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DE-102017204257-B4 - Coated product and manufacturing process

DE102017204257B4DE 102017204257 B4DE102017204257 B4DE 102017204257B4DE-102017204257-B4

Abstract

A method for producing a product, in particular a body, wherein the product is formed from a material consisting predominantly of carbon or a ceramic material, wherein the product is coated with a surface layer by chemical vapor deposition, wherein the product is coated with a surface layer of crystalline silicon nitride, wherein the surface layer is formed on the product at a process temperature of over 1100 °C to 1700 °C, preferably over 1200 °C to 1550 °C, particularly preferably over 1300 °C to 1500 °C, wherein the product is infiltrated with crystalline silicon nitride before the surface layer is formed, wherein the infiltration of the product is carried out by chemical vapor infiltration at a process temperature of over 800 °C to 1700 °C, preferably over 1000 °C to 1550 °C, particularly preferably over 1300 °C to 1500 °C, wherein the surface layer consists of stoichiometric, crystalline Silicon nitride is formed, wherein the crystalline silicon nitride is formed free of carbon, hydrogen, oxygen and metals, characterized in that that in chemical vapor deposition the product is heated to the process temperature in a process chamber and a gas mixture containing at least one silicon-containing and one nitrogen-containing compound is metered into the process chamber, whereby the gas mixture is formed within a process gas nozzle in the process chamber.

Inventors

  • Karl Brennfleck
  • Johannes Galle
  • Dennis Muscutt
  • Volker Rauhut

Assignees

  • SCHUNK KOHLENSTOFFTECHNIK GMBH

Dates

Publication Date
20260513
Application Date
20170314

Claims (10)

  1. A method for producing a product, in particular a body, wherein the product is formed from a material consisting predominantly of carbon or a ceramic material, wherein the product is coated with a surface layer by chemical vapor deposition, wherein the product is coated with a surface layer of crystalline silicon nitride, wherein the surface layer is formed on the product at a process temperature of over 1100 °C to 1700 °C, preferably over 1200 °C to 1550 °C, particularly preferably over 1300 °C to 1500 °C, wherein the product is infiltrated with crystalline silicon nitride before the surface layer is formed, wherein the infiltration of the product is carried out by chemical vapor infiltration at a process temperature of over 800 °C to 1700 °C, preferably over 1000 °C to 1550 °C, particularly preferably over 1300 °C to 1500 °C, wherein the surface layer consists of stoichiometric, crystalline silicon nitride is formed, wherein the crystalline silicon nitride is formed free of carbon, hydrogen, oxygen and metals, characterized in that during chemical vapor deposition the product is heated to the process temperature in a process chamber and a gas mixture with at least one silicon-containing and one nitrogen-containing compound is metered into the process chamber, wherein the gas mixture is formed within a process gas nozzle in the process chamber.
  2. Method according to one of the preceding claims, characterized in that the crystalline silicon nitride is formed in the trigonal, hexagonal and/or cubic modifications.
  3. Method according to one of the preceding claims, characterized in that the surface layer of the product is formed with a layer thickness of 1 µm to 5000 µm, preferably from 1 µm to 1000 µm, and particularly preferably from 5 µm to 100 µm.
  4. Method according to one of the preceding claims, characterized in that the surface layer is formed on the product at a pressure in a process chamber of >1 mbar to 300 mbar, preferably >1 mbar to 60 mbar.
  5. Method according to one of the preceding claims, characterized in that the process chamber is heated by means of a resistance heater or inductively.
  6. Method according to one of the preceding claims, characterized in that ammonia and/or nitrogen is used as the nitrogen-containing compound, and silane, preferably monosilane, disilane, trisilane, dichlorosilane, tetrachlorosilane, and/or trichlorosilane, is used as the silicon-containing compound.
  7. Method according to one of the preceding claims, characterized in that hydrogen, hydrogen chloride and/or argon is used as a further gas.
  8. Method according to one of the preceding claims, characterized in that, during the infiltration of the product, pores in the material of the product are closed or filled with the crystalline silicon nitride.
  9. Method according to one of the preceding claims, characterized in that when infiltrating the product with the crystalline silicon nitride, the product is completely infiltrated, or an infiltration layer with a layer thickness of up to 100 µm, preferably up to 500 µm, and particularly preferably up to 2500 µm is formed.
  10. Crucible, in particular for receiving molten metals or molten silicon, wherein the crucible is made of graphite, carbon fiber reinforced carbon or a ceramic material, wherein at least one wetting surface of a melt receiving area of the crucible is coated with a surface layer of crystalline silicon nitride, wherein at least the wetting surface which is infiltrated with crystalline silicon nitride, characterized in that the surface layer is formed from stoichiometric crystalline silicon nitride, wherein the crystalline silicon nitride is free of carbon, hydrogen, oxygen and metals.

Description

The invention relates to a crucible and a method for producing a product, in particular a body, wherein the product is formed from a material consisting predominantly of carbon or a ceramic material, wherein the product is coated with a surface layer by means of chemical vapor deposition (CVD), wherein the product is coated with a surface layer of crystalline silicon nitride, wherein the surface layer is formed on the product at a process temperature of over 1100 °C to 1700 °C, preferably over 1200 °C to 1550 °C, particularly preferably over 1300 °C to 1500 °C, wherein the product is infiltrated with crystalline silicon nitride before the surface layer is formed, wherein the infiltration of the product is carried out by means of chemical vapor infiltration at a process temperature of over 800 °C to 1700 °C, preferably over 1000 °C to 1550 °C, particularly preferably over 1300 °C to 1500 °C, wherein the surface layer is formed from stoichiometric crystalline silicon nitride, wherein the crystalline silicon nitride is formed free of carbon, hydrogen, oxygen and metals. Products coated by chemical vapor deposition are well-known and used in various applications. For example, it is known to coat crucibles made of carbon, such as CFC or graphite, or of a ceramic material, such as quartz, with a surface layer of amorphous carbon or synthetic diamond using chemical vapor deposition (CVD). Furthermore, in the electronics industry and semiconductor technology, it is known to coat substrates made of ceramic materials with silicon nitride. The formation of a silicon nitride surface layer is regularly carried out using plasma-enhanced chemical vapor deposition (PECVD), for example, for the purpose of passivating the substrate. An amorphous silicon nitride surface layer can be formed using the PECVD process at an operating temperature of 200 °C to 500 °C and an operating pressure of 1 mbar. This silicon nitride layer then contains 5 to 30% hydrogen or oxygen from the process gas. Alternatively, silicon nitride coatings can be applied to suitable substrates using processes such as slip coating, powder coating, flame spraying, and plasma spraying. These silicon nitride coatings are diffusion-open but not gas-tight, not corrosion-resistant, and/or contain hydrogen, oxygen, carbon, or other impurities due to the process. Depending on the type of object being coated with silicon nitride, it may be undesirable for the silicon nitride layer to lack corrosion resistance or contain impurities. Furthermore, such silicon nitride layers, for example, when forming the wetting surface of a crucible, can wear down quickly. It is also possible for impurities contained in the silicon nitride layer to migrate into the melt within the crucible and impair its quality, which is why crucibles are preferably coated with other materials. The US 5 300 322 A This document describes a process for forming a silicon nitride surface layer on a product, wherein the surface layer is applied to, for example , ceramic bodies by means of chemical vapor deposition (CVD) and is at least 1 µm thick. The coating process takes place in an oven heated by a resistance heater. The resulting layer consists of crystalline silicon nitride (β- Si₃N₄ ) and the coating temperature is 1200°C. The US 4 741 925 AThis also describes such a coating process, in which a surface layer of α- Si₃N₄ is produced at 1350°C. Specifically, reaction gases are introduced into a furnace chamber via a pipe located inside the furnace, where they mix. The coating is then applied to a crucible for melting silicon. The journal article “Processing of biomorphic Si 3 N 4 ceramics by CVI-R technique with SiCl 4 /H 2 /N 2 system” ( Ghanem, H., et al., In: J.Eur.Ceram.Soc., Vol. 27, 2007, pp. 2119-2125 )“ deals with the formation of crystalline silicon nitride by chemical vapor infiltration within a carbonized paper. The infiltration takes place in a temperature range of 1300°C to 1450°C, whereby β-Si 3 N 4 is deposited. The DE 39 33 039 A1 Disclosing a coating of CFC molded bodies with silicon nitride, wherein the CFC of the molded body is converted to silicon carbide by infiltration with metallic silicon. Residual pores of the molded body are filled with metallic silicon, this silicon being converted to silicon nitride with nitrogen. The US 5 283 089 A discloses a method for producing ceramic composite materials, wherein a substrate of ceramic fibers is heated at a process temperature between 1100 °C and The material is infiltrated or coated with crystalline silicon nitride at 1400 °C using a CVI/CVD process. A composite material produced using this process can be used as a component for high-temperature applications, for example, in a heating furnace. The AU 1989 042 593 B1 and the CN 1 03 058 696 A Disclosing methods for the production of fiber-reinforced ceramic composite materials. The US 6 284 357 B1 This concerns laminated matrix composite materials. The magazine article “ Chemical vapor