Abstract:
A ruthenium film forming method includes: placing a target substrate in a processing container; supplying ruthenium carbonyl gas together with CO gas as a carrier gas into the processing container, the ruthenium carbonyl gas being generated from solid-state ruthenium carbonyl; supplying additional CO gas into the processing container; and forming a ruthenium film on the target substrate by decomposing the ruthenium carbonyl gas.

Description:
CROSS-REFERENCE TO RELATED APPLICATION 
       [0001]    This application claims priority to Japanese Patent Application No. 2014-035217, filed on Feb. 26, 2014, in the Japan Patent Office, the disclosure of which is incorporated herein in its entirety by reference. 
       TECHNICAL FIELD 
       [0002]    The present disclosure relates to a ruthenium film forming method, a ruthenium film forming apparatus and a semiconductor device manufacturing method. 
       BACKGROUND 
       [0003]    According to demands for high-speed semiconductor devices and miniaturization and high integration of wiring patterns, there has been a need to lower inter-capacitance between wirings and to improve electrical conductivity and electromigration resistance of the wirings. In response to these needs, Cu multilayer wiring technology is attracting attention. In the Cu multilayer wiring technology, copper (Cu), which has higher electrical conductivity and better electromigration resistance than aluminum (Al) or tungsten (W), is used as a wiring material and a low dielectric constant film (low-k film) is used as an interlayer insulating film. 
         [0004]    As a method for forming Cu wiring, it is known that a barrier layer including Ta, TaN, Ti or the like is formed on a low-k film where a trench or hole is formed by means of physical vapor deposition (PVD) represented by sputtering, a Cu seed layer is formed on the barrier layer also by means of PVD, and then Cu plating is conducted on the Cu seed layer. 
         [0005]    However, since the design rule of semiconductor devices is becoming more miniaturized, in the aforementioned method, it is difficult to form the Cu seed layer in the trench or hole by means of PVD having basically low step coverage whereby the Cu film in the trench or hole is formed to have voids. 
         [0006]    In this regard, a method for forming a ruthenium film on a barrier layer by means of chemical vapor deposition (CVD) and then forming a Cu film on the barrier layer has been proposed. The CVD-ruthenium film has better step coverage than the PVD-Cu film and has good adhesivity with a Cu film. Accordingly, the CVD-ruthenium film is effective as a base for burying a Cu film in a minute trench or hole. 
         [0007]    As a method for forming the CVD-ruthenium film, it is known that a ruthenium carbonyl (Ru 3 (CO) 12 ) is used as a film forming source. In the case of using ruthenium carbonyl, it is possible to obtain a high-purity film because impurity components in the film forming source are carbon and oxygen only. 
         [0008]    However, ruthenium carbonyl is easily decomposed at a relatively low temperature. If ruthenium carbonyl is decomposed before reaching a substrate, it is likely that desired step coverage cannot be obtained. In this regard, a technique is known that CO gas, which has an effect of suppressing decomposition of ruthenium carbonyl, is used as a carrier gas. 
         [0009]    With semiconductor devices becoming more miniaturized beyond the 22 nm node, it would be necessary to form an extremely thin ruthenium film having a film thickness of equal to or less than 2 nm with extremely high step coverage. Therefore, it is expected that sufficient step coverage will be difficult to obtain using the aforementioned technique. 
       SUMMARY 
       [0010]    The present disclosure provides a method and apparatus for forming a ruthenium film with better step coverage in comparison with the case using conventional techniques, and a semiconductor device manufacturing method using the ruthenium film. 
         [0011]    According to a first aspect of the present disclosure, there is provided a ruthenium film forming method that includes: placing a target substrate in a processing container; supplying ruthenium carbonyl gas together with CO gas as a carrier gas into the processing container, the ruthenium carbonyl gas being generated from solid-state ruthenium carbonyl; supplying additional CO gas into the processing container; and forming a ruthenium film on the target substrate by decomposing the ruthenium carbonyl gas. 
         [0012]    According to a second aspect of the present disclosure, there is also provided a ruthenium film forming apparatus that includes: a processing container that accommodates a target substrate; a film forming source container that accommodates solid-state ruthenium carbonyl as a film forming source; a carrier gas supply pipe that supplies CO gas as a carrier gas into the film forming source container; a film forming source gas supply pipe that supplies a ruthenium carbonyl gas together with the CO gas as the carrier gas into the processing container, the ruthenium carbonyl gas being generated from the solid-state ruthenium carbonyl in the film forming source container; and an additional CO gas pipe that supplies additional CO gas into the processing container; wherein a ruthenium film is formed on the target substrate by decomposing the ruthenium carbonyl gas. 
         [0013]    According to a third aspect of the present disclosure, there is also provided a semiconductor device manufacturing method that includes: forming a barrier film as a copper diffusion barrier on at least a surface of a concave portion in a substrate, the substrate including an interlayer insulating film and the concave portion being formed in the interlayer insulating film; forming a ruthenium film on the barrier film by the method of the first aspect; and forming a copper film on the ruthenium film by means of physical vapor deposition so that copper as a copper wiring is buried in the concave portion. 
     
    
     
       BRIEF DESCRIPTION OF THE DRAWINGS 
         [0014]    The accompanying drawings, which are incorporated in and constitute a part of the specification, illustrate embodiments of the present disclosure, and together with the general description given above and the detailed description of the embodiments given below, serve to explain the principles of the present disclosure. 
           [0015]      FIG. 1  is a sectional view illustrating an example of a film forming apparatus for performing a ruthenium film forming method according to an embodiment of the present disclosure. 
           [0016]      FIG. 2  is SEM images illustrating a relationship between a flow rate of additional counter CO gas and step coverage when forming a ruthenium film. 
           [0017]      FIG. 3  is a graph illustrating a relationship between a partial pressure ratio of Ru 3 (CO) 12 /CO when forming the ruthenium film and the number of voids observed after an immersion process using a hydrofluoric acid-based chemical liquid. 
           [0018]      FIG. 4  is a flowchart illustrating a Cu wiring forming method (semiconductor device manufacturing method) according to another embodiment of the present disclosure. 
           [0019]      FIGS. 5A to 5F  are sectional process views for explaining the Cu wiring forming method (semiconductor device manufacturing method) according to another embodiment of the present disclosure. 
           [0020]      FIG. 6  is a plan view illustrating an example of a film forming system for use in the Cu wiring forming method according to another embodiment of the present disclosure. 
       
    
    
     DETAILED DESCRIPTION 
       [0021]    Reference will now be made in detail to various embodiments, examples of which are illustrated in the accompanying drawings. In the following detailed description, numerous specific details are set forth in order to provide a thorough understanding of the inventive aspects of this disclosure. However, it will be apparent to one of ordinary skill in the art that the inventive aspects of this disclosure may be practiced without these specific details. In other instances, well-known methods, procedures, systems, and components have not been described in detail so as not to unnecessarily obscure aspects of the various embodiments. 
         [0022]    As a result of repeated research, the inventors of the present disclosure found out that decomposition of ruthenium carbonyl can be suppressed by using CO gas as a carrier gas of a film forming source, i.e., ruthenium carbonyl, and furthermore supplying additional CO gas into a processing container, whereby a ruthenium film can be formed with good step coverage. The present disclosure was completed based on the result. 
       &lt;Ruthenium Film Forming Apparatus&gt; 
       [0023]      FIG. 1  is a sectional view illustrating an example of a film forming apparatus for performing a ruthenium film forming method according to an embodiment of the present disclosure. 
         [0024]    A ruthenium film forming apparatus  100  forms a ruthenium film (hereinafter, also referred to as “Ru film”) by means of CVD. The ruthenium film forming apparatus  100  includes a substantially cylindrical chamber  11  which is airtightly sealed. In the chamber  11 , a susceptor  12  for horizontally holding a wafer W as a target substrate is arranged. The susceptor  12  is supported by a cylindrical supporting member  13  installed at the center of a bottom wall of the chamber  11 . A heater  15  is embedded in the susceptor  12  and is connected to a heater power source  16 . The heater power source  16  is controlled by a heater controller (not shown) based on a detection signal of a thermocouple (not shown) installed in the susceptor  12 , whereby the wafer W is controlled to be a desired temperature through the susceptor  12 . In the susceptor  12 , three wafer elevating pins (not shown) that vertically moves the wafer W supported thereon are installed such that the wafer elevating pins can project and retract with respect to the surface of the susceptor  12 . 
         [0025]    In a ceiling wall of the chamber  11 , a shower head  20  that introduces a processing gas, which is used for forming a Ru film by means of CVD, to the inside of the chamber  11  in a shower form is installed to face the susceptor  12 . The shower head  20  injects a gas supplied from a gas supply mechanism  40  (to be described later) to the inside of the chamber  11 . Two gas inlets  21   a  and  21   b  that introduce a gas are formed in the upper portion of the shower head  20 , and a gas diffusion space  22  is formed in the shower head  20 . A plurality of gas injection holes  23  communicating with the gas diffusion space  22  is formed in the bottom surface of the shower head  20 . 
         [0026]    In the bottom wall of the chamber  11 , an exhaust chamber  31  is installed to protrude downward. An exhaust pipe  32  is connected to the side surface of the exhaust chamber  31 . The exhaust pipe  32  is connected to an exhaust device  33  having a vacuum pump, a pressure control valve and so forth. The inside of the chamber  11  can be set to be a predetermined depressurized state (vacuum state) by operating the exhaust device  33 . 
         [0027]    In the side wall of the chamber  11 , a loading/unloading gate  37  is installed to load and unload the wafer W between the chamber  11  and a transfer chamber (not shown) under a predetermined depressurized state. The loading/unloading gate  37  is opened and closed by a gate valve G. 
         [0028]    The gas supply mechanism  40  includes a film forming source container  41  accommodating ruthenium carbonyl (Ru 3 (CO) 12 ) as a solid-state film forming source S. The film forming source container  41  is surrounded by a heater  42 . A carrier gas supply pipe  43  that supplies CO gas as a carrier gas is inserted into the film forming source container  41  from above. The carrier gas supply pipe  43  is connected to a CO gas supply source  44  that supplies a CO gas. A film forming source gas supply pipe  45  is also inserted into the film forming source container  41 . The film forming source gas supply pipe  45  is connected to the gas inlet  21   a  of the shower head  20 . Therefore, CO gas as a carrier gas is blown from the CO gas supply source  44  to the inside of the film forming source container  41  through the carrier gas supply pipe  43 , and ruthenium carbonyl (Ru 3 (CO) 12 ) gas vaporized in the film forming source container  41  is carried by the CO gas and supplied to the inside of the chamber  11  through the film forming source gas supply pipe  45  and the shower head  20 . In the carrier gas supply pipe  43 , a mass flow controller  46  that controls a flow rate of the carrier gas and valves  47   a  and  47   b  provided at the upstream and downstream of the mass flow controller  46 , respectively, are installed. In the film forming source gas supply pipe  45 , a flowmeter  48  that detects a flow rate of the ruthenium carbonyl (Ru 3 (CO) 12 ) gas and valves  49   a  and  49   b  provided at the upstream and downstream of the flowmeter  48 , respectively, are installed. 
         [0029]    The gas supply mechanism  40  also includes a counter CO gas pipe  51  branched at the upstream of the valve  47   a  in the carrier gas supply pipe  43 . The counter CO gas pipe is connected to the gas inlet  21   b  of the shower head  20 . Therefore, in addition to the ruthenium carbonyl gas, the CO gas from the CO gas supply source  44  is supplied to the inside of the chamber  11 , as an additional counter CO gas, through the counter CO gas pipe  51  and the shower head  20 . In the counter CO gas pipe  51 , a mass flow controller  52  that controls a flow rate of the CO gas and the valves  53   a  and  53   b  provided at the upstream and downstream of the mass flow controller  52 , respectively, are installed. 
         [0030]    The gas supply mechanism  40  also includes a dilution gas supply source  54  and a dilution gas supply pipe  55  having an end portion connected to the dilution gas supply source  54 . The other end portion of the dilution gas supply pipe  55  is connected to the film forming source gas supply pipe  45 . The dilution gas serves as a gas for diluting the film forming source gas. An inert gas such as Ar gas or N 2  gas is used as the dilution gas. The dilution gas also serves as a purge gas for purging residual gases within the film forming source gas supply pipe  45  and the chamber  11 . In the dilution gas supply pipe  55 , a mass flow controller  56  that controls a flow rate of the dilution gas and valves  57   a  and  57   b  provided at the upstream and downstream of the mass flow controller  56 , respectively, are installed. 
         [0031]    The ruthenium film forming apparatus  100  includes a controller  60  that controls each component such as the heater power source  16 , the exhaust device  33 , the gas supply mechanism  40  or the like. The controller  60  controls each component according to a command of a higher level control device. The higher level control device includes a non-transitory storage medium which stores processing recipes for performing the below-described film forming method, and controls the film forming processing according to the processing recipes stored in the non-transitory storage medium. 
       &lt;Ruthenium Film Forming Method&gt; 
       [0032]    Hereinafter, a ruthenium film forming method using the aforementioned ruthenium film forming apparatus  100  will be explained. 
         [0033]    First, the gate valve G is opened to load the wafer W into the chamber  11  through the loading/unloading gate  37 , and then the wafer is placed on the susceptor  12 . The wafer W is heated on the susceptor  12  which is heated by the heater  15  to a temperature of, for example, 150 to 250 degrees C. The inside of the chamber  11  is vacuum-exhausted by the vacuum pump in the exhaust device  33  to a pressure of 2 to 67 Pa. 
         [0034]    Next, the valves  47   a  and  47   b  are opened to blow CO gas as a carrier gas into the film forming source container  41  through the carrier gas supply pipe  43 . In the film forming source container  41 , the solid-state film forming source S is heated by the heater  42  to produce Ru 3 (CO) 12  gas by sublimation. The Ru 3 (CO) 12  gas is carried by the CO gas and introduced into the chamber  11  through the film forming source gas supply pipe  45  and the shower head  20 . On the surface of the wafer W, ruthenium (Ru) produced by thermal decomposition of the Ru 3 (CO) 12  gas is deposited to form a ruthenium film with a predetermined thickness. In some embodiments, the flow rate of the CO gas as a carrier gas may be, for example, 300 mL/min (sccm) or below so that the flow rate of the Ru 3 (CO) 12  gas becomes, for example, 5 mL/min (sccm) or below. Also, a dilution gas may be introduced into the chamber  11  at a predetermined ratio. 
         [0035]    By using the CO gas as a carrier gas as described above, decomposition reaction of Ru 3 (CO) 12  gas described below as formula (1) may be suppressed, and thus the film forming source gas can be supplied to the inside of the chamber  11  while maintaining the structure of Ru 3 (CO) 12  as much as possible. 
         [0000]      Ru 3 (CO) 12 →3Ru+12CO  (1)
 
         [0036]    In the surface of the wafer W placed in the chamber  11 , absorption/desorption reaction of Ru 3 (CO) 12  and CO described below as formula 2 occurs. This reaction is a surface reaction limit which allows a good step coverage when forming a film in a concave portion such as a trench or hole. The absorption/desorption reaction of Ru 3 (CO) 12  and CO is considered as an equilibrium reaction. 
         [0000]      Ru 3 (CO) 12 ( g )←→Ru x (CO) y ( ad )+(12- y )CO( ad )←→3Ru( s )+12CO( g )  (2)
 
         [0037]    Although good step coverage can be obtained by the above surface reaction limit, when considering Cu wirings in more miniaturized upcoming semiconductor devices beyond the 22 nm node, it gets difficult to form a Ru film, which has an extremely thin film thickness of 2 nm or below, as a base of a Cu film with a desired step coverage. As the semiconductor devices become more miniaturized, a concave portion such as a trench or hole is decreased in width and increased in aspect ratio. For that reason, it is necessary to suppress decomposition of Ru 3 (CO) 12  to make the Ru 3 (CO) 12  reach the bottom portion of the fine trench or hole, which is, however, difficult with conventional techniques. 
         [0038]    After reviewing methods for suppressing decomposition of Ru 3 (CO) 12 , it was found that decreasing a partial pressure ratio of Ru 3 (CO) 12 /CO by increasing a partial pressure of CO is effective. In other words, by increasing the partial pressure of CO, the backward reaction in the aforementioned formula 2 becomes more predominant and decomposition of Ru 3 (CO) 12  can be suppressed. 
         [0039]    However, in a case of only increasing the supply of CO gas as a career gas in order to increase the partial pressure of CO, the flow rate of Ru 3 (CO) 12  is also increased. Therefore, it is difficult to sufficiently decrease the partial pressure ratio of Ru 3 (CO) 12 /CO. 
         [0040]    For that reason, in the present embodiment, the counter CO gas pipe  51  is installed to supply, in addition to the CO gas as a carrier gas, the counter CO gas to the inside of the chamber  11 . By introducing, in addition to the ruthenium carbonyl gas, the additional counter CO gas to the inside of the chamber  11  through the counter CO gas pipe  51  and the shower head  20 , the partial pressure ratio of Ru 3 (CO) 12 /CO is decreased. The Ru film is formed under this state. 
         [0041]    Without installing the counter CO gas pipe  51 , the lower limit of the partial pressure ratio of Ru 3 (CO) 12 /CO is 0.0028. However, by supplying the counter CO gas through the counter CO gas pipe  51 , the lower partial pressure ratio of Ru 3 (CO) 12 /CO can be obtained. In some embodiments, the partial pressure ratio of Ru 3 (CO) 12 /CO may be 0.0025 or lower. 
         [0042]    Further, in some embodiments, the flow rate of the CO gas as a carrier gas may be 300 mL/min (sccm) or lower. The flow rate of the CO gas supplied from the counter CO gas pipe  51  may be 100 mL/min (sccm) or above in some embodiments, and may be 100 to 300 mL/min (sccm) in some other embodiments. 
         [0043]    When the Ru film with a desired thickness is formed, the valves  47   a  and  47   b  are closed to stop the Ru 3 (CO) 12  gas supply. Further, the valves  53   a  and  53   b  are closed to stop the counter CO gas supply, and the dilution gas as a purge gas is introduced from the dilution gas supply source  54  to the inside of the chamber  11  to purge the Ru 3 (CO) 12  gas. After that, the gate valve G is opened and the wafer W is unloaded from the loading/unloading gate  37 . 
         [0044]    In practice, a relationship between the flow rate of the counter CO gas (the partial pressure ratio of Ru 3 (CO) 12 /CO) during the Ru film formation and the step coverage was investigated. In the investigation, a TiN film having a thickness of 10 nm was formed in a trench, which has a width of 35 nm and is formed in a SiO 2  film (TEOS film) formed on a wafer, by means of ionized physical vapor deposition (iPVD), and then Ru 3 (C  0 ) 12  gas was supplied with a carrier CO gas having a flow rate of 200 mL/min (sccm). Simultaneously, under a pressure of 13.3 Pa and a susceptor temperature of 200 degrees C., Ru films having a thickness of 1.5 nm were formed on the TiN film while changing the flow rate of a counter CO gas in three stages, i.e., 0 mL/min (sccm), 100 mL/min (sccm) and 200 mL/min (sccm), thereby manufacturing samples A to C, respectively. The samples A to C were subjected to a treatment using hydrofluoric acid-based chemical liquid, and then step coverage was evaluated. Specifically, the samples A to C were immersed in a BHF liquid (a mixed solution of a HF aqueous solution and a NH 4 F aqueous solution) as a hydrofluoric acid-based chemical liquid for three minutes, and then the step coverage was evaluated by counting the number of voids in each sample by means of scanning electron microscope (SEM) observation. Since a TiN film as a base of the Ru film is dissolved in a hydrofluoric acid-based chemical liquid, portions in the TiN film where the Ru film was not normally deposited were dissolved to form voids. Therefore, continuity of the Ru film could be evaluated. 
         [0045]    SEM images of the samples A to C are illustrated in  FIG. 2 . As a result of counting the number of voids in the visual field of the SEM images in  FIG. 2 , seven voids were found in the sample A where the flow rate of the counter CO gas is 0 mL/min (sccm), five voids were found in the sample B where the flow rate of the counter CO gas is 100 mL/min (sccm), and one void was found in the sample C where the flow rate of the counter CO gas is 200 mL/min (sccm). That is to say, it was confirmed that as the flow rate of the counter CO gas increases, i.e., as the partial pressure ratio of Ru 3 (CO) 12 /CO decreases, a better continuity of Ru film and a higher step coverage are obtained. The partial pressure ratios of Ru 3 (CO) 12 /CO calculated from the gas flow rates in the samples A, B and C were 0.0028, 0.0018 and 0.0014, respectively. 
         [0046]    Further, an experiment was conducted while varying the susceptor temperature and the flow rates of the carrier CO gas and counter CO gas, and  FIG. 3  illustrates the relation between the partial pressure ratio of Ru 3 (CO) 12 /CO and the number of voids. It is clearly shown in  FIG. 3  that the number of voids decreases as the partial pressure ratio of Ru 3 (CO) 12 /CO decreases (correlation coefficient is 0.73). It was also confirmed that the step coverage is improved by decreasing the partial pressure ratio of Ru 3 (CO) 12 /CO. 
       &lt;Cu Wiring Forming Method&gt; 
       [0047]    Next, as another embodiment of the present disclosure, a Cu wiring forming method (a semiconductor device manufacturing method) using the Ru film formed as described above will be explained below. 
         [0048]      FIG. 4  is a flowchart illustrating a Cu wiring forming method.  FIGS. 5A to 5F  are sectional process views of the Cu wiring forming method. 
         [0049]    First, a semiconductor wafer (hereinafter simply referred to as “wafer”) W is prepared. The wafer W includes an interlayer insulating film  202 , e.g., a SiO 2  film, a low-k film (SiCO, SiCOH or the like) or the like, formed “on a base structure  201  (details thereof are omitted) and a trench  203  and via (not shown) for connection to an underlayer wiring formed in the interlayer insulating film  202  in a desired pattern (step S 1 ,  FIG. 5A ). In some embodiments, moisture or etching/ashing residue on the surface of the interlayer insulating film  202  in the wafer W may be removed by a degas process or a pre-clean process. 
         [0050]    Next, a barrier film  204  that suppress diffusion of Cu is formed on the entire surface of the interlayer insulating film  202  including surfaces of the trench  203  and the via (step S 2 ,  FIG. 5B ). 
         [0051]    In some embodiments, the barrier film  204  may have high barrier properties against Cu and a low resistance. A Ti film, TiN film, Ta film, TaN film or Ta/TaN double layered film may be appropriately used as the barrier film  204 . Alternatively, a TaCN film, W film, WN film, WCN film, Zr film, ZrN film, V film, VN film, Nb film, NbN film or the like may also be used as the barrier film  204 . The resistance of Cu wirings decreases as the volume of Cu buried in the trench or hole increases. Therefore, in some embodiments, the barrier film  204  may be formed to be extremely thin From this point of view, the thickness of the barrier film  204  may be 1 to 20 nm in some embodiments, and 1 to 10 nm in some other embodiments. The barrier film  204  may be formed by means of iPVD (ionized physical vapor deposition), for example, plasma sputtering. The barrier film  204  may also be formed by means of other PVD methods such as ordinary sputtering, ion plating or the like, or by means of CVD, ALD, plasma CVD or plasma ALD. 
         [0052]    Next, a Ru film  205  as a liner film is formed on the bather film  204  by means of the aforementioned CVD using ruthenium carbonyl (Ru 3 (CO) 12 ) (step S 3 ,  FIG. 5C ). In order to increase the volume of buried Cu to lower the resistance of the Cu wirings, in some embodiments, the Ru film may be formed to be thin, for example, 1 to 5 nm in thickness. 
         [0053]    Ru has a high wettability against Cu. For that reason, by forming a Ru film as a base of Cu, good Cu mobility during the subsequent Cu film formation by means of iPVD can be secured, which suppresses generation of an overhang that may block the trench or hole. Further as described above, by supplying the counter CO gas and decreasing the partial pressure ratio of Ru 3 (CO) 12 /CO, good step coverage can be obtained. For these reasons, it is possible to certainly bury Cu in more miniaturized future trenches or holes without generating voids. 
         [0054]    Subsequently, a Cu film  206  is formed by means of PVD to bury Cu in the trench  203  and via (not shown) (step S 4 ,  FIG. 5D ). In some embodiments, iPVD may be used as PVD, whereby generation of Cu overhangs can be suppressed and good buriability can be obtained. Moreover, a Cu film formed by means of PVD may have higher purity than a copper film formed by means of plating. In some embodiments, in preparation for a planarization process to be performed after the Cu film formation, the Cu film  206  may be further deposited to form an increased portion from the top surface of the trench  203 . In this case, the increased portion of the Cu film  206  may be formed by means of plating, instead of being formed by further performing PVD. 
         [0055]    After forming the Cu film  206 , an annealing process is performed if necessary (step S 5 ,  FIG. 5E ). The annealing process stabilizes the Cu film  206 . 
         [0056]    Thereafter, the entire front surface of the wafer W is polished by means of CMP (Chemical Mechanical Polishing), whereby the Cu film  206  formed on the front surface of the wafer W and the Ru film  205  and the bather film  204  disposed below the Cu film  206  are removed for planarization (step S 6 ,  FIG. 5F ). In this way, a Cu wiring  207  is formed in the trench and via (hole). 
         [0057]    After forming the Cu wiring  207 , an appropriate cap film such as a dielectric cap, a metal cap or the like is formed on the entire front surface of the wafer W including the Cu wiring  207  and the interlayer insulating film  202 . 
         [0058]    By using the aforementioned method, the Ru film can be formed in the fine trenches or holes with high step coverage, whereby the Cu film can be buried without generating voids. Since the Ru film can be formed with high step coverage, the Ru film can be formed to be extremely thin and the volume of Cu in the Cu wirings can be increased more, whereby the resistance Cu wirings can be lowered. Further, the crystal grain of Cu can be increased by burying Cu by means of PVD, whereby the resistance Cu wirings can be lowered. 
       &lt;Film Forming System for Forming Cu Wirings&gt; 
       [0059]    Next, a film forming system suitable for performing the Cu wiring forming method according to the another embodiment of the present disclosure is explained below. 
         [0060]      FIG. 6  is a plan view illustrating an example of a film forming system for use in the Cu wiring forming method according to another embodiment of the present disclosure. 
         [0061]    A film forming system  300  forms a Cu wiring in a wafer W by performing base film formation and Cu film formation. The film forming system  300  includes a first processing part  301  that forms a barrier film and a Ru film, a second processing part  302  that forms a Cu film, a loading/unloading part  303 , and a control part  304 . 
         [0062]    The first processing part  301  includes a first vacuum transfer chamber  311 , two barrier film forming apparatuses  312   a  and  312   b  and two Ru film forming apparatuses  314   a  and  314   b . The barrier film forming apparatuses  312   a  and  312   b  and the Ru film forming apparatuses  314   a  and  314   b  are connected to wall portions of the first vacuum transfer chamber  311 . The Ru film forming apparatuses  314   a  and  314   b  have the same configuration as that of the aforementioned ruthenium film forming apparatus  100 . The location of the barrier film forming apparatus  312   a  and the Ru film forming apparatus  314   a  is in line-symmetric with the location of the barrier film forming apparatus  312   b  and the Ru film forming apparatus  314   b.    
         [0063]    Degas chambers  305   a  and  305   b  that perform a degas process on the wafer W are connected to other wall portions of the first vacuum transfer chamber  311 . In addition, a transfer chamber  305  that transfers the wafer W between the first vacuum transfer chamber  311  and a second vacuum transfer chamber  321  to be described later is connected to the wall portion of the first vacuum transfer chamber  311  disposed between the degas chambers  305   a  and  305   b.    
         [0064]    Each of the barrier film forming apparatuses  312   a  and  312   b , the Ru film forming apparatuses  314   a  and  314   b , the degas chambers  305   a  and  305   b , and the transfer chamber  305  is connected to a corresponding side wall portion of the first vacuum transfer chamber  311  with a gate valve G interposed therebetween, and is communication with and blocked from the first vacuum transfer chamber  311  by opening and closing a corresponding gate valve G. 
         [0065]    The inside of the first vacuum transfer chamber  311  is kept to be a predetermined vacuum atmosphere, and a first transfer mechanism  316  that transfers the wafer W is installed inside of the first vacuum transfer chamber  311 . The first transfer mechanism  316  is arranged in an approximate center of the first vacuum transfer chamber  311 . The first transfer mechanism  316  includes a rotatable and extensible/contractible part  317  and two support arms  318   a  and  318   b  that support the wafer W. The support arms  318   a  and  318   b  are installed at the leading end of the rotatable and extensible/contractible part  317 . The first transfer mechanism  316  transfers the wafer W to and from the barrier film forming apparatuses  312   a  and  312   b , the Ru film forming apparatuses  314   a  and  314   b , the degas chambers  305   a  and  305   b , and the transfer chamber  305 . 
         [0066]    The second processing part  302  includes the second vacuum transfer chamber  321  and two Cu film forming apparatuses  322   a  and  322   b  connected to wall portions of the second vacuum chamber  321  facing each other. The Cu film forming apparatuses  322   a  and  322   b  may be used as an apparatuses that performs all the processes from a concave portion burying process to a film forming process for forming the increased portion. Alternatively, the Cu film forming apparatuses  322   a  and  322   b  may be used for the concave portion burying process only and the increased portion may be formed by plating. 
         [0067]    The degas chambers  305   a  and  305   b  are connected to two wall portions of the second vacuum transfer chamber  321  disposed at the side of the first processing part  301 . The transfer chamber  305  is connected to a wall portion of the second vacuum transfer chamber  321  disposed between the degas chambers  305   a  and  305   b . That is to say, the transfer chamber  305  and the degas chambers  305   a  and  305   b  are all installed between the first vacuum transfer chamber  311  and the second vacuum transfer chamber  321 , and the degas chambers  305   a  and  305   b  are arranged in right and left sides of the transfer chamber  305 . In addition, load lock chambers  306   a  and  306   b , each of which is capable of performing atmospheric transfer and vacuum transfer, are connected to two wall portions of the second vacuum transfer chamber  321  disposed at the side of the loading/unloading part  303 . 
         [0068]    Each of the Cu film forming apparatuses  322   a  and  322   b , the degas chambers  305   a  and  305   b , and the load lock chambers  306   a  and  306   b  is connected to a corresponding wall portion of the second vacuum transfer chamber  321  with a gate valve G interposed therebetween. Each of the Cu film forming apparatuses  322   a  and  322   b , the degas chambers  305   a  and  305   b , and the load lock chambers  306   a  and  306   b  is communicated with the second vacuum transfer chamber  321  by opening a corresponding gate valve G, and is blocked from the second vacuum transfer chamber  321  by closing the corresponding gate valve G. The transfer chamber  305  is connected to the second vacuum transfer chamber  321  without a gate valve interposed therebetween. 
         [0069]    The inside of the second vacuum transfer chamber  321  is kept to be a predetermined vacuum atmosphere, and a second transfer mechanism  326  is installed inside of the second vacuum transfer chamber  321 . The second transfer mechanism  326  loads and unloads the wafer W to and from the Cu film forming apparatuses  322   a  and  322   b , the degas chambers  305   a  and  305   b , the load lock chambers  306   a  and  306   b  and the transfer chamber  305 . The second transfer mechanism  326  is arranged in an approximate center of the second vacuum transfer chamber  321 . The second transfer mechanism  326  includes a rotatable and extensible/contractible part  327  and two support arms  328   a  and  328   b  that support the wafer W. The support arms  328   a  and  328   b  are installed at the leading end of the rotatable and extensible/contractible part  327 . The two support arms  328   a  and  328   b  are installed in the rotatable and extensible/contractible part  327  to face opposite directions from each other. 
         [0070]    The loading/unloading part  303  is installed at the opposite side of the second processing part  302  with the load lock chambers  306   a  and  306   b  interposed therebetween, and includes an air transfer chamber  331  to which the load lock chambers  306   a  and  306   b  are connected. In the upper portion of the air transfer chamber  331 , a filter (not shown) is installed to form a down flow of fresh air. Gate valves G are installed in a wall portion of the air transfer chamber  331  to which the load lock chambers  306   a  and  306   b  are connected. Two connection ports  332  and  333 , to which carriers C accommodating the wafers W as target substrates are connected, are installed in a wall portion of the air transfer chamber  331  opposing the wall portion to which the load lock chamber  306   a  and  306   b  are connected. An alignment chamber  334  that performs alignment of the wafer W is installed in a side wall portion of the air transfer chamber  331 . An air transfer mechanism  336  is installed in the air transfer chamber  331 . The air transfer mechanism  336  loads and unloads the wafer W to and from the carriers C and the load lock chambers  306   a  and  306   b . The air transfer mechanism  336  includes two multi-joint arms, and can move along a rail  338  in the arrangement direction of the carriers C. The air transfer mechanism  336  performs wafer transfer with the wafer W held on a hand  337  installed at the leading end of each of the multi-joint arms. 
         [0071]    The control part  304  controls respective components of the film forming system  300 , for example, the barrier film forming apparatuses  312   a  and  312   b , the Ru film forming apparatuses  314   a  and  314   b , the Cu film forming apparatuses  322   a  and  322   b , and the transfer mechanisms  316 ,  326  and  336 . The control part  304  functions as a higher level control device of controllers (not shown), e.g., the controller  60 , that control the respective components independently. The control part  304  includes a process controller, a user interface, and a storage unit. The process controller consists of a microprocessor (computer) for executing control of the respective components. The user interface includes a keyboard, through which an operator inputs commands for controlling the film forming system  300 , and a display that visualizes and shows operation status of the film forming system  300 . The storage unit stores a control program for executing processes to be performed in the film forming system  300  under a control of the process controller, and a program, i.e., processing recipes, for executing processes in the respective components of the film forming system  300  according to various data and processing conditions. The user interface and the storage unit are connected to the process controller. 
         [0072]    The processing recipes are stored in a non-transitory storage medium of the storage unit. The non-transitory storage medium may be a hard disk or a mobile storage medium such as CD-ROM, DVD, flash memory or the like. The recipes may be transmitted from other devices, for example, through a dedicated line. 
         [0073]    If necessary, an arbitrary recipe is retrieved from the storage unit according to a command received from the user interface and is executed on the process controller, whereby a desired process is performed in the film forming system  300  under a control of the process controller. 
         [0074]    In the film forming system  300 , the wafer W, in which a predetermined pattern including a trench or hole is formed, is taken out from the carrier C and is transferred to the load lock chamber  306   a  or  306   b  by the air transfer mechanism  336 . The load lock chamber  306   a  or  306   b  is depressurized to a degree of vacuum substantially equal to that of the second vacuum transfer chamber  321 . Then, the wafer Win the load lock chamber  306   a  or  306   b  is transferred to the degas chamber  305   a  or  305   b  through the second vacuum transfer chamber  321  by the second transfer mechanism  326 , and is subjected to a degas process. Subsequently, the wafer W is taken out from the degas chamber  305   a  or  305   b  and is transferred to the barrier film forming apparatus  312   a  or  312   b  through the first vacuum transfer chamber  311  by the first transfer mechanism  316 . Then, a barrier film is formed on the wafer W. After forming the barrier film, the wafer W is taken out from the barrier film forming apparatus  312   a  or  312   b  and is transferred to the Ru film forming apparatus  314   a  or  314   b  by the first transfer mechanism  316 . Then, a Ru film is formed on the wafer W as described above. After forming the Ru film, the wafer W is taken out from the Ru film forming apparatus  314   a  or  314   b  and is transferred to the transfer chamber  305  by the first transfer mechanism  316 . After that, the wafer W is taken out from the transfer chamber  305  and is transferred to the Cu film forming apparatus  322   a  or  322   b  through the second vacuum transfer chamber  321  by the second transfer mechanism  326 . Then, a Cu film is formed on the wafer W to bury Cu in the trench and via. At this time, in addition to the burying process of Cu, the increased portion of the Cu film may be also formed in the Cu film forming apparatus  322   a  or  322   b . Alternatively, only the burying process of Cu may be performed in the Cu film forming apparatus  322   a  or  322   b , and the increased portion of the Cu film may be formed by plating. 
         [0075]    After forming the Cu film, the wafer W is transferred to the load lock chamber  306   a  or  306   b , and the load lock chamber  306   a  or  306   b  is restored to atmospheric pressure. Then, the wafer W in which the Cu film is formed is taken out from the load lock chamber  306   a  or  306   b  and is transferred to the carrier C by the air transfer mechanism  336 . The process described above is repeated by a number of times equal to the number of the wafers W in the carrier C. 
         [0076]    According to the film forming system  300 , since the nitrogen plasma processing, the Ru film formation, and the Cu film formation can be carried out in a vacuum without being exposed to atmosphere, oxidization on the surfaces after each process can be prevented. Therefore, high-performance Cu wirings can be obtained. 
         [0077]    The processes from the barrier film formation to the Cu film formation according to the aforementioned embodiment can be carried out by the film forming system  300 . However, the annealing process and the CMP process, which are carried out after the Cu film formation, may be performed on the wafer W taken out from the film forming system  300  by using additional devices. The additional devices may have commonly-used configurations. By constituting a Cu wiring forming system with the additional devices and the film forming system  300  and by controlling the additional devices and the film forming system  300  using a common control unit having the same functions as those of the control part  304 , all the processes of the Cu wiring forming method according to the aforementioned embodiment may be controlled by a single processing recipe. 
       &lt;Other Applications&gt; 
       [0078]    While certain embodiments have been described, this embodiment is not intended to limit the scope of the disclosures. Indeed, the embodiment described herein may be embodied in a variety of other forms. For example, this embodiment shows a case that the Ru film formed according to the present disclosure is used as a base film of the Cu film when forming Cu wirings. However, the present disclosure is not limited to this case. Also, the configurations of the devices have been presented by way of example only, and a variety of configurations of devices may be used. 
         [0079]    While the aforementioned embodiments show an example that the methods of the present disclosure is applied to the wafer having the trench and via (hole), the shape of the concave portion is not limited to having both of a trench and via. Also, the structure of the applied device is not limited to the aforementioned embodiments. The substrate is also not limited to a semiconductor wafer. 
         [0080]    According to the present disclosure, the ruthenium film is formed by supplying additional CO gas to the processing container while using CO as a carrier gas that carries the ruthenium carbonyl gas as a film forming source. Therefore, it is possible to form the ruthenium film with better step coverage in comparison with the conventional method. 
         [0081]    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 disclosures. Indeed, the 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 disclosures. The accompanying claims and their equivalents are intended to cover such forms or modifications as would fall within the scope and spirit of the disclosures.