JP2021155798A - Method of producing alloy thin film, and alloy thin film - Google Patents

Abstract

To provide a method of producing an alloy thin film, capable of controlling a composition ratio of a rare earth element relative to transition metal and capable of producing an alloy thin film of an intended performance, and an alloy thin film.SOLUTION: An alloy thin film comprising a transition metal element and a rare earth element is produced by carrying out electrolytic plating using an aqueous solution comprising one or more species of transition metal elements, one or more species of rare earth elements, a tartaric acid compound, and a citric acid compound, as a plating solution. The tartaric acid compound preferably is tartaric acid, potassium sodium tartrate, or sodium tartrate, and the citric acid compound preferably is sodium citrate, or citric acid.SELECTED DRAWING: Figure 1

Description

The present invention relates to a method for producing an alloy thin film and an alloy thin film.

An alloy single crystal of a rare earth element such as Tb, Dy, or Sm and a transition metal such as Fe, Co, or Ni is known as a magnetostrictive material. In particular, commercially available Terfenol-D, which is known as a magnetostrictive material, is an alloy single crystal having _{a Tb 0.3} Dy _0.7 Fe _{2 composition and has excellent magnetostrictive performance.}

As a method for producing an alloy of such a rare earth element and a transition metal, sodium tartrate is added to an aqueous solution having Fe and Tb to complex them, and this aqueous solution is used as an electrolytic solution by electrolytic plating at room temperature and pH 4. , which deposit a Fe-Tb alloy (e.g., see non-Patent Document 1) and, in an aqueous solution containing Ni and rare earth (Ce or Nd), chelating them by adding citric acid _{(C 6} H 8 _{O 7)} There is a method in which an alloy of Ni and rare earths is deposited by electrolytic plating using this aqueous solution as an electrolytic solution (see, for example, Non-Patent Document 2).

In addition, glycine is added to a solution containing chloride salts of rare earths (La, Ce, Nd) and transition metals (Ni, Fe, Co) to complex them, and this aqueous solution is used as an electrolytic solution to form rare earths by electrolytic plating. A glycine, an amino group, or an aminocarboxylate (EDTA) is added to an aqueous solution of Sm and Co sulfate to deposit an alloy with a transition metal (see, for example, Patent Document 1) to complex them, and this aqueous solution is used. Is used as an electrolytic solution, and an alloy of Sm and Co is deposited by electrolytic plating (see, for example, Patent Document 2). Citrate or sodium citrate is added to an aqueous solution containing _{FeCl 2} and CdCl _{3 to complex them.} In some cases, this aqueous solution is used as an electrolytic solution to deposit an NdFeB alloy by electrolytic plating (see, for example, Non-Patent Document 3).

Further, a dicarboxylic acid or a tricarboxylic acid is added to an aqueous solution containing Co ions and Fe ions to chelate them, and this aqueous solution is used as an electrolytic solution to deposit a Co—Fe alloy by electrolytic plating (for example, Patent Documents). 3) is also available.

J. Gong and E. J. Podlaha, “Electrrodeposition of Fe-Tb Alloys from an Aqueous Electrolyte”, Electrochemical and Solid-State Letters, 2000, 3 (9), p.422-425 L. Wang et el., “Preparation of amorphous rare-earth films of Ni-Re-P (Re = Ce, Nd) by electrodeposition from an aqueous bath”, Surface & Coatings Technology, 2005, 192, p.208-212 Z. Yang et al., “Electroplating mechanism of nanocrystalline NdFeB film”, Trans. Nonferrous Met. Sic. China 25, 2015, p.832-837

U.S. Pat. No. 6,306,276 U.S. Patent Application Publication No. 2012/0049102 Japanese Unexamined Patent Publication No. 2015-108609

In the method for producing an alloy thin film described in Non-Patent Documents 1 to 3 and Patent Documents 1 or 2, only one kind of ligand is used for chelating or complexing a rare earth element and a transition metal, and the alloy thin film is plated. Since the composition ratio of the rare earth element and the transition metal is constant, the composition ratio cannot be changed, and there is a problem that it is difficult to produce an alloy thin film having desired performance. For example, _{Terfenol-D having a composition of Tb 0.3} Dy _0.7 Fe ₂ has excellent magnetostrictive properties as a super-magnetostrictive material if it is a bulk material, but can obtain good magnetostrictive properties with a thin film. There wasn't.

The present invention has been made focusing on such a problem, and is a method for producing an alloy thin film capable of controlling the composition ratio of a rare earth element and a transition metal and producing an alloy thin film having desired performance. And to provide alloy thin films.

In order to achieve the above object, the method for producing an alloy thin film according to the present invention is to plate an aqueous solution containing one or more kinds of transition metal elements, one or more kinds of rare earth elements, tartrate acids, and citric acids. It is characterized in that an alloy thin film having the transition metal element and the rare earth element is produced by performing electrolytic plating as a liquid.

The alloy thin film according to the present invention is characterized by comprising alloy plating containing one or more kinds of transition metal elements and one or more kinds of rare earth elements.

The method for producing an alloy thin film according to the present invention can preferably produce an alloy thin film according to the present invention. According to the method for producing an alloy thin film according to the present invention, chelates of transition metal elements and rare earth elements can be formed and stabilized in an aqueous solution by two kinds of ligands, tartaric acid and citric acid. At this time, both the complex of the transition metal element by tartrate and the complex of the transition metal element by citric acid (complex ion) act as a reducing agent, but the complex of the transition metal element by citric acid (complex ion). ) Works as a stronger reducing agent. Therefore, the reduction voltage of the complexed rare earth element can be adjusted by the ratio of tartrate acids and citric acids. For example, an alloy by electroplating at a practical reduction voltage of about -0.7V to -1.1V. A thin film (alloy plating) can be manufactured. Further, by adjusting the reduction voltage with the ratio of tartaric acids and citric acids, the composition ratio of rare earth elements and transition metals in the alloy thin film to be produced can be controlled, and an alloy thin film having desired performance can be produced. Can be done.

In the method for producing an alloy thin film according to the present invention, the aqueous solution is preferably a sulfuric acid aqueous solution or a hydrochloric acid aqueous solution. In this case, since salts of the transition metal element and the rare earth element are generated in the aqueous solution, it is possible to easily form a chelate of the transition metal element and the rare earth element. Further, since the salt of the transition metal element has a function of reducing the rare earth element, a part of the transition metal element remains as a salt in the aqueous solution, so that an alloy thin film can be produced with a more practical reduction voltage. Can be done. As raw materials, transition metal elements, rare earth elements, sulfuric acid and hydrochloric acid may be prepared separately, but _{sulfides and chlorides of transition metal elements such as FeSO 4} and FeCl ₃ may be used, and the rare earth elements may be used. Sulfurized or chloride may be used.

In the method for producing an alloy thin film and the alloy thin film according to the present invention, the transition metal element preferably forms a complex with citric acid or tartaric acid, and further preferably dissolves in sulfuric acid and hydrochloric acid to form a salt. .. As such a transition metal element, for example, one or more of Fe, Co, Ni, Zn, and Ga are preferable. The standard electrode potentials of these transition metal elements ^{are -0.44V for Fe 2+} , -0.28V for Co ²⁺ , -0.26V for Ni ²⁺ , -0.76V for Zn ²⁺ , and -0.53V for Ga ⁺ . And has a close value. As described above, these transition metal elements can be applied as the transition metal elements of the present invention because they have similar standard electrode potentials and similar chemical properties.

In the method for producing an alloy thin film and the alloy thin film according to the present invention, the rare earth element preferably forms a complex with citric acid or tartaric acid, and further preferably dissolves in sulfuric acid and hydrochloric acid to form a salt. As such a rare earth element, for example, one or more of La, Ce, Nd, Sm, Gd, Tb, Dy, Ho, and Er are preferable. The standard electrode potentials of these rare earth elements are -2.37V for La, -2.34 for Ce, -2.32V for Nd, -2.30V for Sm, -2.29V for Gd, and -2 for Tb. 30V, Dy is -2.29V, Ho is -2.33V, and Er is -2.33, which are close values. As described above, these rare earth elements can be applied as the rare earth elements of the present invention because they have similar standard electrode potentials and similar chemical properties.

In the method for producing an alloy thin film according to the present invention, it is preferable that the aqueous solution contains three or more kinds of the transition metal element and the rare earth element in total. In this case, when two or more kinds of transition metal elements are contained, the composition ratio between the transition metal elements can be controlled by controlling the ion concentration of those transition metal elements in the aqueous solution. When two or more kinds of rare earth elements are contained, the composition ratio between the rare earth elements can be controlled by controlling the ion concentration of the rare earth elements in the aqueous solution. Thereby, the composition of each element can be controlled to produce an alloy thin film according to the present invention, which contains three or more kinds of transition metal elements and rare earth elements in total.

In the method for producing an alloy thin film according to the present invention, the tartaric acids are preferably tartaric acid, potassium sodium tartrate (Rochelle salt), or sodium tartarate. The citric acids are preferably sodium citrate or citric acid.

In the method for producing an alloy thin film according to the present invention, the aqueous solution may contain a supporting electrolyte such as KCl or NaCl. In this case, the supporting electrolyte can impart high conductivity to the aqueous solution and increase the efficiency of electroplating. Further, the aqueous solution preferably has a pH of 3 to 5, and may contain a pH adjusting agent such as NaOH or KOH in order to adjust the pH to 3 to 5.

According to the present invention, it is possible to provide a method for producing an alloy thin film and an alloy thin film capable of controlling the composition ratio of a rare earth element and a transition metal and producing an alloy thin film having desired performance.

It is a graph which shows the relationship between the voltage of a working electrode and the composition of an alloy thin film when the alloy thin film made of TbDyFe is manufactured by the method of manufacturing the alloy thin film of embodiment of this invention. 6 is a graph showing the magnetization characteristics of an alloy thin film made of TbDyFe produced at a reduction voltage of −930 mV by the method for producing an alloy thin film according to the embodiment of the present invention. It is a side view which shows the manufacturing method of the cantilever which deposited the alloy thin film made of TbDyFe on the surface by the manufacturing method of the alloy thin film of embodiment of this invention. It is a perspective view which shows the cantilever manufactured by the manufacturing method of FIG. It is a graph which shows the relationship between the applied magnetic field (Magnetic field) and the magnetostriction coefficient (Magnetostriction coefficient) of the cantilever shown in FIG.

Hereinafter, embodiments of the present invention will be described based on examples and the like.
The method for producing an alloy thin film according to an embodiment of the present invention can suitably produce an alloy thin film according to an embodiment of the present invention.

In the method for producing an alloy thin film according to the embodiment of the present invention, first, an aqueous solution containing one or more kinds of transition metal elements, one or more kinds of rare earth elements, tartaric acids, and citric acids is prepared. The transition metal element is preferably one or more of Fe, Co, Ni, Zn, and Ga. The rare earth element is preferably one or more of La, Ce, Nd, Sm, Gd, Tb, Dy, Ho, and Er. The tartaric acids are preferably tartaric acid, potassium sodium tartrate (Rochelle salt), or sodium tartarate. The citric acid is preferably sodium citrate or citric acid.

Next, electrolytic plating is performed using the prepared aqueous solution as a plating solution. Thereby, the alloy thin film of the embodiment of the present invention can be produced, which comprises alloy plating containing a transition metal element and a rare earth element.

According to the method for producing an alloy thin film according to the embodiment of the present invention, chelates of transition metal elements and rare earth elements can be formed and stabilized in an aqueous solution by two kinds of ligands, tartaric acid and citric acid. At this time, both the complex of the transition metal element by tartrate and the complex of the transition metal element by citric acid (complex ion) act as a reducing agent, but the complex of the transition metal element by citric acid (complex ion). ) Works as a stronger reducing agent. Therefore, the reduction voltage of the complexed rare earth element can be adjusted by the ratio of tartrate acids and citric acids. For example, an alloy by electroplating at a practical reduction voltage of about -0.7V to -1.1V. A thin film (alloy plating) can be manufactured. Further, by adjusting the reduction voltage with the ratio of tartaric acids and citric acids, the composition ratio of rare earth elements and transition metals in the alloy thin film to be produced can be controlled, and an alloy thin film having desired performance can be produced. Can be done.

In the method for producing an alloy thin film according to the embodiment of the present invention, the aqueous solution is preferably a sulfuric acid aqueous solution or a hydrochloric acid aqueous solution. By using a sulfuric acid aqueous solution or a hydrochloric acid aqueous solution as the aqueous solution, salts of the transition metal element and the rare earth element are generated in the aqueous solution, so that it is possible to easily form a chelate of the transition metal element and the rare earth element. Further, since the salt of the transition metal element has a function of reducing the rare earth element, a part of the transition metal element remains as a salt in the aqueous solution, so that an alloy thin film can be produced with a more practical reduction voltage. Can be done. In this case, transition metal elements, rare earth elements, sulfuric acid and hydrochloric acid may be prepared separately as raw materials, but sulfides and chlorides of transition metal elements such as _{FeSO 4} and FeCl _{3 may be used.} Rare earth element sulfides and chlorides may be used.

Further, in the method for producing an alloy thin film according to the embodiment of the present invention, it is preferable that three or more kinds of transition metal elements and rare earth elements are contained in the aqueous solution. When two or more kinds of transition metal elements are contained, the composition ratio between the transition metal elements can be controlled by controlling the ion concentration of those transition metal elements in the aqueous solution. When two or more kinds of rare earth elements are contained, the composition ratio between the rare earth elements can be controlled by controlling the ion concentration of the rare earth elements in the aqueous solution.

An alloy thin film made of TbDyFe, which is a magnetostrictive material, was produced by the method for producing an alloy thin film according to the embodiment of the present invention. First, the following materials were put in 150 cc of pure water to prepare an aqueous solution.
・ FeCl ₃・ 6H ₂ O (powder) 0.5 g
・ FeSO ₄・ 7H ₂ O (powder) 1.8 g
・ Tb ₂ (SO ₄ ) ₃・ 8H ₂ O (powder) 0.3 g
・ Dy ₂ (SO ₄ ) ₃・ 8H ₂ O (powder) 0.7 g
・ Potassium sodium tartrate (KNaC ₄ H ₄ O ₆・ 4H ₂ O) 1.1 g
・ Sodium citrate (Na ₂ H (C ₃ H ₅ O (COO) ₃ ) ・ 1.5 H ₂ O) 0.5 g
・ KCl (powder) 33 g
・ NaOH 1.1 g

The transition metal element is one type of Fe, and the rare earth element is two types, Tb and Dy. KCl is a supporting electrolyte and NaOH is a pH regulator. Further, the prepared aqueous solution becomes a sulfuric acid aqueous solution. The aqueous solution was prepared in an N ₂ atmosphere. If you want to accelerate the complexing reaction of transition metal elements and rare earth elements, you can heat the aqueous solution to about 60 ° C.

Next, electrolytic plating was performed using the prepared aqueous solution as a plating solution. For electrolytic plating, an electrolytic plating apparatus having three electrodes was used, and electrolytic plating was performed while controlling the voltage. The reference electrode of the electroplating apparatus is Ag / AgCl, the counter electrode (anode) is Pt, and the working electrode (cathode) is Cu. The alloy thin film was deposited by electroplating at room temperature. In addition, during deposition, N ₂ was passed through the plating solution (electrolyte solution) to prevent oxygen from entering. The deposition rate of the alloy thin film by electroplating was about 100 to 200 nm / h.

The relationship between the voltage of the working electrode and the composition of the alloy thin film when the alloy thin film made of TbDyFe is deposited by changing the voltage (reduction voltage; Potential) of the working electrode is shown in FIG. The composition of the alloy thin film is measured using energy dispersive X-ray analysis (EDX). As shown in FIG. 1, it was confirmed that the composition ratio of the transition metal element and the rare earth element can be controlled by the voltage of the working electrode. It was also confirmed that an alloy thin film can be produced with a reduction voltage of about −0.9V to -1V.

When sodium citrate was increased by 0.1 g and potassium sodium tartrate was decreased by 0.22 g to deposit an alloy thin film, the composition ratio (at%) of Fe increased by 20 to 30% when the reduction voltage was -935 mV. The composition ratios (at%) of Dy and Tb decreased by 10 to 15%, respectively. Conversely, when sodium citrate was reduced by 0.1 g and sodium potassium tartrate was increased by 0.22 g, the increase / decrease in the composition ratio of the alloy thin film was reversed.

_{The magnetization characteristics of the alloy thin film (Tb 0.36} Dy _0.64 Fe _1.9 ) deposited at a reduction voltage of −930 mV were obtained and shown in FIG. The magnetization characteristics are measured by a vibrating sample magnetometer (VSM). As shown in FIG. 2, the obtained alloy thin film had a holding force of 285 Oe and a saturation magnetization of 7900 Oe.

Next, a cantilever in which an alloy thin film made of a super-magnetostrictive material TbDyFe was deposited on the surface was manufactured, and the magnetostrictive coefficient was measured. The cantilever was manufactured as follows. That is, first, as shown in FIG. 3A, the SOI of the handle layer (Si) 11 has a thickness of 550 μm, the BOX layer (SiO ₂ ) 12 has a thickness of 3 μm, and the device layer (Si) 13 has a thickness of 1.5 μm. A seed layer 14 made of Cu was formed on the surface of the wafer on the device layer 13 side by sputtering. Next, as shown in FIG. 3B, an alloy thin film 15 made of TbDyFe was deposited on the surface of the seed layer 14 by electroplating.

As shown in FIG. 3C, the photoresist 16 is applied to the surface of the alloy thin film 15, and the alloy thin film 15, the seed layer 14 and the device layer 13 are obtained by ion milling and reactive ion etching (RIE). Etched on the pattern. As shown in FIG. 3D, after removing the photoresist 16 on the surface of the alloy thin film 15, the photoresist 17 is applied to the surface on the handle layer 11 side in the same manner, and the handle layer 11 is subjected to deep digging RIE. Was etched into the desired pattern. As shown in FIG. 3 (e), the exposed portion of the BOX layer 12 made of _{SiO 2 was removed by etching with a Vapor HF etching apparatus.} In this way, as shown in FIG. 4, a cantilever in which an alloy thin film 15 made of TbDyFe was formed on the surface of the device layer 13 via a seed layer 14 was manufactured. The portion where the handle layer 11 is left is a fixed portion of the cantilever.

Three types of cantilever with different lengths were manufactured. The lengths are 700 μm, 1000 μm, and 1100 μm, respectively. The width is 100 μm. In each cantilever, the thickness of the seed layer 14 is 300 nm, and the thickness of the alloy thin film 15 is 250 nm.

Various magnetic fields were applied to each cantilever, and the in-plane magnetostriction (magnetostriction coefficient) of the alloy thin film 15 was obtained from the warp of each cantilever at each applied magnetic field. The relationship between the applied magnetic field of each cantilever and the magnetostriction coefficient is shown in FIG. Further, the average value of the magnetostrictive coefficient of each cantilever at each applied magnetic field is obtained and shown in FIG. As shown in FIG. 5, it was confirmed that any cantilever had a very large magnetostrictive coefficient of 1200 ppm or more, and that even a thin film had good magnetostrictive characteristics.

An alloy thin film made of Tb-Fe-Co, which is a super-magnetostrictive material, was produced by the method for producing an alloy thin film according to the embodiment of the present invention. First, the following materials were put in 150 cc of pure water to prepare an aqueous solution.
・ CoSO ₄・ 7H ₂ O 2.1 g
・ FeCl ₃・ 6H ₂ O 0.2 g
・ Tb ₂ (SO ₄ ) ₃・ 8H ₂ O 1 g
・ Potassium sodium tartrate (KNaC ₄ H ₄ O ₆・ 4H ₂ O) 1.8 g
・ Sodium citrate (Na ₂ H (C ₃ H ₅ O (COO) ₃ ) ・ 1.5 H ₂ O) 1.4 g
・ KCl (powder) 33 g
・ NaOH 1.1 g

There are two types of transition metal elements, Fe and Co, and one type of rare earth element, Tb. KCl is a supporting electrolyte and NaOH is a pH regulator. Further, the prepared aqueous solution becomes a sulfuric acid aqueous solution. The aqueous solution was prepared in an N ₂ atmosphere. When it is desired to accelerate the complexing reaction of the transition metal element or the rare earth element, the aqueous solution may be heated to about 50 to 85 ° C.

Next, electrolytic plating was performed using the prepared aqueous solution as a plating solution using the same apparatus as in Example 1. The alloy thin film was deposited by electroplating at room temperature by applying a voltage of -880 mV to the working electrode. In addition, during deposition, N ₂ was passed through the plating solution (electrolyte solution) to prevent oxygen from entering. The deposition rate of the alloy thin film by electroplating was about 100 to 200 nm / h.

When the composition of the deposited alloy thin film was measured using EDX, Tb was 36 at%, Fe was 9 at%, and Co was 55 at%. When the voltage (reduction voltage) applied to the working electrode was changed by -5 mV, the ratio of rare earth elements (Tb) increased by 10% and the ratio of transition metal elements (Fe, Co) decreased. Further, the ratio between the transition metal elements can be adjusted by adjusting the concentration of Fe and Co in the electrolytic solution.

In addition, when sodium citrate was increased by 0.14 g and potassium sodium tartrate was decreased by 0.18 g to deposit an alloy thin film, the composition ratio (at%) of Tb decreased by 10% when the reduction voltage was -880 mV, and Fe and Fe and The composition ratio (at%) of Co increased by 5%, respectively. Conversely, when sodium citrate was reduced by 0.14 g and sodium potassium tartrate was increased by 0.18 g, the increase / decrease in the composition ratio of the alloy thin film was reversed.

11 Handle layer 12 BOX layer 13 Device layer 14 Seed layer 15 Alloy thin film 16, 17 photoresist

Claims (12)

The transition metal element and the rare earth element are obtained by performing electrolytic plating using an aqueous solution containing one or more kinds of transition metal elements, one or more kinds of rare earth elements, tartrate acids, and citric acids as a plating solution. A method for producing an alloy thin film, which comprises producing an alloy thin film having. The method for producing an alloy thin film according to claim 1, wherein the aqueous solution is a sulfuric acid aqueous solution or a hydrochloric acid aqueous solution. The method for producing an alloy thin film according to claim 1 or 2, wherein the transition metal element is one or more of Fe, Co, Ni, Zn, and Ga. The method according to any one of claims 1 to 3, wherein the rare earth element is one or more of La, Ce, Nd, Sm, Gd, Tb, Dy, Ho, and Er. Method for manufacturing alloy thin films. The method for producing an alloy thin film according to any one of claims 1 to 4, wherein the aqueous solution contains three or more kinds of the transition metal element and the rare earth element in total. The method for producing an alloy thin film according to any one of claims 1 to 5, wherein the tartaric acid is tartaric acid, sodium potassium tartrate, or sodium tartarate. The method for producing an alloy thin film according to any one of claims 1 to 6, wherein the citric acid is sodium citrate or citric acid. The method for producing an alloy thin film according to any one of claims 1 to 7, wherein the aqueous solution contains a supporting electrolyte. An alloy thin film comprising an alloy plating containing one or more kinds of transition metal elements and one or more kinds of rare earth elements. The alloy thin film according to claim 9, wherein the transition metal element is one or more of Fe, Co, Ni, Zn, and Ga. The alloy thin film according to claim 9 or 10, wherein the rare earth element is one or more of La, Ce, Nd, Sm, Gd, Tb, Dy, Ho, and Er. The alloy thin film according to any one of claims 9 to 11, wherein the transition metal element and the rare earth element are contained in a total of three or more kinds.

Images