Abstract:
A gas turbo pump assembly for connection to a port of a vacuum chamber and having high throughput with low vibration. The assembly comprises a turbo pump and a vibration damper. The pump has a pump body with an external surface and a center axis defining a first axial end and a second axial end of the pump. The pump also has a pump inlet port, the inlet port being coupled to the vacuum chamber port disposed at the first axial end of the pump, and an exit port disposed proximate the second axial end of the pump. The assembly vibration damper is structured to enclose a substantial portion of the pump in a nested arrangement.

Description:
BACKGROUND OF THE INVENTION 
   The present invention concerns vacuum pumps and, in particular, turbo molecular pumps that are used in semiconductor manufacturing processes requiring a vacuum environment with a pressure lower than atmospheric pressure. More specifically, the present invention concerns the use of vibration dampers between the vacuum pump and a vacuum environment, such as a vacuum chamber, in order to isolate the vacuum environment from any vibration generated by the pump. 
   In semiconductor manufacturing processes, a variety of steps, from layer or film deposition to inspection, are performed in a vacuum environment. However, because the vacuum pump is constructed with extremely tight tolerances extending down to the millimeter range, which enables operation with free molecular flow, the pump can be the source of a significant problem with vibration. This problem is particularly acute with turbo molecular pumps, having a floated rotor and stator construction, where rotational speeds are attained in the range of 50,000 rpm or greater. 
   The achievement of proper vibration isolation between the pump and the vacuum chamber is particularly important where the semiconductor structure is in the submicron range. The unwanted effects of vibration include errors in line deposition and film formation, and even errors in the inspection and quality assurance process, where extremely high accuracy in comparing patterns on a manufactured substrate against a reference pattern is required, and vibration anomalies may lead to erroneous decisions on product quality. 
   Such problems arise in inspection systems using scanning electron microscopes (SEM) or comparably sensitive devices, having less than one micron field of view, where inspection of a specimen (typically a wafer) is performed with the generation of an electron beam applied in a specimen chamber that must be maintained in a low pressure and contamination-free environment. 
   An example of a conventional turbo-molecular pump of the type manufactured by Varian Corp. or Pfiffer Edwards is illustrated in  FIG. 1 , where the pump  100  has a cylindrical outer body  101 . As illustrated in the figure, the pump has a central axis C-C and an inlet port  103  defined by a rim  102  that is adapted to attach directly, or be coupled via a conduit or manifold, to a vacuum chamber (not shown). At an opposite axial end of the cylinder body  101  is an exhaust port  104  to which the contents of the vacuum chamber are exhausted. The pump exhaust port is radially disposed with regard to the central axis C-C and is located on one side of the pump body  101 . Preferably, a conduit  105  for electrical, hydraulic, gas purge and cooling hose connections (collectively  130 ) is also radially disposed. At the same axial end, the bottom of the pump body has a sealing plate  106  that is removable but also serves as a support. The interior of the body  101  defines a chamber containing a rotor  107  that is disposed for rotation along the axis C-C and is supported by magnetic bearings  108  and mechanical bearings  109 . The rotor  107  drives rotating blades  110 , which are disposed radially with respect to the central axis C-C. Stator blades  111 , also disposed radially and interposed between the rotator blades  110 , are affixed to a support adjacent to the inner surface of the body  101 , in a manner well known in the art. The rotor  107  is supported by a frame  112 , and is mounted to the body  101  by vibration damping connectors  113  via arms  114  on the rotor body  112 . A motor  115  is operative to drive the rotor  107  at high speed, in the range of approximately 50,000 rpm or higher. 
   A coupling of the molecular-turbo pump  100  to a vacuum chamber is conventionally implemented with the use of a vibration damper  150 , as illustrated in  FIG. 2 . Elements in  FIG. 2  having a reference numeral identical to those in  FIG. 1  refer to the same structure and are not further described. The vibration damping mechanism  150  is coupled at one end to the rim  102  of the pump  100  at input  103  via a lower clamp  160  and is coupled at the other end to the inlet port  180  via an upper clamp  170 . The clamp  160  fits around the rim  102  and a lower distal end  151 A of the vibration damping structure  150  and is secured by a plurality of bolts (unnumbered). At the opposite distal end  151 B of the vibration damping structure, clamp  170  serves to couple the vibration damper  150  to the structure of the vacuum chamber inlet port  180  and is similarly secured by a plurality of bolts (unnumbered). The coupling of the turbo molecular vacuum pump  100  to the inlet port  180  via the vibration damper  150  defines a “serial-coupled” damper and vacuum pump arrangement. One or more centering rings  162  (which are conventional and available off the shelf, for example, at www.duniway.com) may be secured by the clamps  160 ,  170  and sealed by an O-ring  161 , as is known in the art. 
   The vacuum damper  150  comprises a rubberized support  152  that extends between the connector portions  151 A and  151 B at the opposite distal ends of the damper. The structure is made of a hardened rubber and has coupled to its interior surface a plurality of baffles  153 . The vacuum damper  150  is a conventional design that is available off-the-shelf from several vendors. 
   Although the serial type arrangement illustrated in  FIG. 2  eliminates some of the vibration that originates in the pump  100 , there continues to remain a problem with residual vibration. As illustrated by U.S. patent Pub. 2001/0012488 to Ohtachi et al, entitled VACUUM PUMP, particularly in  FIG. 4  of the Otachi et al publication, a series type connection may be used in which a damper is interposed between an input port of an external container and an outer cylindrical portion of a vacuum pump in order to prevent pump-origin vibration from being propagated to the external container. The damper uses a thin SUS-made cylindrical member bent into a bellow shape, which is coated with a silicon rubber or the like. The damper has a natural frequency of 20 Hz or less. However, the damper requires extra space in the axial direction of about 10 cm, thereby increasing the size, complexity of the structure, and cost of construction, assembly and maintenance. In order to resolve this problem, the Ohtachi et al patent depresses the propagation of vibrations to an external container without the use of a damper, by applying a vibration-absorbing member between a stator portion and a base. Nonetheless, as illustrated in  FIG. 5  of the Otachi et al publication, a bellows and extended flange continues to be required. The disadvantage of such a system is that vacuum power is significantly decreased. The additional distance between the pump input port and the input port of the vacuum chamber, as well as the bellows structure itself, reduces the effective speed of the pump. Thus, for a given pumping requirement, a much larger and more expensive pump is required. 
   The present invention is intended to solve this problem by allowing a direct connection between the pump and a vacuum chamber inlet port, thereby increasing conductance with accompanying reduction in resistance, while providing vibration damping with a damper assembled in a nested fashion about the pump. The nested arrangement may be considered a parallel, rather than serial connection of the damper structure. 
   SUMMARY OF THE INVENTION 
   The present invention is a gas turbo pump assembly for connection to an inlet port of a vacuum chamber, which defines a rigid mounting structure, the assembly having high throughput with low vibration. The assembly comprises a turbo pump having a pump body with an external surface and a center axis defining a direction of gas flow from a first axial end toward a second axial end of said body. The pump also has a pump inlet port, the inlet port being coupled to the vacuum chamber port disposed at the first axial end of the body, and an exit port disposed proximate the second axial end of the body. The assembly further has a vibration damper, structured to enclose a major portion of the pump body in a nested arrangement. 
   In a further feature of the invention, the vibration damper has at least one flexible structure, preferably a bellow damper, that connects between the body of the pump and the rigid mounting structure and encloses a major portion of the body of the pump. 
   The invention further involves a method of reducing the effect of vibration in a gas turbo pump assembly for connection to an inlet port of a vacuum chamber, which defines a rigid mounting structure, so that the assembly has high throughput with low vibration. The method comprises the step of providing a mounting structure on said turbo pump at a first axial end; and a step of connecting a vibration damping assembly to said rigid mounting structure at one end thereof and to the turbo pump at another end thereof in order to enclose a major portion of the turbo pump in a nested arrangement. 

   
     BRIEF DESCRIPTION OF THE DRAWINGS 
       FIG. 1  is a schematic illustration of a prior art turbo molecular vacuum pump. 
       FIG. 2  is an illustration of a prior art serial-coupled connection of a turbo molecular vacuum pump to a vacuum chamber inlet portion via a vibration damping mechanism. 
       FIG. 3  is an illustration of a nested or parallel arrangement of a vibration damper and a turbo molecular vacuum pump, in accordance with a first exemplary embodiment of the present invention. 
       FIG. 4  is an illustration of a nested or parallel arrangement of a vibration damper and a turbo molecular vacuum pump, in accordance with a second exemplary embodiment of the present invention. 
       FIG. 5  is an illustration of a nested or parallel arrangement of a vibration damper and a turbo molecular vacuum pump, in accordance with a third embodiment of the present invention. 
       FIG. 6  is an illustration of a nested or parallel arrangement of a vibration damper and a turbo molecular vacuum pump, in accordance with a sixth embodiment of the present invention. 
       FIGS. 7A-7C  illustrate details of certain forces that are operative to provide damping in the embodiments of  FIGS. 3-5 , respectively. 
   

   DESCRIPTION OF THE PREFERRED EMBODIMENTS 
   While the present invention is described in accordance with certain exemplary embodiments, it is not limited thereto. Numerous alternative structures and corresponding embodiments would be understood by one of ordinary skill in the art based upon the particular embodiments disclosed herein. When presenting the different embodiments, like structures are given the same reference number for consistency. The embodiments presented are only exemplary and the present invention is defined by the appended claims. 
   With reference to  FIG. 3 , an illustration is provided of a first exemplary embodiment of an arrangement of a vibration-damped turbo molecular vacuum pump nested within a vibration damper, forming a gas turbo pump assembly  200 . The gas turbo pump assembly  200  according to the present invention may have a turbo pump  201  with substantially the same arrangement of rotor, stator and motor as that illustrated in  FIG. 1 , including a cylindrical outer body having a central axis C-C, but may differ with regard to the arrangements of conduits and passages and outer body structures, due to features of the invention, as subsequently explained. Disposed at one axial end of the cylindrical body of the pump  201  is a pump rim  202  that defines the end of an input port  203  and from which the pump  201  is suspended. At the opposite axial end of the body of the pump  201 , and disposed in a radial orientation, is an exhaust port  204 , which is arranged in a manner consistent with the conventional pump in  FIG. 1 . However, the bottom end  206  of the pump  201  may have one or more access ports  205 A,  205 B for providing electrical connections  210  or purge and cooling connections  211  to components disposed in the interior of the body of the pump  201 . The purge and cooling connections, which may include a rough pumping port, cooling water inlet and outlet, and bearings gas purge, when provided at the bottom end, allow convenient access for connection and maintenance. While the components, including rotor and stator portions may be similar to those illustrated in  FIG. 1 , the connection at the bottom wall  206  of the pump  201  provides significant advantages for access related to assembly, servicing and repair. Further, the positioning of the access ports  205 A and  205 B frees the side portion of the cylindrical body of the pump  201  for coverage by the vibration damping assembly  230 , which in the illustrated exemplary embodiment comprises a vibration damping structure  250  and a rigid support member  240 . 
   In particular, the vibration damping structure  250 , which has a bottom end support portion  251 A and top end support portion  251 B, is constructed in the same manner as in the damper structure  150 . In this regard, the vibration damping structure  250  also includes bellow  253  and rubberized support  252 . The vibration damping structure  250  is secured to the rigid input port structure  280  by clamp  270  and bolts (unnumbered), which are similar to the clamp  170  in  FIG. 2 . In addition, the opposite end of the vibration damping structure  250  is secured by a clamp  260  and bolts (unnumbered) to a rigid support member  240  that extends from a lower end of the vibration damping structure  250  toward the pump rim  202  for connection. In an exemplary embodiment, the combination of the vibration damping structure  250  and the support member  240  define a vibration damping assembly  230  having a substantially cone shape and being formed around the outside of the pump body in order to effectively suppress vibration. The clamp  260  is designed to affix the bottom end support portion  251 A to the lower portion  241 A of the rigid support member  240 . A plurality of such clamps  260  are provided at plural circumferential positions of the vibration damping assembly  230 . The upper portion  241 B of the rigid support member  240  is secured to the rim  202  of the turbo vacuum pump  201  by welding, or the like, and the lower portion  241 A of the support member  240  is secured to the lower part  251 A by the clamp  260 . With this arrangement, the pump  201  is flexibly affixed at its rim  202 , via the substantially cone-shaped vibration damping assembly  230  to the input port structure  280 , i.e., via the support portion  240  and damper  250 . One or more centering rings  262  may be secured by the clamps  260 ,  270  and sealed by an O-ring  261 , in order to ensure proper alignment of the pump with the rigid input port structure  280 . 
   In operation, with the support member  240  being a rigid part and the flexible bellow damper  250  being a flexible part, and both being disposed in a substantially overlapping cone-shaped arrangement with a common connection at their bottom portions  241 A and  251 A, respectively, an effective damping arrangement can be obtained. In particular, with this structure, the damper will be compressed by the atmospheric pressure and will expand in response to vibration forces, thereby providing the desired damping effect.  FIG. 7A  illustrates the compression forces  254  that apply to the damper structure in this embodiment. 
   With this arrangement, the vibration damper  250  may be structured to surround the majority of the exterior surface of the body of the turbo pump  201 , thereby providing an extensive vibration absorbing structure with the pump nested within the cavity of the vibration absorbing structure. 
   With the transfer of the utility access ports  205 A,  205 B to the bottom plate  206  of the vacuum pump  201 , there is no obstruction to the vibration damper  250  covering a full two-thirds of the axial length of the turbo pump body. Optimally, the vibration damper will cover a significant portion, e.g., 50-90%, of the outer surface of the vacuum pump, however, it must be recognized that movement or other adjustment of the exit port or damper would be needed to achieve the upper range of coverage. 
   Significantly, the vibration damping structure may be an off-the-shelf structure that is simply larger than one used in the serial connection in  FIG. 2 . For example, an ISO 160 size damper may be used instead of an ISO 100 size damper, which would be appropriate for damping in  FIG. 2 . However, because of the direct connection between the inlet port of the pump  203  and the inlet port of the vacuum chamber  280 , a smaller size pump would be required. In particularly, rather than a 500 liter per second pump in a conventional design that is needed to obtain 300 liters per second effective pumping at the vacuum chamber inlet port, a 300 liter per second pump may be used. The difference is significant in both the size and cost of the pump, as the cost for a pump to supply a particular application may be reduced in half. 
     FIG. 4  shows a modification of a gas turbo pump assembly  200  of  FIG. 3 , particularly with respect to the vibration damper structure. Specifically, the embodiment of the gas turbo pump assembly in  FIG. 4  uses a vibration damping assembly  230 ′, which in the illustrated exemplary embodiment comprises a vibration damping structure  250 ′ and a rigid support member  240 ′ that are joined at their lower ends and define a generally cone shape. However, the solid support  240  that was adjacent the body of pump  201  in  FIG. 3  has been replaced by an integrated support structure  250 ′, comprising a combination of flexible bellows  248  and solid mounting top support  246  and bottom support  247 . The top support  246  is attached to the top of the bellows  248  and is secured to the pump rim  202  in the same manner as the top  241 B of the support  241  in  FIG. 3 . The bottom support  247  is attached to the bottom of the flexible bellows  248  and is secured to the bottom of a rigid support portion  240 ′ in the same manner as the bottom  241 A of the support  241  in  FIG. 3 . 
   A detail of the vibration damping assembly  230 ′ in  FIG. 4  is illustrated in  FIG. 7B . With the vibration damping structure  250 ′ disposed closest to the pump and the solid part  240 ′ disposed outside of the vibration damping structure  250 ′, and the top  246  of the damping structure  250  affixed by welding or the like to the rim  202  of the pump and the top of the solid part  240 ′ affixed to the rigid port structure  280 , the damping structure  250 ′ will be extracted by the atmospheric pressure according to forces  255 . This is an opposite reaction to the case in  FIG. 3 , where the damping structure will be compressed. 
     FIG. 5  shows yet another exemplary embodiment of a gas turbo pump assembly with yet another vibration damping arrangement. The embodiment of  FIG. 5  uses a vibration damping assembly  230 ″, which in the illustrated exemplary embodiment comprises a first vibration damping structure  250  and a second vibration damping structure  250 ′ that are joined at their lower ends and define a substantially cone shape. The damping structures  250  and  250 ′ are the same structures as disclosed with respect to  FIGS. 3 and 4 , respectively. The top support  246  of structure  250 ′ is attached to the top of the bellows  248  and is secured to the pump rim  202  in the same manner as the top  241 B of the support  241  in  FIG. 3 . The bottom support  247  is attached to the bottom of the bellows  248  and is secured to the bottom of the damping structure  250  in the same manner as the bottom  241 A of the support  241  in  FIG. 3 . 
   A detail of the vibration damping assembly  230 ″ in  FIG. 5  is illustrated in  FIG. 7C . With the vibration damping structure  250 ′ disposed closest to the pump and the vibration damping structure  250  disposed outside of the vibration damping structure  250 ′, and the top  246  of the damping structure  250  affixed by welding or the like (as indicated by the conventional welding symbol) to the rim  202  of the pump and the top of the damping structure  250 ′ affixed to the rigid port structure  280 , the damping structure  250 ′ will be extracted by the atmospheric pressure and the damping structure  250  will be compressed. This permits the pump to be “floating” by the elimination of both the compression and extraction forces. 
   In  FIG. 6 , which is yet another embodiment of the invention, the body of pump  201  is girdled at a location axially away from the pump rim  202  by a radially extended and rigid support structure  207 , preferably in the form of a support ring or radially extended tab or flange portion that is integrally formed on the body by welding, molding or the like, and whose purpose is explained subsequently. In addition, the opposite end of the vibration damper  250  is secured by a clamp  260  and bolts (unnumbered) to the support portion  207  that is formed around the outside of the body of pump  201  and is rigidly affixed via the support portion  207  on the pump body (or other similar structure for attaching the damper  250  to the lower part of the body) to the rim  202  of the pump. With this structure, the pump is supported at both the top rim and mid body positions, and not just at the top rim  202 , as in the embodiments of  FIGS. 3 ,  4  and  5 . 
   In all cases illustrated in  FIGS. 3 ,  4 ,  5  and  6 , the pump will be nested substantially within the damper arrangement, and will permit a reduction in the loss of pumping speed in prior art designs, easier access to facilities connections and smaller size, thus lower cost. 
   The present invention comprises a combination of a vibration damper having a vacuum pump nested therein, as well as the vibration damper assembly itself, adapted to receive a conventional vacuum pump or specially adapted vacuum pump with bottom-access conduits and/or support ring structures. The vibration damper assembly  230 ,  230 ′ and  230 ″, as disclosed herein, may be sold in kit form, comprising one or more of a vibration damper  250 ,  250 ′, rigid support members  240 ,  240 ′ and bellows  246 - 248 , as illustrated in the figures. The bellows may be made of metal and may be either formed or welded into an appropriate shape. 
   While the present invention has been described in connection with several exemplary embodiments, the invention further contemplates variations thereon, including variations or alternatives in materials, mechanical couplings and supports, that would be known to those skilled in the art.