Abstract:
To overcome the problem associated with liquid or solid process debris from a vacuum process system falling into, and contaminating or damaging, a vacuum pumping arrangement used to evacuate the system, the inlet of the vacuum pumping arrangement is located lower than the outlet of the arrangement. This provides a net flow of gas pumped by the arrangement in a generally upwards direction thereby resisting the passage of contaminants into the arrangement.

Description:
CROSS-REFERENCE TO RELATED APPLICATION 
     This Application is a Section 371 National Stage Application of International Application No. PCT/GB2012/050686, filed Mar. 28, 2012, which is incorporated by reference in its entirety and published as WO2012/140406 A1 on Oct. 18, 2012 and which claims priority to British Patent Application No. 1106310.4 filed Apr. 14, 2011. 
     BACKGROUND 
     The present disclosure relates to a vacuum pumping system comprising a vacuum pumping arrangement. 
       FIG. 4  shows a vacuum pumping system  100  comprising a vacuum pumping arrangement  102  for evacuating gas from a vacuum processing chamber  104 , such as that of a solar panel, flat panel, LED or semi-conductor processing tool. The vacuum pumping arrangement comprises a primary pump  106  and a secondary pump  108  arranged in series. The primary, or roughing, pump  106  exhausts at atmosphere and may be a dry pump such as a screw, roots, claw or scroll pump. The secondary, or high vacuum, pump  108  is connected to the vacuum chamber  104  and exhausts to the inlet of the primary pump. The secondary pump is typically a turbo-molecular pump or mechanical booster pump. 
     The vacuum pumping system  100  comprises a foreline vacuum line  110 , which can be any suitable conduit such as a pipe or hose, connecting the vacuum chamber  102  to the vacuum pumping arrangement  104  and the inlet of the secondary pump  108 . A further foreline conduit  112  connects the exhaust of the secondary pump  108  to the inlet of the primary pump  106 . An exhaust line conduit  114  connects to the exhaust of the primary pump  106 . 
     The vacuum pumping system may further comprise an abatement apparatus  116  for removing noxious substances from the gas evacuated from the vacuum chamber  104 . A valve  118 , such as a bypass valve, diverts gas to a gas storage facility  120  during abatement apparatus downtime. The exhaust line conduit  114  is connected to the valve  118  for ducting gas to either the abatement apparatus  116  or the storage facility  120 . 
     Gas exhausted from the process chamber  104  typically contains contaminants in addition to process gases. The contaminants may comprise particulates, such as silica dust; or liquid precursors, such as TEOS. In the vacuum pumping system shown in  FIG. 4 , the vacuum processing chamber  104  is located above the vacuum pumping arrangement  102  and the vacuum line  110  ducts gas in a generally downwards direction to the inlet of the vacuum pumping arrangement and through the arrangement to the exhaust line. Contaminants present in the gas stream drop under gravity into the vacuum pumping arrangement causing damage or reduced operability. A trap may be provided in the vacuum line  110  between the vacuum chamber and the pumping arrangement assisting in the collection and protection of the vacuum pumping arrangement, but are generally located high above the vacuum pump and are ergonomically difficult to service. 
     The exhaust of the vacuum pumping arrangement is at or proximate floor level. The inlet of the abatement apparatus is generally located in an elevated position, relative to the exhaust of the pumping arrangement, and accordingly the exhaust line  114  is often of considerable length. The extended length of the exhaust line may comprise such disadvantageous features as U-bends and horizontal pipework that can provide an abundance of locations for process by-products to deposit. In order to prevent condensation of exhausted substances it is generally required that valve  118  is heated, as shown, which contributes to the cost of ownership of the vacuum pumping system. 
     It is an object of the invention to provide an improved vacuum pumping system. 
     The discussion above is merely provided for general background information and is not intended to be used as an aid in determining the scope of the claimed subject matter. The claimed subject matter is not limited to implementations that solve any or all disadvantages noted in the background. 
     SUMMARY 
     A vacuum pumping system for evacuating a vacuum chamber, the system comprising a vacuum pumping arrangement for pumping gas from inlet to an outlet thereof, the inlet being located in use lower than the outlet and the net flow of gas pumped by the arrangement is in a generally upwards direction thereby resisting the passage of contaminants into the arrangement. 
     Other preferred and/or optional aspects are defined in the accompanying claims. 
     This Summary is provided to introduce a selection of concepts in a simplified form that are further described below in the Detailed Description. This Summary is not intended to identify key features or essential features of the claimed subject matter, nor is it intended to be used as an aid in determining the scope of the claimed subject matter. 
    
    
     
       BRIEF DESCRIPTION OF THE DRAWINGS 
       In order that the present invention may be well understood, an embodiment thereof, which is given by way of example only, will now be described with reference to the accompanying drawings, in which: 
         FIG. 1  shows schematically a vacuum pumping system; 
         FIGS. 2 and 3  show an example of a vacuum pump of the vacuum pumping arrangement of the system shown in  FIG. 1 ; and 
         FIG. 4  shows schematically a prior art vacuum pumping system. 
     
    
    
     DETAILED DESCRIPTION 
     A vacuum pumping system  10  is shown in  FIG. 1 . The system  10  comprises a vacuum pumping arrangement  12  for evacuating gas from a vacuum chamber  14 , such as processing chamber of a semi-conductor processing tool. The vacuum pumping arrangement comprises a primary pump  16  and a secondary pump  18  arranged in series. The primary, or roughing, pump  16  exhausts at atmosphere and may be a dry pump such as a scroll, screw, roots or claw pump. The secondary, or high vacuum, pump  18  is connected to the vacuum chamber  14  and exhausts to the inlet of the primary pump. The secondary pump is typically a turbo-molecular or mechanical booster pump. 
     The vacuum pumping system  10  comprises a foreline vacuum line  20 , which can be any suitable conduit such as a pipe or hose, connecting the vacuum chamber  14  to the vacuum pumping arrangement  12  and the inlet of the secondary pump  18 . A further conduit  22  connects the exhaust of the secondary pump  18  to the inlet of the primary pump  16 . 
     The vacuum pumping system may further comprise an abatement apparatus  24  for removing noxious substances from the gas evacuated from the vacuum chamber  14 . A valve  26 , such as a bypass valve, diverts gas to a gas storage facility  28  during abatement apparatus downtime. 
     Gas exhausted from the process chamber  14  typically contains contaminants in addition to process gases. The contaminants may comprise particulates, such as silica; and/or liquid precursors, such as TEOS; or even cleaning materials. In the vacuum pumping system shown in  FIG. 4 , the vacuum chamber  104  is located above the vacuum pumping arrangement  102  and the duct  110  ducts gas in a generally downwards direction to the inlet of the vacuum pumping arrangement and through the arrangement to the exhaust line. A problem with this arrangement as discussed above is that contaminants tend to collect in the vacuum pumping arrangement causing damage or loss of efficiency. 
     In the present system as shown in  FIG. 1 , the vacuum pumping arrangement  12 , or at least the secondary pump  18 , pumps gas in a generally upwards direction. In the present example the secondary  18  and primary  16  pumps both pump gas in a generally upwards direction. Accordingly, contaminants do not typically enter the pumping arrangement as to do so they would be required to move against the force of gravity. 
     The inlet  30  to the vacuum pumping arrangement  12  is below the outlet  32  from the arrangement. In the example shown, the inlet is located directly beneath the outlet but it will be appreciated that provided the inlet is below the outlet with respect to gravity any contaminants in the vacuum pumping arrangement will tend towards the inlet  30 . The location of the inlet  30  towards a lower part of the vacuum pumping arrangement as shown means that flow along vacuum line  36  into the vacuum pumping arrangement is an in upwards direction thereby resisting the passage of contaminants into the arrangement. 
     It is preferred in the present system that both the primary and secondary pumps pump in an upwards directions and that respective inlets are lower than respective outlets from the pumps. However, if the most upstream pump pumps in an upwardly direction then depending on requirements such a system may be sufficient to resist the passage of contaminants into both pumps. 
     The vacuum line  20  is connected to the vacuum chamber and extends downwardly along section  34  to a location which is lower than the vacuum pumping arrangement  12 . The vacuum line  20  extends in a generally upwards direction along section  36  to the vacuum pumping arrangement  12 . Sections  34  and  36  are connected by a generally horizontal section  38 . This configuration of pipes provides a section  36  which is connected to the vacuum pumping arrangement  12  from beneath. That is, the section  36  of the vacuum line which is connected to the inlet extends in a generally upwards direction to the inlet so that the gravitational force on the contaminants is greater than the force on the contaminants exerted by the gas flow in an upwardly direction due to the pumping arrangement. Accordingly, contaminants are urged away from, and therefore prevented from reaching, the inlet  30 . Moreover, contaminants tend to be collected in the horizontal section  38  of the pipework and so do not tend to enter the vacuum pumping arrangement  12 . 
     Additionally, a trap  40  may be provided as shown, such as a filter, or cyclone, for trapping contaminants in the flow along the vacuum line  20 . The trap can be located at a relatively low access, near to or at floor level, allowing easy access for maintenance or replacement. This configuration constitutes an advantage over the prior art system in which a trap is located high above floor level and is therefore difficult to access and maintain. 
     In the example shown, the inlet  30  of the vacuum pumping arrangement  12  also constitutes the inlet of the secondary pump  18 . The outlet  42  of the secondary pump  18  is located generally above the inlet  30  so that gas is pumped through the pump in a generally upwards direction. The inlet  44  of the primary pump  16  is located above the outlet  42  of the secondary pump and the further foreline conduit  22  connects the inlet  44  and outlet  42  directing gas in a generally upwards direction. The outlet  32  of the vacuum pumping arrangement  12  constitutes an outlet from the primary pump  16 . The outlet  32  is generally above the inlet  44  so that gas is pumped through the primary pump  16  in a generally upwards direction. 
     In the prior art system  100 , an exhaust line  114  extends from the outlet of the vacuum pumping arrangement  102  to a valve  118 . The valve  118  requires a source of heat external to the vacuum pumping system to reduce condensation of substances in the valve. In the present vacuum pumping system  10 , the valve  26  is conveniently located on or closely adjacent the housing of the primary pump  16  such that it receives heat from the primary pump during use. Accordingly, the valve  26  does not require a source of heat external to the system and instead receives heat energy generated by an existing component of the system. This system allows a reduction in the cost and energy of running the system. The valve  26  may be formed integrally with pump  16  or may be connected to pump  16  by a short length of exhaust line. 
     The valve  26  which may be a by-pass valve connects the primary pump selectively to the abatement apparatus  24  or a customer storage facility  28 . 
     Existing vacuum pumping systems may comprise vacuum pumps having cartridge type vacuum pumping components such that the cartridge or cartridges can be removed, maintained and replaced. Such a cartridge type pump permits convenient retro-fitting of the system described with reference to  FIG. 1  on site to existing vacuum pumping systems. A cartridge type pump is shown in  FIGS. 2 and 3 . 
     Referring to  FIG. 2 , pump  50  comprises a cartridge type vacuum pumping mechanism comprising two cartridges  52 ,  54 . The vacuum pumping mechanism is connected to a drive shaft  56  which is driven by a motor  58  in a first direction of rotation for pumping gas from an inlet  60  to an outlet  62 . The pump comprises motor and gear box (not shown) housing  64  and end plate  66  together with end plates  68 ,  70 . In use, gas is pumped as shown by the arrows from inlet  60  at the top of the pump towards the right of the Figure and exhausted through the outlet  62  at the bottom of the pump. 
     A method of retro-fitting a vacuum pumping arrangement will now be described. The cartridges  52 ,  54  are removed, rotated through 180° and replaced as shown in  FIG. 3 . Components  64 ,  66 ,  68 ,  70  are maintained in the same position in  FIGS. 2 and 3 . As can be seen in  FIG. 3 , replacement of the cartridges relocates the inlet  60  and outlet  62  so that the inlet is at the bottom of the pump, the outlet  62  is at the top of the pump and gas is pumped in a generally upwards direction from the inlet to the outlet. Since the cartridges have been replaced in a rotated position, the motor is driven in an opposing, second, rotational direction to obtain the correct gas flow direction. It will be apparent to those skilled in the art that further minor modifications are required to the existing pump assembly. 
     As shown by the horizontal arrows in  FIG. 3 , the pumping mechanism pumps gas in a generally horizontal direction. However, the net flow of gas from the inlet to the outlet is in a generally upwards direction even though along some of the gas flow path through the pump may be horizontal or even in a downwardly direction. It will be appreciated however that location of the inlet at the bottom of the pump resists the passage of contaminants into the pump from the vacuum line extending from a vacuum processing chamber. 
     The net flow of gas in the present system is in an upwardly direction through the vacuum pumping arrangement  12 . 
     Although the subject matter has been described in language specific to structural features and/or methodological acts, it is to be understood that the subject matter defined in the appended claims is not necessarily limited to the specific features or acts described above. Rather, the specific features and acts described above are disclosed as example forms of implementing the claims.