Vacuum pumping system

Abstract

The present invention relates to a vacuum pumping system ( 10 ) for evacuating a vacuum chamber ( 12 ), the system comprising: a vacuum pump ( 16 ); and a plurality of forelines ( 22, 24 ) for conveying gas to the vacuum pump wherein in a first low vacuum stage of chamber evacuation a first foreline arrangement ( 22 ) can be connected for conveying gas to the vacuum pump and in a second higher vacuum stage of chamber evacuation a second foreline arrangement ( 22, 24 ) comprising one or more of said forelines can be connected for conveying gas to the vacuum pump, wherein the second foreline arrangement has a total cross-sectional area for conveying fluid which is larger than a total cross-sectional area of the first foreline arrangement.

1 . A vacuum pumping system for evacuating a vacuum chamber, the system comprising: a vacuum pump; and a plurality of forelines for conveying gas to the vacuum pump wherein in a first low vacuum stage of chamber evacuation a first foreline arrangement can be connected for conveying gas to the vacuum pump and in a second higher vacuum stage of chamber evacuation a second foreline arrangement comprising one or more of said forelines can be connected for conveying gas to the vacuum pump, wherein the second foreline arrangement has a total cross-sectional area for conveying fluid which is larger than a total cross-sectional area of the first foreline arrangement. 
     
     
         2 . A vacuum pumping system as claimed in  claim 1 , wherein at least one of said forelines in said second foreline arrangement is isolated from the first foreline arrangement during said relatively low vacuum stage of chamber evacuation. 
     
     
         3 . A vacuum pumping system as claimed in  claim 1  or  2 , wherein said second foreline arrangement comprises one or more of said forelines of said first foreline arrangement. 
     
     
         4 . A vacuum pumping system as claimed in  claim 3 , wherein said second foreline arrangement comprises said plurality of forelines. 
     
     
         5 . A vacuum pumping system as claimed in any one of the preceding claims, wherein said first foreline arrangement comprises a first foreline and said second foreline arrangement comprises said first foreline and a second foreline. 
     
     
         6 . A vacuum pumping system as claimed in  claim 5 , wherein said first foreline has a first cross-sectional area which is smaller than the cross-sectional area of the second foreline. 
     
     
         7 . A vacuum pumping system as claimed in  claim 6 , wherein said first foreline has a cross-sectional area in the range of 10 4  to 10 5  mm 2  and said second foreline has a cross-sectional area in the range of 10 5  to 10 6  mm 2 . 
     
     
         8 . A vacuum pumping system as claimed in any one of the preceding claims, comprising a control unit configured for selecting said first foreline arrangement for conveying gas to said vacuum pump during said first relatively low vacuum stage of chamber evacuation and selecting said second foreline arrangement for conveying gas to said vacuum pump when said pressure is reduced below a predetermined pressure or at a predetermined time from commencement of chamber of evacuation. 
     
     
         9 . A vacuum pumping system as claimed in  claim 8 , wherein said predetermined pressure is in the range of 0.1 mbar to 10 mbar. 
     
     
         10 . A vacuum pumping system as claimed in  claim 8  or  9 , wherein said control unit is operably connected to at least one valve for controlling the flow of gas through the first foreline arrangement or the second foreline arrangement according to a control signal received from the control unit. 
     
     
         11 . A vacuum pumping system as claimed in  claim 10 , comprising a first valve upstream of the second foreline and a second valve downstream of the second foreline for isolating the second foreline from the vacuum pumping system. 
     
     
         12 . A vacuum pumping system as claimed in any one of  claims 8  to  11 , wherein said control unit is operably connected to receive a pressure signal from a pressure sensor for sensing a pressure in the vacuum pumping system, wherein said control unit is configured to output a control signal when said pressure signal indicates a reduction of pressure in said system below a predetermined amount. 
     
     
         13 . A vacuum pumping system as claimed in any preceding claim, wherein said first foreline arrangement has a volume which is at least an order of magnitude less than the volume of the vacuum chamber and the second foreline arrangement has a volume which is of the same order of magnitude or greater than the volume of the vacuum chamber. 
     
     
         14 . A vacuum pumping system as claimed in any one of the preceding claims, wherein the total cross-sectional area of the second foreline arrangement is sized so that speed of evacuation is limited by a pumping speed of the vacuum pump and not by the conductance of the second foreline arrangement. 
     
     
         15 . A vacuum pumping system as claimed in any one of the preceding claims, wherein the vacuum pump is connected by one or both foreline arrangements are connected to a second vacuum pump which is connected to the vacuum chamber. 
     
     
         16 . A method of evacuating a vacuum chamber, the method comprising: connecting a first foreline arrangement for conveying fluid to a vacuum pump and evacuating gas through the first foreline arrangement in a first relatively low vacuum stage of chamber evacuation; and connecting a second foreline arrangement for conveying gas to the vacuum pump and evacuating gas through the second foreline arrangement in a second higher vacuum stage of chamber evacuation, wherein the second foreline arrangement has a total cross-sectional area which is larger than the total cross-sectional area of the first foreline arrangement.