Patent Application
20060091005
The present invention relates to an electrolytic processing apparatus, and more particularly to an electrolytic processing apparatus useful for processing a conductive material formed on a surface of a substrate such as a semiconductor wafer or for removing impurities attached to a surface of a substrate. The present invention also relates to a substrate processing apparatus having such an electrolytic processing apparatus.
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 sulfonic acid 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.
The present invention has been made in view of the above drawbacks. It is, therefore, a first object of the present invention to provide an electrolytic processing apparatus 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 a substrate processing apparatus having such an electrolytic processing apparatus.
In order to attain the first object, according to a first aspect of the present invention, there is provided an electrolytic processing apparatus having at least one processing electrode and at least one feeding electrode disposed on the same side as the processing electrode with respect to a workpiece. An organic compound having an ion exchange group is chemically bonded to at least one of a surface of the processing electrode and a surface of the feeding electrode to form an ion exchange material. 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. The term “on the same side as the processing electrode with respect to the workpiece” means that when a conductive film is formed on a surface of the substrate, the conductive film is to be fed (or supplied with electric power) by the feeding electrode and to be brought into contact with or close to the processing electrode. The present invention covers cases where the conductive film is fed through a bevel portion of the workpiece. Thus, the present invention is applicable to electrolytic processing of device wafers having semiconductor devices, circuits, or conductive films formed on a surface thereof.
In the case where liquid such as ultrapure water, which has a large resistivity, is used, it is desirable that the workpiece 10 is brought into contact with or close to the ion exchange material 12a, because it is possible to reduce the electric resistance, the requisite voltage, and hence the power consumption.
Water molecules 20 in the fluid 18, such as ultrapure water, are dissociated efficiently into hydroxide ions 22 and hydrogen ions 24 by the ion exchange materials 12a and 12b. The hydroxide ions 22 thus produced, for example, are supplied to the surface of the workpiece 10 facing the processing electrode 14 by the electric field between the workpiece 10 and the processing electrode 14 and by the flow of the fluid 18. The concentration of the hydroxide ions is thus increased near the workpiece 10 to react the hydroxide ions 22 with atoms 10a in the workpiece 10. Reaction products 26 produced by this reaction are dissolved in the fluid 18 and removed from the workpiece 10 by the flow of the fluid 18 along the surface of the workpiece 10. In this manner, a removal process is performed on the surface of the workpiece 10.
Thus, the removal process according to the present invention employs a purely electrochemical interaction between the reactant ions and the workpiece and clearly differs in the processing principle from CMP, which employs a combination of a physical interaction between a polishing tool and a workpiece and a chemical interaction between a chemical species in a polishing liquid and the workpiece. According to the removal process according to the present invention, the workpiece 10 is processed at a portion facing the processing electrode 14. Therefore, the workpiece 10 can be processed into a desired surface configuration by moving the processing electrode 14.
As described above, the electrolytic processing apparatus according to the present invention employs only a dissolution reaction due to an electrochemical interaction and clearly differs in the processing principle from a CMP apparatus, which employs a combination of a physical interaction between a polishing tool and a workpiece and a chemical interaction between a chemical species in a polishing liquid and the workpiece. Therefore, the removal process can be performed without deteriorating the properties of materials. Even if the workpiece is formed by a material having a low mechanical strength, such as the aforementioned low-k material, the removal process can be performed without any physical damage to the workpiece. Further, when a fluid having an electric conductivity of 500 μS/cm or less, preferably pure water, more preferably ultrapure water, is used as a processing liquid instead of an electrolytic solution used in a conventional electrolytic process, it is possible to remarkably reduce contamination of a surface of the workpiece and to easily treat waste liquid after the electrolytic process.
According to present invention, the ion exchange material having an ion exchange function can be formed directly on the electrode. Therefore, it is possible to reduce the distance between the electrode and the workpiece. Accordingly, it is possible to reduce the distance between the anode and the cathode. Thus, the electrolytic processing apparatus according to the present invention can flexibly cope with small electrodes and various shapes of electrodes. Further, because ion exchange materials can be formed separately on the cathode and the anode, a leakage current can be prevented from being produced between the cathode and the anode.
The organic compound may comprise thiol or disulfide. The ion exchange group may comprise at least one of a sulfonic acid 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).
According to a second aspect of the present invention, there is provided an electrolytic processing apparatus having at least one processing electrode and at least one feeding electrode disposed on the same side as the processing electrode with respect to a workpiece. At least one of the processing electrode and the feeding electrode comprises a conductive carbon material and an ionic dissociation functional group chemically modifying a surface of the conductive carbon material. 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.
The ionic dissociation functional group may comprise 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 electrolytic processing apparatus having at least one processing electrode and at least one feeding electrode disposed on the same side as the processing electrode with respect to a workpiece. At least one of the processing electrode and the feeding electrode comprises a graphite intercalation compound containing alkali metal. 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.
The fluid may comprise pure water, ultrapure water, a liquid having an electric conductivity of 500 μS/cm or less, or an electrolytic solution having an electric conductivity of 500 μS/cm or less.
The electrolytic processing apparatus may have a driving mechanism operable to move the workpiece and at least one of the processing electrode and the feeding electrode relative to each other to provide a relative movement between the workpiece and at least one of the processing electrode and the feeding electrode. The relative movement may comprise a rotational movement, a reciprocating movement, an eccentric rotational movement, a scroll movement, or a combination of these movements. The relative movement may comprise a movement along a surface of the workpiece.
The processing electrode and the feeding electrode may be disposed in a spaced relationship. The organic compound having the ion exchange group may be bonded separately to the processing electrode and the feeding electrode.
The electrolytic processing apparatus may have an electrode unit having the processing electrode, the feeding electrode, and the fluid supply unit.
The processing electrode may comprise a plurality of processing electrodes, and the feeding electrode may comprise a plurality of feeding electrodes. In this case, the plurality of processing electrodes and the plurality of feeding electrodes may alternately be disposed on the same side of the workpiece.
One of the processing electrode and the feeding electrode may be disposed so as to surround the other of the processing electrode and the feeding electrode.
The feeding electrode may comprise a plurality of feeding electrodes provided at a peripheral portion of the processing electrode.
The processing electrode may comprise a plurality of processing electrodes disposed in parallel with each other at equal intervals.
In order to attain the second object, according to a fourth aspect of the present invention, there is provided a substrate processing apparatus having a loading and unloading section for loading and unloading a substrate, the above electrolytic processing apparatus, and a cleaning device for cleaning the substrate. The substrate processing apparatus also has a transfer device for transferring the substrate between the loading and unloading section, the electrolytic processing apparatus, and the cleaning device. The substrate processing apparatus may have a CMP apparatus for chemical mechanical polishing a surface of the substrate.
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.
An electrolytic processing apparatus and a substrate processing apparatus having the electrolytic processing apparatus 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.
As shown in
The substrate holder 42 is coupled to a rotation motor 58 provided on an upper surface of the free end of the arm 40. The rotation motor 58 serves as a first driving mechanism to move the substrate held by the substrate holder 42 and the electrode unit 46 relative to each other. When the rotation motor 58 is actuated, the substrate holder 42 is rotated. The substrate holder 42 may not be rotated continuously and may be rotated intermittently by the rotation motor 58 so as to change the angular direction of the substrate holder 42. Since the arm 40 is vertically and horizontally movable as described above, the substrate holder 42 can be vertically and horizontally moved together with the arm 40.
As shown in
Next, the electrode unit 46 in the present embodiment will be described below. As shown in
As shown in
In the present embodiment, the electrodes 86 of adjacent electrode members 82 are connected alternately to a cathode and an anode of the power supply 48 (see
Depending upon a material to be processed, the electrode connected to the cathode of the power supply 48 may form a feeding electrode, and the electrode connected to the anode of the power supply 48 may form a processing electrode. Specifically, when a material to be processed is copper, molybdenum, iron, or the like, an electrolytic effect is developed on the cathode. Accordingly, the electrode 86a connected to the cathode forms a processing electrode, and the electrode 86b connected to the anode forms a feeding electrode. When a material to be processed is aluminum, silicon, or the like, an electrolytic effect is developed on the anode. Accordingly, the electrode 86b connected to the anode forms a processing electrode, and the electrode 86a connected to the cathode forms a feeding electrode.
As described above, the processing electrodes and the feeding electrodes are arranged alternately in a Y direction of the electrode unit 46, which is perpendicular to a longitudinal direction of the electrode members 82. Accordingly, it is not necessary to provide a feeding portion to feed electric power to a conductive film (a material to be processed) on the substrate W. Therefore, the substrate W can be processed over the entire surface thereof without any unprocessed portions caused by a feeding portion. Further, when a voltage applied between the electrodes 86 is varied between a positive value and a negative value in a pulsed manner, it is possible to dissolve products due to the electrolytic process to improve the flatness of the substrate W through multiple repeated processes. Alternatively, the voltage applied between the electrodes 86 may be varied between a positive value and zero in a pulsed manner or varied between a negative value and zero in a pulsed manner.
As shown in
As shown in
Each of the electrodes 86 in the electrode members 82 has through-holes 100 extending through the electrode 86 from the passage 92 to the ion exchange material 90. Thus, pure water or ultrapure water in the passage 92 is supplied through the through-holes 100 to the ion exchange materials 90. Pure water refers to water having an electric conductivity of 10 μS/cm or less, and ultrapure water refers to water having an electric conductivity of 0.1 μS/cm or less. The use of pure water or ultrapure water, which contains substantially no electrolyte, can prevent undesired impurities such as an electrolyte from adhering to and remaining on the surface of the substrate W when the electrolytic process is performed. Further, copper ions or the like dissolved by the electrolytic process are immediately captured by the ion exchange materials 90 through an ion exchange reaction. Therefore, the dissolved copper ions or the like can be prevented from re-precipitating on other portions of the substrate W or from being oxidized to become fine particles which contaminate the surface of the substrate W.
Instead of pure water or ultrapure water, it is possible to use a liquid having an electric conductivity of 500 μS/cm or less, or any electrolytic solution. For example, an electrolytic solution prepared by adding an electrolyte to pure water or ultrapure water may be used instead of pure water or ultrapure water. The use of such an electrolytic solution can lower an electric resistance and reduce power consumption. A solution of a neutral salt such as NaCl or Na2SO4, a solution of an acid such as HCl or H2SO4, or a solution of an alkali such as ammonia, may be used as the electrolytic solution. These solutions may selectively be used according to the properties of the workpiece.
Further, instead of pure water or ultrapure water, it is also possible to use a liquid prepared by adding a surfactant or the like to pure water or ultrapure water so as to have an electric conductivity of 500 μS/cm or less, preferably 50 μS/cm or less, more preferably 0.1 μS/cm or less (resistivity of 10 MΩ·cm or more). Due to the presence of a surfactant in pure water or ultrapure water, the liquid can form a layer, which functions to evenly inhibit ion migration, at interfaces between the substrate W and the ion exchange materials 90. Therefore, locally concentrated ion exchange (metal dissolution) can be moderated to enhance the flatness of the processed surface. The surfactant should preferably have a concentration of 100 ppm or less. When the electric conductivity is too high, the current efficiency is lowered and the processing rate is lowered. The use of the liquid having an electric conductivity of 500 μS/cm or less, preferably 50 μS/cm or less, more preferably 0.1 μS/cm or less, can attain a desired processing rate.
Next, operation (electrolytic processing) with the substrate processing apparatus in the present embodiment will be described below. First, a cassette accommodating substrates W is placed on one of the loading/unloading units 30. For example, as shown in
The transfer robot 36 receives the reversed substrate W and transfers it to the electrolytic processing apparatus 34. The substrate W is then attracted and held by the substrate holder 42 of the electrolytic processing apparatus 34. The substrate holder 42 holding the substrate W is moved to a processing position, which is located right above the electrode unit 46, by moving the arm 40. The substrate holder 42 is then lowered by the actuation of the vertical movement motor 50 so that the substrate W held by the substrate holder 42 is brought into contact with or close to the surfaces of the ion exchange materials 90 in the electrode unit 46. Then, the rotational motor 58 is actuated to rotate the substrate holder 42 and the substrate W, and the hollow motor 60 is actuated so that the electrode unit 46 makes a scroll movement. Thus, the substrate W and the electrode unit 46 are moved relative to each other. The substrate holder 42 may not be rotated continuously and may be rotated intermittently by the rotation motor 58 so as to change the angular direction of the substrate holder 42. At that time, pure water or ultrapure water is ejected between the substrate W and the electrode members 82 from the ejection slots 98 of the pure water ejection nozzles 96. Further, pure water or ultrapure water is impregnated into the ion exchange materials 90 through the through-holes 100 of the electrodes 86. In the present embodiment, pure water or ultrapure water supplied to the ion exchange materials 90 is discharged from longitudinal ends of the respective electrode members 82.
Then, a predetermined voltage is applied between the processing electrodes and the feeding electrodes by the power supply 48 to produce hydrogen ions and hydroxide ions by the ion exchange materials 90. Thus, the conductive film (copper film 6), which is formed on the surface of the substrate W, is subjected to an electrolytic process through the action of the hydrogen ions or the hydroxide ions on the processing electrodes (e.g., cathodes).
After completion of the electrolytic process, the power supply 48 is disconnected, and the rotation of the substrate holder 42 and the scroll movement of the electrode unit 46 are stopped. Thereafter, the substrate holder 42 is lifted and moved by the arm 40 to deliver the substrate W to the transfer robot 36. The transfer robot 36 receives the substrate W from the substrate holder 42 and transfers it to the reversing machine 32, as needed. By the reversing machine 32, the substrate W is turned upside down. Then, the transfer robot 36 returns the substrate W to the cassette on the loading/unloading unit 30.
In the case where liquid such as ultrapure water, which has a large resistivity, is used, it is possible to reduce the electric resistance by bringing the substrate W into contact with or close to the ion exchange materials 90. Therefore, the requisite voltage can be lowered, and hence the power consumption can be reduced. When the substrate W is brought into contact with the ion exchange materials 90, such contact intends that the electrodes approach the substrate W as close as possible, but not that the electrodes press on the substrate W to provide a physical energy or stress to the workpiece, as in CMP. Accordingly, the electrolytic processing apparatus 34 in the present embodiment employs the vertical movement motor 50 to bring the substrate W into contact with or close to the electrode unit 46, and does not have a pressing mechanism such as usually employed in a CMP apparatus that positively presses a substrate against a polishing tool. Specifically, a CMP apparatus generally presses a substrate against a polishing surface under a pressure of about 20-50 kPa, whereas the electrolytic processing apparatus 34 in the present embodiment can bring the substrate W into contact with the ion exchange materials 90 under a pressure of 20 kPa or less. Even under a pressure 10 kPa or less, a sufficient removal effect can be achieved by the electrolytic processing apparatus 34.
As described above, in the present embodiment, each of the electrode members 82 has the ion exchange material 90 in which an organic compound having an ion exchange group is chemically bonded to the electrode 86 (conductive material). 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 sulfonic acid 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 sulfonic acid 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.
Oxidation or elution caused by electrolytic reactions may be problematic in the electrodes 86 of the electrode members 82. Therefore, it is desirable to use carbon, a noble metal which is relatively inert, conductive oxide, or conductive ceramics as a material for the electrode 86 rather than the metal and metallic compounds that are widely used for electrodes. An electrode using noble metal may be produced as follows. For example, titanium is used as a base material for an electrode, and platinum or iridium is attached to a surface of the base material by plating or coating. Then, the material is sintered at a high temperature for stabilization and maintenance of the strength. Ceramics products are generally obtained by heat treatment of an inorganic material. Various materials, such as oxides, carbides, and nitrides of nonmetal and metal, have been employed as a material for ceramics to produce ceramics products having various properties. Such ceramics products include conductive ceramics.
If an electrode is oxidized, then the electric resistance of the electrode is increased, so that a voltage to be applied should be increased. However, when a surface of an electrode is protected by a material that is unlikely to be oxidized, such as platinum, or a conductive oxide such as iridium oxide, it is possible to prevent the conductivity of the electrode from being lowered due to oxidization of the material of the electrode.
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 sulfonic acid 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.
When the ion exchange material described above is employed in the electrode members 82, the electrode members 82 do not cause problems such that fibers are removed from the ion exchanger during the electrolytic process. Therefore, it is possible to achieve stable processing performance. With an electrolytic processing apparatus according to the present invention, an ion exchange material having an ion exchange function can be bonded directly to an electrode. Therefore, it is possible to reduce the distance between the electrode and the workpiece and hence the distance between the anode and the cathode. Thus, the electrolytic processing apparatus 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 cathode and an anode, a leakage current can be prevented from being produced between the cathode and the anode.
As shown in
The arm 140 is connected to an upper end of a pivot shaft 152, which is coupled to a pivotal movement motor 150. When the pivotal movement motor 150 is actuated, the arm 140 is horizontally pivoted about the pivot shaft 152. The pivot shaft 152 is connected to a vertically extending ball screw 154, which is coupled to a vertical movement motor 156. When the vertical movement motor 156 is actuated, the pivot shaft 152 is vertically moved via the ball screw 154 together with the arm 140.
The substrate holder 42 is coupled to a rotation motor 58 provided on an upper surface of the free end of the arm 140. The rotation motor 58 serves as a first driving mechanism to move the substrate W held by the substrate holder 42 and the electrode unit 146 relative to each other. When the rotation motor 58 is actuated, the substrate holder 42 is rotated. Since the arm 140 is vertically movable and horizontally swingable as described above, the substrate holder 42 can be vertically moved and horizontally pivoted together with the arm 140.
As shown in
In the present embodiment, the feeding electrode 170 is connected to an anode of the power supply 48 via a slip ring 178 (see
As shown in
As with the first embodiment, instead of pure water or ultrapure water, it is possible to use a liquid having an electric conductivity of 500 μS/cm or less, or any electrolytic solution. For example, an electrolytic solution prepared by adding an electrolyte to pure water or ultrapure water may be used instead of pure water or ultrapure water. Further, instead of pure water or ultrapure water, it is also possible to use a liquid prepared by adding a surfactant or the like to pure water or ultrapure water so as to have an electric conductivity of 500 μS/cm or less, preferably 50 μS/cm or less, more preferably 0.1 μS/cm or less (resistivity of 10 MΩ·cm or more).
Next, operation (electrolytic processing) with the substrate processing apparatus in the present embodiment will be described with reference to
The substrate W on the pusher 182 is then attracted and held by the substrate holder 42 of the electrolytic processing apparatus 134. The substrate holder 42 holding the substrate W is moved to a processing position, which is located right above the electrode unit 146, by pivoting the arm 140. The substrate holder 42 is then lowered by the actuation of the vertical movement motor 156 so that the substrate W held by the substrate holder 42 is brought into contact with or close to the surfaces of the ion exchange materials 176 in the electrode unit 146. Then, the rotational motor 58 is actuated to rotate the substrate holder 42 and the substrate W, and the hollow motor 160 is actuated to rotate the electrode unit 146. Thus, the substrate W and the electrode unit 146 are moved relative to each other, i.e., make eccentric rotational movements. At that time, pure water or ultrapure water is ejected between the substrate W and the electrode unit 146 from the ejection slots of the pure water ejection nozzle 180. Then, a predetermined voltage is applied between the processing electrodes 172 and the feeding electrode 170 by the power supply 48 to produce hydrogen ions and hydroxide ions by the ion exchange materials 176. Thus, the conductive film (copper film 6), which is formed on the surface of the substrate W, is subjected to electrolytic processing through the action of the hydrogen ions or the hydroxide ions on the processing electrodes (e.g., cathodes).
When a large number of electrodes are provided as in the present embodiment, even if the electrodes have the same shape, there may be a slight difference in contact area, in height between the respective electrodes, or in thickness between ion exchangers mounted on the respective electrodes. Further, the ion exchangers may be mounted unevenly on the respective electrodes. Accordingly, the processing amount per unit time differs in practice between the respective electrodes. In the present embodiment, when the electrode unit 146 and the substrate W are moved relative to each other during the electrolytic process, a plurality of processing electrodes 172, which have different processing rates per unit time, pass the same point on the surface of the substrate W. Specifically, the processing electrodes 172 and the substrate W are moved relative to each other so that the largest possible number of processing electrodes 172, which have different processing rates per unit time, can pass the same point on the surface of the substrate W. Therefore, even if the processing rate varies between the respective processing electrodes 172, the variation of processing rates can be averaged to equalize the processing rate over the entire surface of the substrate W to within a level of nanometers per minute.
After completion of the electrolytic process, the power supply 48 is disconnected, and the rotations of the electrode unit 146 and the substrate holder 42 are stopped. Thereafter, the substrate holder 42 is lifted and moved by the arm 40 to deliver the substrate W to the transfer robot 36. The transfer robot 36 receives the substrate W from the substrate holder 42 and transfers it to the reversing machine 32, as needed. By the reversing machine 32, the substrate W is turned upside down. Then, the transfer robot 36 returns the substrate W to the cassette on the loading/unloading unit 30.
In the present embodiment, both of the electrode unit 146 and the substrate W are rotated to make eccentric rotational movements. However, any relative movement may be employed between the processing electrodes and a workpiece as long as it allows a plurality of processing electrodes to pass the same point on a surface of the workpiece. Such a relative movement includes a rotational movement, a reciprocating movement, an eccentric rotational movement, and a scroll movement, and any combination of these movements. The relative movement may be a movement along the surface of the substrate W.
The processing electrodes and the feeding electrode in the present embodiment may be replaced with each other. Specifically, the electrode unit may have a circular processing electrode and a number of feeding electrodes arranged over substantially the entire surface of the processing electrode. In this case, the electrolytic processing apparatus employs a single processing electrode. Even though a single processing electrode is used, a processing amount per unit time may vary at some points on the processing electrode. However, with the above arrangement, when the electrode unit and the substrate W are moved relative to each other during the electrolytic process, a plurality of points on the processing electrode, which have different processing rates per unit time, pass the same point on the surface of the substrate W. Specifically, the processing electrode and the substrate W are moved relative to each other so that the largest possible number of points on the processing electrode, which have different processing rates per unit time, can pass the same point on the surface of the substrate W. Therefore, even if the processing rate varies between the respective points on the processing electrode, the variation of processing rates can be averaged to equalize the processing rate over the entire surface of the substrate W to within a level of nanometers per minute.
As shown in
The arm 140 is connected to an upper end of a pivot shaft 152, which is coupled to a pivotal movement motor 150. When the pivotal movement motor 150 is actuated, the arm 140 is horizontally pivoted about the pivot shaft 152. The pivot shaft 152 is connected to a vertically extending ball screw 154, which is coupled to a vertical movement motor 156. When the vertical movement motor 156 is actuated, the pivot shaft 152 is vertically moved via the ball screw 154 together with the arm 140.
The substrate holder 42 is coupled to a rotation motor 58 provided on an upper surface of the free end of the arm 140. The rotation motor 58 serves as a first driving mechanism to move the substrate W held by the substrate holder 42 and the electrode unit 246 relative to each other. When the rotation motor 58 is actuated, the substrate holder 42 is rotated. Since the arm 140 is vertically movable and horizontally swingable as described above, the substrate holder 42 can be vertically moved and horizontally pivoted together with the arm 140.
As shown in
In the present embodiment, it is difficult to supply pure water or ultrapure water to the upper surface of the electrode unit 246 from above the electrode unit 246 during the electrolytic process due to the size relationship between the electrode unit 246 and the substrate holder 42. Accordingly, as shown in
In the present embodiment, the processing electrode 272 is connected to a cathode of the power supply 48, and the feeding electrodes 270 are connected to an anode of the power supply 48. Depending upon a material to be processed, the feeding electrodes 270 may be connected to the cathode, and the processing electrode 272 may be connected to the anode. For example, when a material to be processed is copper, molybdenum, iron, or the like, an electrolytic effect is developed on the cathode. Accordingly, an electrode connected to the cathode forms a processing electrode, and an electrode connected to the anode forms a feeding electrode. For example, when a material to be processed is aluminum, silicon, or the like, an electrolytic effect is developed on the anode. Accordingly, an electrode connected to the anode forms a processing electrode, and an electrode connected to the cathode forms a feeding electrode.
During the electrolytic process, the rotation motor 58 is actuated to rotate the substrate W, and the hollow motor 60 is actuated so that the electrode unit 246 makes a scroll movement about a scrolling center “O” (see
Since the substrate W cannot be processed within the range of the feeding electrodes 270, the processing rate at peripheral portions of the electrode unit 246, in which the feeding electrodes 270 are disposed, is lower than that in other areas. Therefore, an area (region) occupied by the feeding electrodes 270 should preferably be smaller in order to reduce the influence from the feeding electrodes 270 on the processing rate. From this viewpoint, in the present embodiment, the feeding electrodes 270 having a small area are disposed at a plurality of peripheral portions of the processing electrode 272, and at least one of the feeding electrodes 270 is brought into contact with or close to the substrate W during the relative movement. Accordingly, it is possible to reduce an area that is not being processed, as compared to a case where a ring-shaped feeding electrode is disposed at a peripheral portion of the processing electrode 272. Thus, a peripheral portion of the substrate W is prevented from remaining unprocessed.
Next, operation (electrolytic processing) with the substrate processing apparatus in the present embodiment will be described with reference to
The transfer robot 36 receives the reversed substrate W, and transfers it to the electrolytic processing apparatus 234. The substrate W is then attracted and held by the substrate holder 42 of the electrolytic processing apparatus 234. The substrate holder 42 holding the substrate W is moved to a processing position, which is located right above the electrode unit 246, by pivoting the arm 140. The substrate holder 42 is then lowered by the actuation of the vertical movement motor 156 so that the substrate W held by the substrate holder 42 is brought into contact with or close to the surfaces of the ion exchange materials 270a and 272a in the electrode unit 246. Then, the rotational motor 58 is actuated to rotate the substrate holder 42 and the substrate W, and the hollow motor 60 is actuated so that the electrode unit 246 makes a scroll movement about the scrolling center “O”. Thus, the substrate W and the electrode unit 246 are moved relative to each other. At that time, pure water or ultrapure water is ejected between the substrate W and the ion exchange materials 270a, 272a from the fluid supply holes 276 in the processing electrode 272.
Then, a predetermined voltage is applied between the processing electrode 272 and the feeding electrodes 270 by the power supply 48 to produce hydrogen ions and hydroxide ions by the ion exchange materials 270a, 272a. Thus, the conductive film (copper film 6), which is formed on the surface of the substrate W, is subjected to electrolytic processing through the action of the hydrogen ions or the hydroxide ions on the processing electrodes (e.g., cathodes).
At that time, the substrate W is processed at a portion facing the processing electrode 272. Since the substrate W and the processing electrode 272 are moved relative to each other during the electrolytic process as described above, the entire surface of the substrate W can be processed. The diameter of the processing electrode 272 is larger than that of the substrate W, and the center of movement of the processing electrode 272 is continuously located within the inner range of the substrate W. As a result, the frequency that the processing electrode 272 is positioned at any given point on the substrate W can become as uniform as possible over the surface of the substrate W. With this arrangement, it is possible to minimize the size of the electrode unit 246, and hence the whole apparatus can be made considerably compact and lightweight.
After completion of the electrolytic process, the power supply 48 is disconnected, and the rotation of the substrate holder 42 and the scroll movement of the electrode unit 246 are stopped. Thereafter, the substrate holder 42 is lifted and moved by the arm 140 to deliver the substrate W to the transfer robot 36. The transfer robot 36 receives the substrate W from the substrate holder 42 and transfers it to the reversing machine 32, as needed. By the reversing machine 32, the substrate W is turned upside down. Then, the transfer robot 36 returns the substrate W to the cassette on the loading/unloading unit 30.
In the above embodiment, the processing electrode 272 in the electrode unit 246 is formed as a single member. However, the electrode unit 246 may have other types of processing electrodes. For example, as shown in
As described above, with the electrode unit 246 as shown in
In the above embodiment, the electrode unit 246 makes a scroll movement, and the substrate W is rotated. However, any relative movement between the electrode unit 246 and the substrate W can be employed as long as it can move the processing electrode 272 and the substrate W relative to each other. For example, both of the electrode unit 246 and the substrate W may be rotated. In this case, the center of rotation corresponds to the center of movement of the processing electrode.
In the above embodiments, the substrate W is attracted and held in a state in which the substrate W faces downward (face-down). However, the substrate W may be held in a state in which the substrate W faces upward (face-up).
The substrate processing apparatus has a temporary placement stage 638 disposed between the primary cleaning devices 634 and the secondary cleaning devices 636, a first transfer robot 640, a second transfer robot 642, and a monitoring unit 644 disposed adjacent to the loading/unloading units 30. The temporary placement stage 638 has a function of reversing a substrate. The first transfer robot 640 is surrounded by the loading/unloading units 630, the primary cleaning devices 634, and the temporary placement stage 638 and serves as a transfer device for receiving and delivering a substrate W between the loading/unloading units 630, the primary cleaning devices 634, and the temporary placement stage 638. The second transfer robot 642 is surrounded by the temporary placement stage 638, the secondary cleaning devices 636, the pusher 182, and the pusher 632a and serves as a transfer device for receiving and delivering a substrate W between the temporary placement stage 638, the secondary cleaning devices 636, the pusher 182, and the pusher 632a. The monitoring unit 644 monitors a voltage applied between the processing electrode and the feeding electrode or a current flowing therebetween when the electrolytic processing apparatus 134 performs an electrolytic process.
When the substrate W is continuously polished with such a polishing apparatus, a polishing capability of the polishing surface of the polishing pad 650 is lowered. In order to recover the polishing capability of the polishing surface, a dresser 658 is provided in a CMP apparatus 632. The polishing pad 650 is dressed by the dresser 658 at the time, for example, of replacement of a substrate W. Specifically, while a dressing element attached to a lower surface of the dresser 658 is pressed against the polishing pad 650 on the polishing table 652, the polishing table 652 and the dresser 658 are independently rotated to remove polishing particles and polishing wastes attached to the polishing surface and to flatten and dress the entire polishing surface. Thus, the polishing surface is regenerated by the dresser 658.
A cassette accommodating substrates W is placed on one of the loading/unloading units 630. One of the substrates W is picked up from the cassette by the first transfer robot 640. The first transfer robot 640 transfers the substrate W to the temporary placement stage 638, where the substrate W is turned upside down as needed. The second transfer robot 642 receives the substrate W and transfers it to the pusher 182 of the electrolytic processing apparatus 134. The substrate W is then delivered between the pusher 182 and the substrate holder 42 of the electrolytic processing apparatus 134. In the electrolytic processing apparatus 134, a surface of the substrate W is subjected to electrolytic polishing to remove a conductive material (copper film 6), for example. Then, the substrate W is returned to the pusher 182. The second transfer robot 642 receives the substrate from the pusher 182 and transfers it to the pusher 632a of the CMP apparatus 632. The substrate W is then delivered from the pusher 632a to the top ring 654 of the CMP apparatus 632. In the CMP apparatus 632, the surface of the substrate W is subjected to chemical mechanical polishing to remove barrier metal (barrier layer 5), for example. Then, the substrate W is returned to the pusher 632a. The second transfer robot 642 receives the finished substrate from the pusher 632a and transfers it to one of the secondary cleaning devices 636 to perform rough cleaning. Then, the second transfer robot 642 transfers the substrate W to the temporary placement stage 638, where the substrate W is turned upside down as needed. The first transfer robot 640 receives the substrate W and transfers it to one of the primary cleaning devices 634. The substrate is cleaned and dried in the primary cleaning devices 634 and returned to the cassette on the loading/unloading unit 630 by the first transfer robot 640.
In the present embodiment, rough polishing is performed by the electrolytic process in the electrolytic processing apparatus 134, and finishing polishing is performed by chemical mechanical polishing in the CMP apparatus 632. However, rough polishing may be performed by chemical mechanical polishing in the CMP apparatus 632, and finishing polishing may be performed by the electrolytic process in the electrolytic processing apparatus 134. In this case, loads on the CMP process can be reduced. In the present embodiment, the electrolytic processing apparatus in the second embodiment is employed as the electrolytic processing apparatus. However, the electrolytic processing apparatus is not limited to the electrolytic processing apparatus in the second embodiment and can employ any of the electrolytic processing apparatuses in the above embodiments.
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, there are no carbon chains due to an organic compound 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 701, 702 and the workpiece (substrate) 704 and hence the distance between the electrode 701 serving as an anode and the electrode 702 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 701a serving as an anode and the conductive carbon material 702a serving as a cathode are separately bonded to (or chemically modified by) the ionic dissociation functional groups 701b, 702b, a leakage current can be prevented from being produced between the cathode and the anode, i.e., between the electrodes 701 and 702.
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 a substrate processing apparatus or 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 a basic group such as a quaternary ammonium group or a tertiary or lower amino group, or an acidic group such as 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 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, and anodizing a conductive carbon material in an electrolytic solution.
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.
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.
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 18.2MΩ·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.
Thus, it is possible to reduce the distance between the electrodes 711, 712 and the workpiece (substrate) 714 and hence the distance between the electrode 711 serving as an anode and the electrode 712 serving as a cathode. Therefore, the electrolytic processing apparatus can flexibly cope with small electrodes and various shapes of electrodes. Furthermore, because the electrode 711 serving as an anode and the electrode 712 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 711 and 712.
Such an electrode, which includes a graphite intercalation compound containing alkali metal, can be used in a substrate processing apparatus or 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.
The present invention is applicable to an electrolytic processing apparatus useful for processing a conductive material formed on a surface of a substrate such as a semiconductor wafer or for removing impurities attached to a surface of a substrate.
| Number | Date | Country | Kind |
|---|---|---|---|
| 2002-295435 | Oct 2002 | JP | national |
| Filing Document | Filing Date | Country | Kind | 371c Date |
|---|---|---|---|---|
| PCT/JP03/12651 | 10/2/2003 | WO | 3/21/2005 |
