Apparatus for producing silicon carbide single crystals

Abstract

The invention relates to a method for producing a single crystal from silicon carbide, a device having a furnace (401) and a chamber (402) with a crucible (403) and a seed crystal (405) received in the furnace (401), in which an initial material (407) comprising silicon carbide is arranged in the crucible (403), wherein the initial material (407) comprises a mixture of silicon carbide powder (411) and silicon carbide blocks (410).

Description

Technical Field

[0001] This invention relates to an apparatus and method for preparing single crystals from silicon carbide. Background Technology

[0002] Today, single crystals are artificially produced on an industrial scale for various technological applications. Here, growth from the melt, from solution, and from the gas phase can be distinguished based on the phase transition that causes crystallization. In the case of gas phase growth, sublimation, or physical vapor deposition, and chemical vapor deposition methods can be further distinguished. In physical vapor deposition, the material to be grown is heated and evaporated, transforming it into the gas phase. This gas can then be sublimated at the seed crystal under suitable conditions, thereby achieving crystal growth. Polycrystalline raw materials (powders or granules) are typically recrystallized in this way. Chemical vapor deposition operates in a similar manner. In chemical vapor deposition, the material to be grown can only be transformed into the gas phase by an auxiliary material that is chemically bonded to the material, because otherwise the vapor pressure would be too low. Thus, by bonding with the auxiliary material, a higher transport rate towards the seed crystal can be achieved.

[0003] Silicon carbide single crystals are of particular interest, especially due to their semiconductor properties. The preparation of silicon carbide single crystals is carried out in a furnace equipped with a crucible and a seed crystal. In the crucible, silicon carbide raw material is heated, and further crystal growth is achieved by accumulation on the seed crystal. Furthermore, the interior of the processing chamber is evacuated. Graphite is used as the material for the innermost processing chamber containing the crucible. The properties of the silicon carbide raw material are crucial to the quality of the silicon carbide single crystal. Summary of the Invention

[0004] The objective of this invention is to overcome the shortcomings of the prior art and to provide an apparatus by means of which single crystals with higher quality can be prepared.

[0005] The task is solved by the apparatus and method according to the present invention.

[0006] The apparatus for preparing single crystals from silicon carbide according to the invention comprises a furnace and a chamber containing a crucible and a seed crystal housed in the furnace, wherein an initial material comprising silicon carbide is disposed in the crucible, and the initial material comprises a mixture of silicon carbide powder and silicon carbide blocks.

[0007] Advantageously, the silicon carbide block has a particle size in the range of 1 mm to 10 mm and the silicon carbide powder has a particle size in the range of 150 μm to 1000 μm.

[0008] According to an advantageous extension of the device, the initial material comprises silicon carbide powder and silicon carbide blocks in a mixing ratio selected from the range of 25% by weight of silicon carbide powder to 75% by weight of silicon carbide blocks up to 55% by weight of silicon carbide powder to 45% by weight of silicon carbide blocks.

[0009] Of particular advantage is that, with regard to total mass, the initial material comprises silicon carbide powder and silicon carbide blocks in a mixing ratio of 40% by weight of silicon carbide powder to 60% by weight of silicon carbide blocks.

[0010] It is also advantageous that the silicon carbide of the initial material has a purity greater than 5N.

[0011] According to a preferred embodiment, the initial material has different mixing ratios of silicon carbide powder and silicon carbide blocks in different regions of the initial material's height.

[0012] In particular, it is advantageous that the first third of the lower part of the height of the initial material contains silicon carbide powder and silicon carbide blocks in a mixing ratio selected from the range of 55% silicon carbide powder to 45% silicon carbide blocks up to 70% silicon carbide powder to 30% silicon carbide blocks.

[0013] Furthermore, the second third of the height of the initial material contains silicon carbide powder and silicon carbide blocks in a mixing ratio selected from the range of 40% silicon carbide powder to 60% silicon carbide blocks up to 55% silicon carbide powder to 45% silicon carbide blocks.

[0014] It is also advantageous that the upper third third of the height of the initial material contains a mixture of silicon carbide powder and silicon carbide blocks in a mixing ratio selected from the range of 25% silicon carbide powder to 75% silicon carbide blocks up to 40% silicon carbide powder to 60% silicon carbide blocks.

[0015] According to an alternative extension, the initial material is prepared in the form of a pressling.

[0016] The initial material is also advantageous when it is attached to silicon carbide containing elemental silicon, especially when it contains elemental silicon in the form of silicon powder.

[0017] An advantageous extension specifies that the elemental silicon is formed in the initial material in the form of one or more reservoirs.

[0018] Particularly preferably, the storage chamber having elemental silicon is formed as a continuous ring.

[0019] It is particularly advantageous that the elemental silicon forms a share of the total mass of the initial material ranging from 5% to 50% by weight.

[0020] An alternative construction of the device specifies that it includes a storage container for the powdered elemental silicon and an input conduit leading to the crucible.

[0021] It is also advantageous that the crucible is made of graphite.

[0022] To better understand this invention, the following figures will be used to explain it in more detail. Attached Figure Description

[0023] The accompanying diagrams are shown in very simplified schematic form: Figure 1 An apparatus for preparing single crystals by physical vapor deposition is shown; Figure 2 Showing according to Figure 1 Details of the crucible of the apparatus; Figure 3 A second embodiment of an apparatus for preparing single crystals using initial materials formed as compacts is shown; Figure 4 A third embodiment of an apparatus for preparing single crystals is shown; Figure 5 A fourth embodiment of an apparatus for preparing single crystals is shown; Figure 6 A fifth embodiment of an apparatus for preparing single crystals is shown. Detailed Implementation

[0024] First, it should be noted that in different described embodiments, the same parts are given the same reference numerals or the same component names, and the disclosure contained throughout the specification can be meaningfully transferred to the same parts having the same reference numerals or the same component names. Positional statements selected in the specification, such as above, below, side, etc., also pertain to the direct description and the figures shown, and these positional statements should be meaningfully transferred to the new position if the position changes.

[0025] Figure 1A furnace 401 for preparing single crystals by physical vapor deposition is shown. The furnace 401 includes a vacuum-ejectable chamber 402 having a crucible 403 received therein. The crucible 403 is substantially can-shaped, with its upper portion closed by a lid 404. Here, the lower side of the lid 404 of the crucible 403 is configured to hold a seed crystal 405. A starting material 407 is located in the bottom region 406 of the crucible 403; this starting material serves as the raw material for crystal growth on the seed crystal 405 and is gradually depleted during the preparation process.

[0026] The transformation of the initial material 407 to the gas phase can be achieved by heating with the aid of a heating device 408. According to this embodiment, the heating of the initial material 407 and the crucible 403 is performed inductively by the heating device 408. Furthermore, the crucible 403, disposed in the chamber 402, is enclosed by a heat-insulating portion 409 for thermal insulation. Simultaneously, the heat-insulating portion 409 prevents heat loss from the crucible 403 and enables a heat distribution within the crucible 403 that is favorable for the growth process of the crystal on the seed crystal 405.

[0027] Preferably, a glass material (especially quartz glass) is used as the material for the chamber 402. Preferably, the crucible 403 and the heat insulation portion 409 surrounding the crucible are made of graphite, wherein the heat insulation portion 409 is formed by graphite felt.

[0028] By heating the initial material 407, its atoms or molecules transform into the gas phase. In this way, these atoms or molecules can diffuse into and deposit on the seed crystal 405 within the internal space of the crucible 403, thereby achieving crystal growth. Here, the aim is to form a single crystal as free of impurities as possible. The quality of the crystal formed on the seed crystal 405 depends not only on the temperature gradient between the initial material 407 and the seed crystal 405 but also on the evaporation rate of the initial material 407. The latter, in turn, depends on the form in which the raw material of the initial material 407 is provided in the crucible 403. It has proven advantageous that the initial material 407 is formed from a mixture of powdered raw materials and raw materials present in block form.

[0029] Figure 2 Showing according to Figure 1 Details of the crucible 403 of furnace 401. In this embodiment, silicon carbide is provided as a raw material for the initial material 407. Here, the silicon carbide of the initial material 407 comprises not only blocks 410 but also powder 411. Here, the silicon carbide blocks 410 and powder 411 are loosely deposited in the bottom section 406 of the crucible 403. Here, as in... Figure 2As shown in the diagram, the powder 411 and the block 410 exist in a mixed form. It proves advantageous here that the initial material 407 exists in different mixing ratios of block 410 and powder 411 in different height regions of the bottom section 406.

[0030] The manufacturing process of single crystals made of silicon carbide in furnace 401 typically lasts for several days. Here, the consumption of the raw material 407 also depends on the temperature distribution generated in the initial material 407 by the heating device 408, and the evaporation rate of the raw material changes accordingly with the duration of the process. This is because the surface of the initially loosely distributed particles of the raw material 407 is gradually compacted through melting. Different mixing ratios of silicon carbide blocks 410 and silicon carbide powder 411 in different filling regions or at different heights of the bottom section 406 thus filled contribute to a relatively constant evaporation rate of the raw material throughout the correspondingly long duration of the crystallization process. In this respect, the mixing ratio of blocks 410 and powder 411 is significant because the raw material powder 411 is associated with a large surface area and therefore a large evaporation rate, while blocks 410, with a smaller total surface area, result in a smaller evaporation rate.

[0031] According to Figure 2 In the described embodiment, blocks 410 and powder 411 are stacked at height 412 in different mixing ratios. Here, the lower first third of the initial material 407 at height 412 contains 55% to 70% by weight of silicon carbide powder 411. Correspondingly, the lower third of the initial material 407 contains 30% to 45% by weight of silicon carbide blocks 410. The middle second third of the initial material 407 at height 412 contains 40% to 55% by weight of powder 411 and correspondingly complementary 45% to 60% by weight of blocks 410. The upper third of the initial material 407 at height 412 ultimately contains 25% to 40% by weight of silicon carbide powder 411 and correspondingly complementary 60% to 75% by weight of silicon carbide blocks 410.

[0032] The silicon carbide powder 411 has a particle size ranging from 300 μm to 1000 μm. The silicon carbide block 410 has a particle size ranging from 1 mm to 5 mm. It is further specified that high-purity silicon carbide is used. A purity greater than 5N is provided not only for the silicon carbide block 410 but also for the powder 411.

[0033] Regarding the total mass of the initial material 407 that is filled into the bottom region 406 of the crucible 403 at the start of the process, a mixing ratio of 40% by weight of silicon carbide powder 411 to 60% by weight of silicon carbide blocks 410 is set. However, a mixing ratio ranging from 25% by weight of silicon carbide powder 411 to 75% by weight of silicon carbide blocks 410 up to 55% by weight of silicon carbide powder 411 and 45% by weight of silicon carbide blocks 410 is also suitable.

[0034] Figure 3 Showing according to Figure 1 A second embodiment of the apparatus for preparing single crystals is shown. Simplified here, only details of the crucible 403 together with the bottom section 406 are shown. In this case, the initial material 407 of the silicon carbide mixture filled into the bottom region 406 of the crucible 403 is formed by a compact 413. The initial material 407 of the compact 413 also consists of a mixture of silicon carbide powder 411 and silicon carbide blocks 410. (Also shown according to...) Figure 2 As in the embodiment, a varying distribution of the mixing ratio of blocks 410 and powder 411 is provided along the direction of height 412. To manufacture the compact 413, the silicon carbide blocks 410 and the silicon carbide powder 411 are pressed into a compact during the preceding manufacturing process. To manufacture the compact 413, the silicon carbide mixture of the initial material 407 may also be subjected to heat treatment (sintering process).

[0035] Figure 4 Showing according to Figure 1 A third embodiment of the apparatus for preparing single crystals is provided. Here, the mixture of silicon carbide block 410 and silicon carbide powder 411 in the initial material 407 contains additional elemental silicon 414. Preferably, the silicon 414 is mixed into the initial material 407 in the form of fine particles or as powder and also has high purity. Preferably, the elemental silicon 414 has a purity greater than 5N. By adding the silicon 414 to the initial material 407, a silicon deficiency in the silicon carbide mixture of the initial material 407 that occurs during the duration of the crystallization process can be compensated for. In this embodiment, the elemental silicon 414 forms a weight fraction of the total mass of the initial material 407 ranging from 5% to 50% by weight. Preferably, the silicon is mixed into the initial material in the middle second third and the upper third third of the height 412 of the initial material 407.

[0036] Figure 5A fourth embodiment of furnace 401 together with crucible 403 is shown. The receiving space in the bottom section 406 of the crucible 403 forms a substantially rotationally symmetrical, or cylindrical, volume about axis 415. Furthermore, the initial material 407 is formed by a compact 413 consisting of blocks 410 and powder 411 of silicon carbide. Additionally, a storage chamber 416, or reservoir, containing elemental silicon 414 is formed or enclosed within the volume of the compact 413. Preferably, the storage chamber 416 in the compact 413 contains powdered silicon 414. The amount of silicon 414 added to the compact 413 is enclosed within a continuous storage chamber 416, preferably in annular form. The volume of silicon 414 can be, for example, embedded in the compact 413 of the initial material 407 in an annular or toroidal shape.

[0037] Figure 6 An alternative embodiment of the apparatus for preparing single crystals from silicon carbide is shown. Here, in this diagram of furnace 401, only the crucible 403 and the additional storage container 417 for powdered or granular silicon 414 are shown. (This is in contrast to the previous diagram.) Figure 2 In this embodiment, the same method is used initially, where the initial material 407 is also formed from a mixture of silicon carbide blocks 410 and silicon carbide powder 411, and this mixture is loosely piled or deposited in the bottom section 406 of the crucible 403. Elemental silicon 414 can be supplied to the initial material 407 by providing a storage container 417 containing elemental silicon 414, which is added to the silicon carbide at different stages during the crystallization process. For this purpose, an input conduit 418 is provided between the storage container 417, located outside the crucible 403, and the interior of the crucible 403, through which the silicon 414 is supplied. This can be achieved, for example, by means of a screw conveyor (not shown) that supplies the silicon 414 to or through the conduit 418.

[0038] The embodiments illustrate feasible implementation variations. It should be noted that the invention is not limited to the implementation variations specifically described herein, but rather various combinations of the various implementation variations are also feasible, and the feasibility of such variations is within the capabilities of a person skilled in the art, based on the teachings of the specific invention.

[0039] The scope of protection is defined by the claims. However, the claims should be interpreted with reference to the specification and drawings. Individual features or combinations of features of the different embodiments shown and described can constitute an inventive solution in itself. The task upon which such inventive solution is based can be obtained from the specification.

[0040] In the specific specification, all statements of numerical ranges shall be understood as including any and all partial ranges within the stated numerical range. For example, the statement of 1 to 10 shall be understood as including all partial ranges starting from the lower limit of 1 and the upper limit of 10. That is, all partial ranges begin with the lower limit of 1 or greater and end with the upper limit of 10 or less, such as 1 to 1.7, 3.2 to 8.1, or 5.5 to 10.

[0041] Finally, for clarity and to better understand the construction, some elements are not shown to scale and / or are enlarged and / or reduced.

[0042] List of reference numerals

[0043] 401 furnace

[0044] Room 402

[0045] 403 Crucible

[0046] 404 cap

[0047] 405 Seed Crystal

[0048] 406 Bottom Section

[0049] 407 Initial Materials

[0050] 408 Heating Device

[0051] 409 Insulation Section

[0052] 410 pieces

[0053] 411 powder

[0054] 412 Height

[0055] 413 Pressed blank

[0056] 414 Silicon

[0057] 415 axis

[0058] Storage Room 416

[0059] 417 Storage Containers

[0060] 418 Inlet Pipeline

Claims

1. A method for preparing single crystals of silicon carbide using an apparatus comprising a furnace (401) and a chamber (402) receiving a crucible (403) within the furnace (401), wherein a seed crystal (405) and an initial material (407) comprising silicon carbide are disposed in the crucible (403), characterized in that, The initial material (407) comprises a mixture of silicon carbide powder (411) and silicon carbide blocks (410). - The silicon carbide powder (411) has a particle size in the range of 300 μm to 1000 μm. - And the silicon carbide block (410) has a particle size in the range of 1 mm to 10 mm. - And in the first third of the lower part of the height (412) of the initial material (407), silicon carbide powder (411) and silicon carbide blocks (410) are mixed in a ratio selected from the range of 55% silicon carbide powder (411) to 45% silicon carbide blocks (410) up to 70% silicon carbide powder (411) to 30% silicon carbide blocks (410). - And in the second third of the height (412) of the initial material (407), silicon carbide powder (411) and silicon carbide blocks (410) are mixed in a ratio selected from the range of 40% silicon carbide powder (411) to 60% silicon carbide blocks (410) up to 55% silicon carbide powder (411) to 45% silicon carbide blocks (410). - And in the third third of the upper part of the height (412) of the initial material (407), silicon carbide powder (411) and silicon carbide blocks (410) are mixed in the following ratio, which is selected from the range of 25% silicon carbide powder (411) to 75% silicon carbide blocks (410) up to 40% silicon carbide powder (411) to 60% silicon carbide blocks (410).

2. The method according to claim 1, characterized in that, Regarding the total mass, the initial material (407) comprises silicon carbide powder (411) and silicon carbide blocks (410) in a mixing ratio selected from the range of 25% by weight of silicon carbide powder (411) to 75% by weight of silicon carbide blocks (410) up to 55% by weight of silicon carbide powder (411) to 45% by weight of silicon carbide blocks (410).

3. The method according to claim 2, characterized in that, Regarding the total mass, the initial material (407) comprises silicon carbide powder (411) and silicon carbide blocks (410) in a mixing ratio of 40% by weight of silicon carbide powder (411) to 60% by weight of silicon carbide blocks (410).

4. The method according to any one of claims 1 to 3, characterized in that, The initial material (407) has silicon carbide with a purity greater than 5N.

5. The method according to any one of claims 1 to 3, characterized in that, The initial material (407) is made in the form of a compact (413).

6. The method according to any one of claims 1 to 3, characterized in that, Elemental silicon (414) is supplied to the initial material (407) in addition to the silicon carbide.

7. The method according to claim 6, characterized in that, Silicon (414) contains the elemental silicon in the form of silicon powder.

8. The method according to claim 6, characterized in that, The elemental silicon (414) is formed in the initial material (407) in the form of one or more storage chambers.

9. The method according to claim 8, characterized in that, The storage chamber containing the elemental silicon (414) is formed as a continuous ring.

10. The method according to claim 6, characterized in that, The elemental silicon (414) constitutes a share ranging from 5% to 50% by weight in the total mass of the initial material (407).

11. The method according to claim 6, characterized in that, For this purpose, a storage container (417) for the powdered elemental silicon (414) and an input conduit (418) leading to the crucible (403) are used.

12. The method according to any one of claims 1 to 3, characterized in that, The crucible (403) is made of graphite.

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