Abstract:
A plating apparatus can form a plated film having a uniform thickness on a surface to be plated of a substrate without employing a complicated structure, such as a conduction detection means capable of detecting the state of conduction (contact state) of feeding contacts in contact with a conductive portion of the substrate. The plating apparatus includes a substrate holder having a plurality of feeding contacts for contact with a conductive portion provided in a surface of a substrate, wherein the substrate holder includes a feeding ring comprised of a single member and having the feeding contacts disposed at regular intervals along the circumferential direction, a plurality of substrate chucks for contact with the substrate in the vicinity of the contact portions of the feeding contacts with the conductive portion to support the substrate, and a substrate deflection preventing mechanism for preventing deflection of the substrate.

Description:
BACKGROUND OF THE INVENTION  
       [0001]     1. Field of the Invention  
         [0002]     The present invention relates to a plating apparatus for use in carrying out plating of a surface (front surface) to be plated of a substrate, such as a semiconductor wafer, and more particularly to a plating apparatus that can form a plated film having a more uniform thickness on a surface to be plated of a substrate.  
         [0003]     2. Description of the Related Art  
         [0004]     With the recent progress toward higher integration of semiconductor devices, the circuit interconnects are becoming finer and the distance between adjacent interconnects is becoming smaller. Especially, when forming a circuit pattern by optical lithography with a line width of not more than 0.5 μm, it requires that surfaces on which pattern images are to be focused by a stepper be as flat as possible because depth of focus of an optical system is relatively small. It is therefore necessary to flatten a surface of a substrate, such as a semiconductor wafer, and polishing of a surface of a substrate by a chemical-mechanical polishing (CMP) apparatus is widely practiced as a flattening method.  
         [0005]     In order to fill fine trenches and via holes, formed in a surface of a substrate, such as a semiconductor wafer, with an interconnect material in advance of CMP, a technique of carrying out the filling by metal plating, such as copper plating, has been employed. In carrying out the plating, it is important to form a plated film having a uniform thickness. Plating apparatuses adapted to obtain a uniform plated film thickness for semiconductor devices, such as LSIs, which are becoming finer and multi-level structure, include dip-type plating apparatuses and face down-type plating apparatuses. Though the both plating apparatuses materially differ in their structures, they generally use an electrode (cathode) having the same structure.  
         [0006]      FIG. 1  shows a plating apparatus adapted to feed electricity uniformly to a surface (surface to be plated) of a substrate, such as a semiconductor wafer, thereby forming a plated film having a uniform thickness (see WO 99/31304). As shown in  FIG. 1 , the plating apparatus includes a plating tank  10  for holding a plating solution Q, a substrate holder  11  for setting therein a substrate W, such as a semiconductor wafer, and immersing it in the plating solution Q in the plating tank  10 , and an electrode (anode)  13 , facing the substrate W held in the substrate holder  11 , disposed in the plating solution Q. A plated film is formed on the surface (surface to be plated) of the substrate W by applying a predetermined direct-current voltage from a plating power source  14  to between the substrate holder  11  and the electrode (anode)  13 .  
         [0007]     The substrate holder  11  is provided with a feeding section  16  having a plurality of feeding contacts  15  for contacting a surface conductive portion of the substrate W to feed electricity thereto. When the cathode of the plating power source  14  is connected to the feeding contacts  15  and the anode of the plating power source  14  is connected to the electrode  13 , a plating current flows through the electrode (anode)  13 , the plating solution Q, the conductive portion of the substrate W and the feeding contacts  15 .  
         [0008]     Accordingly, if the feeding contacts  15  do not securely contact a conductive film of the substrate W, a plated film cannot be formed sufficiently on the conductive film of the substrate W and the thickness of the plated film can become non-uniform.  
         [0009]      FIG. 2  is a vertical sectional view showing an example of the construction of the feeding section of the substrate holder  11 . As shown in  FIG. 2 , the feeding section includes an annular packing  18  provided on the inner side of an annular frame  17 , and a feeding ring  19  provided on the outer side of the packing  18 . A plurality of feeding contacts  15  is disposed at regular intervals in the feeding ring  19 . The end portions of the feeding contacts  15  contact, like a spring, the surface conductive portion (not shown) of the substrate W, whereby the feeding contacts  15  and the conductive portion of the substrate W are electrically connected. Further, the tip of the packing  18  is pressed against the surface of the substrate W into tight contact with it. This can prevent the plating solution Q from leaking out of the packing  18 , thus preventing the feeding contacts  15 , the feeding ring  19 , etc. from being exposed to the plating solution.  
         [0010]      FIGS. 3 and 4  show conventional different examples of feeding rings  19  each having feeding contacts  15  attached thereto. According to the example shown in  FIG. 3 , the leaf spring-like feeding contacts  15  are attached to the feeding ring  19  at regular intervals. According to the example shown in  FIG. 4 , the feeding ring  19  is divided into a plurality (four in  FIG. 4 ) of divisions electrically insulated from each other by an insulating member  20 , and the leaf spring-like feeding contact  15  is attached to each division.  FIGS. 3 and 4  are perspective views of the respective feeding electrodes  19  with the feeding contacts  15  attached thereto, as viewed from below.  
         [0011]     When the plurality of leaf spring-like feeding contacts  15  are provided in the common feeding ring  19 , as shown in  FIG. 3 , because of a difference in the contact resistance between the feeding contacts, some feeding contacts  15  are relatively easy to pass electric current and some feeding contacts  15  are relatively hard to pass electric current. Accordingly, a thin plated film is formed in that portion of a substrate W which lies in the vicinity of a feeding contact  15  hard to pass electric current.  
         [0012]     When the feeding ring  19  is divided by the insulating members  20  into a plurality of feeding divisions and the leaf spring-like feeding contact  15  is provided in each feeding division, as shown in  FIG. 4 , the feeding divisions of the feeding ring  19  are electrically independent from each other. It is, therefore, possible to reduce the current difference between the feeding contacts  15  by controlling a current value supplied to each feeding contact  15 . However, an electric current is hard to flow between a feeding contact  15  and its adjacent feeding contact  15 , whereby a thin plated film is formed in that portion of a substrate which lies between adjacent feeding contacts  15 .  
         [0013]     In order to improve such variation in the thickness of the plated film, a plating apparatus is disclosed which uses an electrode having feeding contacts which, as a whole, is in the form of a circular ring (see WO 00/03074).  
         [0014]      FIG. 5A  shows a plan view of feeding contacts provided in the feeding section of the substrate holder of the plating apparatus, and  FIG. 5B  shows an enlarged sectional view taken along the line A-A of  FIG. 5A . The feeding section comprises a plurality ( 8  in  FIG. 5A ) of arc-shaped feeding contacts  15  which, as a whole, form a circular ring. Each feeding contact  15   a  includes a plurality ( 12  in  FIG. 5A ) of contact strips  15   a  which are formed integrally. Each feeding contact  15  may be produced by subjecting a metal plate of, for example, phosphor bronze, having elasticity and high electric conductivity, to sheet metal processing or the like.  
         [0015]     By providing the feeding contact  15  having contact strips  15   a,  shown in  FIGS. 5A and 5B , in each feeding division of the feeding ring  19  shown in  FIG. 4 , so as to bring the contact strips  15   a  of the feeding contact  15  into contact with a conductive portion of a substrate W, and correcting a current value supplied to each feeding contact  15 , it become possible to uniformize electric currents flowing through the feeding contacts  15 . In the case where the feeding contacts  15 , each having the feeding strips  15   a,  shown in  FIGS. 5A and 5B , is applied to the feeding ring shown in  FIG. 4 , the distance between adjacent contact strips  15   a  of each feeding contact  15  can be made extremely small. This makes it possible to form a plated film having a uniform thickness in those portions of a substrate which lie around the contact strips  15   a  and between the contact strips  15   a.    
         [0016]     When the feeding contacts  15 , having the contact strips  15   a,  are connected in a ring, the pressure of the contact strips  15   a  on the conductive portion of a substrate upon their contact can be distributed uniformly, i.e., an unbalanced pressure distribution can be prevented.  
         [0017]      FIG. 6  shows another plating apparatus for forming a plated film, such as a copper film, on a surface (surface to be plated) of a substrate W, such as a semiconductor wafer, by performing electroplating. As shown in  FIG. 6 , the plating apparatus  51  includes a substrate holder  11  for holding the substrate W with its front surface facing upwardly, a plating cup  12  to be capped on the substrate W with the open end closed with the substrate W, a sealing member  23  for sealing between the plating cup  12  and the substrate W held by the substrate holder  11 , and an electrode (anode)  13  disposed in the plating cup  12  and opposite to the substrate W at a predetermined distance therefrom. The plating apparatus  51  is provided with a plating power source  14 . An electric current is supplied from the power source  14  with the substrate W as a cathode and the electrode  13  as an anode. A plating solution Q is supplied into the plating cup  12  closed with the substrate W, and a plated film, such as a copper film, is formed on the surface of the substrate W by passing electricity through the plating solution Q within the plating cup  12 .  
         [0018]     In such plating apparatus  51 , electricity is fed to a substrate W through mechanical contact with a conductive portion (not shown) of the substrate W.  
         [0019]     The conventional plating apparatus as shown in  FIG. 6  necessitates a large amount of plating solution for a substrate, such as a semiconductor wafer, and thus entails the problem of diseconomy even if a plated film having a uniform thickness can be formed.  
         [0020]     A plating apparatus, as shown in  FIG. 7 , has therefore been proposed as a plating apparatus directed to the solution of such a diseconomy problem. As shown in  FIG. 7 , the plating apparatus  51  includes an annular frame  32  having packing properties and comprising a metal core  29  and a rubbery sealing member  18  of a synthetic rubber or resin material, having elasticity like a fluorocarbon rubber and chemical resistance. The plating apparatus  51  also include an immersion member (in-liquid immersion member)  34  which is immersed in a plating solution Q, held in a plating solution holding portion defined by the frame  32  and a substrate W, so as to raise the liquid surface of the plating solution Q, thus reducing the necessary amount of plating solution, a holding assembly  33  for holding the immersion member  34  by a rubber shielding ring  35  in order to forcibly immerse the immersion member  34  in the plating solution Q, and an electrode (anode)  13  disposed parallel to the surface of the substrate W and on the immersion member  34 , preferably in contact with the immersion member  34  which is disposed opposite the substrate W at a predetermined distance therefrom.  
         [0021]     The immersion member  34  is composed of, for example, a continuous cell-type porous ceramic, and is non-conductive and thus acts as a resistance. By disposing the immersion member  34  between the substrate W and the electrode  13 , and forming long channels of plating solution in the continuous cells throughout the immersion member  34  to thereby raise the average electric resistance, it becomes possible to uniformize the thickness distribution of a plated film formed on the surface of the substrate. When the electric resistance between the electrode  13  and the substrate W is low, electric current concentrates on the feeding contact side (peripheral region of substrate). This is because of the high resistance of a seed film formed in the substrate surface. The thickness distribution of a plated film formed on the surface of the substrate can therefore be uniformized by disposing a resistance member, which has a higher resistance than the seed film, such as the immersion member  34 , between the electrode  13  and the substrate W.  
         [0022]     In this plating apparatus  51 , feeding contacts  15 , for supplying an electric current from a plating power source  14  to a conductive portion (not shown) of the substrate W, are brought into contact with the peripheral portion of the substrate W on the outer side of a packing portion  43  of the frame  32  by an elastic force, whereby the conductive portion of the substrate W and the feeding contacts  15  are electrically connected. The tip of the packing portion  43  is pressed against the surface of the substrate W into tight contact with it. This can prevent the plating solution Q from leaking out of the packing portion  43 , or the frame  32 , thus preventing the feeding contacts  15  from being exposed to the plating solution Q.  
         [0023]      FIG. 8  is a plan view showing a feeding section in which the arc-shaped feeding contacts  15 , each having a number of feeding strips  15   a,  shown in  FIGS. 5A and 5B , are provided in the feeding ring  19  divided by the insulating members  20  into the feeding sections, shown in  FIG. 4 , so that the feeding strips  15   a  of the feeding contacts  15  are brought into contact with the conductive portion of the substrate W, and in which substrate chucks  21 , for supporting the substrate W, are disposed each between adjacent feeding contacts  15 .  
         [0024]     As apparent from  FIG. 8 , the distance between one feeding strip  15   a  of one feeding contact  15  and an adjacent feeding strip  15   a  of an adjacent feeding contact  15 , disposed on the opposite sides of the substrate chuck  21 , is considerably larger than the distance between adjacent feeding strips  15   a  in each arc-shaped feeding contact  15 .  
         [0025]     When the distances between contacts are not equal (not uniformly distributed) as in this case, a plated film, having a non-uniform thickness or variation in the film thickness, will be formed on a surface of a substrate W, such as a semiconductor wafer, as shown in  FIG. 9 .  
         [0026]     According to the plating apparatus shown in  FIG. 7 , by forcibly immersing the immersion member  34  in a plating solution Q by using the holding assembly  33  to raise the liquid surface of the plating solution Q, the amount of plating solution can be materially reduced as compared to the conventional plating apparatus shown in  FIG. 6 .  
         [0027]     As apparent from  FIG. 7 , however, the peripheral portion of a substrate W lies on the outer side of the packing portion  43  of the frame  32  and does not contact the plating solution Q. This decreases the plating area of the substrate W, and thus lowers the efficiency in the use of substrate W.  
         [0028]     Further, the diameter of the immersion member  34  is considerably smaller than the diameter of the substrate W. Accordingly, as can be seen from  FIG. 7 , even in the region, on the inner side of the packing portion  43  of the frame  32 , where the plating solution Q is present, plating does not substantially progress in that portion of the substrate W which is near the periphery and lies in the region where the electrode  13  is not present overhead. If plating progresses in that portion of the substrate W, i.e., the portion lying outside the immersion member  34  or the electrode  13 , it does only insufficiently as compared to the substrate portion lying underneath the electrode  13 . The poorly plated portion cannot be utilized as a product, that is, the effective plating area is narrowed.  
         [0029]     Furthermore, in order to bring the frame  32  into tight contact with a substrate W, a support (not shown) is provided on the lower surface side of the substrate W in a position corresponding to the frame  32 , so that the substrate W is clamped by the support and the frame  32  to bring the packing portion  43  of the frame  32  into tight contact with the substrate W. Upon the clamping, an intolerable force is applied to the peripheral portion of the substrate W, which would cause warpage of the substrate W and hinder the formation of a plated film having a uniform thickness.  
       SUMMARY OF THE INVENTION  
       [0030]     The present invention has been made in view of the above problems in the prior art. It is therefore a first object of the present invention to provide a plating apparatus which can form a plated film having a uniform thickness on a surface to be plated of a substrate without employing a complicated structure, such as a conduction detection means capable of detecting the state of conduction (contact state) of feeding contacts in contact with a conductive portion of the substrate.  
         [0031]     It is a second object of the present invention to provide a plating apparatus which can make a considerable reduction in an amount of plating solution and can form a plated film having a uniform thickness over an entire surface to be plated of a substrate, such as a semiconductor wafer.  
         [0032]     After intensive study to achieve the above objects, it has been found by the present inventors that variation in the thickness of a plated film formed on a peripheral portion of a substrate, such as a semiconductor wafer, is caused by inequality (non-uniform distribution) in the distances between adjacent feeding contacts. The present invention has been accomplished based on such findings.  
         [0033]     It has also been found that the use of an immersion member having the same diameter as a substrate makes it possible to form a plated film having a uniform thickness over the entire surface, from the center to the periphery, of a substrate. The present invention has been accomplished based on such findings.  
         [0034]     The present invention provides a plating apparatus comprising a substrate holder having a plurality of feeding contacts for contact with a conductive portion provided in a surface of a substrate, wherein the substrate holder includes a feeding ring comprised of a single member and having the feeding contacts disposed at regular intervals along the circumferential direction, a plurality of substrate chucks for contact with the substrate in the vicinity of the contact portions of the feeding contacts with the conductive portion to support the substrate, and a substrate deflection preventing mechanism for preventing deflection of the substrate.  
         [0035]     According to the present invention, feeding contacts are disposed at regular intervals in one feeding ring. Accordingly, the distances between adjacent feeding contacts can be equalized (uniform distribution), whereby the contact resistances at the contact points can be equalized. This can prevent variation in the film thickness of a plated film formed on a peripheral portion of a substrate, such as a semiconductor wafer, and can thus form a plated film having a uniform thickness.  
         [0036]     Further, the substrate, such as a semiconductor wafer, can be held by clamping it from above and below by the integrated feeding ring with the evenly-spaced feeding contacts mounted thereto and the substrate deflection preventing mechanism and, in addition, the substrate chucks are provided in the vicinity of the contact portions of the feeding contacts of the feeding ring with the conductive portion. This can equalize the pressures of the feeding contacts on the substrate and, by the synergistic effect with the uniform distribution of the feeding contacts, can effectively reduce variation in the thickness of a plated film formed in the peripheral region of the substrate.  
         [0037]     The present invention also provides another plating apparatus comprising: a substrate holder having a plurality of feeding contacts for contact with a conductive portion provided in a surface of a substrate and forming, together with the substrate, a plating solution holding portion; an immersion member disposed opposite the substrate, held by the substrate holder, at a predetermined distance therefrom; and an electrode disposed on the immersion member and opposite the substrate, held by the substrate holder, at a predetermined distance therefrom; wherein the feeding contacts are provided opposite the peripheral end portion of the substrate held by the substrate holder.  
         [0038]     According to the present invention, by forming the plating solution holding portion with the substrate holder and a substrate held by the substrate holder, the necessary amount of plating solution for a substrate can be materially reduced. Furthermore, since the immersion member is immersed in a plating solution during plating, the amount of plating solution, corresponding to the amount excluded by the immersion member, can be further reduced. Because of the small amount of plating solution used, the plating solution can be used batchwise, though it may be reused in a circulatory manner.  
         [0039]     By clamping the peripheral portion of a substrate with the substrate holder, and forming the plating solution holding portion with the substrate holder and the substrate, the entire surface of the substrate can be brought into contact with the plating solution. Further, in carrying out plating with the electrode on the immersion member as an anode and the substrate disposed below the immersion member as a cathode, the use of the immersion member and the electrode, whose diameters are equal to or larger than the effective diameter of the substrate, can broaden the effective plating area of the substrate. The immersion member is made of, for example, a continuous cell-type porous ceramic, and is non-conductive and thus acts as a resistance. By forming long channels of plating solution in the continuous cells throughout the immersion member, a plated film having a uniform thickness can be formed over the entire surface of the substrate. When copper plating is carried out, a copper plate is used as the electrode. The term “effective diameter of substrate” refers to the diameter of the peripheral end of that portion of the substrate which is in contact with a plating solution.  
         [0040]     During plating, the feeding contacts are in contact with a plating solution. The feeding contacts are conventionally made of a material that can corrode when exposed to a plating solution. In view of this, a protective film, which is non-conductive and corrosion resistant, may be formed on that portion of each feeding contact which is to contact a plating solution. The protective film allows an electric current to flow easily between the feeding contact and the conductive substrate holder serving as a feeding electrode. Further, the corrosion prevention method, as compared to other conventional methods, can simplify the electrode structure. Such a protective film cannot be formed on that portion of the feeding contact which directly contacts a substrate. Therefore, a plated film grows gradually on that portion of the feeding contact. The plated film, however, can be removed, for example, by applying a voltage, which is reverse to the voltage applied upon plating, between the substrate and the electrode to etch away the plated film.  
         [0041]     Further, with such an electrode structure, the substrate can be clamped from above and below without a stress that causes deflection or warpage of the substrate. This can stabilize the state of electricity feeding, thus stably forming a plated film having a uniform thickness.  
         [0042]     The present invention also provides yet another plating apparatus comprising: a substrate holder having a plurality of feeding contacts for contact with a conductive portion provided in a surface of a substrate; and an immersion member and an electrode each disposed opposite the substrate, held by the substrate holder, at a predetermined distance therefrom, wherein the substrate holder includes a feeding ring comprised of a single member and having the feeding contacts disposed at regular intervals along the circumferential direction, a plurality of substrate chucks for contact with the substrate in the vicinity of the contact portions of the feeding contacts with the conductive portion to support the substrate, and a substrate deflection preventing mechanism for preventing deflection of the substrate, wherein the diameters of the immersion member and the electrode are set to be equal to or larger than the effective diameter of the substrate, and wherein the feeding contacts are provided opposite the peripheral end portion of the substrate held by the substrate holder. 
     
    
     BRIEF DESCRIPTION OF THE DRAWINGS  
       [0043]      FIG. 1  is a diagram schematically showing the construction of a conventional plating apparatus;  
         [0044]      FIG. 2  is a cross-sectional view showing the construction of a feeding section of a conventional substrate holder;  
         [0045]      FIG. 3  is a perspective view, as viewed from below, of a conventional feeding section including a feeding ring having feeding contacts mounted thereto;  
         [0046]      FIG. 4  is a perspective view, as viewed from below, of another feeding section including a feeding ring having feeding contacts mounted thereto, the feeding contacts being electrically insulated from each other;  
         [0047]      FIG. 5A  is a plan view showing the construction of feeding contacts provided in the feeding section of the substrate holder of a conventional plating apparatus, and  FIG. 5B  is a cross-sectional view taken along the line A-A of  FIG. 5A ;  
         [0048]      FIG. 6  is a schematic diagram showing the construction of another conventional plating apparatus;  
         [0049]      FIG. 7  is a schematic cross-sectional view showing the main portion of yet another conventional plating apparatus adapted to reduce an amount of plating solution;  
         [0050]      FIG. 8  is a plan view showing yet another feeding section of a substrate holder of a plating apparatus;  
         [0051]      FIG. 9  is a graph showing the distribution of a thickness of a plated film in a peripheral portion of a substrate as the plated film is formed on a surface of the substrate by using the feeding section of  FIG. 8 ;  
         [0052]      FIG. 10  is a plan view (taken along the line A-A of  FIG. 12 ) showing a feeding ring and feeding contacts, together constituting the feeding section of the substrate holder of a plating apparatus according to an embodiment of the present invention;  
         [0053]      FIG. 11  is a bottom view of the feeding ring shown in  FIG. 10 ;  
         [0054]      FIG. 12 a  cross-sectional view showing the state of electricity feeding from the feeding ring and the feeding contacts shown in  FIG. 10 ;  
         [0055]      FIG. 13  is a perspective view of the substrate chuck shown in  FIG. 12 ;  
         [0056]      FIG. 14  is a perspective view, partly broken away, showing part of the substrate holder of the plating apparatus according to the embodiment of the present invention;  
         [0057]      FIG. 15  is a graph showing the distribution of a thickness of a plated film in a peripheral portion of a substrate as the plated film is formed on a surface of the substrate by using the plating apparatus according to the embodiment of the present invention;  
         [0058]      FIG. 16  is a schematic cross-sectional view showing the main portion of a plating apparatus according to another embodiment of the present invention; and  
         [0059]      FIG. 17  is a schematic cross-sectional view showing the main portion of a plating apparatus according to yet another embodiment of the present invention. 
     
    
     DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENTS  
       [0060]     Preferred embodiments of the present invention will now be described with reference to the drawings. In the drawings, the same parts or members as those shown in  FIGS. 1 through 8  are shown with the same reference numerals.  
         [0061]      FIG. 10  is a plan view (taken along the line A-A of  FIG. 12 ) showing a feeding ring  19  and feeding contacts  15 , together constituting the feeding section of the substrate holder  11  (see  FIG. 1 ) of a plating apparatus according to an embodiment of the present invention. The feeding ring  19 , together with the feeding contacts  15  mounted thereto, forms, as a whole, the circular ring-shaped feeding section.  FIG. 10  shows the connection between the feeding ring  19  and the feeding contacts  15 .  FIG. 11  is a bottom view (as viewed from below) of the feeding ring  19 . A sealing member  23  covering the upper surface of the feeding ring  19  appears between the feeding contacts  15 . Each feeding contact  15  can be produced by subjecting a metal plate of, for example, phosphor bronze, having elasticity and high electric conductivity, to sheet metal processing or the like. Though not shown in  FIG. 11 , holes are formed in the lower surface of the feeding ring  19  at the positions of feeding contacts  15  so that the feeding contacts  15  are screwed up. Instead of the feeding contacts  15 , it is also possible to mount the circular ring-shaped feeding contacts  15 , each having a plurality of contact strips  15   a  integrally formed with the feeding contact, which has the same construction shown in  FIG. 5A , to the feeding ring  19 .  
         [0062]      FIG. 12  is a cross-sectional view showing the state of electricity feeding from the feeding ring  19  and the feeding contacts  15  to a substrate W. Six substrate chucks  21  are provided at regular intervals around an annular flat stage  22  (see  FIG. 14 ) provided to support the peripheral portion of the substrate W from below. The peripheral end portion of the substrate W is placed on the substrate chucks  21  to hold the substrate W by pressing it from above. By holding the substrate W in this manner, the substrate W can be prevented from warping or deflecting. The flat stage  22  is one example of a substrate deflection preventing mechanism. According to this embodiment, the substrate W is adapted to be held by clamping the substrate W from above and below by the sealing member  23  and the flat stage (substrate deflection preventing mechanism)  22 . The feeding contacts  15  project from a lower portion of the feeding ring  19 , and their tips contact the substrate W to feed electricity to the substrate W.  
         [0063]     The substrate chuck  21  has a structure as shown in  FIG. 13 . The feeding contact  15  passes between guides  24 , which are provided for stopping the peripheral end portion of the substrate W, so that the guides  24  and the feeding contacts  15  do not interfere with each other, and electricity can be fed to the substrate W even at the site of substrate chuck  21 , thus avoiding non-uniform feeding of electricity to the substrate W.  
         [0064]      FIG. 14  is a perspective view illustrating the electrode structure of the above-described substrate holder. As shown in  FIG. 14 , the feeding contacts  15  mounted to the feeding ring  19  contact a conductive portion (not shown) formed in the surface of the peripheral portion of the substrate W, which is held by clamping of the peripheral portion from above and below by the substrate chucks  21 , the flat stage  22  and the sealing member  23 , whereby the conductive portion and the feeding contacts  15  are electrically connected.  FIG. 14  shows the substrate holder when the substrate W is on the flat stage  22 . Therefore, the flat stage  22 , lying under the substrate W, is not visible and hence is shown by broken lines. The feeding contacts  15 , lying under the feeding ring  19 , are also invisible and are shown by broken lines. However, the feeding ring  19  is partly broken away to show the substrate chucks  21 , and the substrate W is also broken away as shown. As can be seen from  FIG. 14 , the feeding contact  15  passes between the guides  24  of the substrate chuck  21 .  
         [0065]      FIGS. 10 and 11  clearly show that the electrode contacts  15  are uniformly distributed in the circumferential direction. As a result, as shown in  FIG. 15 , variation in the thickness of a plated film formed on a peripheral portion of a substrate, such as a semiconductor wafer, is considerably improved, or reduced as compared to variation in the thickness of a plated film as formed by use of the feeding section in which the distances between adjacent contacts are not equal (non-uniform distribution of contacts), as shown in  FIG. 9 . Thus, a plated film with sufficiently small thickness variation can be formed on a peripheral portion of a substrate, such as a semiconductor wafer.  
         [0066]     The substrate holder (electrode) of the plating apparatus, described hereinabove, can be advantageously employed not only for a dip-type plating apparatus, but also for a face down-type plating apparatus or a variant thereof equally as well. With respect to a plating solution, besides a copper sulfate plating solution for copper plating, a plating solution for other metal plating can, of course, be used.  
         [0067]     The plating apparatus of the present invention, which, owing to the substrate holder, can form a plated film having a uniform thickness on a substrate, such as a semiconductor wafer, is useful in the field of semiconductor manufacturing, etc. Further, because of the capability to form a plated film having a uniform thickness, the plating apparatus can easily form copper interconnects which have a larger current capacity than aluminum interconnects or the like. The present plating apparatus can therefore be advantageously used especially for the production of semiconductor devices which need fine interconnects.  
         [0068]      FIG. 16  shows a cross-sectional view of the main portion of a plating apparatus according to another embodiment of the present invention.  
         [0069]     This plating apparatus forms a copper film by electroplating on a substrate, such as a semiconductor wafer for a semiconductor device, in particular an LSI which is becoming finer and multi-level structure to meet the demand for higher speed and lower power consumption. As shown in  FIG. 16 , the plating apparatus  51  includes a substrate holder  11  for holding a substrate W with its front surface facing upwardly. A plating solution holding portion for holding a plating solution Q is formed by the substrate holder  11  and the substrate W held by the substrate holder  11 . The plating apparatus  51  includes an immersion member (in-liquid immersion member)  34  disposed opposite the substrate W, held by the substrate holder  11 , at a predetermined distance therefrom, which is to be immersed in the plating solution Q held in the plating solution holding portion to exclude the plating solution Q, a holding assembly  33  for holding the immersion member  34  by a rubber shielding ring  35  in order to forcibly immerse the immersion member  34  in the plating solution Q, an electrode (anode)  13  located within the plating solution holding portion and preferably attached to the upper surface of the immersion member  34 ,and a sealing member  18  for sealing the gap between the substrate W and the substrate holder  11  on the back surface side of the substrate W.  
         [0070]     In the thus-constructed plating apparatus  51 , a plurality of feeding contacts  15  for feeding electricity from a plating power source  14  (see  FIG. 6 ) to a conductive portion of the substrate W are mounted, in the form of fixed pins, to a projecting portion  54 , projecting into the plating solution Q, of the substrate holder  11 . The feeding contacts  15  contact the peripheral end portion of the front surface of the substrate W to feed electricity to the conductive portion of the substrate W. This construction makes it possible to plate a wide area, except the peripheral end portion, of the surface of the substrate W. The feeding contacts  15  are immersed in the plating solution Q when they are in contact with the peripheral end portion of the surface of the substrate W. In this regard, corrosion resistance can be imparted to the feeding contact  15  by the provision of a corrosion resistant coating or by the use of a corrosion resistant material. The feeding contact  15  can be much shorter than the conventional ones shown in  FIG. 7 . The feeding contact  15  may not necessarily be of the shape of a pin, but may be of the shape of a continuous ring extending over the inner circumference of the substrate holder  11 .  
         [0071]     In the plating apparatus  51 , an electric current is supplied from the plating power source  14  (see  FIG. 6 ) with the substrate W as a cathode and the electrode  13  as an anode. A plating solution Q is supplied into the plating solution holding portion formed by the substrate W and the substrate holder  11 , and a copper film is formed on the surface of the substrate W by passing electricity through the plating solution Q in the plating solution holding portion.  
         [0072]     In the plating apparatus  51 , the immersion member  34  needs to achieve the objective of reducing the amount of plating solution Q held in the plating solution holding portion formed by the substrate W and the substrate holder  11 . The immersion member  34  is composed of, for example, a continuous cell-type porous ceramic, and is non-conductive and thus acts as a resistance. By disposing the immersion member  34  between the substrate W and the electrode  13 , and forming long channels of plating solution in the continuous cells throughout the immersion member  34  to thereby raise the average electric resistance, it becomes possible to uniformize the thickness distribution of a plated film formed on the surface of the substrate. When the electric resistance between the electrode  13  and the substrate W is low, electric current concentrates on the feeding contact side (peripheral region of substrate). This is because of the high resistance of a seed film formed in the substrate surface. The thickness distribution of a plated film formed on the surface of the substrate can therefore be uniformized by disposing a resistant material, having a higher resistance than the seed film, i.e., the immersion member  34 , between the electrode  13  and the substrate W. A ceramic, a synthetic resin, a rubber, etc. can be preferably used as a material for the immersion member  34 . A foamed material may be used when a lightweight member is desired. The formed material should be one durable to the plating solution.  
         [0073]     An elastic material, such as a synthetic rubber or resin, is preferably used for the sealing member  18  for sealing the gap between the substrate W and the substrate holder  11  in order to prevent leakage of the plating solution Q in the plating solution holding portion formed by the substrate holder  11  and the substrate W held by the substrate holder  11 . A fluorocarbon rubber having excellent elasticity, heat resistance and chemical resistance is most preferably used.  
         [0074]     Examples of the fluorocarbon rubber include a propylene hexafluoride-chlorotrifluoroethylene-vinylidene fluoride terpolymer rubber, a tetrafluoroethylene-propylene copolymer rubber, a fluorine-containing polyacrylate rubber, a fluorine-containing polyester rubber, and a fluorinated phosphazene rubber.  
         [0075]     A description will now be given of feeding of electricity to a substrate W in the plating apparatus  51 .  
         [0076]     In the plating apparatus  51 , a substrate W is held by the substrate holder  11  by clamping the peripheral portion, as described above. In the plating apparatus  51 , the plurality of fixed pin-shaped feeding contacts  15 , mounted to the projecting portion  54  of the substrate holder  11  as an electrode, lie between the projecting portion  54  and the substrate W, and contact a conductive portion (not shown) of the substrate W to feed electricity thereto. The feeding contacts  15  are disposed at regular intervals over the peripheral portion of the substrate W so that they make point contact or line contact with the surface conductive portion of the substrate W in the entire peripheral area of the substrate W.  
         [0077]     The substrate holder  11  for holding the substrate W by clamping its peripheral portion, together with the feeding contacts  15  disposed between the projecting portion  54  and the surface conductive film of the peripheral portion of the substrate W, constitutes a feeding section. Accordingly, the substrate holder  11  is formed of a conductive material, preferably a metal. The substrate holder  11  protrudes to above the surface of the substrate W at such a height as to sufficiently hold the plating solution Q even when the plating solution Q is excluded by the immersion member  34  and the liquid surface rises. The substrate holder  11  has a tapered inner surface, and the projecting portion  54  for mounting the fixed pin-shaped feeding contacts  15  thereto is formed at the lower end of the tapered surface. The feeding contacts  15  are formed of, for example, copper or a noble metal such as gold, silver or platinum.  
         [0078]     In this plating apparatus  51 , when the substrate W is held by the substrate holder  11 , the feeding contacts  15  come into contact with the surface conductive portion of the peripheral portion of the substrate W, whereby electricity is fed to the surface of the substrate W from the peripheral portion of the substrate W through the conductive portion.  
         [0079]     According to the plating apparatus  51 , by thus carrying out feeding of electricity to the surface (surface to be plated) of the substrate W from the peripheral side of the substrate W and by the evenly-spaced feeding contacts  15 , stable feeding with a uniform current density distribution becomes possible. Accordingly, it becomes possible with the plating apparatus  51  to form, by electroplating, a copper film having a uniform thickness on the surface (surface to be plated) of the substrate W.  
         [0080]     Further, unlike the conventional plating apparatus as shown in  FIG. 7 , there is no need to provide a support on the back surface side of a substrate and clamp the peripheral portion of the substrate by the support and the packing portion of a frame for tight contact of the packing portion with the substrate. There is, therefore, no fear of distortion or warpage of the substrate W, enabling the formation of a plated film having a uniform thickness over the entire surface of the substrate W.  
         [0081]     In addition, the diameters of the immersion member  34  and the electrode  13  are equal to or larger than the effective diameter of the substrate W, and the plating solution Q is present over the entire surface of the substrate W. This can broaden the effective plating area as compared to the conventional plating apparatus shown in  FIG. 7 , and enables the formation of a plated film having a uniform thickness over the entire surface of the substrate W.  
         [0082]      FIG. 17  shows a cross-sectional view of the main portion of a plating apparatus according to yet another embodiment of the present invention.  
         [0083]     The plating apparatus  51  only differs in electrical connection between a substrate W and a substrate holder  11  from the plating apparatus shown in  FIG. 16 . Since the other construction is the same, a description thereof is omitted, and a description is made only of the electrical connection.  
         [0084]     Referring to  FIG. 17 , a substrate holder  11  for clamping the periphery of a substrate W, together with feeding contacts  15  mounted to the substrate holder  11 , constitutes a feeding section. The feeding contacts  15  are for contact with the bevel portion (upper peripheral inclined surface)  46  of the substrate W. As apparent from  FIG. 17 , the inner surface of the substrate holder  11  is only tapered and thus simplified as compared to the substrate holder of  FIG. 16 . Though the feeding contacts  15  are preferably provided on the tapered surface of the substrate holder  11 , it is also possible to place the feeding contacts  15 , in the form of a ring as a whole, on the bevel portion  46  of the substrate W so that they come into electrical contact upon holding of the substrate W by the substrate holder  11 .  
         [0085]     The feeding contacts  15  may only be provided at regular intervals on the tapered surface of the annular substrate holder  11 . Further, feeding of electricity to the substrate W can be carried out in the bevel portion of the substrate W, and not the front surface for which flatness is required in the manufacturing of semiconductor device. Accordingly, the electricity feeding to the substrate W according to this embodiment exerts no adverse influence on flattening of the front surface.  
         [0086]     Further, by simply clamping the feeding contacts  15 , each in the form of a plate-like strip, between the bevel portion of the substrate W and the lower inclined surface of the substrate holder  11 , electrical connection can be made more securely as compared to the case shown in  FIG. 16 .  
         [0087]     In the embodiments shown in  FIGS. 16 and 17 , it is also possible to use, as the feeding contacts  15  provided in the substrate holder  11 , the feeding contacts  15  of the feeding ring  19  used in the embodiment shown in FIGS.  10  to  14 . Further, the plating apparatuses of the embodiments shown in  FIGS. 16 and 17  may also include the substrate chucks  21  and the flat stage  22  as a substrate deflection preventing mechanism, both used in the embodiment shown in FIGS.  10  to  14 .  
         [0088]     This can equalize the contact resistances at the contact points, thereby preventing variation in the film thickness of a plated film formed on a peripheral portion of a substrate, such as a semiconductor wafer. A plated film having a uniform thickness can thus be formed over the broadened effective plating area of the substrate.  
         [0089]     The plating apparatus of the present invention, which can form a plated film having a uniform thickness on a substrate and can take a broad plating area, is useful in the field of the production of articles with a mirror-like surface where the formation of a metal film having a uniform thickness on the surface (surface to be plated) of a substrate, such as a semiconductor wafer, a quartz substrate or a glass substrate, is required.  
         [0090]     The plating apparatus of the present invention, which can form a uniform plated film over the entire surface of a substrate and can take a broad plating area, is especially useful for the production at a low cost of semiconductor devices, in particular LSIs, for use in electronics which are required to be small-sized, high-performance and multifunctional ones.