Electrochemical deposition method, electrochemical deposition apparatus, and microstructure

Abstract

An electrochemical deposition method in which the structure of a substance to be deposited on the surface of a working electrode is determined, an electrochemical deposition apparatus, and a microstructure are provided.

Description

TECHNICAL FIELD

The present invention relates to an electrochemical deposition method in which a voltage is applied or a current is fed between plural electrodes immersed in a solution in which an electrochemically depositable substance such as a metal is dissolved in an ionic state to deposit the substance on the surface of a working electrode, an electrochemical deposition apparatus, and a microstructure having lattices ranging in size from several tens to several hundreds of micrometers.

BACKGROUND ART

Through the progression of microfabrication technology, the propositions of nanometer-size micro devices (nanodevices), as well as an increase in the scale of integration, have been made. For example, researches on nanoperiodic structures of metals, semiconductors, conductive polymers, and so on are being conducted actively in various fields because various functions such as giant magnetoresistance, tunnel magnetoresistance, and photonics, emerge based on their characteristics. As methods for forming nanoperiodic structures, thin-film formation methods such as vapor deposition are established at present. These methods are multi-step techniques in which objective substances are alternately laminated.

However, in the conventional techniques described above, there is a problem that decrease in productivity and increase in cost are inevitable because those techniques each require a multi-step process. And further, it is inevitable that apparatuses for use in the formation of nanoperiodic structures are large in size, which further increases their production cost.

Therefore a self-organizing microfabrication technique called a structural formation based on nonlinear chemical dynamics is devised as a technique by which the above problems can be solved. This technique is a kind of bottom-up approach and is in an embryonic stage; however, it is expected as a technique which brings a drastic paradigm shift to conventional techniques.

Self organization includes static self organization and dynamic self organization; a structure formed by the former is a thermal equilibrium structure, i.e., a static ordered structure and is determined by the principles of intermolecular forces (interatomic forces) and equilibrium thermodynamics. On the other hand, a structure formed by the latter is a pattern which is spontaneously formed in the flow of energy, that is, an ordered structure which emerges in a non-equilibrium system and therefore has various structures in itself in terms of time and space. Dynamic self organization has characteristics such as the manifestation of a drawing effect which static self organization does not exhibit, a self-recovery function, and a long-range interaction; if dynamic self organization can be controlled, it becomes possible to manufacture a microstructure having a desired structure.

Patent Document 1 discloses a method for manufacturing a laminated film in which a conductive support is immersed in an aqueous solution containing metal ions, the potential of the conductive support is oscillated by using the support as an electrode, and metal layers and metal-oxide layers are alternately deposited on the conductive support.

Patent Document 1: Japanese Patent Application Laid-Open No.2002-129374

SUMMARY OF THE INVENTION

Problems to be Solved by the Invention

However, since the mechanism of the dynamic self organization has not yet been established and factors to be controlled required for the control of the self organization has not yet been established, it has been impossible to manufacture a microstructure having a desired structure. Put another way, it has been possible to manufacture microstructures as a result of the changing of manufacturing conditions, though it has been impossible to make them have desired structures. In addition, since the dynamic self organization is present in the flow of energy, there has been the problem that the interception of energy supplied from the outside results in the vanishment of the structures.

The present inventors conducted extensive studies on dynamic self-organization in an electrochemical reaction system. As a result, the studies have produced the finding that when microstructures are manufactured by means of electrochemical oscillations (current oscillations or potential oscillations), structures to be formed are determined based on the waveforms (such as periods and amplitudes) of electrochemical oscillations. With electrochemical reactions, it is easy to control them and even when energy has been intercepted, structures can be accumulated as histories (deposits) and the traces of dynamic space-time orders can be fixed and stored, thereby the structures formed do not vanish. And furthermore, the inventors have made the finding that the waveform of electrochemical oscillation can be controlled in an autocatalysis process by selecting the kinds of substances to be electrochemically deposited (for example, to be electrolytically deposited) and regulating the potential and current of a working electrode.

The present invention has been accomplished based on the above findings, and therefore an object of the invention is to provide an electrochemical deposition method in which the structure of a substance to be deposited on the surface of a working electrode is determined based on the waveform of electrochemical oscillation, i.e., current oscillation or potential oscillation generated by applying a voltage or feeding a current between plural electrodes immersed in a solution in which an electrochemically depositable substance such as a metal is dissolved in an ionic state and then controlling a potential of or a current into one electrode (called “working electrode”) of the electrodes relative to the solution.

Another object of the invention is to provide an electrochemical deposition method in which the electrochemical oscillation is controlled by mixing a reaction inhibitor into the solution and then coupling a negative derivative resistance induced by the reaction inhibitor with a potential drop in the solution to produce an autocatalysis process.

Another object of the invention is to provide an electrochemical deposition method in which the structure of a substance to be deposited on the surface of the working electrode is determined by regulating the concentration of the reaction inhibitor to control a potential of or a current into the working electrode at or with which electrochemical oscillation occurs.

Another object of the invention is to provide an electrochemical deposition method in which the structure of a substance to be deposited on the surface of the working electrode is determined by using a cationic surfactant with a carbon chain comprised of 10 carbon atoms or more as a reaction inhibitor and regulating the length of the carbon chain to control the potential or the current at or with which electrochemical oscillation occurs.

Another object of the invention is to provide an electrochemical deposition method in which the structure of a substance to be deposited on the surface of the working electrode is determined by regulating the concentration of the substance in the solution to control the waveform of electrochemical oscillation.

Another object of the invention is to provide an electrochemical deposition method in which when plural substances are dissolved in the solution in an ionic state, the composition ratio of the structure comprised of the substances is determined by controlling the waveform of electrochemical oscillation.

Another object of the invention is to provide an electrochemical deposition method in which when the structure of the deposited substance determined based on the waveform of the electrochemical oscillation is a multi-layered structure, the thickness and/or the composition ratio of each layer are determined by controlling the waveform of the electrochemical oscillation.

Another object of the invention is to provide an electrochemical deposition method in which the structure of a substance to be deposited on the working electrode is determined based on the waveform of electrochemical oscillation generated by controlling the potential of or the current into the working electrode such that the electrochemical deposition proceeds toward diffusion control.

Another object of the invention is to provide an electrochemical deposition method in which an upper potential or a lower potential is detected at each oscillation of the electrochemical oscillation and the current into the working electrode is controlled based on a variation in the upper or lower potential such that the problem that the spontaneous oscillation ceases because the density of the current gradually lowers and then falls outside a range in which the spontaneous oscillation occurs can be prevented and an electrochemical deposition apparatus.

Another object of the invention is to provide an electrochemical deposition method in which a microlattice structure with superior evenness can be obtained by controlling an effective current density at the working electrode relative to a current density in the solution such that the effective density is substantially constant to make the shape of the microstructure grown on the surface of the working electrode uniform.

Another object of the invention is to provide an electrochemical deposition apparatus capable of continuing the spontaneous oscillation by controlling the current into the working electrode such that the current density at which the spontaneous oscillation occurs can be secured in order to prevent the problem that the spontaneous oscillation ceases because the current density gradually lowers and then falls outside the range in which the spontaneous oscillation occurs.

Another object of the invention is to provide a microstructure which can be produced as, for example, a high-strength electrode with an extremely large surface area whose crystallographically stable planes are exposed by using a substance deposited by using one of the above electrochemical deposition methods as a three-dimensional base structure and depositing another substance on the surface of the substance.

Another object of the invention is to provide a microstructure having an internal porous structure formed by polymerizing the surface of the substance deposited by using one of the above electrochemical deposition methods and another substance to remove the deposited substance.

Means for Solving the Problems

An electrochemical deposition method according to a first aspect of the present invention is an electrochemical deposition method for depositing an electrochemically depositable substance on a surface of a working electrode by applying a voltage or feeding a current between a plurality of electrodes immersed in a solution in which the substance is dissolved in an ionic state, the method comprising:

generating electrochemical oscillation by controlling a potential of or the current through the working electrode relative to the solution; and

depositing the substance with a predetermined structure according to a waveform of the electrochemical oscillation.

In this aspect of the invention, the plural electrodes are immersed in the solution in which the electrochemically depositable substance (such as a metal, a semiconductor, and a conductive polymer) is dissolved in the ionic state and a voltage is applied or a current is fed between the electrodes to electrochemically deposit the dissolved substance on the surface of one electrode (the working electrode) of the electrodes. At the time of the electrochemical deposition, the spontaneous electrochemical oscillation occurs by controlling the potential of or the current into the working electrode relative to the solution. Since the waveform (for example, the period) of the electrochemical oscillation can be controlled by controlling the potential of or the current into working electrode, the structure of the substance to be deposited on the surface of the working electrode can be determined according to the waveform of the electrochemical oscillation. Since the structure is self-formed through the self-organized oscillation phenomenon, individual portions of the structure are laminated in order through the reflection of the history of the oscillation phenomenon. Therefore, the structure is accumulated as a history and the trace of a dynamic space-time order can be fixed and stored, thereby the formed structure does not vanish.

An electrochemical deposition method according to a second aspect of the invention is further comprising:

mixing a reaction inhibitor into the solution; and

generating a state in which the reaction inhibitor attaches to the surface of the working electrode and a state in which the reaction inhibitor detaches therefrom spontaneously and alternately.

In this aspect of the invention, the potential of or the current into the working electrode at or with which the electrochemical oscillation occurs is controlled by coupling a negative derivative resistance induced by the reaction inhibitor and a potential drop in the solution together through the mixing of the reaction inhibitor into the solution to produce an autocatalysis process, that is, to spontaneously and alternately bring about the state in which the reaction inhibitor attaches to the surface of the working electrode and the state in which the reaction inhibitor does not attach to the surface of the working electrode. The reaction inhibitor can be suitably mixed according to chemical reaction systems, which makes it possible to regulate the range of the potential of or the current into the working electrode at or with which the electrochemical oscillation occurs.

An electrochemical deposition method according to a third aspect of the invention is characterized in that the potential of or the current through the working electrode is controlled by regulating a concentration of the reaction inhibitor such that the electrochemical oscillation generates.

In this aspect of the invention, the potential of or the current into the working electrode at or with which the electrochemical oscillation occurs can be controlled by regulating the concentration of the reaction inhibitor. For example, in current oscillation as one form of the electrochemical oscillation, a potential generated by the negative derivative resistance (the potential of the working electrode generated when a current flowing into the working electrode abruptly decreases) can be shifted to the positive or negative side by regulating the concentration of the reaction inhibitor in the solution. Specifically, by increasing the concentration of the reaction inhibitor, the potential at which the current oscillation occurs can be shifted to the positive side. It is clear from the above that the current oscillation occurs at the potential generated by the negative derivative resistance and therefore, when a reaction inhibitor of the same kind is used, the potential at which the current oscillation occurs can be controlled by regulating the concentration of the reaction inhibitor, thereby the structure of a substance to be deposited on the surface of the working electrode can be determined.

An electrochemical deposition method according to a fourth aspect of the invention is characterized in that a cationic surfactant having a carbon chain consisting of 10 carbon atoms or more is used as the reaction inhibitor, and

the potential of or the current into the working electrode is controlled by regulating a length of the carbon chain such that the electrochemical oscillation generates.

In this aspect of the invention, when the cationic surfactant with the carbon chain comprised of 10 carbon atoms or more is used as the reaction inhibitor, the potential of or the current into the working electrode at or with which the electrochemical oscillation occurs can be controlled by regulating the length of the carbon chain. For example, by regulating the length of the carbon chain, the potential effected by the negative differential resistance can be shifted to the positive or negative side. Specifically, by lengthening the carbon chain, the potential at which the current oscillation occurs can be shifted to the positive side. Therefore, when a reaction inhibitor of the same kind is used, the potential at which the current oscillation occurs can be controlled by regulating the length of the carbon chain, thereby the structure of a substance to be deposited on the surface of the working electrode can be determined.

An electrochemical deposition method according to a fifth aspect of the invention is further comprising

controlling the waveform of the electrochemical oscillation by regulating a concentration of the substance.

In this aspect of the invention, by regulating the concentration of the substance in the solution, the potential of or the current into the working electrode can be controlled, that is, the waveform of the electrochemical oscillation can be controlled, and therefore the structure of a substance to be deposited can be determined.

An electrochemical deposition method according to a sixth aspect of the invention is a plurality of substances are dissolved in the solution in an ionic state, and

the method further comprises

determining a composition ratio of the structure by controlling the waveform of the electrochemical oscillation.

In this aspect of the invention, when the plural substances are dissolved in the solution in the ionic state, the composition ratio of the structure comprised of the substances can be determined by controlling the waveform of the electrochemical oscillation. For example, when the structure comprised of the substances is deposited, the substances differ from each other in their deposition amount relative to the potential of the working electrode according to the difference between the degrees of their ionization tendencies. And further, since the waveform of the electrochemical oscillation can be controlled by controlling the potential of the working electrode, the composition ratio of the structure can be determined (controlled) by controlling the deposition amounts of the substances. For example, in a case where metals are used as the substances, they have a property that when the potential of the working electrode has been lowered (when the potential has been set at a lower negative value), the deposition current increases, that is, the deposition amount increases; however, since the ratios of their deposition amounts to the potential differ from each other according to the difference between the degrees of their ionization tendencies, the composition ratio can be changed.

An electrochemical deposition method according to a seventh aspect of the invention is characterized in that the structure of the substance deposited according to the waveform of the electrochemical oscillation is a multilayered structure.

In this aspect of the invention, the substance having the multilayered structure can be deposited on the surface of the working electrode by using the foregoing electrochemical deposition method.

An electrochemical deposition method according to an eighth aspect of the invention is characterized in that one of a thickness and a composition ratio of each layer of the multilayered structure are determined by controlling the waveform of the electrochemical oscillation.

In this aspect of the invention, since the potential of or the current into the working electrode can be controlled, that is, since the waveform of the electrochemical oscillation can be controlled by, for example, regulating the concentration of the substance in the solution, the deposition amount of the substance can be controlled. When a multilayer structure comprised of plural substances is produced, any one of the thickness and the composition ratio or both of each layer can be determined because the deposition amount of each substance can be regulated. Specifically, the thicknesses of the layers can be determined by regulating the concentrations of the substances together while keeping the ratio between the concentrations of the substances constant.

An electrochemical deposition method according to a ninth aspect of the invention is characterized in that metals are used as the substances.

In this aspect of the invention, the metals can be deposited on the surface of the working electrode by using the foregoing electrochemical deposition method.

An electrochemical deposition method according to a tenth aspect of the invention is characterized in that the potential of or the current through the working electrode is controlled such that the electrochemical deposition proceeds under diffusion limited control to generate the electrochemical oscillation.

In this aspect of the invention, the electrochemical oscillation is generated by controlling the potential of or the current into the working electrode such that the electrochemical deposition proceeds under the diffusion limited control. Since an electrochemical phenomenon is produced by a balance between autocatalytic crystal growth in a specific orientation and autocatalytic surface passivation on a thermodynamically stable plane, an ordered microstructure having grown in a direction perpendicular to the working electrode is formed on the surface of the working electrode through the reflection of the history of the electrochemical oscillation. Therefore the structure is accumulated as a history and the trace of a dynamic space-time order can be fixed and stored, thereby the formed structure does not vanish.

An electrochemical deposition method according to an eleventh aspect of the invention is further comprising:

detecting an upper or lower potential on every oscillation of the electrochemical oscillation; and

controlling the current to the working electrode based on variations in the detected upper or lower potentials.

In this aspect of the invention, the upper or lower potential of each oscillation of the electrochemical oscillation is detected and the current into the working electrode is controlled based on the variation in the detected upper or lower potential. The oscillation phenomenon spontaneously occurs at a certain current density which means a threshold value at which a reaction rate-determining process turns to a diffusion limiting process. However, since the effective area of the working electrode gradually increases due to the growth of a microstructure on the surface of the working electrode, the current density gradually lowers and then falls outside a range in which the spontaneous oscillation occurs, thereby the spontaneous oscillation ceases. Therefore the spontaneous oscillation can be continued by controlling the current into the working electrode.

An electrochemical deposition method according to a twelfth aspect of the invention is characterized in that the current to the working electrode is controlled such that an effective current density relative to the solution is substantially constant.

In this aspect of the invention, the shapes (for example, the lattice spacings) of individual microstructures growing on the surface of the working electrode become uniform by controlling the effective current density at the working electrode relative to the solution so as to become constant substantially, thereby a microlattice structure with superior evenness can be formed.

An electrochemical deposition method according to a thirteenth aspect of the invention is characterized in that the waveform of the electrochemical oscillation is controlled by regulating a concentration of the substance.

In this aspect of the invention, since a potential of or a current into the working electrode can be controlled, that is, since the waveform of the electrochemical oscillation can be controlled by regulating the concentrations of the substances in the solution, the structure of a substance to be deposited can be determined. For example, by increasing the ion concentrations of the substances in the solution, each structure of the periodic structure of the substance to be deposited can be increased in size.

An electrochemical deposition apparatus according to a fourteenth aspect of the invention is an electrochemical deposition apparatus for depositing

a substance on a surface of a working electrode by feeding a current between a plurality of electrodes immersed in a solution in which the substance is dissolved in an ionic state and generating electrochemical oscillation, the apparatus comprising:

a detector for detecting an upper or lower potential every oscillation of the electrochemical oscillation; and

a current control unit for controlling the current to the working electrode relative to the solution based on the upper or lower potential detected by the detector.

In this aspect of the invention, the electrodes are immersed in the solution in which the electrochemically depositable substance (such as a metal, a semiconductor, or a conductive polymer) is dissolved in the ionic state, the detecting unit detects the upper or lower potential of each oscillation of the electrochemical oscillation, and the control unit controls the current into the working electrode relative to the solution based on the detected upper or lower potential. The spontaneous electrochemical oscillation is generated by feeding the current between the electrodes, thereby the dissolved substance is electrochemically deposited on the surface of one electrode (the working electrode) of the electrode. The structure of the substance to be deposited can be controlled by controlling a current to be fed to the working electrode.

An electrochemical deposition apparatus according to a fifteenth aspect of the invention is characterized in that the current control unit controls the current to the working electrode, the current corresponding to a current density at which the spontaneous oscillation generates.

In this aspect of the invention, since the current to be fed to the working electrode is controlled such that the current density at which the spontaneous oscillation occurs can be secured, it is possible to solve the problem that since the current density gradually lowers and then falls outside a range in which the spontaneous oscillation occurs, the spontaneous oscillation ceases, and therefore the spontaneous oscillation can be continued.

A microstructure according to a sixteenth aspect of the invention is a microstructure formed by using the substance deposited by using the electrochemical deposition method described above, wherein the microstructure includes a three-dimensional base structure and is provided with a deposit of another substance thereon.

In this aspect of the invention, the microstructure can be used as a high-strength electrode with an extremely large surface area by using the microstructure (for example, the microlattice structure) formed through the use of such a deposition method as a three-dimensional base structure (template) and then depositing another substance (electric conductor) such as platinum on the surface of the microstructure as described above. And further, the microstructure also has the advantage that crystallographically stable planes are exposed.

A microstructure according to a seventeenth aspect of the invention is a microstructure including an internal porous structure shaped by forming the substance deposited by using the electrochemical deposition method described above, polymerizing another substance on a surface of the deposited substance, and removing the deposited substance.

In this aspect of the invention, the microstructure can be produced as a microstructure with a hollow pattern by using the microstructure (for example, the microlattice structure) formed through the use of such a deposition method as a three-dimensional template.

EFFECTS OF THE INVENTION

According to the present invention, an ordered microstructure is spontaneously formed perpendicularly from a substrate by a self-organized oscillation phenomenon. Further, individual portions of the structure to be formed are laminated in order through the reflection of the history of oscillation phenomenon. In this invention, since the electrochemical oscillation phenomenon itself is intended to be controlled, the ordered structure to be formed can be controlled. And further, it becomes possible to form a simple periodic structure, a more complicated three-dimensional ordered structure, and various microlattice structures on the entire surfaces of electrodes at one step and low cost. Still further, by controlling a current fed to the working electrode such that a current density at which the spontaneous oscillation occurs can be secured, it becomes possible to solve the problem that since the current density gradually lowers and then falls outside a range in which the spontaneous oscillation occurs, the spontaneous oscillation ceases, that is, the spontaneous oscillation can be continued, and therefore a microlattice metal aggregate having a size of several millimeters to several centimeters can be formed. Still further, it is also possible to form a three-dimensional ordered structure applicable to metals, semiconductors, conductive polymers, and so on by utilizing the obtained ordered structure itself as a template. Moreover, since the ordered structure is theoretically to an electrochemical deposition reaction of a desired substance by suitably selecting a reaction inhibitor, it is expected that the structure will be applied to the formation of various functional materials. And furthermore, the structure of an apparatus used for the electrochemical deposition is extremely simple, which brings great advantages such as the capability of manufacturing a specified microstructure at extremely low cost.

BRIEF DESCRIPTION OF THE DRAWINGS

FIG. 1 is an explanatory drawing of an electrochemical deposition method according to a first embodiment of the present invention.

FIG. 2 is a graph of current oscillation.

FIG. 3 is an explanatory drawing of an evaluation method for a thin film.

FIG. 4 is an electron microscope photograph of a multilayer film formed by using the electrochemical deposition method according to the first embodiment of the invention and Auger electron spectroscopy results showing the evaluation results of the film.

FIG. 5 is a graph of deposition currents for Cu and Sn relative to the potential of a working electrode.

FIG. 6 is a graph of the correspondence between the waveform of electric oscillation and the composition ratio of a deposit.

FIG. 7 is a graph of the relationship between deposition currents and the potential of the working electrode brought about by using C_XH_2X-1N(CH₃)₃Cl.

FIG. 8 is a graph of the relationship between deposition currents and the potential of the working electrode brought about by using C12TAC.

FIG. 9 is an explanatory drawing of an electrochemical deposition method according to a second embodiment of the invention.

FIG. 10 is a graph of potential oscillation.

FIG. 11 is an electron microscope photograph of an example of a microstructure formed by using the electrochemical deposition method according to the second embodiment of the invention.

FIG. 12 is an explanatory drawing of a periodic structural change corresponding to potential oscillation required for the deposition of Sn.

FIG. 13 is an explanatory drawing of a periodic structural change corresponding to the potential oscillation required for the deposition of Sn.

FIG. 14 is a graph of the potential oscillation required for the deposition of Sn.

FIG. 15 is an electron microscope photograph of a microstructure formed by changing a current value at a working electrode.

FIG. 16 is a graph of potential oscillation required for the deposition of Zn.

FIG. 17 is an electron microscope photograph of microstructures formed by changing the ion concentration of Zn.

FIG. 18 is a graph of the relationship between a potential and a current density.

FIG. 19 is a graph of a change in the potential oscillation with respect to time.

FIG. 20 is an electron microscope photograph taken at points A and B of (a) of FIG. 19.

FIG. 21 is an explanatory drawing of the configuration of an electrochemical deposition apparatus according to a third embodiment of the invention.

FIG. 22 is an explanatory drawing of the control of a current value by a control unit.

FIG. 23 is a graph of an example of the control of the current value by the control unit.

FIG. 24 is an optical microscope photograph of an example of a microstructure formed by using the electrochemical deposition apparatus according to the third embodiment of the invention.

DESCRIPTION OF THE REFERENCE NUMERALS

1 and 11 Positive electrodes

2 and 12 Negative electrodes (working electrodes)

3 and 13 Reference electrodes

4 and 14 Solutions

5 and 15 Liquid tanks

BEST MODE FOR CARRYING OUT THE INVENTION

Embodiments of the present invention will be described below in detail with reference to the drawings.

Embodiment 1

FIG. 1 is an explanatory drawing of an electrochemical deposition method according to a first embodiment of the invention. Incidentally, in this embodiment, a description of a case where current oscillation as one form of electrochemical oscillation is controlled will be presented.

As shown in FIG. 1, conductive metal substrates, i.e., a positive electrode 1 and a negative electrode 2 are arranged oppositely in a liquid tank 5 containing an electrolytic (acid) solution (hereinafter referred to as “solution”) 4 in which plural substances (in this case, Cu and Sn are used) are dissolved in an ionic state, and then a predetermined voltage is applied between the positive electrode 1 and the negative electrode 2. In addition to the two electrodes 1 and 2, a reference electrode 3 is also arranged in the liquid tank 5 and the potential between the negative electrode 2 and the reference electrode 3 is measured. Since the solution 4 can be considered as a conductor, the potential V1 of the negative electrode 2 to the solution 4 can be determined. Furthermore, a reaction inhibitor is admixed into the solution 4 and spontaneous electrochemical oscillation (current oscillation in this case) is generated in the electrochemical deposition reaction of Cu and Sn in the presence of the reaction inhibitor. Examples of the reaction inhibitor include cationic surfactants; thus, Amiet-320 (chemical formula 1), C_XH_2X-1N(CH₃)₃Cl (chemical formula 2), TritonX-100 (chemical formula 3), or the like can be used. Incidentally, it is preferable to admix a citric acid with the solution 4 as a lubricating agent, and therefore in this embodiment, the solution 4 prepared by mixing CuSO₄ at a concentration of 0.15 M, SnSO₄ at a concentration of 0.15 M, H₂SO₄ at a concentration of 0.6 M, a citric acid at a concentration of 0.5 M, and Amiet-320 at a concentration of 0.5 mA was used.

[Chemical Formula 1]

Through the admixture of the reaction inhibitor with the solution 4, a negative derivative resistance induced by the reaction inhibitor and a potential drop in the solution couple with each other, which effects an autocatalysis process. When the potential V1 of the negative electrode 2 is in a predetermined range, minor fluctuations in the concentrations, temperature, and so on are amplified due to the autocatalysis process, thereby the current oscillation occurs as macroscopic and periodic oscillation shown in FIG. 2.

To be more specific, since the solution 4 can be considered as a conductor, ions on the surface of the negative electrode 2 are subjected to a strong electric field, thereby dehydration occurs and the ions turn to absorbing atoms through the reception of electrons from the negative electrode 2. The absorbing atoms diffuse on the surface of the negative electrode 2 and a point at which crystal lattices are formed is reached, thereby a crystal is formed. The attachment and detachment of the reaction inhibitor to and from the negative electrode 2 occur alternately and spontaneously and the oscillation phenomenon occurs with the attachment and detachment of the reaction inhibitor. In this embodiment, the negative electrode 2 functions as a working electrode and a thin film comprised of Cu and Sn and having superior smoothness deposits on the surface of the negative electrode 2 based on the waveform of the generated oscillation. Incidentally, the smoothness results from the admixture of the citric acid, and therefore in a case where the admixture is not done, asperities are left on the surface of the film.

Next, the grown film was evaluated for it properties. FIG. 3 is an explanatory drawing of a method for evaluating the film for its properties. To begin with, the surface of a sample 20 made by growing the thin film 21 was subjected to an Ar etching process with the sample 20 rotated (see FIG. 3(a)) to make a conical hole in the thin film 21 (see FIG. 3(b)). By observing the thin film 21 thus formed from above through the use of an electron microscope, it was confirmed that there are concentric light and dark portions as shown in FIG. 4(a); that is, it was confirmed that the grown thin film has a multilayer structure. And furthermore, the side of the thin film (multilayer film) was analyzed by means of scanning Auger spectroscopy in order to evaluate the composition ratio of the multilayer film, and thereupon it was confirmed that the composition ratio periodically changes as shown in FIG. 4(b).

The multilayer film is grown on the surface of the negative electrode 2 and hence, by shaping the negative electrode 2 into, for example, a cylinder, a multilayer film having superior smoothness can be formed inside the cylinder. According to the electrochemical deposition method of this embodiment, deposits can be grown on the surfaces of electrodes independently of the shapes of the electrodes, and therefore no matter how their shapes are, multilayer films having superior smoothness can be formed on their surfaces. Put another way, through the use of an electrode desirably shaped in advance and the application of the electrochemical deposition method according to the invention, a multilayer film having the desirable shape can be formed on the surface of the electrode.

In the invention, the thin film (an alloy of Cu and Sn) is deposited through the generation of the current oscillation as the multilayer film as described above, and the composition ratio and thickness of the multilayer film and the number of the layers (the number of times the lamination process is performed) are regulated as described below.

<1. Potential of Negative Electrode>

With respect to the potential of the negative electrode (working electrode) where the current oscillation occurs, there is the range of its regulation; therefore, through the regulation of the potential of the working electrode, the waveform of the current oscillation can be controlled, which makes it possible to regulate the composition ratio of the multilayer film and the thicknesses of the layers. That is, one good way to form the multilayer film with a desired composition ratio is to regulate the potential of the working electrode. The potential of the working electrode can be set at a desired value by changing a voltage applied between the positive electrode 1 and the negative electrode 2.

FIG. 5 is a graph of deposition currents for Cu and Sn relative to the potential of the working electrode. The deposition currents for Cu and Sn are each increased by lowering the potential of the working electrode (by using a lower negative potential), and the deposition current for Sn is generated at a lower negative potential as compared with that for Cu. Therefore, by making the setting of the deposition apparatus such that the current oscillation is generated in a state in which the potential of the working electrode is high, the deposition amount of Sn can be made less than that of Cu, that is, the composition ratio of Cu (Cu/(Cu+Sn)) can be increased. In contrast, by making the setting of the deposition apparatus such that the current oscillation is generated in a state in which the potential of the working electrode is low, the composition ratio of Cu can be lowered. In other words, the composition ratio of the deposit can be controlled by regulating the potential of the negative electrode according to the difference between the degrees of the ionization tendencies of the substances in the solution. For example, a multilayer film can be formed by alternately laminating layers comprised of Cu₂Sn₈ and layers comprised of Cu₇Sn₃.

Moreover, through the regulation of the potential of the working electrode, the waveform (for example, the cycle) of the current oscillation is controlled, thereby the thicknesses of the layers can be regulated. For example, the thicknesses of the layers can be increased by lowering the potential of the working electrode; the thicknesses can be decreased by increasing the potential.

<2. Concentrations of Substances in Solution>

The deposition current can be regulated by regulating the concentrations of the substances contained in the solution, and therefore the composition ratio of the thin film can be determined (controlled) by regulating the amount of the deposited substances. For example, the composition ratio of Cu can be increased by increasing the concentration of Cu.

Furthermore, the thicknesses of the layers can be regulated by regulating the concentrations of Cu and Sn together without changing the concentration ratio between Cu and Sn. FIGS. 6(a) and 6(b) are each a graph of the correspondence between the waveform of the electric oscillation and the composition ratio of the deposit. In FIG. 6(a), the concentrations of CuSO₄ and SnSO₄ are 0.15 M and in FIG. 6(b), their concentrations are 0.10 M. The period of the oscillation can be shortened by lowering the concentrations, and thus a multilayer film having a thickness corresponding to the period of the oscillation can be deposited. For example, in this embodiment, when the concentrations are 0.15 M, the layers each having a thickness of 90 nm are deposited and when the concentrations are 0.10 M, the layers each having a thickness of 38 nm are deposited.

<3. Kind and Concentration of Reaction Inhibitor>

When the reaction inhibitor has attached to one place of the substrate due to the fluctuations, the species spreads over the surface of the negative electrode with its phases uniform by virtue of its autocatalysis function, thereby the deposit accumulates on the entire surface of the negative electrode. Since the potential of the negative electrode to which the reaction inhibitor attaches is determined by the kind and concentration of the reaction inhibitor, the potential at which the current oscillation occurs, that is, the waveform of the current oscillation can be controlled by selecting the kind of the reaction inhibitor and by regulating its concentration.

When the above compound C_xH_2x-1N(CH₃)₃Cl was used, it was confirmed that the compound functions as a reaction inhibitor only when the compound has a carbon chain comprised of 10 carbon atoms (C10) or more, that is, only when its composition parameter X is 10 (C10TAC), 12 (C12TAC), or 16 (C16TAC).

The relationship between the kind of the reaction inhibitor and the potential at which the current oscillation occurs was evaluated by using a solution 4 prepared by mixing C_xH_2x-1N(CH₃)₃Cl having a carbon chain composed of 10, 12, or 16 carbon atoms at a concentration of 5 mM into a solution comprised of CuSO₄ at a concentration of 0.15 M, SnSO₄ at a concentration of 0.15 M, H₂SO₄ at a concentration of 0.5 M, and a citric acid at a concentration of 0.5 M.

FIG. 7 is a graph showing the relationship between the deposition current and the potential of the working electrode brought about by using C_xH_2x-1N(CH₃)₃Cl. FIG. 7(a) shows the case where C10TAC is contained in the solution as the reaction inhibitor, FIG. 7(b) shows the case where C12TAC is contained therein, and FIG. 7(c) shows the case where C16TAC is contained therein. The current oscillation occurs based on the potential level of the negative derivative resistance and therefore, when reactive inhibitor of the same kind are used, the potential at which the current oscillation occurs can be shifted to the positive side by using the reaction inhibitor having a longer carbon chain. Therefore, by regulating the length of the carbon chain of the reaction inhibitor, the potential at which the current oscillation occurs can be controlled, that is, the waveform of the current oscillation can be controlled, which makes it possible to form a multilayer film having a structure corresponding to the level of the current oscillation.

The relationship between the concentration of the reaction inhibitor and the potential at which the current oscillation occurs was evaluated by using a solution 4 prepared by mixing C12TAC with a concentration which is not the same as that described above into a solution comprised of CuSO₄ at a concentration of 0.15 M, SnSO₄ at a concentration of 0.15 M, H₂SO₄ at a concentration of 0.25 M, and the citric acid at a concentration of 0.5M.

FIG. 8 is a graph showing the relationship between the deposition current and the potential of the working electrode brought about by using C12TAC. FIG. 8(a) shows the case where the concentration of C12TAC is 2 mM, FIG. 8(b) shows the case where the concentration of C12TAC is 3 mM, and FIG. 8(c) shows the case where the concentration of C12TAC is 4 mM. The current oscillation occurs based on the potential level of the negative derivative resistance and therefore, when reaction inhibitor of the same kind are used, the potential at which the current oscillation can be shifted to the positive side by using the reaction inhibitor with a higher concentration. Accordingly, through the regulation of the concentration of the reaction inhibitor, the potential at which the current oscillation occurs can be controlled, that is, the waveform of the current oscillation can be controlled, which makes it possible to form a multilayer film having a structure corresponding to the level of the current oscillation.

As described in detail above, according to the electrochemical deposition method according to the first embodiment, the multilayer film can be formed on the entire surface of the working electrode at one step and low cost. And further, the method can be theoretically applied to electrochemical deposition reactions of not only metals but semiconductors (such as Cu₂O), conductive polymers (such as polyaniline), and so on by suitably selecting the reaction inhibitor, it is expected that the method will be applied to the production of various functional materials. Furthermore, the structure of an apparatus used for the deposition is extremely simple, and thus a specified microstructure can be manufactured at extremely low cost.

In the embodiment of the invention, the description of the case where the alloy of Cu and Sn is made by using the mixed solution containing Cu and Sn; however, materials which can be used are not limited to such an alloy. Multilayer films are also formed by the electrochemical deposition reaction of Cu in a solution into which phenanthrene (C₁₄H₁₀) acting as a reaction inhibitor is mixed, the electrochemical deposition reaction of Ni in a solution into which a hypophosphorous acid (H₂PO(OH)) is mixed, and so on, and therefore the electrochemical deposition method according to the invention is available to reaction systems in which electric oscillation occurs. Accordingly, a high-quality multilayer structure can be easily formed by using a desired material; for example, it becomes possible to easily produce devices having functions based on multilayer structures such as giant magnetoresistance and tunneling magnetoresistance at low cost.

Moreover, in this embodiment, the description of the current oscillation has been presented as one form of electrochemical oscillations; in addition, it is needless to say that potential oscillation (the oscillation of the potential of the working electrode) can also be utilized, that is, an oscillation phenomenon can be produced by controlling the amount of current to be fed to the working electrode.

Embodiment 2

In the first embodiment, the oscillation phenomenon is produced by mixing the reaction inhibitor into the solution to couple the negative differential resistance induced by the reaction inhibitor with the potential drop of the solution. On the other hand, the potential of or the current into a working electrode can be controlled such that the deposition of substances dissolved in a solution onto the surface of the working electrode proceeds under the diffusion limited control of the substances; a description of such a method will be presented below as a second embodiment, that is, a method for forming a lattice structure on the surface of a working electrode through the control of potential oscillation will be described below.

FIG. 9 is an explanatory drawing of the electrochemical deposition method according to the second embodiment of the invention. Incidentally, in this embodiment, a description of a case where potential oscillation as one form of electrochemical oscillations is controlled will be presented.

As shown in FIG. 9, conductive metal substrates, i.e., a positive electrode 11 and a negative electrode 12 are oppositely arranged in a liquid tank 15 containing an electrolytic solution (hereinafter referred to as “solution”) 14 in which substances (in this case, metals such as Sn and Zn are used) are dissolved in an ionic state, and then a predetermined current is fed between the negative electrode 12 and the positive electrode 11; that is, a constant current source is connected between the negative electrode 12 and the positive electrode 11. Incidentally, the value of an output current from the constant current source can be set suitably. And further, in addition to the two electrodes 11 and 12 described above, a reference electrode 13 is arranged in the liquid tank 15 and a potential between the reference electrode 13 and the negative electrode 12 is measured. Since the solution 14 can be considered as a conductor, a potential V2 of the negative electrode 12 relative to the solution 14 can be determined. By controlling the current such that the proceeding toward the diffusion control of the substances is done under diffusion-controlling conditions in the electrochemical deposition reaction of the substances, spontaneous electrochemical oscillation (in this case, potential oscillation) occurs. Incidentally, in this embodiment, the solution 14 containing Sn²⁺ at a concentration of 0.2 M and NaOH at a concentration of 4 M was used.

By controlling the current such that the proceeding toward the diffusion control is done, an autocatalysis process is produced. When a current value between the negative electrode 12 and the positive electrode 11 falls within a predetermined range, minor fluctuations are amplified by the autocatalysis process, thereby potential oscillation shown in FIG. 10 occurs as macroscopic and periodic oscillation.

Since the oscillation phenomenon is produced by a balance between autocatalytic crystal growth along a specific orientation and autocatalytic surface inactivation on a thermodynamically stable plane, the crystals of the substances grow in a direction perpendicular to the working electrode through the reflection of the history of the potential oscillation, thereby an ordered microstructure is formed on the surface of the negative lo electrode 12 which functions as a working function. When Sn and Zn are used as the substances, Sn is deposited such that a lattice structure is formed as shown in FIG. 11(a) and Zn is deposited such that a structure in which hexagonal plates overlap one after another is formed as shown in FIG. 11(b). It is needless to say that the kinds of the substances are not limited to them; Pb is used, a micro network structure is formed three-dimensionally. Therefore the structure of a substance to be deposited depends on the crystal structure of the substance itself to be deposited.

In order to evaluate how the waveform of the potential oscillation is reflected by the lattice structure, the negative electrode (working electrode) 12 was pulled up from the solution 14 at several potentials at which the potential oscillation occurs to observe the surface of the working electrode through the use of an electron microscope and an optical microscope.

FIGS. 12 and 13 are explanatory drawings of periodical changes in the structure of Sn synchronizing to potential oscillation required for the deposition of Sn. FIG. 12(a) shows the waveform of the potential oscillation required for the deposition of Sn, FIG. 12(b) shows crystal planes and orientations of Sn, and FIG. 13(a), 13(b), and 13(c) are the scanning electron microscope (SEM) photographs, optical microscope (OM) photographs, and schematic depictions of the surface of the negative electrode observed at the potentials A, B, C shown in FIG. 12(a). Incidentally, the amount of current from the constant current source was set such that the density of the current fed between the negative electrode 12 and the positive electrode 11 is −36 mA/cm².

At the negative end of the potential oscillation (potential A of FIG. 12(a)), angular Sn crystals were found and further, it was observed that a (110) plane and a (011) plane as thermodynamically stable orientation planes are exposed at the individual crystals (see FIG. 13(a)). When the potential has risen from the negative end (potential B of FIG. 12(a)), it was observed that needle-shaped Sn crystals deposit from the corners of the angular Sn crystals in <101> directions (see FIG. 13(b)). And further, at the potential of the positive end (potential C of FIG. 12(a)), it was observed that the thermodynamically stable planes of the tips of the needle-shaped Sn crystals are exposed again to initiate crystallization (see FIG. 13(c)). It was clear from the observation results that a lattice structure with a desired shape can be formed by controlling the waveform of the potential oscillation.

Next, a method for controlling the waveform of the potential oscillation will be described below.

<1. Current Value of Working Electrode>

FIG. 14 is a graph of the potential oscillation required for the 5 deposition of Sn; the horizontal axis indicates the lapse of time, and the vertical axis indicates the potential of the working electrode.

FIG. 14 shows the potential oscillation generated when a constant current of −12 mA has been fed between the working electrode, i.e., the negative electrode 12 and the positive electrode 11 up to 62 seconds and a constant current of −20 mA has been fed between the negative electrode 12 and the positive electrode 11 after that. It is apparent that the waveform of the potential oscillation changes by changing the value of the current, that is, after the lapse of 62 seconds. Incidentally, the potential oscillation is unstable up to 42 seconds because the reaction is unstable.

With respect to such a structure formed by changing the current value of the working electrode, the structural parameter of lattices to be formed can be controlled as shown in FIG. 15. That is, in the method for depositing the crystal of Sn according to the embodiment, lattice spacings can be changed by changing the current value. In this embodiment, it is apparent that since the current value was changed during the crystal growth, the lattice spacings changed from a crystal C deposited at the point in time when the current value was changed.

That is, with respect to the current value at which the potential oscillation occurs, there is the range of its regulation; therefore, through the regulation of the current value, the waveform of the potential oscillation can be controlled, thereby the structural parameter of a structure to be formed can be controlled.

<2. Concentrations of Substances in Solution>

The relationship between the concentration of the substance and the waveform of potential oscillation was evaluated by using a solution 14 containing Zn²⁺ at a concentration which is not the same as that described above and NaOH at a concentration of 4 M.

FIG. 16(a), 16(b), and 16(c) are graphs of potential oscillations through which the deposition of Zn was brought about and their horizontal axes indicate lapses of time. FIG. 16(a) shows a potential produced when the ion concentration of Zn is 0.1 M, FIG. 16(b) shows a potential produced when the concentration is 0.2 M, and FIG. 16(c) shows a potential produced when the concentration is 0.5 M. The period of the oscillation can be lengthened by increasing the ion concentration of Zn. FIGS. 17(a), 17(b), and 17(c) are electron microscope photographs of microstructures formed when the ion concentration of Zn was changed. FIG. 17(a) shows the case where the ion concentration of Zn is 0.1M, FIG. 17(b) shows the case where the ion concentration of Zn is 0.2 M, and FIG. 17(c) shows the case where the ion concentration of Zn is 0.5 M, from which it is apparent that the size of hexagonal plates can be increased by increasing the ion concentration.

That is, the waveform of the potential oscillation can also be controlled by regulating the concentration of the substance contained in the solution, and therefore the structural parameter of a structure to be formed can be controlled as described above.

As described in detail above, according to the electrochemical deposition method of the second embodiment, the microstructures inherent in the substances deposited can be formed on the entire surface of the working electrode at one step and low cost. And further, since the structure of the apparatus used for the deposition is extremely simple, a specified microstructure can be produced at extremely low cost.

In this embodiment, the description of the potential oscillation has been presented as one form of electrochemical oscillations; in addition, it is needless to say that such deposition can also be produced by means of current oscillation (the oscillation of current at the working electrode), that is, an oscillation phenomenon can be produced by controlling the potential of the working electrode.

Incidentally, in the potential oscillation as one form of electrochemical oscillations, when the current density is below a threshold value jdl (ca. −25 mA/cm²), the potential spontaneously starts to oscillate as shown in FIG. 18. Put another way, when the current density is low, the electrochemical oscillation does not occur, and therefore it can be said that the threshold value jdl is a boundary at which the reaction rate-determining process turns to the diffusion limiting process. That is, in order to continue the potential oscillation, it is extremely important to maintain the diffusion limiting process through the control of the current density.

FIGS. 19(a) and 19(b) are graphs each showing a change in the potential oscillation with respect to time; the horizontal axes indicate the lapses of times and the vertical axes indicate potentials. FIG. 19(a) shows the case where the constant current is fed between the working electrode (i.e., the negative electrode 12) and the positive electrode 11; in that case, the potential oscillation ceases after a lapse of about 250 seconds (which corresponds to about 75 times in terms of the number of the cycles of the oscillation). This is because the effective area of the working electrode gradually increases through the growth of the microstructure on the surface of the working electrode and then the current density gradually lowers and deviates from the region where the spontaneous oscillation occurs. And furthermore, since the current density lowers each time the growth is repeated as shown in FIG. 20, the lattice spacings of the microstructure growing on the surface of the working electrode gradually shortens, thereby the evenness of the microstructure is impaired. Incidentally, FIGS. 20(a) and 20(b) are electron microscope photographs taken at the points A and B of FIG. 19(a) respectively.

Therefore, as shown in FIG. 19(b), it is preferable to continue the spontaneous oscillation through the keeping of the effective current density done by considering an increase in the effective electrode area and controlling (gradually increasing) the current fed between the working electrode (i.e., the negative electrode 12) and the positive electrode 11 so as to cancel out the effect of the increase in the area.

Embodiment 3

FIG. 21 is an explanatory drawing of the structure of an electrochemical deposition apparatus according to a third embodiment of the invention. Incidentally, in this embodiment, a description of the control of potential oscillation as one form of electrochemical oscillations will be presented.

In the electrochemical deposition apparatus according to the third embodiment of the invention, the conductive metal substrates, i.e., the positive electrode 11 and the negative electrode 12 are oppositely arranged in the liquid tank 15 containing the electrolytic solution (hereinafter referred to as “solution”) 14 in which substances (in this case, metals such as Sn and Zn are used) are dissolved in an ionic state and a current is fed between the negative electrode 12 and the positive electrode 11. And further, in addition to the two electrodes 11 and 12, the reference electrode 13 is arranged in the liquid tank 15. Furthermore, the deposition apparatus is provided with a detecting unit 16 which measures a potential between the reference electrode 13 and the negative electrode 12 and which detects an upper potential or a lower potential at each oscillation of the electrochemical oscillation and a control unit 10 which controls a current to the working electrode relative to the solution based on the upper or lower potential detected by the detecting unit 16. Since the solution 14 can be considered as a conductor, the potential V2 of the negative electrode 12 relative to the solution 14 is determined, and then the control unit 10 controls a current to be fed between the negative electrode 12 and the positive electrode 11 base on the potential V2. Specifically, a constant current source is connected between the negative electrode 12 and the positive electrode 11 and the control unit 10 controls the value of a current fed from the constant current source. In this case, the term upper potential refers to an extreme value in the positive direction (maximum value) of the oscillation, and the term lower potential refers to an extreme value in the negative direction (minimum value) of the oscillation.

FIG. 22 is an explanatory drawing of the control of a current value by the control unit.

FIG. 22(a) shows a potential waveform generated when the potential oscillation occurs; reference letter A denotes an nth oscillation waveform, reference letter B denotes an n+1th oscillation waveform, and reference letter C denotes an n+2th oscillation waveform. Since the microstructure grows at the working electrode through the potential oscillation as described above, the effective electrode area increases and the upper and lower potentials of the potential oscillation are displaced in the negative direction every cycle. And further, when a current I has been fed, a potential loss expressed by the Ohm's law I×R (R is the resistance of the solution) is produced. That is, as shown in FIG. 22(b), a potential loss is produced by the increase in the electrode area ΔA in the process of the crystal growth from the nth generation to the n+1th generation. The current I is proportional to the electrode area A, i.e., the equation I=k×A holds, and an increase in the potential loss is expressed by a product (k∴ΔA)×R. In addition, the displacement ΔU of the upper potential and the lower potential at the potential oscillation (hereinafter exemplified by using the upper potential) is expressed by the following equation: ΔU=(k×ΔA)×R   (equation (1))

A current density j can be defined as follows:

j=I/A (where I is the current value and A is the effective electrode area). In the process of the nth-generation crystal growth, the current density jn is expressed by the equation jn=In/An and in the process of the n+1th-generation crystal growth, the current density jn+1 is expressed by the equation jn+1=(In+ΔI)/(An+ΔA); therefore, in this embodiment, since ΔI is controlled such that jn=n+1, the equation In/An(In+ΔI)/(An+ΔA) holds, from which the following equation is derived: ΔI=In/An×ΔA   (equation (2))

From the equations (1) and (2), the equation ΔI=jn×(U/(k×R)) is derived. And further, since j0=j1= . . . jn, the following equation is derived: ΔI=j0×(ΔU/(k×R))   (equation (3)) where k×R is a parameter dependent upon experimental system including the location of the electrodes and the concentrations of the substances and takes on a constant value. Therefore, after the detection of ΔU, ΔI is calculated from equation (3) based on ΔU to control the value of the current to be fed between the negative electrode 12 and the positive electrode 11, thereby the waveform of next-generation potential oscillation is controlled.

FIG. 23 is a graph of an example of the control of the current value by the control unit; the horizontal axis indicates a lapse of time, and the vertical axis indicates the value of a current fed between the working electrode (i.e., the negative electrode 12) and the positive electrode 11. From FIG. 23, it can be seen that the value of the current fed between the working electrode (i.e., the negative electrode 12) and the positive electrode 11 is increased with the lapse of time. This is because the increase in the effective electrode area was taken into consideration and the current value was gradually increased so as to cancel out the effect of the increase in the effective electrode area, whereby the effective density of the current does not vary, which allows the spontaneous oscillation to continue. Therefore, even when about 250 seconds have elapsed, the potential oscillation does not cease. In this embodiment, it was confirmed that even when about 2000 seconds or more (about 600 cycles in terms of the cycles of the oscillation) have elapsed, the potential oscillation continues.

Furthermore, even when the potential oscillation has been repeated, the current density remains the same, and therefore the lattice spacings of the microstructure growing on the surface of the working electrode remains the same as those of the microstructure formed at the time of the start of the oscillation, whereby the microlattice structure with superior evenness can be formed. As mentioned above, the microstructure with the uniform lattice spacings can be manufactured at low cost by considering the increase in the effective electrode area and gradually increasing the current value so as to cancel out the effect of the increase in the area with the lapse of time. And further, although the lattices range in size from several tens to several hundreds of micrometers, a metal microlattice aggregate having a size of several millimeters to several centimeters can be obtained by using the electrochemical deposition method according to this embodiment as shown in FIG. 24.

As a result, a bulk material having such a microstructure can be obtained and therefore used as a new bulk material for an electrode. The microlattice structure itself of Sn is of limited application; however, a high-strength electrode with an extremely wide surface area can be produced by using the microstructure (for example, the microlattice structure) as a three-dimensional base structure (template) and plating the surface of the microstructure with an electric conductor such as platinum. And furthermore, the bulk material has the advantage that crystallographically stable surfaces are exposed. It is needless to say that materials used as the coating on the microstructure can be selected according to the use of the structure and it can be therefore considered to use copper oxide except for platinum.

On the other hand, a microstructure with a hollow pattern can be produced by using the microstructure (for example, the microlattice structure) described in each embodiment as a three-dimensional template. For example, a polymeric substance having a hollow structure (ants' nest-shaped structure) can be produced by putting the microstructure produced using the deposition method according to each embodiment in a polymer solution to polymerize them and then removing (etching) Sn through the use of an etchant such as hydrochloric acid. Since such a polymeric substance has a porous structure, its application to a filter can be expected. And further, since the lattice spacings can be regulated by controlling the waveform of the electrochemical oscillation, it is also possible to make the polymeric substance have plural structures whose lattice spacings are different.

In the third embodiment, an upper or lower potential of each oscillation of the electrochemical oscillation is detected and the control unit 10 controls a current to be fed between the negative electrode 12 and the positive electrode 11 based on the upper or lower potential; in addition, a current into the working electrode relative to the solution can be controlled by calculating the period of each oscillation of the electrochemical oscillation from the upper or lower potential and securing a current density at which the spontaneous oscillation occurs based on the calculated period.

Up to this point the electrochemical deposition method according to the present invention has been described with reference to the specific embodiments; however, the invention is not limited to these embodiments. Those skilled in the art will appreciate that various modifications or improvements can be made to the structures and functions described in the embodiments of the invention without departing from the sprit and scope of the invention.

Claims

1-17. (canceled)

18. An electrochemical deposition method for depositing an electrochemically depositable substance on a surface of a working electrode by applying a voltage or feeding a current between a plurality of electrodes immersed in a solution in which the substance is dissolved in an ionic state, the method comprising: generating electrochemical oscillation by controlling a potential of or the current through the working electrode relative to the solution; and depositing the substance with a predetermined structure according to a waveform of the electrochemical oscillation.

19. The method according to claim 18, further comprising: mixing a reaction inhibitor into the solution; and generating a state in which the reaction inhibitor attaches to the surface of the working electrode and a state in which the reaction inhibitor detaches therefrom spontaneously and alternately.

20. The method according to claim 18, further comprising controlling the waveform of the electrochemical oscillation by regulating a concentration of the substance in the solution.

21. The method according to claim 18, wherein a plurality of substances are dissolved in the solution in an ionic state, and the method further comprises determining a composition ratio of the structure by controlling the waveform of the electrochemical oscillation.

22. The method according to claim 18, wherein the structure of the substance deposited according to the waveform of the electrochemical oscillation is a multilayered structure.

23. The method according to claim 18, wherein a metal is used as the substance.

24. The method according to claim 18, wherein the potential of or the current through the working electrode is controlled such that the electrochemical deposition proceeds under diffusion limited control to generate the electrochemical oscillation.

25. The method according to claim 19, wherein the potential of or the current through the working electrode is controlled by regulating a concentration of the reaction inhibitor such that the electrochemical oscillation generates.

26. The method according to claim 19, wherein a cationic surfactant having a carbon chain consisting of 10 carbon atoms or more is used as the reaction inhibitor, and the potential of or the current into the working electrode is controlled by regulating a length of the carbon chain such that the electrochemical oscillation generates.

27. The method according to claim 22, wherein one of a thickness and a composition ratio of each layer of the multilayered structure are determined by controlling the waveform of the electrochemical oscillation.

28. The method according to claim 24, further comprising: detecting an upper or lower potential on every oscillation of the electrochemical oscillation; and controlling the current to the working electrode based on variations in the detected upper or lower potentials.

29. The method according to claim 28, wherein the current to the working electrode is controlled such that an effective current density relative to the solution is substantially constant.

30. The method according to claim 24, wherein the waveform of the electrochemical oscillation is controlled by regulating a concentration of the substance in the solution.

31. An electrochemical deposition apparatus for depositing a substance on a surface of a working electrode by feeding a current between a plurality of electrodes immersed in a solution in which the substance is dissolved in an ionic state and generating electrochemical oscillation, the apparatus comprising: a detector for detecting an upper or lower potential every oscillation of the electrochemical oscillation; and a current control unit for controlling the current to the working electrode relative to the solution based on the upper or lower potential detected by the detector.

32. The apparatus according to claim 31, wherein the current control unit controls the current to the working electrode, the current corresponding to a current density at which the spontaneous oscillation generates.

33. A microstructure formed by using the substance deposited by using the electrochemical deposition method according to claim 18, wherein the microstructure includes a three-dimensional base structure and is provided with a deposit of another substance thereon.

34. A microstructure including an internal porous structure shaped by forming the substance deposited by using the electrochemical deposition method according to claim 18, polymerizing another substance on a surface of the deposited substance, and removing the deposited substance.