; 2. An apparatus for producing silicon carbide crystals according to claim 1.

5. when the top ends of the graphite material layers facing the seed crystal are arranged in a descending step shape along the thickness direction of the tubular core member, during the crystal growth process, the crystal growth front edge of the crystal contacts the graphite material layers in sequence, causing the contacted graphite material layers to fall in sequence onto the surface of the raw material; 5. An apparatus for producing silicon carbide crystals according to claim 4.

6. the layer of graphite material being graphite paper, graphite foil or a graphite blanket; 5. An apparatus for producing silicon carbide crystals according to claim 3 or 4.

7. The material of the outer peripheral member is a graphite material, a metal carbide material, or a melt-resistant compound; 2. An apparatus for producing silicon carbide crystals according to claim 1.

8. the diameter of the through hole being essentially equal to the largest crystal growth diameter; 2. An apparatus for producing silicon carbide crystals according to claim 1.

9. 1. A method for producing silicon carbide crystals, comprising: A system for producing silicon carbide crystals is provided, the system for producing silicon carbide crystals comprising a silicon carbide crystal production device, a seed crystal and a heater, the silicon carbide crystal production device comprising a crucible and a crystal expansion and guide assembly, the crucible including a crucible body and a crucible lid, the crucible body having an internal space for receiving a raw material, the heater being disposed around the crucible, the crucible lid for fixing the seed crystal and covering the crucible body, the crystal expansion and guide assembly including an outer rim member and a tubular member. Step (a) including a core member, the outer peripheral member being fixed to the crucible body or between the crucible body and the crucible lid, being located between the seed crystal and the raw material, and having a through hole, the diameter of the through hole being larger than the diameter of the crystal growth surface of the seed crystal, the tubular core member being made of a flexible graphite material having a purity of more than 99.9%, being mechanically connected to the inner wall of the through hole, the inner diameter being equal to or smaller than the diameter of the crystal growth surface of the seed crystal, and the length being shorter than the distance to the raw material; (b) setting a growth pressure of the silicon carbide crystal production device and a growth temperature of the silicon carbide crystal production device by the heater, growing a crystal from the seed crystal, and during the crystal growth process, the outer peripheral member does not react with the crystal, and when the crystal growth front edge of the crystal contacts the tubular core member, the tubular core member falls onto the surface of the raw material. A method for producing silicon carbide crystals.

10. 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, or the tubular core member is formed by winding a plurality of flexible graphite material layers into a tubular shape, and the graphite material layers are stacked in parallel and engaged and connected to the inner wall of the through hole, and the step (b) includes, during the crystal growth process, when the crystal growth front edge of the crystal contacts the graphite material layer / these graphite material layers, the graphite material layer / these graphite material layers drop from the outer edge member onto the surface of the raw material. A method for producing the silicon carbide crystal according to claim 9.

11. the tubular core member is formed by winding a plurality of flexible graphite material layers into a tubular shape, and the top ends of these graphite material layers facing the seed crystal are arranged in a descending step shape along the thickness direction of the tubular core member and are stacked and engaged with the inner wall of the through hole, and the step (b) includes that, during the crystal growth process, when the crystal growth front edge of the crystal contacts these graphite material layers in turn, the contacted graphite material layers fall in turn onto the surface of the raw material. A method for producing the silicon carbide crystal according to claim 9.

12. The step (b) further includes: the unshed graphite material layer prevents free carbon generated when the peripheral member is subjected to heat from entering the crystal. A method for producing a silicon carbide crystal according to claim 10 or 11.

13. The step (b) further includes: after the tubular core member falls onto the surface of the raw material, a space formed between the crystal growth front edge of the crystal and the outer edge member is defined as a crystal expansion region; and the crystal is grown within the crystal expansion region.

10. A method for producing silicon carbide crystals according to claim 9, comprising:

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 the silicon carbide crystal according to claim 9.

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

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