Abstract:
The invention relates to a source chemical container assembly, comprising a metal container functioning as a vacuum chamber and provided with a removable closure, which removable closure seals against the metal container with a metal seal. In order to facilitate easy recharging of the container assembly, compressive force is applied to the metal seal through a tension chain. In a preferred embodiment of the invention the metal seal and the tension chain are provided along a circumference of said metal container. The assembly can comprise an inner container in which the source chemical is contained.

Description:
REFERENCE TO RELATED APPLICATION 
     This application claims the priority benefit under 35 U.S.C. §119(e) to U.S. provisional patent application No. 60/302,774, filed Jul. 3, 2001, the disclosure of which is incorporated herein by reference. 
    
    
     FIELD OF THE INVENTION 
     This invention relates to the field of source chemical container assemblies to contain source chemicals to be delivered to a reaction chamber to perform vapor deposition or related processes in the reaction chamber. 
     BACKGROUND OF THE INVENTION 
     In chemical vapor deposition (CVD) and related vapor deposition techniques, such as atomic layer deposition (ALD), liquid or solid source chemicals are often used. Many of those chemicals react aggressively with moisture and/or oxygen. In order to preserve the purity and volatility of these source chemicals, the container in which they are stored should be vacuum tight to a high degree, compatible with ultra high vacuum (UHV) conditions. It is convenient to use a metal container, which can easily be made UHV compatible and is not susceptible to breakage. 
     However, the container should also comprise a sealable opening to load the chemical into the container or to remove used material from the container. For this purpose such containers are provided with a removable closure. A polymer O-ring typically cannot be used to seal the removable closure against the container because it is not UHV compatible. Another problem related to the use of polymer O-rings is that polymer O-rings slowly deteriorate in contact with many of the chemicals used in such containers. Furthermore, some of the source materials have such a low vapor pressure that the container has to be heated to a high temperature in order to increase the vapor pressure. Such high temperatures are also harmful to polymer O-rings. 
     For these reasons, metal seals are the more appropriate to seal the lid against the container and to seal other connections to the container. In such a seal, a metal sealing gasket is sandwiched between two metal flanges. The flanges are made of a hard construction metal, such as stainless steel, and the metal gasket is made of a ductile metal. By pressing the two flanges together, with the sealing gasket therebetween, a high quality seal is formed. However, the two most widely used metals for metals seals, namely aluminum and copper, are also susceptible to attack by many of the source chemicals. Accordingly, a more chemically resistant material, such as nickel, is preferably employed. One disadvantage of nickel is that it is harder and less ductile than aluminum and copper, such that a nickel gasket requires a higher compressive force to maintain the vacuum integrity of the seal. 
     As shown for the container  10  of  FIG. 1 , the force for compressing metal gaskets against the container flanges is typically exerted by a large number of nuts  12  and bolts  14 , evenly distributed along the circumference of flanges  16 ,  18 , with each bolt sticking through a hole through both flanges  16 ,  18 . When the container  10  needs to be opened or closed a large number of nuts  12  and bolts  14  need to be released or tightened, respectively. This is rather cumbersome, particularly when recharging or discharging the container is performed in a nitrogen purged glove box to avoid exposure of the chemicals to ambient air. 
     It is accordingly an objective of the present invention to avoid these and other disadvantages and to provide in a vacuum tight metal source container for chemicals used in vapor deposition processes. The container should allow easy, convenient and reliable recharging and discharging. 
     SUMMARY OF THE INVENTION 
     The preferred embodiments of the present invention achieve the foregoing and other objectives by providing the metal seal of the removable or openable closure of the container with at least one conical flange and with a tension chain having link parts and thrust pieces. The thrust pieces engage the two flanges so that, upon tensioning the chain, the two flanges are pressed against each other by the thrust pieces. 
     According to an embodiment of the invention, the removable closure is provided in the bottom part of the container. This allows room at the top of the container for connecting tubing for the outflow of the source chemical in the vapor phase and for the inflow of inert carrier gas. Placing the removable closure at the bottom of the container thus avoids space conflicts. 
     According to a further embodiment, a first container as described above forms a vacuum chamber, which is provided with an inner container that contains the source chemical. The container can be loaded into and removed from the first container through the closeable opening. A source chemical assembly including such an inner container is described in Finnish application FI 20001166 of applicant, filed on May 15, 2000 and corresponding U.S. publication No. 2001/0042523, published Nov. 22, 2001. Recharging of the container is thus a very simple operation: releasing the tension from the tension chain, removing the tension chain from the flanges, opening the closure and the used metal sealing gasket and replacing the inner container with another inner container having fresh chemicals, putting the closure together with a new metal sealing gasket and the tension chain in place, and tensioning the chain. Such an operation can easily be performed in a glove box. 
     Metal seals comprising tension chains with thrust pieces to press the flanges together are known. See, e.g., U.S. Pat. No. 5,499,849, issued Mar. 19, 1996 and U.S. Pat. No. 5,707,089, issued Jan. 13, 1998, both to Fend. The disclosures of the &#39;849 patent and the &#39;089 patent are incorporated herein by reference in their entirety. Such devices are commercially available from Evac International, Inc., Switzerland, and are typically used for pressing two flanges of a pipe connection against one another, with a metal sealing gasket between the two flanges. In the preferred embodiments described herein, a closure device similar to that described by Fend for connecting two pipes is used to seal a closure in a metal container for source chemicals used in vapor deposition systems. 
     As outlined above, copper and aluminum are the most frequently used metals for the sealing gaskets. Because of their ductility, these metals show good sealing properties. For the present source chemical container application, it is preferred to use a nickel gasket, nickel alloy gasket, nickel-coated gasket, precious metal (e.g. gold) coated metal gasket or annealed transition metal (e.g., titanium) gasket, depending upon the source chemical to be stored. Annealing of gasket materials forms dislocations in the metal and annealed metal is softer than metal mechanically treated at low temperatures. Nevertheless, gaskets from metals other than aluminum or copper require a larger compressive force to maintain the integrity of the seal, and hence a more robust tension chain. 
    
    
     
       BRIEF DESCRIPTION OF THE DRAWINGS 
       These and other aspects of the invention will be readily apparent from the description below, the appended claims and the drawings, which are meant to illustrate and not to limit the invention, and wherein: 
         FIG. 1  is an isometric view of a source chemical assembly, constructed in accordance with the prior art. 
         FIG. 2  is a front elevational view of a source chemical assembly, similar to that of  FIG. 1 , including a conventional closure device and an internal container (hidden) to facilitate rapid charging and discharging of the source chemicals. 
         FIG. 3  is an isometric, partially cut-away view of the source chemical assembly of FIG.  2 . 
         FIG. 4  is an elevational cross section through a source chemical assembly constructed in accordance with a preferred embodiment of the present invention. 
         FIG. 5  is a cross-sectional view, taken along lines  5 — 5  of  FIG. 4 , illustrating a top view of the tension chain and an enlarged sectional view showing the inner container within the outer container. 
     
    
    
     DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENT 
       FIG. 1  illustrates a source chemical assembly  10  according to the prior art. A metal seal (not shown) is applied between two flanges  16 ,  18 , requiring a large number of bolts  14  individually threaded through nuts  12  to be able to apply a sufficiently high force over the whole sealing surface. 
       FIGS. 2 and 3  illustrate an improvement over conventional source chemical containers used in connection with vapor deposition equipment. In particular, a source chemical container  20  includes an outer container  22  and an inner container  24 . The inner container  24 , shown in the cut-away view of  FIG. 3 , facilitates loading and unloading of the source chemical. Such a system is disclosed in co-owned Finnish application FI 20001166, filed on May 15, 2000 and corresponding U.S. publication No. 2001/0042523, published Nov. 22, 2001 (hereinafter “Kesala”), the disclosure of which is incorporated herein by reference. 
       FIG. 4  indicates a source chemical assembly in accordance with a preferred embodiment in its entirety by reference numeral  25 , and the upper part of the metal container by reference numeral  30 . The upper part  30  includes a rotationally symmetrical sidewall  32  and a top wall  34 . The sidewall  32  is provided at its lower extremity with a flange  36 . While not separately called out in  FIG. 4 , the skilled artisan will readily appreciate that the source chemical assembly is also provided with heaters, such as those described in Kesala (incorporated hereinabove) in order to vaporize the solid or liquid precursor. 
     The bottom part of the metal container is indicated by reference numeral  40 . The bottom part  40  comprises a rotationally symmetrical sidewall  42  and a bottom wall  44 . The sidewall  42  is provided at its upper extremity with a flange  46 . The bottom part  40  serves as a closure for the container, as described below. Additionally, the bottom wall  44  includes a recess  48 , whose function is discussed in more detail below. 
     A metal sealing gasket  50  is received between flanges  36  and  46 . An expanded view of sealing gasket  50  between flanges  36  and  46  is shown at the left side of FIG.  4 . The sealing gasket  50  comprises metal and preferably a metal more resistant to chemical attack than copper or aluminum. In particular, the sealing gasket  50  is preferably formed of nickel, nickel alloy, nickel-coated metal, precious metal (e.g., gold or platinum) coated metal or annealed transition metal (e.g., titanium). 
     Referring to  FIGS. 4 and 5 , the flanges  36  and  46  are shown pressed against each other by a plurality of thrust pieces  52 . As best seen from the view of  FIG. 5 , the thrust pieces  52  are linked together by link pieces  54  and distributed about periphery of the flanges  36 ,  46  (FIG.  4 ). The link pieces  54  are rotatably joined to the thrust pieces  52  by hinges  56 . In the illustrated embodiment, the thrust pieces  52  each include two hinges  56 . As described in U.S. Pat. No. 5,707,089, issued Jan. 13, 1998 to Fend, the disclosure of which is incorporated herein by reference, the link pieces can alternatively be rotatably joined to the thrust pieces by lugs in one of the pieces and recesses or holes in the other piece. As also disclosed in the &#39;089 patent, link pieces on either side of a thrust piece can be rotatably joined to the thrust piece at the same hinge or lugs. At least one of the link/hinge connections among the thrust pieces  52  is replaced by a tensioning bolt  58 , a bore hole through one side of a thrust piece  52  and an internally threaded bore through one of the link pieces  54  or another of the thrust pieces  52 . In the illustrated embodiment, two such tensioning bolts  58  are shown. 
     The thrust pieces  52 , link pieces  54 , hinges  56  and tensioning bolts  58  together define a tensioning chain. In operation, unscrewing the bolts  58  loosens and allows removal of the tensioning chain. Screwing the bolts  58  back into their respective bore holes connects and then tightens the tensioning chain. As best seen from  FIG. 4 , the thrust pieces  52  include sloped inner surfaces configured to pinch the flanges  36 ,  46  together upon application of inward pressure from tightening or tensioning the chain. The embodiment of  FIG. 4  shows both flanges  36 ,  46  being conical, similar to the teachings of U.S. Pat. No. 5,499,849, issued Mar. 19, 1996 to Fend, the disclosure of which is incorporated herein by reference. It will be appreciated that, in other arrangements, one of the flanges can be conical while the other is planar, as illustrated in the &#39;089 patent. 
     Referring again to  FIG. 4 , the metal container is provided with a first gas infeed  60  for the inlet of an inactive or inert gas like nitrogen or argon into the metal container and a gas outlet  70  for the outflow of the inactive gas mixed with source chemical. The gas infeed  60  is connected with an inlet conduit  62 , which is connected to a source of inactive or inert gas (not shown). An inlet valve  61  is provided along the inlet conduit  62 . The gas outlet  70  is connected with an outlet conduit  72 , which leads to the reaction chamber in which the CVD, ALD or related process is performed. An outlet valve  71  is also provided along the conduit  72 . For additional purge possibilities, conduits  74 ,  76  and valve  78  are provided. 
     The source chemical is contained in an inner container  80 , which is provided with a lid  81  and communicates with a gas space in the metal container through a porous lid cover  82 . While the illustrated lid  81  fits over the inner container  80 , it will be understood that the converse arrangement can also be employed. The inner container  80  can be made of glass or any other suitable material that is suitable for contacting the liquid or solid source chemical. As noted above, the recess  48  in the bottom wall  44  of the bottom part  40  is configured to receive and surround the bottom part of inner container  80 . As best seen from the enlarged section at the left side of  FIG. 5 , the upper part  30  of the outer container, and particularly at the point where the sidewall  32  transitions from vertical to conical or flared, includes a plurality of inner grooves  84  to facilitate removal of the inner container  80  from the outer container  30 ,  40  and replacement thereof. For more details about the inner container  80  and possible alternative embodiments, see U.S. patent publication No. 2001/0042523, incorporated by reference hereinabove. 
     In operation, when the source chemical within the container assembly  25  is exhausted, the assembly can be readily recharged. In particular, the valves  61 ,  71  (and, if present,  78 ) are closed and the assembly  25  is placed in a glove box. A fresh inner container  80  of the desired source chemical, typically in solid or liquid form, is also placed in the glove box, and the glove box is sealed and purged with inert gas. By loosening the tensioning bolts  58 , the tensioning chain is loosened and removed from the flanges  36 ,  46  of the outer container  30 ,  40 . The bottom part  40  is separated from the top part  30  and the entire inner container  80 , with exhausted source chemical and any byproducts, is removed and replaced with the fresh inner container  80 . A fresh metal gasket is inserted between the flanges  36 ,  46  and the upper part  30  is replaced over the bottom part  40 . The tensioning chain is then reapplied, the bolts  58  are tightened, and the assembly is prepared for further processing. 
     It will be appreciated by those skilled in the art that various omissions, additions and modifications may be made to the processes described above without departing from the scope of the invention, and all such modifications and changes are intended to fall within the scope of the invention, as defined by the appended claims.