Abstract:
A filament lamp having a filament and an internal lead in which the filament is insulated from contact with the internal lead and prevent from moving during operation to maintain a uniform distribution of light. To this end, the filament lamp includes a luminous tube having an inner wall, and opposing ends on which sealing parts are formed. Multiple filaments are sequentially disposed inside the tube in an axial direction, and internal leads are connected to each filament. An insulating wall is provided along the inner wall of the luminous tube in the axial direction and is disposed around at least one of the multiple filaments. Internal leads running partly parallel to the filaments are positioned between the luminous tube and insulating wall and do not engage the ring supporters of the multiple filaments, which could cause the filaments to move and distribute light in a nonuniform pattern.

Description:
BACKGROUND OF THE INVENTION 
     1. Field of Invention 
     The present invention relates to a filament lamp used for the heat treatment of a semiconductor wafer, solar cell or liquid crystal that provides a uniform distribution of light. 
     2. Description of Related Art 
     A light irradiation-type heat treatment device in the semiconductor manufacturing process has widely been used in the fields of film formation, diffusion and annealing. All of these heat treatment devices are capable of rapidly heating a semiconductor wafer or other plate-like object such that the temperature can be increased to 1000° C. or above within several seconds to several tens of seconds. There is a need for increasing the temperature at a faster speed recently, and consequently a need for increasing the amount of electric power inputted into such heat treatment devices during the time of the heat treatment. This is referred to as a spike anneal in which the temperature is increased at a high speed exceeding 200° C./second and brought down immediately after a desired temperature has been achieved. The spike anneal enables the formation of a very thin diffusion layer (shallow junction) in the semiconductor wafer, thereby enhancing the efficiency of a semiconductor element manufactured on the wafer. 
     If the temperature distribution of a semiconductor wafer should become nonuniform at the time of heating, a phenomenon referred to as slip occurs to the semiconductor wafer. In other words, a defect caused by crystal transition occurs, which may lead to a defective product. It is therefore necessary to use a light irradiation-type heat treatment device for heating, maintaining a high temperature of, and cooling a semiconductor wafer when thermally treating a semiconductor wafer. To provide such a uniform distribution of temperature, Japanese Laid-open Application No. 2006-279008 (corresponding to US 2006/0197454 A1) discloses a filament lamp provided with multiple leads capable of independently supplying electric power to multiple filaments in one luminous tube. This design allows adjustment of the amount of electric power inputted into the multiple filaments, thereby allowing the distribution of temperature over an area to be adjusted to a highly uniform pattern. 
       FIGS. 10(   a ) and  10 ( b ) illustrate a conventional filament lamp  1 .  FIG. 10(   a ) shows a perspective view of the entire filament lamp  1 .  FIG. 10(   b ) shows a sectional view taken by the A-A′ line as shown in  FIG. 10(   a ). 
     A straight-shaped luminous tube  2  has an elliptical cross section, and its both ends are air-tightly sealed with sealing parts  3   a  and  3   b . Inside the luminous tube  2 , coil-shaped filaments  12   a  and  12   b  are provided with multiple ring supporters  12   ar  and  12   br . Ring supporters  12   ar  and  12   br  are spaced lengthwise and are sequentially disposed in the axial direction of the luminous tube  2 . Both ends of the filaments  12   a  and  12   b  are linked with internal leads  13   a ,  13   b ,  13   c  and  13   d  for supplying electric power. The internal leads  13   b  and  13   d  are each covered with an insulating narrow tube made of, for example, quartz glass so that they do not short-circuit to the filaments  12   a  or  12   b  through the ring supporters. 
     The internal leads  13   a ,  13   b ,  13   c , and  13   d  connected to the abovementioned filaments  12   a  and  12   b  extend to the sealing parts  3   a  and  3   b  on both ends and are electrically connected to external leads  14   a ,  14   b ,  14   c , and  14   d  individually via metal foils  11   a ,  11   b ,  11   c , and  11   d , respectively. In other words, the internal leads  13   a  and  13   b  extended to one end side of the filaments  12   a  and  12   b  respectively are electrically connected to the external leads  14   a  and  14   b  on one end side via the metal foils  11   a  and  11   b  at the sealing part  3   a  on one end side, respectively. Similarly, the internal leads  13   c  and  13   d  extended to the other end side are electrically connected to the external leads  14   c  and  14   d  on the other end side via the metal foils  11   c  and  11   d  at the sealing part  3   b  on the other end side, respectively. 
     As shown in  FIG. 10 , the filaments  12   a  and  12   b  are disposed in parallel with the internal leads  13   b  and  13   d  in order to independently supply electric power to the filaments  12   a  and  12   b  inside the luminous tube  2 . The internal leads  13   b  and  13   d  are insulated from the filaments  12   a  and  12   b  by covering them with insulating narrow tubes  8   a  and  8   b . As shown in  FIG. 10(   b ), the filament  12   a  is positioned inside the luminous tube  2  with a ring supporter  12   ar  that is brought into contact with the inner wall of the luminous tube  2 . 
     However, the applicants have observed that the internal lead  13   b  covered with the narrow tube  8   a  protrudes from the inner wall of the smooth luminous tube  2 , and therefore may engage the ring supporter  12   ar . In response to such engagement, the ring supporter  12   ar  might move to either the right or the left in order to expand into a broader space. If the ring supporter  12   ar  deviates from its position, the position of the filament  12   a  also moves. As a result, there may occur a problem in that the distribution of light generated toward an object to be treated may be changed into a nonuniform pattern. 
     SUMMARY OF THE INVENTION 
     In view of the abovementioned problems, the object of the present invention is to provide a filament lamp capable of preventing the position of a filament to move while maintaining a secure insulation of the filament from an internal lead, and maintaining a uniform distribution of light, wherein the filament and the internal lead are disposed inside the luminous tube in parallel with each other in the axial direction of the tube. 
     The first aspect of the invention is the provision of a filament lamp comprising a luminous tube having an inner wall, and opposing ends on which sealing parts are formed, multiple filaments sequentially disposed inside the tube along an axial direction of the tube, internal leads connected to each filament, with at least one of the internal leads running at least partly parallel to at least one of the filaments, and at least one insulating wall disposed along the inner wall in the axial direction of the luminous tube, said at least one insulating wall being disposed around at least one of the multiple filaments, wherein the at least one internal lead running at least partly parallel to at least one filament is provided between the luminous tube and the insulating wall. 
     The second aspect of invention is the filament lamp of the first aspect, wherein a pathway is provided between the luminous tube and the insulating wall along the axis of the tube from one end to the other end of the insulating wall, and wherein the internal lead is provided in the pathway. 
     The third aspect of the invention is the filament lamp of the first aspect, wherein the filament around which the insulating wall is disposed is provided with multiple ring supporters spaced lengthwise. 
     A further aspect of the invention is the filament lamp of the first aspect wherein two insulating walls are spaced apart from each other in the axial direction of the tube. 
     A still further aspect of the invention is the filament lamp of the first aspect wherein two insulating walls are arranged adjacent to each other in the axial direction of the tube. 
     A further aspect of the invention is the filament lamp of either the previous aspect, with the insulating walls disposed adjacent to each other, wherein a notch part is provided on one insulating wall and a collar part on the other insulating wall, and the notch part and the collar part are joined together. 
     According to the first aspect of the invention, since a filament is disposed on the inner side of the insulating wall, the filament can be disposed substantially at the center of the insulating wall. Moreover, since the inner surface of the insulating wall has no protrusion and is smooth, the position of the filament that generates light remains the same. Accordingly, the distribution of light generated toward an object to be treated can be maintained in the filament lamp. 
     Furthermore, since the internal lead provided in parallel with the filament in the axial direction of the tube is disposed between the luminous tube and the insulating wall, the filament can be insulated from the internal lead without covering the internal lead with a narrow tube. 
     According to the second aspect of the invention, since a pathway is provided along the axis of the tube from one end to the other end between the luminous tube and the insulating wall and the internal lead is provided in the pathway, the pathway positions the internal lead. Accordingly, the disposed position thereof inside the luminous tube does not move. It is therefore possible to avoid the problem that light irradiated from the filament is blocked from an object to be treated arising out of the lopsided movement of the position of an internal lead at the time of turning on or off the lamp. 
     According to the third aspect of the invention, since the filament around which the insulating wall is disposed is provided with multiple ring supporters spaced lengthwise, the filament can be disposed substantially at the center of the insulating wall. Besides, since the inner surface of the insulating wall has no protrusion and is smooth, the position of ring supporters remains the same. 
     According to the aspect of the invention, where a notch part is provided on the contact surface between the insulating walls, and a collar part is provided at the position corresponding to the notch part on the contact surface between the insulating walls, it is possible to make the insulating walls unable to rotate independently by joining the notch part and the collar part together. 
    
    
     
       BRIEF DESCRIPTION OF DRAWINGS 
         FIG. 1  is a schematic perspective view of the filament lamp according to the present invention. 
         FIG. 2  is an enlarged schematic perspective view of the filament lamp according to the present invention. 
         FIG. 3  is a schematic partial sectional view of a filament lamp according to the present invention. 
         FIG. 4  is a schematic perspective view of a filament lamp according to the present invention. 
         FIG. 5  is an enlarged schematic perspective view of a filament lamp according to the present invention. 
         FIG. 6(   a ) to ( c ) are a schematic partial sectional views showing a filament lamp according to the present invention. 
         FIG. 7  is a schematic perspective view showing a filament lamp according to the present invention. 
         FIG. 8  is an enlarged schematic perspective view showing a filament lamp according to the present invention. 
         FIGS. 9(   a ) and ( b ) are enlarged schematic perspective views showing the insulating walls of filament lamps according to the present invention. 
         FIGS. 10(   a ) and ( b ) are perspective views showing a conventional filament lamp. 
     
    
    
     DETAILED DESCRIPTION OF THE INVENTION 
       FIG. 1  is a perspective view showing a filament lamp  1  according to the first embodiment. 
     The filament lamp  1  is provided with a luminous tube  2  made of light-transparent material such as quartz glass. On both ends of the luminous tube  2  are formed sealing parts  3   a  and  3   b  with pinch seals in which metal foils  11   a ,  11   b ,  11   c  and  11   d  are buried. The inside of the luminous tube is sealed air-tight. Inside the luminous tube  2 , filaments  12   a  and  12   b , which are made of tungsten, for example, and divided into two parts in the axial direction of the luminous tube  2 , are provided on the same axis along the axis of the luminous tube  2 . 
     The filament  12   a  is electrically connected to an internal lead  13   a  on its one end side that is connected to the metal foil  11   a  and electrically connected to an internal lead  13   d  on the other end side that is connected to the metal foil  11   d.    
     As with the filament  12   a , the filament  12   b  is electrically connected to an internal lead  13   c  on its one end side that is connected to the metal foil  11   c  and electrically connected to an internal lead  13   b  on the other end side that is connected to the metal foil  11   b . The internal lead  13   b  is connected to the other end side of the filament  12   b.    
     Thus, the filament  12   a  is provided with the internal lead  13   b  in parallel in the axial direction of the tube for supplying electric power to the filament  12   b , and the filament  12   b  is provided with the internal lead  13   d  in parallel in the axial direction of the tube for supplying electric power to the filament  12   a.    
     One internal lead  13   a  ( 13   b ) is led to one sealing part  3   a  and the other internal lead  13   d  ( 13   c ) to the other sealing part  3   b . In other word, the internal lead  13   a  and  13   d  ( 13   b  and  13   c ) connected to the filament  12   a  ( 12   b ) are led to different sealing parts  3   a  and  3   b . Accordingly, the filament  12   a  ( 12   b ) and the internal lead  13   b  ( 13   d ), which are charged to different electric potentials, are provided in parallel with each other in the axial direction of the tube in the case that electric power is independently supplied to each filament  12   a  ( 12   b ) from the sealing parts  3   a  and  3   b  on both ends. 
     The metal foils  11   a  and  11   b  buried on the side of the sealing part  3   a  are electrically connected with external leads  14   a  and  14   b  that are each led to the outside from the sealing part  3   a . Similarly, metal foils  11   c  and  11   d  buried on the side of the sealing part  3   b  are electrically connected with external leads  14   c  and  14   d  that are each led to the outside from the sealing part  3   b . In this manner, the filament  12   a  is electrically connected to the external leads  14   a  and  14   d , and the filament  12   b  is electrically connected to the external leads  14   b  and  14   c.    
     Inside the luminous tube  2 , two insulating walls  5   a  and  5   b  made of quartz glass are disposed, and the filaments  12   a  and  12   b  are provided on the inner side of the insulating walls  5   a  and  5   b . The formation is such that the length of the insulating walls  5   a  and  5   b  in the axial direction of the tube is equal to the full length of the filaments  12   a  and  12   b  to which electric power is independently supplied or slightly longer than the full length of the filaments  12   a  and  12   b , respectively. However, the insulating wall  5   a  covering the filament  12   a  is not formed so long as to reach the filament  12   b  connected to the other feed circuit. This is because the structure is such that the internal leads  13   d  and  13   b  can be routed from between the insulating wall  5   a  and the insulating wall  5   b  for supplying electric power to the filaments  12   a  and  12   b.    
       FIG. 2  is an enlarged perspective view of the portion in which the insulating wall  5   b  is formed in the filament lamp  1  according to the first embodiment. 
     The filament  12   b  can be disposed substantially at the center of the insulating wall  5   b  because the filament  12   b  provided with multiple ring supporters  12   br  spaced lengthwise are disposed on the inner side of the insulating wall  5   b  having a substantially cylindrical shape. Moreover, since the inner surface of the insulating wall  5   b  has no protrusion and is smooth, there is no possibility that the positions of the ring supporters  12   br  move lopsidedly. 
     Because the positions of the ring supporters  12   br  do not move lopsidedly, the filament  12   b  can also be disposed and kept substantially at the center of the insulating wall  5   b . Furthermore, since the position of the filament  12   b  that generates light does not move lopsidedly, it is possible to maintain the same distribution of light generated by the filament lamp toward an object to be treated. 
     Besides, the internal lead  13   d , which is provided in parallel with the filament  12   b  in the axial direction of the tube, is disposed between the luminous tube  2  and the insulating wall  5   b . Since the filament  12   b  is disposed on the inner side of the insulating wall  5   b , the filament  12   b  can be insulated from the internal lead  13   d  without covering the internal lead  13   d  with a narrow tube. 
       FIG. 3  is a sectional view of the portion in which the insulating wall  5   b  is formed in the filament lamp  1  according to the first embodiment. 
     On the outer peripheral surface of the insulating wall  5   b  is formed a groove  6  extending from one end to the other end of the insulating wall  5   b  along the tube axis. The formation of the groove  6  on the outer peripheral surface of the insulating wall  5   b  allows forming a gap between the luminous tube  2  and the insulating wall  5   b , and the recessed portion of the groove  6  becomes a pathway extending from one end to the other end of the insulating wall  5   b . The internal lead  13   d  is provided in this pathway. 
     Since the filament  12   b  is disposed on the inner side of the insulating wall  5   b , the diameter of the insulating wall  5   b  must be large to a certain degree in view of the diameter of the filament  12   b  and the high temperature of the insulating wall  5   b  arising out of the heat generated from the filament  12   b . However, the outer diameter of the luminous tube  2  should not be very large in order to provide the filament lamp according to the present invention as a replacement for a conventional type filament lamp in which no insulating wall  5   b  is disposed inside the luminous tube  2 . The diameter of the insulating wall  5   b  can be made so large as to come into contact with the luminous tube  2  by forming the groove  6  on the outer peripheral surface of the insulating wall  5   b  to form a gap extending between the luminous tube  2  and the insulating wall along the axis of the tube and providing the internal leads  13   c ,  13   d  using this gap as a pathway. Accordingly, the insulating wall  5   b  can be disposed inside without making the outer diameter of the luminous tube  2  very large. 
     Moreover, since the filament  12   b  and the internal lead  13   d  are disposed in parallel with each other, the internal lead  13   d  is easily heated by the heat generated from the filament  12   b , which leads to the extension and contraction of the internal lead  13   d  as a result of turning on and off the lamp. If there exists any strain formed at the time of the formation of the internal lead  13   d , the force is applied in a manner of restoring the strain according to the extension and contraction of the internal lead  13   d . However, the position of the disposed internal lead  13   d  does not move lopsidedly because the internal lead  13   d  is positioned in the gap formed between the groove  6  formed in the insulating wall  5   b  and the luminous tube  2  as a pathway. It is therefore possible to avoid the problem that light irradiated from the filament  12   b  is blocked from an object to be treated arising out of the lopsided movement of the position of the internal lead  13   d  at the time of turning on or off the lamp. 
     In the filament lamp  1  according to the first embodiment, a groove is provided on the outer peripheral surface of the insulating walls  5   a  and  5   b  in order to form a pathway. However, the way of forming a pathway is not limited to this embodiment. For example, a groove may be provided on the inner peripheral surface of the luminous tube  2  in place of the outer peripheral surface of the insulating walls  5   a  and  5   b  to form a gap extending along the axis of the tube between the luminous tube  2  and the insulating walls, and this gap is used as a pathway. 
     Next, a description of the procedure for forming the filament lamp  1  according to the first embodiment is given below. 
     First, the internal leads  13   a ,  13   b ,  13   c  and  13   d  are bent to form a specified shape thereof. The filaments  12   a  and  12   b  are connected to the tip ends of the internal leads  13   a ,  13   b ,  13   c  and  13   d . Next, the insulating walls  5   a  and  5   b  are inserted from the ends of the internal leads  13   a ,  13   b ,  13   c  and  13   d  and positioned such that the internal leads  13   a ,  13   b ,  13   c  and  13   d  are provided in the recessed portion of the groove  6 . Furthermore, the metal foils  11   a ,  1   b ,  11   c  and  11   d  are welded to the ends of the internal leads  13   a ,  13   b ,  13   c  and  13   d , and then the external leads  14   a ,  14   b ,  14   c  and  14   d  are welded to the other ends of the metal foils  11   a ,  1   b ,  11   c  and  11   d.    
     A mount insert constituted of the internal leads  13   a ,  13   b ,  13   c  and  13   d , a connecting member  15 , a holding member  4   a , a holding member  4   b , the filaments  12   a  and  12   b , the metal foils  11   a ,  11   b ,  11   c  and  11   d  and the external leads  14   a ,  14   b ,  14   c  and  14   d  thus formed is inserted into the luminous tube  2 . The luminous tube  2  having the mount insert disposed inside is sealed at the portions where the metal foils  11   a  and  11   b , and the metal foils  11   c  and  11   d  are disposed to form the sealing parts  3   a  and  3   b.    
     The following shows specific numerical values.
         Luminous tube
           Outer diameter: 13 mm-16 mm   Thickness: 1.0 mm-1.5 mm   
           Insulating tube
           Length: 30 mm-250 mm   Outer diameter: 10 mm-13 mm   Thickness: 1.0 mm-2.0 mm   Groove (width): 0.7 mm-1.1 mm   Groove (depth): 0.4 mm-0.8 mm   Diameter of lead wire: 0.5 mm-1.0 mm   
           Filament
           Diameter of winding wire: 1.0 mm-4.0 mm   Length: 30 mm-200 mm   
               

       FIG. 4  shows a perspective view of the filament lamp  1  according to the second embodiment. 
     Inside the luminous tube  2  are disposed three filaments  24 ,  25  and  26  in the axial direction of the tube. Internal leads  24   a ,  24   b ,  26   a  and  26   b  connected to both ends of two filaments  24  and  26 , which are disposed proximate to sealing parts  3   a  and  3   b  respectively, extend in the directions of the same sealing parts to be held by the sealing parts  3   a  and  3   b , respectively. Moreover, internal leads  25   a  and  25   b  connected to both ends of the filament  25 , which is disposed between two filaments  24  and  26 , extend toward the opposite directions in the axial direction of the luminous tube  2  to be held at the sealing parts  3   a  and  3   b  on both ends. 
     Specifically, each of the internal leads  24   a  and  24   b  of the filament  24  proximate to the sealing part  3   a  on one end portion extend from the sealing part  3   a  and is connected to the end portion of the filament  24 . Both of these internal leads  24   a  and  24   b  are held at the same sealing parts  3   a  in such a manner as to be connected to metal foils  21   a  and  21   b.    
     On the other hand, the internal leads  25   a  and  25   b  of the filament  25  disposed at the central portion extend toward the sealing parts  3   a  and  3   b  on both ends and are held at the sealing parts  3   a  and  3   b  in such a manner as to be connected to metal foils  22   a  and  22   b , respectively. 
     The filament  26  proximate to the sealing part  3   b  on the other end side is similar to the abovementioned filament  24 . The internal leads  26   a  and  26   b  are held at the sealing part  3   b  on the other end portion in such a manner as to be connected to metal foils  23   a  and  23   b.    
     The metal foils  21   a ,  21   b ,  22   a ,  22   b ,  23   a  and  23   b  are connected with external leads  27   a ,  27   b ,  28   a ,  28   b ,  29   a  and  29   b , respectively. 
     Moreover, glass bridges  4   a  and  4   b  are provided in the vicinity of the sealing parts  3   a  and  3   b  inside the luminous tube  2 . The glass bridges  4   a  and  4   b  are each constituted of a pair of cylindrical glass members, and the internal leads  24   a ,  24   b  and  25   a , and the internal leads  25   b ,  26   a  and  26   b  are held therebetween, respectively. 
     In the abovementioned configuration, no internal lead extends in the vicinity of the filament  25  at the central portion. Accordingly, there is no possibility that light irradiated from the filament  25  positioned immediately above an object to be treated is blocked by an internal lead. As a result, uniform irradiation can be achieved. 
     An insulating wall  5   a  is disposed in a manner of covering the filament  24  proximate to the sealing part  3   a  on one end portion, and an insulating wall  5   b  is disposed in a manner of covering the filament  26  proximate to the sealing part  3   b  on the other end portion. On the other hand, no internal lead extends in the vicinity of the filament  25  at the central portion. Since there is no need for the filament  25  to be insulated from the others, the insulating walls  5   a  or  5   b  is not disposed around the filament  25 . 
       FIG. 5  is an enlarged perspective view in the vicinity of the filament  24  in the filament lamp  1  according to the second embodiment. 
     In the vicinity of the filament  24  are provided the internal lead  24   b  for supplying electric power to the filament  24  and the internal lead  25   a  for supplying electric power to the filament  25  in parallel with each other in the axial direction of the tube. Electric power cannot independently be supplied to each of the filaments  24 ,  25  and  26  unless the filament  24  is insulated from the internal leads  24   b  and  25   a.    
     Inside the luminous tube  2  is disposed the insulating wall  5   a  made of quartz glass, and the filament is provided on the inner side of the insulating wall  5   a . The internal leads  24   b  and  25   a  provided in parallel with the filament  24  in the axial direction of the tube are disposed between the luminous tube  2  and the insulating wall  5   a . Accordingly, the internal leads  24   b  and  25   a  can be isolated from the filament  24  without covering them with a narrow tube. 
     Since multiple ring supporters  24   r  are provided spaced lengthwise on the filament  24 , the filament  24  can be disposed at the center of the insulating wall  5   a  that is substantially cylindrical. Since the inner surface of the insulating wall  5   a  has no protrusion and is smooth, there is no possibility that the positions of the ring supporters  24   r  move lopsidedly. The distribution of light generated by a filament lamp toward an object to be treated can be maintained because the positions of the filament  12   a  and  12   b  that generate light do not change. 
     On the outer peripheral surface of the insulating wall  5   a  is formed a groove  6  extending from one end to the other end of the insulating wall  5   a  along the axis of the tube. The formation of the groove  6  on the outer peripheral surface of the insulating wall  5   a  allows forming a gap between the luminous tube  2  and the insulating wall, and the recessed portion of the groove  6  becomes a pathway extending from one end to the other end of the insulating wall  5   a . The internal leads  24   b  and  25   a  are provided in this pathway. Because the pathway positions the internal leads  24   b  and  25   a , there is no possibility that the internal leads  24   b  and  25   a  move lopsidedly while the filament lamp  1  is turned on. It is therefore possible to avoid the problem that light irradiated from the filament is blocked from an object to be treated arising out of the lopsided movement of the positions of the internal leads  24   b  and  25   a  at the time of turning on or off the lamp. 
     The internal lead  24   b  connected to one end of the filament  24  adjacent to the filament  25  extends from the sealing part  3   a  in parallel with the filament  24 , is bent in the radial direction at its tip end, and is further bent in the axial direction, thereby forming a U-shape. One end of the insulating wall  5   a  is brought into contact with the U-shaped portion of the internal lead  24   b.    
     In the vicinity of the other end of the insulating wall  5   a  is provided a glass bridge  4   a  having the maximum length longer than the inner diameter of the insulating wall  5   a . Accordingly, there is no possibility that the insulating wall  5   a  goes over the glass bridge  4   a  arranged on the side of the sealing part  3   a.    
     The configuration is such that the insulating wall  5   a  does not come off because it is brought into contact with the U-shaped internal lead  24   b  on its end, and the glass bridge  4   a  is disposed in the vicinity of the other end. Accordingly, it can be positioned in a manner of being unable to move in the axial direction of the insulating wall  5   a.    
     The following shows a variation of the filament lamp  1  according to the second embodiment.  FIG. 6  is a sectional view of the filament lamp  1  when it is perpendicularly cut in the vicinity of the filament  24  in the axial direction of the tube. 
     As shown in  FIG. 6(   a ), dimples  71   a  and  71   b  corresponding to the internal leads  24   b  and  25   a  provided between the luminous tube  2  and the insulating wall  5   a  are provided in the luminous tube  2  without providing a groove on the outer peripheral surface on the insulating wall  5   a  in order to position the internal leads  24   b  and  25   a . These dimples  71   a  and  71   b  are used as channels extending from one end to the other end of the insulating wall  5   a.    
     The dimples  71   a  and  71   b  may not need to be provided for the entire length of the internal leads  24   b  and  25   a  in the axial direction yet may be interspersed at several places so that the internal leads  24   b  and  25   a  can be positioned. 
     In addition, as shown in  FIGS. 6(   b ) and ( c ), channels extending from one end to the other end of the axis of the tube can be provided without providing a groove on the outer peripheral surface of the insulating wall  5   a  or the dimples  71   a  and  71   b  in the luminous tube  2 . Channels for positioning the internal leads  24   b  and  25   a  can be provided by making the outer surface of the insulating wall  5   a  and the inner surface of the luminous tube  2  smooth and then disposing particulates of quartz glass  72   a  and  72   b  here and there on the outer surface of the insulating wall  5   a  as shown in  FIG. 6(   b ). Alternatively, as shown in  FIG. 6(   c ), halves of quartz glass (troughs)  73   a  and  73   b  are disposed between the luminous tube  2  and the insulating wall  5   a , and then the internal leads  24   b  and  25   a  are disposed in the gaps, thereby providing channels. 
     As with the dimples  71   a  and  71   b , neither the particulates of quartz glass  72   a  and  72   b  nor the quartz glass troughs  73   a  and  73   b  may need to be provided for the entire length of the internal leads  24   b  and  25   a  in the axial direction yet may be interspersed at several places so that the internal leads  24   b  and  25   a  can be positioned. 
       FIG. 7  is a perspective view showing the filament lamp  1  according to the third embodiment. 
     In the filament lamp  1  according to the third embodiment, as with the filament lamp  1  according to the second embodiment, internal leads  31   a ,  31   b ,  34   a  and  34   b  connected to both ends of two filaments  31  and  34 , which are disposed proximate to sealing parts  3   a  and  3   b  respectively, extend in the direction of the same sealing part proximate to the filaments  31  and  34  to be held by the sealing parts  3   a  and  3   b.    
     On the other hand, unlike the filament lamp  1  according to the second embodiment, at the central portion are disposed two filaments  32  and  33  to which electric power is independently supplied. Internal leads  33   a  and  33   b  connected to the filament  33  are connected to metal foils held in the sealing part  3   b . Internal leads  32   a  and  32   b  connected to the other filament  32  extend in the directions of the sealing parts  3   a  and  3   b  on both ends and are held at the sealing parts  3   a  and  3   b  in such a manner as to be connected to metal foils, respectively. 
     An insulating wall  5   a  is disposed in a manner of covering the filament  31  proximate to the sealing part  3   a  on one end portion, and an insulating wall  5   b  is disposed in a manner of covering the filament  34  proximate to the sealing part  3   b  on the other end portion. Moreover, an insulating wall  5   c  is disposed adjacent to the insulating wall  5   b  in a manner of covering the filament  33  disposed at the center. Thus, the insulating wall  5   c  is disposed around the filament  33  as well if there is a filament  33 , in the vicinity from which internal leads extend, in addition to the filaments  31  and  34  disposed proximate to the sealing parts  3   a  and  3   b , respectively. 
     On the other hand, no internal leads extend in the vicinity of the other filament  32  at the central portion. Since there is no need for the filament  32  to be insulated from the others, the insulating walls  5   a ,  5   b  or  5   c  are not disposed around the filament  32 . 
       FIG. 8  is an enlarged perspective view showing the portion at which the filament  33  and the filament  34  are adjacent to each other in the filament lamp  1  according to the third embodiment. 
     On the outer surface of the insulating wall  5   c  are formed a groove  6  for disposing the internal lead  33   b  connected to one end of the filament  33 , and a groove  6  for disposing the internal lead  32   b  used for supplying electric power to the filament  32 . 
     On the outer surface of the insulating wall  5   b  are formed a groove  6  for disposing the internal lead  33   a  connected to the other end of the filament  33  and a groove  6  for disposing the internal lead  34   b  connected to one end of the filament  34  in addition to the groove  6  for disposing the internal lead  33   b  and the groove  6  for disposing the internal lead  32   b.    
     On the outer surface of the insulating wall  5   b  and  5   c  are formed grooves  6  extending from one end to the other end of the insulating walls  5   b  and  5   c  respectively along the axis of the tube depending on the number of internal leads  32   b ,  33   a ,  33   b  and  34   b  disposed in parallel. The formation of the grooves  6  on the outer surfaces of the insulating walls  5   b  and  5   c  allows forming gaps between the luminous tube  2  and the insulating walls, and the recessed parts of the grooves  6  are used as channels that extend from one end to the other end of the insulating walls  5   b  and  5   c.    
     The internal lead  34   b  and the internal lead  33   a  provided between the insulating wall  5   b  and the luminous tube are bent between the insulating wall  5   b  and the insulating wall  5   c  in the radial direction in order to wire them on the inner sides of the insulating wall  5   b  and the insulating wall  5   c , respectively. 
     The following shows a variation of the filament lamp  1  according to the third embodiment.  FIG. 9  is a perspective view explaining a method for connecting the two adjacent insulating walls  5   b  and  5   c.    
     As shown in  FIG. 9(   a ), it is possible to make the insulating wall  5   c  and the insulating wall  5   b  unable to rotate separately by providing a notch part  51  on the contact surface between the insulating wall  5   b  and the insulating wall  5   c  and a collar part  52  at the position corresponding to the notch part  51  on the contact surface between the insulating wall  5   b  and the insulating wall  5   c , and then joining the notch part  51  and the collar part  52  together. As shown in the drawing, if there is a groove  6  extending between the insulating wall  5   b  and the insulating wall  5   c , it is preferable to have a rotation preventing mechanism constituted of the notch part  51  and the collar part  52 . 
     As shown in  FIG. 9(   b ), a notch part  51  may be formed in a groove  6  formed on the outer peripheral surface of the insulating wall  5   b . The insulating wall  5   b  and the insulating wall  5   c  can be disposed closely to each other by joining the notch part  51  formed in the groove  6  and the collar part  52  formed at the position corresponding to the notch part  51  together. However, the collar part  52  formed on the insulating wall  5   c  does not reach the proximal end of the notch part  51  formed on the insulating wall  5   b . Instead, the formation is such that there is a gap between the collar part  52  and the notch part  51 . The internal leads provided on the groove  6  of the insulating wall  5   b  can be wired to be connected to the filaments inside the insulating wall  5   b  and the insulating wall  5   c  through the gap between the color part  52  and the notch part  51 . 
     In all of the filament lamps as shown in the first embodiment through the third embodiment, the sealing parts  3   a  and  3   b  are pinch-sealed. The configuration of the present invention can be applied to a shrink seal filament lamp as well in place of the pinch-sealed filament lamp. The structural advantage of using the shrink seal at the sealing part is that the internal leads can be inserted into the sealing parts  3   a  and  3   b  and sealed there as they are led along the inner surface of the luminous tube  2 .