JP2003510465A - Electrodeposition method of metal multilayer - Google Patents

Abstract

  (57) [Summary] An electrodeposition method for producing a multilayer structure including a substrate having a thin film layer of Co and Au. The method is performed by providing a current between two electrodes having a potential difference that is immersed in a solution that at least partially contains one or more substrates. This solution contains Co ions and Au ions. The method also includes growing multiple layers on the substrate in the solution. Here, the method is characterized by controlling by changing the current density and / or the applied potential and keeping the concentration of Au ions much lower than the concentration of Co ions.

Description

Detailed Description of the Invention

FIELD OF THE INVENTION The present invention relates to a method for electrodepositing metal multilayers, a multilayer structure made by this method, and an electroplating bath for electrodeposition of thin films.

[Background] With the discovery of a phenomenon called "giant magnetoresistance" or GMR, magnetic multilayers have become important nowadays. A major concern is the ability to detect small magnetic fields, which has many applications such as magnetic data storage and magnetic sensors. However, commonly used deposition techniques are sputtering and chemical vapor deposition (C
VD) and these are more expensive than electrodeposition.

Generally, two types of magnetic materials are used in the computer memory industry. The first type is a hard magnetic material having a coercive force greater than 100 Oe,
The second type is a material having a small coercive force or a soft magnetic material. These two magnetic materials are usually based on all-transition metal magnetic multilayer systems. Here, the non-ferromagnetic layer is 3d,
One of 4d and 5d transition metals or noble metals, such as Cu and Ag having low magnetic susceptibility.

Electrodeposited magnetic multilayers are processed as a substrate having alternating layers of magnetic thin films such as Co, Fe, Ni, etc. and non-magnetic or noble metal layers of low magnetic susceptibility such as Ag or Pt layers. be able to.

Electrodeposited Au / Co multilayers have multiple advantages, properties and significant implications for thin film magnetic device, magnetic sensor, high density magnetic storage, and computer device technologies.

The Au / Co multilayer can also be used as a temperature sensor, which has the advantage of not oxidizing at room temperature.

The electrodeposition process is an electrochemical process in which a current is passed between an anode and a cathode through an aqueous or non-aqueous solution containing metal ions. The ions are reduced and deposited on the cathode as a metal coating. If the anode is made of the metal to be deposited, the anode will dissolve and replenish the solution with metal ions. If an insoluble anode is used, metal salts must be added to the solution periodically to maintain the metal ion content.

The amount of metal deposited follows Faraday's law, so the amount of metal deposited is proportional to the current, time and relative atomic weight of the metal and inversely proportional to the oxidation state of the metal in solution.

The current used for plating does not always have to be provided in continuous flow. For example, in pulse mode plating, it is possible to provide a large amount of current for a short period of time and then no current. Cycle refers to the ratio of the time that is providing current to the time when it is not supplying current, ie the duty cycle and frequency. By varying the duty cycle and frequency, the deposition characteristics can be changed as desired.

[0010]   The deposition process can be generally divided into two, single bath and two bath techniques.

In the single bath technique, magnetic multilayers are grown in an electrolyte containing ions of both components.

The two-bath technique uses one electrolyte for one metal. The parts to be plated are activated, placed in a first solution, plated, rinsed and reactivated, and subsequently placed in a second solution. The disadvantage therefore is an expensive rinse and activation.

The single bath technique has the advantage that the substrate is always kept in the electrolyte and the risk of contamination is limited. However, this technique requires that the reduction potentials of each of the selected components be sufficiently different that each component can be deposited separately.

The properties of the deposited metal are determined by such factors as electrolyte composition, pH, temperature, agitation, potential and current density. Thus, the electrodeposition process can be adjusted, for example, by changing the potential or plating current density.

Factors such as chemical composition, individual layer thickness, interface sharpness, intermixing / alloying at the interface are important with respect to the magnetic properties of the magnetic multilayer coating. Since the electrolyte continuously changes the control of layer thickness growth rate, it is important to maintain the desired thickness of the non-magnetic spacer layer for maximum GMR effect.
Standard spacer layers such as the noble metals Ag and Cu, which have low magnetic susceptibility, have very low induced magnetic moments. Interfacial properties are also important to achieve a sharp interface from the magnetic component to the non-magnetic component.

Recently, many researchers have improved pulsed potentiostatic deposition to introduce a new technique called “nanomaterial-based synthesis” as a template for the production of monolayer as well as multilayer nanowires. However, the conditions for nanowire arrays are still very difficult due to the uncertain electrochemical theory of macroelectrodes. Furthermore, there are many drawbacks here, for example diffusion problems, and long deposition times, such as 24-48 hours, depending on the length of the wire. This is because the diffusion of the electrolyte changes over time. Diffusion, migration or convection can result in migration of ions from the bulk solution to the electrode interface. At the limiting current, the surface concentration is essentially zero (0).

The resulting structure is a one-dimensional structure or composition prepared alloy (CMA) with metal or alloy wire deposits of holes in an insulating matrix called the mold. The nanowire array can be processed so that the light magnetization direction is parallel to the wire axis and perpendicular to the film. These low dimensional structure electrodepositions were prepared from a single electrolyte containing magnetic and non-magnetic metal ions.

Electrodeposited magnetic multilayer materials have been used in the manufacture of computer memory elements. For example, an electrodeposited Au-Co column is an important column because it has high wear resistance. It has a wide range of applications in plated electrical contact of printed circuit boards.

Recently, electrodeposited Au-AuCo multilayers obtained in commercial gold-rich commercial hard gold plating baths have been reported.

However, it is still desirable to make Au—Co multilayer films in an economical manner.

SUMMARY OF THE INVENTION In the present invention, an important parameter of electrodeposition for obtaining an Au—Co multilayer structure is alternating current density, a layer with high Co concentration requires high current density and low agitation. It was found that a layer having a high Au concentration requires a low current density. Further, in the present invention, the concentration of relatively noble ions, or relatively electrically positive metal, in the electrolyte should be lower than the concentration of less noble metals.

In one aspect of the invention, a single bath containing both noble metal / metal ions, eg, Au and Co ions, is used to electrodeposit a noble metal / metal multilayer, eg, Au—Co multilayer. You get this by letting. In this bath, the concentration of gold, a noble metal, in the electrolyte is significantly lower than the concentration of cobalt, a less noble metal. Here, only gold is deposited as a “pure layer” at relatively electrically positive potentials and with low current densities.

By “pure layer” herein is meant that the Au content in the Co layer and the Co content in the Au layer are preferably about 3% and about 1% by weight, respectively. There is.
The upper limit is 5% by weight. The most preferable Co content in the Au layer is 1 to 0.1% by weight or less.

[0024]   Preferably, the multi-layer structure can be manufactured by controlling the constant potential or the constant current.

In one preferred aspect of the present invention, there is provided an electrodeposition method for producing a multi-layer structure including a substrate with Co and Au thin film layers. The method is performed by dipping in an electroplating bath containing at least partially one or more substrates to provide an electric current between two electrodes that are being provided with a potential. Here, the bath contains Co ions and Au ions. The method involves growing multiple layers on a substrate in a bath. This method is controlled by varying the current density and / or the applied voltage and also keeps the concentration of Au ions much lower than the concentration of Co ions.

Here, the term substrate refers to substrates such as plates, foils, etc.
It may be any other type of suitable surface such as rods and the like.

The bath contains 0.2 to 0.7 g / L of Co ions, 0.1 to 0.5 mg / L of Au ions, and an organic acid, and the pH of the bath is 2.5 to 5. 5, the Co ion concentration is about 1,000 times higher than the Au ion concentration. The Au content is preferably 0.
2 to 0.4 mg / L, most preferably about 0.3 mg / L. The organic acid is preferably is a _{C 6 H} 8 _O 6 of 10 to 200 g / L, it is also possible to use other suitable organic acid in an equivalent amount.

[0028] Preferably the potential is a suitable potential for depositing Co ions from open circuit conditions,
Then, another potential suitable for depositing Au ions without depositing Co ions, and then switching back to open circuit conditions, and this switching cycle was repeated as many times as necessary. The use of open circuits during deposition can improve the interface between the films.

In another preferred aspect of the invention, the switching cycle is repeated 10 to 5,000 times, preferably up to 200 times.

Suitably, the reduction potentials of the components are sufficiently different from each other to allow separate electrodeposition of each component.

The Co layer is first deposited at a voltage of -1.0 to -1.3 V and then -0.5.
The voltage is switched to a relatively high voltage such as ~ -0.8V, and then the potential is switched to an open circuit.

[0032]   The new process of the present invention allows operation at temperatures between 20 ° C and 30 ° C.

Another object of the invention is to provide a multi-layer structure comprising a substrate with layers of thin films of Co and Au. Here, the Au content of the Co layer is at most 5% by weight, preferably at most 3% by weight, and the Co content of the Au layer is at most 5% by weight, preferably at most 1% by weight. This multilayer is made by the electrodeposition method by means of immersion in an electroplating bath at least partially containing one or more substrates to provide an electric current between two electrodes which are provided with a potential. This bath contains Co ions and Au ions. The method involves growing multiple layers on a substrate in a bath. This method is controlled by varying the current density and / or the applied voltage and also keeps the concentration of Au ions much lower than the concentration of Co ions.

The multilayer structure of as-obtained very pure Co and Au films according to the invention could not be produced by conventional single bath electrodeposition methods. This method is very advantageous as it is less expensive than methods such as sputtering. It is also possible to make thick layers in a short time.

It is also possible to obtain an Au layer with a maximum Co content of about 1.0 to 0.1% by weight.

[0036]   The multilayer is made by the method of the invention described above.

A further object of the invention is to provide an electroplating bath for electrodeposition of Co and Au thin films. This bath contains 0.2-0.7 g / L of Co ions, 0.1-0.
It contains 5 mg / L of Au ions and organic acid, the pH of the bath is 2.5 to 5.5, and the concentration of Co ions is about 1,000 times the concentration of Au ions. .

Preferably the organic acid is C ₆ H ₈ O ₆ .

Au is preferably present in the bath as a KAu (CN) ₂ complex, the concentration of this complex being about 0.01-0.5 g / L. The purpose of complex formation is to ensure the solubility of Au and to reduce the potential difference between Co and Au so that when Au is electrodeposited,
It is to the extent that Co does not dissolve in an uncontrolled manner. Co is present in the bath as a salt, for example sulfate, sulfamate, pyrophosphate, dissolved in the bath,
Or it exists as a chloride salt. Co is preferably added as CoSO ₄ .7H ₂ O and the concentration is about _{4 to} 100 g / L of CoSO ₄ .7H ₂ O. The acid is used as a pH buffer and the pH is adjusted with hydroxide or carbonate. The preferred pH range is 3.5 to 4.5.

A preferred electroplating bath contains 0.2 to 0.7 g / L of Co ions, 0.1 to 0.5 mg / L of Au ions, 10 to 200 g / L of C ₆ H ₈ O ₆ , and KOH. About 12
0 g / L and the pH of the bath is 3.5-4.5.

There are no known electrolytes available to make pure Au / Co multilayers as the method of the invention and the electroplating bath of the invention. It is advantageous to use a very small amount of Au ions, KAu (CN) ₂ , in the electrolyte. This is because this component is a very expensive component of the electrolyte.

This method can be used in the manufacture of recording devices and magnetic sensors for GMR applications. Furthermore, this method can be used to produce single metal and multilayer nanowires in a very short time. The method can also be used for the production of various types of nanoscale biocomposites and gas sensors such as electronic tongues and micromuscles.

Detailed Description of the Preferred Embodiments FIG. 1 shows an apparatus 100 for rotating a tubular body for electrodeposition. Anode 1
Zero and rotating cathodes 20 are provided to pass an electric current through a solution 30 containing metal and noble metal ions. The substrate 40 is immersed in the solution 30.

Since devices for electrodeposition are known, this device has not been depicted in relative detail. Instead, the invention is described in relative detail by way of example. The present invention is not limited to the examples, which are intended merely to illustrate the present invention.

For example, the concentrations of the components in the electrolyte can be changed within the scope of the present invention without changing the concentration ratio of Co and Au.

The formation of the complex is considered to be apparent to the person skilled in the art, and within the scope of the present invention, the pH influences the stability of the bath.

There may be no stirring or up to 1,000 rpm (corresponding to a surface speed of about 100 cms ⁻¹ ).

Example 1 (Copper Foil Substrate) The apparatus for rotating the cylindrical electrode shown in FIG. 1 was used for electrodeposition. Copper foil (thickness 35 μm) was used as a substrate. The foil was ultrasonically cleaned in a 4% Neutracon solution. Prior to deposition, 775 ml / L phosphonic acid solution and 225 ml / L
The foil was electropolished in L propylene glycol at 350 mA / cm ² for 15 seconds. Foil was then activated in _10% H 2 SO ₄ for 30 seconds.

The charge electrolyte used was the following _{composition: CoSO 4 · 7H 2 O 80g} / L C 6 H 8 O 6 140g / L KAu (CN) 2 0.08g / L KOH 120g / L pH 3 .5-4

If the concentration of Co does not change, then some substance other than CoSO ₄ .7H ₂ O can also be used if appropriate. Therefore, the present invention is not limited to this material. Suitable substances include, for example, persulfates. The CoSO ₄ .7H ₂ O concentration of Example 1 corresponds to 0.285 g / L of Co ions. KAu in this example
The (CN) ₂ concentration corresponds to an Au ion concentration of 0.3 mg / L. Preferably this concentration is used. However, 0.01-0.5 g / L KAu (CN) ₂ can be used.

It is also possible to use some other additive other than C ₆ H ₈ O ₆ having the same “properties”, for example oxalic acid.

The current density can be varied within a given range, preferably it is between 0.1 and 5
It is 0 mAcm ⁻² .

The deposition was performed at room temperature. Multilayer deposition was performed using a computer assisted pulse plating (CAPP) machine equipped with an Axel Akerman A / S conditioning system.

The morphology and composition of the deposit were determined by measuring the energy dispersive x-ray spectrophotometer (E
DS) and scanning electron microscopy (SEM). X-ray diffraction (XRD) analysis was performed at large and small angles with a Philips wide range diffractometer equipped with a Cu tube.

The multilayer structure was examined by cross-section transmission electron microscopy (TEM). Cross-section sample preparation for TEM analysis was made by gluing two Cu strips of about 0.5 x 1 x 2.5 mm with facing multi-layer coatings of Ti lattice, which served as supports for the samples. Prior to the ion-milling process, the flakes were thinned to a thickness of about 50 μm. Finally, electron-transparent samples were obtained using a low-angle Ar ion beam on a Bal-Tec instrument operating at 10 kV.

In order to investigate the quality of the multi-layer and the roughness of the interface between the Co layer and the Au layer, three layers with different thicknesses were used.
Made layer deposits. Different multilayers of 10 nm, 100 nm, 150 nm were characterized by x-ray diffraction. 10 nm multilayer is 6.1 nm Au layer and 4.9 nm
Co layer of 100 nm, a multilayer of 100 nm is a 50 nm Au layer and a 50 nm Co layer.
Layers, as well as a 150 nm multilayer, are 100 nm Au layer and 50 nm C
It consists of o layers.

All peaks can be attributed to Au, Co or Cu peaks. The grain size of Au is 7.3 nm in a multilayer of Co50 nm / Au100 nm, Co50 nm / Au
It is considered to be 5.8 nm for a 50 nm multilayer. Low angle XRD measurements did not show the specific x-ray diffraction as expected with altered chemistry.

Although the surface morphology of the multilayers was observed to be small, a surface with well-defined grain boundaries was observed.

The most preferred complex is cobalt pyrophosphate, although other sources of cobalt are possible.

Example 2 (Production of Nanowires) Au—Co multilayer deposits were prepared in a similar manner as described in Example 1 from a single bath containing both Co and Au ions. Relatively precious metal ion (Au)
Was maintained at a low concentration. Thereby, the reduction rate is limited by mass transfer, so that the concentration of the relatively noble metal in the less noble layer can be minimized. As a result, a multi-layer with a layer of 96 wt% Co and 99 wt% Au can be successfully obtained.

[0061]   High-speed constant-voltage deposition with a pore diameter of 150 to 200 nm and a pore density of 10⁶-10 ⁸ Hole / cm^TwoFor the electrodeposition of nanowire multilayers on 20 μm thick films of
. This is illustrated in FIG. 2, where alternating layers of Au and Co are used.
A film (rod-shaped body) having is shown.

The electrodeposition time was 2 hours. The resulting nanowires nearly contained alternating about 4 nm pure Co layers and 2 nm pure Au layers provided on the film (see Figure 2).
.

In the open circuit, Au was deposited by an autocatalytic reaction. After that, change the voltage to -1.2
V was switched to deposit a Co layer for 8 ms, after which the potential was switched to -0.8 V, corresponding to the potential of pure Au deposition, and finally open circuit again. The cycle process was repeated up to 200 times. Open circuit condition and -0.800V
Since a low concentration of precious metal ions is rapidly consumed at the cathode surface during deposition at
This rapid cycle is very important. As a result, problems with passivation or dissolution of the layer during the change from a negative potential to a relatively positive potential can be solved.

It is possible according to the invention to obtain very pure Au / Co multilayers. The present invention is particularly convenient because such a multilayer has a particularly good GMR. With the method of the invention, this can be achieved in an inexpensive manner and in a short time.

[Brief description of drawings]

[Figure 1]   FIG. 1 shows a device for rotating a tubular body.

[Fig. 2]   FIG. 2 shows a rod with alternating layers of Au and Co.

[Procedure for Amendment] Submission for translation of Article 34 Amendment of Patent Cooperation Treaty

[Submission date] October 16, 2001 (2001.10.16)

[Procedure Amendment 1]

[Document name to be amended] Statement

[Name of item to be amended] Claims

[Correction method] Change

[Contents of correction]

[Claims]

─────────────────────────────────────────────────── ─── Continuation of front page (51) Int.Cl. ⁷ Identification code FI theme code (reference) C25D 7/00 C25D 7/00 K (81) Designated country EP (AT, BE, CH, CY, DE, DK) , ES, FI, FR, GB, GR, IE, IT, LU, MC, NL, PT, SE), OA (BF, BJ, CF, CG, CI, CM, GA, GN, GW, ML, MR , NE, SN, TD, TG), AP (GH, GM, KE, LS, MW, MZ, SD, SL, SZ, TZ, UG, ZW), EA (AM, AZ, BY, KG, KZ, MD, RU, TJ, TM), AE, AG, AL, AM, AT, AU, AZ, BA, BB, BG, BR, BY, BZ, CA, CH, CN, CR, CU, Z, DE, DK, DM, DZ, EE, ES, FI, GB, GD, GE, GH, GM, HR, HU, ID, IL, IN, IS, JP, KE, KG, KP, KR, KZ , LC, LK, LR, LS, LT, LU, LV, MA, MD, MG, MK, MN, MW, MX, MZ, NO, NZ, PL, PT, RO, RU, SD, SE, SG, SI, SK, SL, TJ, TM, TR, TT, TZ, UA, UG, US, UZ, VN, YU, ZA, ZW

Claims (24)

[Claims] 1. A multilayer structure comprising a substrate having thin layers of Co and Au, wherein the content of Au in the Co layer is at most 5% by weight, preferably at most 3% by weight. Co content in the layer is at most 5% by weight, preferably at most 1% by weight
Wherein the multi-layer is made by an electrodeposition method by means of providing an electric current between two electrodes having a potential difference immersed in an electroplating bath at least partially containing one or more substrates, wherein The bath contains Co ions and Au ions, and the method comprises growing the multilayers on the substrate in the bath, wherein the method further comprises changing the current density and / or the applied potential. A multi-layer structure comprising a substrate having a thin layer of Co and Au, which is controlled by modification and keeps the concentration of Au ions well below the concentration of Co ions. 2. The bath contains 0.2 to 0.7 g / L of Co ions, 0.1 to 0.
It contains 5 mg / L of Au ions and an organic acid, and the pH of the bath is 2.5-5.
The multi-layer according to claim 1, characterized in that the concentration of Co ions is 5 and the concentration of Co ions is about 1,000 times larger than the concentration of Au ions. 3. The potential for a specific period is switched from an open circuit condition to a potential for depositing Co ions, and then to another potential for depositing Au ions without depositing Co ions, and thereafter, Multilayer according to claim 2, characterized in that it is switched again to open circuit conditions and this switching cycle is repeated as many times as necessary. 4. Multilayer according to claim 3, characterized in that the switching cycle is repeated up to 10-5,000 times, preferably up to 200 times. 5. Multilayer according to one of the claims 1 to 4, characterized in that the reduction potentials of the components are sufficiently different from each other to allow separate electrodeposition of each component. 6. The Co layer is first deposited at a potential of -1.0 to -1.3 V, after which the potential is switched to a relatively high voltage, for example -0.5 to -0.8 V, after which Multilayer according to any one of claims 1 to 5, characterized in that the potential is switched to an open circuit. 7. The multilayer according to claim 2, wherein the organic acid is C ₆ H ₈ O ₆ in an amount of 10 to 200 g / L. 8. The multilayer according to claim 1, wherein the content of Co in the Au layer is at most 1 to 0.1% by weight. 9. The multilayer according to claim 1, wherein the multilayer structure is a nanowire. 10. A substrate having a thin layer of Co and Au by means of providing an electric current between two electrodes having a potential difference, which is immersed in an electroplating bath at least partially containing one or more substrates. A method for producing an electrodeposited multilayer structure comprising the bath comprising Co ions and Au ions, the method comprising growing the multilayer on the substrate in the bath, wherein: Current density and /
Or controlling this method by changing the applied potential, and Au
An electrodeposition method for producing a multi-layer structure comprising a substrate having a thin film layer of Co and Au, characterized in that the concentration of ions is kept well below the concentration of Co ions. 11. The bath is 0.2 to 0.7 g / L of Co ions, 0.1 to 0.
． It contains 5 mg / L of Au ions and an organic acid, and the pH of the bath is 2.5 to 5
． The method according to claim 10, characterized in that it is 5 and the concentration of Co ions is about 1,000 times greater than the concentration of Au ions. 12. The electrodeposition method according to claim 11, wherein the organic acid is C ₆ H ₈ O ₆ in an amount of 10 to 200 g / L. 13. The potential for a specific period of time is set so that Co ions are deposited from an open circuit condition, another potential after which Co ions are deposited without depositing Co ions, and then again. 13. The electrodeposition method according to claim 12, wherein the electrodeposition method is switched to an open circuit condition, and this switching cycle is repeated as many times as necessary. 14. The electrodeposition method according to claim 13, wherein the switching cycle is repeated 10 to 5,000 times, preferably 200 times. 15. The electrodeposition method according to claim 10, wherein the reduction potentials of the components are sufficiently different from each other to allow separate electrodeposition of each component. . 16. The Co layer is first deposited at a potential of -1.0 to -1.3 V, after which the potential is switched to a relatively high voltage, for example -0.5 to -0.8 V,
After that, the potential is switched to an open circuit, and the electrodeposition method according to any one of claims 10 to 15. 17. The electrodeposition method according to claim 10, wherein the operating temperature is 20 to 30 ° C. 18. The bath contains 0.2 to 0.7 g / L of Co ions, 0.1 to 0.
． It contains 5 mg / L of Au ions and an organic acid, and the pH of the bath is 2.5.
An electroplating bath for electrodeposition of thin films of Co and Au, which is ˜5.5 and the concentration of Co ions is about 1,000 times larger than the concentration of Au ions. 19. The electroplating bath according to claim 18, wherein the organic acid is C ₆ H ₈ O ₆ in an amount of 10 to 200 g / L. 20. Electroplating bath according to claim 19, characterized in that the Au is present in the bath as a KAu (CN) ₂ complex. 21. Electroplating bath according to claim 19, characterized in that the Co is present in the bath as a salt, for example as a sulfate, a sulfamate, a pyrophosphate or a chloride, dissolved in the bath. . 22. Electroplating bath according to claim 21, characterized in that the Co is present in the bath in the form of CoSO ₄ .7H ₂ O. 23. The electroplating bath according to claim 18, wherein the pH is adjusted by hydroxide or carbonate. 24. The method according to claim 1, wherein the pH is 3.5 to 4.5.
The electroplating bath according to any one of 8 to 23.