RU2637845C1 - METHOD FOR PRODUCING SPUTTERING COMPOSITE TARGET CONTAINING HEUSLER ALLOY PHASE OF CO2FeSi - Google Patents

Abstract

FIELD: metallurgy.

SUBSTANCE: method involves mechanical mixing of powders of Co₂FeSi Heusler alloy components, sintering-pressing of produced mixture by means of electro-impulse plasma at 600°c and minimum pressure of 2.5 kN. Sintering is carried out by passing series of direct current pulses up to 5 kA with pulse duration 3.3 ms by filling powder mixture to produce a compact. After this, the produced compact is melted in quartz crucible of induction furnace at 1300°C for 3 hours till complete melting to produce a homogenised ingot. The produced ingot is crushed and ground to produce particles of 1-200 mcm size, and sintering-pressing of composite target is carried out by electro-impulse plasma sintering method with dilatometric shrinkage curve control.

EFFECT: production of homogenised mechanically strong composite target of specified geometry containing Heusler alloy phase of stoichiometric composition.

7 cl, 4 dwg

Description

The invention relates to metallurgy, in particular to the production of products from a metal powder mixture by electropulse sintering, relates to a method for manufacturing a sprayable composite target containing a phase of a Geisler alloy Co ₂ FeSi, which can be used in the production of microelectronics.

Spraying a homogenized target provides layers of uniform composition; the value of uniformity increases with decreasing layer thickness. The porosity of the target has a significant effect on the sputtering speed of the target and, as a consequence, on the deposition rate of the film. The greater the porosity of the target, the more the target is sprayed, i.e. in less time it will be possible to spray a layer of a greater thickness, and vice versa. The sputtering speed of the target with low porosity is lower, the use of such targets allows better control of the thickness of the layers, which is important for thin layers.

From patent US 7973351 B2, cl. H01L 21/02, publ. 05.07.2011, at known sputtering target Co ₂ MnSi, used to form stoichiometric crystalline layer Heusler Co ₂ MnSi to create element magnetoresistive RAM (MRAM) and spin transistor (spin MOSFET). However, in the specified source of information there is no information about the method of manufacturing this target.

From patent US 8070919 B2, cl. B32B 17/06, C23C 14/35, publ. 12/06/11, a known spray target made of a Co ₂ MnSi ingot obtained by electric arc sintering of a stoichiometric mixture of Co, Mn and Si powders. The sprayed target had the composition Co (99.5%, Sigma-Aldrich): Mn (99.98% Sigma-Aldrich): Si (99.95%, Sigma-Aldrich) in the ratio 2: 1: 1, the rate of temperature increase was 50 ° C / min. After preparation of the Co ₂ MnSi ingot, it is pulverized by wet grinding in a ball mill and then pressed into a 2-inch spray target.

The disadvantage of this method of obtaining a spray target of composition Co ₂ MnSi is porosity due to electric arc sintering, leading to a large effective surface, its oxidation and adsorption of moisture and volatile contaminants from the air, probably for this reason, the authors of the patent could not confirm the absence of impurities in the target. The degree of homogenization that the electric arc sintering method can provide is lower compared to the simultaneous melting of all powder components.

A known method of producing a blank of a cathode target with a given chemical composition and the required geometric dimensions (RU 2405062, C23C 14/34, B22F 3/15, B22F 9/10, B22D 7/00, published on November 27, 2010). At the same time, in order to obtain a target blank, molten metal is poured into a ceramic mold to obtain a cylindrical ingot electrode. Then the ingot is melted by plasma during rotation to obtain spherical granules with a diameter of 50-400 microns. The estimated number of spherical granules is poured in a vacuum into a ring-shaped capsule to form a target with a cavity. The capsule is brewed and subjected to hot isostatic pressing, after which the capsule is depressurized and the workpiece is mechanically cleaned by removing the capsule components from it. The cathode target is made of an alloy based on nickel or on the basis of cobalt. As a result, target blanks of stable geometric dimensions are obtained.

The disadvantage of this method is the contamination of the target with a ceramic material, capsule. In addition, isostatic pressing also results in a porous target with the drawbacks mentioned above.

A known method for producing high-density products by sintering billets from compacted nanosized tungsten carbide powders by the method of electric pulse plasma sintering (SPS), which can be used, inter alia, for the manufacture of targets for spraying wear-resistant coatings of extremely loaded critical machine parts, for example crankshafts of heavy armored vehicles , as well as special materials with the effect of dynamic super-strength (RU 2548252 С2, class С04В 35/56, B82Y 40/00, publ. 04.20.15). The initial tungsten carbide powder with a particle size of not more than 110 nm with a volume fraction of WC of at least 99% is subjected to electropulse plasma sintering using a Dr.Sinter Model-625 apparatus manufactured by SPS SYNTEX INC. Ltd. (Japan) under conditions of its pressing in graphite molds at a pressing pressure of 60-70 MPa in a vacuum of 4 Pa with an optimal speed selected from the range of 25-2400 ° C / min at a temperature that is selected depending on the particle size of the initial WC powder . With an increase in the heating rate in the indicated interval, the hardness of the sintered preform increases, while a decrease in its value increases the crack resistance of this preform. The sintering temperature may be 1550-1800 ° C.

The specified method does not provide for the manufacture of sputtering targets containing the phase of the Geisler alloy composition Co ₂ FeSi.

Electropulse sintering (SPS) is a complex physical and mechanical process that takes place at high temperatures in powder materials (Fig. 2). During sintering, the compaction of the powder material occurs, which externally manifests itself in a change in volume, an increase in density and a decrease in porosity. Sintering of powder materials occurs by diffusion mass transfer of a substance under the action of external pressure and internal forces associated primarily with surface tension forces. Diffusion is carried out in certain ways that determine the sintering mechanisms.

There are at least six different sintering mechanisms in powder materials: surface diffusion, bulk diffusion from the particle surface to the bulkhead, gas phase transfer, grain boundary diffusion, bulk diffusion from the grain boundary to the pore, and plastic deformation (Roberto Orru, Roberta Licheri, Antonio Mario Locci, Alberto Cincotti, Giacomo Cao. Consolidation / synthesis of materials by electric current activated / assisted sintering. Materials Science and Engineering R 63, pp. 127-287, 2009).

All these mechanisms lead to the formation and growth of a jumper between the particles, however, only part of them leads to shrinkage and compaction of the powder material. Surface diffusion, volume diffusion from the particle surface to the jumper, transport through the gas phase (mechanisms 1, 2 and 3, see Fig. 2) lead to the growth of the jumper without compaction and are called sealing mechanisms. Grain-boundary diffusion and bulk diffusion from the grain boundary to the pore (mechanisms 4 and 5, see Fig. 2) are the most important mechanisms of compaction of polycrystalline ceramics.

Plastic deformation caused by the movement of dislocations (mechanism 6, see Fig. 2) also leads to compaction (Khrustov VR Development and study of ceramics based on nanopowders of aluminum, zirconium and cerium oxides. Abstract of dissertation for the degree of candidate of technical sciences Ekaterinburg, 2010). At the initial stage of sintering, compaction is caused by macroscopic processes of redistribution of powder particles into a more “dense packing”, then the growth of the jumpers begins. After the appearance of jumpers between the particles and reaching a certain density, diffusion along grain boundaries and volume is turned on. If the diffusion along the grain boundaries is quite intense, then rapid compaction can be observed, but with intensive grain-boundary diffusion, a process that has a negative effect on sintering — grain growth and anomalous growth — can be activated. The main methods for changing the free volume of grain boundaries are related to the microalloying of the boundaries by impurity atoms and the organization of dislocation flows to the boundaries (SW Wang, LD Chen, T. Hirai, Jingkun Guo. Formation of Al ₂ O ₃ grains with different sizes and morphologies during the pulse electric current sintering process. J. Mater. Res., Vol. 16, No. 12, December 2001).

With traditional methods of sintering powder materials (free sintering, hot pressing), heating rates do not exceed tens of degrees and are not able to ensure the formation of high temperature gradients inside the powder. Therefore, to control the diffusion permeability of grain boundaries, it is necessary to use new, high-speed sintering technologies for powder materials. One of the most promising technologies for high-speed sintering is the technology of electropulse sintering.

The method of electropulse sintering is one of a number of highly effective methods for sintering powders, which are currently being intensively developed in many scientific centers. A wide range of possibilities with electrophysical effects on the powder material determines the variety of these methods developed in the CIS countries. These include: electric discharge sintering (EDS) (IP Shapiro, RI Todd, JM Titchmarsh, SG Roberts. Effects of Y2O3 additives and powder purity on the densification and grain boundary composition of Al ₂ O ₃ / SiC nanocomposites. Journal of the European Ceramic Society, 29, pp. 1613-1624, 2009); Electropulse sintering under pressure (EISD) (A.V. Nomoev. Superhardness of ceramics based on nanosized alumina powders with the addition of nanopowders of magnesium oxide and silicon. Journal of Physics and Technology, Volume 36, Issue 21, pp. 46-53. 2010 ); electropulse sintering (J. Wang, SY Lim, SC Ng, CH Chew, LM Gan Dramatic effect of small amount of MgO addition on the sintering of Al ₂ O ₃ -.. 5 vol% SiC nanocomposite Materials Letters, 33, pp 273. -277, 1998); Electropulse pressing (Sheng Guo, Apichart Limpichaipanit, RI Todd. High resolution optical microprobe investigation of surface grinding stress in Al ₂ O ₃ and Al ₂ O ₃ / SiC nanocomposites. Journal of the European Ceramic Society, 31, pp. 97-109, 2011).

In foreign countries, similar methods include: Field assisted sintering technique (FAST), Plasma Assisted Sintering (PAS), Spark Plasma Sintering (SPS), and Electroconsolidation, High Energy High Rate Processing (HEHR), Electric Dis-charge Compaction (EDC) [CC Anya, SG Roberts. Pressureless sintering and elastic constants of Al ₂ O ₃ - SiC nanocomposites. Journal of the European Ceramic Society 17, pp. 565-573, 1997] and a number of others.

The objective of the invention is to develop a method of manufacturing a sprayable homogenized target of a Geisler alloy Co ₂ FeSi, providing the ability to control its porosity.

The technical result from the use of the invention is to obtain homogenized, i.e. homogeneous in composition, mechanically strong composite target of a given geometry (a disk 0.7-1 mm thick, 40 mm in diameter) and the required porosity in the range of 2-40%, containing exclusively the phase of the Geisler alloy of stoichiometric composition Co ₂ FeSi.

In FIG. 1 is a flow chart of a method for manufacturing a spray target containing a phase of a Geisler alloy Co ₂ FeSi.

In FIG. 2 schematically illustrates the sintering-pressing mechanism of a powder mixture using Co ₂ FeSi as an example.

In FIG. Figure 3 presents an x-ray of an ingot showing the presence of the exclusively sought phase, using Co ₂ FeSi as an example.

In FIG. Figure 4 presents the X-ray diffraction pattern of the target, showing the presence of the exclusively sought phase, using Co ₂ FeSi as an example.

The objective is achieved in that in the method of manufacturing sputtering a composite target comprising a phase Heusler alloy Co ₂ FeSi, comprising mechanically mixing powders Heusler alloy Co ₂ FeSi components to give a uniform powder mixture and sintering-pressing, the powder mixture is prepared from high-purity cobalt powder, iron and silicon, while the sintering and pressing of the powder mixture are carried out by the method of electric pulse plasma sintering at a temperature of 600 ° C and a minimum pressure of 2.5 kN, by passing of pulses of direct current up to 5 kA with a pulse duration of 3.3 ms through filling the powder mixture with the formation of a compact, then the resulting compact is melted in a quartz crucible of an induction furnace at 1300 ° C for 3 hours until completely melted to obtain a homogenized ingot of a Heisler alloy Co ₂ FeSi, then the obtained ingot is crushed and ground to obtain particles with a size of 1-200 μm and sintering and pressing of the composite target from the obtained particles are carried out by electropulse plasma sintering with control m dilatometric curve of shrinkage; sintering-pressing of the powder mixture and sintering-pressing of particles of the Geisler alloy Co ₂ FeSi is carried out in the installation of electric pulse plasma sintering DR. Sinter Model SPS-625 in a graphite mold; melting the resulting compact is carried out in an induction furnace VTC 200 Indutherm; crushing and grinding of the ingot of the Geisler alloy Co ₂ FeSi is carried out in the Analysette 3 Spartan FRITSCH analytical sieving screen with the following grinding parameters: dry grinding, the ratio of the mass of the milled material to the mass of grinding media 1: 2-1: 4, the grinding duration from 30 minutes to 2 hours the amplitude of the vibrations of the screen 1.5 mm; the selection of the obtained particles of the Geisler alloy Co ₂ FeSi size of 1-200 μm in a narrow or wide range of sizes; the obtained particles of a Geisler alloy Co ₂ FeSi with a size of 1-200 μm are mixed in a planetary mill Pulverisette 6 FRITSCH; after sintering and pressing the composite target, grinding is carried out.

The invention is carried out as follows.

First, mechanical mixing of high-purity powders of cobalt (Co), iron (Fe) and silicon (Si) is carried out to obtain a mixture of Co ₂ FeSi. The proportions of the components in the mixture are calculated taking into account the mass fractions of the components. Mixing is carried out mechanically until a homogeneous powder mixture is obtained. Despite the thorough mixing of powders, this technology provides only preliminary, less than in the case of complete melting, homogenization.

Then carry out sintering-pressing of the resulting mixture in the installation of electric pulse plasma sintering DR. Sinter Model SPS-625 at a temperature of about 600 ° C with a minimum pressure of about 2.5 kN, by passing through a powder filling in a graphite mold sequences of direct current pulses up to 5 kA, the pulse duration of 3.3 ms. The process is stopped when the volume of the powder is reduced in order to avoid contamination of the chamber due to the melting of the component with a minimum melting point. Schematically, the sintering and pressing mechanisms of the powder mixture are illustrated in FIG. 2. When current flows through the filling of the powder, the oxide films on the surface of the powder particles are destroyed, and the powder is pressed into a porous preform with sufficient strength. Powder compaction is carried out only by magnetic forces, and the particles are connected mainly due to the fusion of contacts between particles with the formation of interparticle isthmuses. The degree of compaction of the powder depends on the parameters of the electrical circuit and the properties of the powder particles.

The result is a compact that can be melted in an induction furnace; powder material could not be melted. A compact is a mechanical mixture of unoxidized powders connected to each other by fusing contacts between particles with the formation of interparticle isthmuses.

To ensure complete homogenization, the resulting compact is melted in a quartz crucible of the VTC 200, Indutherm induction furnace at 1300 ° C for 3 hours. As a result, all components melt, ensuring complete homogenization of the ingot, and obtain a stoichiometric Heisler alloy. A typical x-ray of the obtained ingot, using Co ₂ FeSi as an example, is shown in FIG. 3.

To give the Geisler alloy the required geometry, the obtained Co ₂ FeSi ingot (a disk with a thickness of 0.7-1 mm and a diameter of 40 mm) is crushed and ground in an analytical sieving machine (Analysette 3 Spartan FRITSCH vibrating screen). Particle size, particle size distribution and a combination of particles with different sizes in a narrow or wide range, along with the SPS sintering-pressing parameters, affect the porosity of the final target, which can vary in the range of 2-40%. By varying the grinding parameters, such as the ratio of the mass of the milled material to the mass of grinding media, the presence of surface-active liquid media, the duration and intensity of grinding, a Geisler alloy powder with the desired / specified particle size distribution (1-200 μm) is obtained. To obtain the required porosity, powders of a certain dispersion are selected and combined. In general, the finer the powder, the lower the initial porosity.

The powders obtained after crushing and selection are mixed, for example, in a Pulverisette 6 FRITSCH planetary mill.

SPS sintering-pressing of particles of a Geisler alloy is carried out in a DR electropulse plasma sintering plant. Sinter Model SPS-625. Use the SPS technological conditions for sintering and pressing of particles of the Geisler alloy close to the sintering and pressing conditions of the initial powder mixture. In this case, the dilatometric shrinkage curve is controlled in order to interrupt the sintering process at the desired point and obtain a material with the required porosity in the range from 2 to 40%.

If you want to thin the target, then produce mechanical grinding.

In a series of experiments, homogenized, mechanically strong targets of Heusler alloys of Co ₂ FeSi stoichiometric composition were obtained, which is confirmed by x-ray data (Fig. 4). Against the background of noise, the presence of any other phases is not visible.

In addition, the obtained targets were of a given geometry, made in the form of a disk with a thickness of 0.7-1 mm and a diameter of 40 mm, and also had the required porosity in the range of 2-40%.

The low porosity of the target allows it to be sprayed at a lower speed, leading to a lower deposition rate of the layer, which may be useful for thin layers. The large porosity of the target, on the contrary, leads to a higher sputtering speed and provides the deposition of thick layers in less time.

Samples obtained using the described technology are also interesting as reference ones for calibrating analytical methods for determining the composition of layers of Geisler alloys by XPS, Auger, SIMS, etc.

The following is an example of a specific implementation of the proposed method.

Example 1

1. Mechanically mix the powder of cobalt (Co) (99.95%, 40 microns), iron (Fe) (99.999%, 40 microns) and silicon (Si) (99.999%, 40 microns) based on the production of 18 grams of a mixture of powders Co ₂ FeSi 1 target 40 mm in diameter and about 1 mm thick. The proportions of the components in the mixture are calculated taking into account the mass fractions of the components. Mixing is carried out until a homogeneous powder mixture is obtained.

2. The resulting mixture of powders is sintered in an electric pulse plasma sintering apparatus DR. Sinter Model SPS-625 at a temperature of about 600 ° C, a minimum pressure of about 2.5 kN, by passing sequences of direct current pulses up to 5 kA, a pulse duration of 3.3 ms through a powder filling in a graphite mold. The process is stopped manually when the powder volume is reduced in order to avoid contamination of the chamber due to the melting of the component with a minimum melting point. The output is a mechanically strong compact, which is a mechanical mixture of non-oxidized powders of cobalt (Co), iron (Fe) and silicon (Si), connected to each other due to the fusion of contacts between particles with the formation of interparticle isthmuses.

3. The compact is melted in a quartz crucible of an induction furnace VTC 200, Indutherm at 1300 ° C for 3 hours. The melting of all components ensures their chemical interaction and the production of a homogenized stoichiometric Heisler alloy.

4. The resulting Co ₂ FeSi ingot is crushed and ground in an analytical sieving machine — the Analysette 3 Spartan FRITSCH vibrating screen to obtain a powder. The following grinding parameters are selected: dry grinding, the ratio of the mass of the milled material to the mass of grinding media 1: 2, the grinding time is 30 minutes, the amplitude of the vibrations of the screen is 1.5 mm. The result is a powder with a wide histogram of the distribution of particle sizes from 1 to 200 microns.

5. Using analytical sieves, a powder fraction with a particle size of 150-200 microns is separated, as well as a powder fraction with a particle size of 20-40 microns.

6. The resulting powders are mixed with a narrow particle distribution in the Pulverisette 6 FRITSCH planetary mill in the ratio of 82% of particles with sizes of 150-200 microns and 18% of particles with sizes of 20-40 microns, which ensures an initial porosity of 20%.

7. Sinter particles of the Geisler alloy in SPS-625 in a mold with a diameter of 40 mm to obtain a density of 2 ÷ 5%.

8. Perform mechanical grinding, if you want to thin the target.

The result is a homogenized target of the required mechanical strength (sufficient so as not to damage the target during the deposition process), geometry (diameter - 40 mm, thickness - 0.7 mm), phase composition of Co ₂ FeSi and low porosity of 2 ÷ 5%.

Claims (7)

1. A method of manufacturing a sprayable composite target containing the phase of the Geisler alloy Co ₂ FeSi, comprising mechanically mixing the powders of the components of the Geisler alloy Co ₂ FeSi to obtain a homogeneous powder mixture and its sintering-pressing, characterized in that the powder mixture is prepared from high-purity powders of cobalt, iron and silicon, while sintering and pressing of the powder mixture are carried out by the method of electric pulse plasma sintering at a temperature of 600 ° C and a minimum pressure of 2.5 kN, by passing pulse sequences in direct current up to 5 kA with a pulse duration of 3.3 ms through filling the powder mixture to obtain a compact, then the resulting compact is melted in a quartz crucible of an induction furnace at 1300 ° C for 3 hours until completely melted to obtain a homogenized ingot of Co ₂ FeSi, then the resulting ingot is crushed and milled to obtain particle size of 1-200 microns and pressing-sintering is carried out a composite target of particles obtained by the method of electro-plasma sintering with controlled dilatometric shrinkage curve. 2. The method according to p. 1, characterized in that the sintering-pressing of the powder mixture and sintering-pressing of particles of the Geisler alloy Co ₂ FeSi is carried out in the installation of electric pulse plasma sintering DR. Sinter Model SPS-625 in a graphite mold. 3. The method according to p. 1, characterized in that the melting of the obtained compact is carried out in an induction furnace VTC 200 Indutherm. 4. The method according to p. 1, characterized in that the crushing and grinding of the ingot of the Geisler alloy Co ₂ FeSi is carried out in the Analysette 3 Spartan FRITSCH analytical sieving screen with the following grinding parameters: dry grinding, the ratio of the mass of the milled material to the mass of grinding media 1: 2- 1: 4, grinding duration from 30 minutes to 2 hours, the amplitude of the vibrations of the screen 1.5 mm 5. The method according to p. 1, characterized in that the selection of the obtained particles of the Geisler alloy Co ₂ FeSi size of 1-200 microns in a narrow or wide range of sizes. 6. The method according to p. 1, characterized in that the obtained particles of a Geisler alloy Co ₂ FeSi with a size of 1-200 μm are mixed in a planetary mill Pulverisette 6 FRITSCH. 7. The method according to p. 1, characterized in that after sintering-pressing a composite target carry out grinding.

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