Electrode for electrolytic processing
An electrode for electrolytic processing has a conductive material and an organic compound having an ion exchange group. The organic compound is chemically bonded to a surface of the conductive material. The organic compound comprises thiol or disulfide. The ion exchange group comprises at least one of a sulfo group, a carboxyl group, a quaternary ammonium group, and an amino group. The conductive material includes at least one of gold, silver, platinum, copper, gallium arsenide, cadmium sulfide, and indium oxide (III).
This is a continuation-in-part of International Application No. PCT/JP03/12650, filed Oct. 2, 2003.
BACKGROUND OF THE INVENTION1. Field of the Invention
The present invention relates to an electrode for electrolytic processing, and more particularly to an electrode to be used as a processing electrode to process a substrate and/or a feeding electrode to feed the substrate during an electrolytic process using a fluid, particularly pure water. The present invention also relates to an electrolytic processing apparatus and method using such an electrode. The present invention also relates to a method of promoting to dissociate liquid into ions, and more particularly to a method of promoting dissociation of liquid into ions during an electrolytic process.
2. Description of the Related Art
In recent years, there has been a growing tendency to replace aluminum or aluminum alloy as a metallic material for forming interconnection circuits on a substrate such as a semiconductor wafer with copper (Cu) having a low electric resistivity and a high electromigration resistance. Copper interconnections are generally formed by filling copper into fine recesses formed in a surface of a substrate. As methods for forming copper interconnections, there have been employed chemical vapor deposition (CVD), sputtering, and plating. In any of the methods, after a copper film is formed on substantially the entire surface of a substrate, unnecessary copper is removed by chemical mechanical polishing (CMP).
Subsequently, as shown in
Recently, components in various types of equipment have become finer and have required higher accuracy. As submicronic manufacturing technology has commonly been used, the properties of the materials are greatly influenced by the machining method. Under these circumstances, in a conventional mechanical machining method in which a desired portion in a workpiece is physically destroyed and removed from a surface thereof by a tool, a large number of defects may be produced by the machining, thus deteriorating the properties of the workpiece. Therefore, it is important to perform machining without deteriorating the properties of materials.
Some processing methods, such as chemical polishing, electrochemical machining, and electrolytic polishing, have been developed in order to solve the above problem. In contrast to the conventional physical machining methods, these methods perform removal processing or the like through a chemical dissolution reaction. Therefore, these methods do not suffer from defects such as formation of an altered layer and dislocation due to plastic deformation, so that processing can be performed without deteriorating the properties of the materials.
In an electrochemical machining process, particularly in an electrochemical machining process using pure water or ultrapure water, an ion exchanger such as an ion exchange membrane or an ion exchange fiber is employed to increase the processing rate. Pure water refers to water having a resistivity of 0.1 MΩ·cm or more at 25° C., and ultrapure water refers to water having a resistivity of 10 MΩ·cm or more at 25° C. Ion exchangers generally comprise an ion exchange resin or an ion exchange membrane in which an ion exchange group, such as a sulfo group, a carboxyl group, a quaternary ammonium group (═N+═), or a tertiary or lower amino group, is bonded to a base material, such as a copolymer of styrene and divinylbenzene, or a fluororesin. Further, there has been known an ion exchange fiber in which an ion exchange group is introduced into nonwoven fabric by graft polymerization.
However, with respect to the conventional ion exchange resin or ion exchange fiber, when the electrodes 810 and 820 have a small size (i.e., a small diameter), the ion exchangers 830 and 840 cannot be disposed separately on the surfaces of these electrodes 810 and 820. Therefore, the anode 810 and the cathode 820 have to be covered with an ion exchanger extending over both of the anode 810 and the cathode 820.
In such a case, if the distance L1 between the anode 810 and the cathode 820 is smaller than the distance L2 between the electrodes 810, 820 and metal (e.g., copper) as the workpiece 850, then an electric current flows between the electrodes 810 and 820 more than between the electrodes 810, 820 and the workpiece 850. Therefore, the distance L1 between the electrodes 810 and 820 should be set to be larger than the distance L2 between the electrodes 810, 820 and the workpiece 850.
However, the thicknesses of the ion exchangers 830, 840 prevent the distance L2 between the electrodes 810, 820 and the workpiece 850 from being sufficiently reduced. Accordingly, the anode 810 and the cathode 820 cannot be disposed as close to each other as would be preferred. As a result, the anode 810 and the cathode 820 have limitations in their shapes or the like.
Further, a conventional ion exchange fiber is problematic in that fibers may be removed from the ion exchanger during an electrolytic process so that the removed fibers cause variations of processing properties according to time elapsed. It has been feared that seams of the fibers may have an influence on the surface roughness of the workpiece. From this point of view, in order to flatten the entire surface of a workpiece, attempts have been made to wind a meshed ion exchange fiber around nonwoven fabric and attach it to a cylindrical electrode. However, when an ion exchanger has an uneven thickness, the flatness of the surface of the workpiece may be influenced by the uneven thickness of the ion exchanger.
SUMMARY OF THE INVENTIONThe present invention has been made in view of the above drawbacks. It is, therefore, a first object of the present invention to provide an electrode for electrolytic processing which can achieve stable processing performance and can flexibly cope with small electrodes and various shapes of electrodes.
A second object of the present invention is to provide an electrolytic processing apparatus and method using such an electrode.
A third object of the present invention is to provide a method of promoting to dissociate liquid into ions which can achieve stable processing performance.
In order to attain the first object, according to a first aspect of the present invention, there is provided an electrode for electrolytic processing. The electrode has a conductive material and an organic compound having an ion exchange group. The organic compound is chemically bonded to a surface of the conductive material.
According to the present invention, an ion exchange material having an ion exchange function can be bonded directly to a conductive material. Thus, the conductive material with the ion exchange material can be used as an electrode for electrolytic processing. With such an arrangement, it is possible to reduce the distance between an electrode and a workpiece and hence the distance between an electrode serving as an anode and an electrode serving as a cathode. Therefore, the electrode according to the present invention can flexibly cope with small electrodes and various shapes of electrodes. Furthermore, because ion exchange materials can be bonded separately to a conductive material serving as an anode and a conductive material serving as a cathode, a leakage current can be prevented from being produced between the anode and the cathode.
The organic compound may comprise thiol or disulfide. The ion exchange group may comprise at least one of a sulfo group, a carboxyl group, a quaternary ammonium group, and an amino group. The conductive material may include at least one of gold, silver, platinum, copper, gallium arsenide, cadmium sulfide, and indium oxide (III).
The conductive material should preferably have meshes because such meshes can allow water to pass therethrough to decompose water efficiently. When a workpiece is brought into contact with the electrode during an electrolytic process, scratches may be produced on a surface of the workpiece. From this point of view, it is desirable that a workpiece is not brought into contact with the electrode during an electrolytic process.
According to a second aspect of the present invention, there is provided an electrode for electrolytic processing. The electrode has a conductive carbon material and an ionic dissociation functional group. A surface of the conductive carbon material is chemically modified by the ionic dissociation functional group.
With such an electrode, the surface of the electrode has catalysis for decomposing water molecules into ions. Therefore, it is possible to reduce the distance between an electrode and a workpiece and hence the distance between an electrode serving as an anode and an electrode serving as a cathode. Therefore, the electrode according to the present invention can flexibly cope with small electrodes and various shapes of electrodes. Furthermore, because each of an electrode serving as an anode and an electrode serving as a cathode can have catalysis, a leakage current can be prevented from being produced between the anode and the cathode.
The ionic dissociation functional group may comprise a sulfo group or a carboxyl group. The ionic dissociation functional group may comprise at least one of a quaternary ammonium group, and a tertiary or lower amino group. The conductive carbon material may comprise glassy carbon, fullerene, or carbon nanotubes.
According to a third aspect of the present invention, there is provided an electrode for electrolytic processing. The electrode has a graphite intercalation compound containing alkali metal.
With such an electrode, water molecules are considered to be decomposed into ions by alkali metal intercalated between layers of the graphite. Therefore, it is possible to reduce the distance between an electrode and a workpiece and hence the distance between an electrode serving as an anode and an electrode serving as a cathode. Therefore, the electrode according to the present invention can flexibly cope with small electrodes and various shapes of electrodes. Furthermore, because each of an electrode serving as an anode and an electrode serving as a cathode can have catalysis, a leakage current can be prevented from being produced between the anode and the cathode.
In order to attain the second object of the present invention, according to a fourth aspect of the present invention, there is provided an electrolytic processing apparatus having a processing electrode and a feeding electrode to feed a workpiece. The electrolytic processing apparatus also has a workpiece holder for holding the workpiece and bringing the workpiece into contact with or close to the processing electrode. The electrolytic processing apparatus includes a power supply for applying a voltage between the processing electrode and the feeding electrode, and a fluid supply unit for supplying a fluid between the workpiece and the processing electrode. At least one of the processing electrode and the feeding electrode employs any one of the aforementioned electrodes.
According to a fifth aspect of the present invention, there is provided an electrolytic processing method. A workpiece is fed through a feeding electrode. A voltage is applied between the feeding electrode and a processing electrode. A fluid is supplied between the workpiece and the processing electrode. The workpiece is brought into contact with or close to the processing electrode. At least one of the processing electrode and the feeding electrode employs any one of the aforementioned electrodes.
In order to attain the third object of the present invention, according to a sixth aspect of the present invention, there is provided a method of promoting dissociation of liquid into ions by a conductive material to which an organic compound having an ion exchange group is chemically bonded.
The organic compound may comprise thiol or disulfide. The ion exchange group may comprise at least one of a sulfo group, a carboxyl group, a quaternary ammonium group, and an amino group. The conductive material may include at least one of gold, silver, platinum, copper, gallium arsenide, cadmium sulfide, and indium oxide (III).
The above and other objects, features, and advantages of the present invention will be apparent from the following description when taken in conjunction with the accompanying drawings which illustrate preferred embodiments of the present invention by way of example.
BRIEF DESCRIPTION OF THE DRAWINGS
An electrode and an electrolytic processing apparatus using an electrode according to embodiments of the present invention will be described below with reference to the accompanying drawings. In the following embodiments, a substrate is used as a workpiece and processed by an electrolytic processing apparatus. However, the present invention is applicable to any workpiece other than the substrate.
According to the present invention, an ion exchange material having an ion exchange function can be bonded directly to a conductive material as a base material. Thus, the conductive material with the ion exchange material can be used as an electrode for electrolytic processing, as shown in
As described above, each of the electrodes has the ion exchange material in which an organic compound having an ion exchange group is chemically bonded to the electrode. The term “bond” means that a material having an ion exchange group is bonded to a conductive material by chemical bond, not by an adhesive or the like. In a usual ion exchange resin, a material having an ion exchange group is “bonded” to an organic matter included in the resin.
It is desirable that the conductive material to which an organic compound is bonded has meshes, e.g., a lattice pattern or a form of a punching metal, because such meshes can allow water to pass therethrough to decompose water efficiently.
Such an electrode can be produced as follows. There will be described an example in which sodium 1-propanethiol-3-sulfonate (HSC3H6—SO3Na) was used as an organic compound having an ion exchange group and was bonded directly to a platinum (Pt) substrate to produce an electrode. A sodium salt of sulfo group is substituted at the 3-end of 1-propanethiol to form sodium 1-propanethiol-3-sulfonate (thiol).
First, a flat platinum substrate, for example, having a length of 34 mm, a width of 12.5 mm, and a thickness of 0.5 mm, was prepared. An organic matter on a surface of the platinum substrate was removed by a sulfuric acid and hydrogen peroxide aqueous solution. Then, the platinum substrate was immersed in an aqueous solution of sodium 1-propanethiol-3-sulfonate, which had a concentration of several milimoles/liter, for about 12 hours. Sodium 1-propanethiol-3-sulfonate has hydrophilicity under the influence of a sulfo group as a functional group. Therefore, while the surface of the platinum substrate was hydrophobic before the immersion, the surface of the platinum substrate became hydrophilic after the immersion so that thiol is bonded to the surface of the platinum substrate. Thus, a flat platinum electrode (Pt—SC3H6—SO3Na), which has a catalyst (an ion dissociation function), could be produced.
The catalysis in dissolution reactions of water molecules was measured on the platinum electrode modified by sodium 1-propanethiol-3-sulfonate, which is hereinafter referred to as a thiol platinum electrode. Specifically, a thiol platinum electrode produced as described above was installed into an experimental device having parallel plate electrodes, and electrolysis was performed with ultrapure water. The current-voltage properties were measured for the following cases. Further, the current-voltage properties were measured for a comparative experiment in which normal platinum electrodes were used as an anode and a cathode.
(1) A thiol platinum electrode was used as an anode, and a normal platinum electrode was used as a cathode.
(2) A normal platinum electrode was used as an anode, and a thiol platinum electrode was used as a cathode.
A fluororesin sheet was disposed between the electrodes. Areas of the electrodes facing each other were set to be about 0.4 cm2. The distance between the electrodes was adjusted by the thickness of the fluororesin sheet. Measurements were conducted under two conditions in which the distance between the electrodes was 50 μm and 12 μm.
It can be seen from
In the above example, platinum was used as the conductive material to which the organic compound was bonded. However, the conductive material is not limited to platinum. For example, metal such as gold, silver, or copper may be used as the conductive material. Alternatively, the conductive material may comprise a glass substrate having an Au film, or GaAs (gallium arsenide), CdS (cadmium sulfide), In2O3 (indium oxide (III)), carbon (graphite), or the like. According to another experiment, it has been confirmed that current-voltage properties similar to the above could be achieved in the case of using a glass substrate having an Au film. Further, an organic conductive material such as a polyaniline based material or carbon nanotubes may be used as the conductive material. Specifically, an organic compound having an ion exchange group may be bonded directly to an organic conductive material.
In the above example, thiol was used as the organic compound to be bonded to the conductive material. However, the organic compound is not limited to thiol. For example, disulfide or an organic conductive material such as a polyaniline based material or carbon nanotubes may be used as the organic compound. Further, the ion exchange group is not limited to a sulfo group as described above. For example, a carboxyl group, a quaternary ammonium group, or an amino group may be used as the ion exchange group. According to an experiment, it has been confirmed that effects similar to those described above could be achieved when a carboxyl group was used as an ion exchange group of thiol.
An electrode according to the present invention is applicable to an electrolytic processing apparatus as shown in
As shown in
As shown in
As shown in
The processing electrode 34 is coupled to a vertically movable rotating shaft 36 extending along the shaft center O-O. Thus, the processing electrode 34 can be rotated about the shaft center O-O in accordance with the rotation of the rotating shaft 36. The processing electrode 34 can be moved vertically so as to adjust the distance between the processing electrode 34 and the workpiece W held by the workpiece holder 30. As with the workpiece holder 30, the rotating shaft 36 is supported in the radial and thrust directions by a hydrostatic bearing (not shown) using ultrapure water. When an electrolytic process is performed, the processing electrode 34 is lowered so as to bring a lower end portion of the ion exchange material 34b into contact with or close to a surface of the workpiece held by the workpiece holder 30.
The electrolytic processing apparatus has the power supply 38 for applying a voltage between the processing electrode 34 and the workpiece W held by the workpiece holder 30. In this embodiment, for example, in order to perform an electrolytic process of copper as the workpiece, the processing electrode 34 is connected to a cathode of the power supply 38, and workpiece (copper) W is connected to an anode of the power supply 38. However, depending upon the types of workpieces, the processing electrode 34 may be connected to the anode of the power supply 38, and the workpiece W may be connected to the cathode of the power supply 38.
As described above, the workpiece holder 30 is rotatable about the vertical axis, and the processing electrode 34 is rotatable about the horizontal axis. The workpiece holder 30 and the processing electrode 34 are respectively rotated in directions such that the ultrapure water 10 is revolved. An ultrapure water supply nozzle 40 for supplying ultrapure water at a high pressure between the workpiece W held by the workpiece holder 30 and the processing electrode 34 is disposed at the upstream side of the directions of the rotation. While at least one of the processing electrode 34 and the workpiece W is being rotated, the ultrapure water 10 is supplied between the processing electrode 34 and the workpiece W from the upstream side of the directions of the rotation to effectively remove bubbles or machining products which would remain between the processing electrode 34 and the workpiece W.
As shown in
With the electrolytic processing apparatus thus constructed, the workpiece W is held by the workpiece holder 30, and the processing electrode 34 is lowered so as to bring the ion exchange material 34b of the processing electrode 34 into line contact with or close to a surface of the workpiece W. In this state, ultrapure water 10 within the machining chamber 12 is purified by the ultrapure water circulation/purification device 22 and circulated. The processing electrode 34 is connected to the cathode of the power supply 38, and the workpiece W is connected to the anode of the power supply 38, so that a voltage is applied between the processing electrode 34 and the workpiece W. At that time, the workpiece holder 30 and the processing electrode 34 are simultaneously rotated in directions such that the ultrapure water 10 is revolved. The ultrapure water is supplied between the processing electrode 34 and the workpiece W at a high pressure from the ultrapure water supply nozzle 40 disposed at the upstream side of the directions of the rotation. Hydrogen ions and hydroxide ions are produced by a chemical reaction occurring on a solid surface of the ion exchange material (catalyst) 34b to perform removal of the surface of the workpiece W. In this case, a flow of the ultrapure water 10 is formed in the machining chamber 12 and passed through the ion exchange material 34b to produce a large amount of hydrogen ions and hydroxide ions. Thus, a large amount of hydrogen ions or hydroxide ions are supplied onto the surface of the workpiece W to efficiently perform the electrolytic process.
As described above, the workpiece holder 30 and the processing electrode 34 are simultaneously rotated in directions such that the ultrapure water 10 is revolved. The ultrapure water is supplied between the processing electrode 34 and the workpiece W at a high pressure from the ultrapure water supply nozzle 40 disposed at the upstream side of the directions of the rotation. Accordingly, the ultrapure water 10 present between the workpiece W and the processing electrode 34 can effectively be replaced with new ultrapure water, so that gas and machining products produced upon the electrolytic process can efficiently be removed to realize a stable electrolytic process.
An electrode according to the present invention is also applicable to an electrolytic processing apparatus as shown in
With this electrolytic processing apparatus, since the area of the processing portion is reduced, the ultrapure water 10 can easily be supplied to a portion around the processing portion. Accordingly, the electrolytic process can be performed under stable conditions. Ultrapure water may not be necessarily ejected from the ultrapure water supply nozzle 40. For example, instead of ejecting ultrapure water, the electrolytic processing apparatus may employ a tank which holds ultrapure water therein and immerses an electrode and a workpiece in the ultrapure water.
Since any chemical material, including abrasive particles and dense chemical liquids, other than ultrapure water is not used in the electrolytic processing apparatus, the machining chamber 14 may be contaminated only by reaction products produced during electrochemical processing. Thus, it is possible to simplify or dispense with a cleaning process of a substrate after the electrolytic process. Circulation of the ultrapure water can reduce the amount of wastewater. Further, since it is not necessary to treat any chemical liquids, operating cost can remarkably be reduced.
In the above embodiments, an organic compound having an ion exchange group is chemically bonded to a surface of an electrode to form an ion exchanger on the surface of the electrode. Specifically, gold, silver, platinum, copper, indium oxide, or the like is used as an electrode material (conductive material), and thiol, disulfide, or the like is used as an organic compound having an ion exchange group. Such an organic compound is chemically bonded to the electrode material to introduce the ion exchange group into the electrode material. Instead of using such an electrode, a surface of a conductive carbon material may be chemically modified by an ionic dissociation functional group. Specifically, a conductive carbon material is used as an electrode material, and an ionic dissociation functional group is effectively introduced directly into a surface of the carbon of the conductive carbon material by inorganic reactions. In such a case, bondings having no carbon chains due to an organic compound can be produced between the electrode material and the ionic dissociation functional group (or an ion exchange group). Therefore, the thickness of the chemical modification layer can be reduced, and the durability (or the resistance to removal) and the conductivity of the ionic dissociation functional group can be improved.
Thus, it is possible to reduce the distance between the electrodes 201, 202 and the workpiece (substrate) 204 and hence the distance between the electrode 201 serving as an anode and the electrode 202 serving as a cathode. Therefore, the electrolytic processing apparatus can flexibly cope with small electrodes and various shapes of electrodes. Furthermore, because the conductive carbon material 201a serving as an anode and the conductive carbon material 202a serving as a cathode are separately bonded to (or chemically modified by) the ionic dissociation functional groups 201b, 202b, a leakage current can be prevented from being produced between the cathode and the anode, i.e., between the electrodes 201 and 202.
Such an electrode, which has a conductive carbon material and an ionic dissociation functional group chemically modifying a surface of the conductive carbon material, can be used in an electrolytic processing apparatus of the above embodiments shown in
The ionic dissociation functional group, which chemically modifies the surface of the conductive carbon material, comprises at least one kind of basic groups selected from a quaternary ammonium group and tertiary and lower amino groups, or an acidic group such as a sulfo group or a carboxyl group.
When the electrode is to be used to process a relatively large area of about 1 cm2 or more, the conductive carbon material should preferably comprise a carbon material that has a flat and smooth surface and can be processed in shape with high accuracy, such as glassy carbon. When the electrode is to be used to perform fine processing at a level of 1 μm or less than 1 μm, fullerene or nanomolecules such as carbon nanotubes should preferably be used as the conductive carbon material. It is desirable that the conductive carbon material has meshes because such meshes can allow water to pass therethrough to decompose water efficiently.
Methods of chemically modifying a conductive carbon material with an ionic dissociation functional group such as an ion exchange group include immersing a conductive carbon material in a chemical liquid, electrical discharge processing a conductive carbon material in a gaseous phase, anodizing a conductive carbon material in an electrolytic solution, and modifying a conductive carbon material by graft polymerization.
For example, as a method of immersing a conductive carbon material in a chemical liquid, a conductive carbon material is immersed in an oxidizing solution such as a nitric acid. With this method, a surface of the conductive carbon material can be readily chemically modified by an ionic dissociation functional group such as a carboxyl group. When a conductive carbon material is immersed in heated sulfuric acid, a surface of the conductive carbon material can be chemically modified by an ionic dissociation functional group such as a sulfo group. Further, a conductive carbon material may be immersed in a mixture of concentrated sulfuric acid and concentrated nitric acid to nitride the conductive carbon material, and then tin and the nitrided conductive carbon material may be immersed in, for example, hydrochloric acid. In this case, the conductive carbon material can be chemically modified by an ionic dissociation functional group such as an amino group.
For example, as a method of electrical discharge processing a conductive carbon material in a gaseous phase, plasma is formed in a gas containing oxygen by RF electrical discharge (13.25 MHz), and a conductive carbon material is exposed to the plasma. With this method, a surface of the conductive carbon material can be chemically modified by an ionic dissociation functional group such as a carboxyl group. Plasma may be formed in a nitrogen atmosphere by electrical discharge, and a conductive carbon material may be exposed to the plasma. In such a case, an ionic dissociation functional group having basicity can be introduced into the conductive carbon material. These methods can suitably be used to chemically modify a conductive carbon material by an ionic dissociation functional group. See S. S. Wong, A. T. Woolley, E. Joselevich, C. M. Leiber, Chem. Phys. Lett., 306 (1999) 219.
In a method of anodizing a conductive carbon material in an electrolytic solution, a conductive carbon material is usually used as an anode. Metal such as platinum (Pt), gold (Au), lead (Pb), and zinc (Zn), and any carbon material can be used as a cathode. See J. H. Wandass, J. A. Gardella, N. L. Weinberg, M. E. Bolster, L. Salvati, J. Electrochem. Soc., 134 (1987) 2734. The electrolytic solution may contain nitric acid, sulfuric acid, phosphoric acid, hydrochloric acid, hydrobromic acid, or salts having ions contained in these acids. Such salts include salts of alkali metal such as lithium, sodium, and potassium, salts of alkaline-earth metal such as magnesium, calcium, and barium, ammonium salt, sulfonium salt, phosphonium salt, and salts of Fe, Cu, and lanthanoide metal. Practically, a single electrolytic solution or a mixture of these kinds of electrolytic solutions is used. Although it is desirable that the electrolytic current density is in a range of from about 1 to about 100 mA/cm2, the method is not limited to these conditions. With this method, a surface of a carbon material is chemically modified by a carboxyl group.
In a method of modifying a conductive carbon material by graft polymerization, for example, graft chains are introduced into a conductive carbon material by a radiation-induced graft polymerization, which comprises a gamma irradiation and a graft polymerization. Then, the introduced graft chains are aminated to introduce a quaternary ammonium group. The capacity of an introduced ion exchange group is determined according to the amount of graft chains introduced. The graft polymerization may be conducted by the use of a monomer such as acrylic acid, styrene, glicidyl methacrylate, sodium styrenesulfonate, or chloromethylstyrene. The amount of the graft chains can be controlled by adjusting the monomer concentration, the reaction temperature, and the reaction time. Further, the introduced graft chains may be treated with heated sulfuric acid to introduce a sulfo group or treated with heated phosphoric acid to introduce a phosphate group. In the graft polymerization, a radioactive ray (γ-ray, electron beam, or ultraviolet ray) may be applied to a base material for pre-irradiation to generate a radical so that the radical reacts with a monomer. Alternatively, a base material may be impregnated with a monomer and irradiated with a radioactive ray (γ-ray, electron beam, or ultraviolet ray) for simultaneous irradiation to perform a radical polymerization.
According to the method of electrical discharge processing a conductive carbon material in a gaseous phase, an electrode in which a carboxyl group was introduced into a conductive carbon material was produced as follows. Two rod-like electrodes, which were moistened with water, were spaced at about 3 cm. An alternating voltage of 100 V was applied between the electrodes. A carbon rod (conductive carbon material), which was moistened with water, was inserted into between electrodes. Arc discharge was caused in an atmosphere to treat a surface of the carbon rod by the arc discharge so as to introduce a carboxyl group into the surface of the carbon rod (conductive carbon material). The carbon rod was made of graphite having a diameter of 6 mm. Each end of the carbon rod was rounded. The water used was ultrapure water, which had a resistivity of 18.2 MΩ·cm.
The current-voltage properties were measured in an experimental device in which the carbon rod thus treated was used as an anode, and a platinum plate was used as a cathode. The experimental device had an acrylic container holding ultrapure water therein, which has a resistivity of 18.2 MΩ·cm. The carbon rod and the platinum plate faced each other in the container. After the distance between the carbon rod and the platinum plate was adjusted by a micrometer, a voltage was applied between the carbon rod and the platinum plate while ultrapure water was supplied between the carbon rod and the platinum plate. At that time, a flowing current was measured. The distance between the carbon rod and the platinum plate was set to be 15 μm.
Further, the current-voltage properties were measured in a manner similar to the above for a comparative experiment in which a carbon rod before the surface treatment by the arc discharge was used as an anode, and a platinum plate was used as a cathode.
According to the method of anodizing a conductive carbon material in an electrolytic solution, an electrode in which a carboxyl group was introduced into a conductive carbon material was produced as follows. A carbon rod (conductive carbon material) was used as an anode and anodized in an H2SO4 solution of 20 weight % at a current density of 12.5 mA/cm2 for 30 minutes. A platinum plate (Pt) was used as a facing electrode. The carbon rod was made of graphite having a diameter of 6 mm. Each end of the carbon rod was rounded. The current-voltage properties of the anodized carbon rod were measured under conditions similar to the above example. The distance between the carbon rod and the platinum plate was set to be 15 μm.
Further, the current-voltage properties were measured in a manner similar to the above example for a comparative experiment in which a carbon rod before the surface treatment by anodization was used as an anode, and a platinum plate was used as a cathode.
The carbon rod into which a carboxyl group was introduced by anodization was used as a processing electrode to perform an electrolytic process of a copper film formed on a silicon substrate. The electrolytic process was conducted at a voltage of 60 V and a current of 1.07 mA for 10 seconds while the distance between electrodes was 25 μm. As a result of the electrolytic process, the maximum processed depth was 144 nm. At that time, the current efficiency was about 48%. The current efficiency refers to a ratio of the quantity of electricity used to process the copper film to the entire quantity of electricity passed. The current efficiency was calculated on the assumption that copper was eluted as bivalent ions or bivalent ionic compounds.
The carbon rod into which a carboxyl group was not introduced by anodization was used as a processing electrode to perform an electrolytic process of a copper film formed on a silicon substrate. The electrolytic process was conducted at a voltage of 60 V and a current of 0.043 mA for 60 seconds. As a result of the electrolytic process, the maximum processed depth was 12 nm. At that time, the current efficiency was about 3.3%.
Thus, it can be seen that the carbon rod into which a carboxyl group was introduced by anodization had increased current during the electrolytic process and increased current efficiency as compared to the carbon rod into which the carboxyl group was not introduced.
Instead of using an electrode in which a surface of a conductive carbon material is chemically modified by an ion dissociation functional group, a graphite intercalation compound containing alkali metal may be used as an electrode. It is generally desirable that high orientated pyrolytic graphite (HOPG) is used as graphite (carbon material) in the graphite intercalation compound. However, when sodium is intercalated as alkali metal between layers of the graphite, it is desirable that low orientated graphite is used as the graphite in the graphite intercalation compound. The graphite intercalation compound should preferably have meshes because such meshes can allow water to pass therethrough to decompose water efficiently.
According to the method of immersing a conductive carbon material in a chemical liquid, an electrode in which a sulfo group was introduced into a conductive carbon material was produced as follows. A carbon rod (conductive carbon material) was immersed in 97% sulfuric acid, which was heated to 210° C., for 3 hours. The carbon rod was made of graphite having a diameter of 6 mm. Each end of the carbon rod was rounded. When surface bondings (peaks of a 2p-orbital of a sulfur atom) of the carbon rod (conductive carbon material), which had been subjected to surface treatment, were analyzed by electron spectroscopy for chemical analysis (ESCA), there were observed a peak of 170.5 eV which represents a bonding of C—SO3—C or C—SO4—C and a peak of 171.2 eV which represents a bonding of C—SO3H. Accordingly, a sulfo group was considered to be introduced into a surface of the conductive carbon material. The current-voltage properties of the carbon rod that had been subjected to surface treatment of immersing the carbon rod in a chemical liquid were measured under conditions similar to the above example. The distance between the carbon rod and the platinum plate was set to be 15 μm.
Further, the current-voltage properties were measured in a manner similar to the above example for a comparative experiment in which a carbon rod before immersion in heated sulfuric acid to introduce a sulfo group was used as an anode, and a platinum plate was used as a cathode.
The carbon rod into which a sulfo group was introduced by immersion in sulfuric acid was used as a processing electrode to perform an electrolytic process of a copper film formed on a silicon substrate. The electrolytic process was conducted at a voltage of 40 V and a current of 0.087 mA for 30 seconds while the distance between electrodes was 25 μm. As a result of the electrolytic process, the maximum processed depth was 144 nm. At that time, the current efficiency was about 47%. The maximum processed depth and the current efficiency were obviously larger than those in the aforementioned comparative experiment.
Thus, it can be seen that when the carbon rod into which a sulfo group was introduced by immersion in sulfuric acid had increased current during the electrolytic process and increased current efficiency as compared to the carbon rod into which the sulfo group was not introduced.
Thus, it is possible to reduce the distance between the electrodes 301, 302 and the workpiece (substrate) 304 and hence the distance between the electrode 301 serving as an anode and the electrode 302 serving as a cathode. Therefore, the electrolytic processing apparatus can flexibly cope with small electrodes and various shapes of electrodes. Furthermore, because the electrode 301 serving as an anode and the electrode 302 serving as a cathode have catalysis, a leakage current can be prevented from being produced between the cathode and the anode, i.e., between the electrodes 301 and 302.
Such an electrode, which includes a graphite intercalation compound containing alkali metal, can be used in an electrolytic processing apparatus of the above embodiments shown in
Methods of synthesizing a graphite intercalation compound include a gaseous phase constant-pressure reaction method, a liquid phase contact reaction method, a solid phase pressurizing method, and a solvent method. The gaseous phase constant-pressure reaction method comprises disposing alkali metal and graphite at different positions in a glass tube, sealing the glass tube under a vacuum, and heating the graphite and the alkali metal while controlling the temperatures thereof The positions into which the alkali metal is intercalated and the amount of the alkali metal intercalated can be adjusted by controlling the temperatures of the alkali metal and the graphite. For example, when potassium is intercalated into HOPG, the temperatures are set at about 250° C. The liquid phase contact reaction method comprises directly contacting a compound containing alkali in a liquid phase with graphite to react with each other. The solid phase pressurizing method comprises contacting alkali metal with graphite, pressurizing the graphite to about 5 to about 20 atmospheres (about 0.5 to about 2 MPa), and heating the graphite to about 200° C. The solvent method comprises dissolving alkali metal in a solvent such as an ammonium solvent, and immersing graphite in the solvent.
According to the liquid phase contact reaction method, an electrode made of a graphite intercalation compound containing alkali metal was produced (synthesized) as follows. Sodium nitrate, which has a melting point of 308° C., was heated and melted in a crucible by a burner. A graphite plate, which had a length of 12.5 mm, a width of 34 mm, and a thickness of 0.5 mm, was immersed in the melted sodium nitrate and heated therein for 2 to 3 minutes. Then, the graphite plate was removed from the crucible and cooled in air. Thus, an electrode made of a graphite intercalation compound having sodium intercalated between layers of the graphite was produced. Then, the current-voltage properties were measured in an experimental device as shown in
Further, the current-voltage properties were measured in a manner similar to the above for a comparative experiment in which a graphite plate in which sodium was not intercalated between layers of the graphite was used as the electrode.
In the above example, graphite was immersed in a liquid in which sodium nitrate was heated and melted. However, the graphite may be immersed in any salts containing alkali metal, such as potassium nitrate.
A dilute chemical liquid may be added as an additive to pure water. For example, 2-propanol (IPA) may be added to pure water to adjust the polarity of the pure water.
Although certain preferred embodiments of the present invention have been shown and described in detail, it should be understood that various changes and modifications may be made therein without departing from the scope of the appended claims.
Claims
1. An electrode for electrolytic processing, said electrode comprising:
- a conductive material; and
- an organic compound having an ion exchange group, said organic compound being chemically bonded to a surface of said conductive material.
2. The electrode according to claim 1, wherein said organic compound comprises an organic compound selected from the group consisting of thiol and disulfide.
3. The electrode according to claim 1, wherein said ion exchange group comprises at least one of ion exchange groups selected from the group consisting of a sulfo group, a carboxyl group, a quaternary ammonium group, and an amino group.
4. The electrode according to claim 1, wherein said conductive material includes at least one of gold, silver, platinum, copper, gallium arsenide, cadmium sulfide, and indium oxide (III).
5. An electrode for electrolytic processing, said electrode comprising:
- a conductive carbon material; and
- an ionic dissociation functional group chemically modifying a surface of said conductive carbon material.
6. The electrode according to claim 5, wherein said ionic dissociation functional group comprises a sulfo group or a carboxyl group.
7. The electrode according to claim 5, wherein said ionic dissociation functional group comprises at least one of ion exchange groups selected from the group consisting of a quaternary ammonium group, and a tertiary or lower amino group.
8. The electrode according to claim 5, wherein said conductive carbon material comprises a conductive carbon material selected from the group consisting of glassy carbon, fullerene, and carbon nanotubes.
9. An electrode for electrolytic processing, said electrode comprising a graphite intercalation compound containing alkali metal.
10. An electrolytic processing apparatus comprising:
- a processing electrode;
- a feeding electrode to feed a workpiece;
- a workpiece holder for holding the workpiece and bringing the workpiece into contact with or close to said processing electrode;
- a power supply for applying a voltage between said processing electrode and said feeding electrode, and
- a fluid supply unit for supplying a fluid between the workpiece and said processing electrode,
- wherein at least one of said processing electrode and said feeding electrode comprises the electrode according to claim 1.
11. An electrolytic processing method, comprising:
- feeding a workpiece through a feeding electrode;
- applying a voltage between the feeding electrode and a processing electrode;
- supplying a fluid between the workpiece and the processing electrode; and
- bringing the workpiece into contact with or close to the processing electrode,
- wherein at least one of the processing electrode and the feeding electrode comprises the electrode according to claim 1.
12. A method of promoting dissociation of liquid into ions by a conductive material to which an organic compound having an ion exchange group is chemically bonded.
13. The method according to claim 12, wherein the organic compound comprises an organic compound selected from the group consisting of thiol and disulfide.
14. The method according to claim 12, wherein the ion exchange group comprises at least one of ion exchange groups selected from the group consisting of a sulfo group, a carboxyl group, a quaternary ammonium group, and an amino group.
15. The method according to claim 12, wherein the conductive material comprises a material including at least one of gold, silver, platinum, copper, gallium arsenide, cadmium sulfide, and indium oxide (III).
16. An electrolytic processing apparatus comprising:
- a processing electrode;
- a feeding electrode to feed a workpiece;
- a workpiece holder for holding the workpiece and bringing the workpiece into contact with or close to said processing electrode;
- a power supply for applying a voltage between said processing electrode and said feeding electrode, and
- a fluid supply unit for supplying a fluid between the workpiece and said processing electrode,
- wherein at least one of said processing electrode and said feeding electrode comprises the electrode according to claim 5.
17. An electrolytic processing apparatus comprising:
- a processing electrode;
- a feeding electrode to feed a workpiece;
- a workpiece holder for holding the workpiece and bringing the workpiece into contact with or close to said processing electrode;
- a power supply for applying a voltage between said processing electrode and said feeding electrode, and
- a fluid supply unit for supplying a fluid between the workpiece and said processing electrode,
- wherein at least one of said processing electrode and said feeding electrode comprises the electrode according to claim 9.
18. An electrolytic processing method, comprising:
- feeding a workpiece through a feeding electrode;
- applying a voltage between the feeding electrode and a processing electrode;
- supplying a fluid between the workpiece and the processing electrode; and
- bringing the workpiece into contact with or close to the processing electrode,
- wherein at least one of the processing electrode and the feeding electrode comprises the electrode according to claim 5.
19. An electrolytic processing method, comprising:
- feeding a workpiece through a feeding electrode;
- applying a voltage between the feeding electrode and a processing electrode;
- supplying a fluid between the workpiece and the processing electrode; and
- bringing the workpiece into contact with or close to the processing electrode,
- wherein at least one of the processing electrode and the feeding electrode comprises the electrode according to claim 9.
Type: Application
Filed: Mar 10, 2005
Publication Date: Aug 25, 2005
Inventors: Yuzo Mori (Katano-shi), Hidekazu Goto (Kyoto-shi), Yasushi Toma (Fujisawa-shi)
Application Number: 11/076,067