Patent Publication Number: US-2021164095-A1

Title: Tungsten Film-Forming Method, Film-Forming System and Storage Medium

Description:
CROSS-REFERENCE TO RELATED APPLICATION 
     This application is based upon and claims the benefit of priority from Japanese Patent Application No. 2018-029006, filed on Feb. 21, 2018, the entire contents of which are incorporated herein by reference. 
     TECHNICAL FIELD 
     The present disclosure relates to a tungsten film-forming method, a film-forming system and a storage medium. 
     BACKGROUND 
     In LSI, tungsten is widely used for parts requiring a heat resistance, such as a MOSFET gate electrode, a contact with a source/drain, a word line of a memory and the like. In recent years, a chemical vapor deposition (CVD) method with good step coverage is used for a deposition process of tungsten. 
     In the related art, when forming a tungsten film by the CVD method, from the viewpoint of adhesion to a silicon layer and suppression of a reaction, there has been used a method in which a TiN film is formed as a barrier layer on a silicon layer and a tungsten film is formed on the TiN film. Furthermore, in the related art, a nucleation process for facilitating uniform tungsten film formation is performed prior to main film formation of the tungsten film by the above reaction. 
     SUMMARY 
     Some embodiments of the present disclosure provide a technique capable of reducing the resistance of a tungsten film. 
     According to one embodiment of the present disclosure, there is provided a tungsten film-forming method, including: forming a silicon film on a substrate in a reduced pressure atmosphere by disposing the substrate having a protective film formed on a surface of the substrate in a processing container; forming an initial tungsten film by supplying a tungsten chloride gas to the substrate having the silicon film formed thereon; and forming a main tungsten film by supplying a tungsten-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 diagram showing an example of a schematic overall configuration of a film-forming system according to an embodiment of the present disclosure. 
         FIG. 2  is a sectional view showing an example of a schematic configuration of a first film-forming apparatus according to an embodiment of the present disclosure. 
         FIG. 3  is showing an example of a schematic configuration of a second film-forming apparatus according to an embodiment of the present disclosure. 
         FIG. 4  is a flowchart showing an example of a flow of respective steps of a film-forming method according to an embodiment of the present disclosure. 
         FIGS. 5A to 5D  are sectional views schematically showing an example of the states of a wafer in the respective steps of the film-forming method according to an embodiment of the present disclosure. 
         FIG. 6  is a diagram showing an example of a gas supply sequence at the time of forming a silicon film according to an embodiment of the present disclosure. 
         FIG. 7  is a diagram showing an example of a gas supply sequence at the time of forming an initial tungsten film according to an embodiment of the present disclosure. 
         FIG. 8  is a diagram showing an example of a layer configuration of a wafer according to an embodiment of the present disclosure. 
         FIG. 9  is a diagram showing an example of a layer configuration of a wafer according to a comparative example. 
         FIG. 10  is a diagram showing an example of a change in resistivity with respect to a thickness of a tungsten film. 
         FIG. 11  is a sectional view showing another example of the schematic configuration of the film-forming apparatus according to an embodiment of the present disclosure. 
     
    
    
     DETAILED DESCRIPTION 
     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 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. 
     Hereinafter, embodiments of a tungsten film-forming method and a film-forming system of the present disclosure will be described in detail with reference to the drawings. In the drawings, the same or corresponding parts are designated by like reference numerals. In addition, the technique disclosed herein is not limited by the embodiments. 
     [System Configuration] 
     In the present embodiment, a case where film formation is performed by a film-forming system including a plurality of film-forming apparatuses will be described as an example. First, a film-forming system according to the present embodiment will be described.  FIG. 1  is a diagram showing an example of a schematic overall configuration of a film-forming system according to an embodiment. The film-forming system  100  is configured to form a tungsten film by forming a silicon film on a substrate having a protective film, for example, an AlO film formed on a surface thereof, replacing the silicon film to form an initial tungsten film, and forming a main tungsten film on the initial tungsten film. In the present embodiment, a case where the substrate is a silicon wafer will be described by way of example. 
     As shown in  FIG. 1 , the film-forming system  100  includes one first film-forming apparatus  101  for forming a silicon film, one second film-forming apparatus  102  for forming an initial tungsten film, and one third film-forming apparatus  103  for forming a main tungsten film. The first film-forming apparatus  101 , the second film-forming apparatus  102  and the third film-forming apparatus  103  are connected to three wall portions of a vacuum transfer chamber  301  having a heptagonal shape in a plan view via gate valves G, respectively. The inside of the vacuum transfer chamber  301  is evacuated by a vacuum pump and kept at a predetermined degree of vacuum. In other words, the film-forming system  100  is a multi-chamber type vacuum processing system, in which a tungsten film can be continuously formed without breaking the vacuum. That is, all of the processes performed in the processing containers of the first film-forming apparatus  101 , the second film-forming apparatus  102 , and the third film-forming apparatus  103  are performed without exposing a silicon wafer W (hereinafter referred to as “wafer W”) to the air. 
     The configurations of the first film-forming apparatus  101  and the second film-forming apparatus  102  will be described later. The third film-forming apparatus  103  is, for example, an apparatus that forms a tungsten film (W) by alternately or simultaneously supplying, for example, a tungsten-containing gas and a hydrogen-containing gas onto the wafer W by ALD (Atomic Layer Deposition) or CVD (Chemical Vapor Deposition) in a vacuum atmosphere chamber. The tungsten-containing gas is, for example, a WF 6  gas, and the hydrogen-containing gas is, for example, a H 2  gas. 
     Three load lock chambers  302  are connected to the remaining three wall portions of the vacuum transfer chamber  301  via gate valves G 1 . At the opposite side of the vacuum transfer chamber  301  across the load lock chambers  302 , an atmospheric transfer chamber  303  is provided. The three load lock chambers  302  are connected to the atmospheric transfer chamber  303  via the gate valves G 2 . The load lock chambers  302  control a pressure between the atmospheric pressure and the vacuum when the wafer W is transferred between the atmospheric transfer chamber  303  and the vacuum transfer chamber  301 . 
     Three carrier attachment ports  305  to which carriers (FOUPs or the like) C for accommodating wafers W are attached are provided on the wall portion of the atmospheric transfer chamber  303  opposite to the wall portion to which the load lock chambers  302  are attached. An alignment chamber  304  for aligning the wafer W is provided on a sidewall of the atmospheric transfer chamber  303 . A down-flow of clean air is formed in the atmospheric transfer chamber  303 . 
     Inside the vacuum transfer chamber  301 , a transfer mechanism  306  is provided. The transfer mechanism  306  transfers the wafer W to the first film-forming apparatus  101 , the second film-forming apparatus  102  and the load lock chambers  302 . The transfer mechanism  306  includes two independently-movable transfer arms  307   a  and  307   b.    
     Inside the atmospheric transfer chamber  303 , a transfer mechanism  308  is provided. The transfer mechanism  308  is configured to transfer the wafer W to the carriers C, the load lock chambers  302  and the alignment chamber  304 . 
     The film-forming system  100  includes an overall control part  310 . The overall control part  310  includes a main control part such as a CPU (computer) or the like, an input device (a keyboard, a mouse, etc.), an output device (a printer, etc.), a display device (display, etc.), and a storage device (storage medium). The main control part controls the respective constituent parts of the first film-forming apparatus  101  and the respective constituent parts of the second film-forming apparatus  102 . Further, the main control part controls an exhaust mechanism, a gas supply mechanism and a transfer mechanism  306  of the vacuum transfer chamber  301 , an exhaust mechanism and a gas supply mechanism of the load lock chamber  302 , a transfer mechanism  308  of the atmospheric transfer chamber  303 , a driving system of the gate valves G, G 1  and G 2 , and the like. The main control part of the overall control part  310  causes the film-forming system  100  to perform a predetermined operation, for example, based on a processing recipe stored in a storage medium built in the storage device or in a storage medium set in the storage device. The overall control part  310  may be a higher-level control part of the control parts of the respective units, such as the control part  6  of the first film-forming apparatus  101  and the second film-forming apparatus  102  which will be described later. 
     Next, the operation of the film-forming system  100  configured as described above will be described. The following processing operation is executed based on the processing recipe stored in the storage medium in the overall control part  310 . 
     First, the carrier C containing wafers W is attached to the carrier attachment port  305  of the atmospheric transfer chamber  303 . An AlO film as a protective layer is formed on the surface of the wafer W. The transfer mechanism  308  of the atmospheric transfer chamber  303  takes out the wafer W from the carrier C and loads it into the alignment chamber  304 . The alignment chamber  304  performs alignment of the wafer W. In the atmospheric transfer chamber  303 , the gate valve G 2  of one of the load lock chambers  302  is opened. The transfer mechanism  308  takes out the aligned wafer W from the alignment chamber  304 . The transfer mechanism  308  loads the taken-out wafer W into the load lock chamber  302  from the opened gate valve G 2 . After loading the wafer W, the gate valve G 2  of the load lock chamber  302  is closed. The load lock chamber  302  into which the wafer W has been loaded is evacuated. 
     When the load lock chamber  302  reaches a predetermined degree of vacuum, the gate valve G 1  of the load lock chamber  302  is opened. The transfer mechanism  306  takes out the wafer W from the load lock chamber  302  by one of the transfer arms  307   a  and  307   b.    
     The gate valve G of the first film-forming apparatus  101  is opened. The transfer mechanism  306  loads the wafer W held by one of the transfer arms into the first film-forming apparatus  101  and returns the empty transfer arm to the vacuum transfer chamber  301 . The gate valve G of the first film-forming apparatus  101  is closed. The first film-forming apparatus  101  performs a film-forming process of a silicon film on the loaded wafer W. 
     After completion of the film-forming process of the silicon film, the gate valve G of the first film-forming apparatus  101  is opened. The transfer mechanism  306  unloads the wafer W from the first film-forming apparatus  101  by one of the transfer arms  307   a  and  307   b . The gate valve G of the second film-forming apparatus  102  is opened. The transfer mechanism  306  loads the wafer W held by one of the transfer arms into the second film-forming apparatus  102  having the gate valve G opened, and returns the empty transfer arm to the vacuum transfer chamber  301 . The gate valve G of the second film-forming apparatus  102  into which the wafer W has been loaded is closed. The second film-forming apparatus  102  performs a film-forming process of an initial tungsten film on the loaded wafer W. 
     After completion of the film-forming process of the initial tungsten film, the gate valve G of the second film-forming apparatus  102  is opened. The transfer mechanism  306  unloads the wafer W from the second film-forming apparatus  102  by one of the transfer arms  307   a  and  307   b . The gate valve G of the third film-forming apparatus  103  is opened. The transfer mechanism  306  loads the wafer W held by one of the transfer arms into the third film-forming apparatus  103  with the gate valve G opened, and returns the empty transfer arm to the vacuum transfer chamber  301 . The gate valve G of the third film-forming apparatus  103  into which the wafer W has been loaded is closed. The third film-forming apparatus  103  performs a film-forming process of a main tungsten film on the loaded wafer W. 
     After the main tungsten film is formed, the gate valve G of the third film-forming apparatus  103  is opened. The transfer mechanism  306  unloads the wafer W from the third film-forming apparatus  103  by one of the transfer arms  307   a  and  307   b . The gate valve G 1  of one of the load lock chambers  302  is opened. The transfer mechanism  306  loads the wafer W on the transfer arm into the load lock chamber  302 . The gate valve G 1  of the load lock chamber  302  into which the wafer W has been loaded is closed. The inside of the load lock chamber  302  into which the wafer W has been loaded is returned to the atmospheric pressure. The gate valve G 2  of the load lock chamber  302  whose inside has been returned to the atmospheric pressure is opened. The transfer mechanism  308  takes out the wafer W in the load lock chamber  302  from the opened gate valve G 2 . The transfer mechanism  308  returns the taken-out wafer W to the carrier C. 
     The above processes are performed concurrently on a plurality of wafers W, whereby the film-forming process of the tungsten film for a predetermined number of wafers W is completed. 
     As described above, by constituting the film-forming system  100  with one first film-forming apparatus  101 , one second film-forming apparatus  102  and one third film-forming apparatus, it is possible to realize the formation of the silicon film, the formation of the initial tungsten film and the formation of the main tungsten film with high throughput. The film-forming system  100  of the present embodiment is illustrated as a vacuum processing system equipped with three film-forming apparatuses. However, as long as a plurality of film-forming apparatuses can be mounted on a vacuum processing system, the number of film-forming apparatuses is not limited thereto. The number of film-forming apparatuses may be four or more. 
     [Configuration of Film-Forming Apparatus] 
     The first film-forming apparatus  101  and the second film-forming apparatus  102  have substantially the same configuration. Hereinafter, the configuration of the first film-forming apparatus  101  will be mainly described. As for the configuration of the second film-forming apparatus  102 , different parts will be mainly described. 
     The configuration of the first film-forming apparatus  101  will be described.  FIG. 2  is a sectional view showing an example of the schematic configuration of the first film-forming apparatus according to the present embodiment. The first film-forming apparatus  101  includes a processing container  1 , a mounting table  2 , a shower head  3 , an exhaust part  4 , a gas supply mechanism  5  and a control part  6 . 
     The processing container  1  is made of a metal such as aluminum or the like and has a substantially cylindrical shape. The processing container  1  accommodates a wafer W as a substrate to be processed. A loading/unloading port  11  for loading or unloading the wafer W is formed on the side wall of the processing container  1 . The loading/unloading port  11  is opened and closed by a gate valve  12 . An annular exhaust duct  13  having a rectangular cross section is provided on the main body of the processing container  1 . A slit  13   a  is formed in the exhaust duct  13  along the inner peripheral surface. An exhaust port  13   b  is formed in the outer wall of the exhaust duct  13 . On the upper surface of the exhaust duct  13 , a top wall  14  is provided so as to close the upper opening of the processing container  1 . The space between the exhaust duct  13  and the top wall  14  is hermetically sealed by a seal ring  15 . 
     The mounting table  2  horizontally supports the wafer W in the processing container  1 . The mounting table  2  is formed in a disk shape having a size corresponding to the wafer W and is supported by a support member  23 . The mounting table  2  is made of a ceramic material such as aluminum nitride (AlN) or the like, or a metallic material such as aluminum, nickel alloy or the like. A heater  21  for heating the wafer W is buried in the mounting table  2 . The heater  21  is supplied with electric power from a heater power supply (not shown) to generate heat. Then, an output of the heater  21  is controlled by a temperature signal of a thermocouple (not shown) provided in the vicinity of the upper surface of the mounting table  2 , whereby the wafer W is controlled to a predetermined temperature. In the mounting table  2 , a cover member  22  formed of ceramics such as alumina or the like is provided so as to cover the outer peripheral region of the upper surface and the side surface. 
     On the bottom surface of the mounting table  2 , a support member  23  for supporting the mounting table  2  is provided. The support member  23  extends downward from the center of the bottom surface of the mounting table  2  through a hole formed in the bottom wall of the processing container  1 . The downwardly-extending lower end of the support member  23  is connected to an elevating mechanism  24 . The mounting table  2  is raised and lowered via the support member  23  by the elevating mechanism  24  between a processing position shown in  FIG. 2  and a transfer position located below the processing position as indicated by a two-dot chain line so that the wafer W can be transferred. A flange portion  25  is attached to the support member  23  on the lower side of the processing container  1 . Between the bottom surface of the processing container  1  and the flange portion  25 , there is provided a bellows  26  which isolates the atmosphere inside the processing container  1  from an external air and which expands and contracts in response to the upward/downward movement of the mounting table  2 . 
     Three wafer support pins  27  are provided in the vicinity of the bottom surface of the processing container  1  so as to protrude upward from an elevating plate  27   a . In  FIG. 2 , two of the three wafer support pins  27  are shown. The wafer support pins  27  are raised and lowered via the elevating plate  27   a  by an elevating mechanism  28  provided below the processing container  1 . The wafer support pins  27  are inserted through the through holes  2   a  provided in the mounting table  2  located at the transfer position and can protrude and retract with respect to the upper surface of the mounting table  2 . By moving the wafer support pins  27  up and down, the delivery of the wafer W between the transfer mechanism (not shown) and the mounting table  2  is performed. 
     The shower head  3  supplies a processing gas into the processing container  1  in a shower shape. The shower head  3  is made of a metal and is provided so as to face the mounting table  2 . The shower head  3  has substantially the same diameter as the mounting table  2 . The shower head  3  includes a main body portion  31  fixed to the top wall  14  of the processing container  1  and a shower plate  32  connected to a lower portion of the main body portion  31 . A gas diffusion space  33  is formed between the main body portion  31  and the shower plate  32 . In the gas diffusion space  33 , gas introduction holes  36  and  37  are provided so as to penetrate the top wall  14  of the processing container  1  and the center of the main body portion  31 . An annular protrusion  34  protruding downward is formed in the peripheral edge portion of the shower plate  32 . Gas discharge holes  35  are formed on the inner flat surface of the annular protrusion  34 . In a state in which the mounting table  2  is located at the processing position, a processing space  38  is formed between the mounting table  2  and the shower plate  32 , and the upper surface of the cover member  22  and the annular protrusion  34  come close to each other to form an annular gap  39 . 
     The exhaust part  4  evacuates the inside of the processing container  1 . The exhaust part  4  includes an exhaust pipe  41  connected to the exhaust port  13   b  and an exhaust mechanism  42  having a vacuum pump, a pressure control valve and the like connected to the exhaust pipe  41 . In a process, the gas in the processing container  1  is moved to the exhaust duct  13  via the slit  13   a  and is exhausted from the exhaust duct  13  through the exhaust pipe  41  by the exhaust mechanism  42 . 
     The gas supply mechanism  5  is connected to the gas introduction holes  36  and  37  and is capable of supplying various gases used for film formation. In the present embodiment, a silicon film is formed on the wafer W by supplying a SiH 4  (silane) gas and a B 2 H 6  (boron) gas from the gas supply mechanism  5 . By forming the silicon film using the SiH 4  gas and the B 2 H 6  gas, it is possible to improve the adhesion of the silicon film with respect to the wafer W. The gas used for forming the silicon film is not limited to the combination of the SiH 4  and the B 2 H 6 . For example, the gas used for forming the silicon film may be DCS or Si 2 H 6 . 
     For example, the gas supply mechanism  5  includes a SiH 4  gas supply source  51   a , an N 2  gas supply source  52   a , an N 2  gas supply source  53   a , a B 2 H 6  gas supply source  55   a , an N 2  gas supply source  56   a  and an N 2  gas supply source  57   a  as gas supply sources for forming a silicon film. In the gas supply mechanism  5  shown in  FIG. 2 , the respective gas supply sources are shown separately. However, the gas supply sources capable of being used in common may be used in common. 
     The SiH 4  gas supply source  51   a  supplies a SiH 4  gas into the processing container  1  via a gas supply line  51   b . In the gas supply line  51   b , a flow rate controller  51   c , a storage tank  51   d  and a valve  51   e  are installed sequentially from the upstream side. On the downstream side of the valve  51   e , the gas supply line  51   b  is connected to the gas introduction hole  36 . The SiH 4  gas supplied from the SiH 4  gas supply source  51   a  is temporarily stored in the storage tank  51   d  before being supplied into the processing container  1 , pressurized to a predetermined pressure in the storage tank  51   d , and then supplied to the processing container  1 . The supply and cutoff of the SiH 4  gas to be supplied from the storage tank  51   d  to the processing container  1  is performed by the valve  51   e . By temporarily storing the SiH 4  gas in the storage tank  51   d  in this manner, the SiH 4  gas can be stably supplied into the processing container  1  at a relatively large flow rate. 
     The N 2  gas supply source  52   a  supplies an N 2  gas as a carrier gas into the processing container  1  via a gas supply line  52   b . In the gas supply line  52   b , a flow rate controller  52   c , a storage tank  52   d  and a valve  52   e  are installed sequentially from the upstream side. On the downstream side of the valve  52   e , the gas supply line  52   b  is connected to the gas supply line  51   b . The N 2  gas supplied from the N 2  gas supply source  52   a  is temporarily stored in the storage tank  52   d  before being supplied into the processing container  1 , pressurized to a predetermined pressure in the storage tank  52   d , and then supplied into the processing container  1 . The supply and cutoff of the N 2  to be supplied from the storage tank  52   d  to the processing container  1  is performed by the valve  52   e . By temporarily storing the N 2  gas in the storage tank  52   d  in this manner, the N 2  gas can be stably supplied into the processing container  1  at a relatively large flow rate. 
     The N 2  gas supply source  53   a  supplies an N 2  gas as a carrier gas into the processing container  1  via a gas supply line  53   b . In the gas supply line  53   b , a flow rate controller  53   c , a valve  53   e  and an orifice  53   f  are installed sequentially from the upstream side. On the downstream side of the orifice  53   f , the gas supply line  53   b  is connected to the gas supply line  51   b . The N 2  gas supplied from the N 2  gas supply source  53   a  is continuously supplied into the processing container  1  during the film formation on the wafer W. The supply and cutoff of the N 2  gas to be supplied from the N 2  gas supply source  53   a  to the processing container  1  are performed by the valve  53   e . The gas is supplied to the gas supply line  51   b  at a relatively large flow rate by the storage tanks  51   d  and  52   d . The gas supplied to the gas supply line  51   b  is prevented from flowing back to the gas supply line  53   b  by the orifice  53   f.    
     The B 2 H 6  gas supply source  55   a  supplies a B 2 H 6  gas into the processing container  1  via a gas supply line  55   b . In the gas supply line  55   b , a flow rate controller  55   c , a storage tank  55   d  and a valve  55   e  are installed sequentially from the upstream side. On the downstream side of the valve  55   e , the gas supply line  55   b  is connected to the gas introduction hole  37 . A B 2 H 6  gas supplied from the B 2 H 6  gas supply source  55   a  is temporarily stored in the storage tank  55   d  before being supplied into the processing container  1 , pressurized to a predetermined pressure in the storage tank  55   d , and then introduced into the processing container  1 . The supply and cutoff of the B 2 H 6  gas to be supplied from the storage tank  55   d  to the processing container  1  are performed by the valve  55   e . By temporarily storing the B 2 H 6  gas in the storage tank  55   d  in this manner, the B 2 H 6  gas can be stably supplied into the processing container  1  at a relatively large flow rate. 
     The N 2  gas supply source  56   a  supplies an N 2  gas as a carrier gas into the processing container  1  via a gas supply line  56   b . In the gas supply line  56   b , a flow rate controller  56   c , a storage tank  56   d  and a valve  56   e  are installed sequentially from the upstream side. On the downstream side of the valve  56   e , the gas supply line  56   b  is connected to the gas supply line  55   b . The N 2  gas supplied from the N 2  gas supply source  56   a  is temporarily stored in the storage tank  56   d  before being supplied into the processing container  1 , pressurized to a predetermined pressure in the storage tank  56   d , and then supplied into the processing container  1 . The supply and cutoff of the N 2  gas to be supplied from the storage tank  56   d  to the processing container  1  is performed by the valve  56   e . By temporarily storing the N 2  gas in the storage tank  56   d  in this manner, the N 2  gas can be stably supplied into the processing container  1  at a relatively large flow rate. 
     The N 2  gas supply source  57   a  supplies an N 2  gas as a carrier gas into the processing container  1  via a gas supply line  57   b . In the gas supply line  57   b , a flow rate controller  57   c , a valve  57   e  and an orifice  57   f  are installed sequentially from the upstream side. On the downstream side of the orifice  57   f , the gas supply line  57   b  is connected to the gas supply line  55   b . The N 2  gas supplied from the N 2  gas supply source  57   a  is continuously supplied into the processing container  1  during the film formation on the wafer W. The supply and cutoff of the N 2  gas to be supplied from the N 2  gas supply source  57   a  to the processing container  1  are performed by the valve  57   e . The gas is supplied to the gas supply line  55   b  at a relatively large flow rate by the storage tanks  55   d  and  56   d . The gas supplied to the gas supply line  55   b  is prevented from flowing back to the gas supply line  57   b  by the orifice  57   f.    
     The operation of the first film-forming apparatus  101  configured as described above is generally controlled by the control part  6 . The control part  6  is, for example, a computer, and includes a CPU (Central Processing Unit), a RAM (Random Access Memory), a ROM (Read Only Memory), an auxiliary storage device, and the like. The CPU operates based on a program stored in the ROM or the auxiliary storage device, and controls the overall operation of the apparatus. The control part  6  may be provided inside the first film-forming apparatus  101  or may be provided outside the first film-forming apparatus  101 . When the control part  6  is provided outside the first film-forming apparatus  101 , the control part  6  can control the first film-forming apparatus  101  by a wire or wireless communication means. 
     Next, the configuration of the second film-forming apparatus  102  will be described.  FIG. 3  is a sectional view showing an example of the schematic configuration of the second film-forming apparatus according to the embodiment. The second film-forming apparatus  102  has the same configuration as the first film-forming apparatus  101  except for the gas to be used and the gas supply mechanism  5  for supplying the gas. The parts of the second film-forming apparatus  102  which are the same as those of the first film-forming apparatus  101  are denoted by like reference numerals, and a description thereof will be omitted. Different points will be mainly described. 
     The gas supply mechanism  5  is connected to gas introduction holes  36  and  37 , and is capable of supplying various gases used for film formation. In the present embodiment, a tungsten chloride gas and a hydrogen gas are supplied from the gas supply mechanism  5  to form an initial tungsten film on the wafer W. In the present embodiment, a case where a WCl 6  gas is used as tungsten chloride gas is described by way of example. However, a WCl 5  gas may be used. Further, the gas used for forming the initial tungsten film is not limited to the combination of the tungsten chloride gas and the hydrogen gas. For example, depending on process conditions such as a temperature, a pressure and the like, the initial tungsten film may be formed by only the tungsten chloride gas. 
     For example, the gas supply mechanism  5  includes a WCl 6  gas supply source  61   a , an N 2  gas supply source  62   a , an N 2  gas supply source  63   a , a H 2  gas supply source  64   a , a H 2  gas supply source  65   a , an N 2  gas supply source  66   a , and an N 2  gas supply source  67   a  as a gas supply source of a gas for forming the initial tungsten film. Even in the gas supply mechanism  5  shown in  FIG. 3 , the respective gas supply sources are separately shown. However, the gas supply sources capable of being used in common may be used in common. 
     The WCl 6  gas supply source  61   a  supplies a WCl 6  gas into the processing container  1  via a gas supply line  61   b . In the gas supply line  61   b , a flow rate controller  61   c , a storage tank  61   d  and a valve  61   e  are installed sequentially from the upstream side. On the downstream side of the valve  61   e , the gas supply line  61   b  is connected to the gas introduction hole  36 . The WCl 6  gas supplied from the WCl 6  gas supply source  61   a  is temporarily stored in the storage tank  61   d  before being supplied into the processing container  1 , pressurized to a predetermined pressure in the storage tank  61   d , and then supplied into the processing container  1 . The supply and cutoff of the WCl 6  gas to be supplied from the storage tank  61   d  to the processing container  1  is performed by the valve  61   e . By temporarily storing the WCl 6  gas in the storage tank  61   d  in this way, the gas supply mechanism  5  can stably supply the WCl 6  gas into the processing container  1  at a relatively large flow rate. 
     The N 2  gas supply source  62   a  supplies an N 2  gas as a purge gas into the processing container  1  via a gas supply line  62   b . In the gas supply line  62   b , a flow rate controller  62   c , a storage tank  62   d  and a valve  62   e  are installed sequentially from the upstream side. On the downstream side of the valve  62   e , the gas supply line  62   b  is connected to the gas supply line  61   b . The N 2  gas supplied from the N 2  gas supply source  62   a  is temporarily stored in the storage tank  62   d  before being supplied into the processing container  1 , pressurized to a predetermined pressure in the storage tank  62   d , and then supplied into the processing container  1 . The supply and cutoff of the N 2  gas to be supplied from the storage tank  62   d  to the processing container  1  is performed by the valve  62   e . By temporarily storing the N 2  gas in the storage tank  62   d  in this way, the gas supply mechanism  5  can stably supply the N 2  gas into the processing container  1  at a relatively large flow rate. 
     The N 2  gas supply source  63   a  supplies an N 2  gas as a carrier gas into the processing container  1  via a gas supply line  63   b . In the gas supply line  63   b , a flow rate controller  63   c , a valve  63   e  and an orifice  63   f  are installed sequentially from the upstream side. On the downstream side of the orifice  63   f , the gas supply line  63   b  is connected to the gas supply line  61   b . The N 2  gas supplied from the N 2  gas supply source  63   a  is continuously supplied into the processing container  1  during the film formation on the wafer W. The supply and cutoff of the N 2  gas to be supplied from the N 2  gas supply source  63   a  to the processing container  1  are performed by the valve  63   e . The gas is supplied to the gas supply lines  61   b  and  62   b  at a relatively large flow rate by the storage tanks  61   d  and  62   d . The gas supplied to the gas supply lines  61   b  and  62   b  is prevented from flowing back to the gas supply line  63   b  by the orifice  63   f.    
     The H 2  gas supply source  64   a  supplies a H 2  gas as a reducing gas into the processing container  1  via a gas supply line  64   b . In the gas supply line  64   b , a flow rate controller  64   c , a valve  64   e  and an orifice  64   f  are installed sequentially from the upstream side. On the downstream side of the orifice  64   f , the gas supply line  64   b  is connected to the gas introduction hole  37 . The H 2  gas supplied from the H 2  gas supply source  64   a  is continuously supplied into the processing container  1  during the film formation on the wafer W. The supply and cutoff of the H 2  gas to be supplied from the H 2  gas supply source  64   a  to the processing container  1  are performed by the valve  64   e . The gas is supplied to the gas supply lines  65   b  and  66   b  at a relatively large flow rate by the storage tanks  65   d  and  66   d  which will be described later. The gas supplied to the gas supply lines  65   b  and  66   b  is prevented from flowing back into the gas supply line  64   b  by the orifice  64   f.    
     The H 2  gas supply source  65   a  supplies a H 2  gas as a reducing gas into the processing container  1  via a gas supply line  65   b . In the gas supply line  65   b , a flow rate controller  65   c , a storage tank  65   d  and a valve  65   e  are installed sequentially from the upstream side. On the downstream side of the valve  65   e , the gas supply line  65   b  is connected to the gas supply line  64   b . The H 2  gas supplied from the H 2  gas supply source  65   a  is temporarily stored in the storage tank  65   d  before being supplied into the processing container  1 , pressurized to a predetermined pressure in the storage tank  65   d , and then supplied into the processing container  1 . The supply and cutoff of the H 2  gas to be supplied from the storage tank  65   d  to the processing container  1  is performed by the valve  65   e . By temporarily storing the H 2  gas in the storage tank  65   d  in this way, the gas supply mechanism  5  can stably supply the H 2  gas into the processing container  1  at a relatively large flow rate. 
     The N 2  gas supply source  66   a  supplies an N 2  gas as a purge gas into the processing container  1  via a gas supply line  66   b . In the gas supply line  66   b , a flow rate controller  66   c , a storage tank  66   d  and a valve  66   e  are installed sequentially from the upstream side. On the downstream side of the valve  66   e , the gas supply line  66   b  is connected to the gas supply line  64   b . The N 2  gas supplied from the N 2  gas supply source  66   a  is temporarily stored in the storage tank  66   d  before being supplied into the processing container  1 , pressurized to a predetermined pressure in the storage tank  66   d , and then supplied into the processing container  1 . The supply and cutoff of the N 2  gas to be supplied from the storage tank  66   d  to the processing container  1  are performed by the valve  66   e . By temporarily storing the N 2  gas in the storage tank  66   d  in this manner, the gas supply mechanism  5  can stably supply the N 2  gas into the processing container  1  at a relatively large flow rate. 
     The N 2  gas supply source  67   a  supplies an N 2  gas as a carrier gas into the processing container  1  via a gas supply line  67   b . In the gas supply line  67   b , a flow rate controller  67   c , a valve  67   e  and an orifice  67   f  are installed sequentially from the upstream side. On the downstream side of the orifice  67   f , the gas supply line  67   b  is connected to the gas supply line  64   b . The N 2  gas supplied from the N 2  gas supply source  67   a  is continuously supplied into the processing container  1  during the film formation on the wafer W. The supply and cutoff of the N 2  gas to be supplied from the N 2  gas supply source  67   a  to the processing container  1  are performed by the valve  67   e . The gas is supplied to the gas supply lines  65   b  and  66   b  at a relatively large flow rate by the storage tanks  65   d  and  66   d . The gas supplied to the gas supply lines  65   b  and  66   b  is prevented from flowing back to the gas supply line  67   b  by the orifice  67   f.    
     [Film-Forming Method] 
     Next, a tungsten film-forming method, which is performed using the film-forming system  100  configured as described above, will be described.  FIG. 4  is a flowchart showing an example of the flow of respective steps of a film-forming method according to an embodiment.  FIGS. 5A to 5D  are sectional views schematically showing an example of the states of a wafer in the respective steps of the film-forming method according to the embodiment. 
     First, in the film-forming method according to the present embodiment, a wafer W ( FIG. 5A ) having an AlO film as a protective layer formed on the surface of a silicon film having a recess such as, for example, a trench or a hole, is prepared. In reality, a recess such as a trench or a hole (contact hole or via hole) is formed in the wafer W. However, for the sake of convenience, the recess is omitted in  FIGS. 5A to 5D . 
     The first film-forming apparatus  101  forms a silicon film on the wafer W (step S 1 :  FIG. 5B ). For example, the first film-forming apparatus  101  alternately supplies a SiH 4  gas and a B 2 H 6  gas into the processing container  1  to form a silicon film (Si (Si—B)). Details of the process of forming the silicon film will be described later. 
     The second film-forming apparatus  102  supplies a WCl 6  gas and a H 2  gas into the processing container  1  to form an initial tungsten film (Init. W) on the surface of the wafer W (step S 2 :  FIG. 5C ). Details of the process of forming the tungsten film will be described later. 
     The third film-forming apparatus  103  supplies a tungsten-containing gas, for example, a WF 6  gas and a H 2  gas into the processing container  1  to form a main tungsten film (Main W) on the surface of the wafer W (step S 3 :  FIG. 5D ). 
     [Formation of Silicon Film] 
     Next, the flow of forming the silicon film by the first film-forming apparatus  101  will be described.  FIG. 6  is a diagram showing an example of a gas supply sequence at the time of forming the silicon film according to the embodiment. 
     The control part  6  of the first film-forming apparatus  101  controls the heater  21  of the mounting table  2  to heat the wafer W to a predetermined temperature (for example, 250 to 550 degrees C.). Further, the control part  6  controls the pressure control valve of the exhaust mechanism  42  to regulate the pressure in the processing container  1  to a predetermined pressure (for example, 1.0×10 1  to 1.0×10 4  Pa). 
     The control part  6  opens the valves  53   e  and  57   e  and supplies a carrier gas (N 2  gas) at a predetermined flow rate (for example, 100 to 10000 sccm) from the N 2  gas supply sources  53   a  and  57   a  into the processing container  1  via the gas supply lines  53   b  and  57   b , respectively. In parallel with the supply of the carrier gas (N 2  gas) into the processing container  1 , the control part  6  supplies a SiH 4  gas and a B 2 H 6  gas from the SiH 4  gas supply source  51   a  and the B 2 H 6  gas supply source  55   a  to the gas supply line  51   b  and  55   b . Since the valves  51   e  and  55   e  are closed, the SiH 4  gas and the B 2 H 6  gas are respectively stored in the storage tanks  51   d  and  55   d , and the pressure in the storage tanks  51   d  and  55   d  is increased. Further, the control part  6  supplies an N 2  gas from the N 2  gas supply source  52   a  and the N 2  gas supply source  56   a  to the gas supply lines  52   b  and  56   b , respectively. Since the valves  52   e  and  56   e  are closed, the N 2  gas is stored in the storage tanks  52   d  and  56   d , respectively, and the pressure in the storage tanks  52   d  and  56   d  is increased. 
     The control part  6  opens the valve  51   e  and supplies the SiH 4  gas stored in the storage tank  51   d  into the processing container  1  (step S 11 ). 
     After a predetermined time (for example, 0.05 to 20 seconds) has elapsed since the opening of the valve  51   e , the control part  6  closes the valve  51   e  and stops the supply of the SiH 4  gas into the processing container  1 . In addition, the control part  6  stops the supply of the SiH 4  gas, opens the valves  52   e  and  56   e , and supplies the N 2  gas stored in the storage tanks  52   d  and  56   d  into the processing container  1  (step S 12 ). At this time, since the purge gas is supplied from the storage tanks  52   d  and  56   d  having an increased pressure, the purge gas is supplied into the processing container  1  at a relatively large flow rate, for example, a flow rate (for example, 500 to 10000 sccm) larger than the flow rate of the carrier gas. Therefore, the SiH 4  gas remaining in the processing container  1  is promptly discharged to the exhaust pipe  41 , and the inside of the processing container  1  is changed from the SiH 4  gas atmosphere to the atmosphere containing the N 2  gas in a short time. On the other hand, as the valve  51   e  is closed, the SiH 4  gas supplied from the SiH 4  gas supply source  51   a  to the gas supply line  516  is stored in the storage tank  51   d , and the pressure in the storage tank  51   d  is increased. 
     After a predetermined time (for example, 0.05 to 20 seconds) has elapsed since the opening of the valves  52   e  and  56   e , the control part  6  closes the valves  52   e  and  56   e  and stops the supply of the N 2  gas from the gas supply line  52   b  and the gas supply line  56   b  into the processing container  1 . In addition, the control part  6  stops the supply of the N 2  gas, opens the valve  55   e , and supplies the B 2 H 6  gas stored in the storage tank  55   d  into the processing container  1  (step S 13 ). As a result, silicon is deposited on the wafer W. As the valve  52   e  is closed, the N 2  gas supplied from the N 2  gas supply source  52   a  to the gas supply line  52   b  is stored in the storage tank  52   d , and the pressure in the storage tank  52   d  is increased. Furthermore, as the valve  56   e  is closed, the N 2  gas supplied from the N 2  gas supply source  56   a  to the gas supply line  56   b  is stored in the storage tank  56   d , and the pressure in the storage tank  56   d  is increased. 
     After a predetermined time (for example, 0.05 to 20 seconds) has elapsed since the opening of the valve  55   e , the control part  6  closes the valve  55   e  and stops the supply of the B 2 H 6  gas into the processing container  1 . In addition, the control part  6  stops the supply of the B 2 H 6  gas, opens the valves  52   e  and  56   e , and supplies the N 2  gas stored in the storage tanks  52   d  and  56   d  into the processing container  1  (step S 14 ). At this time, since the purge gas is supplied from the storage tanks  52   d  and  56   d  having an increased pressure, the purge gas is supplied into the processing container  1  at a relatively large flow rate, for example, a flow rate (for example, 500 to 10000 sccm) larger than the flow rate of the carrier gas. Therefore, the B 2 H 6  gas remaining in the processing container  1  is promptly discharged to the exhaust pipe  41 , and the inside of the processing container  1  is changed from the B 2 H 6  gas atmosphere to the atmosphere containing the N 2  gas in a short time. On the other hand, as the valve  55   e  is closed, the B 2 H 6  gas supplied from the B 2 H 6  gas supply source  55   a  to the gas supply line  556  is stored in the storage tank  55   d , and the pressure in the storage tank  55   d  is increased. 
     After a predetermined time (for example, 0.05 to 20 seconds) has elapsed since the opening of the valves  52   e  and  56   e , the control part  6  closes the valves  52   e  and  56   e  and stops the supply of the N 2  gas from the gas supply line  52   b  and the gas supply line  56   b  into the processing container  1 . As the valve  52   e  is closed, the N 2  gas supplied from the N 2  gas supply source  52   a  to the gas supply line  52   b  is stored in the storage tank  52   d , and the pressure in the storage tank  52   d  is increased. Furthermore, as the valve  56   e  is closed, the N 2  gas supplied from the N 2  gas supply source  56   a  to the gas supply line  56   b  is stored in the storage tank  56   d , and the pressure in the storage tank  56   d  is increased. 
     The control part  6  forms a silicon film having a desired film thickness by repeating the cycle of steps S 11  to S 14  for a plurality of cycles (for example, 10 to 1000 cycles). 
     The gas supply sequence and the process gas conditions at the time of forming the silicon film shown in  FIG. 6  are nothing more than examples, and the present disclosure is not limited thereto. The silicon film may be formed by using other gas supply sequences and other process gas conditions. 
     [Formation of Initial Tungsten Film] 
     Next, a flow of forming an initial tungsten film by the second film-forming apparatus  102  will be described.  FIG. 7  is a diagram showing an example of a gas supply sequence at the time of forming an initial tungsten film according to an embodiment. 
     The control part  6  of the second film-forming apparatus  102  controls the heater  21  of the mounting table  2  to heat the wafer W to a predetermined temperature (for example, 250 to 650 degrees C.). Further, the control part  6  controls the pressure control valve of the exhaust mechanism  42  to adjust the pressure in the processing container  1  to a predetermined pressure (for example, 1.3×10 1  to 8.0×10 3  Pa). 
     The control part  6  opens the valves  63   e  and  67   e  and supplies a carrier gas (N 2  gas) at a predetermined flow rate (for example, 100 to 3000 sccm) from the N 2  gas supply sources  63   a  and  67   a  to the gas supply lines  63   b  and  67   b , respectively. Further, the control part  6  opens the valve  64   e  and supplies a H 2  gas at a predetermined flow rate (for example, 500 to 30000 sccm) from the H 2  gas supply source  64   a  to the gas supply line  64   b . Moreover, the control part  6  supplies a WCl 6  gas and a H 2  gas from the WCl 6  gas supply source  61   a  and the H 2  gas supply source  65   a , respectively, to the gas supply lines  61   b  and  65   b . At this time, since the valves  61   e  and  65   e  are closed, the WCl 6  gas and the H 2  gas are respectively stored in the storage tanks  61   d  and  65   d , and the pressure in the storage tanks  61   d  and  65   d  is increased. 
     Next, the control part  6  opens the valve  61   e , supplies the WCl 6  gas stored in the storage tank  61   d  into the processing container  1  as a precursor, and causes the WCl 6  gas to be adsorbed on the surface of the wafer W (step S 21 ). In parallel with the supply of the WCl 6  gas into the processing container  1 , the control part  6  supplies a purge gas (N 2  gas) from the N 2  gas supply sources  62   a  and  66   a  to the gas supply lines  62   b  and  66   b , respectively. At this time, by closing the valves  62   e  and  66   e , the purge gas is stored in the storage tanks  62   d  and  66   d , and the pressure in the storage tanks  62   d  and  66   d  is increased. 
     After a predetermined time (for example, 0.05 to 5 seconds) has elapsed since the opening of the valve  61   e , the control part  6  closes the valve  61   e . Furthermore, the control part  6  closes the valve  61   e  and opens the valves  62   e  and  66   e  to stop the supply of the WCl 6  gas into the processing container  1  and to supply the purge gas stored in the storage tanks  62   d  and  66   d  into the processing container  1  (step S 22 ). At this time, since the purge gas is supplied from the storage tanks  62   d  and  66   d  having an increased pressure, the purge gas is supplied into the processing container  1  at a relatively large flow rate, for example, a flow rate (for example, 500 to 10000 sccm) larger than the flow rate of the carrier gas. Therefore, the WCl 6  gas remaining in the processing container  1  is promptly discharged to the exhaust pipe  41 , and the inside of the processing container  1  is changed from the WCl 6  gas atmosphere to the atmosphere containing the H 2  gas and the N 2  gas in a short time. On the other hand, as the valve  61   e  is closed, the WCl 6  gas supplied from the WCl 6  gas supply source  61   a  to the gas supply line  61   b  is stored in the storage tank  61   d , and the pressure in the storage tank  61   d  is increased. 
     After a predetermined time (for example, 0.05 to 5 seconds) has elapsed since the opening of the valves  62   e  and  66   e , the control part  6  closes the valves  62   e  and  66   e , opens the valve  65   e , and stops the supply of the purge gas into the processing container  1 . In addition, the control part  6  stops the supply of the purge gas, supplies the H 2  gas stored in the storage tank  65   d  into the processing container  1 , and reduces the WCl 6  gas adsorbed on the surface of the wafer W (step S 23 ). At this time, due to the closing of the valves  62   e  and  66   e , the purge gas supplied from the N 2  gas supply sources  62   a  and  66   a  to the gas supply lines  62   b  and  66   b , respectively, is stored in the storage tanks  62   d  and  66   d , and the pressure in the storage tanks  62   d  and  66   d  is increased. 
     After a predetermined time (for example, 0.05 to 5 seconds) has elapsed since the opening of the valve  65   e , the control part  6  closes the valve  65   e , opens the valves  62   e  and  66   e , and stops the supply of the H 2  gas into the processing container  1 . Furthermore, the control part  6  stops the supply of the H 2  gas and supplies the purge gas stored in the storage tanks  62   d  and  66   d  into the processing container  1  (step S 24 ). At this time, since the purge gas is supplied from the storage tanks  62   d  and  66   d  having an increased pressure, the purge gas is supplied into the processing container  1  at a relatively large flow rate, for example, a flow rate (for example, 500 to 10000 sccm) larger than the flow rate of the carrier gas. Thus, the H 2  gas remaining in the processing container  1  is promptly discharged to the exhaust pipe  41 , and the inside of the processing container  1  is changed from the H 2  gas atmosphere to the atmosphere containing the H 2  gas and the N 2  gas in a short time. On the other hand, as the valve  65   e  is closed, the H 2  gas supplied from the H 2  gas supply source  65   a  to the gas supply line  65   b  is stored in the storage tank  65   d , and the pressure in the storage tank  65   d  is increased. 
     The control part  6  forms an initial tungsten film having a desired film thickness by repeating the cycle of steps S 21  to S 24  for a plurality of cycles (for example, 50 to 2000 cycles). 
     The gas supply sequence and the process gas conditions at the time of forming the initial tungsten film shown in  FIG. 7  are nothing more than examples, and the present disclosure is not limited thereto. The tungsten film may be formed by using other gas supply sequences and other process gas conditions. 
     [Action and Effect] 
     Next, the actions and effects of the film-forming method according to the present embodiment will be described.  FIG. 8  is a diagram showing an example of the layer configuration of the wafer according to the present embodiment.  FIG. 8  shows an example of the layer configuration of the wafer W on which films are formed by the film-forming method according to the present embodiment. In the wafer W, an AlO layer as a protective layer is formed on a silicon (SiO 2 ) layer, and a silicon film (Si) is formed on the AlO layer from the viewpoint of adhesion and reaction suppression. In the wafer W, an initial tungsten film (Init. W) is formed on the silicon film, and a main tungsten film (Main W) is formed on the initial tungsten film, whereby a low-resistance tungsten film is formed. 
     One example of the process conditions of the film-forming method according to the embodiment will now be summarized below. 
     Silicon Film 
     Temperature: 250 to 550 degrees C. 
     Pressure: 1 to 100 Torr 
     SiH 4 : 100 to 1000 sccm
 
B 2 H 6  gas: 100 to 1000 sccm
 
Carrier gas (N 2 ): 100 to 10000 sccm
 
Purge gas (N 2 ): 500 to 30000 sccm
 
     Time: 
     SiH 4  gas: 0.05 to 20 seconds
 
Purge: 0.05 to 20 seconds
 
B 2 H 6  gas: 0.05 to 20 seconds
 
Purge: 0.05 to 20 seconds
 
     Initial Tungsten Film 
     Temperature: 400 to 650 degrees C. 
     Pressure: 1 to 60 Torr 
     WCl 6  gas: 50 to 1500 mg/min
 
Carrier gas (N 2 ): 100 to 3000 sccm
 
Purge gas (N 2 ): 500 to 10000 sccm
 
H 2  gas: 500 to 30000 sccm
 
     Time: 
     WCl 6  gas: 0.05 to 5 seconds
 
Purge: 0.05 to 5 seconds
 
H 2  gas: 0.05 to 5 seconds
 
Purge: 0.05 to 5 seconds
 
     Main Tungsten Film 
     Temperature: 250 to 550 degrees C. 
     Pressure: 0.1 to 20 Torr 
     WF 6  gas: 100 to 500 sccm
 
Carrier gas (N 2 ): 500 to 10000 sccm
 
Purge gas (N 2 ): 0 to 10000 sccm
 
H 2  gas: 500 to 20000 sccm
 
     Time: 
     WF 6  gas: 0.05 to 15 seconds
 
Purge: 0.05 to 15 seconds
 
H 2  gas: 0.05 to 15 seconds
 
Purge: 0.05 to 15 seconds
 
     A tungsten film can be formed on the wafer W by forming a silicon film before depositing tungsten. The silicon film may have a thickness of about 0.5 to 3 nm in some embodiments. Further, the initial tungsten film may have a thickness of about 0.5 to 6 nm. As a result, in the wafer W, grains of tungsten to be deposited can be caused to grow large and the resistance of the tungsten film can be reduced. 
     The effects will be described using a comparative example.  FIG. 9  is a diagram showing an example of a layer configuration of a wafer according to a comparative example.  FIG. 9  shows an example of a layer configuration of a conventional wafer W. In the wafer W, an AlO layer as a protective layer is formed on a silicon (SiO 2 ) layer, and a TiN film having a thickness of, for example, 2 nm is formed on the AlO layer from the viewpoint of adhesion and reaction suppression. Then, in the wafer W, a nucleation step is performed and a tungsten nucleation film (Nuc) having a thickness of, for example, 3 nm is formed on the TiN film. Then, in the wafer W, a low-resistance tungsten film (W) is formed on the nucleation film. 
     An example of the process conditions for forming each film of the comparative example will be described below. 
     Nucleation Film 
     Temperature: 250 to 550 degrees C. 
     Pressure: 1 to 100 Torr 
     WF 6  gas: 10 to 500 sccm
 
Carrier gas (N 2 ): 500 to 10000 sccm
 
Purge gas (N 2 ): 0 to 10000 sccm
 
H 2  gas: 500 to 20000 sccm
 
SiH 4  gas: 10 to 1000 sccm
 
     Time: 
     WF 6  gas: 0.05 to 15 seconds
 
Purge: 0.05 to 15 seconds
 
SiH 4  gas: 0.05 to 15 seconds
 
Purge: 0.05 to 15 seconds
 
     Tungsten Film 
     Temperature: 250 to 550 degrees C. 
     Pressure: 0.1 to 20 Torr 
     WF 6  gas: 100 to 500 sccm
 
Carrier gas (N 2 ): 1000 to 10000 sccm
 
Purge gas (N 2 ): 0 to 10000 sccm
 
H 2  gas: 500 to 20000 sccm
 
     Time: 
     WF 6  gas: 0.05 to 15 seconds
 
Purge: 0.05 to 15 seconds
 
H 2  gas: 0.05 to 15 seconds
 
Purge: 0.05 to 15 seconds
 
       FIG. 10  is a diagram showing an example of a change in resistivity with respect to the thickness of the tungsten film.  FIG. 10  shows a change in resistivity depending on the thickness of the tungsten film in the layer configuration of the present embodiment shown in  FIG. 8  and the layer configuration of the comparative example shown in  FIG. 9 . In the example of  FIG. 10 , the thickness of the tungsten film is measured from the interface with the AlO layer. That is, in the layer configuration of the present embodiment, the thickness of the silicon film (Si), the initial tungsten film (Init. W) and the main tungsten film (Main W) is regarded as the thickness of the tungsten film. In the layer configuration of the comparative example, the thickness of the TiN film, the nucleation film (Nuc) and the tungsten film (W) is regarded as the thickness of the tungsten film. In the example of  FIG. 10 , there is shown the resistivity normalized with reference to the resistivity of the comparative example when the thickness is 10 nm. As shown in  FIG. 10 , the resistivity of the layer configuration of the present embodiment is lower than that of the comparative example. 
     Conventionally, when forming a tungsten film on a wafer W, as shown in  FIG. 9 , a TiN film is formed as a barrier layer on a silicon layer of the wafer W, and a nucleation film is formed on the TiN film. Then, in the wafer W, a tungsten film (W) is formed on the nucleation film. Conventionally, when forming the tungsten film on the wafer W, the thickness corresponding to the TiN film is also required. In addition, the nucleation film has a high resistance. As the tungsten film is formed thinner, the resistance grows higher. Therefore, in the case of reducing the thickness of the entire tungsten film, the tungsten film has a high resistance due to the influence of the TiN film and the nucleation film. 
     In the LSI, the wiring is miniaturized, and the reduction in the resistance of the wiring is required. For example, in a three-dimensional stacked semiconductor memory such as a 3D NAND flash memory or the like, a tungsten film is formed as a word line. For the sake of miniaturization, it is required to further reduce the resistance of the tungsten film. 
     On the other hand, in the layer configuration of the present embodiment, it is possible to reduce the resistance of the tungsten film even when the thickness of the tungsten film is made small for the purpose of miniaturization. 
     In this embodiment, there has been described the case where the initial tungsten film is formed by the combination of the tungsten chloride gas and the hydrogen gas. However, the present disclosure is not limited thereto. For example, in the second film-forming apparatus  102 , the initial tungsten film may be formed by using only the tungsten chloride gas without using the hydrogen gas. For example, the second film-forming apparatus  102  may intermittently supply only tungsten chloride to form an initial tungsten film. As the tungsten chloride gas, for example, a WCl 6  gas or a WCl 5  gas may be used. Process conditions for forming the initial tungsten film with the tungsten chloride gas are as follows. 
     Tungsten Film 
     Temperature: 400 to 650 degrees C. 
     Pressure: 1 to 600 Torr 
     Tungsten chloride gas (WCl 5  or WCl 6 ): 50 to 1500 mg min
 
Carrier gas (N 2 ): 500 to 3000 sccm
 
Purge gas (N 2 ): 1000 to 10000 sccm
 
     Time: 
     Tungsten chloride gas (WCl 5  or WCl 6 ): 0.05 to 300 seconds 
     Furthermore, in the present embodiment, there has been described the case where the silicon film and the initial tungsten film are formed by separate film-forming apparatuses. However, the present disclosure is not limited thereto. For example, as shown in  FIG. 11 , the silicon film, the initial tungsten film and the main tungsten film may be formed by a single film-forming apparatus including a gas supply mechanism for forming a silicon film and a gas supply mechanism for forming a tungsten film. Further, the wafer W may be transferred through the respective film-forming apparatuses under the atmospheric pressure. 
     As described above, in the tungsten film-forming method according to the present embodiment, the wafer W having a protective film, for example, an AlO film formed thereon is disposed in the processing container  1 , and the silicon film is formed on the wafer W in a reduced pressure atmosphere. In the tungsten film-forming method, the initial tungsten film is formed by supplying the tungsten chloride gas to the wafer W having the silicon film formed thereon. In the tungsten film-forming method, the main tungsten film is formed by supplying the tungsten-containing gas onto the initial tungsten film. This makes it possible to reduce the resistance of the tungsten film. 
     Furthermore, in the method of forming the initial tungsten film among the tungsten films according to the present embodiment, the tungsten film is formed by alternately supplying the tungsten chloride gas and the hydrogen gas. This makes it possible to quickly form the tungsten film. 
     Moreover, in the tungsten film-forming method according to the present embodiment, the silicon film is formed by alternately supplying the SiH 4  gas and the B 2 H 6  gas. This makes it possible to improve the adhesion of the silicon film to the wafer W. 
     In addition, in the tungsten film-forming method according to the present embodiment, the film thickness of the silicon film is set to 0.5 to 3 nm. This makes it possible to stably form the tungsten film. 
     Although the embodiment has been described above, various modifications may be made without being limited to the above-described embodiment. For example, although a semiconductor wafer has been described as an example of a substrate, the semiconductor wafer may be silicon, or a compound semiconductor such as GaAs, SiC, GaN or the like. Furthermore, the substrate is not limited to the semiconductor wafer, but may be a glass substrate used for an FPD (flat panel display) such as a liquid crystal display device or the like, a ceramic substrate, and the like. 
     According to the present disclosure, it is possible to reduce the resistance of a tungsten film. 
     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.