RU2678354C1 - METHOD FOR PRODUCING SPRAYABLE COMPOSITE TARGET FROM Co2MnSi HEUSLER ALLOY - Google Patents

Abstract

FIELD: technological processes.

SUBSTANCE: invention relates to the manufacture of sprayable composite targets of Co₂MnSi Heusler alloy, which can be used in the production of microelectronics. Method involves mechanical mixing of the powders of the alloy components to obtain a homogeneous powder mixture and sintering it. Sintering the powder mixture is carried out by the method of electropulse plasma sintering in a graphite mold at a temperature of 600 °C and a minimum pressure of 2.5 kN by passing sequences of DC pulses of 5,000 A with a pulse duration of 3.3 ms through the filling of the powder mixture to obtain a composite target. Target porosity is monitored based on the data of the dilatometric shrinkage curve.

EFFECT: mechanically strong, not oxidized, composite targets of an alloy with a porosity in the range of 10–30 % are obtained.

1 cl, 3 dwg, 1 ex

Description

The present invention relates to metallurgy, in particular to the production of products from a mixture of metal powders by electropulse sintering, relates to a method for manufacturing sprayable composite targets of a Geisler alloy Co ₂ MnSi, which can be used in the production of microelectronics.

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 is 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. Another important problem for Heisler alloy targets is the need to provide an unoxidized target. Otherwise, targets with the incorporated composition of Co ₂ MnSi turn out to be non-magnetic and high-resistance, which does not allow their use for the production of spin electronics devices.

The solution of the above problems is aimed at the development of this invention.

One of the methods for creating sputtering targets is the cold pressing method followed by annealing in an inert gas atmosphere (nitrogen, argon). Testing this technology on our components showed the need to remove an unacceptably large amount of oxygen. Targets with the incorporated composition of Co ₂ MnSi and Co ₂ FeSi turned out to be non-magnetic and high-resistance.

From patent US 7973351 B2, cl. H01L 21/02, publ. 05-07-2011 known sputtering target of 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. B32 B17 / 06, C23C 14/35, publ. 12/06/11, a spray target made of a Co ₂ MnSi ingot obtained by the method of electric arc sintering of a stoichiometric mixture of Co, Mn, and Si powders is known. 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 disadvantages of this method of teaching a sprayed target of composition Co ₂ MnSi is the porosity of the latter, which leads to a large effective surface, its oxidation and adsorption of moisture and volatile contaminants from the air, which will make it difficult to obtain pure stoichiometric alloy layers, it will require long-term annealing of the target in vacuum (deoxidation reaction) in addition, the manufacture of targets by this technology is more time-consuming and time-consuming, in comparison with the described invention.

A known method of producing a cathode target blank 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. This technology is also much more complex and expensive.

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 original 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 Co ₂ MnSi composition.

Electropulse sintering (Spark Plasma Sintering, abbreviated SPS) is a complex physical and mechanical process that takes place at high temperatures in powder materials (Fig. 1). 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. Yekaterinburg, 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 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, Dec 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. The most promising high-speed sintering technology 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 the electrophysical impact on the powder material determines the variety of these methods. 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 pressure sintering (EISD) (A.V. Nomoev. Superhardness of ceramics based on nanodispersed alumina powders with the addition of nanopowders of magnesium oxide and silicon. 36, no. 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 d.), Electropulse pressing (Sheng Guo, Apichart Limpichaipanit, RI Todd. High resolution optical microprobe investigation of surface grinding stress in Al2O3 and Al ₂ O ₃ / SiC nanocomposites. Journal of the European Ceramic Society, 31, pp. 97-109, 2011), developed in the CIS countries. 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 the creation of a new method for producing a mechanically strong composite target from a Heisler alloy Co ₂ MnSi.

The technical result from the use of the present invention is to obtain a mechanically strong non-oxidized composite target of the Geisler alloy Co ₂ MnSi of the required geometry (disk thickness 0.7-1 mm, diameter 40 mm) and porosity (in the range of 10-30%).

This is achieved by the fact that in the method of manufacturing a sprayable composite target from a Geisler alloy Co ₂ MnSi, comprising mechanical mixing of powders of components of the Geisler alloy Co ₂ MnSi to obtain a homogeneous powder mixture and its sintering, the powder mixture is prepared from high-purity powders of cobalt, manganese and silicon, moreover sintering of the powder mixture is carried out by the method of electropulse plasma sintering in a graphite mold at a temperature of 600 ° C and a minimum pressure of 2.5 kN by passing sequences of pulses of constant a current of 5000 A with a pulse duration of 3.3 ms through backfilling of the powder mixture to obtain a composite target from a Geisler alloy Co ₂ MnSi, while controlling the porosity of the target based on the dilatometric shrinkage curve data; sintering of the powder mixture is carried out in the installation of electric pulse plasma sintering DR. Sinter Model SPS-625.

In FIG. 1 schematically shows an installation for electropulse sintering.

In FIG. 2 shows the mechanisms of sintering of the powder mixture, where: 1 - surface diffusion, 2 - volume diffusion from the particle surface to the jumper, 3 - transfer through the gas phase, 4 - grain boundary diffusion, 5 - volume diffusion from the grain boundary to the pore, 6 - plastic deformation , 7 - time, 8 - grain boundary.

In FIG. Figure 3 shows a typical radiograph of a target, using Co ₂ MnSi as an example.

The proposed method is as follows.

First, mechanical mixing of high-purity powders of cobalt (Co), manganese (Mn) and silicon (Si) is carried out to obtain the compound Co ₂ MnSi. 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.

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, a minimum pressure of about 2.5 kN, by passing sequences of direct current pulses up to 5000 A, a pulse duration of 3.3 ms through a powder filling in a graphite mold. 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 dilatometric shrinkage curve is controlled so that the sintering process can be interrupted at the desired point, avoiding contamination of the chamber as a result of melting of the component with a minimum melting temperature, and obtaining a material with the required porosity. As a result, the powder is compressed with sufficient strength and porosity in the range of 10-30%.

The required target diameter is provided by the selection of a mold of the corresponding diameter, and the thickness by the amount of powder and porosity.

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

In a series of experiments, stoichiometric targets from a Heisler alloy Co ₂ MnSi were obtained, which is confirmed by X-ray diffraction data for the Heisler alloy (Fig. 3). Against the background of noise, the presence of any other phases is not visible.

Thus, the proposed method eliminates the oxidation of the target, and also provides the ability to control its porosity. This ensures the production of a mechanically strong composite target of the Geisler alloy Co ₂ MnSi porosity in the range of 10-30%. In addition, the proposed method allows to obtain a target of the desired geometry (diameter 40 mm, thickness 0.7-1 mm).

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%), particle size - 40 microns, 11.64 g.), Manganese (Mn) (99.999%), particle size - 40 microns, 4.86 g.) And silicon (Si ) (99.999%), particle size - 40 microns, 1.53 g.) Based on the production of 18.3 g. a mixture of powders of Co ₂ MnSi per 1 target with a diameter of 40 mm and a thickness of about 0.7 mm 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, minimum pressure (about 2.5 kN), by passing sequences of direct current pulses (up to 5000 A, pulse duration 3.3 ms) through a powder filling and a graphite mold. In the sintering-pressing process, based on the dilatometric shrinkage curve data, the sintering-pressing process is interrupted when the porosity of 10% is reached). It’s important not to overdo it, because due to the melting of the component with a minimum melting point, contamination of the chamber may occur.

The result is a target with mechanical strength sufficient not to damage the target during sputtering, geometry (diameter - 40 mm, thickness - 0.7 mm), porosity of about 10%) and phase composition of Co ₂ MnSi.

Claims (2)

1. A method of manufacturing a sprayable composite target from a Geisler alloy Co ₂ MnSi, comprising mechanically mixing the powders of the components of the Geisler alloy Co ₂ MnSi to obtain a homogeneous powder mixture and sintering, characterized in that the powder mixture is prepared from high-purity powders of cobalt, manganese and silicon, and sintering of the powder mixture is carried out by the method of electropulse plasma sintering in a graphite mold at a temperature of 600 ° C and a minimum pressure of 2.5 kN by passing sequences of pulses of constant a current of 5000 A with a pulse duration of 3.3 ms through backfilling of the powder mixture to obtain a composite target from a Geisler alloy Co ₂ MnSi, while controlling the porosity of the target on the basis of the dilatometric shrinkage curve data. 2. The method according to p. 1, characterized in that the sintering of the powder mixture is carried out in the installation of electropulse plasma sintering DR Sinter Model SPS-625.

Images