Patent Publication Number: US-2012037613-A1

Title: Element wire contact prevention member and method for maintenance of heater device

Description:
CROSS-REFERENCE TO RELATED APPLICATION 
     This application claims the benefit of Japanese Patent Application No. 2010-179592, filed on Aug. 10, 2010, in the Japan Patent Office, the disclosure of which is incorporated herein their entirety by reference. 
     TECHNICAL FIELD 
     The present disclosure relates to a method for maintenance of a heater device installed in a heating apparatus for heat treatment of an object to be heated, such as a semiconductor wafer or the like, and an element wire contact prevention member for preventing contact between element wires. 
     BACKGROUND 
     In general, a semiconductor wafer formed of a silicon substrate or the like is repeatedly subjected to the processes of film formation, oxidation, diffusion, annealing, etching, and so on in order to form a semiconductor integrated circuit. In addition, in performing these processes, a so-called batch type heat treatment apparatus is used for simultaneous treatment of a plurality of semiconductor wafers. For example, such a heat treatment apparatus includes an elongated quartz processing container. Specifically, in the elongated quartz processing container, a plurality of semiconductor wafers is accommodated in a wafer boat supported by over a plurality of stages and hermetically sealed. In this example, it is arranged that the atmosphere within this processing container is exhausted by an exhaustion unit while required process gas is being fed into this processing container by a gas feed means. 
     In addition, a heater device for heating the semiconductor wafers is placed to surround an outer circumference of this processing container. For example, this heater device is formed by spirally winding a heater element wire around an inner circumference of a cylindrical adiabatic layer. A pitch (gap) of this spiral heater element wire is set to be, for example, about 10 to 30 mm. The semiconductor wafers are then subjected to heat treatment such as film formation treatment, oxidation treatment, or annealing treatment while being heated to a predetermined temperature by the heater device. 
     However, the heater element wire, which is used in the heater device applied for the heating apparatus as described above, cannot avoid permanent elongation which results from its repeated use. The term “permanent elongation” refers to elongation resulted from deterioration of the heater element wire itself, but it does not refer to thermal elongation and contraction generated by heating and/or cooling. 
     Such permanent elongation may lead to deformation of the spirally-wound heater element wire itself. This may cause a problem that, when the heater element wire is deformed to be bent to contact an adjacent heater element wire, excessive heat is generated due to contact resistance of the contact portion so that the contact portion is fused, or, in worst case, the wire may be disconnected due to a spark or the like. 
     SUMMARY 
     The present disclosure provides some embodiments of an element wire contact prevention member for preventing contact between heater element wires and a method for maintenance of a heater device. 
     According to one embodiment of the present disclosure, there is provided an insulative element wire contact prevention member which is installed in a heater device having heater element wires spirally wound around the circumference of an object to be heated, wherein the element wire contact prevention member is interposed between the heater element wires in a portion at which a gap between the heater element wires becomes narrower than that at the time of arrangement of the heater element wires due to deformation of the heater element wires. 
     According to another embodiment of the present disclosure, there is provided an insulative element wire contact prevention member which is installed in a heater device having heater element wires having a wave shape or a bent shape of a repeated U-turn pattern disposed on the circumference of an object to be heated, wherein the element wire contact prevention member is interposed between the heater element wires in a portion at which a gap between the heater element wires becomes narrower than that at the time of arrangement of the heater element wires due to deformation of the heater element wires. 
     According to another embodiment of the present disclosure, there is provided a method for maintenance of a heater device which includes heater element wires spirally wound around the circumference of an object to be heated, comprising: detecting a portion at which a gap between the heater element wires becomes narrower than that at the time of arrangement of the heater element wires due to deformation of the heater element wires; and installing an element wire contact prevention member according to the above embodiment between the heater element wires in the narrowed portion. 
     According to another embodiment of the present disclosure, there is provided a method for maintenance of a heater device which includes heater element wires having a wave shape or a bent shape of a repeated U-turn pattern disposed on the circumference of an object to be heated, comprising: detecting a portion at which a gap between the heater element wires becomes narrower than that at the time of arrangement of the heater element wires due to deformation of the heater element wires; and installing an element wire contact prevention member according to the above embodiment between the heater element wires in the narrowed portion. 
    
    
     
       BRIEF DESCRIPTION OF THE DRAWINGS 
       The accompanying drawings, which are incorporated in and constitute a part of the specification, illustrate embodiments of the present disclosure, and together with the general description given above and the detailed description of the embodiments given below, serve to explain the principles of the present disclosure. 
         FIG. 1  is a schematic configuration view showing one example of a heat treatment apparatus having a heater device to which an element wire contact prevention member is applied according to an embodiment of the disclosure. 
         FIG. 2  is a sectional view of the heater device. 
         FIG. 3  is an enlarged sectional view of a portion of the heater device. 
         FIG. 4  is a perspective view of one example of the element wire contact prevention member according to an embodiment of the disclosure. 
         FIG. 5  is a sectional view of a heater device illustrating narrowed gaps between heater element wires due to deformation of the wire. 
         FIG. 6  is an enlarged sectional view of a heater device where an element wire contact prevention member is mounted between the heater element wires in a narrowed gap portion. 
         FIG. 7A  is a photograph showing a state that an element wire contact prevention member is not mounted between heater element wires. 
         FIG. 7B  is a photograph showing a state that an element wire contact prevention member is interposed and mounted between heater element wires. 
         FIG. 8A  is a view of an example of embodiment demonstrating a modification of the element wire contact prevention member. 
         FIG. 8B  is an enlarged sectional view of a heater device where the modified element wire contact prevention member, which is shown in  FIG. 8A , is mounted and interposed between heater element wires in a narrowed portion. 
         FIG. 9  is a view showing a modification of arrangement of the heater element wire. 
     
    
    
     DETAILED DESCRIPTION 
     An embodiment of an element wire contact prevention member and a method for maintenance of a heater device will now be described in detail with reference to the drawings.  FIG. 1  is a schematic configuration view of one example of a heat treatment apparatus having a heater device to which an element wire contact prevention member is applied according to an embodiment of the disclosure.  FIG. 2  is a sectional view of the heater device, and  FIG. 3  is an enlarged sectional view of a portion of the heater device.  FIG. 4  is a perspective view of one example of the element wire contact prevention member according to an embodiment of the disclosure. In the following description, an object to be heated will be illustrated with a semiconductor wafer. 
     To begin with, a heat treatment apparatus will be described below. As shown in  FIG. 1 , this vertical heat treatment apparatus  2  includes a cylindrical processing container  4  whose longitudinal direction lies vertically. This processing container  4  has a double tube structure, which generally comprises an outer barrel  6  which is made of a heat-resistant material, for example, quartz, and an inner barrel  8  which is concentrically placed inside of the outer barrel  6  and is made of, for example, quartz. The outer barrel  6  and the inner barrel  8  have their respective bottoms which are supported by a manifold  10  which is made of stainless steel or the like and is fixed to a base plate  12 . 
     In addition, a disc-like cap  14  made of, for example, stainless steel or the like, is air-tightly mounted in an opening at the bottom of the manifold  10  with a seal member  16  such as an O-ring. A rotatable shaft  20  is inserted in substantially the center of the cap  14  under an airtight state produced by, for example, a magnetic fluid seal  18 . The bottom of the shaft  20  is connected to a rotation mechanism  22  and the top thereof is fixed to a table  24  made of, for example, stainless steel. 
     Further, a heat reservoir  26  made of quartz is placed on the table  24  and a wafer boat  28  made of, for example, quartz is loaded, as a holder, on the heat reservoir  26 , A plurality of (e.g., 50 to 150) semiconductor wafers W as objects to be heated is accommodated in the wafer boat  28  with a pitch of, for example, 10 mm therebetween. The wafer boat  28 , the heat reservoir  26 , the table  24 , and the cap  14  are integrally loaded/unloaded into/from the processing container  4  by means of an elevating mechanism, such as a boat elevator  30 . A gas introduction unit  32  for introducing required gas into the processing container  4  is placed in a lower portion of the manifold  10 . 
     The gas introduction unit  32  has a gas nozzle  34  which is airtightly installed through the manifold  10 . Although only one gas nozzle is shown in this example, one or more gas nozzles  34  may be actually provided depending on the kind of gas used. The required gas is introduced into the processing container  4  under control of its flow rate by the gas nozzle  34 . In addition, a gas outlet  36  is provided in an upper portion of the manifold  10  and is connected to an exhaustion system  38 . Specifically, the exhaustion system  38  has an exhausting passage  40  connected to the gas outlet  36 . Further, a pressure regulating valve  42  and a vacuum pump  44  are disposed in order in the course of the exhausting passage  40 , thereby allowing the internal atmosphere of the processing container  4  to be exhausted with its regulated pressure. Additionally, a processing container made entirely of quartz without providing any manifold  10  has also been known. 
     In addition, a heater device  48  for heating the wafers W is provided to surround the outer circumference of the wafers W or the processing container  4 . Specifically, the heater device  48  includes a cylindrically-shaped adiabatic layer  50  which surrounds the outer circumference of the processing container  4  and has a ceiling. This adiabatic layer  50  is made of, for example, a mixture of silica and alumina, which are low thermal-conductive, flexible, and amorphous, and has a thickness of about 2 to 4 cm. The inner surface of the adiabatic layer  50  is separated by a predetermined distance from the outer surface of the processing container  4 . In addition, a protection cover  51  made of, for example, stainless steel, is mounted on the outer circumference of the adiabatic layer  50  to cover its entire surface. 
     In addition, a heater element wire  52  is disposed to spirally wind around the inner circumference of the adiabatic layer  50 . In this example, the heater element wire  52  is disposed to wind throughout the overall side of the adiabatic layer  50  and is arranged to cover the overall height of the processing container  4 . In other words, it is configured that the adiabatic layer  50  is disposed on the outer circumference of the heater element wire  52 . The spirally wound heater element wire  52  has a pitch, for example, in a range of 10 to 30 mm and a diameter in a range of 1 to 14 mm. Accordingly, the distance L 1  (see  FIG. 2 ) between adjacent heater element wires  52  in the vertical direction is set to be, for example, in a range of 5 to 16 mm. 
     Material for this heater element wire  52  is formed by a resistance heating conductor which includes, for example, iron, chromium, aluminum, or the like as main material. For example, a Kanthal heater (registered trademark) may be used as the heater element wire  52 . Alternatively, other carbon wire heaters may be used as the heater element wire  52 . 
     In this example, the heater element wire  52  is divided into a plurality of zones in the height direction, for example, four zones from the first to the fourth zone, each of which may be independently temperature-controlled based on temperature detected by a thermocouple (not shown) provided in the adiabatic layer  50  for each of the zones. The number of zones for division is not limited to the above value. 
     In this example, if a heat treatment apparatus for wafers with 300 mm of diameter is used, the diameter of the heater device is about 600 mm. The length of the heater element wire  52  for each of the first to fourth zones is set to be for example, in a range of ten to several tens meters. in addition, as shown in  FIG. 2 , a plurality of element wire holding frames  54  extending in the vertical direction is disposed at a predetermined equal interval along the inner circumference of the cylindrically-shaped adiabatic layer  50 . 
     As shown in  FIG. 3 , these element wire holding frames  54  have a shape like a concavo-convex comb, in which heater element wires  52  are accommodated in concave portions  56  to prevent misalignment of the heater element wires  52 . The distance L 2  (see  FIG. 2 ) between adjacent element wire holding frames  54  is set to be, for example, in a range of 10 to 15 cm. These element wire holding frames  54  are made of insulative ceramic material. 
     When a repeated heat treatment for the semiconductor wafers W is performed using the above-configured heat treatment apparatus  2 , the heater element wire  52  may undergo deformation with time, which may result in permanent elongation of the heater element wire  52 , thereby producing portions with a narrower gap between the wires than that of the initial arrangement. An element wire contact prevention member  62  according to an embodiment of the present disclosure, shown in  FIG. 4 , is mounted in the narrowed portion between the heater element wires  52  when performing maintenance of the heater device. This element wire contact prevention member  62  is formed of a plate-like member  62  and made of an insulative material. 
     This plate-like member  62  is made into a rectangular shape and has an acute-angled leading end  64 , which is so designed that it can be easily inserted into the flexible adiabatic layer  50 . The thickness of this plate-like member  62  is set to be within a range of 0.5 to 5 mm, for example, 1.5 mm in this example. Its width H 1  is set to be within a range of 5 to 30 mm, for example, 10 mm in this example. Its length H 2  is set to be within a range of 20 to 50 mm, for example, 40 mm in this example. 
     In addition, this plate-like member  62  may be preferably rigid, insulative, and heat-resistant and be made of, for example, ceramic material. An example of this ceramic material may include, for example, alumina (Al 2 O 3 ), aluminum nitride (AlN), or the like. 
     Next, a method for maintenance of the heater device used in the above-configured heat treatment apparatus will be described. First, the reference is made to heat treatment of semiconductor wafers W. The wafer boat  28  with a plurality of raw wafers W loaded thereon is accommodated in the processing container  4  by being ascended by the boat elevator  30  from below the processing container  4 , and the opening at the bottom of the container is hermetically sealed by the cap  14 . Then, the processing container  4  is vacuumized below a predetermined pressure using the exhaustion system  38 , and at the same time, the wafers W are heated to a predetermined treatment temperature at which heat treatment is carried out, by increasing electric current applied to the heater element wire  52  of the heater device  48 , and maintained at the predetermined temperature. Then, a regulated process gas is introduced from the gas nozzle  34  of the gas introduction unit  32  at the lower portion of the processing container  4  into the processing container  4 , and then, heat treatment is carried out by making the gas flow upward in the inner barrel  8  and flow between the wafers. 
     The gas flowing in the inner barrel  8  rebounds from the ceiling of the processing container  4  and is discharged out by the exhaustion system  38  through a gap between the inner barrel  8  and the outer barrel  6 , as described above. The heat treatment carried out in this example may include treatments such as film formation, oxidation, diffusion, and annealing, in each of which different process gas is used depending on the type of treatment. The treatment temperature is also varied depending on the type of treatment. For example, the heat treatment is carried out at a high temperature in a range of 300 to 800° C. 
     When the above heat treatment is repeated for the semiconductor wafers W, the heater element wire  52  may undergo deformation with time, as described above, which may result in permanent elongation of the heater element wire  52 , thereby producing portions with a narrower gap between the wires than that at the initial arrangement of the element wire. In this case, the heater element wire  52  is elongated, for example, by about 0.00085% per heat treatment (1 RUN). 
     The portion with a narrower gap between the heater element wire  52  than that at the time of initial arrangement of the wire (at the time of manufacturing) may be observed by an operator in a regular or irregular maintenance operation or the like.  FIG. 5  is a sectional view of a heater device illustrating narrowed gaps between the heater element wires due to deformation of the wire, and  FIG. 6  is an enlarged sectional view of a heater device where an element wire contact prevention member is mounted between the heater element wires in a narrowed gap portion. In  FIG. 6 , a portion of the heater element wire  52  is deformed, as indicated by an arrow  71 , to produce a narrowed portion  70  between the heater element wires  52 . When the narrower portion  70  is observed as described above, an operator installs the element wire contact prevention member  60 , as shown in  FIG. 4 , in the narrowed portion  70  between the heater element wires  52 . 
     At this installation, the leading end  64  of the element wire contact prevention member  60  comprising the plate-like member  62  having the acute-angled leading end  64  is inserted into the flexible adiabatic layer  50  so that it can be interposed between the heater element wires  52  at the narrowed portion  70 , as indicated by an arrow  72  in  FIG. 6 . In  FIG. 5 , the element wire contact prevention member  60  is disposed in every narrowed portion  70  to be interposed between the heater element wires  52 . 
     In this manner, as the element wire contact prevention member  60  is disposed in the portion at which a gap between the heater element wires is narrowed, it is possible to prevent contact between the heater element wires  52 . This can prevent fusion and disconnection between heater element wires, and hence extend durability of the heater element wire. Such a maintenance operation is performed, for example, once or several time a year. 
     As described above, according to the above embodiment, as the element wire contact prevention member  60  is interposed between the heater element wires  52  in the portion  70  at which the gap between the heater element wires  51  becomes narrower than that at the time of the initial arrangement of the heater element wire  52  due to deformation of the heater element wire  52 , it is possible to prevent contact, fusion, and disconnection between the heater element wires  52 . 
     &lt;Actual Mounting State of Element Wire Contact Prevention Member&gt; 
     Next, with reference to  FIGS. 7A and 7B , a state in which the above-described element wire contact prevention member  60  is actually disposed and mounted and a state in which the member  60  is not disposed will be described.  FIG. 7A  is a photograph showing a state that an element wire contact prevention member is not mounted between heater element wires.  FIG. 7B  is a photograph showing a state that an element wire contact prevention member is interposed and mounted between heater element wires. 
     As shown in  FIG. 7A , where permanent elongation is produced due to repeated use of the heater device and a narrowed gap between heater element wires due to deformation or bend of the heater element wires is left as it is, contact between adjacent heater element wires may produce a spark or the like to fuse the heater element wires. On the contrary, as shown in  FIG. 7B , when the insulative element wire contact prevention member according to an embodiment of the present disclosure is provided in a portion at which a gap between the heater element wires is narrowed due to deformation or bend of the heater element wires, it is possible to prevent contact and fusing between the heater element wires even in later use. 
     The typical average lifespan of the heater element wires was about 22 months. However, where the element wire contact prevention member  60  is interposed and mounted during actual maintenance of the heater device of the heat treatment apparatus, the average lifespan of the heater element wires has extended to about 42 months. 
     Although it has been illustrated in the above embodiment that the element wire contact prevention member  60  is supported by penetrating its leading end into the adiabatic layer  50 , the present disclosure is not limited thereto, but the element wire contact prevention member  60  may be supported by inserting it between the heater element wires  52  with a gap therebetween narrowed. In this case, as a modification of the element wire contact prevention member  60 , shown in  FIG. 8A , it is preferable that separation prevention projections  76  are provided in both ends of the plate-like member  62  to prevent the element wire contact prevention member  60  from being separated from the heater element wires  52 .  FIG. 8B  is an enlarged sectional view of a heater device where the modified element wire contact prevention member, which is shown in  FIG. 8A , is mounted and interposed in a narrowed portion between the heater element wire. 
     In addition, although it has been illustrated in the above embodiment that the heater element wire  52  of the heater device  48  is spirally wound, the present disclosure is not limited thereto, but the heater element wire  52  may have any other shape of arrangement.  FIG. 9  is a view showing a modification of arrangement of the heater element wire  52 . In this modification, the heater element wire  52  has a wave shape or a bent shape having a repeated U-turn pattern instead of the spiral shape. The element wire contact prevention member  60  according to an embodiment of the present disclosure may be also applied to the heater element wire  52  having such a shape. 
     In addition, although it has been illustrated in the above embodiment that the heat treatment apparatus is exemplified as the processing container  4 , which is formed in the double tube structure and has the inner barrel  8  and the outer barrel  6 , the present disclosure is not limited thereto, but may be applied to the processing container  4  having a single tube structure. In addition, although the heater device  48  installed in the heat treatment apparatus  2  has been illustrated in the above embodiment, the present disclosure is not limited thereto, but may be applied to, for example, a drier, an electric furnace, or the like, which is configured such that an object to be heated is accommodated in a container and the heater device  48  is arranged on the outer circumference of the container. Such a drier may dry, for example, quartz parts as well as cleaned semiconductor wafers. As another example, such an electric furnace may be used to manufacture glass, ceramics and so on. 
     In addition, although it has been illustrated in the above embodiment that the heater element wire  52  has the circular cross-section, the shape of cross-section of the heater element wire  52  is not limited to a specific one. For example, the present disclosure may be applied to a plate-like heater element wire having a rectangular cross-section. 
     In addition, although it has been illustrated in the above embodiment that the semiconductor wafers mainly made of a silicon substrate are employed as objects to be heated, the present disclosure is not limited thereto. For example, the semiconductor wafers according to the present disclosure may include, but is not limited to, a silicon substrate, a compound semiconductor substrate such as GaAs, SiC, and GaN, or a glass or ceramics substrate used for a liquid crystal display device. 
     The above-described embodiments of an element wire contact prevention member and a method for maintenance of a heater device may provide the following advantageous functional results: since the element wire contact prevention member is interposed between the heater element wires in a portion at which a gap between the heater element wires becomes narrower due to deformation of the heater element wires than that at the time of arrangement of the heater element wires, it is possible to prevent contact, fusion, and disconnection between the heater element wires. 
     While certain embodiments have been described, these embodiments have been presented by way of example only, and are not intended to limit the scope of the disclosures. Indeed, the novel methods and apparatuses described herein may be embodied in a variety of other forms; furthermore, various omissions, substitutions, and changes in the form of the embodiments described herein may be made without departing from the spirit of the disclosures. The accompanying claims and their equivalents are intended to cover such forms or modifications as would fall within the scope and spirit of the disclosures.