Patent Publication Number: US-11387112-B2

Title: Surface processing method and processing system

Description:
CROSS-REFERENCE TO RELATED APPLICATIONS 
     This application is based upon and claims the benefit of priority from Japanese Patent Application Nos. 2018-189432 and 2019-107422, filed on Oct. 4, 2018, and Jun. 7, 2019, respectively, the entire contents of which are incorporated herein by reference. 
     TECHNICAL FIELD 
     The present disclosure relates to a surface processing method and a processing system. 
     BACKGROUND 
     For example, Patent Documents 1 to 3 disclose processes of removing a natural oxide film produced when a metal of a contact member and a surface of a silicon film of a wiring layer are naturally oxidized during semiconductor manufacturing. 
     PRIOR ART DOCUMENT 
     Patent Documents 
     
         
         Japanese Laid-Open Patent Publication No. H6-224150 
         Japanese Laid-Open Patent Publication No. H7-22416 
         Japanese Laid-Open Patent Publication No. H9-321006 
       
    
     SUMMARY 
     According to an embodiment of the present disclosure, there is provided a method of performing a surface processing on a substrate having a metal layer formed on a bottom portion of a recess formed in an insulating film, the method including: supplying a halogen-containing gas into a processing chamber in which the substrate is loaded; and removing a metal oxide from the bottom portion of the recess using the halogen-containing gas. 
    
    
     
       BRIEF DESCRIPTION OF DRAWINGS 
       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. 
         FIG. 1  is a schematic plan view illustrating an example of a processing system used for a surface processing method according to an embodiment. 
         FIG. 2  is a vertical cross-sectional view illustrating an example of a processing chamber used for the surface processing method according to an embodiment. 
         FIG. 3  is a view representing an example of the experimental results of selectivity in a surface processing according to an embodiment. 
         FIG. 4  is a flowchart illustrating an example of a surface processing according to an embodiment. 
         FIGS. 5A to 5C  are schematic cross-sectional views of a wafer, illustrating respective steps of a surface processing and a film forming method according to an embodiment. 
         FIG. 6  is a flowchart illustrating an example of a surface processing according to a modification of an embodiment. 
         FIGS. 7A to 7D  are schematic cross-sectional views of a wafer, illustrating respective steps of a surface processing and a film forming method according to a modification of an embodiment. 
     
    
    
     DETAILED DESCRIPTION 
     Hereinafter, embodiments of the present disclosure will be described with reference to the accompanying drawings. In each of the drawings, the same components are denoted by the same reference numerals, and redundant descriptions may be omitted. In the following detailed description, numerous specific details are set forth in order to provide a thorough understanding of the present disclosure. However, it will be apparent to one of ordinary skill in the art that the present 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. 
     When a metal film of tungsten or the like is exposed from the bottom portion of a recess, such as a trench, a via hole, a contact hole or the like, which is formed in an insulating film such as a silicon oxide film, a surface of the metal film is naturally oxidized to form a metal oxide film. In this state, when a metal film (e.g., a ruthenium film) is embedded in the recess to form a ruthenium wiring layer, contact resistance due to the metal oxide film is increased. 
     Therefore, in order to reduce the contact resistance value, the ruthenium film is embedded in the recess after removing the metal oxide film. In an etching process of removing the metal oxide film, in order to avoid the shape of the recess of the insulating film from being changed, a condition for not etching the insulating film is required. Thus, the present embodiment provides a surface processing method and a processing system which are capable of removing a metal oxide film with high selectivity. That is, the present disclosure provides a surface processing technique capable of removing a metal oxide film with high selectivity without etching the insulating film by setting an etching rate of the metal oxide film to be higher than that of the insulating film having the recess by a predetermined level. 
     &lt;Processing System&gt; 
     First, a processing system used for a surface processing method according to an embodiment will be described with reference to  FIG. 1 .  FIG. 1  is a schematic plan view illustrating an example of the processing system used for the surface processing method according to an embodiment. 
     The processing system includes processing chambers  11  to  14 , a vacuum transfer chamber  20 , load-lock chambers  31  and  32 , an atmospheric transfer chamber  40 , load ports  51  to  53 , gate valves  61  to  68 , and a control device  70 . 
     The processing chamber  11  includes a stage  11   a  configured to place a semiconductor wafer W (hereinafter, referred to as a “wafer W”) thereon, and is connected to the vacuum transfer chamber  20  via a gate valve  61 . Similarly, the processing chamber  12  includes a stage  12   a  configured to place the wafer W thereon, and is connected to the vacuum transfer chamber  20  via a gate valve  62 . The processing chamber  13  includes a stage  13   a  configured to place the wafer W thereon, and is connected to the vacuum transfer chamber  20  via a gate valve  63 . The processing chamber  14  includes a stage  14   a  configured to place the wafer W thereon, and is connected to the vacuum transfer chamber  20  via a gate valve  64 . The interior of each of the processing chambers  11  to  14  is depressurized to a predetermined vacuum atmosphere such that a predetermined process (e.g., an etching process, a film forming process, a cleaning process, an ashing process or the like) is performed on the respective wafer W in the interior of the respective processing chamber. The operation of each part for the respective processes in the processing chambers  11  to  14  is controlled by the control device  70 . 
     The interior of the vacuum transfer chamber  20  is depressurized to a predetermined vacuum atmosphere. In addition, a transfer mechanism  21  is provided in the vacuum transfer chamber  20 . The transfer mechanism  21  transfers the wafer W between the processing chambers  11  to  14 , and the load-lock chambers  31  and  32 . The operation of the transfer mechanism  21  is controlled by the control device  70 . 
     The load-lock chamber  31  has a stage  31   a  configured to place the wafer W thereon, and is connected to the vacuum transfer chamber  20  via the gate valve  65  and to the atmospheric transfer chamber  40  via the gate valve  67 . Similarly, the load-lock chamber  32  has a stage  32   a  configured to place the wafer W thereon, and is connected to the vacuum transfer chamber  20  via the gate valve  66  and to the atmospheric transfer chamber  40  via the gate valve  68 . Each of the load-lock chambers  31  and  32  is configured such that the interior thereof is switched between an air atmosphere and a vacuum atmosphere. In addition, the switching of the interior of each of the load-lock chambers  31  and  32  between the vacuum atmosphere and the air atmosphere is controlled by the control device  70 . 
     The interior of the atmospheric transfer chamber  40  is set to be the air atmosphere. For example, a down-flow of clean air is formed inside the atmospheric transfer chamber  40 . In addition, the vacuum transfer chamber  40  is provided with a transfer mechanism  41 . The transfer mechanism  41  transfers the wafer W between the load-lock chambers  31  and  32 , and a carrier C in each of the load ports  51  to  53 , as will be described later. The operation of the transfer mechanism  41  is controlled by the control device  70 . 
     The load ports  51  to  53  are provided in the wall of a long side of the atmospheric transfer chamber  40 . The carrier C in which the wafers W are accommodated or an empty carrier C is mounted in each of the load ports  51  to  53 . A front opening unified pod (FOUP) may be used as the carrier C. 
     The gate valves  61  to  68  are configured to be openable/closable. In addition, the opening/closing of each of the gate valves  61  to  68  is controlled by the control device  70 . 
     The control device  70  controls the entire processing system by controlling the operations of the processing chambers  11  to  14 , the operations of the transfer mechanisms  21  and  41 , the opening/closing of each of the gate valves  61  to  68 , the switching of the interior of each of the load-lock chambers  31  and  32  between the vacuum atmosphere and the air atmosphere, and the like. 
     Next, an example of the operation of the processing system will be described. For example, the control device  70  opens the gate valve  67  and controls the transfer mechanism  41  to transfer the wafer W accommodated in, for example, the carrier C in the load port  51  to the stage  31   a  of the load-lock chamber  31 . The control device  70  closes the gate valve  67  to set the interior of the load-lock chamber  31  to a vacuum atmosphere. 
     The control device  70  opens the gate valves  61  and  65 , and controls the transfer mechanism  21  to transfer the wafer W in the load-lock chamber  31  to the stage  11   a  of the processing chamber  11 . The control device  70  closes the gate valves  61  and  65 , and operates the processing chamber  11 . Thus, a predetermined process (e.g., a metal oxide film removal process to be described later) is performed on the wafer W inside the processing chamber  11 . 
     Subsequently, the control device  70  opens the gate valves  61  and  63  and controls the transfer mechanism  21  to transfer the wafer W processed inside the processing chamber  11  to the stage  13   a  of the processing chamber  13 . The control device  70  closes the gate valves  61  and  63 , and operates the processing chamber  13 . Thus, a predetermined process (e.g., a ruthenium embedding process to be described later) is performed on the wafer W inside the processing chamber  13 . 
     The control device  70  may transfer the wafer W processed in the processing chamber  11  to the stage  14   a  of the processing chamber  14  in which a process similar to the process in the processing chamber  13  is capable of being performed. In the present embodiment, the wafer W in the processing chamber  11  is transferred to the processing chamber  13  or the processing chamber  14  depending on the operation states of the processing chamber  13  and the processing chamber  14 . With this configuration, it is possible for the control device  70  to perform the predetermined process (e.g., the ruthenium embedding process to be described later) on the plurality of wafers W in parallel using the processing chamber  13  and the processing chamber  14 . This makes it possible to improve productivity. 
     The control device  70  controls the transfer mechanism  21  to transfer the wafer W processed in the processing chamber  13  or  14  to the stage  31   a  of the load-lock chamber  31  or the stage  32   a  of the load-lock chamber  32 . The control device  70  sets the interior of the load-lock chamber  31  or the load-lock chamber  32  to an air atmosphere. The control device  70  opens the gate valve  67  or the gate valve  68 , and controls the transfer mechanism  41  to transfer the wafer W in the load-lock chamber  32  to, for example, the carrier C in the load port  53 , to be accommodated in the carrier C. 
     As described above, with the processing system illustrated in  FIG. 1 , while the wafers W are being processed in the respective processing chambers, it is possible to perform a predetermined surface processing on each wafer W without exposing the wafers W to the air, namely without breaking the vacuum. 
     &lt;Processing Apparatus&gt; 
     Next, an exemplary configuration of a processing apparatus  100  for providing the processing chambers  11  to  14  used for the surface processing method according to an embodiment will be described with reference to  FIG. 2 .  FIG. 2  is a schematic cross-sectional view of an example of the processing apparatus  100 . The processing apparatus  100  illustrated in  FIG. 2  removes a metal oxide film using the reaction of gas. In the processing apparatus  100 , no plasma is used for etching. For example, the processing apparatus  100  supplies a halogen-containing gas into the processing chamber to remove a tungsten oxide film, which is an example of the metal oxide film. The tungsten oxide film is an example of a natural oxide film formed on a surface layer of a metal layer formed of tungsten. Hereinafter, the processing apparatus  100  used for the processing chamber  11  will be described as an example. 
     The processing apparatus  100  includes a processing container  108 , a stage  107 , a shower head  103 , an exhauster  104 , a gas supply mechanism  105 , and a controller  106 . The processing container  108  is made of a metal such as aluminum, and has a substantially cylindrical shape. The processing container  108  accommodates a semiconductor wafer (hereinafter, referred to as a “wafer W”) which is an example of a substrate to be processed. A loading/unloading port  111  through which the wafer W is loaded and unloaded is formed in the sidewall of the processing container  108 , and is opened/closed by a gate valve  112 . An annular exhaust duct  116  having a rectangular cross section is provided on a main body of the processing container  108 . The exhaust duct  116  has a slit  113   a  formed along the inner peripheral surface thereof. An exhaust port  113   b  is formed in an outer wall of the exhaust duct  116 . A ceiling wall  114  is provided on the exhaust duct  116  so as to close an upper opening of the processing container  108 . The exhaust duct  116  and the ceiling wall  114  is hermetically sealed from each other with a seal ring  115 . 
     The stage  107  horizontally supports the wafer W inside the processing container  108 . The stage  107  is formed in a disk shape having a size corresponding to the wafer W. The stage  107  is formed of a ceramic material, such as aluminum nitride (AlN), or a metal material, such as aluminum or nickel alloy. A heater  121  is embedded in the stage  107  so as to heat the wafer W. The heater  121  generates heat with power provided from a heater power supply (not illustrated). Then, the temperature of the wafer W is controlled to a predetermined temperature by controlling the output of the heater  121  based on a temperature signal provided from a thermocouple (not illustrated) installed in the vicinity of an upper surface of the stage  107 . A cover member  122  formed of ceramic such as alumina is provided in the stage  107  so as to cover an outer peripheral area of the upper surface of the stage  107  and a side surface thereof. 
     A support member  123  is provided on a lower surface of the stage  107  to support the stage  107 . The support member  123  extends downward of the processing container  108  from the center of the lower surface of the stage  107  through a hole formed in a bottom wall of the processing container  108 . A lower end of the support member  123  is connected to a lifting mechanism  124 . The stage  107  is moved upward and downward between a processing position illustrated in  FIG. 2  and a transfer position as indicated by a dashed double-dotted line below the processing position via the support member  123  by the lifting mechanism  124 . The wafer W can be transferred at the transfer position. A flange  125  is mounted on the support member  123  below the processing container  108 . A bellows  126  configured to isolate an internal atmosphere of the processing container  108  from ambient air, is provided between the bottom surface of the processing container  108  and the flange  125 . The bellows  126  expands and contracts with the upward-downward movement of the stage  107 . 
     Three wafer support pins  127  (only two are illustrated) that protrude upward from a lifting plate  127   a  are provided in the vicinity of the bottom surface of the processing container  108 . The wafer support pins  127  are moved upward and downward via the lifting plate  127   a  by a lifting mechanism  128  provided below the processing container  108 . The wafer support pins  127  are inserted into respective through holes  107   a  formed in the stage  107  when the stage  107  is located at the transfer position, and are configured to be moved upward and downward on the upper surface of the stage  107 . By moving upward and downward the wafer support pins  127 , the wafer W is transferred between a wafer transfer mechanism (not illustrated) and the stage  107 . 
     The shower head  103  supplies a processing gas into the processing container  108  in the form of a shower. The shower head  103  is made of a metal, and is provided to face the stage  107 . The shower head  3  has a diameter substantially equal to that of the stage  107 . The shower head  103  includes a main body  131  fixed to the ceiling wall  114  of the processing container  108  and a shower plate  132  connected to a lower portion of the main body  131 . A gas diffusion space  133  is formed between the main body  131  and the shower plate  132 . Gas introduction holes  136  and  137  formed to penetrate through the center of the main body  131  and the ceiling wall  114  of the processing container  108  are connected to the gas diffusion space  133 . A protruded portion  134  annularly protruding downward is formed on a peripheral edge of the shower plate  132 . Gas ejection holes  135  are formed in a flat surface inward of the protruded portion  134 . In the state in which the stage  107  is located at the processing position, the processing chamber  11  is formed between the stage  107  and the shower plate  132 . An upper surface of the cover member  122  and the protruded portion  134  are close to each other so as to form an annular gap  139 . 
     The exhaust part  104  exhausts the interior of the processing container  108 . The exhaust part  104  includes an exhaust pipe  141  connected to the exhaust port  113   b , and an exhaust mechanism  142  connected to the exhaust pipe  141 . The exhaust mechanism  142  includes a vacuum pump, a pressure control valve and the like. During the processing, the gas in the processing container  108  reaches the exhaust duct  116  via the slit  113   a , and is exhausted from the exhaust duct  116  through the exhaust pipe  141  by the exhaust mechanism  142 . 
     The gas supply mechanism  105  supplies the processing gas into the processing container  108 . The gas supply mechanism  105  includes a WF 6  gas source  151   a , a hydrogen gas source  153   a.    
     The WF 6  gas source  151   a  supplies a WF 6  gas, which is an example of a halogen-containing gas, into the processing container  108  via a gas supply line  151   d . A flow rate controller  151   b  and a valve  151   c  are provided in the gas supply line  151   d  from the upstream side. The downstream side of the valve  151   c  in the gas supply line  151   d  is connected to the gas introduction hole  137 . The supply and cutoff of the WF 6  gas into the processing container  108  are performed by the valve  151   c.    
     The hydrogen gas source  153   a  supplies a hydrogen gas into the processing container  108  via a gas supply line  153   d . A flow rate controller  153   b  and a valve  153   c  are provided in the gas supply line  153   d  from the upstream side. The downstream side of the valve  153   c  in the gas supply line  153   d  is connected to the gas introduction hole  136 . The supply and cutoff of the hydrogen gas into the processing container  108  are performed by the valve  153   c.    
     The controller  106  may be a computer, and includes a central processing unit (CPU), a random access memory (RAM), a read only memory (ROM), an auxiliary storage device, and the like. The CPU operates based on a program stored in the RAM, the ROM or the auxiliary storage device, and controls the operations of the processing apparatus  100 . The controller  106  may be provided either inside or outside the processing apparatus  100 . In the case where the controller  106  is provided outside the processing apparatus  100 , the controller  106  is capable of controlling the processing apparatus  100  through a wired or wireless communication means. 
     &lt;Selectivity&gt; 
     Next, the experimental results of selectivity at the time of the surface processing according to an embodiment will be described with reference to  FIG. 3 .  FIG. 3  represents an example of the experimental results of an etching rate (E/R) when a silicon oxide film (SiO 2 ) and a tungsten oxide film are etched using the WF 6  gas, other halogen gases, or an argon gas supplied from the WF 6  gas source  151   a  illustrated in  FIG. 2 . The tungsten oxide film is an example of the metal oxide film. In this experiment, ClF 3 , WCl 5 , and WCl 6  gases were used as the other halogen gases. 
     In this experiment, an etching rate of a tungsten oxide film formed by a chemical vapor deposition (CVD) process and a silicon oxide film formed by a thermal oxidation process (ThOx) was measured. Specifically, an etched amount of the silicon oxide film was measured using a spectroscopic ellipsometer as a measurement device, and an etched amount of the tungsten oxide film was measured through an X-ray analysis (XPS, XRF). The XPS (X-ray photoelectron spectroscopy) is a measurement performed by an X-ray photoelectron spectroscopy method, and the XRF (X-ray fluorescence) is a measurement performed by an X-ray reflectance method. In this experiment, a plasma etching apparatus using a capacitively coupled plasma (CCP) was used for etching using the argon gas. A high-frequency power supply was connected to a lower electrode (stage) of the plasma etching apparatus. A high-frequency power of 13.56 MHz was applied to the lower electrode from the high-frequency power supply. In addition, the temperature of the stage was set to room temperature. When other gases of ClF 3 , WF 6 , WCl 5 , WCl 6 , and SOCl 2  were used, no plasma was used but a thermal reaction was used. 
     As a result of conducting experiments under the above conditions, as shown in the graph of  FIG. 3 , in the etching using each of the ClF 3 , WF 6 , WCl 5 , and WCl 6  gases, the etching rate of the tungsten oxide film was at least three times that of the silicon oxide film. In addition, it can be seen that, in the etching using each of the ClF 3 , WF 6 , WCl 5 , and WCl 6  gases, the etching rate of the tungsten oxide film to the silicon oxide film, namely the selectivity of the tungsten oxide film to the silicon oxide film, is higher than that of the etching using the argon gas. 
     Furthermore, as shown in the graph of  FIG. 3 , in the etching using an SOCl 2  (thionyl chloride) gas, which is an example of the halogen-containing gas, the silicon oxide film was not etched at all when the tungsten oxide film was etched by 1.85 nm. Therefore, it can be seen that, by using the SOCl 2  gas, it is possible to remove a tungsten oxide film  102   a  without changing the shape of the recess  113  of the insulating film  110  as the silicon oxide film. 
     In a physical etching through the sputtering of the argon gas, the selectivity is low. Thus, it is impossible to remove only the tungsten oxide film  102   a , the shape of the recess  113  of the insulating film  110  as the silicon oxide film may be changed. In contrast, a chemical etching is promoted by using at least one of the WF 6 , WCl 5 , WCl 6 , ClF 3 , and SOCl 2  gases. Thus, the insulating film as the silicon oxide film is not etched and at least one of the WF 6 , WCl 5 , WCl 6 , ClF 3 , and SOCl 2  gases reacts with the tungsten oxide film etching. This makes it possible to perform etching with high selectivity. From the above, in the surface processing method according to the present embodiment, it is possible to remove the metal oxide film with high selectivity without etching the insulating film through the etching using at least one of the ClF 3 , WF 6 , WCl 5 , WCl 6 , and SOCl 2  gases. 
     &lt;Surface Processing Method According to an Embodiment&gt; 
     Accordingly, in the present embodiment, a metal oxide film is etched away by a halogen-containing gas with high selectivity. A surface processing method that includes removing a metal oxide film using the WF 6  gas, which is an example of a halogen containing gas, will be described with reference  FIG. 4  and  FIGS. 5A to 5C .  FIG. 4  is a flowchart illustrating an example of the surface processing method according to an embodiment.  FIGS. 5A to 5C  are schematic cross-sectional views illustrating the wafer W supplied to the processing system. 
     As illustrated in  FIG. 5A , the wafer W supplied to the processing system is formed by laminating an insulating film  110  on a base film  101 . A metal layer of tungsten (hereinafter, referred to as a “tungsten layer  102 ”) is formed on the base film  101 . A surface layer of the tungsten layer  102  is naturally oxidized to form a tungsten oxide film  102   a.    
     In the present embodiment, as illustrated in  FIG. 4 , first, the wafer W having the above structure is prepared (step S 1 ). The wafer W is transferred into the processing container  108 . Specifically, in the state in which the valves  151   c  and  153   c  of  FIG. 2  are closed, the gate valve  112  is opened, and the wafer W is transferred into the processing container  108  by a transfer mechanism (not illustrated). The wafer W is placed on the stage  107  located at the transfer position. The transfer mechanism is withdrawn from the interior of the processing container  108 , and subsequently, the gate valve  112  is closed. The stage  107  is moved up to the processing position to form the processing chamber  11 . In addition, the internal pressure of the processing container  108  is adjusted to a predetermined pressure by the pressure control valve of the exhaust mechanism  142 . 
     Returning back to  FIG. 4 , subsequently, the valve  151   c  is opened and the WF 6  gas is supplied from the WF 6  gas source  151   a  to the gas supply line  151   d  (step S 2 ). At this time, since the valve  153   c  remains in the closed state, the H 2  gas is not supplied. Thus, the wafer W is exposed to the WF 6  gas in the processing chamber  11  so that the tungsten oxide film is removed. 
     After a predetermined period of time (e.g., 10 sec to 600 sec) elapses after the valve  151   c  is opened, the valve  151   c  is closed to stop the supply of the WF 6  gas. Thereafter, the wafer W is unloaded from the processing container  108  in the reverse procedure to that at the time of loading the wafer W into the processing container  108 . The unloaded wafer W is loaded into the processing chamber  13  or the processing chamber  14  through the vacuum transfer chamber  20  kept at a vacuum. A ruthenium film is formed on the wafer W in the processing chamber  13  or the processing chamber  14  (step S 3 ). Then, the process is terminated. 
     The surface processing method according to the present embodiment includes a step of providing the substrate having the metal layer in the bottom portion of the recess  113  formed in the insulating film  110  as illustrated in  FIG. 5A , a step of supplying the halogen-containing gas into the processing chamber  11 , and a step of removing the metal oxide film from the bottom portion of the recess  113  using the halogen-containing gas. 
     Although the processing apparatus  100  having the processing chamber  11  has been described, the processing apparatus may have a configuration that is the same as or different from that of the processing apparatus having the processing chambers  12  to  14 . 
     The insulating film  110  formed on the base film  101  as illustrated in  FIGS. 5A to 5C  may be a silicon-containing film, such as a silicon oxide film, a silicon film, a silicon nitride film or the like. However, the insulating film  110  is not limited to a single-layer film such as the silicon oxide film, the silicon film, or the silicon nitride film, and may be any of stacked films obtained by combining different silicon-containing films with each other, such as a stacked film of the silicon oxide film and the silicon nitride film. The recess  113 , such as a trench, a via hole, or a contact hole, is formed in the insulating film  110 . The tungsten layer  102  is exposed from the bottom portion of the recess  113 . Thus, the surface of the tungsten layer  102  is naturally oxidized to form the tungsten oxide film  102   a.    
     Process conditions used in the step of removing the tungsten oxide film  102   a  illustrated in step S 2  of  FIG. 4  are as follows. 
     (Process Conditions in Tungsten Oxide Film Removal Step)
         Gas: at least one of WF 6 , WCl 5 , WCl 6 , ClF 3 , and SOCl 2      Wafer temperature: for WF 6 , WCl 5 , WCl 6 , 400 degrees C. or higher
           for ClF 3 , 200 degrees C. or lower   for SOCl 2 , 100 to 300 degrees C.   
           Time period: 10 to 600 sec       

       FIG. 5B  is a schematic cross-sectional view illustrating the wafer W after the tungsten oxide film  102   a  is removed. In the step of removing the tungsten oxide film  102   a  illustrated in step S 2  of  FIG. 4 , the tungsten oxide film  102   a  is removed by performing the chemical etching using the halogen-containing gas having a high selectivity of the tungsten oxide film  102   a  relative to the insulating film  110 . This makes it possible to etch the tungsten oxide film  102   a  with high selectivity. 
     For example, in the sputtering as a physical reaction, the shape of the recess  113  such as a trench, a via hole, or a contact hole may be collapsed. In the recent fine process, the collapse of the shape has a great influence on the process. Thus, fine shape accuracy is required for the process. In the surface processing method according to the present embodiment, it is possible to effectively remove the tungsten layer  102  using the halogen-containing gas with high selectivity while maintaining the shape of the recess  113  through the high selectivity chemical etching based on the halogen-containing gas. From the above experimental results, it is preferable to use at least one of the WF 6 , WCl 5 , WCl 6 , ClF 3 , and SOCl 2  gases as the halogen-containing gas in the step of removing the tungsten oxide film  102   a.    
     The step of removing the tungsten oxide film  102   a  is a chemical reaction-based etching process. For example, when the WF 6  gas is supplied as a halogen-containing gas, oxygen atoms in the tungsten oxide film  102   a  and tungsten (W) in the WF 6  gas are combined with each other to produce tungsten oxyfluoride (W—F—O x ). The tungsten oxyfluoride thus produced is a volatile gas, and thus is released outward of the recess  113 . This makes it possible to remove the tungsten oxide film  102   a.    
     Meanwhile, the insulating film  110  as a silicon oxide film is less likely to be etched than the tungsten oxide film  102   a  due to the selectivity shown in  FIG. 3 . In the present embodiment, the step of removing the tungsten oxide film  102   a  performs a thermal reaction-based process without having to use plasma. This makes it possible to remove the tungsten oxide film  102   a  without collapsing the shape of the insulating film  110 . 
     In the step of removing the tungsten oxide film  102   a , in the case where the SOCl 2  gas is used and impurities caused by the SOCl 2  gas remains on the surface of the tungsten layer  102 , a subsequent step of removing the impurities may be performed prior to the step of embedding ruthenium. The subsequent step of removing the impurities may be an example of a process that includes supplying the H 2  gas, reducing the impurities caused by the SOCl 2  gas into hydrogens, and volatilizing away the hydrogens, but is not limited thereto. 
     After the tungsten oxide film  102   a  is removed in the processing chamber  11 , the wafer W is transferred to the processing chamber  13  or the processing chamber  14 . The process of the ruthenium embedding step is performed in the processing chamber  13  or the processing chamber  14  (see  FIG. 1 ). Here, an example in which the process of the ruthenium embedding step is performed in the processing chamber  13  will be described. 
     A CVD apparatus or the like may be used as the processing chamber  13  which performs the process of the ruthenium embedding step. First, a ruthenium-containing gas is supplied into the processing chamber  13  into which the wafer W has been loaded. For example, dodecacarbonyl triruthenium (Ru 3 (CO) 12 ) is supplied into the processing chamber  13 , and the wafer W placed on the stage  13   a  is heated by the heater embedded in the stage  13   a.    
     The Ru 3 (CO) 12  adsorbed onto the surface of the wafer W undergoes a thermal decomposition so that a ruthenium film is formed on the wafer W. Here, in the film forming method based on the thermal decomposition of Ru 3 (CO) 12 , a film forming rate at the surface of the tungsten layer  102  is higher than that at the side surface of the insulating film  110  as the silicon oxide film formed in the recess  113 . 
     Thus, ruthenium is embedded from the bottom portion of the recess  113  in a bottom-up manner to form a ruthenium-embedded portion. This makes it possible to embed ruthenium from the bottom portion of the recess  113  in a bottom-up manner, and to suppress the generation of voids and seams. 
       FIG. 5C  is a schematic cross-sectional view illustrating the wafer W after the ruthenium embedding step is completed. In the ruthenium embedding step, as indicated by long arrows in  FIG. 5C , a ruthenium-embedded portion  210  is formed from the bottom portion of the recess  113  in a bottom-up manner. In addition, as indicated by short arrows in  FIG. 5C , a ruthenium film is also gradually formed on side surfaces of the recess  113 . In this manner, the ruthenium film is gradually formed in a conformal manner while suppressing the occurrence of voids and seams, so that the ruthenium-embedded portion  210  embedded in the entire recess  113  is formed. In the ruthenium embedding step, in the case of forming the ruthenium-embedded portion  210  using Ru 3 (CO) 12 , the temperature of the stage may be controlled to about 100 to 250 degrees C. 
     Although the ruthenium embedding step has been described to be performed using Ru 3 (CO) 12 , the ruthenium-containing gas is not limited to Ru 3 (CO) 12 . For example, a gas containing Ru 3 (CO) 12  (but not containing oxygen gas), (2,4-dimethylpentadienyl)(ethylcyclopentadienyl)ruthenium: (Ru(DMPD)(EtCp)), bis(2,4-dimethylpentadienyl)Ruthenium: (Ru(DMPD) 2 ), 4-dimethylpentadienyl(methylcyclopentadienyl)Ruthenium: (Ru(DMPD)(MeCp)), Bis(Cyclopentadienyl)Ruthenium: (Ru(C 5 H 5 ) 2 ). Cis-dicarbonylbis(5-methylhexane-2,4-dionate)ruthenium(II), or bis(ethylcyclopentadienyl)Ruthenium(II): Ru(EtCp) 2  may be used as the ruthenium-containing gas. 
     In the ruthenium embedding step according to an embodiment, a ruthenium film forming method in which oxygen gas is not used as a gas supplied to the processing chamber  13  may be used. This makes it possible to prevent the surface of the tungsten layer  102  on the bottom portion of the recess  113  from being oxidized again by the oxygen gas. 
     &lt;Surface Processing Method According to Modification&gt; 
     Next, a surface processing method according to a modification of the embodiment will be described with reference to  FIG. 6  and  FIGS. 7A to 7D .  FIG. 6  is a flowchart illustrating an example of the surface processing method according to an embodiment.  FIGS. 7A to 7D  are schematic cross-sectional views of the wafer, illustrating a surface processing and respective steps of a film forming method according to the modification of the embodiment. 
     In this modification, after the step of removing the tungsten oxide film  102   a , a step of forming a tungsten film on the bottom portion of the recess  113  using a halogen-containing gas and a hydrogen gas is performed, and subsequently, a step of embedding ruthenium in the recess  113  is performed. 
     In this modification, after the tungsten oxide film  102   a  is removed in the processing chamber  11  of the processing apparatus  100  of  FIG. 2 , a tungsten film is formed using an atomic layer deposition (ALD) method in the same processing chamber  11 . 
     The surface processing method including the step of removing a tungsten oxide film according to this modification will be described with reference to  FIG. 6 . In this modification, first, as illustrated in  FIG. 7A , a wafer W in which an insulating film  110  is stacked on a base film  101  and a tungsten layer  102  is formed in a recess  113  of the insulating film  110  is provided (step S 11 ). The wafer W is loaded into the processing container  108 . 
     Subsequently, the valve  151   c  is opened, and the WF 6  gas is supplied from the WF 6  gas source  151   a  to the gas supply line  151   d  (step S 12 ). At this time, since the valve  153   c  remains in the closed state, the H 2  gas is not supplied. Thus, the wafer W is exposed to the WF 6  gas in the processing chamber  11  to remove a tungsten oxide film  102   a.    
     Subsequently, after a predetermined period of time elapses after the valve  151   c  is opened, the WF 6  gas and the H 2  gas are supplied into the processing container  108  by alternately opening and closing the valve  151   c  and the valve  153   c  (step S 13 ). Thus, the wafer W is alternately exposed to the WF 6  gas and the H 2  gas in the processing chamber  11  so that a tungsten film is formed. 
     Subsequently, it is determined whether or not the film formation of the tungsten film is completed (step S 14 ). When a film formation time elapses, it is determined that the film formation of the tungsten layer is completed, and the valves  151   c  and  153   c  are closed to stop the supply of the WF 6  gas and the H 2  gas. Thus, on the tungsten layer  102  from which the tungsten oxide film  102   a  has been removed, a tungsten layer having a predetermined film thickness corresponding to the removed portion is formed. Thus, it is possible to repair the upper surface of the tungsten layer  102  to restore the shape thereof. 
       FIG. 7C  is a schematic cross-sectional view of the wafer W after the tungsten film forming step. By performing the tungsten film forming step, a tungsten layer  102 ′ having a predetermined film thickness corresponding to the removed portion is formed on the tungsten layer  102 . Thus, in the ruthenium film forming step as a subsequent step, it is possible to form a ruthenium film on the tungsten layer  102 ′ in a bottom-up manner without changing the shape of the bottom portion of the recess  113  after the tungsten oxide film  102   a  is removed. 
     Thereafter, the wafer W is unloaded from the processing container  108  in the reverse procedure to that at the time of loading the wafer W into the processing container  108 . The unloaded wafer W is loaded into the processing chamber  13  or the processing chamber  14  through the vacuum transfer chamber  20  without breaking the vacuum. The ruthenium film is formed on the wafer W in the processing chamber  13  or the processing chamber  14  (step S 15 ). This process is terminated. 
     In step S 14  of  FIG. 6 , instead of the film forming time, a film thickness of the formed tungsten layer  102  may be measured. If it is determined that the film thickness reaches a predetermined value or more, control may be performed to stop the supply of the WCl 6  gas and the H 2  gas. 
     Process conditions used in the tungsten film forming step are as follows.
         (Process Conditions in Tungsten Film Forming Step)   Gas: at least one of WF 6 , WCl 5 , and WCl 6 , and H 2  gases   Wafer temperature: for WF 6 , WCl 5 , or WCl 6 , 400 degrees C. or higher   Time period: 10 sec to 600 sec       

     In the tungsten film forming step, the film forming process using the ALD method is performed, and plasma is not used. Thus, it is possible to form the tungsten layer  102  without collapsing the shape of the insulating film  110 , thereby returning the shape of the bottom portion of the recess  113  to the original state thereof. 
     The process including the step of removing the tungsten oxide film  102   a  and the step of forming the tungsten film may be performed in different processing chambers, but it is preferable to execute the process in the same processing chamber  11 . The reason is that in an etching process used in the step of removing the tungsten oxide film  102   a , a fluorine-containing substance may remain in the processing chamber  11  as a reaction product generated during the etching process. Therefore, by performing the process of the tungsten film forming step in the same processing chamber  11 , it is possible to cause the hydrogen gas and the fluorine-containing substance to react with each other, and discharge them. It is possible to remove the fluorine-containing substance in the processing chamber  11  while executing the tungsten film forming step. Furthermore, by performing the process including the two steps in the same processing chamber  11 , it is possible to eliminate a period of transfer time and to enhance productivity. 
     The halogen-containing gas used in the step of removing the tungsten oxide film  102   a  and the halogen-containing gas used in the step of forming the tungsten film may be the same gas. For example, by using any one of WF 6 , WCl 5 , and WCl 6  gases which are tungsten halides, in the step of removing the tungsten oxide film  102   a , the same gas may also be used in the step of forming the tungsten film. This further improves productivity. When the ClF 3  gas is used in the step of removing the tungsten oxide film  102   a , the ClF 3  gas may also be used in a step of cleaning the processing container  108 . 
     In some embodiments, in order to diffuse the halogen-containing gas to the bottom portion of the recess  113 , a tank may be provided at the upstream side of the valve  151   c . The halogen-containing gas may be stored in the tank. The valve  151   c  may be opened to discharge the halogen-containing gas having an increased pressure. 
     In some embodiments, in order to diffuse the hydrogen gas to the bottom portion of the recess  113 , a tank may be provided at the upstream side of the valve  153   c . The hydrogen gas may be stored in the tank. The valve  153   c  may be opened to discharge the hydrogen gas having an increased pressure. 
     As described above, with the surface processing method according to the embodiment, it is possible to remove the metal oxide film with high selectivity. With the processing system according to the embodiment, it is possible to continuously perform the step of removing the tungsten oxide film  102   a  and the step of embedding ruthenium on the wafer W without breaking the vacuum while respective processes are performed on the wafer W in the respective processing chambers. With the processing system according to the modification of the embodiment, it is possible to continuously perform the step of removing the tungsten oxide film  102   a , the step of forming the tungsten film and the step of embedding ruthenium on the wafer W without breaking the vacuum while respective processes are performed on the wafer W in the respective processing chambers. Furthermore, it is possible to perform the step of removing the tungsten oxide film  102   a  and the step of forming the tungsten film in the same processing chamber. 
     In the foregoing, the embodiments of the present disclosure have been described in detail. However, the present disclosure is not limited to the embodiments described above. In the embodiments described above, various modifications, substitutions or the like may be applicable without departing from the scope of the present disclosure. In addition, the matters described in the aforementioned embodiments may be combined unless a conflict arises. 
     The number of processing chambers  11  to  14 , the number of vacuum transfer chambers  20 , the number of load-lock chambers  31  and  32 , the number of atmospheric transfer chambers  40 , the number of load ports  51  to  53 , and the number of gate valves  61  to  68  are not limited to those illustrated in  FIG. 1 , but may be any number. Although the ruthenium embedding step has been described to be performed in the processing chambers  13  and  14  in the processing system, the ruthenium embedding step may be performed in the processing chambers  12  to  14 . It is possible to improve productivity by performing ruthenium embedding steps on different wafers in parallel using a plurality of processing chambers. In addition, the processing chamber  12  may be used as a processing chamber in which the step of removing the metal oxide film is performed like the processing chamber  11 . From the viewpoint of productivity, the number of processing apparatuses that perform the metal oxide film removing step and the ruthenium embedding step may be arbitrarily set in view of the system configuration. 
     That is to say, the number of processing chambers of the present disclosure may be one, but may be preferably two or more. The processing chambers of the present disclosure may include a first processing chamber in which a step of removing, from a substrate having a metal layer formed in a bottom portion of a recess formed in an insulating film, a metal oxide film on a surface of the metal layer, is performed, and a second processing chamber in which a step of embedding ruthenium from the bottom portion of the recess is performed. The processing chambers of the present disclosure may include the first processing chamber, the second processing chamber, and a third processing chamber in which a step of forming a tungsten film on the metal layer is performed. 
     Any of a capacitively coupled plasma (CCP) type, an inductively coupled plasma (ICP) type, a radial line slot antenna (RLSA) type, an electron cyclotron resonance plasma (ECR) type, and a helicon wave plasma (HWP) type is applicable to the processing chambers of the present disclosure. 
     According to an aspect, it is possible to provide a surface processing method and a processing system which are capable of removing a metal oxide film with high selectivity.