Abstract:
This electroplating apparatus includes a substrate disposed above an insoluble anode and a filter disposed between the insoluble anode and the substrate for removing oxygen generated from the insoluble anode. The above construction can provide a plating apparatus using an insoluble anode that allows easy placing and removal of the substrate and prevents poor deposition and poor filling caused by accumulation, on the substrate, of oxygen generated at the insoluble anode.

Description:
BACKGROUND OF THE INVENTION  
         [0001]    1. Field of the Invention  
           [0002]    The present invention relates to an electroplating apparatus and more specifically to a structure of an electroplating apparatus for forming a metal film on a substrate.  
           [0003]    2. Description of the Background Art  
           [0004]    The principle of electroplating lies in that a voltage is applied to a cathode and an anode to deposit a metal from an electrolyte on the cathode side. In the reaction on the cathode side, electrons are supplied from the electrode to metal ions in the electrolyte, whereby the metal is deposited. The reaction on the anode side can be roughly classified into two by an anode material.  
           [0005]    If the metal to be deposited on the substrate is used as the anode material, the metal of the anode releases electrons to cause reaction in which the ions are eluted into the electrolyte. Such an anode is referred to as a soluble anode. On the other hand, if a metal nobler than the metal to be deposited on the substrate is used as the anode material, hydroxide ions (OH—) in the electrolyte release electrons at the anode to cause a reaction in which water and oxygen are generated. Such an anode is referred to as an insoluble anode.  
           [0006]    An electroplating method using a soluble anode has an advantage in that the amount of metal ions in the electrolyte can be maintained to be constant because the same amount of metal as the metal deposited on the substrate is supplied from the soluble anode to the electrolyte.  
           [0007]    [0007]FIG. 16 is a cross section view illustrating a structure of a Cu electroplating apparatus using a soluble anode, which is shown in Proc. of 1993 VLSI Multilevel Interconnection Conference, pp. 470-477. Referring to FIG. 16, this Cu electroplating apparatus includes a plating tank  1 , a soluble anode  2 , an electrolyte  3 , a conductive layer  5  formed on a substrate  4 , a substrate holder  6  for holding the substrate  4 , a contact electrode  7 , an electrolyte inlet  8  having an opening end  8   a , and an electrolyte outlet  9 . The electrolyte  3  is introduced from the electrolyte inlet tube  8  into the plating tank  1 , and is discharged from the electrolyte outlet  9  by overflowing. The soluble anode  2  is disposed in the electrolyte  3 , and the substrate  4  fixed to the substrate holder  6  is disposed at an upper part opposite to the soluble anode  2 . By thus disposing the substrate  4  at an upper part of the plating tank  1 , the substrate  4  can be easily taken in and out of the electrolyte tank  1  without discharging the electrolyte.  
           [0008]    An electric current must be passed in order to perform electroplating. For this purpose, the conductive layer  5  referred to as a seed layer is formed on the substrate  4 . By this construction, the electric current is supplied from the contact electrode  7  to the conductive layer  5 , whereby the electroplating can be performed. Further, by the construction of this Cu electroplating apparatus, a mechanism for rotating the substrate holder  6  can be adopted to make a better film thickness distribution.  
           [0009]    However, according to the method using this Cu electroplating apparatus, the volume of the soluble anode  2  decreases according as the electroplating is performed, thereby changing the distance between the soluble anode  2  and the cathode. This results in a disadvantage of change in the distribution of the thickness of the formed film or in the film quality.  
           [0010]    Further, according to the plating method using this Cu electroplating apparatus, it is necessary to form a coating film called a black film on the surface of the soluble anode  2  in order to carry out the elution of soluble anode  2  smoothly. This black film is constructed with oxide of phosphorus, oxide of copper, or the like added to the soluble anode  2 . Since the adhesion strength of the black film is extremely weak, this will be disadvantageously a cause of particles in the electrolyte  3 .  
           [0011]    On the other hand, by an electroplating method using an insoluble anode, the anode is not eluted, so that the aforesaid problem is not raised. However, one of the problems involved in the electroplating method using an insoluble anode is generation of oxygen at the anode. If the substrate  4  is disposed above the anode in the same manner as in the electroplating apparatus using a soluble anode, the generated oxygen is accumulated on the surface of the substrate  4 , thereby obstructing deposition of the metal on the substrate surface. In particular, if the substrate surface has irregularities, oxygen is accumulated in the recessed part to obstruct the deposition of the metal in the recessed part of the substrate surface, so that the recessed part is poorly filled.  
           [0012]    Hitherto, in order to prevent such a problem, a construction is adopted in which the substrate  4  is disposed below the anode in a conventional electroplating apparatus using an insoluble anode. FIG. 17 is a view illustrating a structure of a conventional Cu electroplating apparatus disclosed in Japanese Patent Laying-Open No. 06-280098/1994. This Cu electroplating apparatus includes a plating tank  1 , an electrolyte  3 , a substrate  4 , a conductive layer  5  on the substrate  4 , a substrate holder  6 , a contact electrode  7 , an electrolyte inlet tube  8  having an opening end  8   a , an electrolyte outlet  9 , an insoluble anode  10 , and a seal  11 .  
           [0013]    As shown in FIG. 17, in the conventional electroplating apparatus using an insoluble anode, a construction is adopted in which the substrate  4  is disposed below the anode. Therefore, the electrolyte  3  in the plating tank  1  must be discharged in exchanging the substrate  4 . This results in a problem of long period of time for performing a plating process on the substrate  4 .  
           [0014]    Further, a small amount of the electrolyte  3  remains in the plating tank  1 , thereby raising a problem that it is difficult to control the amount of the electrolyte. Also, there will be a problem such that the residual electrolyte  3  adheres to the seal  11 , and the electrolyte  3  adheres onto the surface of the conductive layer  5  on which the metal film is to be formed next, thereby raising a problem of corrosion of the conductive layer  5 . Furthermore, corrosion of the conductive layer  5  causes poor contact between the contact electrode  7  and the conductive layer  5 . Also, a problem may be mentioned in which the residual electrolyte  3  drips down on the outside of the plating tank  1  to corrode a wiring and others of the electroplating apparatus.  
           [0015]    Further, since the substrate holder  6  cannot be rotated due to structural reasons, there will be a problem of poor film thickness distribution.  
         SUMMARY OF THE INVENTION  
         [0016]    The object of the present invention is to provide an electroplating apparatus having a structure in which the cathode is disposed above the anode in the electroplating apparatus using an insoluble anode.  
           [0017]    The electroplating apparatus according to the present invention is an electroplating apparatus in which a plating tank is filled with an electrolyte and a voltage is applied between a cathode and an anode disposed in the plating tank to form a metal film on a substrate on a cathode side, the electroplating apparatus including: an anode made of an insoluble material that is not eluted into the electrolyte at the time of forming the metal film; a cathode disposed above the anode; and a means disposed between the anode and the cathode for preventing oxygen generated at the time of forming the metal film, from reaching the substrate.  
           [0018]    Disposal of such a means can prevent oxygen generated at the anode from reaching the cathode. As a result of this, deposition of metal on the cathode surface can be prevented from being obstructed by accumulation of generated oxygen on the cathode surface. In particular, this effect is great if the cathode surface has irregularities. This can provide a good thickness distribution of the film formed on the cathode.  
           [0019]    Further, in order to realize the present invention in a more preferable state, a mesh filter is disposed between the anode and the cathode. Furthermore, in order to remove oxygen with certainty, the filter is disposed to include the anode in a plan view.  
           [0020]    Here, if oxygen is accumulated on the filter, the electric field distribution and the electrolyte flow are disturbed to cause non-uniform thickness distribution of the formed film and poor reproducibility of film forming. In order to avoid such a state, the following modes are adopted.  
           [0021]    As a preferable mode of the invention, the filter has a shape which is sloped upwards as viewed from a central part to an outer peripheral part of the filter. By adopting this shape, the oxygen that has reached the filter can be smoothly guided upwards.  
           [0022]    Further, as a preferable mode of the invention, the filter has one or more openings circumferentially disposed in a vicinity of an outer peripheral part. Adoption of this configuration makes it possible to allow oxygen to escape from the openings disposed in the outer peripheral part of the filter. As a result of this, oxygen escapes outward through the outside of the cathode, so that the oxygen can be allowed to escape without reaching the cathode.  
           [0023]    Further, as a preferable mode of the invention, the electroplating apparatus further includes an electrolyte inlet tube in the plating tank for introducing the electrolyte; the electrolyte inlet tube penetrates through a central part of the anode; and an opening end of the electrolyte inlet tube is disposed on an upper surface side of the anode. Further, as a more preferable mode of the invention, a lower outlet for letting the electrolyte out is disposed on a side surface of the electrolyte inlet tube positioned below the anode. Adoption of this construction makes it possible to form a flow of the electrolyte oriented from the central part towards the outer peripheral part of the filter, whereby the oxygen that has reached the filter can be smoothly guided to the openings.  
           [0024]    Further, as a preferable mode of the invention, an opening is disposed at a central part of the filter. Adoption of this construction makes it easier to control the flow of the electrolyte, whereby a more uniform film thickness distribution can be obtained.  
           [0025]    Further, as a preferable mode of the invention, the opening end of the electrolyte inlet tube is disposed to be in communication with the opening disposed at the central part of the filter. Furthermore, as a more preferable mode, the electrolyte inlet tube is disposed to extend to the opening. Furthermore, as a more preferable mode, an upper outlet for letting the electrolyte out is disposed on a side surface of the electrolyte inlet tube positioned between the filter and the anode. Further, as a preferable mode of the invention, the filter includes a hanging part that allows communication between the opening of the filter and the opening end of the electrolyte inlet tube. By this construction, the filter can be used even if the mechanical strength of the filter is small. Also, by disposing an upper outlet or lower and upper outlets, it is possible to make a flow of the electrolyte along the side surface of the plating tank  1 .  
           [0026]    Further, as a preferable mode of the invention, an outer peripheral part of the filter is connected to a lower end of a cylindrical member disposed in an inside of the plating tank. By this construction, an oxygen outlet is formed between the plating tank and the cylindrical member, whereby the oxygen captured by the filter can be discharged to the outside with certainty through this oxygen outlet. Therefore, the captured oxygen can be prevented from returning to the cathode side again.  
           [0027]    The foregoing and other objects, features, aspects and advantages of the present invention will become more apparent from the following detailed description of the present invention when taken in conjunction with the accompanying drawings. 
       
    
    
     BRIEF DESCRIPTION OF THE DRAWINGS  
       [0028]    [0028]FIG. 1 is a cross section view illustrating an overall construction of an electroplating apparatus  100 A according to a first embodiment of the present invention;  
         [0029]    [0029]FIG. 2 is a perspective view of a filter  12 A;  
         [0030]    [0030]FIG. 3 is a cross section view illustrating an overall construction of an electroplating apparatus  100 B according to a second embodiment of the present invention;  
         [0031]    [0031]FIG. 4 is a perspective view of a filter  12 B;  
         [0032]    [0032]FIG. 5 is a cross section view illustrating an overall construction of an electroplating apparatus  100 C according to a third embodiment of the present invention;  
         [0033]    [0033]FIG. 6 is a cross section view illustrating an overall construction of an electroplating apparatus  100 D according to a fourth embodiment of the present invention;  
         [0034]    [0034]FIG. 7 is a cross section view illustrating an overall construction of an electroplating apparatus  100 E according to a fifth embodiment of the present invention;  
         [0035]    [0035]FIG. 8 is a perspective view of a filter  12 E;  
         [0036]    [0036]FIG. 9 is a cross section view illustrating an overall construction of an electroplating apparatus  100 F according to another mode of the fifth embodiment of the present invention;  
         [0037]    [0037]FIG. 10 is a perspective view of a filter  12 F;  
         [0038]    [0038]FIG. 11 is a cross section view illustrating an overall construction of an electroplating apparatus  100 G according to a sixth embodiment of the present invention;  
         [0039]    [0039]FIG. 12 is a cross section view illustrating an overall construction of an electroplating apparatus  100 H according to a seventh embodiment of the present invention;  
         [0040]    [0040]FIG. 13 is a cross section view illustrating an overall construction of an electroplating apparatus  100 J according to an eighth embodiment of the present invention;  
         [0041]    [0041]FIG. 14 is a cross section view illustrating an overall construction of an electroplating apparatus  100 K according to a ninth embodiment of the present invention;  
         [0042]    [0042]FIG. 15 is a perspective view of a filter body  12  of a filter  12 K;  
         [0043]    [0043]FIG. 16 is a cross section view illustrating a structure of an electroplating apparatus using a soluble anode; and  
         [0044]    [0044]FIG. 17 is a cross section view illustrating a structure of an electroplating apparatus using an insoluble anode. 
     
    
     DESCRIPTION OF THE PREFERRED EMBODIMENTS  
       [0045]    Hereafter, electroplating apparatus according to various embodiments of the present invention will be described referring to the attached drawings.  
         [0046]    (First Embodiment)  
         [0047]    Referring to FIGS. 1 and 2, an electroplating apparatus  100 A according to the first embodiment of the present invention will be described.  
         [0048]    (Construction of Electroplating Apparatus  100 A)  
         [0049]    Referring to FIG. 1, the electroplating apparatus  100 A includes a plating tank  1 , an electrolyte  3 , a substrate  4 , a conductive layer  5  on the substrate  4 , a substrate holder  6 , a contact electrode  7 , an electrolyte inlet tube  8  having an opening end  8   a , an electrolyte outlet  9 , an insoluble anode  10 , and a filter  12 A.  
         [0050]    The electrolyte  3  is introduced from the electrolyte inlet tube  8  into the plating tank  1 , and is discharged from the electrolyte outlet  9  by overflowing. The insoluble anode  10  is disposed in the electrolyte  3  at a lower part opposite to the substrate  4  fixed to the substrate holder  6 .  
         [0051]    When electroplating is carried out by supplying an electric current from the contact electrode  7  to the conductive layer  5 , oxygen is generated at the insoluble anode  10 . In order to remove this oxygen, the filter  12 A is disposed between the insoluble anode  10  and the substrate  4  to cross the plating tank  1  above the insoluble anode  10 . This filter  12 A can prevent the oxygen from reaching the substrate  4 . In order to effectively remove the oxygen, the filter  12 A is disposed to include the insoluble anode  10  in a plan view.  
         [0052]    (Shape of filter  12 A)  
         [0053]    Referring to FIG. 2, the shape of the filter  12 A will be described. The filter  12 A has a filter body  12 , and a plurality of openings  13  are circumferentially disposed in an outer peripheral region of the filter body  12 . By disposing the openings  13 , the oxygen captured by the filter body  12  can be removed to the outside through the openings  13 . If the oxygen is not removed, the oxygen will be accumulated on the filter body  12 , whereby the electric field distribution and the electrolyte flow will be disturbed to cause poor film thickness distribution. As a result, problems will be raised such as poor reproducibility of film forming.  
         [0054]    In order to remove oxygen with certainty, the openings  13  are disposed outside of the insoluble anode  10 . In order to prevent the removed oxygen from returning to the substrate  4  side, the openings  13  are disposed outside of the substrate  5 . Further, the filter body  12  is disposed to have a shape sloped upwards (an inverted conical shape) as viewed from the central part to the outer peripheral part of the filter body  12 . The oxygen captured by the filter body  12  is guided smoothly to the openings  13  by this slope. The slope angle (angle of elevation) of the filter body  12  relative to the horizontal direction is about 20°. Further, the filter body  12  is made of PTFE, and has a mesh diameter (roughness) of about 1 μm.  
         [0055]    (Comparison Experiment)  
         [0056]    A comparison experiment was carried out on the Cu electroplating methods by using the electroplating apparatus  100 A of this embodiment and the conventional electroplating apparatus that does not include the filter  12 A. A silicon wafer having an oxidized surface was used as the substrate  4 , and a groove having a width of 1 μm and a depth of 0.5 μm was formed in the oxide film by photolithography and dry etching. A Cu film was deposited thereon by sputtering to a thickness of 100 nm as the conductive layer  5 , and then a Cu film was deposited to a thickness of 500 nm by electroplating.  
         [0057]    The electrolyte at this time is composed of sulfuric acid, water, and copper sulfate, and contains a commercially available additive added thereto. The flow rate of the electrolyte and the electric current were set to be 5 L/min. and  5 A, respectively. In the case without the filter  12 A, a lot of defects were observed in which the groove was not filled with a Cu film. In contrast, in the case with the filter  12 A, particular defects were not observed. Such a defect seems to have been generated because Cu could not be deposited due to accumulated oxygen in the groove. It is found out that generation of such defects can be prevented by disposing the filter  12 A.  
         [0058]    Here, in this embodiment, the filter body  12  was made of PTFE. However, one can make use of another polymer material such as Teflon resin or polypropylene. Further, one can make use of a ceramic material. As the ceramic material, Al2O3, SiC, and others can be used. Also, the filter body  12  was made of a mesh having a diameter (roughness) of about 1 Mm. However, in order to remove oxygen, it is sufficient to use a mesh having a diameter (roughness) smaller than 250 μm. A film was formed by changing the mesh diameter (roughness). The results are shown in the following Table 1. When the filter body  12  was made of a mesh having a diameter (roughness) smaller than 250 μm, no defects were observed.  
         [0059]    Here, if the filter body  12 A is made of ceramics, the filter is porous, and its roughness is determined by its pore (hole) size. The mesh diameter (roughness) at this time is represented by the pore (hole) size.  
                                           TABLE 1                           Filter diameter and film forming results            Mesh diameter (roughness)   Filling of groove                        0.5   μm   Without defects           1   μm   Without defects           5   μm   Without defects           10   μm   Without defects           20   μm   Without defects           100   μm   Without defects           250   μm   With defects                      
 
         [0060]    Further, as shown in the following Table 2, if the slope angle (angle of elevation) of the filter body  12  is not larger than 5°, it is found out that oxygen is accumulated on the filter body  12 . The slope angle needed for smooth removal of oxygen may differ depending on the material of the filter body  12  and the flow rate of the electrolyte. However, the slope angle is preferably larger than 5°.  
                             TABLE 2                           Slope angle of filter and presence of accumulated oxygen                Slope angle of filter   Accumulated oxygen                       30°   Absent           20°   Absent           10°   Absent            5°   Present            0°   Present                      
 
         [0061]    (Function and Effect)  
         [0062]    As described above, according to the electroplating apparatus  100 A of this embodiment, since the substrate  4  is disposed above the insoluble anode  10 , the substrate  4  can be easily taken in and out, and there is no need for discharging the electrolyte in the plating tank  1  after the electroplating is finished. Further, since a mechanism (not illustrated) for rotating the substrate holder  6  can be adopted, the film thickness distribution can be made better. Since the contact electrode  7  can be easily washed, the electrolyte adhering to the contact electrode  7  can be easily removed after the electroplating is finished, thereby preventing corrosion of the conductive layer on the next substrate.  
         [0063]    Further, if the electroplating is carried out, oxygen is generated on the insoluble anode  10 . However, since the filter  12 A is disposed for removal of the oxygen, the oxygen can be prevented from reaching the substrate  4 .  
         [0064]    Also, since the openings  13  are disposed in the filter  12 A and an upward slope is disposed towards the outside, the oxygen captured by the filter  12 A can be smoothly discharged, thereby avoiding disturbance of the electric field distribution and the flow of the electrolyte and making a better thickness distribution of the film formed on the substrate  4 .  
         [0065]    (Second Embodiment)  
         [0066]    Referring to FIGS. 3 and 4, an electroplating apparatus  100 B according to the second embodiment will be described.  
         [0067]    (Construction)  
         [0068]    In the construction of the electroplating apparatus  100 A of the first embodiment, the filter  12 A has a slope angle. However, a flat filter  12 B may be used such as shown in FIGS. 3 and 4. Here, like or corresponding parts in the electroplating apparatus  100 B of the second embodiment are denoted with the same reference numerals as in the electroplating apparatus  100 A of the first embodiment, and their detailed description is omitted.  
         [0069]    First, referring to FIG. 3, the characteristic construction of the electroplating apparatus  100 B of this embodiment lies in that a through-hole  10   a  is disposed at the center of the insoluble anode  10 , and the electrolyte inlet tube  8  is inserted so that the opening end  8   a  is positioned at the upper surface of the through-hole  10   a , whereby the flow of the electrolyte  3  hits the central region of the filter  12 B. Also, referring to FIG. 4, the filter  12 B includes openings  13  which are circumferentially disposed in the outer peripheral part of the filter body  12  having a flat shape.  
         [0070]    (Function and Effect)  
         [0071]    As shown in FIG. 3, the flow of the electrolyte  3  that has reached the filter  12 B is divided into a component passing through the filter  12 B and a component extending from the center to the outer periphery of the filter  12 B. The oxygen captured by the filter  12 B is guided to the outer peripheral part of the filter  12 B by the flow oriented from the center to the outer periphery of the filter  12 B, and is discharged through the openings  13  disposed in the outer peripheral part of the filter  12 B. By thus using the flow of the electrolyte  3 , the captured oxygen can be effectively discharged even if a flat filter  12 B is used.  
         [0072]    A Cu electroplating was carried out with the electroplating apparatus of this embodiment using a substrate prepared in the same manner as the substrate  4  described in the first embodiment. A Cu film was deposited to a thickness of 500 nm, but no particular defects were observed.  
         [0073]    Further, use of the flat filter  12 B has a merit in that the filter  12 B can be easily prepared, and its cost can be reduced. Also, the filter  12 B has a function of adsorbing an additive. By using a flat shape in which the area of the filter  12 B is reduced to the minimum, such a problem can be reduced to the minimum. Also, as compared with the structure of the first embodiment, this embodiment has merits in that the flow of the electrolyte is simple, and the film thickness distribution is good. In the first embodiment, the distribution of the thickness in the surface of the Cu film deposited to a thickness of 500 nm on an 8-inch wafer had a [standard deviation/average value] of 10%, whereas in this embodiment the [standard deviation/average value] was 6%, thereby showing an improvement. Here, the thickness of Cu film was measured by fluorescent X-ray. Here, the [standard deviation/average value] of 6% means that, when the film thickness is measured at plural points (49 points in this embodiment) in the wafer surface by fluorescent X-ray, the standard deviation/average value of the film thickness is 6%.  
         [0074]    (Third Embodiment)  
         [0075]    Referring to FIG. 5, an electroplating apparatus  100 C according to the third embodiment will be described. Here, like or corresponding parts in the electroplating apparatus  100 C of the third embodiment are denoted with the same reference numerals as in the electroplating apparatus  100 A and  100 B of the first and second embodiments, and their detailed description is omitted.  
         [0076]    (Construction)  
         [0077]    The electroplating apparatus  100 C of this embodiment shown in FIG. 5 as a construction obtained by combination of the electroplating apparatus  100 A of the first embodiment and the electroplating apparatus  100 B of the second embodiment, and has a construction with the filter  12 C having an inverted conical shape and a construction of forming a flow of the electrolyte oriented from the central part to the outer peripheral part of the filter  12 C.  
         [0078]    A Cu electroplating was carried out with the electroplating apparatus  100 C of this embodiment using a substrate prepared in the same manner as the substrate  4  described in the first embodiment. A Cu film was deposited to a thickness of 500 nm, but no particular defects were observed on the substrate.  
         [0079]    Further, as shown in the following Table 3, accumulation of oxygen occurred on the filter when the flow rate of the electrolyte was 5 L/min. in the second embodiment, whereas the accumulation of oxygen was not generated in this embodiment even if the flow rate of the electrolyte was 1 L/min. Thus, in this Example, oxygen can be removed more efficiently, thereby providing a merit of high degree of freedom in setting the flow rate of the electrolyte.  
                                       TABLE 3                           Flow rate of electrolyte and presence of accumulated oxygen                Accumulated oxygen                Second   Third       Flow rate of electrolyte   Embodiment   Embodiment                1 L/min.   Present   Absent        5 L/min.   Present   Absent       10 L/min.   Absent   Absent                  
 
         [0080]    Also, in this embodiment, the distribution of the thickness in the surface of the Cu film deposited to a thickness of 500 nm on an 8-inch wafer had a [standard deviation/average value] of 6%, thereby showing an improvement in the same manner as in the second embodiment.  
         [0081]    As described above, according to the electroplating apparatus  100 C of this embodiment, the oxygen captured by the filter can be more efficiently removed, as compared with the electroplating apparatus of the first and second embodiments, thereby effectively avoiding disturbance of the electric field distribution and the flow of the electrolyte and providing a still better thickness distribution of the film formed on the substrate.  
         [0082]    (Fourth Embodiment)  
         [0083]    Referring to FIG. 6, an electroplating apparatus  100 D according to the fourth embodiment will be described. Here, like or corresponding parts in the electroplating apparatus  100 D of the fourth embodiment are denoted with the same reference numerals as in the electroplating apparatus  100 A to  100 C of the first to third embodiments, and their detailed description is omitted.  
         [0084]    (Construction)  
         [0085]    A characteristic construction of the electroplating apparatus  100 D of this embodiment shown in FIG. 6 lies in that, as compared with the construction of the electroplating apparatus  100 C of the third embodiment, a lower outlet  8   b  is disposed at a part of the electrolyte inlet tube  8  in the vicinity of the rear surface of the insoluble anode  10 . The electrolyte  3  flowing from the lower outlet  8   b  forms a flow along the side surface of the plating tank  1 .  
         [0086]    (Function and Effect)  
         [0087]    By forming such a flow of the electrolyte  3 , the oxygen discharged from the openings  13  of the filter  12 C can be prevented from returning to the substrate side again. Also, it is possible to prevent the electrolyte  3  from staying on the rear side of the insoluble anode  10  which causes uncontrollable state of the composition of the staying electrolyte  3 .  
         [0088]    A Cu electroplating was carried out with the electroplating apparatus  100 D of this embodiment using a substrate prepared in the same manner as the substrate  4  described in the first embodiment. A Cu film was deposited to a thickness of 500 nm using a substrate prepared in the same manner as the substrate described in the first embodiment, but no particular defects were observed on the substrate. Further, the accumulation of oxygen was not generated even if the flow rate of the electrolyte was 1 L/min.  
         [0089]    (Fifth Embodiment)  
         [0090]    Referring to FIGS. 7 and 8, an electroplating apparatus  100 E according to the fifth embodiment will be described. Here, like or corresponding parts in the electroplating apparatus  100 E of the fifth embodiment are denoted with the same reference numerals as in the electroplating apparatus  100 A to  100 D of the first to fourth embodiments, and their detailed description is omitted.  
         [0091]    (Construction)  
         [0092]    When the electroplating apparatus  100 E of this embodiment is compared with the electroplating apparatus  100 B of the second embodiment, an opening  13   a  is disposed at the central part of the filter  12 E.  
         [0093]    (Function and Effect)  
         [0094]    Referring to FIG. 8, by disposing the opening  13   a  at the central part of the filter  12 E, a part of the flow of the electrolyte  3  introduced from the electrolyte inlet tube  8  can reach the substrate  4  without being hindered by the filter  12 E. Thus, by reducing the effect of the filter  12 E on the flow of the electrolyte  3  from the electrolyte inlet tube  8 , the flow of the electrolyte  3  can be controlled more to obtain a more uniform film thickness distribution.  
         [0095]    Further, since the pressure difference received by the filter  12 E can be reduced, a finer filter can be used. A Cu electroplating was carried out with the electroplating apparatus  100 E of this embodiment using a substrate prepared in the same manner as the substrate  4  described in the first embodiment. A Cu film was deposited to a thickness of 500 nm, but no particular defects were observed on the substrate. Also, the distribution of the thickness in the surface of the Cu film deposited to a thickness of 500 nm on an 8-inch wafer had a [standard deviation/average value] of 3%, thereby showing a good value.  
         [0096]    In the electroplating apparatus  100 E shown in FIG. 7, a flat plane-like filter  12 E is used; however, the same effect may be obtained even in the case of an electroplating apparatus  100 F using a filter  12 F having a slope as shown in FIGS. 9 and 10.  
         [0097]    (Sixth Embodiment)  
         [0098]    Referring to FIG. 11, an electroplating apparatus  100 G according to the sixth embodiment will be described. Here, like or corresponding parts in the electroplating apparatus  100 G of the sixth embodiment are denoted with the same reference numerals as in the electroplating apparatus  100 A to  100 F of the first to fifth embodiments, and their detailed description is omitted.  
         [0099]    (Construction)  
         [0100]    A characteristic construction of the electroplating apparatus  100 G of this embodiment shown in FIG. 11 lies in that an opening  13   a  is disposed at the central part of a filter  12 G; the electrolyte inlet tube  8  is disposed to extend to the opening  13   a  so as to allow communication between the opening  13   a  and the opening end  8   a  of the electrolyte inlet tube  8 ; and the opening  13   a  is fixed to the opening end  8   a . Further, the opening  13   a  disposed at the central part of the filter  12 G is disposed, in a plan view, in the inside of the through-hole  10   a  disposed also in the insoluble anode  10 . Here, the filter  12 G includes openings  13  in the same manner as the filter in each of the aforesaid embodiments.  
         [0101]    Further, in the same manner as the electroplating apparatus  100 D of the fourth embodiment, a construction is adopted in which a lower outlet  8   b  is disposed at a part of the electrolyte inlet tube  8  in the vicinity of the rear surface of the insoluble anode  10 , whereby the electrolyte  3  flowing out of the lower outlet  8   b  forms a flow along the side surface of the plating tank  1   
         [0102]    (Function and Effect)  
         [0103]    By adopting such a structure, the filter  12 G can be held by the side surface of the plating tank  1  and the electrolyte inlet tube  8 , so that the filter  12 G can be used even if the mechanical strength of the filter  12 G is small. Also, as compared with the construction of the electroplating apparatus  100 F shown in FIG. 9, it is possible to eliminate the possibility of oxygen passing through the opening  13   a  of the filter  12 G.  
         [0104]    Further, by forming such a flow of the electrolyte  3 , the oxygen discharged from the openings  13  of the filter  12 G can be prevented from returning to the substrate side again. Also, it is possible to prevent the electrolyte  3  from staying on the rear side of the insoluble anode  10  which causes uncontrollable state of the composition of the staying electrolyte  3 .  
         [0105]    A Cu electroplating was carried out with the electroplating apparatus  100 G of this embodiment using a substrate prepared in the same manner as the substrate described in the first embodiment. A Cu film was deposited to a thickness of 500 nm using a substrate prepared in the same manner as the substrate described in the first embodiment, but no particular defects were observed on the substrate. Further, the accumulation of oxygen was not generated even if the flow rate of the electrolyte was 1 L/min.  
         [0106]    A Cu electroplating was carried out with the electroplating apparatus  100 G of this embodiment using a substrate prepared in the same manner as the substrate  4  described in the first embodiment. A Cu film was deposited to a thickness of 500 nm, but no particular defects were observed on the substrate. Also, the distribution of the thickness in the surface of the Cu film deposited to a thickness of 500 nm on an 8-inch wafer had a [standard deviation/average value] of 3%, thereby showing a good value.  
         [0107]    Here, in this embodiment, the filter  12 G is shown to have a slope; however, the same effect may be obtained even if the filter  12 G does not have a slope.  
         [0108]    (Seventh Embodiment)  
         [0109]    Referring to FIG. 12, an electroplating apparatus  100 H according to the seventh embodiment will be described. Here, like or corresponding parts in the electroplating apparatus  100 H of the seventh embodiment are denoted with the same reference numerals as in the electroplating apparatus  100 A to  100 G of the first to sixth embodiments, and their detailed description is omitted.  
         [0110]    (Construction)  
         [0111]    A characteristic construction of the electroplating apparatus  100 H of this embodiment shown in FIG. 12 lies in that, as compared with the electroplating apparatus  100 G of the sixth embodiment, an upper outlet  8   c  is further disposed at a part of the electrolyte inlet tube  8  which is protruding upwards from the insoluble anode  10 .  
         [0112]    (Function and Effect)  
         [0113]    By thus disposing an upper outlet  8   c , a flow of the electrolyte  3  oriented from the central part to the outer peripheral part of the filter  12 G is formed, thereby producing an effect that the captured oxygen can be removed more efficiently. A Cu electroplating was carried out with the electroplating apparatus  100 H of this embodiment using a substrate prepared in the same manner as the substrate  4  described in the first embodiment. A Cu film was deposited to a thickness of 500 nm, but no particular defects were observed on the substrate. Also, the distribution of the thickness in the surface of the Cu film deposited to a thickness of 500 nm on an 8-inch wafer had a [standard deviation/average value] of 3%, thereby showing a good value.  
         [0114]    Here, in this embodiment, the filter  12 G is shown to have a slope; however, the same effect may be obtained even if the filter  12 G does not have a slope.  
         [0115]    (Eighth Embodiment)  
         [0116]    Referring to FIG. 13, an electroplating apparatus  100 J according to the eighth embodiment will be described. Here, like or corresponding parts in the electroplating apparatus  100 J of the eighth embodiment are denoted with the same reference numerals as in the electroplating apparatus  100 A to  100 H of the first to seventh embodiments, and their detailed description is omitted.  
         [0117]    (Construction)  
         [0118]    A characteristic construction of the electroplating apparatus  100 J of this embodiment shown in FIG. 13 lies in that an opening  13   a  is disposed at the central part of the filter  12 J, and a hanging part  12   b  that extends downwards from the opening  13   a  and is fixed to the electrolyte inlet tube  8  is disposed in order to allow communication between the opening  13   a  and the opening end  8   a  of the electrolyte inlet tube  8 . Here, the filter  12 J includes openings  13  in the same manner as the filter of each of the aforesaid embodiments.  
         [0119]    Further, in the same manner as the electroplating apparatus  100 D of the fourth embodiment, a construction is adopted in which a lower outlet  8   b  is disposed at a part of the electrolyte inlet tube  8  in the vicinity of the rear surface of the insoluble anode  10 , whereby the electrolyte  3  flowing out of the lower outlet  8   b  forms a flow along the side surface of the plating tank  1   
         [0120]    (Function and Effect)  
         [0121]    By adopting such a structure, the filter  12 J can be held by the side surface of the plating tank  1  and the electrolyte inlet tube  8 , so that the filter  12 J can be used even if the mechanical strength of the filter  12 J is small. Further, since the electrolyte inlet tube  8  does not protrude above the insoluble anode  10 , the electrolyte inlet tube  8  can be prevented from giving an influence on the electric field distribution. Also, as compared with the construction of the electroplating apparatus  100 F shown in FIG. 9, it is possible to eliminate the possibility of oxygen passing through the opening  13   a  of the filter  12 G.  
         [0122]    Further, by forming such a flow of the electrolyte  3 , the oxygen discharged from the openings  13  of the filter  12 G can be prevented from returning to the substrate side again. Also, it is possible to prevent the electrolyte  3  from staying on the rear side of the insoluble anode  10  which causes uncontrollable state of the composition of the staying electrolyte  3 .  
         [0123]    A Cu electroplating was carried out with the electroplating apparatus  100 J of this embodiment using a substrate prepared in the same manner as the substrate described in the first embodiment. A Cu film was deposited to a thickness of 500 nm, but no particular defects were observed on the substrate. Also, the distribution of the thickness in the surface of the Cu film deposited to a thickness of 500 nm on an 8-inch wafer had a [standard deviation/average value] of 2%, thereby showing a good value.  
         [0124]    Here, in this embodiment, the filter  12 J is shown to have a slope; however, the same effect may be obtained even if the filter  12 J does not have a slope.  
         [0125]    (Ninth Embodiment)  
         [0126]    Referring to FIGS. 14 and 15, an electroplating apparatus  100 K according to the ninth embodiment will be described. Here, like or corresponding parts in the electroplating apparatus  100 K of the ninth embodiment are denoted with the same reference numerals as in the electroplating apparatus  100 A to  100 H and  100 J of the first to eighth embodiments, and their detailed description is omitted.  
         [0127]    (Construction)  
         [0128]    A characteristic construction of the electroplating apparatus  100 K of this embodiment shown in FIGS. 14 and 15 lies in that the filter body  12  of the filter  12 K does not include openings  13  for allowing oxygen to escape, and instead, an upwardly extending cylindrical member  12   c  is disposed at the outer peripheral part of the filter body  12 , whereby an oxygen outlet  14  is formed by the side wall  12   c  and the plating tank  1 . Here, in this embodiment, an explanation has been given on the case in which the filter body  12  does not include openings  13 ; however, this does not exclude a structure in which the openings  13  are disposed.  
         [0129]    (Function and Effect)  
         [0130]    By thus forming the oxygen outlet  14 , the oxygen captured by the filter  12 K is discharged to the outside with certainty through the oxygen outlet  13 , so that the captured oxygen does not return to the substrate side again.  
         [0131]    A Cu electroplating was carried out with the electroplating apparatus  100 K of this embodiment using a substrate prepared in the same manner as the substrate described in the first embodiment. A Cu film was deposited to a thickness of 500 nm, but no particular defects were observed on the substrate. Also, the distribution of the thickness in the surface of the Cu film deposited to a thickness of 500 nm on an 8-inch wafer had a [standard deviation/average value] of 3%, thereby showing a good value.  
         [0132]    Here, the construction of the electroplating apparatus of each of the above-described embodiments is only an example, and it is not to be limited to the aforesaid modes, so that the characteristic structure of each electroplating apparatus can be suitably combined for use. For example, the oxygen outlet  14  constructed in the aforesaid ninth embodiment can be applied to the electroplating apparatus of each of the aforesaid embodiments.  
         [0133]    Further, each of the aforesaid embodiments discloses a structure in which an electrolyte inlet tube  8  is disposed as a preferable mode; however, a structure in which an electrolyte inlet tube  8  is not disposed or a construction in which a flow is given to the electrolyte by another means can be adopted.  
         [0134]    According to the electroplating apparatus based on the present invention, since a means for preventing the oxygen generated at the time of forming a metal film from reaching the substrate is disposed between the cathode and the anode, the oxygen generated at the anode can be prevented from reaching the cathode. As a result, it is possible to prevent accumulation of generated oxygen on the surface of the cathode and to prevent deposition of the metal on the cathode surface from being obstructed. This can make a better thickness distribution of the film formed on the cathode.  
         [0135]    Although the present invention has been described and illustrated in detail, it is clearly understood that the same is by way of illustration and example only and is not to be taken by way of limitation, the spirit and scope of the present invention being limited only by the terms of the appended claims.