Patent Publication Number: US-2011064885-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. 3  is a schematic cross section of a conventional deposition apparatus  200 . 
     The deposition apparatus  200  comprises the following components: a chamber  201 ; 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 a 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 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  penetrate the upper end of a 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 busbars  210  is secured to a connector  211  that is connected to the upper end of the columnar support  206 , a 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  to the heater  209 . The upper hollow end of the columnar support  206  is also closed by an upper lid  212 . 
     A susceptor  220  on which to place the wafer  203  is installed inside the chamber  201 . The susceptor  220  can be rotated. That is, a hollow rotary shaft  221  surrounds the hollow columnar support  206 . The rotary shaft  221  is attached to the base  202  such that the rotary shaft  221  can rotate around the 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 . 
     During the deposition process by the above apparatus  200 , the heater  209  of the wafer heating means  205 , located below the susceptor  220 , heats the wafer  203  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 , thereby depositing 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 hot (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 inside of the chamber  201  is exposed to an extremely high temperature at the time of wafer heating during vapor-phase deposition. Thus, the components of the deposition apparatus  200  need to be formed of highly heat-resistant materials. 
     Regarding the wafer heating means  205 , the heater  209 , subject to the highest temperature, is typically formed of high-purity silicon carbide (SiC), and the electrically-conductive busbars  210  for supporting the heater  209  are of SiC-coated carbon. These SiC and SiC-coated carbon materials, though low in flexibility and prone to cracking, are typically used because they are less likely to cause metal contamination during wafer heating. In other words, it is of greater importance to select a material for wafer heating means that prevents metal contamination during wafer heating rather than whether or not the material is high in flexibility and heat resistance. 
     Regarding the rod electrodes  208  inside the hollow columnar support  206 , on the other hand, it is more important to ensure and improve electrical conductivity because the rod electrodes  208  are subject to lower temperatures than the heater  209  and its nearby components. Thus, the rod electrodes  208  are typically formed of metallic molybdenum; such rod-shaped molybdenum electrodes excel in electrical conductivity and rigidity. 
     However, the rod electrodes  208  are sometimes exposed to high temperatures (700 to 800 degrees Celsius or higher) within the chamber  201 . In such a case, impurities may be released from the metallic molybdenum that constitutes the rod electrodes  208 , or the molybdenum may thermally decompose itself; in either case, the wafer  203  is likely to be contaminated. 
     Therefore, conventional apparatuses or methods for film deposition are not satisfactory for preventing metal contamination of wafers, which inevitably calls for a new deposition apparatus and method. 
     The present invention has been contrived to address the above issues. That is, one object of the present invention is to provide a film deposition apparatus that prevents, at the time of heating a wafer, contamination of the wafer, which is attributable to the metal rod electrodes located inside a hollow columnar support that extends into a chamber. 
     Another object of the present invention is to provide an apparatus and method for film deposition that prevent, during wafer heating, the metal rod electrodes located inside a hollow columnar support that extends into a chamber from being heated to high temperatures. 
     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, a 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 for supporting the heater; a rotary drum for supporting the susceptor at an upper section thereof and for housing the heater and the busbar, and 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 and a columnar support for supporting the electrode assembly. 
     The electrode assembly includes a rod electrode and an electrically-conductive connector, attached to an upper end section of the rod electrode, for supporting the busbar. 
     The rod electrode is a hollow cylindrical shape having upper and lower openings. A purge gas is fed from the lower opening of the rod electrode so that the purge gas can pass through the inside of the rod electrode and be discharged from the upper opening of the rod electrode into the rotary drum. 
     According to another aspect of the present invention, in a method for depositing a film on a surface of a substrate, the substrate is placed on a susceptor installed on a rotary drum housed by in chamber; the substrate is heated while rotating the rotary drum by a rotary shaft provided at a lower section of the chamber; a deposition gas is fed into the chamber. 
     A heater is provided inside the rotary drum. 
     The substrate is heated by conducting electricity to the heater with the use of a hollow rod electrode having upper and lower openings, while feeding a purge gas from the lower opening of the rod electrode so that the purge gas can flow through the inside of the rod electrode. 
    
    
     
       BRIEF DESCRIPTION OF THE DRAWINGS 
         FIG. 1  is a schematic cross section of a film deposition apparatus according to an embodiment of the present invention. 
         FIG. 2  is a bottom view schematically illustrating the bottom structure of a rotary drum of the deposition apparatus according to the embodiment of the present invention. 
         FIG. 3  is a schematic cross section of a conventional deposition 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 film deposition apparatus  100  of 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 hollow columnar support  105 , which protrudes from the base  104 . 
     A rotary shaft  112  is attached to a base  104  so 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, a 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 . Shaping the upper portion of the columnar support  105  as above allows reliable attachment of the wafer heating means  120 , which will later be described 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 molybdenum rod electrodes  108  are each shaped like a hollow cylinder 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 . The upper end of each of the rod electrodes  108 , on the other hand, is connected to and closed by the connector  124 . As illustrated in  FIG. 1 , an opening  118  is provided at an upper side section of each of the rod electrodes  108 , which section is located inside the rotary drum  111 . The columnar support  105  also has through holes, located inside the rotary drum  111 , that communicate with the openings  118  of the rod electrodes  108 . 
     Thus, the 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  108 , then passes through the openings  118  of the rod electrodes  108  and through the through holes of the columnar support  105 , and is eventually discharged into the rotary drum  111  located inside the chamber  102 . 
       FIG. 2  is a bottom view schematically illustrating the bottom structure of the rotary drum  111  of the deposition apparatus  100 . 
     As illustrated in  FIG. 2 , 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  and through the through holes of the columnar support  105 . 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 . 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  so 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. 
     It should be noted that the reason the openings  118  through which to discharge the purge gas  117  are provided at the upper side sections of the rod electrodes  108  is to efficiently cool electrode assemblies  107  each comprising a connector  124  and a rod electrode  108 . 
     The openings  118  at the upper side sections of the rod electrodes  108  also help prevent the purge gas  117  from being directed to the vicinity of the wafer  101  located at an upper section of the rotary drum  111  after the purge gas  117  has passed through the rod electrodes  108 . 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 . 
     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. 
     With the above configuration of the rod electrodes  108  and their nearby components, it is possible to prevent the metal rod electrodes  108  from being heated to an extremely high temperature at the time of heating the silicon wafer  101 , thereby preventing metal contamination of the wafer  101  by the rod electrodes  108 . 
     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. 
     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 . The hydrogen gas passed through the hollow rod electrodes  108  can cool the electrode assemblies  107 . 
     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 embodiment of the invention, it is possible to provide a film deposition apparatus that prevents, at the time of heating a wafer, the metal rod electrodes located inside a hollow columnar support that extends into a chamber from being heated to a high temperature, so that the wafer cannot be contaminated by the metal rod electrodes. 
     In accordance with the second embodiment of the invention, it is possible to provide a film deposition method that prevents, at the time of heating a wafer, the metal rod electrodes located inside a hollow columnar support that extends into a chamber from being heated to a high temperature, so that the wafer cannot be contaminated by the metal rod electrodes. 
     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 first 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 a surface of a substrate by feeding a deposition gas into its chamber and heating the substrate inside the chamber. 
     Obviously many modifications and variations of the present invention are possible in the light of the above teachings. 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. 2009-216289, 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.