Patent Publication Number: US-2022228285-A1

Title: Plating method, insoluble anode for plating, and plating apparatus

Description:
TECHNICAL FIELD 
     The present invention relates to a plating method, an insoluble anode for plating, and a plating apparatus. 
     BACKGROUND ART 
     Heretofore, a wiring has been formed in a fine wiring groove, hole or resist opening provided in a surface of a semiconductor wafer or the like, and a bump (a protruding electrode) to be electrically connected to an electrode of a package or the like has been formed on the surface of the semiconductor wafer or the like. As a method of forming this wiring and bump, for example, an electroplating method, an evaporation method, a printing method, a ball bump method or the like is known, but with increase in an I/O number of semiconductor chips and for a finer pitch, the electroplating method is becoming often used in which miniaturization is possible and performance is relatively stable. 
     A plating apparatus for use in the electroplating method includes a substrate holder holding a substrate of a semiconductor wafer or the like, an anode holder holding an anode, and a plating solution tank that stores a plating solution containing a large number of types of additives. When a substrate surface of the semiconductor wafer or the like is plated in this plating apparatus, the substrate holder is disposed to face the anode holder in the plating solution tank. In this state, the substrate and the anode are energized, and accordingly a plating film is formed on the substrate surface. In addition, the additive has an effect of accelerating or suppressing a film formation speed of the plating film, an effect of improving film quality of the plating film, and the like. 
     Heretofore, a soluble anode that dissolves in the plating solution or an insoluble anode that does not dissolve in the plating solution has been used as the anode. In a case where the plating is performed by using the insoluble anode, oxygen is generated by reaction between the anode and the plating solution. The additive in the plating solution reacts with this oxygen and is decomposed. There is a problem that, when the additive is decomposed, the additive loses the above-described effects, and a desired film cannot be obtained on the substrate surface (e.g., see PTL 1). To prevent this problem, the additive may be added to the plating solution as required to keep concentration of the additive in the plating solution in a predetermined concentration or more. However, the additive is expensive, and hence it is desirable to inhibit the decomposition of the additive as much as possible. 
     Furthermore, a technology of forming a plurality of through electrodes made of a metal such as copper and extending through the substrate in an up-down direction in an interior of the substrate is known as means for conducting between respective layers when stacking a conductor substrate on each of multiple layers (e.g., see PTL 1).  FIG. 14  is a diagram showing an example of manufacturing a substrate including a through electrode. First, as shown in  FIG. 14A , a substrate W is prepared in which a plurality of recesses  112  for through electrodes that open upward are formed in an interior of a base material  110  made of silicon or the like, for example, by a lithography and etching technology. Each of the recesses  112  for the through electrodes has a diameter, for example, from 1 to 100 μm, especially from 10 to 20 μm, and a depth, for example, from 70 to 150 μm. Then, a seed layer  114  made of copper or the like is formed as a power supply layer for electroplating on the surface of the substrate W by sputtering or the like. 
     Next, the surface of the substrate W is electroplated with copper, and as shown in  FIG. 14B , an interior of each recess  112  for the through electrode of the substrate W is filled with a copper plating film  116 , and the copper plating film  116  is deposited on the surface of the seed layer  114 . 
     Afterward, as shown in  FIG. 14C , excessive portions of the copper plating film  116  and seed layer  114  on the base material  110  are removed by chemical mechanical polishing (CMP) or the like, and additionally, a back surface side of the base material  110  is polished and removed until a bottom surface of the copper plating film  116  with which the interior of the recess  112  for the through electrode is filled is exposed to outside. Consequently, the substrate W is completed in which a plurality of through electrodes  118  made of copper (the copper plating films  116 ) and extending through the substrate in the up-down direction are included. 
     In the recess  112  for the through electrode, a ratio of a depth to a diameter, that is an aspect ratio, is generally large, and it usually takes long period of time to completely fill the interior of the recess  112  for the through electrode having such a large aspect ratio with the copper film (the plating film) formed by electroplating without causing a defect such as a void in the recess. 
     CITATION LIST 
     Patent Literature 
     
         
         PTL 1: Japanese Patent Laid-Open No. 7-11498 
       
    
     SUMMARY OF INVENTION 
     Technical Problem 
     Heretofore, a method of increasing a surface area of an anode and decreasing an anode current density during plating has been performed as a method of decreasing an amount of oxygen to be generated around the anode to reduce consumption of an additive in a plating solution. Here, when a substrate including a via or a hole having a large aspect ratio for forming a through electrode is plated, a current during plating is reduced so that a defect such as a void is not caused. However, according to investigation by present inventors, it has been found that the consumption of the additive might increase even during the plating of the substrate in which the through electrode is to be formed. More specifically, according to the investigation by the present inventors, it has been seen that, when the anode current density during the plating is excessively small, the generation of oxygen decreases, but instead, generation of hypochlorous acid increases, and decomposition of the additive is accelerated due to effect of increased hypochlorous acid. 
     Furthermore, in a case where the surface area of the anode is changed to regulate the anode current density to reduce the consumption of the additive, there is concern that, when the surface area of the anode is simply changed, uniformity of plating formed on the substrate might be impaired. 
     The present invention has been developed in view of the above problems, and one of objects thereof is to provide a plating method, an insoluble anode and a plating apparatus capable of reducing consumption of an additive in a plating solution, when plating a substrate including a via or a hole for forming a through electrode. 
     Solution to Problem 
     According to an embodiment of the present invention, a plating method is provided, and the plating method includes the steps of preparing a substrate including a via or a hole for forming a through electrode, preparing a plating solution tank that is divided, by a diaphragm, into an anode tank in which an insoluble anode is disposed and a cathode tank in which the substrate is disposed, and electroplating the substrate with an anode current density when plating the substrate in the plating solution tank being equal to or more than 0.4 ASD (A/cm 2 ) and equal to or less than 1.4 ASD. According to this plating method, generation of oxygen and hypochlorous acid during the plating can be inhibited, and consumption of an additive in a plating solution can be reduced. 
     According to another embodiment of the present invention, an insoluble anode for plating that is disposed in a plating solution tank for use in the plating is provided, and the insoluble anode includes a power supply point to be connected to a power source, a ring electrode having a ring shape around the power supply point, and a connection electrode connecting the power supply point and the ring electrode. According to this insoluble anode for plating, generation of oxygen and hypochlorous acid during the plating can be inhibited, and consumption of an additive in a plating solution can be reduced. Furthermore, in-plane uniformity of plating formed on the substrate can be improved. 
    
    
     
       BRIEF DESCRIPTION OF DRAWINGS 
         FIG. 1  is a schematic view showing a plating apparatus according to a first embodiment; 
         FIG. 2  is a plan view of an anode holder according to the present embodiment; 
         FIG. 3  is a side cross-sectional view of an anode holder  60  taken along the 3-3 line shown in  FIG. 2 ; 
         FIG. 4  is an exploded perspective view of the anode holder in a state where a holder base cover is removed; 
         FIG. 5  is a plan view of the anode holder in the state where the holder base cover is removed; 
         FIG. 6  is a flowchart showing an example of a plating method in the present embodiment; 
         FIG. 7  is a view showing a first example of an anode in the present embodiment; 
         FIG. 8  is a view showing a second example of the anode in the present embodiment; 
         FIG. 9  is a view showing a third example of the anode in the present embodiment; 
         FIG. 10  is a view showing a fourth example of the anode in the present embodiment; 
         FIG. 11  is a view showing a fifth example of the anode in the present embodiment; 
         FIG. 12  is a view showing a sixth example of the anode in the present embodiment; 
         FIG. 13  is a schematic view showing a plating apparatus according to a second embodiment; and 
         FIG. 14  is a view showing an example of manufacturing of a substrate including a through electrode. 
     
    
    
     DESCRIPTION OF EMBODIMENTS 
     Hereinafter, embodiments of a plating method, an insoluble anode for plating and a plating apparatus according to the present invention will be described with reference to the accompanying drawings. In the accompanying drawings, the same or similar element is denoted with the same or similar reference sign, and in descriptions of the respective embodiments, a description concerning the same or similar element may not be repeated. Also, characteristics illustrated in the respective embodiments are also applicable to another embodiment as long as the characteristics of the embodiments are not contradictory to each other. 
     First Embodiment 
       FIG. 1  is a schematic view showing a plating apparatus according to a first embodiment. As shown in  FIG. 1 , the plating apparatus includes a plating solution tank  50  holding a plating solution inside, an anode  40  disposed in the plating solution tank  50 , an anode holder  60  holding the anode  40 , and a substrate holder  18 . The substrate holder  18  removably holds a substrate W such as a wafer, and is configured to immerse the substrate W into the plating solution in the plating solution tank  50 . The plating apparatus according to the present embodiment is an electroplating apparatus that applies current through the plating solution to plate a surface of the substrate W with a metal. As the anode  40 , used is an insoluble anode made of, for example, titanium coated with iridium oxide or platinum that does not dissolve in the plating solution. 
     The substrate W is, for example, a semiconductor substrate, a glass substrate, or a resin substrate. The metal with which the surface of the substrate W is plated is, for example, copper (Cu), nickel (Ni), tin (Sn), Sn—Ag alloy, or cobalt (Co). 
     The anode  40  and the substrate W are arranged to extend in a vertical direction, that is, so that plate surfaces of the anode  40  and the substrate W face in a horizontal direction and face each other in the plating solution. The anode  40  is connected to a positive electrode of a power source  90  via the anode holder  60 , and the substrate W is connected to a negative electrode of the power source  90  via the substrate holder  18 . When a voltage is applied between the anode  40  and the substrate W, current flows to the substrate W, and a metal film is formed on the surface of the substrate W in the presence of the plating solution. 
     The plating solution tank  50  includes a plating solution storage tank  52  in which the substrate W and the anode  40  are arranged, and an overflow tank  54  disposed adjacent to the plating solution storage tank  52 . The plating solution in the plating solution storage tank  52  flows over a side wall of the plating solution storage tank  52  to flow into the overflow tank  54 . 
     One end of a plating solution circulation line  58   a  is connected to a bottom of the overflow tank  54 , and the other end of the plating solution circulation line  58   a  is connected to a bottom of the plating solution storage tank  52 . A circulation pump  58   b , a constant temperature unit  58   c  and a filter  58   d  are attached to the plating solution circulation line  58   a . The plating solution flows over the side wall of the plating solution storage tank  52  to flow into the overflow tank  54 , and further flows from the overflow tank  54  through the plating solution circulation line  58   a  to return to the plating solution storage tank  52 . Thus, the plating solution circulates between the plating solution storage tank  52  and the overflow tank  54  through the plating solution circulation line  58   a.    
     The plating apparatus further includes a regulation plate  14  that regulates a potential distribution on the substrate W, and a paddle  16  that stirs the plating solution in the plating solution storage tank  52 . The regulation plate  14  is disposed between the paddle  16  and the anode  40 , and includes an opening  14   a  for limiting an electric field in the plating solution. The paddle  16  is disposed in the vicinity of the surface of the substrate W held by the substrate holder  18  in the plating solution storage tank  52 . The paddle  16  is made of, for example, titanium (Ti) or resin. The paddle  16  reciprocates in parallel with the surface of the substrate W, to stir the plating solution so that metal ions are sufficiently and uniformly supplied to the surface of the substrate W during the plating of the substrate W. 
       FIG. 2  is a plan view of the anode holder  60 ,  FIG. 3  is a side cross-sectional view of the anode holder  60  taken along the 3-3 line shown in  FIG. 2 ,  FIG. 4  is an exploded perspective view of the anode holder  60  in a state where a holder base cover  63  is removed, and  FIG. 5  is a plan view of the anode holder  60  in the state where the holder base cover  63  is removed. Note that  FIG. 5  shows, for convenience, the anode holder  60  in a state where a grip  64 - 2  is transparent. Furthermore,  FIGS. 4 and 5  show, for convenience, the anode holder  60  in a state where the anode  40  is removed. Further, in the present description, “up” and “down” refer to an upward direction and a downward direction in a state where the anode holder  60  is vertically housed in the plating solution tank  50 . Similarly, in the present description, “a front surface” refers to a surface on a side on which the anode holder  60  faces the substrate holder, and “a back surface” refers to a surface on a side opposite to the front surface. 
     As shown in  FIGS. 2 to 4 , the anode holder  60  according to the present embodiment includes a substantially rectangular holder base  62  including an inner space  61  that houses the anode  40 , a pair of grips  64 - 1  and  64 - 2  formed in an upper part of the holder base  62 , and a pair of arms  70 - 1  and  70 - 2  similarly formed in the upper part of the holder base  62 . Also, the anode holder  60  includes the holder base cover  63  that partially covers a front surface of the holder base  62 , a diaphragm  66  disposed on a front surface of the holder base cover  63  to cover the inner space  61 , and an outer edge mask  67  disposed on a front surface of the diaphragm  66 . Additionally, in the present embodiment, the inner space  61  of the anode holder  60  corresponds to “an anode tank”, and an outer space corresponds to “a cathode tank”. 
     As shown in  FIGS. 2 and 5 , the holder base  62  includes a hole  71  extending from an outer surface of a lower part to the inner space  61  of the holder base, and communicating with the inner space  61 . Also, the holder base  62  includes an air outlet  81  for exhausting air of the inner space  61 , between the grips  64 - 1  and  64 - 2  in the upper part of the holder base. When the holder base  62  is immersed into the plating solution, the plating solution flows through the hole  71  into the inner space  61 , and air of the inner space  61  is exhausted from the air outlet  81 . Furthermore, in a case where the insoluble anode is used as the anode  40 , oxygen generated from the anode  40  during the plating is also exhausted through the air outlet  81 . The air outlet  81  is closed with a lid  83  formed so that the exhaust of air is not obstructed. 
     Also, as shown in  FIG. 3 , an annular opening  63   a  having a diameter larger than a diameter of the anode  40  is formed in a substantially central portion of the holder base cover (base body)  63 . The holder base cover  63  forms the inner space  61  together with the holder base  62 . The diaphragm  66  is disposed on a front surface of the opening  63   a , to close the inner space  61 . A diaphragm retainer  68  is attached in front of an outer peripheral edge of the diaphragm  66 , and the outer edge mask  67  is disposed in front of the diaphragm retainer  68 . Also, an annular first sealing member  84  including, for example, an O-ring or the like is disposed along the opening  63   a  in the front surface of the holder base cover  63 . The diaphragm  66  is pressed onto the first sealing member  84  by the diaphragm retainer  68 , to seal the opening  63   a . That is, a gap between the diaphragm  66  and the inner space  61  can be sealed with the first sealing member  84 . Consequently, the inner space  61  and the outer space are divided by the diaphragm  66 . 
     The diaphragm  66  is, for example, an ion exchange membrane such as a cation exchange membrane, or a neutral diaphragm. During plating, cations can pass through the diaphragm  66  from an anode side to a cathode side while any additive in the plating solution does not pass. A specific example of the diaphragm  66  is YUMICRON (registered trademark) manufactured by Yuasa Membrane Systems Co., Ltd. 
     The outer edge mask  67  is a plate-shaped member including an annular opening in a central portion, and is detachably attached to a front surface of the diaphragm retainer  68 . The outer edge mask  67  is disposed to control the electric field in the surface of the anode  40  during the plating. The outer edge mask  67  may have a diameter of the opening that is larger than an outer diameter of the anode  40 , and may have an outer shape smaller than an outer shape of the anode  40 . Alternatively, the anode holder  60  does not have to include the outer edge mask  67 . 
     The holder base cover  63  is fixed to the holder base  62  by screw connection, welding or the like, and the holder base cover  63  is closely connected to the holder base  62 . Alternatively, the holder base cover  63  may be formed integrally with the holder base  62 . 
     As shown in  FIGS. 2, 4 and 5 , the grips  64 - 1  and  64 - 2  are coupled with the holder base  62  via couplings  62 - 1  and  62 - 2  formed in the upper part of the holder base  62 . The grips  64 - 1  and  64 - 2  are formed to extend from the couplings  62 - 1  and  62 - 2  toward a center of the holder base  62 . The grips  64 - 1  and  64 - 2  are gripped with an unshown chuck, when the anode holder  60  is conveyed to the plating solution tank  50 . 
     An electrode terminal  82  for applying a voltage to the anode  40  is disposed in a lower part of the arm  70 - 1  extending outward from the couplings  62 - 1  and  62 - 2 . The electrode terminal  82  is connected to the positive electrode of the power source  90 , when the anode holder  60  is housed in the plating solution tank. Also, the anode holder  60  includes a power supply member  89  extending from the electrode terminal  82  to a substantially central portion of the inner space  61 . The power supply member  89  is a substantially plate-shaped conductive member, and electrically connected to the electrode terminal  82 . 
     As shown in  FIG. 3 , the anode  40  is fixed to a front surface of the power supply member  89  with a fixing member  88  including, for example, a screw and the like. Consequently, the voltage can be applied from the power source  90  to the anode  40  via the electrode terminal  82  and the power supply member  89 . 
     An annular opening  62   a  for changing the anode  40  is formed in a substantially central portion of the holder base  62 , that is, at a position corresponding to the fixing member  88 . The opening  62   a  communicates with a back surface side of the inner space  61 , and is covered with a lid  86 . On a back surface side of the holder base  62 , an annular second sealing member  85  including, for example, an O-ring or the like is disposed along the opening  62   a . A gap between the opening  62   a  and the lid  86  is sealed with the second sealing member  85 . 
     The lid  86  is removed when the anode  40  is changed. Specifically, for example, with elapse of useful life of the anode  40 , an operator removes the lid  86 , and removes the fixing member  88  via the opening  62   a . The operator removes the outer edge mask  67  from the diaphragm retainer  68 , and removes the anode  40  from the inner space  61 . Subsequently, the operator houses another anode  40  in the inner space  61 , and fixes the anode  40  to the front surface of the power supply member  89  with the fixing member  88  via the opening  62   a . Lastly, the operator seals the opening  62   a  with the lid  86 , and attaches the outer edge mask  67  to the diaphragm retainer  68 . 
     A weight  87  is attached to a back surface of the holder base  62 . Consequently, the anode holder  60  can be prevented from floating on a surface of water due to buoyancy, when the anode holder  60  is immersed into the plating solution. 
     As shown in  FIG. 5 , the anode holder  60  further includes a valve  91  configured to seal the hole  71 , a spring  96  for biasing the valve  91  to close the valve  91 , a shaft  93  for transmitting biasing force of the spring  96  to the valve  91 , a push rod  95  as an operation member that operates the valve  91  to open and close the valve, and an intermediate member  94  for transmitting, to the shaft  93 , force applied to the push rod  95 . 
     The valve  91  is disposed in the holder base  62  so that the hole  71  can be sealed on an inner side of the holder base  62 . The shaft  93  is disposed along an up-down direction in the holder base  62 . The shaft  93  has one end coupled to the valve  91 , and the other end coupled to the spring  96 . Consequently, the shaft  93  transmits the biasing force of the spring  96  to the valve  91 , and the valve  91  is biased so that the hole  71  is sealed with the valve  91  on the inner side of the holder base  62 . 
     Thus, the anode holder  60  includes the valve  91  that seals the hole  71 , so that the hole  71  can be sealed, after the anode holder  60  is immersed into the plating solution to fill the inner space  61  with the plating solution. Consequently, if oxygen, hypochlorous acid or monovalent copper is generated in the vicinity of the anode  40 , proceeding of decomposition of the additive can be inhibited, because the outer space and the inner space  61  are divided. Alternatively, in the plating apparatus, the anode holder  60  may be disposed in the plating solution storage tank  52  in a state where a base liquid is put in the plating solution storage tank  52 , the inner space  61  of the anode holder  60  may be filled with the base liquid and then sealed, and a liquid containing the additive may be put in the plating solution storage tank  52  to prepare the plating solution in the outer space. In this case, the inner space  61  of the anode holder  60  does not store the additive, and hence consumption of the additive in the vicinity of the anode  40  can be reduced more. However, the present invention is not limited to this example, and the anode holder  60  may be disposed in the plating solution storage tank  52  in a state where the plating solution containing the additive is put in the plating solution storage tank  52 , and the inner space  61  of the anode holder  60  may be filled with the plating solution containing the additive and then sealed. 
     Next, a description will be made as to a plating method of the present embodiment with reference to  FIG. 6 . Note that in the following description, steps are described in order for ease of a description, but the plating method is not limited to the steps to be executed in order as in  FIG. 6  and the following description. That is, the respective steps may be executed by changing the order of the steps unless there is any contradiction. 
     In the plating method of the present embodiment, first, the substrate W including the via or the hole for forming the through electrode is prepared (S 10 ). As an example, as shown in  FIG. 14A , the substrate W is prepared in which a plurality of recesses  112  for the through electrodes that open upward are formed in the base material  110  made of silicon or the like, for example, by a lithography and etching technology. Each recess  112  for the through electrode has a diameter, for example, from 1 to 100 μm, preferably from 5 to 20 μm, and a depth, for example, from 70 to 150 μm. Note that in the substrate W, a hole extending through the substrate in the up-down direction may be formed in place of or in addition to the recesses (vias) for the through electrodes. 
     Subsequently, a plating solution tank is prepared (S 20 ). In the present embodiment, the plating solution tank  50  in the above-described plating apparatus is prepared. The plating solution tank  50  is divided, by the diaphragm  66 , into the inner space  61  (the anode tank in which the anode  40  is disposed) and the outer space (the cathode tank in which the substrate W is disposed). 
     Next, the anode  40  is designed and prepared (S 30 ). Specifically, the anode  40  is designed and prepared in terms of size and shape so that current density in the anode  40  (hereinafter, referred to as “the anode current density)”) when plating the substrate W in the plating solution tank  50  is equal to or more than 0.4 ASD (A/cm 2 ) and equal to or less than 1.4 ASD. This is based on finding, according to investigation by the present inventors, that the consumption of the additive in the plating solution can be reduced especially when the anode current density is equal to or more than 0.4 ASD and equal to or less than 1.4 ASD. That is, if the anode current density during plating is large (e.g., in excess of 1.4 ASD), an amount of oxygen to be generated around the anode  40  increases, and the consumption of the additive in the plating solution increases. On the other hand, if the anode current density during the plating is excessively small (e.g., less than 0.4 ASD), an amount of hypochlorous acid to be generated around the anode  40  increases, and the consumption of the additive in the plating solution increases. Then, when the anode current density during the plating is equal to or more than 0.4 ASD and equal to or less than 1.4 ASD, the consumption of the additive in the plating solution can be suitably reduced. Consequently, in a process of S 30 , the anode  40  is designed and prepared based on the substrate W or the like to be plated so that the anode current density during the plating is equal to or more than 0.4 ASD and equal to or less than 1.4 ASD. Here, it is preferable to design the anode  40  so that the anode current density is equal to or more than 0.4 ASD, especially equal to or more than 0.5 ASD, or equal to or more than 0.6 ASD. Also, it is preferable to design the anode  40  so that the anode current density is equal to or less than 1.4 ASD, especially equal to or less than 1.3 ASD, equal to or less than 1.2 ASD, equal to or less than 1.1 ASD, or equal to or less than 1.0 ASD. 
     As a specific example of the design of the anode  40 , first, a current amount (or a cathode current density) during the plating is determined in accordance with an area and shape of the substrate W. Here, in the present embodiment, the recesses  112  for the through electrodes are formed in the substrate W. and hence a comparatively small current amount is determined so that a defect such as a void is not caused. The current amount during the plating may only be set by using a known method. The setting does not form core of the present invention, and hence a detailed description will not be made. Then, the anode  40  is designed by determining, based on the set current amount, the size and shape of the anode  40  so that the anode current density is a desired current density. A preferable shape of the anode  40  for satisfying the current density will be described later. 
     Then, the substrate W prepared in S 10  and the anode  40  prepared in S 30  are arranged in the plating solution tank  50  prepared in S 20 , and electroplating is performed at the anode current density that is equal to or more than 0.4 ASD and equal to or less than 1.4 ASD (S 40 ). It is preferable that the anode current density during the plating is equal to or more than 0.4 ASD, especially equal to or more than 0.5 ASD, or equal to or more than 0.6 ASD. Also, it is preferable that the current density during the plating is equal to or less than 1.4 ASD, especially equal to or less than 1.3 ASD, equal to or less than 1.2 ASD, equal to or less than 1.1 ASD, or equal to or less than 1.0 ASD. Thus, the anode current density is set within a predetermined range, so that the generation of oxygen and hypochlorous acid around the anode  40  can be inhibited, and the consumption of the additive in the plating solution can be reduced. 
     Next, a description will be made as to an example of the specific shape of the anode  40  of the present embodiment.  FIG. 7  is a view showing a first example of the anode of the present embodiment. An anode  40 A shown in  FIG. 7  includes a power supply point  402  connected to the power source  90  via the anode holder  60 , a ring electrode  410  having a ring shape around the power supply point, and a connection electrode  404  connecting the power supply point  402  and the ring electrode  410 . 
     The power supply point  402  is connected to the power supply member  89  (see  FIG. 4 ) of the anode holder  60 . In the present embodiment, the connection electrode  404  and the ring electrode  410  are not directly connected to the power supply member  89  of the anode holder  60 , but are connected via the power supply point  402 . However, the present invention is not limited to this example, and at least parts of the connection electrode  404  and the ring electrode  410  may be directly connected to the power supply member  89 . The power supply point  402  is circular when viewed from front (substrate W side), and a plurality of holes are formed to attach the power supply point to the power supply member  89 . However, the power supply point  402  is not limited to this shape, as long as the power supply point is configured to be connectable to the power source  90 . 
     The ring electrode  410  defines an outer edge of the anode  40 A. It is preferable that an outer diameter of the ring electrode  410  is smaller than a diameter of the opening  63   a  of the anode holder  60 . It is also preferable that an outer shape of the ring electrode  410  is substantially similar to an outer shape of the substrate W. For example, it is preferable that when the substrate W is circular, the ring electrode  410  is annular, and that when the substrate W is quadrangular, the ring electrode  410  has a quadrangular frame shape formed with four sides. In the example shown in  FIG. 7 , the connection electrode  404  linearly connects the power supply point  402  and the ring electrode  410 . A plurality of connection electrodes  404  are provided at respective predetermined angles from the power supply point  402 , and in the example shown in  FIG. 7 , eight connection electrodes  404  are provided radially around the power supply point  402 . The ring electrode  410  and the connection electrode  404  may have about the same cross-sectional shape as a cross section that is a plane perpendicular to a longitudinal direction. For example, each of the ring electrode  410  and the connection electrode  404  may have a cross section that is a square, especially a square with each side being 1 mm, a square with each side being 2 mm, or a square with each side being 3 mm. However, the present invention is not limited to this example, and the ring electrode  410  and the connection electrode  404  may have a cross section that is, for example, rectangular, polygonal or circular. 
     The anode  40  is formed into this shape, and accordingly, when the plating is performed to form the through electrode in the substrate W, the consumption of the additive in the plating solution can be reduced by regulating the anode current density. Furthermore, in-plane uniformity of plating formed on the substrate W can be improved. Here, to improve the in-plane uniformity of the plating formed on the substrate W, it is preferable that the anode  40  has a rotationally symmetric shape around the power supply point  402 . 
     Subsequently, a description will be made as to a modification of the anode  40 .  FIG. 8  is a view showing a second example of the anode of the present embodiment. An anode  40 B shown in  FIG. 8  is different from the anode  40 A shown in  FIG. 7  in the ring electrode  410 , and the anodes have the same shape except the ring electrode  410 . The anode  40 B includes, as the ring electrode  410 , a first ring electrode  410   a  that defines an outer edge of the anode  40 B, and a second ring electrode  410   b  having a diameter smaller than a diameter of the first ring electrode  410   a . The first ring electrode  410   a  and the second ring electrode  410   b  are concentrically arranged around the power supply point  402 . The first ring electrode  410   a  includes a configuration similar to a configuration of the ring electrode  410  of the anode  40 A shown in  FIG. 7 , and is connected to the power supply point  402  via the connection electrode  404 . In the anode  40 B, the connection electrode  404  has one end connected to the power supply point  402 , and the other end connected to the first ring electrode  410   a . Also, the connection electrode  404  is connected to the second ring electrode  410   b  in an intermediate portion between the one end and the other end. Consequently, the second ring electrode  410   b  is connected to the power supply point  402  via the connection electrode  404 . Each of the first ring electrode  410   a  and the second ring electrode  410   b  may have about the same cross-sectional shape as in the connection electrode  404 , in the same manner as in the ring electrode  410  of the anode  40 A. 
       FIG. 9  is a view showing a third example of the anode of the present embodiment. An anode  40 C shown in  FIG. 9  is different from the anode  40 A shown in  FIG. 7  in the ring electrode  410 , and the anodes have the same shape except the ring electrode  410 . The anode  40 C includes, as the ring electrode  410 , a first ring electrode  410   a  that defines an outer edge of the anode  40 C, a second ring electrode  410   b  having a diameter smaller than a diameter of the first ring electrode  410   a , and a third ring electrode  410   c  having a diameter smaller than the diameter of the second ring electrode  410   b . The first to third ring electrodes  410   a  to  410   c  are concentrically arranged around the power supply point  402 . The first ring electrode  410   a  and the second ring electrode  410   b  have a configuration similar to a configuration of the ring electrode of the anode  40 B shown in  FIG. 8 , and are connected to the power supply point  402  via the connection electrode  404 . In the anode  40 C, the connection electrode  404  is connected to the second ring electrode  410   b  and the third ring electrode  410   c  in an intermediate portion. Consequently, the second ring electrode  410   b  and the third ring electrode  410   c  are connected to the power supply point  402  via the connection electrode  404 . Each of the first to third ring electrodes  410   a  to  410   c  may have about the same cross-sectional shape as in the connection electrode  404 , in the same manner as in the ring electrode  410  of the anode  40 A. Note that as shown in  FIGS. 7 to 9 , the anode  40  is not limited to the anode including one to three ring electrodes  410 , and may include four or more ring electrodes  410 . 
       FIG. 10  is a view showing a fourth example of the anode of the present embodiment. An anode  40 D shown in  FIG. 10  is different from the anode  40 A shown in  FIG. 7  in the connection electrode  404 , and the anodes have the same shape except the connection electrode  404 . The anode  40 D includes, as the connection electrode  404 , an electrode extending in an up-down direction and a right-left direction and connecting the power supply point  402  and the ring electrode  410 . That is, in the anode  40 A shown in  FIG. 7 , connection electrodes  404  are arranged radially from the power supply point  402  in eight directions, but in the anode  40 D shown in  FIG. 10 , the connection electrodes  404  are arranged radially from the power supply point  402  in four directions. Note that as shown in  FIGS. 7 and 10 , the anode  40  is not limited to the anode including the connection electrodes  404  arranged radially in eight directions or four directions, and may include any number of connection electrodes  404 . Also, the anode  40  may include two or more ring electrodes  410  regardless of the number of the connection electrodes  404 . 
       FIG. 11  is a view showing a fifth example of the anode of the present embodiment. An anode  40 E shown in  FIG. 11  is different from the anode  40 A shown in  FIG. 7  in the connection electrode  404 , and the anodes have the same shape except the connection electrode  404 . The anode  40 A described above and shown in  FIG. 7  includes a plurality of linear electrodes as the connection electrodes  404 , but in the anode  40 E shown in  FIG. 11 , each of a plurality of connection electrodes  404  has a curved shape. Also, in this case, it is preferable that the connection electrodes  404  are formed so that the anode  40 E has a rotationally symmetric shape around the power supply point  402 . Note that also in the examples shown in  FIGS. 8 to 10 , the connection electrode  404  may have a curved shape. 
       FIG. 12  is a view showing a sixth example of the anode of the present embodiment. An anode  40 F shown in  FIG. 12  is the same as the anode  40 A shown in  FIG. 7  except that a cover  420  is attached to the power supply point  402 . The cover  420  covers a front surface in the power supply point  402  (a surface facing the substrate W) to improve the uniformity of the plating formed on the substrate W. The cover  420  may be made of a highly insulating resin such as polyvinyl chloride (PVC) or polypropylene (PP). In the example shown in  FIG. 12 , the cover  420  includes a plate-shaped part  421  having a circular shape with a diameter more than a diameter of the power supply point  402 , and a fitting part  422  protruding rearward from the plate-shaped part  421 . The plate-shaped part  421  is disposed to control an electric field on an anode surface, and may have a size determined by simulation, experiment or the like to improve the uniformity of the plating formed on the substrate W. Also, the fitting part  422  is disposed to attach the cover  420  to the power supply point  402 . An inner peripheral surface of the fitting part  422  has a shape corresponding to a shape of an outer peripheral side surface of the power supply point  402 . Also, the fitting part  422  includes a plurality of recesses corresponding to the connection electrodes  404  extending from the power supply point  402 . According to this configuration, the cover  420  can be attached by fitting the fitting part  422  from front into the power supply point  402 . However, the present invention is not limited to this example, and the cover  420  may be attached to the power supply point  402  by use of a fastener such as a screw, or an adhesive or the like. The cover  420  is disposed to cover the power supply point  402  from the front, and accordingly the uniformity of the plating formed on the substrate W can be improved. Alternatively, the cover  420  may be attached to the anodes  40 B to  40 E shown in  FIGS. 8 to 11 . 
     Second Embodiment 
       FIG. 13  is a schematic view showing a plating apparatus according to a second embodiment. The plating apparatus according to the second embodiment is different from the plating apparatus according to the first embodiment in that a diaphragm  66  is not attached to an anode holder  60 , but is attached to an opening  14   a  in a regulation plate  14 . In the following description, a description that overlaps with that of the first embodiment will not be repeated. 
     In the plating apparatus according to the second embodiment, a shield box  160  is disposed in a plating solution storage tank  52 , and accordingly, an interior of the plating solution storage tank  52  is divided into an anode tank  170  inside the shield box  160  and a cathode tank  172  outside the shield box. In the example shown in  FIG. 13 , the anode holder  60  holding an anode  40  and the regulation plate  14  are arranged in the anode tank  170 , and a paddle  16  and a substrate holder  18  (cathode) are arranged in the cathode tank  172 . 
     The shield box  160  includes an opening  160   a  at a position corresponding to the opening  14   a  of the regulation plate  14 . Also, a tubular part that defines the opening  14   a  of the regulation plate  14  is fitted into the opening  160   a  of the shield box  160 . According to this configuration, the anode tank  170  communicates with the cathode tank  172  through the opening  14   a  of the regulation plate  14 . Then, in the second embodiment, the diaphragm  66  is attached to the opening  14   a  of the regulation plate  14 , and the anode tank  170  and the cathode tank  172  are divided by the diaphragm  66 . Alternatively, the diaphragm  66  may be attached from an anode tank  170  side in the regulation plate  14 , or may be attached from a cathode tank  172  side. Furthermore, the diaphragm  66  may be attached to the regulation plate  14  by an arbitrary method, and is attached to the regulation plate  14  by use of an annular diaphragm retainer  68  as an example. 
     In the plating apparatus of the second embodiment, a plating solution in the cathode tank  172  flows over a side wall of the plating solution storage tank  52  to flow into an overflow tank  54 . On the other hand, the plating solution in the anode tank  170  is configured not to overflow. Further, a liquid discharge line  190  in which an on-off valve  186  is disposed is connected to the anode tank  170 . For example, when the diaphragm  66  is changed, the plating solution (base liquid) in the anode tank  170  can be discharged through the liquid discharge line  190 . 
     Also, in the plating apparatus according to the second embodiment, a base liquid supply line  158  is connected to a plating solution circulation line  58   a . The base liquid supply line  158  is not intended to supply the plating solution to the plating solution storage tank  52  during plating of a substrate W, but is used to first supply the base liquid to the plating solution storage tank  52  for performing plating, that is, used only for so-called initial make-up of an electrolytic bath. The base liquid supply line  158  is provided with a first supply valve  151 . Also, in the plating apparatus of the second embodiment, a connection line  192  is disposed to connect the plating solution circulation line  58   a  and the liquid discharge line  190 . The connection line  192  is provided with a second supply valve  152 . Further, the plating apparatus of the second embodiment is provided with an additive supply line  159  for supplying an additive to the cathode tank  172 . The additive supply line  159  is provided with a third supply valve  153 . Usually, the first to third supply valves  151  to  153  are closed. 
     According to the plating apparatus of the second embodiment, the first supply valve  151  and the second supply valve  152  are opened only during the initial make-up of the electrolytic bath, and the base liquid from the base liquid supply line  158  is supplied through the liquid discharge line  190  and the plating solution circulation line  58   a  into the anode tank  170  and the cathode tank  172 . Then, the third supply valve  153  is opened, to supply the additive only to the cathode tank  172 . According to this configuration, the anode tank  170  does not store the additive, and hence consumption of the additive in the vicinity of the anode  40  can be reduced. 
     In the plating apparatus of the second embodiment described above, the plating solution storage tank  52  is divided into the anode tank  170  and the cathode tank  172  by the shield box  160  and the regulation plate  14 . Then, the diaphragm  66  is disposed in the opening  14   a  of the regulation plate  14 . Also, in this configuration, the substrate W is plated with the anode current density being equal to or more than 0.4 ASD and equal to or less than 1.4 ASD when plating the substrate W to form the through electrode, in the same manner as in the plating apparatus of the first embodiment. Consequently, generation of oxygen and hypochlorous acid during the plating can be inhibited, and the consumption of the additive in the plating solution can be reduced. 
     The present embodiments described above can also be described in aspects as follows. 
     [Aspect 1] 
     According to Aspect 1, a plating method is provided, and the plating method includes the steps of preparing a substrate including a via or a hole for forming a through electrode, preparing a plating solution tank that is divided, by a diaphragm, into an anode tank in which an insoluble anode is disposed and a cathode tank in which the substrate is disposed, and electroplating the substrate with an anode current density when plating the substrate in the plating solution tank being equal to or more than 0.4 ASD and equal to or less than 1.4 ASD. According to this plating method, generation of oxygen and hypochlorous acid during the plating can be inhibited, and consumption of an additive in a plating solution can be reduced. 
     [Aspect 2] 
     According to Aspect 2, in Aspect 1, the insoluble anode includes a power supply point to be connected to a power source, a ring electrode having a ring shape around the power supply point, and a connection electrode connecting the power supply point and the ring electrode. According to Aspect 2, in-plane uniformity of plating formed on the substrate can be improved. 
     [Aspect 3] 
     According to Aspect 3, in Aspect 2, the ring electrode includes a first ring electrode having a first diameter, and a second ring electrode having a second diameter smaller than the first diameter. 
     [Aspect 4] 
     According to Aspect 4, in Aspect 2 or 3, the connection electrode linearly connects the power supply point and the ring electrode. 
     [Aspect 5] 
     According to Aspect 5, in Aspects 2 to 4, the insoluble anode has a rotationally symmetric shape around the power supply point. 
     [Aspect 6] 
     According to Aspect 6, in Aspects 2 to 5, a cover that covers a region of the power supply point of the insoluble anode facing the substrate is attached to the power supply point. According to Aspect 6, an electric field on an anode surface can be controlled by the cover, and the in-plane uniformity of the plating formed on the substrate can be improved. 
     [Aspect 7] 
     According to Aspect 7, in Aspects 2 to 6, the insoluble anode is held by an anode holder, the anode holder includes an opening opened to face the substrate, and a size of the ring electrode of the insoluble anode is smaller than a size of the opening. 
     [Aspect 8] 
     According to Aspect 8, in Aspects 1 to 7, the diaphragm is an ion exchange membrane or a neutral diaphragm. 
     [Aspect 9] 
     According to Aspect 9, an insoluble anode for plating that is disposed in a plating solution tank for use in the plating is provided, and the anode includes a power supply point to be connected to a power source, a ring electrode having a ring shape around the power supply point, and a connection electrode connecting the power supply point and the ring electrode. According to Aspect 9, generation of oxygen and hypochlorous acid during the plating can be inhibited, and the consumption of the additive in the plating solution can be reduced. Furthermore, the in-plane uniformity of the plating formed on the substrate can be improved. 
     [Aspect 10] 
     According to Aspect 10, a plating apparatus is provided, and includes a plating solution tank configured to store a plating solution, the insoluble anode for plating according to Aspect 9, and a diaphragm that divides the plating solution tank into an anode tank in which the insoluble anode is disposed and a cathode tank in which a substrate is disposed. According to Aspect 10, the plating apparatus includes the anode for plating of Aspect 9, and can exhibit effects similar to those of Aspect 9. 
     The embodiments of the present invention have been described above based on several examples, but the above embodiments of the present invention are described to facilitate understanding of the present invention, and do not limit the present invention. The present invention may be changed or modified without departing from the scope, and needless to say, the present invention includes equivalents to the invention. Also, in a range in which at least some of the above-described problems can be solved or a range in which at least some of effects are exhibited, any arbitrary combination or omission of respective constituent components described in the claims and description is possible. 
     The present application is based on and claims the benefit of priority of Japanese Patent Application No. 2019-93404 filed on May 17, 2019. All disclosed contents including the description, claims, drawings and abstract of Japanese Patent Application No. 2019-93404 are entirely incorporated herein by reference. All disclosure including the description, claims, drawings and abstract of Japanese Patent Laid-Open No. 7-11498 (PTL 1) is entirely incorporated herein by reference. 
     REFERENCE SIGNS LIST 
     
         
         
           
               14  regulation plate 
               14   a  opening 
               16  paddle 
               18  substrate holder 
               40  and  40 A to  40 F anode (insoluble anode) 
               50  plating solution tank 
               52  plating solution storage tank 
               54  overflow tank 
               60  anode holder 
               61  inner space 
               62  holder base 
               63  holder base cover 
               66  diaphragm 
               67  outer edge mask 
               68  diaphragm retainer 
               402  power supply point 
               404  connection electrode 
               410  ring electrode 
               410   a  first ring electrode 
               410   b  second ring electrode 
               410   c  third ring electrode 
               420  cover