Abstract:
A method and apparatus are set forth capable of processing a substrate with a high uniformity within the surface area even for a thin feeding layer. The method comprises arranging a counter electrode and the substrate to confront each other; providing a membrane between the counter electrode and the substrate to define a substrate side region and a counter electrode side region. The substrate side region and the counter electrode side region are capable of accommodating respective electrolytes. The substrate side region and the counter electrode side region are supplied with respective electrolytes having different specific resistances. A processing current is also supplied between the substrate and the counter electrode.

Description:
[0001]    This is a continuation of Ser. No. 10/854,252, filed May 27, 2004. 
     
    
     BACKGROUND OF THE INVENTION 
       [0002]    1. Field of the Invention 
         [0003]    The present invention relates to a method and apparatus for processing a substrate, and more specifically to a process and apparatus for electrolytically processing a substrate, such as electroplating interconnect materials such as copper on a surface of the substrate formed with fine interconnect patterns for thereby forming LSI interconnects, or removing a metal film formed on the surface by an electrolytic etching process. 
         [0004]    2. Description of the Related Art 
         [0005]    Lately, as for an interconnect material for forming electric interconnections on a semiconductor substrate, copper having a low electric resistance and a high anti-electromigration property is replacing aluminum or aluminum alloys. Since it is difficult to form copper into an interconnect shape through a conventional anisotropic etching, which is effective for aluminum, copper interconnects are formed through a process called a “copper damascene technology” in which copper is filled inside fine recesses formed on the substrate surface. Other methods such as chemical vapor deposition (CVD) or sputtering may deposit a copper film on the whole surface of the substrate, and requires removing of unnecessary portion of copper through a chemical mechanical planarization (CMP) process or electrolytic etching process. 
         [0006]      FIG. 5  shows a flowchart for a conventional manufacturing process of the above described substrate W having the copper interconnects. In the first place, as shown in  FIG. 5  ( a ), a substrate W comprising a semiconductor base  1  formed with semiconductor devices or elements is prepared, on which an oxide film  2  made of SiO 2  is deposited on a conductor layer  1   a , fine recesses for interconnect such as via holes  3  or interconnect trenches  4  are formed by a lithographic etching process, a barrier layer  5  made of TaN or the like is formed thereon, and a seed layer  7  is further formed on the barrier layer  5  as a feeder layer for electroplating. 
         [0007]    By plating copper on the surface of the substrate W, as shown in  FIG. 5(   b ), a copper film  6  fills the via holes  3  or interconnect trenches  4  as well as covers the surface of the oxide film  2 . Then, the copper film  6  and barrier layer  5  on the oxide film  2  is removed by the CMP or electrolytic etching process to substantially level the surface of the copper film  6  filling the via holes  3  and interconnect trenches  4  with the exposed surface of the oxide film  2 . Thus, the interconnect made of the copper film  6  is formed. 
         [0008]    As described above, as aluminum is replaced by copper for the interconnect material, apparatuses for electroplating copper films or electrolytically etching copper films has been catching eyes of the industry. 
         [0009]    When forming a copper interconnect using a copper sulfide solution or a copper complex solution as plating solution and the substrate Was a cathode, a soluble anode is generally used such as an electrolytic copper or a phosphorus containing copper. 
         [0010]      FIG. 6  shows a general assembly of the above mentioned conventional copper plating apparatus employing a so-called “face-up” design. This plating apparatus comprises an electroplating unit  10 , and a plating solution supply system  12  for supplying and recovering an electrolyte as a plating solution to and from the electroplating unit  10 . The electroplating unit  10  comprises: a substrate holder  14  arranged elevatable and rotatable for detachably supporting a substrate W with the surface facing upward; a bath forming member  16  shaped in a tapered hollow cylinder and assembled on the periphery of the substrate W supported by the substrate holder  14  to surround a space on the substrate W; and an electrode head  18  arranged elevatable, rotatable, and located above the substrate holder  14 . 
         [0011]    The bath forming member  16  has a smaller outer diameter at the lower end than the substrate W, and a top inner diameter larger than both the lower end thereof and the outer diameter of the electrode head  18  (the outer diameter of the porous member  22  described below). A seal portion is formed between the lower end of the bath forming member  16  and the substrate surface during operation to make a plating bath in a region (substrate side region) defined by the bath forming member  16  and the substrate surface. 
         [0012]    The electrode head  18  comprises a housing  26  having a open lower end covered by a porous member or diaphragm  22  for defining an anode chamber  24  within the housing  26 , in which an anode  20  is accommodated. A power source  28  for supplying plating current between the seed layer  7  (shown in  FIG. 5(   a )) formed on a surface of the substrate W held by the substrate holder  14  and the anode  20 . 
         [0013]    The plating solution supply system  12  is for reserving and supplying a plating solution (electrolyte) Q such as a copper sulfide plating solution, for example, and comprises: a reservoir tank  30 ; a couple of plating solution supply lines  32 ,  34  extending from the reservoir tank  30  and connected to the electroplating unit; and a couple of plating solution discharge lines  36 ,  38  for returning the plating solution from the electroplating unit  10  to the reservoir tank  30 . The plating solution supply system  12  supplies the same plating solution from the reservoir tank  30  to a substrate side region which is defined between the substrate W and the porous member  22  and to an anode side region defined inside the anode chamber  24 , and returns the plating solution discharged from those regions to the reservoir tank  30 . 
         [0014]    Thus, a self-controlled system is constructed capable of automatically supplying copper ions at the anode side region to compensate copper ions decreased at the substrate side region. Supply lines may be provided individually for both regions but discharged lines are returned to the same tank. The plating apparatus is mostly operated using an insoluble anode as the anode  20 . It can be also used with soluble anode which is isolated with a porous membrane called an “anode bag”. 
         [0015]      FIG. 7  shows another conventional plating apparatus employing a so-called “face-down” design. This plating apparatus comprises an electrolytic plating unit  40  having a substrate holder  42  elevatable and rotatable for detachably supporting a substrate W with the surface facing downward, and a plating vessel  44  for accommodating a plating solution, which are arranged in an above-and-below relationship. Inside the plating vessel  44 , an anode chamber  50  is defined which is circumferentially partitioned by a separation wall  46  and covered atop with a porous membrane, in which an anode  52  is arrange as a counter electrode to the substrate W at a position to confront the substrate W. Other structures are similar to the apparatus shown in  FIG. 6 . This apparatus also provides a self-controlled system for automatically supplying copper ions at the counter electrode side region to compensate those decreased at the substrate side region. 
         [0016]    As the LSIs are highly integrated, metal films such as the seed layer or a feeder layer has become progressively thin for an electrolytic processing process such as an electroplating or electrolytically etching process. As the feeder layer becomes thinner, variance of plating potential within the surface area of the substrate W becomes larger. Therefore, as shown in  FIG. 6 , a thickness of the plating film becomes larger at a position close to the feeding point to the substrate W, and becomes progressively thin at positions away from the feeding point, that is, close to the center of the substrate W. This means that uniformity of the plating characteristics within the surface area of the substrate W is lowered, and that an effective surface area or a device field ratio has become decreased for the substrate W. In the electrolytic etching process, as shown in  FIG. 8 , an etching rate is large at a position close to the feeding point and smaller at positions away from the feeding point. 
         [0017]    The present invention has been accomplished to solve the above described problems, and an object of the invention is to provide a method and apparatus for electrolytically processing a substrate in which the deposition or etching can be performed with a high uniformity within the surface area even for a thin feeding layer. 
       SUMMARY OF THE INVENTION 
       [0018]    According to one aspect of the present invention, a method for processing a substrate comprises: arranging a counter electrode and the substrate to confront each other; providing a membrane between the counter electrode and the substrate to define a substrate side region and a counter electrode side region, the substrate side region and the counter electrode side region capable of accommodating respective electrolytes; supplying the substrate side region and the counter electrode side region with respective electrolytes having different specific resistances; and supplying a processing current between the substrate and the counter electrode. 
         [0019]    By supplying the counter electrode side region partitioned by the membrane with an electrolyte having a possible maximum specific resistance, and the substrate side region with a normal process electrolyte, processing of the substrate can be performed with a high uniformity within the surface area of the substrate even for a thin feeder layer with indefinitely high resistance. The electrolyte supplied to the anode side region may be provided only with a function as an electrolyte capable of conducting electricity so that processing ability is not lowered. 
         [0020]    The membrane may comprise at least one of a porous membrane, a porous structural member, and an ion exchange membrane. The porous membrane or porous structural member comprises mutually communicating fine pores capable of maintaining electrolyte. Specifically, the porous member may be made of but is not limited to: a sintered compact of polyethylene or polypropylene; a laser worked porous member made of a Teflon (trade name) etc.; porous ceramics; sponges; and woven or non woven fabrics. 
         [0021]    The substrate may be formed with fine interconnect recesses for receiving a metal material through plating, and a feeder layer for feeding the substrate with a plating current, and the fine interconnect recesses has a width not more than 0.3 μm and the feeder layer has a thickness not more than 0.05 μm. The present invention is particularly effective for the feeder layer as thin as not more than 0.05 μm, when plating copper interconnections in an LSI, for example. The interconnections here are extremely fine with a width of not more than 0.3 μm. 
         [0022]    The substrate may be set as an anode, and the counter electrode may be set as a cathode to electroplate copper to the substrate, and the electrolyte supplied to the counter electrode side region may have a larger specific resistance than the electrolyte supplied to the substrate side region. As for the electrolyte supplied to the counter electrode side region, a dilute sulfuric acid is exemplified. It may comprise but not limited to other solutions such as an aqueous solution of copper sulfide, or a mixed solution of copper sulfide and a dilute sulfuric acid. 
         [0023]    The electrolyte supplied to the counter electrode side region may be a copper free electrolyte solution. 
         [0024]    The counter electrode may comprise an insoluble material. Although the invention is particularly effective when using an insoluble material as the counter electrode, soluble materials is applicable. 
         [0025]    According to another aspect of the present invention, an apparatus for processing a substrate comprises: a vessel for accommodating the substrate; a counter electrode arranged to confront the substrate; a membrane arranged between the counter electrode and the substrate to define a substrate side region and a counter electrode side region, the substrate side region and the counter electrode side region capable of accommodating respective electrolytes; electrolyte supply systems for respectively supplying the substrate side region and the counter electrode side region with respective electrolytes having different specific resistances; and a power source for supplying a processing current between the substrate and the counter electrode. 
         [0026]    The membrane may comprise at least one of a porous membrane, a porous structural member, and an ion exchange membrane. 
         [0027]    The electrolyte supply system for supplying the electrolyte to the counter electrode side region may comprise a specific resistance detector for detecting specific resistance of electrolyte and a specific resistance adjuster for adjusting specific resistance of electrolyte based on an output of the specific resistance detector. It is possible to provide an electrolyte of a regularly controlled constant specific resistance to the counter electrode side region. 
         [0028]    The substrate may be set as a cathode, and the counter electrode may be set as an anode, and the counter electrode may comprise a mesh-like member made of an insoluble material. 
         [0029]    The apparatus may further comprise a gas discharge line for discharging a gas generated at the anode. It is possible to prevent the oxygen gas from reaching the substrate to generate particles. 
     
    
     
       BRIEF DESCRIPTION OF THE DRAWINGS  
         [0030]      FIG. 1  is a schematic diagram showing an electrolytic processing apparatus according to an embodiment of the present invention applied to an electroplating apparatus; 
           [0031]      FIG. 2  shows a graph of a relationship between a location in the substrate surface and a film thickness for a plating process using the apparatus shown in the  FIG. 1  and a conventional apparatus; 
           [0032]      FIG. 3  shows a schematic diagram of an electrolytic processing apparatus according to another embodiment of the present invention applied to an electrolytic etching apparatus; 
           [0033]      FIG. 4  shows a schematic diagram of an electrolytic processing apparatus according to another embodiment of the present invention applied to an electroplating apparatus; 
           [0034]      FIG. 5  is a schematic diagram of showing a process of forming a copper interconnect; 
           [0035]      FIG. 6  is a schematic diagram showing the conventional electroplating apparatus; 
           [0036]      FIG. 7  is a schematic diagram showing another conventional electroplating apparatus; and 
           [0037]      FIG. 8  shows a graph showing a relationship between the plated film thickness and a location within the substrate surface when plating and etching by using conventional apparatus. 
       
    
    
     DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENTS  
       [0038]    The embodiment of the present invention will be described with reference to the attached drawings. The same or corresponding structures with those in the conventional apparatus shown in  FIG. 6  or  FIG. 7  are designated with the same numerals and the explanation will be omitted. 
         [0039]      FIG. 1  shows an electrolytic processing apparatus according to an embodiment of the present invention applied to an electroplating apparatus. As shown in  FIG. 1 , the plating apparatus comprises an electroplating unit  10  and a couple of electrolyte supply systems  12   a ,  12   b  for supplying and recovering an electrolyte to and from the electroplating unit  10 . 
         [0040]    The electroplating unit  10  comprises a substrate holder  14 , a bath forming member  16  shaped in a tapered hollow cylinder, and an electrode head  18 . The bath forming member  16  has a smaller outer diameter at the lower end than the substrate W, and a top inner diameter larger than both the lower end thereof and the outer diameter of the electrode head  18  (the outer diameter of the porous member  22  described below). A seal portion is formed between the lower end of the bath forming member  16  and the substrate surface during operation to make a plating bath in a region (substrate side region) defined by the bath forming member  16  and the substrate surface. 
         [0041]    The electrode head  18  comprises a housing  26  having a open lower end covered by a porous member or diaphragm  22  for defining an anode chamber  24  within the housing  26 , in which an anode  20  is accommodated. A power source  28  for supplying plating current between the seed layer  7  (shown in  FIG. 5(   a )) formed on a surface of the substrate W held by the substrate holder  14  and the anode  20 . 
         [0042]    The porous member  22  is made of a porous membrane or a porous structural member in the embodiment and can be replaced by an ion exchange membrane. The porous membrane or porous structural member comprises mutually communicating fine pores capable of maintaining electrolyte. Specifically, the porous member  22  may be made of but is not limited to: a sintered compact of polyethylene or polypropylene; a laser worked porous member made of a Teflon (trade name) etc.; porous ceramics; sponges; and woven or non woven fabrics. 
         [0043]    One of the electrolyte supply systems  12   a  is for supplying a plating solution (processing liquid) Q 1  such as a copper sulfide plating solution to a substrate side region, which is defined between the substrate W held by the substrate holder  14  and the porous member  22 . The electrolyte supply systems  12   a  comprises: a reservoir tank  30   a  for accommodating a plating solution Q 1 ; a plating solution supply line  32   a  and a plating solution discharge line  36   a  extending from the reservoir tank  30   a  and connected to the substrate side region. 
         [0044]    Another electrolyte supply system  12   b  is for supplying an electrolyte solution (electrolyte) Q 2  free of copper such as a dilute sulfuric acid to an anode side region (counter electrode side region), which is partitioned by the porous member  22  and defined within the anode chamber  24 . The electrolyte supply system  12   b  comprises: a reservoir tank  30   b  for accommodating an electrolyte solution Q 2 ; a plating solution supply line  32   b  and a plating solution discharge line  36   a  extending from the reservoir tank and connected to the housing  26 . 
         [0045]    The electrolyte Q 2  has a specific resistance (electric conductivity) ρ 2  larger than the specific resistance ρ 1  of the plating solution Q 1 , as expressed by ρ 2 &gt;ρ 1 . 
         [0046]    The anode  20  is comprised of a mesh-like member made of an insoluble material such as an insoluble metal such as platinum or titanium, or a base metal plated with platinum etc. such as a titanium mesh plate coated with iridium oxide, for example. By using the insoluble electrode, there is no need of exchanging the electrode, and by using the mesh-like member, the plating solution or generated gases can flow through the electrode. 
         [0047]    When using an insoluble material for the anode  20 , oxygen gas is generated at the surface of the anode  20  during operation. A gas discharge line  60  is connected to the top wall of the housing  26 , in this embodiment, for exhausting accumulated gases in the anode chamber  24 , which is provided with a vacuum pump  62 . The vacuum pump evacuates the oxygen gas to prevent it from reaching the substrate W to generate particles. The pressure within the anode chamber  24  is preferably controlled at a preset value by a feedback control within the process. 
         [0048]    In the electrolyte supply system  12   b , a specific resistance detector  64  for detecting the specific resistance of the electrolyte Q 2  within the reservoir tank  30   b  and a specific resistance adjuster  66  for adjusting the specific resistance of electrolyte Q 2  based on the detected signal by the specific resistance detector  64  are provided. These devices make it possible to provide an electrolyte Q 2  of a regularly controlled constant specific resistance to the interior (counter electrode side region) of the anode chamber  24 . When plating copper, a 0.03-0.05% phosphorus containing copper can be used as the anode  20  to suppress generation of slimes. 
         [0049]    One exemplified process using the electroplating apparatus is described for filling copper in via holes  3  and interconnect trenches  4  formed on a surface of the substrate W as shown in  FIG. 5(   a ) and  FIG. 5(   b ). 
         [0050]    In the first place, as shown in  FIG. 5  ( a ), the substrate W is prepared, on which fine recesses for interconnect such as via holes  3  or interconnect trenches  4  are formed in the oxide film  2 , and a barrier layer  5  made of TaN etc. and a seed layer  7  as a feeder layer for electroplating are formed in turn. Since the present invention is particularly effective for the seed layer as thin as not more than 0.05 μm, when plating copper interconnections in an LSI, for example. The interconnections here are extremely fine with a width of not more than 0.3 μm (shown in  FIG. 6(   c )). 
         [0051]    The substrate W is supported by the substrate holder  14  with the surface facing upward and is elevated to a position at which the periphery of the substrate W is made to pressure contact with the bath forming member  16  to liquid tightly seal there. The electrode head  18  readily accommodating the electrolyte solution Q 2  within the anode chamber  24  is lowered until the distance between the upper (front) surface of the substrate W and the lower surface of the porous member  22  is a predetermined value. 
         [0052]    At this state, a predetermined amount of plating solution Q 1  is supplied or circulated to the substrate side region defined between the substrate W and the electrode head  18  and surrounded by the bath forming member  16 . At the same time, the electrolyte Q 2  contained in the anode side region partitioned by the porous member  22  within the anode chamber  24  is supplied to the area above the substrate W by pressurizing inside the anode chamber  24  or releasing the air tightness of the anode chamber  24 . By applying a plating voltage between the seed layer  7  of the substrate W and the anode  20  with the power source  28  to supply plating current and by rotating the substrate W together with electrode head  18  as is necessary, electroplating is performed on the surface of the substrate W. 
         [0053]    As described above, the anode side region (counter electrode side region) partitioned by the porous member  22  is supplied with the electrolyte Q 2  with a maximum specific resistance ρ 2  as possible, and by supplying the substrate side region with an ordinary plating solution Q 1 , it is possible to uniformly plate the substrate W even the seed layer  7  has a resistance indefinitely high. Therefore, while the conventional process provides a larger thickness film at the periphery close to the feed point than the central area, the present invention can deposit a uniform thickness film on the whole surface of the substrate W. Thus, the present invention can enhance uniformity within the surface area to prevent decrease of an effective surface area or device field ratio within the substrate surface. 
         [0054]    The electrolyte Q 2  supplied to the anode side region may be provided only with a function as an electrolyte capable of conducting electricity so that the throughput or processing ability of the plating apparatus is not lowered. 
         [0055]    After plating a predetermined time to fill copper within the via holes or interconnect trenches  4  as well as to deposit a copper film  6  on the oxide film  2 , application of plating voltage between the seed layer  7  and anode  20  is stopped to finish the plating process. Then, the electrode head  18  is elevated, the substrate holder  14  is lowered, and the substrate surface after plating is cleaned with deionized water etc. and is dried. Then, the substrate W is transferred to the next process stage. 
         [0056]      FIG. 3  shows another embodiment of the present invention applied to an electrolytic etching apparatus. The difference between this embodiment and that shown in  FIG. 1  is that the electrolyte supply system (plating solution supply system)  12   a  shown in  FIG. 1  is replaced by an electrolyte supply system (etching solution supply system)  12   c  comprising a reservoir tank  30   c , an etching solution supply line  32   c , and an etching solution discharge line  36   c  for supplying etching solution Q 3  such as a phosphoric acid solution. Another difference is that the electroplating unit  10  is replaced by an electrolytic etching unit  70  comprising a cathode  74  provided within a cathodic chamber  72  of the electrode head  18 , so that power is supplied from the power source  28  between the substrate W as an anode and the cathode  74  to perform etching of the substrate W. 
         [0057]      FIG. 4  shows a processing apparatus according to another embodiment of the present invention applied to an electroplating apparatus. The electroplating apparatus utilizes an electroplating unit  40  having a substrate holder  42  and a plating vessel  44  arranged in an above-and-below relationship. Inside the plating vessel  44 , an anode chamber  50  is defined which is circumferentially partitioned by a separation wall  46  and covered atop with a porous membrane  48 , in which an anode  52  is provided as a counter electrode to confront the substrate W. In the embodiment, a 0.03-0.05% phosphorus containing copper is used as the anode  52  to suppress generation of slimes. 
         [0058]    The plating solution Q 1  is supplied through the electrolyte supply system  12   a  into the interior of the plating vessel  44  from the bottom of the region surrounded by the outer wall of the plating vessel  44  and the separation wall  46  of the anode chamber  50 , and overflows the plating vessel  44  to return to the reservoir tank  30   a  through the return line  36   a  to thereby be circulated. The electrolyte Q 2  is supplied to the anode chamber  50  from the reservoir tank  30   b  through the supply line  32   b  through the center of the bottom and is discharged from the peripheral area of the bottom of the anode chamber through the discharge line  36   b  to return to the reservoir tank  30   b  to be circulated. Other structures are the same as that shown in  FIG. 1 . 
         [0059]    In this embodiment, the substrate W formed with a seed layer  7  as a feeder layer is supported by the substrate holder  42  with the surface facing downward, is lowered below the top of the plating vessel  44  until it covers a part of the top opening of the plating vessel  44 , and is halted there. 
         [0060]    At this state, the plating solution Q 1  is supplied to the substrate side region partitioned by the separation wall  46  and membrane  48 , that is, an area within the plating vessel  44  except for the anode chamber  50 , via the electrolyte supply system  12   a . The electrolyte supply system  12   a  contains and supplies a plating solution Q 1  such as a copper sulfide plating solution. Concurrently, the electrolyte Q 2  is supplied and circulated to the anode side region within the anode chamber  50 , which is defined by the separation wall  46  and the membrane  48 , via the electrolyte supply system  12   b . The electrolyte supply system  12   b  contains and supplies an electrolyte Q 2  such as dilute sulfuric acid. At this state, plating voltage is applied by the power source  28  between the seed layer  7  and the anode  52  to supply plating current, and the substrate W is rotated as is necessary, to thereby electroplate the surface of the substrate W. After a predetermined time of operation, plating is finished. 
         [0061]    In the above embodiment, copper is used as the interconnect material. However, instead of copper, any copper alloys, silver, or silver alloys can be used. 
         [0062]    In the embodiment of the present invention, the counter electrode side region partitioned by the membrane  22 ,  48  is supplied with an electrolyte having a possible maximum specific resistance, and the substrate side region is supplied with a normal process electrolyte, so that deposition or etching can be performed with a high uniformity within the surface area of the substrate W even for a thin feeder layer  7 . Therefore, it can provide a uniform film thickness, uniform interconnect filling properties, or uniform etching properties within the surface area even when processing a substrate W of a large diameter, so that semiconductor devices can be stably manufactured with a high yield.