Abstract:
Apparatus for supporting the heater filament of the reactor in Chemical Vapor Deposition (CVD) system. The apparatus includes a recess or aperture disposed in a filament support plate; an electrically isolated rod supporting at least one of the coils of the filament, and extends into the recess or aperture in the support plate. A thermally insulating sleeve surrounds the rod. The post and sleeve arrangement provide a controlled and adjustable amount of lateral and vertical movement to the rod and filament to prevent damage to the filament caused by thermal expansion while providing lateral and vertical support to the filament.

Description:
REFERENCE TO RELATED APPLICATIONS 
   This application claims priority from U.S. provisional application Ser. No. 60/775,169 filed Feb. 21, 2006 

   BACKGROUND AND SUMMARY OF THE INVENTION 
   This application is directed to substrate heating apparatus within the preferred embodiment of Chemical Vapor Deposition (CVD) apparatus and more specifically to an arrangement for supporting the heater filament of a deposition reactor. 
   Chemical Vapor Deposition (CVD) systems are widely used to deposit elemental, mixed phase and compound films in the manufacture of electronic devices, such as integrated circuits formed by the sequential or simultaneous deposition of compounds upon a heated substrate, which is usually in the form of a wafer that is typically mounted on a “susceptor” which may or may not rotate. The reactants are transported to the surface of the substrate, in the gas phase, by typically one or more carrier gases. The elements deposit on the wafer surface, forming the desired compound and any undesirable by-products are pumped away in a gaseous form. A heating element (filament) is mounted below the susceptor and heats the wafers. It is desirable to have the filament close to the susceptor to minimize power loses. 
   The filament of the heater assembly is subject to a number of problems which can lead to damage or failure, among these problems are: 1) warpage (into and out of its plane; such warping can cause the filament to contact the fixed or rotating susceptor leading to damage to the susceptor and filament 2) temperature asymmetries across the wafer and/or hardware (differential thermal expansion as it heats and cools or where different zones experience different values of heat loss leading to different local temperatures) 3) differing temperatures along the coils (where different zones experience different values of heat loss leading to different local temperatures) 4) lateral expansion which can cause adjacent coils to short out which can lead to catastrophic failure of the filament 5) reactivity with the process environment including reactivity with supporting elements such as insulators 6) fatigue wherein aging embrittlement leads to cracking failure in unsupported filaments (which are subject to general process system induced vibrations), among others. The problems are exacerbated by the increasing temperatures that are used in many advanced deposition methodologies. 
   The present invention is directed to apparatus for supporting the heater filament of the reactor in Chemical Vapor Deposition (CVD) system. The apparatus includes a recess or aperture disposed in a filament support plate; a rod is joined to at least one of the coils of the filament, and extends into the recess or aperture in the support plate. A thermally insulating sleeve surrounds the rod. The post and sleeve arrangement provide a controlled and adjustable amount of lateral and vertical movement to the rod and filament to prevent damage to the filament caused by thermal expansion while providing lateral and vertical support to the filament. 

   
     BRIEF DESCRIPTION OF THE DRAWINGS 
       FIG. 1  illustrates a general overview of a Chemical Vapor Deposition (CVD) System; 
       FIG. 2  illustrates a standard arrangement for supporting the heater element in a heater unit within a CVD system; 
       FIG. 3  illustrates a first embodiment of the present invention for use with filaments that are prone to sagging and or warpage and or lateral movement; 
       FIG. 4  illustrates a second embodiment of the present invention generally for use with filaments that are not prone to sagging but are subject to warpage and lateral movement; 
       FIG. 5  illustrates a third embodiment of the present invention wherein the filament is supported from sagging and the filament may be attached to the pins or allowed to slide laterally on top of the pins; 
       FIG. 6  is a perspective view of filament support plate (as shown in  FIG. 5  but without the filament) to illustrate an exemplary arrangement of the components of the filament restraining system; and 
       FIG. 7  is a sectional view of a filament support plate for use with a thermocouple to monitor the operating temperature of the filament. 
   

   DESCRIPTION OF THE PREFERRED EMBODIMENTS 
     FIG. 1  illustrates a Chemical Vapor Deposition (CVD) System  10  which, in general overview: includes a reactor chamber  14 , sealed to the atmosphere, in which is mounted a gas and vapor distribution housing (showerhead—not shown) for the film growth reactant and carrier gases. The distribution housing directs the reactant gases over one or more substrate wafers  16 , mounted, in this example, on a rotatable susceptor  18  which is rotated through a shaft  20  by a motor  22  mounted externally from reactor chamber  12 , and which are heated by a heater unit  24 . The reactant and carrier gases generated by external sources (not shown) are distributed though the distribution housing and flow over heated wafers  16  where the gases will decompose (react at the wafer surface) and deposit their compounds, thereafter an exhaust unit  26  will remove the spent gases from reactor chamber  14 . 
     FIG. 2  illustrates the standard arrangement for supporting the heater element in a heater unit within a CVD system. Heater unit  24  includes a generally circular support plate  30  and a serpentine (or otherwise patterned) heater element (filament)  32 . Disposed between plate  30  and element  32  are a number of cylindrical ceramic rods  34  upon which element  32  rests. Ceramic rods  34  provide support for element  32  and serve to thermally insulate it from support plate  30 . Ceramic rods  34  prevent element  32  from sagging as it softens when heated by the operating current that flows through it. However, rods  34  only prevent element  32  from sagging downwardly, but do nothing to prevent element  32  form warping upwardly or moving laterally. Such warping can cause the filament to contact susceptor  18  leading to damage to susceptor  18  and filament  32 . Lateral expansion of filament  32  can cause adjacent coils to short out, which can lead to catastrophic failure of filament  32 . While vertical ceramic posts could be used to separate filament traces; they can crack or a warping filament can rise along their sides. At sufficient temperature insulating rods  34  have been known to react with element  32 . These problems have caused a significant shortening of the average life of filaments  32  as well as damaging the other components of the CVD system or contaminating of the depositing material or imposing operational temperature limits lower than the filament material itself can tolerate. These problems are only exacerbated by the increasing temperatures that are used in advanced deposition methodologies. 
     FIG. 3  illustrates a first embodiment of the present invention generally for use with filaments that are prone to sagging and or warpage. Such filaments are generally employed in a variety of CVD systems; including oxide systems as shown.  FIG. 3  is a sectional view through a heater assembly that includes a filament support plate  40 , filament  42  and ceramic filament support rods  44 , as such these components are similar to those described above in  FIG. 2 . However, filament support plate  40  includes a plurality of regularly spaced apertures  46  in each of which is located a filament restraining system  50 . Filament support plate  40  can be metallic or a ceramic insulating material. Filament restraining system  50  includes a threaded post  52  which is attached, such as by welding, bolting, pinning or riveting to filament  42 . Post  52  is preferably made of a material which is thermally compatible with the material of filament  42  so that it has the same or nearly the same thermal expansion characteristics as that of filament  42 . In some cases it may be preferred that the filament and post material are exactly the same. Surrounding the post is an annular insulating sleeve  54  which is preferably constructed from a material which is thermally resistant such as quartz or ceramic materials. In practice, the spacing between the sleeving material and the filament may be made large to either include a number of heat shields or reduce the heat load on the insulating sleeving materials. Surrounding sleeve  54  is a ceramic bottom cap  56  which has an inwardly disposed lip upon which the bottom of sleeve  54  rests. Threaded to the bottom of post  52  are locking nuts  58 ,  60  which support a retaining washer  62 . Optional heat reflecting shields  64 ,  66  may be added to the bottom of the assembly and heat diffuser plates may be added above the filament but below the wafer plane. 
   The purpose of filament restraining system  50  is not to fixedly secure filament  42  in place, rather its purpose is to permit filament  42  a predetermined and adjustable degree of movement both laterally and vertically to accommodate the inherent thermal expansion of the filament without causing damage to it and/or the other components of the deposition apparatus. To this end apertures  46  in filament support plate  40  and insulating sleeves  54  are designed such that sleeves  54  are smaller than apertures  46  so that filament  42  and attached posts  52  may shift laterally when filament  42  is heated. Further, the inner diameter of sleeves  54  is larger than that of the outer diameter of posts  52 . The clearances between sleeves  54 , posts  52  and apertures  46  are configured so that the lateral movement of filament  42  is permitted but constrained such that adjacent coils of  42  cannot contact each other and short out, thus avoiding damage. Furthermore apertures  46  in filament support plate  40  may be made oblong in cross section rather than circular to accommodate the controlled expansion of filament  42   
   Similarly, locking nuts  58 ,  60  threaded to posts  52  are preferably positioned so as to permit a limited degree of vertical movement of filament  42 . Locking nuts  58 ,  60  are adjusted so that that any vertical movement (warping) of filament  42  is permitted but constrained to prevent it from contacting rotating susceptor  18 . Thus, by selection of the clearances between sleeves  54  and apertures  46  and the adjustment of locking nuts  58 ,  60  on posts  52 , the operator of the CVD system can control the movement of filament  42  before damage can occur to either the filament itself or the other components of the CVD system. 
     FIG. 4  illustrates a second embodiment of the present invention which is generally for use with filaments that are not prone to sagging but are subject to warpage and lateral movement. Such filaments are generally employed in oxidizing or refractory CVD systems.  FIG. 4  is a sectional view through a heater assembly that includes a filament support plate  70  and a filament  72  but does not include ceramic filament support rods. Filament support plate  70  includes a plurality of regularly spaced apertures  76  through which a filament restraining system  78  extends. Filament restraining system  78  includes a threaded post  80  which is joined, such as by welding, bolting or riveting to filament  72 . Post  80  is preferably made of a material which is compatible with the material of filament  72  so that it has the same or nearly the same thermal expansion characteristics as that of filament  72 . Loosely surrounding post  80  is an annular insulating sleeve  82  which is preferably constructed from a material which is thermally resistant such as quartz or ceramic. Surrounding sleeve  82  is a ceramic bottom cap  84  which has an inwardly disposed lip upon which the bottom of sleeve  82  rests. Threaded to the bottom of post  52  are locking nuts  86 ,  88 . Joined to the upper portion of post  80  is a collar  90  which serves to limit the downward motion of filament  72  as it abuts the top of sleeve  82 . Sleeve  82  has a wider middle portion  92  which rests in a widened portion  94  of apertures  76 . A heat insulating or conducting reflecting shield  96  may be optionally disposed above filament support plate  70 . While only one such shield is shown, multiple shields may be used. Similarly, while only a heat shield is shown below the filament, a cylindrical shield having a diameter larger than the filament may surround the filament to reflect lateral heat radiation. 
   As was the case with the arrangement of  FIG. 3  the purpose of filament restraining system  78  is preferably not to fixedly secure filament  72  in place, rather its purpose is to permit filament  72  a predetermined degree of movement both laterally and vertically. To this end the clearances between sleeves  54  and apertures  76 , as well as the clearances between posts  80  and sleeves  54 , are configured so that filament  72  and posts  80  may shift laterally when filament  72  is heated. The clearances between sleeves  80  and apertures  76  are adjusted so that the lateral movement of filament  72  is constrained such that adjacent coils of  72  cannot contact each other resulting in a direct electrical short. Apertures  76  in filament support plate  40  may also be oblong in cross section rather than circular to accommodate the controlled expansion of filament  72 . Similarly, locking nuts  86 ,  88  threaded to posts  80  are preferably positioned so as to permit a limited degree of vertical movement of filament  72  to prevent it from contacting rotating susceptor  18 . Thus by selection of the clearances between sleeves  80  and apertures  76  and the adjustment of locking nuts  86 ,  88  the operator of the CVD system can control the movement of filament  72  before damage can occur to either the filament itself or the other components of the CVD system. Collar  90  serves to limit the downward motion of filament  72  as it abuts the top of sleeve  82  and the downward motion of sleeves  80  are limited by the abutment of wider middle portion  92  against filament support plate  70 . Insulating sleeve  84  limits the extent to which the filament can rise vertically. 
     FIG. 5  illustrates a third embodiment of the present invention.  FIG. 5  is a sectional view through a wafer substrate heater assembly that includes a filament support plate  100  and a filament  102 . Filament support plate  100  includes a plurality of regularly spaced apertures  103 , however these apertures do not fully extend through the width of filament support plate  100 . A filament restraining system  104  is disposed in each aperture  102 . Filament restraining system  104  includes an annular insulating sleeve  106  which has an aperture  108  with closed lower end  110  and which is preferably constructed from a material which is thermally resistant such as quartz or ceramic. In this configuration a vertical post  112  is either used solely to prevent the filament from sagging or may be joined, such as by welding or riveting to filament  102  and rests against the closed lower end  110  of annular insulating sleeve  106 . Post  112  is again preferably made of a material which is thermally compatible with the material of filament  102  so that it has the same thermal expansion characteristics as that of filament  102 . A heat insulating/reflecting shield  114  may be optionally disposed above filament support plate  100 . In the cases where the primary concerns are sagging and lateral expansion, the post  112  does not need to be attached to the filament and it may, in fact, be more advantageous to allow the filament to slide over the pin. The difference here is that post  112  can be made of a metal that can withstand higher filament contact temperatures than a ceramic. An important feature is that post  112  is located and supported in its insulating sleeve to an extent that it does not catch on the filament. Further, at lower temperatures a ceramic post  112  could be used in this configuration as well. 
   The operation of filament restraining system  104  is again preferably not to fixedly secure filament  102  in place, rather its purpose is to permit filament  102  a predetermined degree of movement both laterally and vertically. As such the clearances between sleeves  106  and apertures  102 , as well as the clearances between posts  112  and sleeves  106 , are configured so that filament  102  and posts  112  is allowed to shift laterally when filament  72  is heated. The clearances between sleeves  106  and apertures  102  are adjusted so that the lateral movement of filament  102  is constrained such that adjacent coils of filament  102  cannot contact each other and short out. Apertures  102  in filament support plate  40  may also be oblong in cross section rather than circular to accommodate the controlled expansion of filament  102 . As posts  112  are a loose fit in apertures  108  of insulating sleeve  106  serves filament  102  may move up and down vertically in a controlled manner the downward motion of filament  72  is limited as by the abutment of posts  112  with the closed lower end  110  of sleeve  108  which also removed the need for ceramic support rods in this embodiment. 
     FIG. 6  is a perspective view of filament support plate  120  with the filament not shown to illustrate an exemplary arrangement of the components  122  of filament restraining system, which may in accordance any of the embodiments described heretofore is preferred. As shown herein this exemplary arrangement comprises radial “spokes” extending outwardly from the center of filament support plate  120  to the edges. Of course many other exemplary arrangements are possible. The arrangement configuration, spacing and number of filament restraining systems may be varied depending on the support needs of the filament to be used in the CVD application at hand. 
   The present invention may also utilize a thermocouple to monitor the operating temperature of the filament.  FIG. 7  is a sectional view of a filament support plate  140  having a filament  142  which is supported by number of filament support rods  144  which extend through a filament heat shield  146 . Filament support plate  140  includes apertures  148  which have a larger diameter at their upper end, through which filament support rods  144  extend. Located in one or more of apertures  148  is a thermocouple isolation sleeve  150  in which is disposed a thermocouple  152  (with junction). Thermocouple isolation sleeve  150  has a larger diameter at its so that it rests in aperture  148  upper end to support and isolate thermocouple  150 . Disposed above thermocouple isolation sleeve  150  is a thermocouple insulating isolation disc  154 . Isolation sleeve  150  and isolation disc  154 , which are preferably formed from insulating materials, serve to isolate thermocouple  152  from filament support plate  140  so that it may accurately monitor the operating temperature of filament  142 . 
   The invention has been described with respect to heated substrate preferred embodiments for film deposition on a wafer surface. However, as those skilled in the art will recognize, modifications and variations in the specific details which have been described and illustrated may be resorted to without departing from the spirit and scope of the invention as defined in the appended claims. For example, similar problems are experienced in reactors wherein the wafer substrate assembly rotates using planetary rotation or where the wafer substrate assembly is not rotated at all. The number and distribution of heat shields or heat reflectors below the filament surface may be varied in number and the number and distribution of heat diffusers above the filament surface. The locking bolt structure may be replaced by a variety of mechanisms including but not limited to locking ring clips or cotter pins. The described supporting pins may have a variety of terminations including rounds, flats, bars and the like.