Abstract:
A multi-chamber installation ( 1 ) treats objects under vacuum. An evacuation system ( 5 ) is connected to a plurality of chambers ( 2, 3, 4 ). To reduce the complexity of the evacuation process, a forepump ( 5 ) has several stages ( 11, 12, 13 ). Each of said stages is connected to one of the chambers ( 2, 3, 4 ).

Description:
BACKGROUND OF THE INVENTION 
   The invention relates to a multi-chamber installation for treating objects under vacuum, in which an evacuation system that is connected to the chambers. Moreover, the present invention relates to a method for evacuating said installation as well as an evacuation system therefor. 
   Multi-chamber installations of the aforementioned kind are known. They serve the purpose of degassing, coating (metallization, for example) or etching substrates. Known methods of this kind include chemical vapor deposition (CVD). and processes for producing digital video disks (DVDs). Commonly, such an installation is equipped with a process chamber, with one or several pre-chambers with load lock function being located upstream. The load locks are opened for the period of time while introducing or removing substrates, so that high pressure variations occur differing from chamber to chamber. 
   In the instance of a multi-chamber installation equipped with two chambers, it is known to employ two separate vacuum pumps in order to be able to evacuate as rapidly as possible each of the chambers after closing the corresponding load lock. 
   It is the task of the present invention to reduce in the instance of multi-chamber installations of the aforementioned kind or similar kind, the complexity for the evacuation system. 
   SUMMARY OF THE INVENTION 
   This task is solved by the present invention through the characteristic features of the patent claims. 
   In that each of the stages is equipped with an inlet and in that each of the inlets is connected to one of the chambers, now only one vacuum pump is required in order to produce the desired pressures—be they approximately the same or also different—in the different chambers as rapidly as possible and maintain these. Several pumps each with a drive motor are no longer required. Also installation complexity—both mechanical and also electrical—is reduced. Preferably the pump stages are operated in parallel so that they have the function of two independent vacuum pumps. 
   An exemplary oil-sealed rotary vane forevacuum pump is illustrated in U.S. Pat. No. 5,156,532. 
   Typical forevacuum pumps are oil-sealed rotary vane pumps as they are known, for example, from DE-U-90 07 544. 
   Further advantages and details of the present invention shall be explained with reference to the examples of embodiments depicted schematically in drawing  FIGS. 1 to 4 . 

   
     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  depicts a multi-chamber installation with three chambers and a three stage forevacuum pump, 
       FIG. 2  depicts a multi-chamber installation with two vacuum chambers and a two-stage forevacuum pump, 
       FIG. 3  depicts a multi-chamber installation according to drawing  FIG. 2  with an additional high vacum pump, and 
       FIG. 4  depicts a sectional view through a two-stage forevacum pump. 
   

   DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENTS 
   In the drawing figures, the multi-chamber installation is generally designated as  1 , the chambers with  2 ,  3  and  4 , and the evacuation system with  5 . In the instance of the chambers  2  to  4 , these each include a process chamber  2 , to which further chambers  3 ,  4 , (in drawing  FIG. 1 ) or only  4  (in drawing  FIG. 2 ,  3 ) are associated. Slotted load locks are schematically depicted and designated as  6 ,  7 , and  8 . The evacuation system  5  is designed as a multi-stage forevacuum pump. 
   In the example of the embodiment in accordance with drawing  FIG. 1 , three chambers  2 ,  3 ,  4  are present. Correspondingly, the forevacuum pump  5  has three stages  11 ,  12 ,  13  each with one inlet  14 ,  15 , respectively  16 . Each of the inlets  14 ,  15 ,  16  is connected via one each connecting line  17 ,  18 , respectively in  19  to one of the chambers  2 ,  3 ,  4 . The outlets  20 ,  21 ,  22  of the pump stages  11 ,  12 ,  13  open out within the pump  5  into a joint discharge line, so that the pump  5  has only one outlet  23 . In the instance of the pumping stages  11 ,  12 ,  13  having different pumping capacities, it is then expedient to connect the stage with the highest pumping capacity to the process chamber  2 , so that there sufficiently low pressures are attainable as rapidly as possible. 
   In the embodiment according to drawing  FIG. 2 , only two chambers  2 ,  4  and correspondingly two pump stages  11 ,  13  are provided. Located in the connecting lines  17  and  19  are valves  24  and  25  in order to separate from the evacuation system  5  one or both chambers  2 ,  4  in case these are vented. 
   In the embodiment according to drawing  FIG. 3 , there is located in the connecting line  17  a turbomolecular vacuum pump  26  and—on its delivery side—a valve  27 . High vacuum pumps of this kind excel through higher pumping capacities and lower ultimate pressures compared to forevacuum pumps, however, they require a forevacuum pump which in the instance of the case presented, forms the pumping stage  11 . This embodiment is expedient for processes being performed in the process chamber  2  in which relatively low pressures (10 −2  mbar, for example) shall be attained as rapidly as possible. Forevacuum pumps are also capable of attaining ultimate pressures of approximately 1 mbar to 5×10 −2  mbar; however, through the utilisation of high vacuum pumps it is possible to attain even lower pressures significantly faster. 
   Drawing  FIG. 4  depicts a partial sectional view through a commercial two-stage forevacuum pump  5  which has been modified for utilisation in a multi-chamber installation. Said forevacuum pump is equipped with an outer casing  28  with an oil sump  29 . Accommodated in the outer casing  28  is the actual pump  31 , a rotary vane vacuum pump  31  with two stages  11  and  13 . It comprises three discs  32 ,  33 ,  34  with pump rings  35 ,  36  accommodated in between. The pump rings  35 ,  36  form of the pump chambers  37 ,  38 , in which there is located one each eccentrically arranged rotor  41 , respectively  42  with its vanes  43 , respectively  44 . The rotor  42  is linked to the shaft  45  of a drive motor not depicted. Moreover, the bearing stubs of the rotors  41 ,  42  are linked to each other in the area of the disk  33 . The diameter of the rotors  41 ,  42  is equal, their lengths are different. Thus there result for the two pump stages  11 ,  13  different pumping capacities. When employing the presented pump as a two-stage vacuum pump with series connected pump stages  11 ,  13 , the longer pump stage forms the inlet pump stage and the shorter one the delivery pump stage. 
   The pump  5  presented has been modified such that the pump stages  11 ,  13  may be operated in parallel. The inlet equipped with an anti-suck back valve  46  which is present in any case in pumping stage  11  serves as inlet  14 . The outlet of pumping stage  11 , not depicted in detail, is no longer linked to the inlet of the pumping stage  13 , but instead opens out below the felt hat  47 . The pumping stage  13  has been equipped with an independent intake port  48  forming the inlet  16 . The intake port  48  is linked via pipe section  49  run out of the casing  28  to the pump chamber  37 . The not depicted outlet of this pumping stage  13  also opens out under the felt hat  47 . The felt hat  47  serves the purpose of calming down the flow and coarsely separating the oil. Further separators which need to be connected to the outlets  23  need, compared to the state-of-the-art, to be present only once. 
   The invention has been described with reference to the preferred embodiments. Modifications and alterations may occur to others upon reading and understanding the preceding detailed description. It is intended that the invention be constructed as including all such modifications and alterations insofar as they come within the scope of the appended claims or the eqiuivalents thereof.