Patent Publication Number: US-2015068911-A1

Title: Copper plating apparatus, copper plating method and method for manufacturing semiconductor device

Description:
CROSS-REFERENCE TO RELATED APPLICATIONS 
     This application is based upon and claims the benefit of priority from U.S. Provisional Patent Application 61/876,976, filed on Sep. 12, 2013; the entire contents of which are incorporated herein by reference. 
    
    
     FIELD 
     Embodiments described herein relate generally to a copper plating apparatus, a copper plating method and a method for manufacturing a semiconductor device. 
     BACKGROUND 
     Conventionally, interconnects, etc., are formed by plating copper on a silicon substrate when manufacturing a semiconductor device. Due to the shrinking of semiconductor devices in recent years, it is also necessary to increase the precision of the copper plating. Further, it is necessary to reduce the processing cost of the copper plating. 
    
    
     
       BRIEF DESCRIPTION OF THE DRAWINGS 
         FIG. 1  is a drawing showing a copper plating apparatus according to an embodiment; 
         FIG. 2  is a flowchart showing the copper plating method according to the embodiment; 
         FIG. 3A  to  FIG. 3D  are drawings showing the copper plating method according to the embodiment; and 
         FIG. 4  is a graph showing the change over time of the dust count of a comparative example, where the horizontal axis is the plating processing time after placing a new copper member, and the vertical axis is the dust count. 
     
    
    
     DETAILED DESCRIPTION 
     A copper plating apparatus according to an embodiment includes a plating tank configured to have a copper member and a plating member being disposed in an interior of the plating tank, a blocking film configured to partition the interior of the plating tank into an anode chamber where the copper member is to be disposed and a cathode chamber where the plating member is to be disposed, the blocking film being configured to transmit copper ions and not transmit an additive agent, a supply unit configured to supply the additive agent to the anode chamber, and a power supply configured to apply a voltage between the copper member and the plating member. 
     A copper plating method according to an embodiment includes disposing a copper member in an anode chamber of a plating tank, supplying plating liquid including an additive agent to the anode chamber, disposing a first plating member in a cathode chamber partitioned from the anode chamber by a blocking film configured to transmit copper ions and not transmit the additive agent, and supplying the plating liquid including the additive agent to the cathode chamber. The method includes applying a voltage to cause the copper member to be positive and the first plating member to be negative to perform copper plating on the first plating member and form a black film at a surface of the copper member. The method includes replacing the first plating member with a second plating member after the black film is formed. And the method includes applying a voltage to cause the copper member to be positive and the second plating member to be negative to perform copper plating on the second plating member while supplying the additive agent to the cathode chamber without supplying the additive agent to the anode chamber. 
     An embodiment of the invention will now be described with reference to the drawings. 
       FIG. 1  is a drawing showing a copper plating apparatus according to the embodiment. 
     As shown in  FIG. 1 , a plating cell  10 , a plating liquid supply unit  11 , an additive agent supply unit  12 , and a plating liquid recovery unit  13  are provided in the copper plating apparatus  1  according to the embodiment. In the copper plating apparatus  1 , multiple plating cells  10  are provided for one set of the plating liquid supply unit  11 , the additive agent supply unit  12 , and the plating liquid recovery unit  13 . 
     The plating liquid supply unit  11  is a unit that supplies a plating liquid  106  (VMS: Vergin Make up Solution) not including an additive agent  107  (referring to  FIG. 3A ) to the plating cell  10 . The plating liquid  106  is, for example, an aqueous copper sulfate solution. The additive agent supply unit  12  is a unit that supplies the additive agent  107  to the plating liquid  106 . The additive agent  107  includes, for example, an accelerator that promotes the plating, a suppressor that suppresses the plating, and a leveler that levels the plating layer. The accelerator includes, for example, SPS (bis 3-sulfopropyl disulfide disodium). The suppressor includes, for example, PEG (polyethylene glycol). The leveler includes, for example, various dielectrics. The plating liquid recovery unit  13  is a unit that recovers the used plating liquid  106 . A pump (not shown) and a filter (not shown) are provided in the plating liquid supply unit  11 ; and a pump (not shown) and a filter (not shown) are provided in the additive agent supply unit  12 . 
     An external tank  20  is provided in the plating cell  10 ; and a plating tank  21  is provided inside the external tank  20 . A blocking film  22  is provided in the interior of the plating tank  21 . The interior of the plating tank  21  is partitioned into an anode chamber  23  and a cathode chamber  24  by the blocking film  22 ; the anode chamber  23  is positioned at the lower portion of the plating tank  21  interior; and the cathode chamber  24  is positioned at the upper portion of the plating tank  21  interior. The blocking film  22  is a film, e.g., a membrane, e.g., an ion exchange film, that transmits copper ions and does not transmit the polymer material that is the component of the additive agent  107 . 
     A resistance film  25  is provided inside the cathode chamber  24  of the plating tank  21 . The resistance film  25  is made of an insulating material such as a resin, a ceramic, etc., is a plate in which many fine holes are formed, and is a film used to provide resistance to the flow of the copper ions. The plating thickness formed on the silicon wafer becomes uniform by interposing the resistance film  25  between the anode and the cathode. Stepped portions for holding the blocking film  22  and the resistance film  25  are formed at the inner side surface of the plating tank  21 . To this end, the inner diameter of the plating tank  21  decreases downward in stages. 
     Also, a power supply plate  26  is provided at the bottom portion of the plating tank  21  to hold a copper member  100 , which is used as the plating material, and to apply a potential to the copper member  100 . Above the plating tank  21 , a holder  27  is provided to hold a silicon wafer  102 , which is the plating member, cause the silicon wafer  102  to rotate, and apply a potential. A power supply  28  is provided outside the external tank  20  to apply a voltage between the power supply plate  26  and the holder  27  to cause the power supply plate  26  to be positive and cause the holder  27  to be negative. 
     In the plating cell  10 , a bath  31  that holds the plating liquid, pumps  32  and  33  that cause the plating liquid to flow, and filters  34  and  35  that remove dust from the plating liquid are provided outside the external tank  20 . 
     Further, a conduit  41  is connected between the anode chamber  23  of the plating tank  21  and the pump  32 ; a conduit  42  is connected between the pump  32  and the filter  34 ; and a conduit  43  is connected between the filter  34  and the anode chamber  23 . Thereby, an anode-side circulation water path  37  in which the plating liquid  106  circulates in the order of (anode chamber  23 -conduit  41 -pump  32 -conduit  42 -filter  34 -conduit  43 -anode chamber  23 ) is made. 
     Also, a conduit  44  is connected between the bottom portion of the external tank  20  and the bath  31 ; a conduit  45  is connected between the bath  31  and the pump  33 ; a conduit  46  is connected between the pump  33  and the filter  35 ; and a conduit  47  is connected between the filter  35  and the cathode chamber  24  of the plating tank  21 . Thereby, a cathode-side circulation water path  38  in which the plating liquid  106  circulates in the order of (cathode chamber  24 -external tank  20 -conduit  44 -bath  31 -conduit  45 -pump  33 -conduit  46 -filter  35 -conduit  47 -cathode chamber  24 ) is made. 
     On the other hand, a conduit  48  is connected between the plating liquid supply unit  11  and the anode chamber  23 . A valve  49  is provided partway through the conduit  48 . A conduit  57  is connected between the bath  31  and a portion of the conduit  48  that is more on the plating liquid supply unit  11  side than is the valve  49 . A valve  58  is provided partway through the conduit  57 . A conduit  51  is connected between the additive agent supply unit  12  and the bath  31 . A valve  52  is provided partway through the conduit  51 . A conduit  53  is connected between the additive agent supply unit  12  and the conduit  41 . A valve  54  is provided partway through the conduit  53 . Thereby, the additive agent supply unit  12  can supply the additive agent  107  to the anode-side circulation water path  37  via the conduit  53  and the valve  54 . 
     A conduit  55  is connected between the anode chamber  23  and the bath  31 . A valve  56  is provided partway through the conduit  55 . A conduit  59  is interposed between the bath  31  and the plating liquid recovery unit  13 . A valve  60  is provided partway through the conduit  59 . 
     The operation of the copper plating apparatus  1 , i.e., a copper plating method according to the embodiment, will now be described. The copper plating method according to the embodiment is a portion of a method for manufacturing a semiconductor device. 
       FIG. 2  is a flowchart showing the copper plating method according to the embodiment. 
       FIG. 3A  to  FIG. 3D  are drawings showing the copper plating method according to the embodiment. 
     In  FIG. 3A  to  FIG. 3D , the additive agent  107  is schematically illustrated by the gray circles. 
     First, as shown in  FIG. 1 , the copper plating apparatus  1  is prepared. In the copper plating apparatus  1  at this stage, the blocking film  22  and the resistance film  25  are not mounted inside the plating tank  21 ; the copper member  100  and the silicon wafer  102  are not mounted as well; and the plating liquid  106  is not introduced. Further, all of the valves are closed. 
     Then, as shown in step S 1  of  FIG. 2 , a new copper member  100  is prepared; and the surface of the copper member  100  is cleaned. For example, the surface of the copper member  100  is etched using sulfuric acid or aqueous hydrogen peroxide; and subsequently, water rinse is performed. 
     Continuing as shown in step S 2 , the copper member  100  is placed inside the anode chamber  23  of the plating tank  21  and connected to the power supply plate  26 . 
     Then, as shown in step S 3 , the anode chamber  23  interior is filled with the plating liquid  106  (the VMS) that does not include the additive agent  107 . Specifically, the pump (not shown) inside the plating liquid supply unit  11  is caused to operate; the valve  49  is opened; and the pump  32  is caused to operate. Thereby, the plating liquid  106  (the VMS) is supplied from the plating liquid supply unit  11  to the interior of the anode chamber  23  via the conduit  48 ; and the plating liquid  106  circulates through the anode-side circulation water path  37 . When the anode chamber  23  is filled with the plating liquid  106 , the valve  49  is closed. 
     Continuing as shown in step S 4 , the additive agent  107  is supplied to the conduit  41  by opening the valve  54 . Thereby, the additive agent  107  flows into the anode-side circulation water path  37 , mixes with the plating liquid  106 , and is supplied to the interior of the anode chamber  23 . At this time, the concentration of the additive agent  107  in the plating liquid  106  is set to be, for example, not less than 1 ppm. Subsequently, the valve  54  is closed. 
     Then, as shown in step S 5  of  FIG. 2  and  FIG. 3A , the plating cell  10  is assembled. Specifically, the blocking film  22  is mounted inside the plating tank  21 ; and the resistance film  25  is mounted. Then, a dummy silicon wafer  101  is mounted to the holder  27 . Then, the plating liquid  106  is supplied to the interior of the anode chamber  23  by opening the valve  49 . The plating liquid  106  that is supplied to the interior of the anode chamber  23  passes through the blocking film  22 , enters the cathode chamber  24  as well, and fills the entire plating tank  21 . 
     Continuing, the plating liquid  106  and the additive agent  107  that overflow from the plating tank  21  accumulate at the bottom portion of the external tank  20  and are returned to the bath  31  via the conduit  44 . Also, by opening the valve  60 , a portion of the plating liquid  106  and the additive agent  107  can be recovered into the plating liquid recovery unit  13  via the conduit  59 . Thereby, new plating liquid  106  is constantly supplied to the interior of the plating cell  10 . 
     Further, by causing the pump  33  to operate, the plating liquid  106  is circulated inside the cathode-side circulation water path  38 . Then, by causing the additive agent supply unit  12  to operate and by opening the valve  52 , the additive agent  107  is introduced to the interior of the bath  31  and is supplied to the interior of the cathode chamber  24  via the cathode-side circulation water path  38 . Therefore, at this stage as shown in  FIG. 3A , a mixed liquid of the plating liquid  106  and the additive agent  107  is supplied to both the interior of the anode chamber  23  and the interior of the cathode chamber  24 . However, the plating liquid  106  and the additive agent  107  that are inside the anode chamber  23  and the plating liquid  106  and the additive agent  107  that are inside the cathode chamber  24  are circulated independently through the circulation water paths. Although the plating liquid  106  can move between the anode chamber  23  and the cathode chamber  24  via the blocking film  22 , the movement of the additive agent  107  is blocked by the blocking film  22 . 
     Then, as shown in step S 6  of  FIG. 2  and  FIG. 3B , a voltage is applied by the power supply  28  to cause the copper member  100  to be positive and the silicon wafer  101  to be negative. Thereby, a copper plating layer  110  is formed by copper plating being performed on the surface of the dummy silicon wafer  101 . At this time, monovalent copper ions (Cu + ) and bivalent copper ions (Cu 2+ ) are produced from the copper member  100  and reach the silicon wafer  101  by moving through the plating liquid  106 . Then, the ions bond with electrons at the surface of the silicon wafer  101  and precipitate as simple copper. 
     At this time, foreign matter  112  forms at the copper plating layer  110  due to the monovalent copper ions (Cu + ). The formation of the foreign matter  112  reduces the uniformity of the copper plating layer  110  and mixes into the plating liquid  106  to become dust. On the other hand, inside the anode chamber  23 , a black film  108  is formed on the surface of the copper member  100  by the additive agent  107  reacting with the copper. The black film  108  is made of, for example, a mixture of Cu 2 Cl 2 , Cu 2 O, and Cu 3 P. 
     In this process, it is favorable for the plating amount for the silicon wafer  101  to be not less than (S×14) coulombs, where the surface area of the region where the surface of the copper member  100  contacts the plating liquid  106  is S (cm 2 ). Thereby, the black film  108  can be reliably formed. For example, in the case where the copper member  100  is a circular plate having a diameter of 300 mm and one face of the copper member  100  contacts the plating liquid  106 , the surface area S is about 706.5 cm 2 . In such a case, because 706.5×=9891, it is sufficient to perform plating of 10 kilocoulombs or more. If necessary, a plurality of the dummy silicon wafers  101  may be used sequentially. 
     Then, as shown in step S 7  of  FIG. 2 , the quality of the copper plating layer  110  formed on the silicon wafer  101  is inspected. Then, if the quality is defective, the flow returns to step S 6 ; and the plating processing of the dummy silicon wafer  101  is continued. On the other hand, if the quality is good, the flow proceeds to step S 8  to transition to the main plating processing. 
     Continuing as shown in step S 8  of  FIG. 2  and  FIG. 3C , the dummy silicon wafer  101  is removed from the holder  27 ; and the silicon wafer  102  for the main plating is mounted. Because, the additive agent  107  is not supplied to the interior of the anode chamber  23  after the start of the plating processing of the dummy shown in step S 6 , the concentration of the additive agent  107  of the plating liquid  106  inside the anode chamber  23  decreases as the plating processing of the dummy progresses. On the other hand, because the additive agent  107  is supplied continuously to the interior of the cathode chamber  24  via the conduit  51 , the concentration of the additive agent  107  inside the cathode chamber  24  is substantially constant. 
     Then, as shown in step S 9  of  FIG. 2  and  FIG. 3D , copper plating of the silicon wafer  102  is performed by the power supply  28  again applying the voltage. At this time, although the additive agent  107  is supplied to the interior of the cathode chamber  24  via the conduit  51 , the additive agent  107  is not supplied to the interior of the anode chamber  23 . Although the copper plating layer  110  is formed on the surface of the silicon wafer  102  by the plating processing, the monovalent copper ions (Cu + ) substantially are not produced because the surface of the copper member  100  is covered with the black film  108 ; and, accordingly, the foreign matter  112  substantially does not form. Also, the additive agent  107  that remained inside the anode chamber  23  is consumed by the copper plating processing and substantially no longer exists. 
     Thus, the copper plating layer  110  can be formed on the surface of the silicon wafer  102  for the main plating. Then, when the plating processing of one silicon wafer  102  ends, the silicon wafer  102  is removed from the copper plating apparatus  1 ; a new silicon wafer  102  is mounted to the copper plating apparatus  1 ; and the plating processing is continued. Thus, the plating processing can be performed sequentially for multiple silicon wafers  102  until the copper member  100  is consumed and can no longer be used. When the copper member  100  is replaced, the main plating processing shown in step S 9  is performed after re-implementing the preparation processes shown in steps S 1  to S 8  described above. 
     Then, a conductive member such as an interconnect, etc., can be formed on the silicon wafer  102  by selectively forming the copper plating layer  110  on the silicon wafer  102  in step S 9 , or by uniformly forming the copper plating layer  110  in step S 9  and subsequently performing patterning. Thereafter, the semiconductor device can be manufactured by performing the necessary processing. 
     Effects of the embodiment will now be described. 
     In the embodiment, the plating liquid  106  including the additive agent  107  is supplied to the interior of the anode chamber  23  in the dummy plating process shown in step S 6  of  FIG. 2  and  FIG. 3B . Therefore, the black film  108  can be formed quickly on the surface of the copper member  100 . Thereby, in the main plating process shown in step S 9  of  FIG. 2  and  FIG. 3D , the production of the monovalent copper ions can be suppressed; and the formation of the foreign matter  112  on the silicon wafer  102  can be suppressed. As a result, a uniform copper plating layer  110  can be formed on the silicon wafer  102 . Further, dust that is due to the foreign matter  112  coming off into the plating liquid  106  can be prevented from occurring. 
     Also, in the embodiment, after introducing a constant amount of the additive agent  107  into the anode chamber  23  at the start of the dummy plating process, the plating processing is performed by supplying only the plating liquid  106  to the interior of the anode chamber  23  without supplying the additive agent  107 . Thereby, the black film  108  can be prevented from being formed to be excessively thick; and the black film  108  can be prevented from coming off and becoming dust. Also, the cost of the plating processing can be suppressed because the additive agent  107  that is inside the anode chamber  23  is not consumed excessively. On the other hand, because the additive agent  107  is supplied continuously to the interior of the cathode chamber  24 , the copper plating layer  110  can be formed stably. 
     A comparative example will now be described. 
       FIG. 4  is a graph showing the change over time of the dust count of the comparative example, where the horizontal axis is the plating processing time after placing a new copper member, and the vertical axis is the dust count. 
     In the comparative example, the plating processing was performed using a new copper member  100  by supplying the plating liquid  106  not including the additive agent  107  to the interior of the anode chamber  23  and by supplying the plating liquid  106  including the additive agent  107  to the interior of the cathode chamber  24 . 
     As a result, as shown in  FIG. 4 , after a constant amount of time has elapsed after the start of the plating processing, the dust count inside the plating liquid  106  greatly increases and subsequently decreases. It is considered that the increase of the dust count is because the black film  108  is not formed on the surface of the copper member  100 , monovalent copper ions are formed, and the foreign matter  112  forms on the silicon wafer because the additive agent  107  is not supplied to the interior of the anode chamber  23 . When the foreign matter  112  forms at the copper plating layer  110 , open defects occur easily for interconnects in the case where the interconnects are formed from the copper plating layer  110 . 
     Further, it is considered that the reason that the dust count decreased after increasing once is because the additive agent  107  entered the anode chamber  23  little by little via the blocking film  22 ; and thereby, the black film  108  was formed. Therefore, it also may be considered to perform the plating processing by utilizing this phenomenon and waiting until the dust count decreases. However, in such a case, it is necessary to continue the plating processing of the dummy until the black film  108  is formed by the additive agent  107  leaking into the anode chamber  23  and the formation of the foreign matter  112  decreases sufficiently; and the productivity of the plating processing decreases. In an example, dummy plating processing for several days is necessary until the black film  108  is formed by the additive agent  107  leaking via the blocking film  22  and the dust count decreases. Conversely, according to the embodiment described above, transition to the main plating processing is possible when the plating processing of the dummy is performed for several minutes. 
     It also may be considered to not provide the blocking film  22  and to perform the plating processing by supplying the plating liquid  106  including the additive agent  107  to the entire interior of the plating tank  21 . However, in such a case, the black film  108  that has become too thick comes off, mixes into the plating liquid  106 , and causes defects such as embedding defects, etc. Moreover, the consumption of the additive agent  107  is high; and the cost of the plating processing increases. Further, it is necessary to frequently replace the filters  34  and  35  because the dust increases; and this also causes the cost to increase. 
     According to the embodiment described above, a copper plating apparatus, a copper plating method, and a method for manufacturing the semiconductor device can be realized to perform inexpensive and high-precision copper plating. 
     While certain embodiments have been described, these embodiments have been presented by way of example only, and are not intended to limit the scope of the inventions. Indeed, the novel embodiments described herein may be embodied in a variety of other forms; furthermore, various omissions, substitutions and changes in the form of the embodiments described herein may be made without departing from the spirit of the inventions. The accompanying claims and their equivalents are intended to cover such forms or modifications as would fall within the scope and spirit of the invention.