RU2763358C1 - Method for gas-phase deposition of tantalum carbide on the surface of products - Google Patents

Abstract

FIELD: nanotechnology.

SUBSTANCE: invention relates to a method for gas-phase deposition of coatings of tantalum carbides on the surface of the product and can be used to create protective coatings with high hardness, resistance to erosion and ablation, for example, on graphite products and carbon-carbon composites in combustion chambers and nozzles of aircraft engines, to create wear-resistant hard coatings and coatings with high antifriction properties, for coatings that play the role of a diffusion barrier for oxygen and other elements in microelectronics products, in such as a gate electrode in n-type oxide-metal-semiconductor structures, for coatings accumulating solar energy and solar cells promising for manufacturing. The method for gas-phase deposition of tantalum carbides on the surface of the product includes the supply of tantalum halide vapors, carbon halide vapors and reducing metal vapors to the surface of the product. Vapors of these substances are transported in streams of inert carrier gases through various channels to the surface of the product. When tantalum carbides are deposited on the surface of the product near the surface, the reagents are mixed with the elemental composition of the mixture with the ratios Ta/C from 0.1 to 10 and Me/(G1+G2) from 0.1 to 10 and heating of reagents to temperatures of 850-1400 K, while Me is a reducing metal, G1 is a halogen used in Ta halide, G2 is a halogen used in carbon halide.

EFFECT: deposition of a coating of tantalum carbides on the surface of products is ensured at lower deposition temperatures, with reduced requirements to the equipment used and increased safety of deposition processes to obtain coatings of improved quality.

5 cl, 1 dwg

Description

The present invention relates to a method for the deposition of tantalum carbide on the surface of products and can be used to create protective coatings with high hardness, resistance to erosion and ablation, for example, on products made of graphite and carbon-carbon composites in combustion chambers and nozzles of aircraft engines, to create wear-resistant hard coatings and coatings with high antifriction properties, for coatings that play the role of a diffusion barrier for oxygen and other elements in microelectronic products, such as a gate electrode in n-type oxide-metal-semiconductor structures, for coatings that store solar energy and are promising to create solar cells.

A known method of obtaining highly dispersed coatings of refractory tantalum carbides by hydrolysis of organic solutions of metal-containing complex compounds with polymers. The resulting gel is dried at temperatures of 293-523 K and subjected to pyrolysis at 623-873 K, and then carbothermal synthesis is carried out at temperatures of 873-1473 K and a pressure of 10 ^-1 -10 ^-4 Pa (Patent RU No. RU 2333888 C1, published on 20.09. 2008, IPC C01 B 31/30). During the synthesis, the Ta/C ratio can be varied by changing the composition of the components in the initial mixture, and the resulting carbides are of high purity.

The disadvantage of this method is the difficulty of obtaining spatially ordered coatings. The thickness and density of the resulting coatings, as a rule, are heterogeneous in area, especially on parts of complex shape, due to uneven spreading of the gel over the surface and shrinkage of the coating during drying and firing. In addition, the production of coatings by this method is expensive, which is determined by the high cost of organometallic reagents.

A known method of forming TaC films on a Cu substrate by methods of plasma-assisted atomic layer deposition (PEALD - Plasma Enhanced Atomic Layer Deposition). (Patent US No. US 7407876 B2 published on 5.08.2008, IPC C23C 16/32) The formation of the tantalum carbide coating is carried out until the desired thickness is obtained by alternating processes: a) deposition of an organic tantalum compound on the substrate, b) exposure of the substrate to the plasma of the reducing agent - H _2c ) surface treatment with argon plasma. The use of plasma activation makes it possible to lower the temperature of the film formation reaction below 673 K.

The disadvantage of this method is the high cost of the used organometallic reagents, which, moreover, are able to polymerize when heated during their evaporation and subsequent passage of the reaction zone. Polymerization products are unsuitable as reagents and can be deposited in the evaporation chamber and gas pipelines, leading to equipment inoperability. The disadvantage of PEALD technology lies in its unsuitability for products of complex shape and products with internal cavities. In addition, the adhesion of the obtained protective coatings is low, since at low temperatures a zone of diffuse interaction of the coating with the substrate is not formed and, in addition, damage to the surface of the product is possible during ion bombardment.

A known method of obtaining finely crystalline (grain size 1-10 μm) dense, homogeneous and defect-free pyrolytic tantalum carbide on a substrate heated to 1493-1653 K from a vapor-gas mixture, with a volume ratio of components, vol.%: TaCl ₅ from 2.5 to 11 ; CH ₄ from 1 to 7; H ₂ from 2.5 to 26 and the rest is He (Patent SU No. SU508561, published on March 30, 1976, IPC C23C 16/32).

The disadvantage of this method of deposition of tantalum carbide is due to the fact that the deposition process is possible only on substrates having a melting temperature significantly higher than the process temperature, which is quite high. In addition, at high temperatures, the resulting chlorine will have a high activity, which can lead not only to corrosion of the reactor materials, but also to corrosion of the substrate on which the coating is applied. It should be taken into account that the use of hydrogen can lead to hydrogenation and hydrogen embrittlement of the materials of the reaction chamber, coating, substrate, which will lead to deterioration of the coating properties.

As a prototype of the invention, a method was adopted for forming coatings of tantalum carbide on carbon materials using chemical vapor deposition from tantalum halides, such as tantalum pentachloride TaCl ₅ , and hydrocarbons, such as methane CH ₄ or ethane C ₂ H ₆ , fed into the reaction chamber with gas - a carrier with argon, hydrogen or a mixture thereof (JP Patent No. JP 2009298916, published 12/29/2009, IPC C23C 16/32) (or EP 2520691 A1 published 11/07/2012 Bulletin 2012/45). The patent states that with an increase in the molecular weight of the hydrocarbon, the activation energy decreases and the temperature for obtaining coatings decreases, therefore, instead of CH _4, it is recommended to use ethane C ₂ H ₆ as a carbon source to reduce the precipitation temperature. In the method, it is proposed to first form tantalum carbide nuclei on the surface of the carbon substrate at temperatures of 1123-1223 K and a reduced pressure of ^~ 10 ³ Pa, and then carry out the growth of tantalum carbide crystals into coatings with a gradual increase in temperature by 100 degrees per hour. The Ta/C ratio in the coating is set by the concentration of carbon in the gas supplied to the reaction chamber, which is from 2 to 25 times greater than the concentration of tantalum. This makes it possible to obtain a gradient coating with a ratio from Ta/C=2 in the layer adjacent to the carbon to Ta/C=1 in the outer layer. Additionally, to reduce the porosity of the coating, it is heat treated at temperatures of at least 1873 K.

In this method, the use of ethane instead of methane and a decrease in pressure in the working chamber makes it possible to slightly reduce the temperature of deposition of tantalum carbides, compared with the previous method. In addition, carrying out the deposition with increasing temperature allows a slight improvement in the quality of the coatings. However, the deposition temperature remains quite high, and all the disadvantages associated with the possibility of destruction of the materials of the working chamber and deterioration of the properties of the coating and substrate due to their hydrogenation, hydrogen embrittlement and high-temperature interaction with chlorine and hydrogen chloride remain. In addition, the use of hydrogen requires caution due to its flammability and explosiveness.

Figure 1 shows a diagram of a part of the reactor with the placement of the initial reagents - tantalum bromide and cadmium in a batcher-mixer, where:

1. Tantalum halide

2. Reducing metal

3. Nozzle inserts with nozzle mixer

4. Substrate

5. Heater

6, 8. Channels for supplying an inert carrier gas.

7. Channel for supplying a mixture of an inert carrier gas with a carbon source.

The technical result of this invention is to reduce the requirements for the equipment used, to reduce the deposition temperature of tantalum carbides, to improve the quality of coatings and to increase the safety of deposition processes.

The technical result is achieved by using a reducing metal as a reducing agent, and a carbon halide pair as a carbon source, moreover, a pair of tantalum halide, carbon halide and a vapor of the reducing metal are transported in flows of inert carrier gases through various channels to the surface of the product, and during deposition tantalum carbides on the surface of the product near the surface, mixing of the reagents is ensured so that the elemental composition of the mixture has ratios Ta / C from 0.1 to 10 and Me / (G1 + G2) from 0.1 to 10 and heating of the reagents to temperatures of 850 - 1400 K.

In addition, cadmium is used as a reducing metal.

_{In addition, CCl 4} is used as a source of carbon - carbon halide.

In addition, tantalum bromide TaBr _{5 is} used as the tantalum halide.

In addition, tantalum iodide is used as the tantalum halide, while iodine vapor is added to the tantalum iodide vapor stream.

The use of a reducing metal (instead of hydrogen) as a reducing agent will improve the safety of coating deposition, reduce the requirements for the equipment used, and improve the quality of coatings due to the absence of a negative effect of hydrogen on materials and the need for equipment that provides hydrogen supply to the reactor and its subsequent disposal.

The use of cadmium as a reducing metal helps to reduce the overall temperature of the deposition process, since cadmium vapor is volatile at relatively low temperatures.

The use of CCl ₄ as a carbon source makes it possible to simplify the equipment due to the fact that CCl ₄ is a volatile liquid under normal conditions. Due to the easy dissociation of CCl ₄ during heating, the deposition temperature of the coatings can be lowered. In addition, CCl _{4 is} fire and explosion-proof.

The use of tantalum bromide makes it possible to reduce the deposition temperature due to the high volatility of TaBr ₅ at relatively low temperatures and the relatively low heat of formation.

Separate supply of reagents through the channels due to the lack of contact between them will prevent their early interaction and will improve the quality of the coating.

The essence of the invention lies in the fact that for the deposition of tantalum carbides on the surface and internal cavities of products of complex shape, the reduction of vapors of tantalum halides and carbon halides with vapors of a reducing metal is used, in accordance with the reactions:

where G1 and G2 are one of F, Cl, Br, I, and Me is one of the metals Cd, Zn, Mg, Al, K, Na, Li.

For reactions (1, 2) to proceed, tantalum halide, carbon halide, and reducing metal are evaporated in different evaporators. The resulting vapors are transported through separate channels by flows of inert carrier gases (helium or argon) to prevent their premature interaction away from the surface of the product (substrate). Near the substrate, the pairs are mixed, heated to the deposition temperature, and interact depending on the ratio of the supplied reagents according to reaction (1) and/or (2), which leads to the deposition of tantalum carbides on the substrate. The composition, quality, and thickness of coatings will be determined by the temperature and time of deposition, the type of supplied reagents, their concentration in carrier gas flows, and other parameters. During deposition, it is recommended to maintain the ratio of elements in the set of reagents Ta/C from 0.1 to 10 and Me/(G1+G2) from 0.1 to 10 and heating the reagents to temperatures of 850–1400 K.

Consider the optimal choice of reagents for reactions (1) and (2) for the following conditions: 1) deposition at atmospheric pressure, 2) evaporation temperatures of the initial reagents should be lower than the deposition temperature, 3) the deposition temperature of tantalum carbides should be no higher than 1123 K , which corresponds to the minimum temperature specified for the prototype, 4) by-products of reactions (1) and (2) must evaporate at the temperature of deposition of carbides.

Tantalum halides evaporate intensively above 473 K (except for iodide), while their volatility and heat of formation increase in the series TaI ₅ >TaBr ₅ >TaCl ₅ >TaF ₅ [Levy RA, Investigation of chemically vapor deposited tantalum for medium caliber gun barrel protection, Reportof SERDP project WP-1425, New Jersey Inst, of Technology, 2008.]. Tantalum iodide partially decomposes already during evaporation, which makes it difficult to use, since it is difficult to control its content in vapors. Tantalum chloride and fluoride are volatile, but have relatively high heats of formation, which implies rather high temperatures of their thermal decomposition. Tantalum bromide is optimal for use, since it is volatile at relatively low temperatures (vapour pressure of 10 Torr at 473 K) and has a heat of formation (-144 kJ / mol) less than that of TaCl ₅ and TaF ₅ , which contributes to its thermal decomposition .

At 773 K, the volatility of reducing metal vapors decreases in the series K>Na>Cd>Zn>Li>Mg>Al. Working with alkali metals is quite difficult. Zn, Mg, and Al at 773 K have a low volatility, which does not allow high performance of reactions (1) and (2). As a reducing metal, it is optimal to use cadmium, which has a relatively high volatility (saturated vapor pressure of 10 Torr at 763 K) [A.G. Kalandarishvili, V.K. Mikheev, P.D. Chilingarishvili, Experimental determination of saturated vapor pressure of magnesium and cadmium, TVT, 1988, volume 26, issue 5, 1016-1018]). In addition, the relatively high volatility of cadmium bromides and chlorides will not allow them to coprecipitate together with carbides already at 850 K.

To optimize the deposition conditions in the TaBr ₅ -CCl ₄ -Cd-He system, thermodynamic calculations of the equilibrium compositions formed in the system at temperatures T=673-1673 K, pressure P=1.01⋅10 ⁵ Pa and molar ratios of the initial components (TaBr ₅ +CCl ₄ +Cd)/He=10-3; Ta/(Ta+C)=0.01-0.909; Cd/(Cd+hal)=0-0.952 (hal=Cl+Br) (Goncharov, OY Thermodynamics of the Chemical Vapor Deposition of Carbides in the System TaBr ₅ -CCl ₄ -Cd. Inorganic Materials 37, 237-242 (2001 ) https://doi.org/10.1023/A:1004109212945). As a result, it was obtained that:

1) the deposition of pure tantalum carbides is possible at temperatures above Τ=840, since cadmium chlorides co-precipitate with decreasing temperature;

2) monocarbide TaC _y (y=0.815÷1) can be obtained at T=840÷1100 K, the maximum degree of conversion of tantalum into TaC=0.6 is achieved at 973 K and ratios Ta/C=1.5 and 0.6<Cd / hal<9, and the composition TC ₀₉₁ is deposited at T=913 K and the ratio Ta/C=1.5 and Cd/hal=9.

3) carbide Ta _2-z C (z=0.085÷0.199) can be obtained at T=960÷1070 K, the maximum degree of conversion of tantalum to Ta _2-z C ^~ 0.6 is achieved at 973 K and ratios Ta/C=3 and 0.5<Cd / hal<9, and the composition Ta _1.915 C is deposited at T=973 K and Ta/C=3 and Cd/hal=0.5;

4) the maximum degree of transformation of tantalum into carbides ^~ 0.9 is achieved at ratios Ta/C<1 and 0.6<Cd/hal<9 in the two-phase region during the deposition of TaC+C compositions.

Example. The figure shows a diagram of a part of the reactor with the placement of the initial reagents - tantalum halide and reducing metal in a batcher-mixer (Patent RU No. RU 2640369, published on December 28, 2017, IPC C23C 16/45504), which has two evaporators installed one above the other with spiral channels , into which tantalum bromide 1 and cadmium 2 are loaded and coaxially installed nozzle liners 3 with a mixer in the form of a nozzle in the lower part, forming channels for supplying a saturated vapor-gas mixture into the reaction chamber to the substrate 4 heated by the heater 5.

Helium carrier gas is supplied through channels 6, 7, 8. Helium supplied through channel 6 is saturated with tantalum bromide vapor in evaporator 1 at temperatures of 180–250°C (453–523 K) and is transported through the central nozzle insert 3 to sample 4. channel 7 is supplied with a flow of helium carrier gas saturated with carbon halide vapor - CCl ₄ and then goes to the sample through a separate channel in the nozzle insert 3. Helium supplied through channel 8 is saturated with cadmium vapor in evaporator 2 at temperatures of 400-500 ° C (673- 773 K) and is transported to sample 4 via external nozzle liner 3. The design of the dosing mixer makes it possible to maintain the content of vapors close to their content in saturated steam by controlling the evaporation temperatures in each of the evaporators 1 and 2, and, therefore, to set the ratio of tantalum bromide to cadmium at the required level. Heater 5 maintains the temperature of tantalum deposition from 850 K to 1400 K.

Claims (5)

1. The method of gas-phase deposition of tantalum carbides on the surface of the product, including the supply of reagents: tantalum halide vapor, carbon source vapor and reducing agent vapor to the product surface, characterized in that a reducing metal is used as a reducing agent, and carbon halide vapor is used as a carbon source , moreover, vapors of tantalum halide, carbon halide and vapors of the reducing metal are transported in flows of inert carrier gases through various channels to the surface of the product, and when tantalum carbides are deposited on the surface of the product near the surface, mixing of the reagents is ensured with the elemental composition of the mixture with Ta / C ratios from 0.1 to 10 and Me/(G1+G2) from 0.1 to 10 and heating the reagents to temperatures of 850-1400 K, while Me is the reducing metal, G1 is the halogen used in the Ta halide, G2 is the halogen used in carbon halide. 2. The method according to p. 1, characterized in that CCl ₄ is used as the carbon halide. 3. The method according to p. 1, characterized in that cadmium is used as the reducing metal. 4. The method according to p. 1, characterized in that tantalum bromide is used as tantalum halide. 5. The method according to claim 1, characterized in that tantalum iodide is used as the tantalum halide, while iodine vapor is added to the tantalum iodide vapor stream.

Images