Abstract:
A top-flow fluid pump that is made from a high-purity fluroplastic material is disclosed. The pump is used to circulate extremely corrosive fluids that are heated to temperatures of 160-180° C. through at least one filtration unit. The pump can be used in a semiconductor etching system. The pump utilizes the driven side of an impeller to generate a suction force that draws the corrosive fluid into a pumping chamber from at least one inlet port. A pedestal support or shaft sleeve, through which a motor drive shaft extends, is modified to create an annular passageway that permits the corrosive fluid to enter the pumping chamber from the inlet. With the inlet design of the present invention, a drive motor seal assembly is no longer subjected to corrosive fluid because the seal assembly is positioned on the suction side of the impeller. In a “dead headed” condition, the corrosive fluid flow stops completely as the fluid within the pumping chamber simply remains in shear.

Description:
CROSS REFERENCE TO RELATED APPLICATIONS 
     This application claims the benefit of Provisional U.S. patent application Ser. No. 60/154,573, filed Sep. 17, 1999. 
    
    
     BACKGROUND OF THE INVENTION 
     The present invention relates to the fluid pumping and filtration arts. It finds particular application in conjunction with a top-flow centrifugal fluid pump for use in pumping highly-corrosive fluids, such as used in a semi-conductor etching system, and will be described with particular reference thereto. However, it should be appreciated that the present invention may also find application in conjunction with other systems and applications where the pumping and/or filtration of fluids is performed. 
     FIG. 1 illustrates an exemplary impeller-type fluid pump and filtration unit A for a semi-conductor etching system. The pump and filtration unit is disclosed in commonly-owned U.S. Pat. No. 5,021,151, which is hereby incorporated by reference for all that it teaches. 
     Briefly, the pump and filtration unit A includes a housing  10  having a pump chamber  12  and a filter chamber  14  spaced apart from the pump chamber. The pump and filter chambers  12 ,  14  communicate through an intermediate passageway or bore  16 . An inlet port  18  of the housing communicates with an inlet  20  of the pump chamber. An outlet port  22  of the housing communicates with an outlet  24  of the filter chamber. A centrifugal-type fluid pump within the housing  10  includes an impeller  26  positioned within the pump chamber  12 . A hollow impeller shaft sleeve  28  is secured to the impeller and extends through a bore  30  in the housing. A drive motor assembly  32  is secured to the housing by an adapter plate  34 . An output shaft  36  of the drive motor extends through the adapter plate  34  and impeller shaft sleeve  28  and is secured to the impeller  26 . A replaceable filter element  38  is located within the filter chamber  14 . 
     The impeller  26  is formed from a first section  40  and a second section  42 , each of which has a plurality of impeller vanes associated therewith. In particular, the impeller vanes  44  associated with first impeller section  40  draw fluid from the inlet port  20  to the pump chamber  12  in a direction toward the drive motor assembly  32 . The impeller vanes  46  associated with the second impeller section  42  move fluid more efficiently than the impeller vanes  44  associated with the first section  40 . As a result, a positive suction force is created by the impeller vanes  46  to prevent fluid from being pushed up into the bore  30  and potentially reaching the drive motor unit  32 . 
     In operation, the pump and filtration unit A is located in a tank or tub together with a weir basket that holds microelectronic circuits or chips. The tub contains a corrosive chemical solution or fluid (e.g. corrosive acid(s) heated to 160-180° C.) which overflows the top of the basket and engulfs the unit A, and which is intended to etch the microelectronic circuits or chips. When the pump and filtration unit A is energized, the corrosive fluid is drawn from the inlet port  16  to the pump chamber  12  by the impeller  26 . The impeller then pumps the fluid into the filtration chamber  14  and through the filter  38  before being discharged back into the tub at the outlet  22 . Notwithstanding the positive suction force generated by the second impeller section  42 , a seal assembly  48  (FIG. 2) such as a labyrinth seal assembly further prevents corrosive fluid from flowing between the shaft sleeve  38  and the adapter plate  34  to the drive motor assembly  32 . 
     It should be appreciated that the drive motor assembly provides a very efficient means of pumping fluids when coupled to the centrifugal-type pump. High rotational speeds of the centrifugal-type pump  26  can produce high fluid-flow rates at moderate outlet pressures. However, when the outlet pressure increases (such as when the filter  38  becomes at least partially blocked with particles generated by the etching process), the fluid flow drops off sharply beyond the design parameters of the pump. In the most extreme case when the pump is “dead headed” (i.e. outlet  22  and/or  24  is blocked completely), the pressure created by the first impeller section  40  can force the corrosive fluid up the bore  30 , past the seal assembly  48 , and into the drive motor assembly  32 . When pumping aggressive (i.e. highly-corrosive) fluids, this can result in the premature failure of the drive motor and/or the drive bearings. 
     Accordingly, it has been considered desirable to develop a new and improved top-flow centrifugal fluid pump for use in pumping corrosive fluids, which pump meets the above-stated needs and overcomes the foregoing difficulties and others while providing better and more advantageous results. 
     SUMMARY OF THE INVENTION 
     The present invention is directed to a fluid pump that is made from a high-purity fluroplastic material. The pump is used to circulate extremely corrosive fluids that are heated to temperatures of 160-180° C. through at least one filtration unit. The pump can be used in a semiconductor etching system. The pump utilizes the driven side of an impeller to generate a suction force that draws the corrosive fluid into a pumping chamber from at least one inlet port. 
     A pedestal support or shaft sleeve, through which a motor drive shaft extends, is modified to create an annular passageway that permits the corrosive fluid to enter the pumping chamber from the inlet. With the inlet design of the present invention, a drive motor seal assembly is no longer subjected to corrosive fluid because the seal assembly is positioned on the suction side of the impeller. In a “dead headed” condition the corrosive fluid flow stops completely as the fluid within the pumping chamber simply remains in shear. 
     Thus, in one aspect of the present invention a fluid pump is disclosed. The fluid pump includes a housing defining a pump chamber; a single fluid inlet communicating with the pump chamber; an impeller positioned within the pump chamber; and a drive shaft extending through the fluid inlet and coupled to the impeller. 
     In a second aspect of the present invention, a corrosive fluid pumping system including a tub adapted to hold a corrosive fluid and a fluid pump is disclosed. The fluid pump includes a housing defining a pump chamber; a single fluid inlet communicating with the pump chamber; an impeller positioned within the pump chamber; and a drive shaft extending through the fluid inlet and coupled to the impeller. 
     Accordingly, one advantage of the present invention is the provision of a fluid pump that prevents corrosive fluid from reaching a drive motor unit during a worst-case, “dead-headed” operating condition of the fluid pump. 
     Another advantage of the present invention is the provision of a fluid pump having at least one inlet port positioned intermediate a pumping chamber and a drive motor housing. 
     Yet another advantage of the present invention is the provision of a fluid pump having an impeller that draws fluid into a pumping chamber in a direction away from a drive motor housing. 
     Still further advantages of the present invention will become apparent to those of ordinary skill in the art upon reading and understanding the following detailed description of the preferred embodiments. 
    
    
     BRIEF DESCRIPTION OF THE DRAWINGS 
     The invention may take form in various components and arrangements of components, and in various steps and arrangements of steps. The drawings are only for purposes of illustrating the preferred embodiments and are not to be construed as limiting the invention. 
     FIG. 1 is a front elevation view, in partial cross-section, of a pump and filtration unit according to the prior art; 
     FIG. 2 is a longitudinal cross-sectional view, taken along the line  2 — 2  of FIG. 3, of a top-flow centrifugal fluid pump according to a first preferred embodiment of the present invention; 
     FIG. 3 is a cross section view of an impeller of the top-flow centrifugal fluid pump taken along the line  3 — 3  of FIG. 2; 
     FIG. 4 is a front elevation view of a top-flow centrifugal fluid pump and dual filtration unit according to a second preferred embodiment of the present invention; 
     FIG. 5 is a top view of the top-flow centrifugal fluid pump and dual filtration unit of FIG. 4; 
     FIG. 6 is a front elevation view of a pump body of the top-flow centrifugal fluid pump and dual filtration unit of FIG. 4; 
     FIG. 7 is a top view of the pump body of FIG. 6; 
     FIG. 8 is a side elevation view of a pump pedestal of the top-flow centrifugal fluid pump and dual filtration unit of FIG. 4; 
     FIG. 9 is a longitudinal cross-sectional view of the pump pedestal taken along the line  9 — 9  of FIG. 8; 
     FIG. 10 is an exploded side elevation view, in partial cross section, of an impeller assembly of the top-flow centrifugal fluid pump and dual filtration unit of FIG. 4; 
     FIG. 11 is an end elevation view of the impeller assembly taken along the line  11 — 11  of FIG. 10; 
     FIG. 12 is a cross section view of the impeller assembly taken along the line  12 — 12  of FIG. 10; 
     FIG. 13 is a side elevation view of an exemplary semiconductor etching system that incorporates a top-flow centrifugal fluid pump and dual filtration unit of the present invention; and 
     FIG. 14 is a top plan view of the semiconductor etching system of FIG.  13 . 
    
    
     DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENTS 
     With reference now to FIGS. 2 and 3, a top-flow centrifugal fluid pump  100  incorporates the features of the present invention therein. The pump  100  includes a housing  102  with a cavity  104  at a first end of the housing and a counter-bored recess  106  at a second end of the housing. An end plate  108  is sealed to the first end of the housing. 
     The end plate  108  and the cavity  104  cooperate to define a closed pump chamber  110 . The pump chamber  110  is surrounded by two opposing outlet passageways  112  that spiral radially outward in an involute manner from opposing sides of the pump chamber  110 . In particular, one end of each passageway  112  communicates with the pump chamber  110 , and the other end of each passageway communicates with a respective outlet port  114  that extends through the housing. The outlet ports are oriented in generally opposite directions through the housing  102 . 
     A central bore  116  extends longitudinally between the pump chamber  110  and the counter-bored recess  106 . The counter-bored recess is adapted to receive an adapter plate  117  and an attached drive motor assembly (not shown). A plurality of circumferentially-spaced inlets  118  extend radially through the pump housing  102  and communicate with the central bore  116  at a location intermediate the pump chamber  110  and the counter-bored recess  106 . 
     An impeller  120  is positioned within the pumping chamber  110 . In the embodiment being described, the impeller  120  includes a first or cap portion  122  and a second or driven portion  124 . The second or driven portion  124  includes a plurality of impeller vanes  126  associated therewith. The first and second impeller portions  122 ,  124  can be joined together in any suitable manner such as by threaded male and female members  127 ,  128 , respectively. 
     A hollow shaft sleeve  130  extends through the central bore  116 . A first or distal end of the shaft sleeve  130  is secured to the impeller second section  124 , such as by cooperating threaded portions  131  and  132 , and a second or proximal end of the shaft sleeve  130  passes through the adapter plate  117  at a second end. A seal assembly  133  such as a labyrinth seal assembly is interposed between the shaft sleeve  130  and the adapter plate  117  to prevent corrosive fluid from reaching the drive motor assembly. A motor output shaft  134  extends through the center of the shaft sleeve  130  and is secured to the impeller  120  for rotation therewith. 
     The inlet ports  118  communicate with the pump chamber  110  through an annular passageway  136  defined between the shaft sleeve  130  and the cylindrical side wall defining the central bore  116 . The size and shape of the passageway  136  can be optimized to control the flow of corrosive fluid from the inlet ports  118  to the pump chamber  110 . 
     Any one or more of the top-flow centrifugal fluid pump  100  components including the pump housing  102 , first and second impeller portions  122 ,  124 , and shaft sleeve  130  can be made from or coated with suitable corrosion and high-temperature resistant materials such as PTFE (polytetrafluoroethylene), quartz, etc. 
     In operation, the pump  100  is placed in a tank or tub of corrosive fluid so that the inlet ports  118  are fully submerged. It should be appreciated that the corrosive fluid will rise to a certain level within the central bore  116  as the pump housing is submerged within the corrosive fluid. When the drive motor is energized, the motor output shaft  134  and attached impeller  120  and shaft sleeve  130  are caused to rotate. As a result, a positive suction force is generated by the rotating impeller vanes  126  associated with the second impeller portion  124 . The suction force draws corrosive fluid from the inlet ports  118  through the passageway  136  and into the pump chamber  110 . The suction force also draws the column of corrosive fluid within the bore  116  away from the seal assembly  133 . Thus, corrosive fluid is drawn into the pump chamber  110  in a direction away from the seal assembly  133 , and then into the spiral passageways  112  and outlet ports  114 . One or more suitable filtration units can be connected to one or both of the outlet ports  114  to provide a filtration capability to the top-flow fluid pump  100 . 
     In a worst case scenario where both outlet ports  114  are blocked (i.e. the pump  100  is “dead-headed”), the flow of corrosive fluid completely stops and the fluid within the pump chamber  110  remains in shear. That is, the impeller  120  is unable to draw additional fluid into the pumping chamber  110  through the annular passageway  136  from the inlet ports  118 . Further, in contrast with the impeller  26  (FIG.  1 ), the rotating impeller  120  does not drive or otherwise pump or force corrosive fluid back up into the bore  116  toward the seal assembly  133 . Even if the corrosive fluid does reach the seal assembly  133 , no forces are generated by the impeller  120  that would cause the seal assembly  133  to fail and thus expose the drive motor unit and/or drive bearings to the corrosive fluid. 
     Referring now to FIGS. 4 and 5, a top-flow centrifugal fluid pump and dual filtration unit  200  is shown. The fluid pump and filtration unit  200  includes a pump housing or body  202 , a pump pedestal  204  mounted to the pump body  202 , a drive motor assembly  206  mounted to the pump pedestal  204 , an impeller assembly  208  supported within the pump pedestal  204 , a first filtration unit  210   a  mounted to the pump body  202 , and a second filtration unit  210   b  mounted to the pump body  202 . Each of the filtration units  210   a,    210   b  conventionally includes a housing  211   a,    211   b  that supports a conventional cartridge-type filter element  212   a,    212   b.  It should be appreciated that dual filtration paths reduce back pressure on the pumping unit and extend the time between filter changes, relative to the single filtration stage  14  associated with pumping and filtration unit A (FIG.  1 ). 
     With reference now to FIGS. 6 and 7, the pump body  202  includes three contoured cavities  214 - 218  that are recessed from a first or upper surface  220  thereof. The two end cavities  214 ,  218  define filtration manifolds, while the center cavity  216  defines a pump or impeller chamber  222 . Dual pump chamber outlet passageways  224   a,    224   b  extend between opposing side walls of the pump chamber  216  and the respective filtration manifolds  214 ,  218 . It should be appreciated that the dual opposing outlets  224   a,    224   b  enhance centering an impeller  244  (described further below) of the impeller assembly  208  within the pump chamber  222  during operation of the unit  200 . 
     The pump chamber passageways  224   a,    224   b  define inlets to the respective filtration manifolds  214 ,  218 . Filtration unit outlet passageways  226   a,    226   b  extend between the respective manifolds  214 ,  218  and a pump body side wall  228 . Circumferentially spaced-apart flanges  230  extend partially over the cavities  214 ,  218  from the pump body upper surface  220 . The flanges  230  provide cam surfaces for securing the filter housings  211   a,    211   b  (FIG. 4) to the pump body  202  in a “twist lock” manner. 
     Referring now to FIGS. 8 and 9, the pump pedestal  204  includes a tubular side wall  232 . As described in detail below, the tubular side wall  232  concentrically surrounds an impeller shaft sleeve  246  that is rotatably supported within the pump pedestal  204 . The pump pedestal  204  and shaft sleeve  246  cooperate to define an annular fluid cavity  233  within the pump pedestal  204 . An enlarged end plate  234  is secured to one end of the tubular side wall  232 . The end plate  234  includes a central aperture  236 . A counter-bored recess  238  is provided at the opposing end of the tubular sidewall. The recess  238  is adapted to receive a mounting or adapter plate  240  (FIG. 4) associated with the drive motor assembly  206 . A plurality (e.g. two) of pump inlet apertures or ports  242  extend through the side wall  232  proximate the end plate  234 . The size or area of the apertures  242  is maximized or otherwise optimized to reduce the pressure drop on the suction side of the fluid pump. 
     As best shown in FIG. 9, an annular passageway  243  is defined between an outer surface of the impeller shaft sleeve  246  and the cylindrical side wall defining the end plate central bore  236 . The size and shape of the annular passageway  243  can be optimized to control the flow of corrosive fluid from the inlet ports  242  to the pump chamber  222 . The pump pedestal end plate  234  mounts over the pump body cavity  216  to define the pump chamber  222 . It is contemplated that the pump pedestal  204  can be secured to the pump body  202  with a suitable threaded screw or nut/bolt arrangement. Alternatively, the pump pedestal  204  can be secured to the pump body  202  with camming flanges that cooperate to form a twist lock arrangement in the same manner as the described above with respect to the filtration units  210   a,    210   b.    
     With reference to FIGS. 10-12, the impeller assembly  208  comprises an impeller  244  and a shaft sleeve  246 . In the embodiment being described, the impeller  244  is formed from a first or cover section  248  and a second or driven section  250 . The impeller  244  is formed from two separate sections to facilitate the manufacture thereof. However, it is contemplated that the impeller  244  can be formed as a unitary structure, if desired. 
     The impeller cover section  244  includes an outer surface  252  that tapers in a radially outward direction at an angle α of about 30°. An inner surface  254  of the cover section  244  includes a plurality of threads  256  adapted to threadably engage mutually corresponding threads  258  associated with the impeller driven section  250 . The impeller driven section  250  further includes an annular end wall  259  surrounding an open central cavity  260 . A plurality of impeller blades or vanes  262  extend or otherwise spiral radially outward from the cavity  260  to an outer circumference of the impeller. In an assembled state of the impeller  244 , the blades or vanes  262  are bounded by the impeller cover  248  and the annular end wall  259 . In the embodiment being described, the impeller driven section  250  includes six impeller blades  262 . However, any number of impeller blades is contemplated. A central aperture  264  extends through the impeller second section  250  and includes an internally threaded section  266  thereof. 
     The shaft sleeve  246  is formed from a tubular side wall  268 . A threaded end section  270  of the sleeve  246  cooperates with the threaded section  266  of the impeller driven section  250  to rotatably secure the shaft sleeve  246  to the impeller  244 . A rotatable output shaft  272  associated with the drive motor assembly  206  extends through the hollow center of the shaft sleeve  246  and is rotatably secured to the impeller driven section  250  by a suitable threaded nut arrangement (not shown). Other attachment arrangements are contemplated. The diameter of the impeller cavity  260  is greater than the diameter of the shaft sleeve  246  so that an annular impeller inlet port  274  is formed when the shaft sleeve  246  is secured to the impeller driven section  250 . An upper end  276  of the shaft sleeve  246  passes through the adapter plate  240 . A conventional seal assembly  278 , such as a labyrinth seal assembly, is interposed between the exterior surface of the shaft sleeve  246  and the adapter plate  240  to prevent corrosive fluid from reaching the drive motor assembly  206 . 
     Thus, in an assembled state of the top-flow centrifugal fluid pump and dual filtration unit  200 , as shown in FIG. 4, i) the pump pedestal  204  is secured to the pump body  202 , ii) the drive motor assembly  206  is secured to the pump pedestal  204 , iii) the impeller assembly  208  extends centrally though the pump pedestal  204 , and iv) the drive motor output shaft  272  extends through the shaft sleeve  246  and is secured to the impeller  244  to rotatably suspend the impeller  244  within the pump chamber  222  of the pump body  202 . It should be appreciated that the impeller assembly  208  can be removed from the unit  200  by simply removing the pump pedestal  204  from the pump body  202 . That is, the pump body  202  and filtration units  210   a,    210   b  can remain in position within the semiconductor etching system tank or tub  280  (FIGS. 13 and 14) when servicing the impeller assembly  208 . In contrast, the impeller  26  (FIG. 1) of the pumping and filtration unit A, must be serviced (i.e. removed) through the inlet  18  thus requiring the housing  10  to be removed from the tub. 
     With the impeller  244  suspended within the pump chamber  222 , the tapered lower surface  252  of the impeller cover section  248  conforms with the tapered lower surface  216   a  (FIG. 6) of the pump block cavity  216 . As a result, a fluid bearing is formed between the conforming tapered surfaces  216   a,    252  to reduce the potential for wear and particle generation during operation of the unit  200 . 
     Referring now to FIGS. 13 and 14, an exemplary a semi-conductor etching system B incorporating the top-flow centrifugal fluid pump and dual filtration unit  200  of FIGS. 4-12 is shown. The etching system B can also incorporate the top-flow centrifugal fluid pump  100  of FIGS. 2 and 3. However, the parallel filter arrangement of the top-flow centrifugal fluid pump and dual filtration unit  200  yields a reduced pressure drop at the designed flow rates, creating a more efficient system. 
     The etching system B includes tank or tub  280  and a weir basket  282  that holds microelectronic circuits or chips. The tub  280  contains a corrosive chemical solution or fluid (e.g. corrosive acid(s) heated to 160-180° C.) which is intended to etch the microelectronic circuits or chips. The pump and filtration unit  200  is positioned within the tub  280  such that the pump inlets  242  and the filtration unit outlets  226   a,    226   b  are fully submerged below the surface of the corrosive fluid within the tub  280 . 
     As a result, the corrosive fluid will rise to a certain level within the inner annular fluid cavity  233  of the pump pedestal  204 . When the drive motor assembly  206  is energized, the motor output shaft  272  and attached impeller  244  and shaft sleeve  246  are caused to rotate together. As a result, a positive suction force is generated by the rotating impeller vanes  262  associated with the second impeller section  250 . The suction force draws corrosive fluid from the inlet ports or apertures  242  through the annular passageway  243  and impeller inlet  274 , and into the pump chamber  222 . The suction force also draws the column of corrosive fluid within the annular fluid cavity  233  away from the seal assembly  278 . Thus, corrosive fluid is drawn into the pump chamber  222  in a direction away from the seal assembly  278 , then into the spiral passageways  224   a,    224   b,  and through the filtration units  210   a,    210   b  to be filtered before being discharged from the outlet ports  226   a,    226   b.    
     In a worst case scenario where both outlet ports  226   a,    226   b  are blocked (i.e. the pump unit  200  is “dead-headed”), the flow of corrosive fluid completely stops and the fluid within the pump chamber  222  remains in shear. That is, the impeller  244  is unable to draw additional fluid into the pumping chamber  222  through the annular passageway  243  and impeller inlet  274  from the inlet ports  242 , and does not drive or otherwise pump or force corrosive fluid back up into the annular fluid cavity  133  toward the seal assembly  278 . Even if the corrosive fluid level does reach the seal assembly  278 , no forces are generated by the impeller  244  that would cause the seal assembly  278  to fail and thus expose the drive motor unit and/or drive bearings  106  to the corrosive fluid. 
     Any one or more of the top-flow centrifugal fluid pump and dual filtration unit components including the pump body  202 , pump pedestal  204 , impeller assembly components including the first and second impeller sections  248 ,  250  and shaft sleeve  246 , and filtration unit housings  211   a,    211   b  can be made from or coated with suitable corrosion and high-temperature resistant materials such as PTFE (polytetrafluoroethylene), quartz, etc. 
     The top-flow centrifugal fluid pump  100  and/or the top-flow centrifugal fluid pump and dual filtration unit  200  of the present invention can include a shaft seal purge arrangement that prevents corrosive fumes from the corrosive fluid within the tub  280  (FIGS. 13 and 14) from entering and contaminating the drive motor assembly. More particularly, with reference to FIG. 1, the pump and filtration unit A further includes a gas delivery channel  50  with a threaded outer end  52 . The channel  50  extends radially inward from an outer periphery of the adapter plate  34  to the central bore  30 . A suitable gas delivery tube  54  can be threadably secured to the channel end  52 . The tube  52  delivers a neutral gas, such as nitrogen or carbon dioxide, to the bore  30  and the outer periphery of the shaft sleeve  28 . Thus, neutral gas flows upward into the drive motor housing  32  to prevent corrosive fumes from doing the same. The pump pedestal  204  (FIGS. 8 and 9) includes a plurality of apertures  284  that are suitable for delivering a neutral gas to the outer periphery of the shaft sleeve  246 . Exhausting the purge gas out of the tank  280  reduces the generation of particles within the corrosive fluid. 
     The invention has been described with reference to the preferred embodiments. Obviously, modifications and alterations will occur to others upon reading and understanding the preceding description. It is intended that the invention be construed as including all such modifications and alterations.