Abstract:
A gate valve useful for pumping a high-vacuum processing chamber. The valve housing includes a first port for attachment to the vacuum chamber and a second port on the opposed wall and aligned with the first port for the external mounting of a pneumatic or other actuator having a shaft supporting on its end a valve gate plate within the housing. An expandable bellows sealed between the gate plate and the actuator surrounds shaft. The actuator can press the valve plate against a valve seat around the first port to close the valve or withdraw the plate to the opposed wall to provide high pumping conductance. A third port in the housing disposed from the valve is connected to the high-vacuum pump. The gate plate may be water cooled through channels in the shaft. An auxiliary vacuum pump, such as a cryo pump, may be placed inside the valve housing.

Description:
RELATED APPLICATION 
     This application claims benefit of provisional application 61/460,077, filed Dec. 27, 2010. 
    
    
     FIELD OF THE INVENTION 
     The invention relates generally to valves. In particular, the invention relates to gate valves for high-vacuum pumping of processing chambers. 
     BACKGROUND ART 
     Similarly to many types of substrate processing, the formation of semiconductor integrated circuits often involves the processing of wafers or other substrates in a vacuum chamber. As schematically illustrated in the cross-sectional view of  FIG. 1 , an example processing system  10  includes a vacuum chamber  12  accommodating a pedestal  14  for supporting a substrate  16  inserted into the vacuum chamber  12  through a selectively opened valve or load/lock chamber  18 . Processing gas is metered into the vacuum chamber  12  through a gas inlet  20 , which may be in the form of a showerhead overlying the pedestal  14 . A high-vacuum pump  22  connected to the vacuum chamber  12  through a pump port  24  pumps the vacuum chamber  12  and exhausts spent processing gas. 
     Such a processing system  10  may be used for etching, chemical vapor deposition (CVD), or sputtering (physical vapor deposition, PVD) depending on the choice of the processing gas and chamber configuration. For thermal processes, the pedestal  14  may be resistively heated to several hundred degrees centigrade to activate the chemical process. For plasma processes, the processing gas may be electrically excited into a plasma for activating the processes. Plasma processes generally involve lower temperatures but the plasma itself can generate heat. Plasma etching and plasma-enhanced CVD generally require that the chamber be background pumped of impurities to a high vacuum in the range of up to about 10 −6  Torr. Such a processing system  10  may also be adapted to plasma sputtering in which an argon plasma sputters deposition material from a target placed in opposition to the pedestal  14 . Plasma sputtering generally requires background pumping to an ultra-high vacuum of 10 −9  Torr to prevent oxidation of the sputtered material. The vacuum pump  22  may be implemented as a turbo pump for a high vacuum. Although not illustrated, one or more mechanical low-vacuum pumps limited to about 10 −3  Torr of pumped vacuum are usually used to pre-pump the vacuum chamber  12 , to pump the load/lock chamber  18 , and to back-pump the high-vacuum pump  22 . 
     A gate valve  30  is interposed between the pump port  24  and the high-vacuum pump  22  to selectively isolate the vacuum chamber  12  from the high-vacuum pump  22 . In the conventional design of  FIG. 1 , the high-vacuum pump  22  directly underlies the pump port  24  on the same vertical pumping axis. Corresponding apertures in opposed sides of a valve body  32  on the same pumping axis are vacuum sealed respectively to a flange  34  of the vacuum chamber  12  and to the high-vacuum pump  22  to allow direct vertical pumping of the vacuum chamber  12 . A gate trolley  36  is rollably supported within the valve body  32  on bearings  38  to allow it to move horizontally, that is, perpendicularly to the pumping axis. An air cylinder  40  mechanically moves a shaft  42  which is fixed to a base plate  44  of the gate trolley  36  to move it along the horizontal axis. A gate plate  48  is mechanically coupled to the base plate  44  through toggle links  50  and is biased toward the base plate  44  by a tension spring  46 . 
     A gate valve  30  is interposed between the pump port  24  and the high-vacuum pump  22  to selectively isolate the vacuum chamber  12  from the high-vacuum pump  22 . In the conventional design of  FIG. 1 , the high-vacuum pump  22  directly underlies the pump port  24  on the same vertical pumping axis. Corresponding apertures in opposed sides of in a valve body  32  on the same pumping axis are vacuum sealed respectively to a flange  34  of the vacuum chamber  12  and to the high-vacuum pump  22  to allow direct vertical pumping of the vacuum chamber  12 . A gate trolley  36  is rollably supported within the valve body  32  on bearings  38  to allow it to move horizontally, that is, perpendicularly to the pumping axis. An air cylinder  40  mechanically moves a shaft  42  which is fixed to a base plate  44  of the gate trolley  36  to move it along the horizontal axis. A gate plate  48  is mechanically coupled to the base plate  44  through toggle links  50  and is biased toward the base plate  44  by a tension spring  46 . 
     A distal end  52  of the gate plate  48  extends beyond that of the base plate  44 . However, when the air cylinder  40  pushes the base plate  44  of the gate trolley  36  to the closed position (illustrated on the right) adjacent the pump port  24 , the distal end  52  encounters a stop in the valve body  32  and causes the gate plate  48  to rise and seal the pump port  24 , thus closing the gate valve  30 . When the air cylinder  40  retracts its shaft  42 , the gate plate  48  moves away from the stop, the tension spring  36  lowers the gate plate  48 , and the gate trolley  36  moves to the open position (illustrated on the left) away from the pump port  24 . 
     This conventional design includes mechanical elements suffering from friction and wear. High impact force is required to convert the horizontal motion to vertical sealing, that is, two axis of motion, creating shock waves, vibration, and backlash. The guide bearings tend to fail from high stress and chemical deposits. Preventive maintenance is complex. In the case of a high-temperature environment, thermal expansion can cause binding and accelerated wear. 
     In U.S. Pat. No. 7,731,151, I have disclosed a pendulum valve with an expandable gate which can be used in the configuration of  FIG. 1 . However, this pendulum valve requires two actuators and includes many mechanical parts and seals. 
     SUMMARY OF THE INVENTION 
     One aspect of the invention is a vacuum gate valve having a gate plate supported on and fixed to an axially movable shaft and a sealing surface on a side of the gate plate opposite the shaft to engage and seal to a corresponding surface, for example, an O-ring in the gate plate engaging a valve seat in the valve housing. 
     Another aspect of the invention includes a vacuum substrate processing chamber having a valve body sealed to a chamber wall around a pumping aperture. An actuator protruding from a valve body wall opposite the pumping aperture projects into the valve body an axially movable shaft supporting a gate plate. The gate plate supported on the shaft is movable to seal the pumping aperture on its side opposite the shaft, thus closing the valve, or to withdraw the gate plate to near the valve body opposite the pumping aperture, thus opening the valve. An expandable bellows encloses the shaft inside the valve body and has ends vacuum sealed to the gate plate and the actuator or associated wall of the valve body. A vacuum pump, especially a high-vacuum pump such as a turbo pump, is sealed to another aperture in a wall of the valve body. A low-vacuum pump may be connectable through another port in the pump valve body. 
     The actuator may be pneumatic, motorized mechanical, such as a ball-screw drive, or manual. 
     An auxiliary pump, for example, a cryo pump or a getter pump, may be disposed inside the valve body. 
    
    
     
       BRIEF DESCRIPTION OF THE DRAWINGS 
         FIG. 1  is a schematic cross-sectional view of a vacuum processing chamber and a conventional vacuum gate valve. 
         FIG. 2  is a schematic side cross-sectional view of a vacuum processing chamber and a vacuum gate valve according to one embodiment of the invention. 
         FIG. 3  is a side cross-sectional view of a valve actuator including coolant lines in the valve shaft supporting a substrate pedestal. 
         FIG. 4  is a top cross-sectional view of the pedestal of  FIG. 3  taken along section line  4 - 4  and including a cooling channel. 
         FIG. 5  is a side cross-sectional view of a vacuum processing chamber and a gate valve of the invention including two features of a mechanical drive and an auxiliary vacuum pump. 
     
    
    
     DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENTS 
     One embodiment of a processing system  60  of the invention, illustrated in the cross-sectional view of  FIG. 2 , includes a gate valve  62  having a gate plate  64  which is vertically moved within a valve housing  66  between the illustrated sealed position adjacent the pump port  24  and an open position closely adjacent the bottom of the valve body  66 . The gate plate  64  is supported on the top of a shaft  67  fixed to the gate plate  64  through a detachable mount  68  The bottom of the shaft  67  is vertically moved by an actuator, such as a pneumatic cylinder  70 , in which the shaft  67  is fixed to a piston  72  vertically movable in but pressure sealed to sides of a piston cylinder  74  of the air cylinder  70 . The top of the air cylinder  70  is vacuum sealed through a removable collar  75  around an aperture  76  in the bottom wall of the valve body  66  underlying the pump port  24 . Preferably, the shaft  67  penetrates the upper wall of the air cylinder  70  through a sliding seal, such as an O-ring  77 , which only needs to stand off pneumatic and atmospheric pressures Gas inlets  78 ,  80  are positioned respectively above and below the range limits of the piston  72  and communicate with two air spaces separated by the piston  72 . Pressure sources selectively connected to the gas inlets  78 ,  80  can pneumatically vertically move the shaft  67  and hence the gate plate  64  between the open and closed positions. In one type of pneumatic operation, positive pressure applied through the bottom inlet  80  and atmospheric pressure admitted to the upper inlet  78  will move the shaft  67  upward to seal the valve plate  64  to a valve seat in the upper wall of the valve body  66  and thus close the gate valve  62  while the opposite set of pressure conditions will move the shaft  67  downward to place the valve plate  64  near the bottom of the valve body  66  and thus open the gate valve  62  and leave a wide pumping cross section. 
     The pneumatic force is continued while the gate plate  64  is in the closed position so as to slightly compress a ring seal  82  between the gate plate  64  and a sealing surface or valve seat of the valve body  66  surrounding an aperture  84  in the upper wall of the valve body  66  juxtaposed to and aligned with the pump port  24 . The ring seal  82 , which may be elastomeric, e.g., an O-ring, or a soft metal ring, may be captured in an O-ring groove or similar structure in the periphery of the gate plate  64  or in the valve body  66 . It is understood that the valve seat against which the ring seal  82  engages could be located on the flange  34  with a sufficiently large aperture  84  in the top wall to allow passage of the valve plate  64 . In this case, the flange  34  can be considered part of the top wall of the valve body  66 . Preferably, the gate plate  64  and upper wall aperture  84  are circular for ease of fabrication and ready alignment but other shapes are possible. The gate plate  64  preferably includes a planar annular periphery except for the O-ring groove but its central area may be non-planar as long as it provides a vacuum wall. The shaft  67  of the gate valve  62  acts as the stem and the gate plate  64  as the head of a modified poppet valve having its sealing surface on the opposite side of the head from the stem. 
     An expandable bellows  86  encloses the shaft  67  and its two ends are vacuum sealed to the mechanical mount  68  on the gate plate  64  and to the top wall of the air cylinder  70 , for example, by welding, to isolate the shaft  67  and the piston cylinder  72  from the vacuum within the valve body  66 . The pressure inside the bellows  86  may be atmospheric or even slightly pressurized. It is possible to mount the bellows  86  to the collar  75  or inside the valve body  66  with only the shaft  67  extending through the aperture  76  in the bottom wall of the valve body  66 . An optional relief passage  87  (see  FIG. 3 ) in the top wall of the air cylinder  70  connects the interior of the bellows  86  to atmosphere and the O-ring  77  slidably seals the shaft  67  to the top wall of the air cylinder  70 . 
     The high-vacuum pump  22  is sealed around a pump aperture  88  in the valve body  66 . In the illustrated embodiment, the pump aperture  88  is horizontally displaced from the pump port  24  and the gate valve  62 , that is, from the opposed apertures  76 ,  84  in the valve body  66 . Preferably, the cross section of the valve body  66  between the pump port  24  and the pump aperture  88  is at least as large as the cross section of the pump port  24  and its wall aperture  84  and of the pump aperture  88  in order to decrease the gas flow impedance degrading high-vacuum pumping. The reduced impedance also depends on the valve plate  64  being withdrawn close enough to the bottom of the valve body  66  that there is a similarly large horizontal cross section between the top of the withdrawn gate plate  64  and the top wall of the valve body  66 . The movement of the gate valve  62  is completely vertical and involves no rubbing engagement in the valve body  66  aside from the O-ring seals, thereby reducing particulates. The valve body  66  can be rough pumped through a valved pumping port  89  prior to high-vacuum pumping by the high-vacuum pump  22 . 
     Although  FIG. 2  illustrates the high-vacuum pump  22  and its pump aperture  88  to be in the bottom wall of the valve body  66 , they may be located in any of the five walls away from the gate valve  62 . For example, in another embodiment, the pump aperture  88  is formed in a vertical wall of the valve body  66  adjacent the horizontal wall apertures  76 ,  84  but below the gate plate  64  in its closed position. However, the illustrated location of the high-vacuum pump  22  on the bottom wall projecting below the processing chamber  12  in otherwise unused space provides a reduced footprint. 
     The single-axis movement of the gate valve of the invention allows optional simple cooling of the valve plate  64  when it is exposed to high processing temperatures inside the vacuum processing chamber  12 . As illustrated in the cross-sectional side view of  FIG. 3 , the shaft  67  supporting the gate plate  64  optionally includes two axially extending coolant channels  92 ,  94  which have upper ends connected to respective ends of a convolute cooling channel  96  formed in the gate plate  64 , as shown in the cross-sectional top view of  FIG. 4  taken along section line  4 - 4  of  FIG. 3 . A circular plate may be welded to the top of the gate plate  64  to enclose the cooling channel  96 . The shaft  67  is fixed and sealed to the piston  72  but extends through it and its lower end extends out the bottom of the air cylinder  70 . The two coolant channels  92 ,  94  are thus exposed to ambient and may be connected to the supply and drain of a cooling system, such as a liquid refrigeration unit to supply chilled liquid coolant, such as water, to cool the gate plate  64  and its O-ring  82 . 
     Other types of actuators may be used in place of the air cylinder. For example, the shaft  67  may be coupled to a mechanical drive driven by a reversible electric motor. In a motorized mechanical embodiment illustrated in the cross-sectional view of  FIG. 5 , a motor  100  rotates a gear  103  which is engaged to a gear  103  on top of an elongated nut  108  rotatably supported on bearings  104  and inside of which is threaded the shaft  67 . Bearings  105  allow the shaft  67  to move vertically but not to rotate so that the shaft  67  forms a ball screw. As a result, as the motor  100  rotates the nut, the shaft  67  moves up or down between the open and closed positions of the gate valve. The figure also shows a drive casing  106  attached by screws  107  to the bottom wall of valve body  66 . Alternatively, the shaft  67  may be threaded and rotated through a nut fixed to the valve body. For some applications, manual rotation of the worm drive or threaded shaft may be sufficient. For manual actuation, the actuator can be considered to be the handle turning the shaft. Mechanical actuation, for example, through a motor allows the gate plate  64  to assume multiple positions away from the pumping port  24  and the sealing surface and thus to variably throttle the high-vacuum pumping. This figure does not illustrate the bellows  86  surrounding the shaft  67 , which operates similarly to that illustrated in  FIGS. 2 and 4 . 
     In another aspect of the invention, the valve body may accommodate other equipment. For example, as additionally illustrated in  FIG. 5 , an auxiliary pump  110  may be placed in the valve body  66 . As an example, a turbo pump is effective for use as the main high-vacuum pump  22  but is not efficient at pumping some gases such as water vapor and non-inert gas. In such a situation, the auxiliary pump  110  may be a cryo pump, a getter pump, or other type of pump operating together with the main high-vacuum pump  22 . In other types of applications, a getter pump can be added for hydrogen pumping or analysis instruments such as a low-pressure or high-pressure vacuum gauge may be added to measure performance of base pressure or to diagnose the integrity of the roughing pump before its failure to thereby protect system performance. One possible diagnostic instrument is a residual gas analyzer (RGA), which measures over time the composition of a gas mixture and partial pressures of the gases in the mixture, thereby capable of determining the gas resulting from contamination or a leak. 
     The metal bellows allows a valve mechanism in which no mechanically moving parts are exposed to a vacuum or to possibly deleterious processing gases. Although the bellows provides a simple and dependable vacuum seal for the moving shaft, it is understood that sliding vacuum seals or other means may be substituted. 
     The invention provides a number of advantages. The turbo pump is located away from the pump port of the processing chamber and is thus somewhat protected from debris falling out of the processing chamber. The large cross section of the valve body does not significantly reduce the pumping conductance. The valve mechanism is relatively compact and does not require a large footprint. In the illustrated embodiment, it can be fit under the processing chamber. The valve mechanism utilizes low force and thus experiences reduced stress, wear, and vibration. Unlike the conventional valve of  FIG. 1 , there is no back lash. The mechanism is highly reliable and has demonstrated a lifetime of 1.5 million cycles. If the actuator is electrically powered, the valve can act as a throttling valve and as a slow pumping valve. Most of its parts are not exposed to wear or vacuum and thus can be fabricated from aluminum or stainless steel. The valve works in any orientation. For example, the pump port may be placed on the side wall or top wall of the processing chamber.