Patent Publication Number: US-2023133485-A1

Title: Electrode filament connection member, chemical vapor deposition apparatus, and method for manufacturing recording medium substrate

Description:
CROSS-REFERENCE TO RELATED APPLICATIONS 
     This application is based on and claims priority to Japanese Patent Application No. 2021-176218, filed on Oct. 28, 2021, the entire contents of which are incorporated herein by reference. 
     BACKGROUND OF THE INVENTION 
     1. Field of the Invention 
     The disclosure herein relates to an electrode filament connection member, a chemical vapor deposition apparatus, and a method for manufacturing a recording medium substrate. 
     2. Description of the Related Art 
     Chemical vapor deposition (CVD) methods are methods for forming films on surfaces of substrates by chemical reaction in vapor phase. The CVD methods are suitable for mass production and are widely used because only a relatively small apparatus is required for production, the film formation speed is high, and the composition and the thickness of films formed can be controlled with high accuracy. 
     Examples of such CVD methods include CVD methods using electrode filaments such as a hot filament CVD method and a hot filament-plasma CVD method. In the CVD methods using the electrode filaments, an electrode filament connection member is used to connect a wire from a power source provided outside a chamber and an electrode filament provided inside the chamber. 
     For example, Patent Document 1 describes an electrode filament connection member that connects a wire from a cathode power source and a cathode filament provided inside a chamber. 
       FIG.  7    is a cross-sectional view illustrating a configuration of a conventional electrode filament connection member. As illustrated in  FIG.  7   , an electrode filament connection member  7  includes a head portion  71  having a cylindrical shape, a collar portion  72  having a disk shape, and a rod portion  73  having a cylindrical shape. The collar portion  72  is provided at an end of the head portion  71  and has a diameter larger than that of the head portion  71 . The rod portion  73  extends from the collar portion  72  to the side opposite to the head portion  71 , and has a diameter smaller than that of the collar portion  72 . 
     In a CVD apparatus, the head portion  71  is located inside a chamber, and an electrode filament is attached to one end of the head portion  71 . With the electrode filament being attached, the collar portion  72  functions as an umbrella that prevents solids produced in the chamber from adhering to the attachment portion of the electrode filament connection member  7 . The rod portion  73  passes through the outer wall of the chamber, and a wire from a power source is connected to a part, on the outside of the chamber, of the rod portion  73 . 
     Patent Document 2 describes a socket that passes through a vacuum chamber wall and connects a cathode and a power source. The surface of the socket of Patent Document 2 is roughened by metal spraying or the like in order to prevent a carbon film adhering to the surface of the socket from peeling off. 
     However, such CVD methods using an electrode filament have a problem in that solids produced in a chamber, such as a component derived from a source gas, adhere to an electrode filament connection member, are deposited on the electrode filament connection member, and fall off within the chamber. For conventional electrode filament connection members as illustrated in Patent Document 1 and  FIG.  7   , solids may get deposited in a recess  74  between the head portion  71  and the collar portion  72 , may develop into a large lump, and in turn may fall off. 
     In the socket of Patent Document 2, there is room for improvement in preventing deposition and falling-off of solids produced in the chamber. 
     RELATED-ART DOCUMENTS 
     Patent Documents 
     Patent Document 1: WO 2016/024361 
     Patent Document 2: Japanese Laid-open Patent Publication No. 2000-222724 
     SUMMARY OF THE INVENTION 
     It is desirable to provide an electrode filament connection member, a CVD apparatus, and a method for manufacturing a recording medium substrate that can prevent solids produced in a chamber from being deposited and falling off when a film is formed on a substrate in the chamber by a CVD method using an electrode filament. 
     One aspect of the present disclosure provides an electrode filament connection member for attaching to a chemical vapor deposition apparatus so as to pass through an outer wall of the chemical vapor deposition apparatus in which an electrode filament is disposed in a chamber defined by the outer wall. The electrode filament connection member forms an electrical connection between a wire from a power source provided outside the chamber and the electrode filament. The electrode filament connection member includes a head portion that is provided in the chamber and attached to the electrode filament; and a rod portion that extends from the head portion through the outer wall so as to be connected to the wire. The head portion includes an electrode filament attachment portion at a tip end portion, and a side surface that is parallel to an axial direction or is gradually widened from the tip end portion toward the outer wall. The rod portion passes through the outer wall in the axial direction. An outer shape of the side surface of the head portion conforms to an outer shape of the electrode filament connection member when viewed in projection along the axial direction. 
     Another aspect of the present disclosure provides a chemical vapor deposition apparatus in which an electrode filament is disposed in a chamber defined by an outer wall. The chemical vapor deposition apparatus includes an electrode filament connection member configured to pass through the outer wall and to electrically connect a wire from a power source provided outside the chamber and the electrode filament. The electrode filament connection member includes a head portion that is provided in the chamber and attached to the electrode filament, and a rod portion that extends from the head portion through the outer wall so as to be connected to the wire. The head portion includes an electrode filament attachment portion at a tip end portion, and a side surface that is parallel to an axial direction or is gradually widened from the tip end portion toward the outer wall. The rod portion passes through the outer wall in the axial direction. An outer shape of the side surface of the head portion conforms to an outer shape of the electrode filament connection member when viewed in projection along the axial direction. 
     Yet another aspect of the present disclosure provides a method for manufacturing a recording medium substrate. The method includes performing a film deposition process by a chemical vapor deposition apparatus in which an electrode filament is disposed in a chamber defined by an outer wall. The chemical vapor deposition apparatus includes an electrode filament connection member configured to be attached so as to pass through the outer wall and to electrically connect a wire from a power source located outside the chamber and the electrode filament. The electrode filament connection member includes a head portion that is provided in the chamber and attached to the electrode filament, and a rod portion that extends from the head portion through the outer wall so as to be connected to the wire. The head portion includes an electrode filament attachment portion at a tip end portion, and a side surface that is parallel to an axial direction or is gradually widened from the tip end portion toward the outer wall. The rod portion passes through the outer wall in the axial direction. An outer shape of the side surface of the head portion conforms to an outer shape of the electrode filament connection member when viewed in projection along the axial direction. 
    
    
     
       BRIEF DESCRIPTION OF THE DRAWINGS 
       Other objects and further features of the present invention will be apparent from the following detailed description when read in conjunction with the accompanying drawings, in which: 
         FIG.  1    is a diagram schematically illustrating an example of a CVD apparatus according to an embodiment of the present invention; 
         FIG.  2    is a cross-sectional view illustrating an example of a filament socket according to an embodiment of the present invention; 
         FIG.  3    is a diagram illustrating the filament socket of  FIG.  2    as viewed from the inside of a chamber in an axial direction; 
         FIG.  4    is a cross-sectional view of a filament socket according to a modification of the present invention; 
         FIG.  5    is a cross-sectional view of a filament socket according to a modification of the present invention; 
         FIG.  6    is a cross-sectional view of a filament socket according to a modification of the present invention; and 
         FIG.  7    is a cross-sectional view illustrating a configuration of a conventional electrode filament connection member. 
     
    
    
     DESCRIPTION OF THE EMBODIMENTS 
     In the following, embodiments of the present invention will be described in detail. In order to facilitate understanding of the description, the same components in the drawings are designated by the same reference numerals, and the description thereof will not be repeated. In addition, the components in the drawings may not be to scale. As used herein, “to” indicating a numerical range means that the numerical range includes numerical values given before and after “to” as its lower limit value and its upper limit value, unless otherwise specified. 
     In the following embodiments, an electrode filament is disposed in a chamber defined by the outer wall of a CVD apparatus. An electrode filament connection member is configured to be attached to the CVD apparatus so as to pass through the outer wall of the CVD apparatus, and to electrically connect a wire from a power source provided outside the chamber and the electrode filament. In the following description, the electrode filament connection member is a cathode filament socket of a hot filament-plasma CVD apparatus, but can be applied to any other CVD apparatus as long as a method using a filament is used. 
     1. CVD Apparatus 
     1-1. Apparatus Configuration 
       FIG.  1    is a diagram schematically illustrating an example of a CVD apparatus according to an embodiment of the present invention. A CVD apparatus  1  is an apparatus configured to perform a film deposition process on a substrate W in a chamber C. The shape of the substrate W is not particularly limited, but may be, for example, a disk shape. The CVD apparatus  1  according to the present embodiment can perform the film deposition process on both surfaces of the substrate W, and substantially the same components , which will be described later, in the chamber C are provided on both sides of the substrate W; however,  FIG.  1    depicts components provided at one side of the substrate W. Note that the CVD apparatus  1  may be configured to perform the film deposition process on only one surface of the substrate W. 
     As illustrated in  FIG.  1   , the CVD apparatus  1  includes an outer wall  11 , a cathode filament  12 , which is an electrode filament, filament sockets  13 , each of which is an electrode filament connection member, a cathode power source  14 , which is a power source, an anode  15 , an anode power source  16 , a gas introduction port  17 , a gas exhaust port  18 , a substrate holder  19 , an ion acceleration power source  20 , and an inner shield  21 . The CVD apparatus  1  may include any other components as necessary. 
     The chamber C, which is an airtight interior space, is defined by the outer wall  11 . The chamber C defined by the outer wall  11  houses the cathode filament  12 , the anode  15 , the substrate holder  19 , and the substrate W. The film forming process is performed on the substrate W in the chamber C. Any other components may be housed in the chamber C as necessary. As will be described later in detail, the outer wall  11  has socket attachment holes  111  through which the filament sockets  13  pass. 
     The cathode filament  12  may be composed of one wire or may be composed of a plurality of wires. If the cathode filament  12  is composed of a plurality of wires, the cathode filament  12  is preferably composed of stranded wires. The material of the cathode filament  12  may be, for example, tungsten or the like, but is not limited thereto. 
     The filament sockets  13  are attached to the outer wall  11  in a state in which the filament sockets  13  pass through the socket attachment holes  111  of the outer wall  11 . The filament sockets  13  electrically connect the cathode filament  12  in the chamber C and a wire from the cathode power source  14 . The two filament sockets  13  are provided, and the filament sockets  13  electrically connect respective ends of the cathode filament  12  separately to the wire from the cathode power source  14  provided outside the chamber C. 
     The filament sockets  13  are attached to the outer wall  11  such that airtightness in the chamber C can be maintained. In the present embodiment, the filament sockets  13  are conductors. Specifically, the material of the filament sockets  13  is preferably copper or the like. Each of the filament sockets  13  and the outer wall  11  is electrically insulated by an insulating member  13 A. Examples of the insulating member include an insulator. The filament sockets  13  will be described later in detail with reference to  FIG.  2   . 
     The cathode power source  14  is an alternating current power source. The voltage of the cathode power source  14  is preferably in a range from  100 V to  300 V, but is not limited to this range. Terminals of the cathode power source  14  are connected to the respective filament sockets  13 . With this configuration, an alternating voltage is applied to the cathode filament  12 , and the cathode filament  12  is heated by a current flowing therethrough. One of the terminals of the cathode power source  14  is connected to earth E. 
     The anode  15  includes an anode plate  151 . The anode plate  151  surrounds the cathode filament  12 , and the side, closer to the substrate W, of the anode plate  151  is open. The anode plate  151  has a tapered shape that widens toward the substrate W. The anode plate  151  may have a curved surface. The anode plate  151  is electrically insulated from the outer wall  11 . In the example of  FIG.  1   , the anode plate  151  also covers the vicinity of portions, to which the filament sockets  13  are attached, of the inner surface of the outer wall  11 . In this example, the anode plate  151  has through holes  152  such that the anode plate  151  does not contact the filament sockets  13 , as will be described later in detail. 
     The anode power source  16  is a direct current power source. The voltage of the anode power source  16  is preferably in a range from 0V to  300 V, but is not limited to this range. A positive electrode of the anode power source  16  is connected to the anode  15 , and a negative electrode of the anode power source  16  is connected to the other terminal, which is not connected to the earth E, of the cathode power source  14 . A wire that connects the anode  15  and the anode power source  16  is electrically insulated from the outer wall  11  by an insulating member  16 A. 
     The gas introduction port  17  introduces a source gas from an external gas supply source (not illustrated) into the chamber C. In the present embodiment, examples of the source gas include an organic compound. Examples of the organic compound include, but are not limited to, hydrocarbons such as methane, ethane, benzene, and toluene. 
     The gas exhaust port  18  exhausts the gas in the chamber C to the outside. The pressure in the chamber C is controlled by the gas exhaust port  18 . A device that controls the pressure in the chamber C is not particularly limited, but may be a pump or the like. 
     The substrate holder  19  holds the substrate W in the chamber C. The substrate holder  19  may be configured to move the position of the substrate W by being equipped with a drive device (not illustrated). The substrate W may be moved in the vertical direction or the horizontal direction with respect to the surface of the substrate, or may be moved in a direction oblique to the vertical direction or the horizontal directions. 
     The ion acceleration power source  20  is a direct current power source. The voltage of the ion acceleration power source  20  is preferably in a range from 50V to 1000V, but is not limited to this range. Further, the voltage of the ion acceleration power source  20  may be appropriately varied according to the progress of a process. A positive electrode of the ion acceleration power source  20  is connected to the earth E, and a negative electrode of the ion acceleration power source  20  is connected to the substrate W. A wire connecting the ion acceleration power source  20  to the substrate W may be attached to the inside of the substrate holder  19 . The wire connecting the ion acceleration power source  20  to the substrate W is electrically insulated from the outer wall  11  by an insulating member  20 A. 
     The inner shield  21  covers the inner surface of the outer wall  11  between the anode plate  151  and the substrate W. The inner shield  21  prevents solids produced in the chamber C from adhering to the inner surface of the outer wall  11 . The inner shield  21  is spaced apart from the anode plate  151 . In this example, the source gas entering from the gas introduction port  17  flows between the inner shield  21  and the anode plate  151  and enters the chamber C. The inner shield  21  preferably has a floating potential. 
     1-2. Operation of Apparatus 
     With the above-described configuration, the cathode filament  12  generates heat by a current supplied from the cathode power source  14 . The heat generated by the cathode filament  12  and discharge between the cathode filament  12  and the anode  15  cause the source gas to be converted into a plasma. The substrate W has a negative potential by the ion acceleration power source  20 . Therefore, the plasma is accelerated toward the substrate W and collides with the surface of the substrate W, thereby causing a film including a component derived from the source gas to be formed on the surface of the substrate W. 
     2. Filament Socket 
     A filament socket, which is an electrode filament connection member, according to an embodiment will be described in detail.  FIG.  2    is a cross-sectional view illustrating an example of a filament socket according to an embodiment. Two filament sockets  13  connected to respective sides of the cathode filament  12  have the same configuration. In the present embodiment, the configuration of a filament socket  13  illustrated in  FIG.  2    is merely an example, and can be appropriately changed to the extent that the object of the present embodiment can be achieved. In the present embodiment, an end (a tip end portion), located inside the chamber C, of the filament socket  13  is referred to as “one end”, and an end, located outside the chamber C, of the filament socket  13  is referred to as “the other end”. 
     As used herein, the “tip end portion” refers to the tip end of the filament socket  13  or a region including the tip end of the filament socket  13  and its vicinity. As will be described later, if a head portion  131  of the filament socket  13  has a tip end surface  133 , the tip end portion means the tip end surface  133 . If the head portion  131  of the filament socket  13  does not have the tip end surface  133 , the tip end portion refers to the tip end of the filament socket  13  and its surrounding region. 
     As illustrated in  FIG.  2   , the outer wall  11  has a socket attachment hole  111  through which the filament socket  13  passes, and the filament socket  13  is attached through the socket attachment hole  111 . In the socket attachment hole  111 , the insulating member  13 A is interposed between the filament socket  13  and the outer wall  11 . As the insulating member  13 A, an insulator or the like can be used, for example. In  FIG.  2   , in the socket attachment hole  111  of the outer wall  11 , the insulating member  13 A surrounds a rod portion  132 , which will be described later, of the filament socket  13  while in contact with the entire periphery of the rod portion  132 . The outer periphery of the insulating member  13 A is surrounded by the outer wall  11  while in contact with the outer wall  11 . This configuration allows the outer wall  11  and the filament socket  13 , that is, the outer wall  11  and the wire from the cathode power source  14  to be electrically insulated while maintaining airtightness in the chamber C. 
     The anode plate  151  has a through hole  152  through which the filament socket  13  passes. The diameter of the through hole  152  is larger than the outer diameter of the rod portion  132 , which will be described later, of the filament socket  13 , and the anode plate  151  is spaced apart from the rod portion  132 . That is, a gap is provided between the filament socket  13  and the anode plate  151 , and the filament socket  13  is attached so as not to contact the anode plate  151 . The gap between the filament socket  13  and the anode plate  151  is preferably determined based on the voltage between these components such that dielectric breakdown does not occur. 
     The filament socket  13  includes the head portion  131  and the rod portion  132 . The head portion  131  is located in the chamber C, and the cathode filament  12  is attached to the head portion  131 . The rod portion  132  extends from the head portion  131  through the outer wall  11  to the outside of the chamber C, and the wire from the cathode power source  14  provided outside the chamber C is connected to the rod portion  132 . In the following description, a direction in which the rod portion  132  passes through the outer wall is referred to as an axial direction Ax. In the present embodiment, the axial direction Ax is orthogonal to a portion of the inner surface of the outer wall  11  defining the chamber C, where the rod portion  132  passes through the outer wall  11  (socket attachment hole  111 ). 
     The head portion  131  includes the tip end surface  133 , an electrode filament attachment portion  134 , a side surface  135 , a connection surface  136 , a filament fixing hole  137 , and a tool attachment hole  138 . The tip end surface  133  is located inside the chamber C, the electrode filament attachment portion  134  is provided in the tip end surface  133 , the side surface  135  extends from the tip end surface  133  toward the outer wall  11 , that is, toward the outside of thechamber C, and the connection surface  136  is formed at a connecting portion between the side surface  135  and the rod portion  132 . 
     The tip end surface  133  is a flat surface orthogonal to the axial direction Ax; however, the tip end surface  133  may be a tapered surface that widens from the electrode filament attachment portion  134  toward the side surface  135  or may be a spherical surface that projects toward the inside of the chamber C. 
     The tip end surface  133  may have a fine uneven pattern such as knurling. This configuration can prevent solids or the like produced in the chamber C from being deposited and developing into a large lump. Examples of the solids produced in the chamber C include, but are not limited to, a component, such as carbon, derived from the source gas. If the tip end surface  133  has a fine uneven pattern, the tip end surface  133  is an enveloping surface of the uneven pattern. Note that the depth of the fine uneven pattern from the enveloping surface is ⅒ or less and is preferably 1/20 or less of the maximum length of the filament socket  13  when viewed in projection along the direction in which the filament socket  13  is attached through the outer wall  11 . 
     The electrode filament attachment portion  134  is a hole provided in the tip end surface  133 , and the cathode filament  12  is inserted into the electrode filament attachment portion  134 . 
     The electrode filament attachment portion  134  is not limited to a hole as illustrated in  FIG.  2   , and may be, for example, a hook projecting from the tip end surface  133  toward the inside of the chamber C. In this case, the cathode filament  12  may have an engagement structure corresponding to the hook. For example, the cathode filament  12  may have a hook shape or a ring shape. 
     The side surface  135  is gradually widened from the tip end surface  133 , located inside the chamber C, toward the outer wall  11  (connection surface  136 ). 
     As illustrated in  FIG.  2   , the side surface  135  is preferably a continuous surface. The side surface  135  may be a tapered surface whose diameter increases from the tip end surface  133  toward the connection surface  136 . When viewed from a direction orthogonal to the axial direction Ax of the filament socket  13 , the side surface  135  may be a curved surface protruding outward from the tip end surface  133  toward the connection surface  136 , or may be a curved surface recessed inward from the tip end surface  133  toward the connection surface  136 . 
     As will be described later, the outer shape of the side surface  135  of the head portion  131  conforms to the outer shape of the filament socket  13  when viewed in projection along the direction in which the filament socket  13  is attached through the outer wall  11 . That is, as illustrated in  FIG.  2   , the maximum diameter of the side surface  135  is the outer diameter of the connection surface  136 , and is also the maximum diameter of the filament socket  13 . With this configuration, a discontinuous recess (for example, the recess  74  of  FIG.  7   ) can be eliminated. solids or the like produced in the chamber C can be prevented from being deposited on the surface of the filament socket  13  and developing into a large lump. 
     The side surface  135  may have a fine uneven pattern such as knurling. This configuration can prevent solids or the like produced in the chamber C from being deposited and developing into a large lump. If the side surface  135  has a fine uneven pattern, the side surface  135  is an enveloping surface of the uneven pattern. Note that the depth of the fine uneven pattern from the enveloping surface is ⅒ or less and preferably 1/20 or less of the maximum length of the filament socket  13  when viewed in projection along the direction in which the filament socket  13  is attached through the outer wall  11 . 
     In the example of  FIG.  2   , the connection surface  136  is a flat surface connecting the end, on the outer wall  11  side, of the side surface  135  to the end, on the one end side, of the rod portion  132 . The connection surface  136  is apart from the outer wall  11 . Note that the shape of the connection surface  136  is not limited thereto. The connection surface  136  may have a tapered surface that narrows toward the outside of the chamber C. The connection surface  136  does not need to be a continuous surface, and may have projections and recesses. 
     As illustrated in  FIG.  2   , the filament fixing hole  137  may be provided in the side surface  135 . Note that the filament fixing hole  137  is not necessarily provided, and may be provided as necessary. 
     The filament fixing hole  137  is a hole that crosses the hole of the electrode filament attachment portion  134  and passes through the head portion  131 . The filament fixing hole  137  may be a screw hole, and the inner wall of the filament fixing hole  137  may have thread grooves. Two screw members  137 A and  137 B, having grooves on the outer peripheral surfaces thereof and serving as fixing members, are inserted into the filament fixing hole  137  from both sides of the filament fixing hole  137 , and sandwich the cathode filament  12 . The cathode filament  12  is fixed in the filament fixing hole  137  by being sandwiched between the screw members  137 A and  137 B. 
     In the present embodiment, the two screw members  137 A and  137 B are provided in the filament fixing hole  137 ; however, the cathode filament  12  may be fixed by fixing members other than the two screw members  137 A and  137 B. Further, the screw members  137 A and  137 B are not necessarily provided depending on the structure of the electrode filament attachment portion  134 . For example, the screw members  137 A and  137 B are not necessarily provided if the electrode filament attachment portion  134  has the hook shape. 
     As illustrated in  FIG.  2   , the tool attachment hole  138  may be provided in the side surface  135 . Note that the tool attachment hole  138  is not necessarily provided, and may be provided as necessary. 
     The tool attachment hole  138  is a hole that passes through the head portion  131 . A tool for removing the filament socket  13  from the outer wall  11  is inserted into the tool attachment hole  138 . If a tool is not needed to attach or remove the filament socket  13 , the tool attachment hole  138  needs not necessarily be provided. 
     As illustrated in  FIG.  2   , the rod portion  132  is fixed in a state in which the rod portion  132  passes through the socket attachment hole  111  of the outer wall  11  via the insulating member  13 A. The rod portion  132  has a cylindrical shape; however, the rod portion  132  may have a polygonal column shape such as a square shape, or the outer wall of the rod portion  132  may be tapered. 
     The rod portion  132  may have a wire connection hole  139  extending from the other end toward the one end of the filament socket  13 . A terminal  141  of the wire from the cathode power source  14  may be inserted into the wire connection hole  139  such that the filament socket  13  is connected to the wire from the cathode power source  14 . 
     Note that a connection structure between the rod portion  132  and the wire from the cathode power source  14  is not limited thereto. For example, a through hole may be provided in the side surface of the rod portion  132  and the terminal  141  of the wire may be fitted in the through hole. 
     As the material of the filament socket  13 , an electrically conductive material is used such that the cathode filament  12  and the wire from the cathode power source  14  is electrically connected through the filament socket  13 . 
       FIG.  3    is a diagram illustrating the filament socket  13  of  FIG.  2    as viewed from the inside of the chamber C in the axial direction Ax. For the filament socket  13  illustrated in  FIG.  3   , lines other than the solid line indicating the head portion  131  (side surface  135 ) and the tip end surface  133 , and the dotted lines indicating the rod portion  132 , the insulating member  13 A, and the through hole  152  are not depicted for convenience of description. 
     As illustrated in  FIG.  3   , the outer shape of the side surface  135  of the head portion  131  conforms to the outer shape of the filament socket  13 . That is, the outer shape of the side surface  135  of the head portion  131  conforms to the outer shape of the filament socket  13  when viewed in projection along the axial direction Ax. 
     Note that a protruding portion, such as a reinforcing rib extending along the axial direction Ax, may be provided on part of the side surface  135  as necessary. In this case, the protruding portion is not the side surface  135 , and thus, the outer shape of the filament socket  13  does not need to conform to the outer shape of the side surface  135  including the protruding portion. 
     With the filament socket  13  being attached through the outer wall  11 , the socket attachment hole  111  of the outer wall  11  is located inward relative to the outer shape of the side surface  135  of the head portion  131 . That is, with the filament socket  13  being attached through the outer wall  11 , the socket attachment hole  111  is located inward relative to the outer shape of the side surface  135  (the outer shape of the side surface  135  of the head portion  131  is located outward relative to the attachment hole  11 ) when viewed in projection along the axial direction Ax of the socket attachment hole  111 . With this configuration, the head portion  131  of the filament socket  13  serves as an umbrella that prevents solids produced in the chamber C from adhering to a portion to which the filament socket  13  is attached, specifically, to the insulating member  13 A, and as a result, a short circuit between the filament socket  13  and the outer wall  11  can be suppressed. 
     With the filament socket  13  being attached through the outer wall  11 , the through hole  152  of the anode  15  is located inward relative to the outer shape of the side surface  135  of the head portion  131 . That is, with the filament socket  13  being attached through the outer wall  11 , the through hole  152  is located inward relative to the outer shape of the side surface  135  of the head portion  131  when viewed in projection along the axial direction Ax of the through hole  152  of the anode  15 . With this configuration, the head portion  131  of the filament socket  13  serves as an umbrella that prevents solids produced in the chamber C from entering through a gap between the rod portion  132  of the filament socket  13  and the through hole  152  of the anode plate  151  and contaminating the inner surface of the outer wall  11 . 
     3. Filament Sockets According to Modifications 
     The side surface  135  of the head portion  131  can be designed to have any suitable shape as long as the filament socket  13  is formed such that solids produced in the chamber C are not deposited on the side surface  135  of the filament socket  13 . In the following, filament sockets  13  according to modifications will be described. 
     3-1. First Modification 
       FIG.  4    is a cross-sectional view of a filament socket  13  according to a first modification. As illustrated in  FIG.  4   , in the first modification, the head portion  131  does not have a tip end surface, and a side surface  135  is gradually widened from an electrode filament attachment portion  134  toward the outer wall  11  (toward the outside of the chamber C). The electrode filament attachment portion  134  is provided at a tip end portion, specifically, at an end portion, located inside the chamber C, of the filament socket  13 . 
     With this configuration, the edge of the tip end surface  133  (see  FIG.  2   ) inside the chamber C can be removed, thereby preventing solids adhering to the filament socket  13  from falling off. 
     3-2. Second Modification 
       FIG.  5    is a cross-sectional view of a filament socket  13  according to a second modification. As illustrated in  FIG.  5   , in the second modification, the angle of a side surface  135  of a head portion  131  with respect to the axial direction Ax gradually decreases from a tip end surface  133  toward the outer wall  11  (toward the outside of the chamber C). That is, the side surface  135  has a curved surface that curves outward from the tip end surface  133  to a connection surface  136 . 
     Further, an edge between the tip end surface  133  and the side surface  135  may be provided in a rounded shape or the like, such that the tip end surface  133  and the side surface  135  form a continuous surface. 
     Further, a part, on the rod portion  132  side (closer to the outside of the chamber C), of the side surface  135  may be a cylindrical surface that is parallel to the axial direction Ax. 
     Note that the angle of the side surface  135  of the head portion  131  with respect to the axial direction Ax may gradually increase from the tip end surface  133  toward the outer wall  11 . That is, the side surface  135  may have a curved surface that curves inward from the tip end surface  133  to the connection surface  136 . 
     3-3. Third Modification 
       FIG.  6    is a cross-sectional view of a filament socket  13  according to a third modification. As illustrated in  FIG.  6   , in the third modification, a side surface  135  of a head portion  131  is a cylindrical surface that is parallel to the axial direction Ax. The diameter of the cylindrical surface forming the side surface  135  is larger than the diameter of the rod portion  132 . Therefore, the outer shape of the side surface  135  of the head portion  131  conforms to the outer shape of the filament socket  13 . 
     4. Method for Manufacturing Recording Medium Substrate 
     In a method for manufacturing a recording medium substrate according to an embodiment, a film deposition process for forming a film, including a component derived from a source gas, on the surface of a substrate W is performed by the CVD apparatus  1 . As a result, a recording medium substrate used as a magnetic recording medium or the like is manufactured (the recording medium substrate may be the magnetic recording medium or the like). 
     5. Effects of Embodiments 
     The filament socket  13  according to an embodiment is attached to the CVD apparatus  1  so as to pass through the outer wall  11  of the CVD apparatus  1  in which the cathode filament  12  is provided in the chamber C defined by the outer wall  11 . The filament socket  13  electrically connects the wire from the cathode power source  14  provided outside the chamber C and the cathode filament  12  provided inside the chamber C. 
     The filament socket  13  includes the head portion  131  that is provided in the chamber C and attached to which the cathode filament  12 , and the rod portion  132  that extends from the head portion  131  through the outer wall  11  and connected to the wire from the cathode power source  14 . 
     In the example of  FIG.  2   , the head portion  131  includes the electrode filament attachment portion  134  provided at the tip end portion located inside the chamber C, and the side surface  135  that is gradually widened from the tip end surface  133  toward the outer wall  11  (connection surface  136 ). Note that, as in the first modification, the head portion  131  does not necessarily have a tip end surface, and the side surface  135  may extend outward from the tip end portion, to which the cathode filament  12  is attached, toward the outside of the chamber C. Further, as in the second modification, the angle of side surface  135  with respect to the axial direction Ax may be changed, and part of the side surface  135  may be parallel to the axial direction Ax. Further, as in the fourth modification, the side surface  135  may be parallel to the axial direction Ax. 
     When the axial direction Ax is defined as a direction in which the rod portion  132  passes through the outer wall  11 , the outer shape of the side surface  135  of the head portion  131  conforms to the outer shape of the filament socket  13  when viewed in projection along the axial direction Ax. 
     In the filament socket  13 , the outer shape of the head portion  131  is larger than the outer shape of the rod portion  132  when viewed in projection along the axial direction Ax. Therefore, the head portion  131  functions as an umbrella that prevents solids produced in the chamber C from adhering to the inner surface of the outer wall  11 . Accordingly, when a film is formed on the substrate W in the chamber C by the CVD method using the cathode filament  12 , the filament socket  13  can prevent solids produced in the chamber C from adhering to the socket attachment hole  111  of the outer wall  11  through which the filament socket  13  is attached. 
     Further, the filament socket  13  does not have any recess like the recess  74  between the head portion  71  and the collar portion  72  of the conventional electrode filament connection member illustrated in  FIG.  7   . Therefore, the filament socket  13  can prevent solids produced in the chamber C from being deposited on the head portion  131 , developing into a large lump, and falling off. 
     The CVD apparatus  1  according to an embodiment includes the filament socket  13 . Accordingly, when a film is formed on the substrate W in the chamber C by the CVD method using the cathode filament  12 , the filament socket  13  can prevent solids produced in the chamber C from adhering to the socket attachment hole  111  of the outer wall  11  through which the filament socket  13  is attached. Further, because the CVD apparatus  1  includes the filament socket  13 , it is possible to prevent solids produced in the chamber C from being deposited on the head portion  131 , developing into a large lump, and falling off. 
     The method for manufacturing a recording medium substrate according to an embodiment uses the filament socket  13 . Accordingly, in the method for manufacturing a recording medium substrate according to the embodiment, when a film is formed on the substrate W in the chamber C by the CVD method using the cathode filament  12 , solids produced in the chamber C can be prevented from adhering to the socket attachment hole  111  of the outer wall  11  through which the filament socket  13  is attached. In addition, because the method for manufacturing a recording medium substrate according to the embodiment uses the filament socket  13 , solids produced in the chamber C can be prevented from being deposited on the head portion  131 , developing into a large lump, and falling off. 
     Accordingly, the electrode filament connection member, the CVD apparatus, and the method for manufacturing a recording medium substrate that can prevent contamination of the outer wall  11  of the chamber C and can also prevent solids produced in the chamber C from being deposited and falling off when a film is formed on the substrate W in the chamber C by the CVD method using the cathode filament  12 , can be provided. 
     According to an embodiment, an electrode filament connection member, a CVD apparatus, and a method for manufacturing a recording medium substrate that can prevent solids produced in a chamber from being deposited and falling off when a film is formed on a substrate in the chamber by a CVD method using an electrode filament, can be provided. 
     Although the embodiments have been described above, the embodiments are merely examples and not to be construed as limiting the present invention. The embodiments may be implemented in various other forms, and various combinations, omissions, substitutions, modifications, or the like may be made without departing from the scope of the present invention. The embodiments and modifications thereof fall within the scope of the claimed invention and equivalents thereof.