Process for Producing a Silicon Carbide-Containing Body

Abstract

The present invention relates to a process for producing a silicon carbide-containing body (100), characterized in that the process has the following process steps: a) providing a mixture (16) comprising a silicon source and a carbon source, the silicon source and the carbon source being present together in particles of a solid granular material; b) arranging a layer of the mixture (16) provided in process step a) on a carrier (12), the layer of the mixture (16) having a predefined thickness; and c) treating the mixture (16) arranged in process step b) over a locally limited area with a temperature within a range from 1400 C. to 2000 C. according to a predetermined three-dimensional pattern, the predetermined three-dimensional pattern being selected on the basis of the three-dimensional configuration of the body (100) to be produced. Such a process allows simple and inexpensive production even of complex structures from silicon carbide.

Claims

1. Method for producing a silicon carbide-containing body, the method comprising: a) providing a mixture with a silicon source and a carbon source, wherein the silicon source and the carbon source are present together in particles of a solid granular material; b) disposing a layer of the mixture provided in process step a) on a carrier, wherein the layer of the mixture has a predefined thickness; and c) locally limited treating the mixture disposed in process step b) at a temperature in a range from approximately 1400 C. to 2000 C. according to a predetermined spatial pattern, wherein the predetermined spatial pattern is selected based on the spatial configuration of the body to be produced.

2. Method according to claim 1, wherein process step c) is carried out by use of a laser.

3. Method according to claim 1, wherein process steps b) and c) are repeatedly carried out in succession.

4. Method according to claim 3, wherein between two successively process steps c) the distance between the carrier and a heat source for treating the mixture with a temperature in a range from approximately 1400 C. to 2000 C. is increased.

5. Method according to claim 1, wherein prior to process step b) a separation layer for at least partially separating the silicon carbide-containing body to be produced from the carrier is applied onto the carrier.

6. Method according to claim 5, wherein as a separation layer a layer of the mixture is applied onto the carrier, wherein said separation layer is treated locally limited at a temperature in a range from approximately 1400 C. to 2000 C. in order to form at least one connection from the carrier to the silicon carbide-containing body to be produced.

7. Method according to claim 1, wherein at least process step c) is at least partly carried out under a protective gas.

8. Method according to claim 1, wherein at least one process step is carried out by use of a dopant.

9. Method according to claim 8, wherein at least process step c) is carried out partly under a protective gas and partly under a gas comprising a gaseous dopant, or at least process step c) is carried out partly under a gas comprising a first gaseous dopant and partly under a gas comprising a second gaseous dopant.

10. Method according to claim 1, wherein the mixture provided in process step a) at least partially comprises a silicon source, a carbon source and a dopant, wherein the silicon source and the carbon source and the dopant are together present in particles of a solid granular material.

11. Method of claim 10, wherein the mixture provided in process step a) is partially configured such that the silicon source and the carbon source are present together in particles of a solid granular material, and that the particles comprise no dopant, and that the mixture is further partially configured such that the silicon source and the carbon source are present together with a dopant in particles of solid granular material or that the mixture is partially configured such that the silicon source and the carbon source are present together with a first dopant in particles of the solid granular material and that the mixture is further partially configured such that the silicon source and the carbon source are present together with a second dopant in particles of the solid granular material.

12. Method according to claim 1, wherein the mixture provided in process step a) is provided by use of a sol-gel process.

13. Method according to claim 12, wherein the sol-gel process comprises at least the following process steps: d) providing a precursor mixture comprising a silicon precursor, a carbon precursor and optionally a dopant, wherein the precursor mixture is present in a solvent; e) treating the precursor mixture at an elevated temperature under drying the precursor mixture; and f) optionally heating the dried precursor mixture to a temperature in a range from approximately 800 C. to 1200 C., in particular in a range from approximately 900 C. to 1100 C.

14. Method according to claim 1, wherein the mixture provided in process step a) comprises particles of the solid granular material with a particle size which is set based on the predetermined spatial pattern.

15. Method according to claim 1, wherein the thickness of the layer of the mixture is in a range from 1 m to 10 m.

Description

[0067] It shows:

[0068] FIG. 1 a schematic illustration of a silicon carbide-containing body which is producible by a method according to the present invention;

[0069] FIG. 2 a schematic illustration of a first process step of a method according to the present invention;

[0070] FIG. 3 a schematic illustration of another process step of a method according to the present invention;

[0071] FIG. 4 a schematic illustration of another process step of a method according to the present invention;

[0072] FIG. 5 a schematic illustration of another process step of a method according to the present invention;

[0073] FIG. 6 a schematic illustration of a first process step of a method according to the present invention;

[0074] FIG. 7 a schematic illustration of a first process step of a method according to the present invention;

[0075] FIG. 8 a schematic illustration of a first process step of a method according to the present invention; and

[0076] FIG. 9 a schematic illustration of a first process step of a method according to the present invention.

[0077] FIG. 1 shows a schematic illustration of a silicon carbide-containing body 100, which is producible by a method according to the present invention. For example, the body 100 consists of silicon carbide. The body 100 can basically have substantially any shape and geometry and due to its design of silicon carbide is extremely robust against chemical and/or mechanical and/or thermal influences. For example, the body 100 may be configured of crystalline silicon carbide and thereby be present for example in the form 3C-SiC.

[0078] FIG. 2 schematically shows a first step of a method according to the present invention for producing the body 100. FIG. 2 shows a reactor 10, which, for example, may be sealable gas-tight and can be filled with an inert gas, such as argon, or a dopant-containing gas, such as nitrogen. In the reactor 10 a carrier 12 is provided which comprises a carrier plate 14 which may serve as a support for a mixture 16. The mixture 16 includes a silicon source and a carbon source and optionally a dopant, wherein the silicon source and the carbon source and optionally the dopant are present together in particles of a solid granular material. Moreover, a laser 18 is provided which is able to emit laser radiation 20.

[0079] FIG. 2 shows that the mixture 16 at first forms an intermediate layer 15, which is intended to at least partially separate the body 100 to be produced from the carrier 12.

[0080] FIG. 3 shows that the laser radiation 20 can thermally treat the mixture 16 of the intermediate layer 15. In detail, it is provided that a locally limited treatment of the mixture 16 disposed in process step b) at a temperature in a range of 1400 C. to 2000 C. is carried out. By the action of the laser radiation 20 on the mixture 16, the latter is heated, wherein silicon carbide is formed from the mixture 16 in treated areas 22, whereas in untreated areas 24, i.e. in areas which are not treated by the laser beam, the mixture 16 is still present. In the embodiment shown here, the treated areas 22 occurring in FIG. 3 each form connections 23 which fix the body 100 to be produced to the carrier 12 or the carrier plate 14, respectively, wherein in the untreated areas 24 a separation between the body 100 and the carrier 12 is provided.

[0081] FIG. 4 shows that a further layer of the mixture 16 is applied onto the intermediate layer 15. For this purpose, prior to the application of the further layer of the mixture 16, or prior to the temperature treatment the carrier 12 or the carrier plate 14 may be displaced such that the distance to the laser 18 is increased, in particular by the amount of thickness of the newly deposited layer. To this end, the carrier 12 or the carrier plate 14 is in particular configured movable, as shown by the arrow. With this layer the production of the body 100 begins. To this end, as shown in FIG. 5, a locally limited treatment of the mixture 16 or the uppermost layer thereof at a temperature in a range of 1400 C. to 2000 C. according to a predetermined spatial pattern is carried out, wherein the predetermined spatial pattern is selected based on the spatial configuration of the body 100 to be produced. For this purpose, similar to the formation of the connections 23, the laser 18 may be movable two-dimensionally, in particular in a plane parallel to the orientation of the carrier plate 14 or in a plane perpendicular to the propagation direction of the laser radiation 20, as shown by the arrows.

[0082] By the action of the laser radiation 20 on the mixture 16 the mixture is heated, wherein silicon carbide is formed in the treated areas 22 from the mixture, whereas in untreated areas 24, that is, in areas which are not treated by the laser beam 20, the mixture 16 is still present.

[0083] FIG. 6 shows that after the temperature treatment of the mixture 16 a further layer is applied onto the treated layer of the mixture 16, which may also be treated locally limited by the laser 18 and depending on a body to be produced. For this purpose, prior to the application of the further layer of the mixture 16 or prior to the temperature treatment the carrier 12 or the carrier plate 14 can again be displaced such that the distance from the laser 18 is increased, in particular by the amount of thickness of the newly applied layer. To this end, the carrier 12 or the carrier plate 14 is in particular configured movable, as shown by the arrow.

[0084] By means of the further temperature treatment by use of the laser 18 or the laser radiation silicon carbide 20 can be formed locally limited in the further layer, too, as shown in FIG. 7.

[0085] FIG. 8 shows a further process step in which after the temperature treatment of the mixture a further layer is applied on the treated layer of the mixture 16, which can also be treated locally limited by the laser 18 and depending on a body to be produced. For this purpose, prior to the application of the further layer of the mixture 16 or prior to the temperature treatment the carrier 12 or the carrier plate 14 can again be displaced such that the distance to the laser 18 is increased, in particular by the amount of thickness of the newly applied layer.

[0086] By means of the further temperature treatment by the laser 18 or the laser radiation silicon carbide 20 can be formed locally limited in the further layer, too, as shown in FIG. 9.

[0087] By means of a substantially arbitrary structure of the individual layers of the mixture 16 the silicon carbide-containing body 100 can be formed, which may correspond to the treated areas 22 in FIG. 6. The untreated areas 24 essentially comprise only the untreated mixture 16, which can be easily removed from the body 100. In this way, the body 100 can be finished in a simple manner by further removing the connections 23.

[0088] An exemplary method for producing such a body 100 is described in the following embodiment.

EMBODIMENT

[0089] The example described below relates to the production of a silicon carbide-containing body 100 by use of a sol-gel process for forming the starting mixture 16.

[0090] Preparation of the sol-gel SiC precursor: In the following the chemical composition, the sol-gel treatment with various drying process steps at 70 C. to 200 C., and the final production of the SiC solid granular material at 1000 C. are described.

[0091] Liquid sugar, tetraethylorthosilicate and ethanol are mixed to form a sol and gelatinized at 60-70 C. under airtight conditions. The composition for one batch was (a) a colloidal suspension of 135 g tetraethylorthosilicate (TEOS) in 168.7 g ethanol dissolved as a silicon source and (b) a solution of 68 g sucrose as a carbon source, in 75 g distilled water, to which 37.15 g hydrochloric acid (HCl) is added as a catalyst for forming invert sugar. Then, the solution (a) was mixed with the liquid sugar (b) under stirring. Alternatively, instead of the solution (b) liquid sugar (invert sugar, 122 g 70%) can also be used directly. Then no water and only a very small amount of hydrochloric acid (5.2 g) are added, since this is only required for the start of gelling process. This sol is aged at 50 C. and then dried at 150-200 C.

[0092] In order to obtain relatively coarser granules in the range of some 10 m or below a temporary stirring process is carried out during the aging and/or the drying process. This granular material or powder is freed of remaining unwanted reaction products at 1000 C. in a nitrogen or argon gas stream, and finally optionally ground.

[0093] A modification of the SiC precursor for the purpose of doping of SiC nanofibers can be implemented. An n-type doping may be carried out e.g. with nitrogen (exemplary additives: nitric acid, ammonium chloride, potassium nitrate or melamine), or with phosphorus (exemplary additives: potassium dihydrogen phosphate or disodium hydrogen phosphate). A p-type doping can be carried out e.g. with boron (exemplary additive: di-sodium tetraborate) or with aluminum (additive: aluminum powder). The dopants are added to the sol, the amounts are dependent upon the specific additive and the desired dopant concentration.

[0094] The mixture thus produced can be converted to silicon carbide by a heat treatment at a temperature in a range from 1400 C. to 2000 C., whereby a silicon carbide-containing body can be formed. In detail, an n-doped mixture with a grain size of 2 mm can be heated by the beam of a fiber laser pumped by high-performance laser diodes, in a volume of about 8 mm.sup.3 to a temperature of about 1600 to 1700 C. for about 0.2 seconds. The previously black mixture powder becomes solid green 3CSiC.