Patent Publication Number: US-2005115838-A1

Title: Electrolytic processing apparatus and method

Description:
TECHNICAL FIELD  
      This invention relates to an electrolytic processing apparatus and method, and more particularly to an electrolytic processing apparatus and method useful for processing a conductive material present in the surface of a substrate, such as a semiconductor wafer, or for removing impurities adhering to the surface of a substrate.  
     BACKGROUND ART  
      In recent years, instead of using aluminum or aluminum alloys as a material for forming interconnection circuits on a substrate such as a semiconductor wafer, there is an eminent movement towards using copper (Cu) which has a low electric resistivity and high electromigration resistance. Copper interconnects are generally formed by filling copper into fine recesses formed in the surface of a substrate. There are known various techniques for forming such copper interconnects, including CVD, sputtering, and plating. According to any such technique, a copper film is formed in the substantially entire surface of a substrate, followed by removal of unnecessary copper by chemical mechanical polishing (CMP).  
       FIGS. 8A through 8C  illustrate, in sequence of process steps, an example of forming such a substrate W having copper interconnects. As shown in  FIG. 8A , an insulating film  2 , such as an oxide film of SiO 2  or a film of low-k material, is deposited on a conductive layer  1   a  in which semiconductor devices are formed, which is formed on a semiconductor base  1 . A contact hole  3  and a trench  4  for interconnects are formed in the insulating film  2  by the lithography/etching technique. Thereafter, a barrier layer  5  of TaN or the like is formed on the entire surface, and a seed layer  7  as an electric supply layer for electroplating is formed on the barrier layer  5 .  
      Then, as shown in  FIG. 8B , copperplating is performed on to the surface of the substrate W to fill the contact hole  3  and the trench  4  with copper and, at the same time, deposit a copper film  6  on the insulating film  2 . Thereafter, the copper film  6  and the barrier layer  5  on the insulating film  2  are removed by chemical mechanical polishing (CMP) so as to make the surface of the copper film  6  filled in the contact hole  3  and the trench  4  for interconnects and the surface of the insulating film  2  lie substantially on the same plane. An interconnection composed of the copper film  6  as shown in  FIG. 8C  is thus formed.  
      Components in various types of equipments have recently become finer and have required higher accuracy. As sub-micro manufacturing technology has commonly been used, the properties of materials are largely influenced by the processing method. Under these circumstances, in such a conventional machining method that a desired portion in a workpiece is physically destroyed and removed from the surface thereof by a tool, a large number of defects may be produced to deteriorate the properties of the workpiece. Therefore, it becomes important to perform processing without deteriorating the properties of the materials.  
      Some processing methods, such as chemical polishing, electrolytic processing, and electrolytic polishing, have been developed in order to solve this problem. In contrast with the conventional physical processing, these methods perform removal processing or the like through 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.  
      A processing method, which makes use of a catalytic reaction of the ion exchanger and carries out processing in ultrapure water, has been developed as electrolytic processing.  FIG. 9  illustrates the principle of this electrolytic processing.  FIG. 9  shows the ionic state when an ion exchanger  12   a  mounted on a processing electrode  14  and an ion exchanger  12   b  mounted on a feeding electrode  16  are brought into contact with or close to a surface of a workpiece  10 , while a voltage is applied via a power source  17  between the processing electrode  14  and the feeding electrode  16 , and a liquid  18 , e.g. ultrapure water, is supplied from a liquid supply section  19  between the processing electrode  14 , the feeding electrode  16  and the workpiece  10 . In the case of this electrolytic processing, water molecules  20  in the liquid  18  such as ultrapure water are dissociated efficiently by using the ion exchangers  12   a ,  12   b  into hydroxide ions  22  and hydrogen ions  24 . The hydroxide ions  22  thus produced, for example, are carried, by the electric field between the workpiece  10  and the processing electrode  14  and by the flow of the liquid  18 , to the surface of the workpiece  10  opposite to the processing electrode  14  whereby the density of the hydroxide ions  22  in the vicinity of the workpiece  10  is enhanced, and the hydroxide ions  22  are reacted with the atoms  10   a  of the workpiece  10 . The reaction product  26  produced by this reaction is dissolved in the liquid  18 , and removed from the workpiece  10  by the flow of the liquid  18  along the surface of the workpiece  10 . Removal processing of the surface of the workpiece  10  is thus effected.  
      With the electrolytic processing of an electrically conductive material carried out by using an ion exchanger in the above-described manner, it is not possible to directly apply thereto a numerical control mechanism generally employed in conventional mechanical processing. In this regard, an electrolytic processing method utilizes a chemical interaction between OH −  ions and the atoms of a workpiece. Accordingly, the processing phenomenon occurs even when a workpiece and a tool (electrode) is not in contact with each other. Electrolytic processing is thus differentiated in the processing principle from mechanical processing in which processing is effected by physical destruction of a workpiece. More specifically, in a common mechanical processing, processing is effected by allowing a workpiece and a tool, which are in contact with each other, to make a relative movement so as to physically destruct the workpiece. The progress of processing may be stopped by releasing the contact between the workpiece and the tool e.g. when a processing amount is reached to an intended processing amount The processing does not progress any more even when the tool passes over the surface of the workpiece. On the other, according to the electrolytic processing method which utilizes a chemical interaction between the reaction species and a workpiece, as described above, the processing phenomenon occurs when the amount of the reaction species reaches a certain level, even when the tool (electrode) is not in contact with the workpiece. Accordingly, the processing phenomenon inevitably occurs when the tool (electrode) passes over the surface of a portion of the workpiece in which a predetermined amount of processing has been effected.  
      Accordingly, in order to perform processing of an electrically conductive material with a high processing precision that follows an intended form of a processed workpiece, by the electrolytic processing method utilizing the chemical interaction between the reaction species and the workpiece, such a control system is needed that does not simply control the contact state (position of tool) between the workpiece and the tool as is the case of mechanical processing, but also control the chemical interaction between the reaction species, such as OH −  ions, and the atoms of the workpiece.  
     DISCLOSURE OF INVENTION  
      The present invention has been made in view of the above situation in the background art. It is therefore an object of the present invention to provide an electrolytic processing apparatus and method that can effect processing of a workpiece, having in the surface an electrically conductive material as a to-be-processed material, with high processing precision and can produce an intended form of processed workpiece with high accuracy of form.  
      In order to achieve the above object, the present invention provides an electrolytic processing apparatus, comprising: a holder for detachably holding a workpiece; a processing electrode that can come close to or into contact with the workpiece held by the holder; a feeding electrode for feeding electricity to the workpiece held by the holder; an ion exchanger disposed in at least one of the space between the workpiece and the processing electrode and the space between the workpiece and the feeding electrode; a fluid supply section for supplying a fluid between the workpiece and at least one of the processing electrode and the feeding electrode, in which the ion exchanger is present; a power source for applying a voltage between the processing electrode and the feeding electrode; a drive section for allowing the workpiece held by the holder and the processing electrode, facing each other, to make a relative movement; and a numerical controller for effecting a numerical control of the drive section.  
      The electrolytic processing apparatus makes it possible to compare the form of a workpiece before or during processing with an intended form of the workpiece after processing and determine the processing amount corresponding to the coordinate difference between the two forms, input parametric data corresponding to the processing amount to the numerical controller and, based on the inputted data, effect a numerical control of the drive section that allows the workpiece held by the holder and the processing electrode, facing each other, to make a relative movement. The electrolytic processing apparatus, carried out under such a numerical control, can produce the intended form of processed workpiece with high accuracy of form.  
      The power source may supply an electric current or a voltage controlled at a constant value between the processing electrode and the feeding electrode.  
      In electrolytic processing, the processing rate is constant when the electric current following between a processing electrode and a feeding electrode is controlled at a constant value. In this case, the processing amount is determined by the product of the electric current value and the processing time. Accordingly, in the case where the electric current flowing between a processing electrode and a feeding electrode is controlled at a constant value, an intended form of processed workpiece can be obtained with high accuracy of form only by numerically controlling the processing time, i.e. a period of time during which the workpiece and the processing electrode face each other, so that the electrolytic processing phenomenon occurs (residence time).  
      The numerical controller may numerically control, for example, the relative movement speed between the workpiece held by the holder and the processing electrode via the drive section.  
      When carrying out electrolytic processing while allowing the workpiece held by the holder and the processing electrode, facing each other, to make a relative movement with changing relative speeds, the changing relative movement speeds may be numerically controlled. This makes it possible to process a certain point in the processing surface of the workpiece for an optimum processing time (residence time).  
      Alternatively, the numerical controller may numerically control a stop time in a relative step movement of the workpiece held by the holder and the processing electrode via the drive section.  
      When carrying out electrolytic processing while allowing the workpiece held by the holder and the processing electrode, facing each other, to make a relative step movement, the stop time in the movement is numerically controlled. This makes it possible to process a certain point in the processing surface of the workpiece for an optimum processing time (residence time).  
      The term “relative step movement” herein refers to such a relative movement that either one or both of the workpiece and the processing electrode move so that the processing electrode makes a repetition of a certain-distance movement and stop over the workpiece.  
      The present invention provides an electrolytic processing method, comprising: providing a processing electrode, a feeding electrode and an ion exchanger disposed in at least one of the space between a workpiece held by a holder and the processing electrode and the space between the workpiece and the feeding electrode; allowing the processing electrode to be close to or in contact with the workpiece held by the holder while feeding electricity from the feeding electrode to the workpiece; supplying a fluid to the space between the workpiece and at least one of the processing electrode and the feeding electrode, in which the ion exchanger is present; applying a voltage between the processing electrode and the feeding electrode; and allowing the workpiece held by the holder and the processing electrode, facing each other, to make a relative movement while numerically controlling the movement by a numerical controller.  
      The electrolytic processing method may be comprising: measuring the form of the workpiece before and/or during processing; inputting coordinate data on the measured form and on an intended form after processing of the workpiece to the numerical controller; and numerically controlling the relative movement speed between the workpiece held by the holder and the processing electrode according to the coordinate difference between the measured form and the intended form.  
      The electrolytic processing method may be comprising: measuring the form of the workpiece before and/or during processing; inputting coordinate data on the measured form and on an intended form after processing of the workpiece to the numerical controller; and numerically controlling a stop time in a relative step movement of the workpiece held by the holder and the processing electrode according to the coordinate difference between the measured form and the intended form.  
      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 illustrates preferred embodiments of the present invention by way of example. 
    
    
     BRIEF DESCRIPTION OF DRAWINGS  
       FIG. 1  is a longitudinal sectional front view of an electrolytic processing apparatus according to a first embodiment of the present invention;  
       FIG. 2  is a diagram illustrating the relationship between the pre-processing form and an intended post-processing form of a workpiece;  
       FIG. 3  is a block diagram illustrating an example of numerical control by the electrolytic processing apparatus of  FIG. 1 ;  
       FIG. 4  is a longitudinal sectional front view of an electrolytic processing apparatus according to a second embodiment of the present invention;  
       FIG. 5  is a schematic perspective view of an electrolytic processing apparatus according to a third embodiment of the present invention;  
       FIG. 6  is a block diagram illustrating an example of numerical control by the electrolytic processing apparatus of  FIG. 5 ;  
       FIG. 7  is a schematic perspective view of an electrolytic processing apparatus according to a fourth embodiment of the present invention;  
       FIGS. 8A through 8C  are diagrams illustrating, in sequence of process steps, an example of the formation of copper interconnects; and  
       FIG. 9  is a diagram illustrating the principle of electrolytic processing as carried out by using an ion exchanger. 
    
    
     BEST MODE FOR CARRYING OUT THE INVENTION  
      Preferred embodiments of the present invention will now be described with reference to the drawings. Though the below-described embodiments refer to application to electrolytic processing apparatuses (electrolytic polishing apparatuses) which use a substrate as a workpiece to be processed and remove (polish) copper formed on the surface of the substrate, the present invention is of course applicable to other workpiece, and to other electrolytic processing.  
       FIG. 1  shows an electrolytic processing apparatus according to a first embodiment of the present invention. This electrolytic processing apparatus includes a substrate holder  30  for attracting and holding the substrate W with its front surface facing upward (so-called “face-up” manner) , and an electrode head  38  having a disc-shaped electrode section  36  made of an insulating material. The electrode section  36  has, embedded therein, fan-shaped processing electrodes  32  and feeding electrodes  34  that are disposed alternately with their surfaces (lower faces) exposed. The electrode head  38  is positioned above the substrate holder  30 . An ion exchanger  40  consisting of laminated layers (lamination) is mounted on the lower surface of the electrode section  36  so as to cover the surfaces of the processing electrodes  32  and the feeding electrodes  34 .  
      The substrate holder  30  is connected directly to the upper end of a supporting shaft  42  which is supported rotatably. A motor  44  as a first drive section for making the relative movement between the substrate W held by the substrate holder  30  and the processing electrodes  32  is disposed beside the supporting shaft  42 . A timing belt  46  is engaged between the supporting shaft  42  and the motor (first drive section)  44  so that the substrate holder  30  and the substrate W held by the substrate holder  30  rotate integrally by the actuation of the motor (first drive section)  44 .  
      The electrode head  38  is connected downwardly to the free end of a pivot arm  48  which can pivot horizontally. The base portion of the pivot arm  48  is connected to the upper end of a hollow pivot shaft  54  which moves vertically via a ball screw  52  by the actuation of a motor  50  for vertical movement. A motor  56 , as a second drive section for making the relative movement between the substrate W held by the substrate holder  30  and the processing electrodes  32 , is positioned beside the pivot shaft  54 , and allows to move vertically with the pivot shaft  54 . A timing belt  58  is engaged between the pivot shaft  54  and the motor (second drive section)  56  so that the pivot shaft  54  and the pivot arm  48  pivots (rotates) integrally by the actuation of the motor (second drive section)  56 .  
      Further, the electrode head  38  is connected directly to a hollow motor  60  as a third drive section for making the relative movement between the substrate W held by the substrate holder  30  and the processing electrodes  32  so as to rotate by the actuation of the hollow motor (third drive section)  60 .  
      In this embodiment, the ion exchanger  40  is of a three-layer structure (lamination) consisting of a pair of strongly acidic cation-exchange fibers  62   a ,  62   b  and a strongly acidic cation-exchange membrane  62   c  interposed between the fibers  62   a ,  62   b . The ion exchanger (laminate)  40  has a good water permeability and a high hardness and, in addition, the exposed surface (lower surface) to be opposed to the substrate W has a good smoothness. The construction of the ion exchanger  40  may be arranged such that the ion-exchange membrane is used for the exposed surface and the laminate of the ion-exchange fibers is arranged above the exposed ion-exchange membrane.  
      Each of the laminated layers  62   a ,  62   b  and  62   c  of the ion exchanger  40  preferably carries a strongly acidic cation-exchange group (sulfonic acid group) , however, an ion exchanger carrying a weakly acidic cation-exchange group (carboxyl group), an ion exchanger carrying a strongly basic anion-exchange group (quaternary ammonium group), or an ion exchanger carrying a weakly basic anion-exchange group. (tertiary or lower amino group) may be used.  
      The nonwoven fabric carrying a strongly basic anion-exchange group can be prepared by, for example, the following method: A polyolefin nonwoven fabric having a fiber diameter of 20-50 μm and a porosity of about 90% is subjected to the so-called radiation graft polymerization, comprising γ-ray irradiation onto the nonwoven fabric and the subsequent graft polymerization, thereby introducing graft chains; and the graft chains thus introduced are then aminated to introduce quaternary ammonium groups there into. The capacity of the ion-exchange groups introduced can be determined by the amount of the 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. Thus, the degree of grafting, i.e. the ratio of the weight of the nonwoven fabric after graft polymerization to the weight of the nonwoven fabric before graft polymerization, can be made 500% at its maximum. Consequently, the capacity of the ion-exchange groups introduced after graft polymerization can be made 5 meq/g at its maximum.  
      The nonwoven fabric carrying a strongly acidic cation-exchange group can be prepared by the following method: As in the case of the nonwoven fabric carrying a strongly basic anion-exchange group, a polyolefin nonwoven fabric having a fiber diameter of 20-50 μm and a porosity of about 90% is subjected to the so-called radiation graft polymerization comprising γ-ray irradiation onto the nonwoven fabric and the subsequent graft polymerization, thereby introducing graft chains; and the graft chains thus introduced are then treated with a heated sulfuric acid to introduce sulfonic acid groups there into. If the graft chains are treated with a heated phosphoric acid, phosphate groups can be introduced. The degree of grafting can reach 500% at its maximum, and the capacity of the ion-exchange groups thus introduced after graft polymerization can reach 5 meq/g at its maximum.  
      The base material of each of the laminated layers  62   a ,  62   b  and  62   c  of the ion exchanger  40  may be a polyolefin such as polyethylene or polypropylene, or any other organic polymer. Further, besides the form of a nonwoven fabric, the ion exchanger may be in the form of a woven fabric, a sheet, a porous material, net or short fibers, etc.  
      When polyethylene or polypropylene is used as the base material, graft polymerization can be effected by first irradiating radioactive rays (γ-rays or electron beam) onto the base material (pre-irradiation) to thereby generate a radical, and then reacting the radical with a monomer, whereby uniform graft chains with few impurities can be obtained. When an organic polymer other than polyolefin is used as the base material, on the other hand, radical polymerization can be effected by impregnating the base material with a monomer and irradiating radioactive rays (γ-rays, electron beam or UV-rays) onto the base material (simultaneous irradiation). Though this method fails to provide uniform graft chains, it is applicable to a wide variety of base materials.  
      By using each of the laminated layers  62   a ,  62   b  and  62   c  of the ion exchanger  40  made of a nonwoven fabric, which liquid can flows therethrough, having an anion-exchange group or a cation-exchange group, it becomes possible that the ion-exchange reaction between ions in the liquid and the ion-exchange group of the ion exchanger can be easily taken place.  
      When each of the laminated layers  62   a ,  62   b  and  62   c  of the ion exchanger  40  has only one of anion-exchange group and cation-exchange group, a limitation is imposed on electrolytically processible materials and, in addition, impurities are likely to form due to the polarity. In order to solve this problem, the anion exchangers and the cation exchangers may be superimposed, or each of the laminated layers  62   a ,  62   b  and  62   c  of the ion exchanger  40  may carry both of an anion-exchange group and a cation-exchange group per se, whereby a range of materials to be processed can be broadened and the formation of impurities can be restrained.  
      Further, by making the ion exchanger  40  a multi-layer structure consisting of laminated layers of ion-exchange materials, such as a nonwoven fabric, a woven fabric and a porous membrane, it is possible to increase the total ion exchange capacity of the ion exchanger  40 , whereby formation of an oxide, for example, in removal (polishing) processing of copper, can be restrained to thereby avoid the oxide adversely affecting the processing rate. In this regard, when the total ion exchange capacity of an ion exchanger  40  is smaller than the amount of copper ions taken in the ion exchanger  40  during removal processing, the oxide should inevitably be formed on the surface or in the inside of the ion exchanger  40 , which adversely affects the processing rate. Thus, the formation of the oxide is governed by the ion exchange capacity of an ion exchanger, and copper ions exceeding the capacity should become the oxide. The formation of an oxide can thus be effectively restrained by using, as the ion exchanger, a multi-layer ion exchanger composed of laminated layers of ion-exchange materials which has enhanced total ion exchange capacity.  
      The ion exchanger  40  should preferably have water permeability and water-absorbing properties. Further, it is desirable that at least the material to be opposed to the workpiece has a high hardness and good surface smoothness. For example, a commercially-available foamed polyurethane “IC 1000” (manufactured by Rodel, Inc.) , generally employed as a pad for CMP, is hard and excellent in wear resistance. By providing a number of through-holes, this product can be used as a material for each of the laminated layers of the ion exchanger  40 . It is possible to provide holes in a resin plate, thereby making the plate water-permeable for use in the ion exchanger  40 . It is of course desirable that the quality of the material has “water-absorbing properties”.  
      According to this embodiment, a plurality of fan-shaped electrode plates  64  are disposed in the electrode section  36  in the circumference direction, and the cathode and anode of a power source  68  are alternately connected, via a slip ring  66 , to the electrode plates  64 . The electrode plates  64  connected to the cathode of the power source  68  become the processing electrodes  32  and the electrode plates  64  connected to the anode of the power source  68  become the feeding electrodes  34 . This applies to processing of e.g. copper, because electrolytic processing of copper proceeds on the cathode side.  
      Depending upon a material to be processed, the cathode side can be a feeding electrode and the anode side can be a processing electrode. More specifically, when the material to be processed is copper, molybdenum, iron or the like, electrolytic processing proceeds on the cathode side, and therefore the electrode plates  64  connected to the cathode of the power source  68  should be the processing electrodes  32  and the electrode plates  64  connected to the anode should be the feeding electrodes  34 . In the case of aluminum, silicon or the like, on the other hand, electrolytic processing proceeds on the anode side. Accordingly, the electrode plates connected to the anode of the power source should be the processing electrodes and the electrode plates connected to the cathode should be the feeding electrodes.  
      By thus disposing the processing electrodes  32  and the feeding electrodes  34  separately and alternately in the circumferential direction of the electrode section  36 , fixed feeding portions to supply electricity to a conductive film (portion to be processed) of the substrate is not needed, and processing can be effected to the entire surface of the substrate. Further, be changing the positive and negative in a pulse manner or alternately, an electrolysis product can be dissolved and the flatness of the processed surface can be enhanced by the multiplex repetition of processing.  
      With respect to the processing electrode  32  and the feeding electrode  34 , oxidation or dissolution thereof due to an electrolytic reaction is generally a problem. In view of this, it is preferred to use, as a base material of the feeding electrode  34 , carbon, a noble metal that is relatively inactive, a conductive oxide or a conductive ceramics, rather than a metal or metal compound widely used for electrodes. A noble metal-based electrode may, for example, be one obtained by plating or coating platinum or iridium onto a titanium electrode, and then sintering the coated electrode at a high temperature to stabilize and strengthen the electrode. Ceramics products are generally obtained by heat-treating inorganic raw materials, and ceramics products having various properties are produced from various raw materials including oxides, carbides and nitrides of metals and nonmetals. Among them there are ceramics having an electric conductivity. When an electrode is oxidized, the value of the electric resistance generally increases to cause an increase of applied voltage. However, by protecting the surface of an electrode with a non-oxidative material such as platinum or with a conductive oxide such as an iridium oxide, the decrease of electric conductivity due to oxidation of the base material of an electrode can be prevented.  
      A pure water nozzle  70  as a pure water supply section for supplying pure water or ultrapure water toward the space between the substrate W held by the substrate holder  30  and the lowered electrode head  38  is disposed above the substrate holder  30 . Pure water or ultrapure water is thus supplied to the ion exchanger  40 . Pure water herein refers to a water having an electric conductivity of not more than 10 μS/cm, and ultrapure water refers to a water having an electric conductivity of not more than 0.1 μS/cm. The electric conductivity of the present invention refers herein to that at 25° C., latm. Instead of pure water or ultrapure water, a liquid having an electric conductivity of not more than 500 μS/cm or any electrolytic solution may be used. By supplying such a liquid during processing, the instability factors of processing, such as process products and dissolved gases, can be removed, and processing can be effected uniformly with good reproducibility.  
      The electrolytic processing apparatus is provided with a numerical controller  72  for effecting numerical control of the drive sections, i.e. the motor (first drive section)  44 , the motor (second drive section)  56  and the motor (third drive section)  60 , which allow the substrate W held by the substrate holder  30  and the processing electrodes  32 , facing each other, to make a relative movement. The motors (drive sections)  44 ,  56  and  60  are thus numerically controllable servomotors, and their rotation angles and rotational speeds are numerically controlled by an output signal from the numerical controller  72 .  
      According to this embodiment, during electrolytic processing carried out while being flowed an electric current at a constant value between the processing electrodes  32  and the feeding electrodes  34 , the numeral controller  72  numerically controls: the rotational speed of the substrate W, held by the substrate holder  30 , via the motor (first drive section)  44 ; the speed of the horizontal movement of the electrode head  38 , by pivoting of the pivot arm  48 , via the motor (second drive section)  56 ; and the rotational speed of the electrode head  38  via the motor (third drive section)  60 .  
      An example of the numerical control will now be described with reference to  FIGS. 2 and 3 . First, as shown in  FIG. 2 , the form of a substrate (workpiece) before processing is measured. Specifically, various coordinate points of the pre-processing form are measured in a X-Y-Z coordinate system (in which the Z axis is orthogonal to the X-Y plane as a datum plane). The measured pre-processing form data is inputted to the numerical controller  72 . Further, with respect to a coordinate point (x, y, Z 1 ) of the pre-processing form, the corresponding coordinate point (x, y, Z 2 ) of an intended post-processing form is also inputted as intended form data to the numerical controller  72 . In addition, unit processing form data (movement speed per motor control signal pulse) e.g. on form and on processing rate is inputted to the numerical controller  72  in advance or at an arbitrary time.  
      When electrolytic processing is carried out under control of the electric current flowing between the processing electrodes  32  and the feeding electrodes  34  at a constant value, the processing rate is constant thereby the processing amount is determined by the product of the current value and the processing time. Accordingly, in the case where the electric current flowing between the processing electrodes  32  and the feeding electrodes  34  is controlled at a constant value, an intended form of processed substrate can be obtained with high accuracy of form only by numerically controlling the processing time, i.e. a period of time during which the substrate W and the processing electrodes  32  face each other, so that the electrolytic processing phenomenon occurs (residence time).  
      Thus, according to this embodiment, a processing amount Z 1 -Z 2  in the Z direction is determined at each coordinate point based on the data inputted in the numerical controller  72 . Based on the processing amount Z 1 -Z 2 , the rotational speed of the substrate W, held by the substrate holder  30 , via the motor (first drive section)  44 ; the speed of the horizontal movement of the electrode head  38 , by pivoting of the pivot arm  48 , via the motor (second drive section)  56 ; and the rotational speed of the electrode head  38  via the motor (third drive section)  60  are determined for each coordinate point, and the signal is inputted to the motors (drive sections)  44 ,  56  and  60  so as to numerically control the motors (drive sections)  44 ,  56  and  60 .  
      Next, electrolytic processing by this electrolytic processing apparatus will be described.  
      First, a substrate W, e.g. a substrate W as shown in  FIG. 8B  which has in its surface a copper film  6  as a conductor film (portion to be processed), is attracted and held by the substrate holder  30 , and the electrode head  38  is moved by the pivot arm  48  to a processing position right above the substrate W held by the substrate holder  30 . The electrode head  38  is then lowered by the actuation of the motor  50  for vertical movement, so that the ion exchanger  40  mounted on the lower surface of the electrode section  36  of the electrode head  38  contacts or gets close to the upper surface of the substrate W held by the substrate holder  30 .  
      Next, an electric power is applied from the power source  68  to between the processing electrodes  32  and the feeding electrodes  34 , while the electric current flowing between the processing electrodes  32  and the feeding electrodes  34  being controlled at a constant value, and the substrate holder  30  and the electrode head  38  are rotated. Further, the pivot arm  48  is pivoted to move the electrode head  38  horizontally. At the same time, pure water or ultrapure water is supplied from the pure water nozzle  70  disposed above the electrode substrate holder  30  to between the substrate W and the electrode head  38 , thereby filling pure water or ultrapure water into the space between the processing and feeding electrodes  32 ,  34  and the substrate W. Thereby, electrolytic processing of the conductor film (copper film  6 ) formed on the substrate W is effected by hydrogen ions or hydroxide ions produced in the ion exchanger  40 .  
      More specifically, pure water or ultrapure water is dissociated into OH −  ions and H +  ions with the aid of a catalytic reaction in the ion exchanger  40 . The OH −  ions transfer the electric charges in the vicinity of the processing electrodes  32  and become OH radicals. The OH radicals are reacted with the copper film  6  of the substrate W to thereby effect removal (polishing) processing of the copper film  6 . In order to shut off H 2  gas generated at the feeding electrodes  34 , a gas-impermeable ion membrane may be used as the strongly acidic cation-exchange membrane  62 . The H 2  gas is thus shut off, and is discharged out by the flow of pure water or ultrapure water produced by the rotation of the electrode section  36 .  
      More specifically, by allowing pure water or ultrapure water to flow within the ion exchanger  40 , a sufficient amount of water can be supplied to a functional group (sulfonic acid group in the case of an ion exchanger carrying a strongly acidic cation-exchange group) thereby to increase the amount of dissociated water molecules, and the process product (including a gas) formed by the reaction between the conductor film (copper film  6 ) and hydroxide ions (or OH radicals) can be removed by the flow of water, whereby the processing efficiency can be enhanced. The flow of pure water or ultrapure water is thus necessary, and the flow of water should desirably be constant and uniform. The constancy and uniformity of the flow of water leads to constancy and uniformity in the supply of ions and the removal of the process product, which in turn leads to constancy and uniformity in the processing.  
      By making the ion exchanger  40  of a laminate of a multi-layer structure, the total ion-exchange capacity of the ion exchanger (laminate)  40  can be increased, whereby the reaction products (oxides and ions) of the electrolytic reaction can be prevented from accumulating in the ion exchanger  40  in an amount exceeding the accumulation capacity of the laminate. In this regard, if the reaction products are accumulated in the laminate in an amount exceeding the accumulation capacity, the accumulated products may change their forms, and such transformed products can adversely affect the processing rate and its distribution. Moreover, the flatness of the processed surface of the substrate can be enhanced by using, as the ion exchanger  40 , one having a high hardness or one having a good surface smoothing, or by using both of them.  
      In advance, the pre-processing form data, intended form data and the unit processing form data are inputted to the numerical. controller  72 . Electrolytic processing is carried out while numerically controlling: the rotational speed of the substrate w, held by the substrate holder  30 , via the motor (first drive section)  44 ; the speed of the horizontal movement of the electrode head  38 , by pivoting of the pivot arm  48 , via the motor (second drive section)  56 ; and the rotational speed of the electrode head  38  via the motor (third drive section)  60 .  
      In the electrolytic processing, the electric current flowing between the processing electrodes  32  and the feeding electrodes  34  is controlled at a constant value to thereby fix the processing rate while the relative movement between the substrate W and the processing electrodes  32  being numerically controlled. The electrolytic processing can produce an intended form of processed substrate (workpiece) W with high accuracy of form.  
      After completion of the electrolytic processing, the power source  68  is disconnected, the rotation of the substrate holder  30  and the electrode head  38  are stopped, and pivoting of the pivot arm  48  is stopped. Thereafter, the electrode head  38  is raised, and processed substrate W held by the substrate holder  30  is transferred to next process.  
      This embodiment shows the case of supplying pure water, preferably ultrapure water, to the space between the electrode section  36  and the substrate W. The use of pure water or ultrapure water containing no electrolyte upon electrolytic processing can prevent extra impurities such as an electrolyte from adhering to and remaining on the surface of the substrate w. Further, copper ions or the like dissolved during electrolytic processing are immediately caught by the ion exchanger  40  through the ion-exchange reaction. This can prevent the dissolved copper ions or the like from re-precipitating on the other portions of the substrate W, or from being oxidized to become fine particles which contaminate the surface of the substrate W.  
      Ultrapure water has a high resistivity, and therefore an electric current is hard to flow therethrough. A lowering of the electric resistance is made by shortening a distance between the electrode and the workpiece, or interposing the ion exchanger between the electrode and the workpiece. Further, an electrolytic solution, when used in combination with electrolytic solutions, can further lower the electric resistance and reduce the power consumption. When electrolytic processing is conducted by using an electrolytic solution, the portion of a workpiece that undergoes processing ranges over a slightly wider area than the area of the processing electrode. In the case of the combined use of ultrapure water and the ion exchanger, on the other hand, since almost no electric current flows through ultrapure water, electric processing is effected only within the area of a workpiece that is equal to the area of the processing electrode and the ion exchanger.  
      It is possible to use, instead of pure water or ultrapure water, an electrolytic solution obtained by adding an electrolyte to pure water or ultrapure water. The use of such an electrolytic solution can further lower the electric resistance and reduce the power consumption. A solution of a neutral salt such as NaCl or Na 2 SO 4 , a solution of an acid such as HCl or H 2 SO 4 , or a solution of an alkali such as ammonia, may be used as the electrolytic solution, and these solutions may be selectively used according to the properties of the workpiece. When the electrolytic solution is used, it is preferred to provide a slight interspace between the substrate W and the ion exchanger  40  so that they are not in contact with each other.  
      Further, it is also possible to use, instead of pure water or ultrapure water, a liquid obtained by adding a surfactant or the like to pure water or ultrapure water, and having an electric conductivity of not more than 500 μS/cm, preferably not more than 50 S/cm, more preferably not more than 0.1 μS/cm (resistivity of not less than 10 MΩ·cm). Due to the presence of a surfactant in pure water or ultrapure water, the liquid can form a layer, which functions to inhibit ion migration evenly, at the interface between the substrate W and the ion exchanger  40 , thereby moderating concentration of ion exchange (metal dissolution) to enhance the flatness of the processed surface. The surfactant concentration is desirably not more than 100 ppm. When the value of the electric conductivity is too high, the current efficiency is lowered and the processing rate is decreased. The use of the liquid having an electric conductivity of not more than 500 μS/cm, preferably not more than 50 μS/cm, more preferably not more than 0.1 μS/cm, can attain a desired processing rate.  
      According to the embodiment, the processing rate can be considerably enhanced by interposing the ion exchanger  40  between the substrate W and the processing and feeding electrodes  32 ,  34 . In this regard, electrochemical processing using ultrapure water is effected by a chemical interaction between hydroxide ions in ultrapure water and a material to be processed. However, the amount of the hydroxide ions acting as reactant in ultrapure water is as small as 10 −7  mol/L under normal temperature and pressure conditions, so that the removal processing efficiency can decrease due to reactions (such as an oxide film-forming reaction) other than the reaction for removal processing. It is therefore necessary to increase hydroxide ions in order to conduct removal processing efficiently. A method for increasing hydroxide ions is to promote the dissociation reaction of ultrapure water by using a catalytic material, and an ion exchanger can be effectively used as such a catalytic material. More specifically, the activation energy relating to water-molecule dissociation reaction is lowered by the interaction between functional groups in an ion exchanger and water molecules, whereby the dissociation of water is promoted to thereby enhance the processing rate.  
      Further, according to this embodiment, the ion exchanger  40  is brought into contact with or close to the substrate W upon electrolytic processing. When the ion exchanger  40  is positioned close to the substrate W, though depending on the distance therebetween, the electric resistance is large to some degree and, therefore, a somewhat large voltage is necessary to provide a requisite electric current density. However, on the other hand, because of the non-contact relation, it is easy to form flow of pure water or ultrapure water along the surface of the substrate W, whereby the reaction product produced on the substrate surface can be efficiently removed. In the case where the ion exchanger  40  is brought into contact with the substrate W, the electric resistance becomes very small and therefore only a small voltage needs to be applied, whereby the power consumption can be reduced.  
      If a voltage is raised to increase the current density in order to enhance the processing rate, an electric discharge can occur when the electric resistance between the electrode and the substrate (workpiece to be processed) is large. The occurrence of electric discharge causes etch pits on the surface of the workpiece, thus failing to form an even and flat processed surface. To the contrary, since the electric resistance is very small when the ion exchanger  40  is in contact with the substrate W, the occurrence of an electric discharge can be avoided.  
       FIG. 4  shows an electrolytic processing apparatus according to a second embodiment of the present invention. The electrolytic processing apparatus has a ring-shaped contact holding plate  80  at the periphery of the upper surface of the substrate holder  30 . A plurality of inwardly-protruding contacts  82  as feeding electrodes are mounted at a given pitch to the contact holding plate  80 . Further, the electrode head  38  is provided with a processing electrode  84  instead of the electrode section  36  used in the embodiment of  FIG. 1 . The processing electrode  84  is connected to the cathode of the power source  68  via a slip ring  86 , and the contacts (feeding electrodes)  82  are connected to the anode of the power source  68 . The other construction is the same as the apparatus shown in  FIG. 1 .  
      According to this embodiment, when a substrate W is held by the substrate holder  30 , the contacts (feeding electrodes)  82  contact the copper layer  6  as a to-be-processed material, deposited on the surface of the substrate W as shown in  FIG. 8B . Electrolytic processing can be carried in the same manner as in the preceding embodiment Thus, the electrode head  38  is lowered, and a electric current is applied from the power source  68  to between the processing electrode  84  and the contacts (feeding electrodes)  82  at a constant value while the substrate holder  30  and the electrode head  38  being rotated, and the pivot arm  48  being pivoted to move the electrode head  38  horizontally. At the same time, pure water or ultrapure water is supplied from the pure water nozzle  70  to between the substrate W and the processing electrode  84 . Electrolytic processing of the conductive film (copper film  6 ) of the substrate W is thus effected.  
      In advance of the electrolytic processing, as with the processing embodiment described above, the pre-processing form data, the intended form data, the unit processing form data are inputted to the numerical controller  72  so as to numerically control: the rotational speed of the substrate W, held by the substrate holder  30 , via the motor (first drive section)  44 ; the speed of the horizontal movement of the electrode head  38 , by pivoting of the pivot arm  48 , via the motor (second drive section)  56 ; and the rotational speed of the electrode head  38  via the motor (third drive section)  60 . The electrolytic processing carried out under such a control can produce an intended form of processed substrate W with high accuracy of form.  
       FIG. 5  shows an electrolytic processing apparatus according to a third embodiment of the present invention. The electrolytic processing apparatus includes a substrate holder  100  for attracting and holding a substrate W with its front surface facing upward, and a columnar or cylindrical processing electrode  102  disposed above the substrate holder  100 . The processing electrode  102  is coupled to the free end of a horizontally-extending rotating shaft  104  that is rotatable and vertically movable. An ion exchanger  106  is mounted tightly on the outer circumferential surface of the processing electrode  102 . The substrate holder  100  and the processing electrode  102  are disposed in a processing bath (not shown) filled with a fluid, such as ultrapure water or pure water, that is, they are immersed in the fluid.  
      The substrate holder  100  is coupled to the upper surface of a rotating body  108  that rotates about a Z axis in the direction of θ. The rotating body  108  is mounted on the upper surface of an X-Y table  118  which includes an X stage  112  that moves in the X direction by the actuation of a motor  110  as a first drive section for allowing the substrate W, held by the substrate holder  100 , and the processing electrode  102  to make a relative movement in the X direction, and a Y stage  116  that moves in the Y direction by the actuation of a motor  114  as a second drive section for allowing the substrate W, held by the substrate holder  100 , and the processing electrode  102  to make a relative movement in the Y direction.  
      A wire extending from the cathode of a power source  120  is connected to the processing electrode  102 , and a wire extending from the anode is connected to a feeding electrode  122  that is connected to an electric conductor, e.g. copper film  6  formed in the substrate W as shown in  FIG. 8B , and feeds electricity to the conductor.  
      The processing bath is provided with a fluid nozzle as a fluid supply section for supplying a fluid, such as pure water or ultrapure water, into the processing bath.  
      The electrolytic processing apparatus is provided with a numerical controller  124  for effecting a numerical control of the drive sections, i.e. the motor  110  (first drive section) and the motor  114  (second drive section), which allow the substrate W, held by the substrate holder  100 , and the processing electrode  102 , facing each other, to make a relative movement. The motors (drive sections)  110 ,  114  are thus numerically controllable servomotors, and their rotation angles and rotational speeds are numerically controlled by an output signal from the numerical controller  124 .  
      An example of the numerical control will now be described with reference to  FIG. 6 . First, as illustrated in  FIG. 2 , the form of the substrate (workpiece) before processing is measured by measuring various coordinate points of the pre-processing form in an X-Y-Z coordinate system (in which the Z axis is orthogonal to the X-Y plane as a datum plane). The measured pre-processing form data is inputted to the numerical controller  124 . Further, with respect to a coordinate point (x, y, Z 1 ) of the pre-processing form, the corresponding coordinate point (x, Y, Z 2 ) of an intended post-processing form is also inputted to the numerical controller  124 . In addition, unit processing form date (movement speed per motor control signal pulse) e.g. on form and on processing rate is inputted to the numerical controller  124  in advance or at an arbitrary time.  
      According to this embodiment, a processing amount Z 1 -Z 2  in the Z direction is determined at each coordinate point based on the data inputted in the numerical controller  124 . Based on the processing amount Z 1 -Z 2 , a period of time during which the substrate W held by the substrate holder  100  is stopped via the motor (first drive section)  110  and the motor (second drive section)  114 , is determined, and the signal is inputted to the motors (drive sections)  110 ,  114  so as to numerically control the motors  110 ,  114 .  
      According to this embodiment, e.g. a substrate W as shown in  FIG. 8B , having copper film  6  as a conductive film (to-be-processed portion)in the surface, is attracted and held by the substrate holder  100 . The ion exchanger  106  mounted on the surface of the processing electrode  102  is brought close to or into contact with the surface (upper surface) of the substrate W. Electrolytic processing is then carried out by supplying an electric current from the power source  120  to between the processing electrode  102  and the feeding electrode  122  at a constant value while rotating the processing electrode  102 .  
      During the electrolytic processing, a step movement, i.e. a repetition of a movement and stop of the substrate W in the X or Y direction, is carried out by the X-Y table  118 . For this operation, as described above, the pre-processing form date, the intended form data and the unit processing form data are inputted to the numerical controller  124  in advance, thereby numerically controlling the stop time of the substrate W held by the substrate holder  100  via the motor (first drive section)  110  and the motor (second drive section)  114 . The electrolytic processing performed with such a controlled relative step movement can produce the intended form of processed substrate with high accuracy of form.  
      The term “relative step movement” herein refers to such a relative movement that either one or both of the substrate W and the processing electrode  102  move so that the processing electrode  102  makes a repetition of a certain distance-movement and stop over the substrate W.  
       FIG. 7  shows an electrolytic processing apparatus according to a fourth embodiment of the present invention. This embodiment differs from the third embodiment shown in  FIG. 5  in the use of a spherical or oval processing electrode  102   a .  
      When the processing electrode  102   a  is lowered, an ion exchanger  106   a , which is mounted on the surface of the processing electrode  102   a , is brought into point contact with the substrate W. The processing electrode  102   a  is allowed to rotate while the ion exchanger is in such contact with the substrate W. The other construction is the same as the third embodiment.  
      According to this embodiment, the area of a portion (point) under processing is small, whereby supply of ultrapure water or pure water to around the processing portion can be made with ease, enabling a stable processing.  
      According to the above-described embodiments, the drive sections, which allow the substrate held by the substrate holder and the processing electrode to make a relative movement, are numerically controlled while the electric current flowing between the processing electrode and the feeding electrode is controlled at a constant value. It is, however, also possible to control the voltage applied between the processing electrode and the feeding electrode at a constant value, determine the electric current flowing between the processing electrode and the feeding electrode from the relationship between the voltage and electric current, and numerically control the drive sections based on the electric current thus determined.  
      The measurement of the form of a substrate (workpiece) may be carried out not only before processing but also at any time during processing any number of times. In this connection, there is a case where the actual processing time becomes different from a predetermined processing time. The difference can lead to a lowered accuracy of form of the resulting processed substrate. Such a lowering of accuracy may be eliminated or reduced by effecting in-processing measurement of the substrate as many times as possible. Thus, an increased number of in-processing measurements can generally enhance the processing precision.  
      As described hereinabove, the present invention makes it possible to compare the form of a workpiece before or during processing with an intended form of the workpiece after processing and determine the processing amount corresponding to the coordinate difference between the two forms, input parametric data corresponding to the processing amount to the numerical controller and, based on the inputted data, effect numerical control of the drive section that allows the workpiece held by the holder and the processing electrode, facing each other, to make a relative movement. The electrolytic processing, carried out under such a numerical control, can produce the intended form of processed workpiece with high accuracy of form.  
      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.  
     Industrial Applicability  
      This invention relates to an electrolytic processing apparatus and method useful for processing a conductive material present in the surface of a substrate, such as a semiconductor wafer, or for removing impurities adhering to the surface of a substrate.