Abstract:
A vacuum exhaust system can improve the operating efficiency of the vacuum exhaust system while reducing the system cost, to quickly attain a vacuum in the auxiliary chambers without increasing the size of the vacuum pumps. The vacuum exhaust system comprises a first pumping section and a second pumping section disposed downstream of and in series with the first pumping section. A main exhaust passage is provided to communicate a main chamber with a suction port of the first pumping section, and an auxiliary exhaust passage is provided to communicate an auxiliary chamber with a suction port of the second pumping section.

Description:
BACKGROUND OF THE INVENTION  
         [0001]    1. Field of the Invention  
           [0002]    The present invention relates to a vacuum exhaust system for use in evacuating a processing chamber for advanced products such as semiconductor devices, for example.  
           [0003]    2. Description of the Related Art  
           [0004]    A conventional arrangement of a vacuum exhaust system used in semiconductor device manufacturing processes to evacuate a processing chamber for carrying out such process as etching and chemical vapor deposition (CVD) of semiconductor wafers is shown in FIG. 8. A main chamber (processing chamber)  10  is connected on both sides to auxiliary chambers (load lock chambers)  12   a ,  12   b , for loading and unloading purposes through respective gates  14 . Each auxiliary chamber  12   a ,  12   b  is isolated from or open to the external environment by a gate  15 .  
           [0005]    The main chamber  10  is connected to a vacuum pump  18  through an exhaust path  16  having a valve  20 , and each auxiliary chamber  12   a ,  12   b  is connected similarly to a vacuum pump  24  through an exhaust path  22  having a valve  26 . It has been customary to use rotary oil pumps for the vacuum pumps  18 ,  24 , but lately, dry pumps are used primarily for this type of work.  
           [0006]    In this type of apparatus, in order to access the main chamber  10  while it is under vacuum, loading or unloading of a workpiece into the main chamber  10  requires that an auxiliary chamber  12  be evacuated first, and the gate  14  opened next so as to avoid exposing the main chamber  10  to external atmosphere. This is done to prevent the main chamber  10  and associated piping from contamination as well as to improve productivity by shortening the time for re-starting.  
           [0007]    In such conventional systems, a vacuum pump is provided for each chamber to evacuate individual chambers, therefore, working efficiency of each vacuum pumps is low. If the number of main chambers  10  is increased in an effort to raise productivity, it leads to a problem that the number of vacuum pumps need to be increased, leading ultimately to a large size facility and higher running costs. If an attempt is made to shorten the time for evacuating the auxiliary chambers, a higher capacity for each pump is required, thus aggravating the above problems even further.  
         SUMMARY OF THE INVENTION  
         [0008]    It is an object of the present invention to provide a vacuum exhaust system to enable as much sharing of vacuum pumps as possible, to improve the operating efficiency of the vacuum exhaust system while reducing the system cost, or to quickly attain a vacuum in the auxiliary chambers without increasing the size of the vacuum pumps.  
           [0009]    The object has been achieved in a vacuum exhaust system for evacuating a main chamber and at least one associated auxiliary chamber comprising: a first pumping section; a second pumping section disposed downstream of and in series with the first pumping section; a main exhaust passage communicating the main chamber with a suction port of the first pumping section; at least one auxiliary exhaust passage communicating the auxiliary chamber with a suction port of the second pumping section.  
           [0010]    Accordingly, the main chamber can be evacuated with two pumping sections arranged in series, and the auxiliary chambers are evacuated with one of the pumping sections, thereby increasing the operating efficiency of each pumping section while keeping the capacity of each pump as small as practicable.  
           [0011]    The first and second pumping sections may share a common drive motor. Accordingly, one multi-stage vacuum pump can manage the task of evacuating an entire processing system so that the number of vacuum pumps can be reduced compared with a case of providing a vacuum pump for each auxiliary chamber. However, the first pumping section and the second pumping section may be provided with individual drive sections.  
           [0012]    The pumping sections may be controlled so as to obtain a minimum fluctuation in pressure, according to a pressure measured inside the main chamber. Accordingly, pressure changes can be held to a minimum in the main chamber which is an important chamber for processing advanced products such as semiconductor devices.  
           [0013]    Another aspect of the invention is a vacuum exhaust system for evacuating a main chamber and a plurality of associated auxiliary chambers, the plurality of auxiliary chambers having a connecting passage connecting each other which can be opened or closed to equalize pressure in the auxiliary chambers. Accordingly, vacuum environment present inside an auxiliary chambers can be utilized to lower the pressure of another auxiliary chamber which may be at an atmospheric pressure so that evacuation time can be significantly reduced to improve the operating efficiency of the overall evacuation operation.  
       
    
    
     BRIEF DESCRIPTION OF THE DRAWINGS  
       [0014]    [0014]FIG. 1 is a schematic diagram of a first embodiment of the vacuum exhaust system of the present invention;  
         [0015]    [0015]FIG. 2 is a time-chart showing the control steps for the first system shown in FIG. 1;  
         [0016]    [0016]FIG. 3 is a schematic diagram of a variation of the first system;  
         [0017]    [0017]FIG. 4 is a schematic diagram of another embodiment of the vacuum exhaust system of the present invention;  
         [0018]    [0018]FIG. 5 is a time-chart showing the control steps for the second system shown in FIG. 4;  
         [0019]    [0019]FIG. 6 is a variation of the second system;  
         [0020]    [0020]FIG. 7 is a schematic diagram of a third embodiment of the vacuum exhaust system of the present invention; and  
         [0021]    [0021]FIG. 8 is a schematic diagram of a conventional vacuum exhaust system.  
     
    
     DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENTS  
       [0022]    Preferred embodiments will be presented in the following with reference to the drawings.  
         [0023]    [0023]FIGS. 1 and 2 relate to a first embodiment of the vacuum exhaust system of the present invention, which includes, as in the conventional systems, a main chamber  10  for carrying out processes such as etching and CVD of semiconductor wafers. An auxiliary chamber  12   a  is attached, through a gate  14   a , to the main chamber  10  on the loading-side, and an auxiliary chamber  12   b  is attached, through a gate  14   b , to the main chamber  10  on the unloading-side. Each of the auxiliary chambers  12   a ,  12   b  is isolated from and connected to the outside atmosphere through respective gates  15   a ,  15   b.    
         [0024]    To exhaust three chambers  10 ,  12   a ,  12   b , one two-stage pump  34  is used. The two-stage pump  34  has a first pumping section  30   a  on the upstream side, and a second pumping section  30   b  on the downstream side. The pumping sections  30   a ,  30   b  share a common shaft connected to a variable-speed motor  32 . The two-stage pump  34  is provided with a suction port  34   a , and an exhaust port  34   b , and an intermediate port  34   c  opening at a location between the pumping section  30   a ,  30   b . The exhaust passage  16  for the main chamber  10  is connected through a valve  20  to the suction port  34   a , and the exhaust passages  22   a ,  22   b , respectively, for auxiliary chambers  12   a ,  12   b , are connected though respective valves  26   a ,  26   b  to the intermediate port  34   c.    
         [0025]    As shown in FIG. 2, performance of the two-stage pump  34  is designed so as to enable exhaustion of the main chamber  10  at a first rotation speed n 1 , and to enable exhaustion of the main chamber  10  and one of the auxiliary chamber  12   a ,  12   b  concurrently at a second rotation speed n 2  which is larger than n 1 . This exhaustion system is provided with a control section  38  to control the operating parameters such as on/off and rotational speed for the variable speed motor  32  according to output signal from a pressure sensor  36  provided inside the main chamber  10 . Speed control can be effected by following a certain pre-selected pattern in sequence or by feedback control to follow signals output from the sensor  36 .  
         [0026]    Operation of the vacuum exhaust system in first embodiment will be explained with reference to FIG. 2 showing the time-sequence of a processing workpiece. First, the gate  15   a  is opened to load the workpiece into the auxiliary chamber  12   a , and the gate  15   a  is closed. Next, valves  26   a ,  20  are opened and the pump  34  is operated at the higher second speed n 2 , and the rotation speed is gradually reduced back to the first speed n 1  during a time interval (t 1 -t 2 ) so that the auxiliary chamber  12   a  and the main chamber  10  are both evacuated. After the main chamber  10  reaches a required pressure, workpiece processing operation can be started.  
         [0027]    While the processing is proceeding in the main chamber  10 , the auxiliary chamber  12   b  will also be evacuated. The pump  34  is operated at the higher second speed n 2  and the rotation speed is gradually reduced back to the first speed n 1  during a time interval (t 2 -t 3 ). After the auxiliary chamber  12   b  is exhausted, the pump  34  is operated at the first speed n 1  to complete the processing in the main chamber  10  during a time interval (t 3 -t 4 ).  
         [0028]    Next, the gate  14   b  is opened to unload the processed workpiece from the main chamber  10  to the auxiliary chamber  12   b  at time t 4 . During the processing interval in the main chamber  10 , a new workpiece is placed inside the auxiliary chamber  12   b  by opening the gate  15   a , so that the interior pressure is at an atmospheric pressure. At this point, the steps from time t 1  are repeated. In the meantime, the gate  15   b  is opened to remove the processed workpiece from inside the auxiliary chamber  12   b.    
         [0029]    By following the steps described above, the embodied exhaustion system enables to operate the system with one pump by suitably switching the evacuation process among the main chamber and the auxiliary chambers thereby reliably maintaining the required load locking functions. And since the emphasis is placed on exhausting the main chamber by using a multi-stage pump, lowering of gas exhausting capability of the main chamber is avoided.  
         [0030]    In the above case, although the rotation speed was controlled sequentially according to a pre-determined pattern, it is permissible to use a feedback control according to signals output from a pressure sensor  36 . When valves  26   a ,  20  are opened to evacuate the auxiliary chamber  12   a  and the main chamber  10 , opening of the valve  26   a  causes the pressure in the mid-chamber  35  of the pump  34  to increase, and the pump capacity is lowered so that the interior pressure in the main chamber  10  is also increased. To avoid such critical pressure fluctuation in the main chamber  10 , the interior pressure can be monitored by a pressure sensor  36  so as to control the rotation-speed of the pump  34  at a speed between the second speed n 2  and the first speed n 1 .  
         [0031]    [0031]FIG. 3 shows a variation of the first embodiment, which uses two individual pumps connected in series. A first stage booster pump  42  is connected in series with a second stage main pump  46 . Each pump is driven by separate variable speed motors  40 ,  44 , whose speeds can be controlled separately by a control section  38 .  
         [0032]    The exhaust passage  16  of the main chamber  10  is connected through a valve  20  to a suction port  42   a  of the booster pump  42 , and the exhaust port of booster pump  42  and the suction port of main pump  46  are connected through a connecting pipe  50  having an intermediate port  52 . The exhaust passages  22   a ,  22   b  of the auxiliary chambers  12   a ,  12   b  are connected through the valves  26   a ,  26   b  to the intermediate port  52 . Operational characteristics of this embodiment system are the same as those in the first case, and their explanations will be omitted.  
         [0033]    In this example also, the rotation speed of the pump can be feedback controlled using the output signals from a pressure sensor  36 . In this example, rotation speed of main pump  46  and booster pump  42  can be controlled independently to enable more precise control of the pressure.  
         [0034]    [0034]FIG. 4 is a schematic diagram of another embodiment of the vacuum exhaust system. This system includes: a connecting passage  60  to connect both auxiliary chambers  12   a ,  12   b  shown in FIG. 1 to equalize the vacuum pressure; and a valve  62  for opening or closing the connecting passage  60 . The valve  62  is controlled by a control section  38  to open in advance when either the auxiliary chamber  12   a  or  12   b  is exhausted.  
         [0035]    The embodied vacuum exhaust system is used, for example, when exhausting the auxiliary chamber  12   a  after it has been loaded with a workpiece so that it is at an atmospheric pressure, in a way that the valve  62  is opened before the valve  26   a  is opened to evacuate with the multi-stage pump  34  (at time t 5 ). At this time, the auxiliary chamber  12   b  has a processed workpiece passed from the main chamber so that its interior pressure is maintained at some low pressure. Therefore, by opening the valve  62 , air flows from the auxiliary chamber  12   a  to auxiliary chamber  12   b  so that both chambers attain a common pressure intermediate between an atmospheric pressure and vacuum.  
         [0036]    After this stage, valve  62  is closed, and as in FIG. 1, pump  34  is operated at a higher second speed n 2  (at time t 6 ) to exhaust both auxiliary chamber  12   a  and main chamber  10 . In this case, because the initial pressure in the auxiliary chamber is less than an atmospheric pressure, the length of time required to exhaust the auxiliary chamber is reduced compared with the system shown in FIG. 1. In the auxiliary chamber  12   b , gate  15   b  is opened and the processed workpiece is withdrawn. This system thus allows to utilize the reduced-pressure environment of the auxiliary chamber  12   b , which is normally discarded to waste, to shorten the evacuation time of the auxiliary chamber  12   a . This feature further contributes to increasing the operating efficiency of the overall vacuum exhaust system.  
         [0037]    Similarly, when exhausting the auxiliary chamber  12   b , valve  62  is first opened temporarily (time t 7 ) to introduce the vacuum environment in the auxiliary chamber  12   a  before an unprocessed workpiece has been loaded into the auxiliary chamber  12   b  (time t 7 -t 8 ) so that auxiliary chamber  12   b  can be reduced in pressure, and then the multi-stage pump  34  is operated at a fast speed. Thus, the exhaustion time for the auxiliary chamber  12   b  can be shortened.  
         [0038]    [0038]FIG. 6 shows a variation of the system shown in FIG. 4. This system is based on the variation based on the third embodiment shown in FIG. 3, and includes a connecting path  60  and a valve  62  which is designed to be opened before evacuating either of the auxiliary chamber  12   a  or  12   b.    
         [0039]    [0039]FIG. 7 shows a third embodiment, and includes auxiliary chambers  12   a ,  12   b  having dedicated exhaust passages  22   a ,  22   b , provided with respective vacuum pump  24   a ,  24   b  respectively, connected with connecting passage  60 , and within the connecting passage  60 , a valve  62  which is designed to open prior to evacuating either auxiliary chamber  12   a  or  12   b . This system also enables to utilize waste vacuum, as in the systems shown in FIGS. 3 and 6, to shorten the exhaustion time required to evacuate the auxiliary chambers  12   a ,  12   b.