Patent Publication Number: US-2011064878-A1

Title: Apparatus and method for film deposition

Description:
BACKGROUND OF THE INVENTION 
     1. Field of the Invention 
     The present invention relates to an apparatus and a method for film deposition. 
     2. Background Art 
     A single-wafer deposition apparatus is often used to deposit a monocrystalline film, such as a silicon film or the like, on a substrate wafer, thereby forming an epitaxial wafer. 
       FIG. 5  is a schematic cross section of a conventional deposition apparatus  200 . The deposition apparatus  200  comprises the following components: a chamber  201  inside which a monocrystalline film, such as a silicon film or the like, is deposited on a substrate wafer  203 ; a base  202  on which to place the chamber  201 ; a gas inlet port  215  for supplying a deposition gas  204  into the chamber  201 ; and wafer heating means  205  for heating the wafer  203  on which to deposit a film. Inside the base  202  is a hollow columnar support  206  that extends upwardly into the chamber  201 . 
     Attached to the upper and lower ends of the hollow columnar support  206  are, respectively, the wafer heating means  205  and an electrode securing unit  207 , the latter of which serves as a lower lid for closing the lower end of the columnar support  206 . Inside the columnar support  206  are two rounded rod electrodes  208  which extend through the electrode securing unit  207  and are thus secured to the columnar support  206 . The two rod electrodes  208 , typically formed of metallic molybdenum, penetrate the upper end of the columnar support  206 , extending up to the wafer heating means  205  located inside the chamber  201 . 
     The wafer heating means  205  comprises a heater  209  and two electrically-conductive busbars  210  for supporting the heater  209 . Each of the busbars  210 , typically formed of silicon carbide (SiC) or SiC-coated carbon, is secured to an electrically-conductive connector  211  that is connected to the upper end of the columnar support  206 , which means that the heater  209  is connected to the columnar support  206  via the connectors  211  and the busbars  210 . Further, the two rod electrodes  208  are each connected to one of the connectors  211 . 
     Therefore, electricity can be conducted from the two rod electrodes  208  through the connectors  211  and the busbars  210  to the heater  209 . The upper hollow end of the columnar support  206  is also closed by an upper lid  212 . 
     A hollow rotary shaft  221  surrounds the columnar support  206 . The rotary shaft  221  is attached to the base  202  such that the rotary shaft  221  can rotate around the hollow columnar support  206  via a bearing not illustrated. The rotation of the rotary shaft  221  is achieved by a motor  222 . 
     A rotary drum  223  is installed on the upper end of the rotary shaft  221  that extends upwardly into the chamber  201 . Installed on the top surface of the rotary drum  223  is a susceptor  220  on which to place the wafer  203 . Therefore, the susceptor  220  inside the chamber  201  can be rotated above the wafer heating means  205  by the motor  222  rotating the rotary shaft  221  and the rotary drum  223 . 
     Upon the deposition process by the above apparatus  200 , the heater  209  of the wafer heating means  205 , located below the susceptor  220 , receives electricity from the rod electrodes  208  through the connectors  211  and the busbars  210 , thereby heating the wafer  203  placed on the susceptor  220  while the wafer  203  is being rotated. The apparatus  200  then supplies the deposition gas  204  through the gas inlet port  215  to deposit an epitaxial film on the wafer  203 . 
     During such vapor-phase deposition, the heating by the wafer heating means  205  may cause the temperature of the wafer  203  to become extremely high (e.g., higher than 1000 degrees Celsius). 
     JP-A-5-152207 also discloses a deposition apparatus similar to the above, in which a single wiring component penetrates a lower lid of a hollow columnar support and is secured to the columnar support at its upper and lower sections. 
     As stated above, the foregoing apparatus  200  supplies electricity from the rod electrodes  208  to the heater  209 , with the electrically-conductive connectors  211 , typically formed of metallic molybdenum, being connected to the electrically-conductive busbars  210  that supports the heater  209  and also to the rod electrodes  208 . One problem with the apparatus  200  is that, in some cases, it has unwanted spaces at the joints between the connectors  211  and the busbars  210  and at the joints between the connectors  211  and the rod electrodes  208 . 
     Such joint spaces are due primarily to the difference in the materials used for the busbars  210 , the connectors  211 , and the rod electrodes  208 . Typically, the busbars  210  are formed of carbon, and the connectors  211  and the rod electrodes  208  are of metallic molybdenum. Because these materials have different rates of thermal expansion, wafer heating during vapor-phase deposition may cause unwanted tiny spaces at the joints between, for example, the busbars  210  and the connectors  211 . 
     In such a case, the deposition gas  204  may flow into the tiny spaces, attaching by-products or causing corrosion. This may in turn increase the electric resistance of the joints, which necessitates more frequent maintenance of the wafer heating means  205 , the rod electrodes  208 , and the like and eventually shortens the mechanical life of the apparatus. 
     The present invention has been contrived to address the above issues. That is, one object of the invention is to provide a film deposition apparatus that prevents, at the time of film deposition onto a silicon wafer or the like, a deposition gas from flowing into the joint between a busbar for supporting a heater and a connector for supporting the busbar and into the joint between the connector and a rod electrode for conducting electricity to the heater. 
     Another object of the present invention is to provide a film deposition apparatus that prevents, at the time of film deposition onto a silicon wafer or the like, a deposition gas from flowing into the joint between a busbar and a connector and into the joint between the connector and a rod electrode, thereby also preventing attachment of by-products or corrosion at the joints. 
     Still another object of the present invention is to provide a film deposition method that prevents, at the time of film deposition onto a silicon wafer or the like, a deposition gas from flowing into the joint between a busbar for supporting a heater and a connector for supporting the busbar and into the joint between the connector and a rod electrode for conducting electricity to the heater, thereby also preventing attachment of by-products or corrosion at the joints. 
     Other challenges and advantages of the present invention are apparent from the following description. 
     SUMMARY OF THE INVENTION 
     According to one aspect of the present invention, the film deposition apparatus comprises a chamber; a susceptor for placing thereon a substrate, the susceptor being located inside the chamber; a heater for heating the substrate; 
     an electrically-conductive busbar used to support the heater; a rotary drum for supporting the susceptor at an upper section thereof and for housing the heater and the busbar; a rotary shaft, located at a lower section of the chamber, for rotating the rotary drum. 
     The rotary shaft houses an electrode assembly for conducting electricity through the busbar to the heater; a columnar support for supporting the electrode assembly, wherein the electrode assembly includes: a hollow rod electrode having upper and lower openings; an electrically-conductive connector for securing an upper end section of the rod electrode, with the upper end section penetrating the connector and supporting the busbar, wherein a joint surface between the busbar and the connector is provided with: a clearance that is located around and communicates with the upper opening of the rod electrode; a groove that communicates with the clearance; and a plurality of gas outlet ports that extend outwardly from the groove, wherein a purge gas is fed from the lower opening of the rod electrode so that the purge gas can pass through the inside and the upper opening of the rod electrode and be discharged through the clearance, the groove, and the gas outlet ports into the rotary drum. 
     According to another aspect of the present invention, in a method of depositing a film on a surface of a substrate, the method comprising the steps of: placing the substrate on a susceptor installed on a rotary drum housed by a chamber; heating the substrate while rotating the rotary drum by a rotary shaft provided at a lower section of the chamber; and feeding a deposition gas into the chamber, wherein a heater is provided inside the rotary drum, wherein the heater includes: 
     an electrically-conductive busbar used to support the heater; 
     an electrically-conductive connector used to support the busbar; and a hollow rod electrode, having upper and lower openings, that penetrates the connector and extends up to a joint surface between the busbar and the connector, and wherein the substrate is heated by conducting electricity to the heater through the rod electrode, while feeding a purge gas from the lower opening of the rod electrode so that the purge gas can be discharged through the joint surface between the busbar and the connector. 
    
    
     
       BRIEF DESCRIPTION OF THE DRAWINGS 
         FIG. 1  is a schematic cross section of apparatus. 
         FIG. 2  is an enlarged cross section schematic showing the clearance between an electrode assembly and a busbar of apparatus. 
         FIG. 3  is across section illustrating the groove provided at the bottom joint surface of a busbar. 
         FIG. 4  is a bottom view schematic showing the bottom of the rotary drum  111  of apparatus. 
         FIG. 5  is a schematic cross section of apparatus. 
     
    
    
     DETAILED DESCRIPTION OF THE EMBODIMENTS 
       FIG. 1  is a schematic cross section of a film deposition apparatus  100  according to an embodiment of the present invention. In this preferred embodiment, a silicon wafer  101  is used as a substrate on which to deposit a film. Of course, it is also possible to use other wafers formed of different materials if so required. 
     The deposition apparatus  100  includes a deposition chamber  102  inside which a film is deposited on the wafer  101  and a base  104  on which to place the deposition chamber  102 . Inside the base  104  is a non-electrically-conductive, hollow, columnar support  105  that extends upwardly into the chamber  102 . 
     An upper portion of the chamber  102  is provided with a deposition gas inlet port  103 . The inlet port  103  is designed to supply a deposition gas  115  after the wafer  101  is heated, so that a crystalline film can be deposited on the top surface of the wafer  101 . In the present embodiment, trichlorosilane is used as the deposition gas  115 . After mixed with a hydrogen gas, which acts as a carrier gas, the deposition gas  115  is fed through the gas inlet port  103  into the chamber  102 . 
     Although not illustrated, a flow straightening vane with multiple through holes may be provided on the upstream side of the flow direction of the deposition gas  115  (the direction is illustrated by the topside arrows of  FIG. 1 ). The deposition gas  115  is fed through the inlet port  103  and directed toward the top surface of the wafer  101 . 
     The chamber  102  houses a hollow rotary drum  111 , and a susceptor  110  on which to place the wafer  101  is provided on the top surface of the rotary drum  111 . The rotary drum  111  is supported by a hollow rotary shaft  112  and houses an upper portion of the columnar support  105 , which protrudes from the base  104 . 
     The rotary shaft  112  is attached to the base  104  such that the rotary shaft  112  can rotate around the columnar support  105  via a bearing not illustrated. The rotation of the rotary shaft  112  is achieved by a motor  113 . When the motor  113  causes the rotary shaft  112  to rotate, the rotary drum  111  attached to the rotary shaft  112  also starts to rotate, and so does the susceptor  110  attached to the rotary drum  111 . 
     The upper hollow end of the columnar support  105  is closed by an upper lid  106 , and wafer heating means  120  is provided above the columnar support  105 . 
     Although not illustrated, a radiation thermometer is provided at an upper section outside the chamber  102  to measure the surface temperature of the wafer  101  while the wafer  101  is being heated. It is preferred that the chamber  102  and the flow straightening vane (not illustrated) be formed of quartz because, as known in the art, the use of quartz prevents the chamber  102  and the flow straightening vane from affecting the temperature measurement by the radiation thermometer. After the temperature measurement, its data is sent to a control device not illustrated. 
     The control device controls the operation of a three-way valve (not illustrated) installed inside a path through which the hydrogen gas flows. Specifically, when the temperature of the wafer  101  reaches or exceeds a particular value, the control device activates the three-way valve to control the supply of the hydrogen gas to the chamber  102 . The control device also controls the output of a heater  121 . 
     The main components of the film deposition apparatus  100  will now be described more in detail. 
     As illustrated in  FIG. 1 , the upper portion of the columnar support  105  which is located above the main cylindrical structure of the support  105  can be shaped to have a ring or flange structure whose diameter is greater than the outer diameter of the main cylindrical structure of the support  105 . The ring or flange structure can also be provided with an upwardly extending rim around its outer circumference, as is also illustrated in  FIG. 1 . 
     The height of the rim is set in such a way as not to prevent the discharge of a purge gas from a groove  132  and gas outlet ports  133 , both described later, which are provided at the joint surface between a connector  124  and a busbar  123 . Shaping the upper portion of the columnar support  105  as above allows reliable attachment of the wafer heating means  120 , which will also be described later in detail. 
     Installed inside the hollow columnar support  105  are two electrode assemblies  107 . Each of the electrode assemblies  107  includes a hollow rod electrode  108  formed of metallic molybdenum (Mo) and also includes an electrically-conductive connector  124 , fixed to the upper end of the rod electrode  108 , for supporting an electrically-conductive busbar  123 . 
     The rod electrodes  108  are each shaped like a hollow cylinder (although square, hexagonal, triangle are also acceptable) having upper and lower openings as stated above, and the lower hollow end of each of the rod electrodes  108  communicates with a purge gas supply port  116  from which to supply a purge gas  117 . 
     In the present embodiment, we set the outer diameter of each of the rod electrodes  108  to 8 mm and the inner diameter of each (i.e., the diameter of the hollow portion of each) to 4 mm. The outer diameter is set to a value that allows the columnar support  105  to house the rod electrodes  108 . The inner diameter is determined such that the purge gas  117  can flow smoothly inside the rod electrodes  108  and such that the rod electrodes  108  can maintain sufficient electrical conductivity. It is preferred in the present embodiment that the outer diameter of each of the rod electrodes  108  be from 6 mm to 10 mm and the inner diameter of each from 2 mm to 6 mm. 
       FIG. 2  is an enlarged cross section schematically illustrating the joint between an electrode assembly  107  and a busbar  123  of the deposition apparatus  100  according to the embodiment of the invention. 
     The busbar  123  is secured to a connector  124  via bolts  135  that penetrate the busbar  123  and the connector  124  and via nuts  136 . As illustrated in  FIG. 2 , the upper opening  118  of the rod electrode  108  secured to the connector  124  extends upwardly beyond the joint surface between the connector  124  and the busbar  123 . Thus, a clearance  131  is provided in the lower joint section of the busbar  123  so that the busbar  123  cannot block the upper opening  118  of the rod electrode  108 . 
     The clearance  131  can be provided at the lower joint section of the busbar  123  as stated above or instead provided at the upper joint section of the connector  124  by cutting away some upper portion of the connector  124  around the rod electrode  108 . Alternatively, both the busbar  123  and the connector  124  can be machined to provide the clearance  131 . 
     The clearances  131  of  FIG. 1  are provided by forming concave portions in the lower joint sections of the busbars  123 , as in  FIG. 2 . 
       FIG. 3  is a cross section illustrating a groove  132  provided at the bottom joint surface of a busbar  123  according to the embodiment of the present invention. 
     As illustrated in  FIG. 3 , the groove  132  is provided at the lower joint section of the busbar  123  such that the groove  132  communicates with a clearance  131 . The groove  132  also communicates with multiple gas outlet ports  133  that extend outwardly from the groove  132 . Provided at the joint surface between the busbar  123  and its associated connector  124  of the deposition apparatus  100  according to the embodiment of the invention are thus the clearance  131 , the groove  132 , and the gas outlet ports  133 , all of which communicate with each other. 
     Note that the groove  132  that communicates with the clearance  131  can instead be provided at the upper joint section of the associated connector  124 . Alternatively, the groove  132  can be provided at both the lower joint section of the busbar  123  and the upper joint section of the connector  124 . 
     The two left-side circles of  FIG. 3  depict the bolts  135  of  FIG. 2  (not illustrated in  FIG. 1 ) that penetrate the busbar  123  to secure it to its associated connector  124 . 
     Note also that, as is similar to the groove  132 , the gas outlet ports  133  can instead be provided at the upper joint section of the connector  124  such that they communicate with the clearance  131 . Alternatively, the gas outlet ports  133  can also be provided at both the lower joint section of the busbar  123  and the upper joint section of the connector  124 . 
     When the clearance  131  is to be provided at the upper joint section of the connector  124  as stated above, it is preferred that the groove  132  and the gas outlet ports  133  be provided there, too. Instead, it is of course possible to provide the groove  132  and the gas outlet ports  133  at the lower joint section of the busbar  123  or at both the lower joint section of the busbar  123  and the upper joint section of the connector  124 . 
     With the above configuration of the deposition apparatus  100 , the upper openings  118  of the hollow rod electrodes  108  act as outlet ports through which to supply the purge gas  117  from the lower openings of the rod electrodes  108 . Specifically, when the purge gas  117  is fed through the lower openings of the rod electrodes  108  from the purge gas supply ports  116 , the purge gas  117  moves upward through the rod electrodes  118 , passing through the openings  118  of the rod electrodes  108 . The purge gas  117  further passes through the clearances  131 , the grooves  132 , and the gas outlet ports  133 , all located at the joint surfaces between the busbars  123  and the connectors  124 , and is eventually discharged into the rotary drum  111  located inside the chamber  102 . 
       FIG. 4  is a bottom view schematically illustrating the bottom structure of the rotary drum  111  of the deposition apparatus  100 . 
     As illustrated in  FIG. 4 , multiple outlet ports  119  extend through the bottom section of the rotary drum  111 . The outlet ports  119  are designed to discharge the purge gas  117  from the rotary drum  111  into the chamber  102  when the purge gas  117  is fed into the rotary drum  111  through the openings  118  of the rod electrodes  108 . After the deposition process, the purge gas  117  is discharged, together with the deposition gas  115 , out of the chamber  102  through an exhaust port (not illustrated) of the chamber  102 . 
     The supply of the purge gas  117  from the purge gas supply ports  116  is also controlled by the above-mentioned control device (not illustrated), which, as stated above, controls the supply of the hydrogen gas to the chamber  102 . Thus, the hydrogen gas can be used both as the purge gas  117  and as the carrier gas for the deposition gas  115 . It is also possible for the control device to use another purge gas source (not illustrated) to supply an inert gas, such as nitrogen gas and argon gas, as the purge gas  117 . 
     To deposit a silicon crystalline film on a wafer, it is preferred to use a hydrogen gas or a nitrogen gas as the purge gas  117 . To deposit a silicon carbide (SiC) crystalline film at 1600 degrees Celsius, it is preferred to use a less reactive argon gas as the purge gas  117 . When depositing a film of gallium nitride (GaN), on the other hand, it is preferred to use a hydrogen gas as the purge gas  117 . 
     As stated above, the purge gas  117  is fed from the lower openings of the hollow rod electrodes  108  to let it pass through the rod electrodes  108 . The purge gas  117  further passes through the clearances  131 , the grooves  132 , and the gas outlet ports  133 , all located at the joint surfaces between the busbars  123  and the connectors  124 , and is eventually discharged into the rotary drum  111  located inside the chamber  102 . 
     Consequently, even if unwanted spaces are present in the joints between the connectors  124  and the busbars  123  and in the joints between the connectors  124  and the rod electrodes  108 , the deposition apparatus  100  of the present embodiment is capable of preventing the deposition gas  115  from flowing into those spaces during film deposition onto a silicon wafer. 
     Moreover, by achieving the above, the deposition apparatus  100  is also capable of preventing attachment of by-products to and corrosion of those joints. 
     The rod electrodes  108  housed by the hollow columnar support  105 , though subject to lower temperatures than the heater  121  and its nearby components, are sometimes exposed to high temperatures (e.g., 700 to 800 degrees Celsius or higher) within the chamber  102 . In such a case, impurities may be released from the metallic molybdenum that constitutes the rod electrodes  108 , or the molybdenum may thermally decompose itself; in either case, the wafer  101  is likely to be contaminated. 
     To prevent such contamination of the wafer  101  as well, the purge gas  117  is fed through the rod electrodes  108 . This makes it possible to cool the rod electrodes  108  so that the rod electrodes  108  cannot be heated to a high temperature during wafer heating and also to control the temperatures of the rod electrodes  108  such that the temperatures do not reach the range of 700 to 800 degrees Celsius, in which contaminants are likely to be released from the rod electrodes  108  formed of molybdenum. 
     As stated above, when the purge gas  117  flows out of the gas outlet ports  133  located at the joints between the busbars  123  and the connectors  124 , the purge gas  117  is discharged from the outlet ports  119  of the rotary drum  111  and then from the exhaust port (not illustrated) of the chamber  102 . Thus, the purge gas  117  that has flowed through the rod electrodes  108  is prevented from being directed toward the vicinity of the wafer  101  located at an upper section of the rotary drum  111 . Note also that the reason the purge gas  117  is discharged from the outlet ports  119  of the bottom section of the rotary drum  111  into the chamber  102  is to prevent the purge gas  117  from moving upward inside the rotary drum  111 , so that the purge gas  117  cannot contaminate the silicon wafer  101 . 
     The connectors  124  of the electrode assemblies  107  are shaped such that the connectors  124  extend toward the outer circumference of the columnar support  105  from the upper ends of the rod electrodes  108 . Thus, the electrode assemblies  107 , each comprising a connector  124  and a rod electrode  108 , are L-shaped. Each of the connectors  124  is also formed of metallic molybdenum, meaning the entire electrode assemblies  107  are formed of metallic molybdenum. 
     As stated above, the connectors  124  can be provided with the clearance  131 , the groove  132 , and the gas outlet ports  133 , through which to pass the purge gas  117  discharged from the upper openings  118  of the rod electrodes  108 . 
     With reference again to  FIG. 1 , an electrode securing unit  109  is attached to the lower end of the columnar support  105 . The electrode securing unit  109  secures the rod electrodes  108 , which extend upwardly through the electrode securing unit  109 . The electrode securing unit  109  also serves as a lower lid for closing the lower end of the hollow columnar support  105 . 
     The wafer heating means  120  comprises the following components: the heater  121  for heating the silicon wafer  101 ; and the two arm-like busbars  123  for supporting the heater  121 . The lower ends of the busbars  123  are attached to the connectors  124  via bolts or the like, as illustrated in  FIG. 2 . 
     The heater  121  is formed of silicon carbide (SiC), and the two busbars  123  for supporting the heater  121  are electrically conductive and formed of a SiC-coated carbon material, for example. Since both the connectors  124  and the rod electrodes  108  are formed of molybdenum as stated above, electricity can be conducted from the electrode assemblies  107  through the busbars  123  to the heater  121 . 
     The lower surfaces of the connectors  124  are at least partially in contact with the top surface of the upper portion of the columnar support  105 , which portion protrudes from the main cylindrical structure of the support  105 . Further, at least one of each of the busbars  123  and each of the connectors  124  is in contact with the upwardly extending rim of the upper portion of the columnar support  105  at two points at least. 
     Since the electrode securing unit  109  is attached to the lower end of the columnar support  105 , that is, located outside the chamber  102 , it is less exposed to high temperatures. Thus, the material for the electrode securing unit  109  can be selected from among a relatively wide range of materials. It is preferred to use a material which is moderate in thermal resistance and flexibility. An example of such a material is resin, and a fluorine resin is particularly preferred because it is less subject to degradation under the above temperature environment. 
     Described next is a method for film deposition of the present invention. Deposition of a silicon epitaxial film on the silicon wafer  101  takes the following steps. 
     The wafer  101  is first loaded into the chamber  102 . The wafer  101  is placed on the susceptor  110 , and the rotary drum  111  then starts rotation to rotate the wafer  101  at 50 rpm or thereabout. 
     Next, the heater  121  is activated to heat the wafer  101  gradually up to, for example, 1150 degrees Celsius, a film deposition temperature. After the radiation thermometer (not illustrated) registers 1150 degrees Celsius, meaning that the temperature of the wafer  101  has reached that value, then, the rotational speed of the wafer  101  is increased gradually. Thereafter, the deposition gas  115  is fed from the deposition gas inlet port  103  via the flow straightening vane (not illustrated) and directed toward the top surface of the wafer  101 . 
     When the heater  121  starts heating the wafer  101 , the purge gas  117  (hydrogen gas) is introduced into the hollow rod electrodes  108  through the purge gas supply ports  116  as instructed by the control device (not illustrated), so that the hydrogen gas can cool the rod electrodes  108 . As stated above, the purge gas  117  flows through the inside of the rod electrodes  108 , then passing through the upper openings  118  of the rod electrodes  108 , the clearances  131 , the grooves  132 , and the gas outlet ports  133 . 
     As a result, even if unwanted spaces are present in the joints between the connectors  124  and the busbars  123  and in the joints between the connectors  124  and the rod electrodes  108 , the deposition gas  115  is prevented from flowing into those spaces due to the flow of the purge gas  117 . 
     Even after the supply of the deposition gas  115 , the radiation thermometer continues to measure the temperature of the wafer  101 , and after the temperature reaches a particular value, the control device activates the three-way valve (not illustrated) to control the supply of the carrier gas (hydrogen gas) into the chamber  102 . 
     After an epitaxial film of a particular thickness is deposited on the wafer  101 , the supply of the deposition gas  115  is stopped. The supply of the carrier gas can also be stopped at the same time; alternatively, it can also be stopped after the temperature of the wafer  101 , as measured by the radiation thermometer, becomes lower than a particular value. After the deposition process, the supply of the purge gas  117  to the rod electrodes  108  is also stopped when the temperature of the wafer  101  becomes lower than a particular value. 
     Finally, the wafer  101  is transferred out of the chamber  102  after the temperature of the wafer  101  is reduced to a particular value. 
     The features and advantages of the present invention may be summarized as follows: 
     In accordance with the first aspect of the invention, it is possible to provide a film deposition apparatus that prevents, at the time of wafer heating, a deposition gas from flowing into the joint between the busbar used for supporting the heater and the connector used for supporting the busbar and also into the joint between the connector and the rod electrode used for conducting electricity to the heater, thereby also preventing attachment of by-products to and corrosion of these joints. 
     In accordance with the second aspect of the invention, it is possible to provide a film deposition method that prevents, at the time of wafer heating, a deposition gas from flowing into the joint between the busbar used for supporting the heater and the connector used for supporting the busbar and also into the joint between the connector and the rod electrode used for conducting electricity to the heater, thereby also preventing attachment of by-products to and corrosion of those joints. 
     The present invention is not limited to the above-described embodiments but can be embodied in various forms without departing from the scope of the invention. The epitaxial deposition apparatus employed in the present embodiment is only meant to be an example of a film deposition apparatus, and the invention is not limited thereto. Any other apparatus can be used as long as it is capable of depositing a film on the surface of a substrate by feeding a deposition gas into the chamber and heating the substrate inside the chamber. 
     Obviously many modifications and variations of apparatus and/or methods are possible in light of the present invention. It is therefore to be understood that within the scope of the appended claims the invention may be practiced otherwise than as specifically described. 
     The entire disclosure of a Japanese Patent Application No. 2009-216288, filed on Sep. 17, 2009 including specification, claims, drawings and summary, on which the Convention priority of the present application is based, are incorporated herein.