Abstract:
A slitvalve that uses magnetic energy to move a door in a direction normal to the plane of the wall is disclosed. An electrically switchable magnet is used to draw the door toward the wall to seal an aperture in the wall. Compressed Dry Air or other mechanisms may be employed to move the door between a first open position and a second closed position. A method of passing a workpiece between two different environments utilizing this magnetic slitvalve is also disclosed.

Description:
TECHNICAL FIELD 
       [0001]    Embodiments of the present invention relate to methods and apparatus for providing an automated gas tight seal of an opening, more specifically, an electric switchable magnet slitvalve for sealing chambers in a semiconductor tool. 
       BACKGROUND 
       [0002]    Semiconductor workpieces are processed within process chambers. Workpieces are typically moved from one chamber to another by automated means. Often, each chamber must be environmentally isolated from other chambers. Consequently, the workpieces are typically moved between chambers by the use of load locks. These load locks serve to isolate a particular chamber from its outside environment. Additionally, a difference in pressure may exist on either side of the load lock. For example, near vacuum conditions may exist within the chamber, while the outside environment may be at standard atmospheric pressure. Thus, the load must also seal the chamber against these differences in pressure. 
         [0003]    Load locks typically include a slitvalve, which includes a wall with an aperture included therein, and an associated movable door assembly. The movable door assembly may include a first portion, referred to as the door, which is at least as large as the aperture, and a movable shaft. In a first position, the door is moved away, such as vertically downward, so that the aperture is open and workpieces can be moved therethrough. In a second position, the door is disposed to cover the aperture, thereby separating the regions on opposite sides of the wall from each other. 
         [0004]    The door is typically driven and held in place by the use of compressed dry air (CDA). For example, an air cylinder may serve to move the door in a first direction, where the first direction is defined as a direction parallel to the plane of the wall, between the first and second positions. To seal, the door must also be moved in a second direction, normal to the plane of the wall. In some embodiments, the door is biased against the wall through the use of air cylinders. In other embodiments, the door expands in the second direction, which serves to seal the door against the aperture. 
         [0005]    These methods require an excessive amount of CDA. Also, the movement of the door in the second direction often results in bending or excessive tension of the shaft, which reduces the effectiveness and reliability of the load lock. Furthermore, the pressure applied by the door against the wall is uneven, typically necessitating a heavier, thicker door. 
         [0006]    Therefore, it would be beneficial if there were a slitvalve that required less CDA and was more reliable. 
       SUMMARY 
       [0007]    Systems and method comprising a slitvalve using magnetic energy are disclosed. In a first embodiment, the slitvalve comprises a wall defining an aperture; an electrically switchable magnet disposed in a location of the wall; and a movable door assembly, comprising a door having magnetically attracted material, disposed so as correspond to the location of the electrically switchable magnet when the door is in a closed position; and an actuator to move the door in a first direction parallel to a plane of the wall between the closed position and an open position. 
         [0008]    In a second embodiment, the slitvalve comprises a wall defining an aperture; a movable door; a first actuator to move the door in a first direction, parallel to a plane of the wall; and an electrically switchable magnet to move the door in a second direction, normal to the plane of the wall. 
         [0009]    In another embodiment, a method of passing a workpiece between two environments is disclosed. The method of passing a workpiece from a first environment to a second environment, separated from the first environment by a wall having an aperture therethrough, where the aperture is sealed using a movable door, the method comprises providing a magnetically attracted material on the door; deactivating an electrically switchable magnet disposed in the wall, thereby releasing the magnetically attracted material from the wall; using a force to maintain separation between the wall and the door; using an actuator to move the door from a second position to a first position; passing the workpiece through the aperture when the door is in the first position; using the actuator to move the door to the second position; and activating the electrically switchable magnet to attract the magnetically attracted material in the door, thereby sealing the door to the wall. 
     
    
     
       BRIEF DESCRIPTION OF THE FIGURES 
         [0010]    For a better understanding of the present disclosure, reference is made to the accompanying drawings, which are incorporated herein by reference and in which: 
           [0011]      FIG. 1A  is an isometric view of a slitvalve according to one embodiment in the first, open position; 
           [0012]      FIG. 1B  is an isometric view of the slitvalve of  FIG. 1A  in the second closed position; 
           [0013]      FIG. 2  represents a rear view of the wall of the slitvalve of  FIG. 1A ; 
           [0014]      FIG. 3  represents a front view of the door of the slitvalve of  FIG. 1A ; 
           [0015]      FIG. 4  represents a second embodiment of the wall of the slitvalve; 
           [0016]      FIG. 5  represents the magnetic fields associated with a first configuration of magnets shown in  FIG. 4 ; 
           [0017]      FIG. 6  represents the magnetic fields associated with a second configuration of magnets; and 
           [0018]      FIG. 7  is a flowchart illustrating the operation of a slitvalve according to one embodiment. 
       
    
    
     DETAILED DESCRIPTION 
       [0019]      FIG. 1  is an isometric view of the slitvalve  10  in the first, or open position, in accordance with one embodiment. The slitvalve  10  includes a wall  20  with an aperture  30 . The wall  20  may be constructed of aluminum or any other suitable material. The slitvalve  10  also includes a movable door assembly  40 , which has a movable shaft  41  attached to a door  45 . The door  45  may also be constructed from aluminum or any other suitable material. The movable shaft  41  may be in communication with an actuator  50 , such as an air cylinder or other pneumatic or mechanical device. The actuator  50  is used to move the shaft  41 , and consequently the door  45 , in a first direction, indicated by arrows  43 , where the first direction is parallel to the plane of the wall  20 . The door  45  may be attached to the movable shaft  41  using one or more flexure plates  46 . These flexure plates  46  allow for some movement in a second direction, normal to the plane of the wall  20 , indicated by arrows  47 . Although flexure plates  46  are described below, any suitable mechanism that allows movement along second direction  47  may be used. For example, linear bearings may be employed to achieve this movement. Additionally, other mechanisms, such as shaft and ball slides, may also be employed. 
         [0020]    CDA may be used to actuate the movable shaft in the first direction  43 , thereby moving the door  45  from a first open position, shown in  FIG. 1A , to a second closed position, shown in  FIG. 1B . 
         [0021]    Unlike prior art devices, the slitvalve  10  uses magnetic force to move the door  45  in the second direction  47  and to hold the door  45  against the wall  20 . One or more electrically switchable magnets may be used to create the desired magnetic field. An electrically switchable magnet is defined as a magnet whose magnet field can be modified through the application of electrical current. In one embodiment, an electrically switchable magnet may comprise an electromagnet, where a wire is wrapped around a ferrite material. Application of current in one direction polarizes the ferrite material in one orientation, while application of current in the opposite direction polarizes the ferrite material in the opposite direction. The lack of electrical current eliminates the magnetic field. In a second embodiment, the electrical switchable magnet may be an electrical switchable permanent magnet. An electrical switchable permanent magnet has two states; an active state where a magnetic field is present and a second passive state where no magnetic field exists. This can be achieved in a number of ways. In one embodiment, a permanent magnet is arranged with an electromagnet, which either accentuates the inherent magnetic field of the permanent magnet, or short circuits it. In a second embodiment, a permanent magnet is arranged with a second rotatable permanent magnet, which either accentuates the inherent magnetic field or short circuits it. In a third embodiment, a permanent magnet is arranged with a second permanent magnet, which is wound with an electrical coil. The polarity of the second permanent magnet can be reversed by a brief application of voltage, thereby creating two states where the magnetic field is either accentuated or short circuited. One additional quality of electrical switchable permanent magnets is their ability to maintain state in the absence of electrical current. These electrical switchable permanent magnets may be made from, for example, alnico or rare earth metals, such as neodymium, and samarium-cobalt. In other words, electrical current is only needed to set the magnet in one of its two states. After that, the electrical switchable permanent magnet will maintain that state until an electrical current is used to change to the other state. 
         [0022]      FIG. 2  shows a wall  20 , having a plurality of electrically switchable magnets  200  disposed thereon. These electrically switchable magnets  200  may be embedded in the wall  20  in some embodiments. In some embodiments, these electrically switchable magnets  200  are disposed around at least a portion of the perimeter of the aperture  30 . For example, the electrically switchable magnets  200  may be disposed along the top and bottom edges of the aperture  30 . In another embodiment, the electrically switchable magnets  200  may be disposed along each edge of the aperture  30 . Other configurations of the electrically switchable magnets  200  are also within the scope of the disclosure. These electrically switchable magnets  200  are actuated by a power source (not shown), which is electrically coupled to the magnets  200  using conduits  230 . 
         [0023]    As shown in  FIG. 3 , magnetically attracted material  300 , such as steel or iron, is disposed on or in the door  45 . The position of the magnetically attracted material  300  is selected to correspond to the locations of the electrically switchable magnets  200  when the door  45  is in the second closed position. In other embodiments, the magnetically attracted material  300  is disposed on the wall  20 , while the electrically switchable magnets  200  are disposed on the door  45 . 
         [0024]    In operation, the electrically switchable magnets  200  are first set to their non-magnetic state. After this, since the door  45  is no longer being held in place, the door  45  can be moved in the first direction, by actuation of the air cylinder  50  through the use of CDA. When returning the door  45  to the second closed position, the air cylinder  50  is actuated so as to extend the shaft  41  to move the door  45  in the first direction  43 . When the door  45  has reached its second closed position, the electrically switchable magnets  200  are set to their magnetically energized state. This action draws the magnetically attracted material  300 , and consequently the door  45 , toward the wall  20 , thereby sealing it in place. The magnitude of the magnetic field exerted by the electrically switchable magnets  200  can be selected according to the design criteria of the application. For some embodiments, the magnetic field generated by each electrically switchable magnet  200  may be hundreds of pounds, such as greater than 500 pounds each. To improve the quality of the seal between the door  45  and the wall  20 , an o-ring seal (not shown) may be placed on the wall  20 , the door  45  or on both the wall  20  and the door  45 . 
         [0025]    As stated above, flexure plates  46  attach the door  45  to the movable shaft  41 . These plates  46  may have a spring like quality, allowing them to stretch and compress. The flexure plates  46  may be constructed of any suitable material, such as metal or a polymer. When the door  45  is being drawn to the wall  20  due to the magnetic field, flexure plates  46  stretch, allowing the door  45  to move in the second direction  47  toward the wall  20 . When the electrically switchable magnets  200  are set to the passive state, the flexure plates  46  may compress back to their natural shape, thereby drawing the door  45  away from the wall  20 . The ability of the flexure plates  46  to stretch minimizes the moment force that is exerted on the movable shaft  41 , thus improving its reliability and useable life. As stated above, other mechanisms may be used to allow movement along the second direction  47 . 
         [0026]    In some embodiments, a force may be used to maintain separation between the door  45  and the wall  20 , especially while the door  45  is traveling between its first open position and second closed position. In one embodiment, as shown in  FIG. 2 , magnets  210 , disposed in or on the wall  20 , are arranged in linear arrays  211   a ,  211   b  corresponding to the door&#39;s direction of travel  43 . These magnets  210  may be permanent magnets, such as neodymium magnets. These magnets  210  may be arranged such that the same pole (north or south) of each magnet faces the outer surface of the wall  20 . In one embodiment, two linear arrays of magnets  211   a ,  211   b  are employed, where one linear array of magnets  211   a  or  211   b  is disposed on each side of the aperture  30 . 
         [0027]    Similar sets of linear arrays  311   a ,  311   b  of magnets  310  may be disposed on the door  45 , as shown in  FIG. 3 . These magnets  310  may also be permanent magnets, and are arranged such that the same pole is exposed on the surface of the door  45 . These magnets  310  may be arranged in opposed pole alignment with the magnets  210 . Each linear array  311   a ,  311   b  is located on the door  45  so as to spatially align with a corresponding linear array  211   a ,  211   b  on the wall  20 . In this embodiment, two linear arrays  311  are shown, one on either side of the door  45 . In this way, the magnets  210  of the wall  20  and the magnets  310  of the door  45  repel each other and will maintain separation between the door  45  and the wall  20 , when the electrically switchable magnets  200  are in their passive state. By configuring these magnets  210 ,  310  as linear arrays  211 ,  311 , the repulsion force is maintained through the full travel of the door  45 , as it moves from its open position to its closed position. The use of linear arrays also serves to minimize the number of magnets required to create the desired repulsion force, and serves as a separation mechanism. 
         [0028]    In this embodiment, the force of the electrically switchable magnets  200  must be sufficient to overcome the repulsion force between magnets  210  and  310 , and hold the door  45  to the wall  20  with sufficient force. For example, if the desired force of the door  45  against the wall  20  is 400 pounds, and the repulsion force of the magnets  210  and  310  is 200 pounds, the electrically switchable magnets  200  should exert a force of at least 600 pounds. 
         [0029]    In another embodiment, magnets  210 ,  310  may be electrically switchable magnets, such as electromagnets. In this embodiment, these electromagnets  210 ,  310  are disabled when the electrically switchable magnets  200  are set to their active state. These electromagnets  210 ,  310  would then be energized prior to actuating the air cylinder  50  to insure separation between the door  45  and the wall  20  when the door  45  is moving. 
         [0030]    In another embodiment, shown in  FIG. 4 , the magnets on wall  20  are arranged in a first set  400  on one side of the aperture  30 , where this first set has two linear arrays of magnets: an inner linear array  401   a , closer to the aperture  30  and a outer array  401   b , disposed further from the aperture  30 . A second set of magnets  410 , also having an inner linear array  411   a  and an outer array  411   b , is disposed on the other side of the aperture  30 . All of these linear arrays  401   a ,  401   b ,  411   a ,  411   b  are configured with the same pole facing outward. In this embodiment, the door  45  has two linear arrays  311   a ,  311   b , as shown in  FIG. 3 . 
         [0031]      FIG. 5  shows an expanded top view of the interaction between the magnets disposed on the wall  20  and the door  45  in one configuration. This configuration of linear arrays  401   a ,  401   b  creates a magnetic field  500  with two peaks  510 ,  511  and a trough  520  therebetween, as shown in  FIG. 5 . The linear array  311   b  (see  FIG. 3 ) of magnets  310  on the door  45  are disposed so as to be located in this trough  520 . The magnetic peaks  510 ,  511  on either side of magnets  310  serve to align and hold the magnets  310  in place. A similar magnetic field  530  exists between linear arrays  411   a ,  411   b , such that two magnetic peaks  540 ,  541  and a trough  550  therebetween are created. The linear array  311   a  (see  FIG. 3 ) of magnets  310  on the opposite edge of the door  45  is disposed in this trough  550 . This creates an alignment mechanism, such that the door  45  moves along the desired path in the direction  43  and cannot move from side to side. Thus, this configuration of magnets provides a separation mechanism and an alignment mechanism. 
         [0032]      FIGS. 4 and 5  illustrate two sets  400 ,  410  of magnets, each having two linear arrays  401   a ,  401   b ,  411   a ,  411   b , respectively, on the wall  20  and two sets each with one linear array  310   a ,  311   b  on the door  45 . However, other embodiments are possible. For example, multiple linear arrays of magnets may be disposed on the door  45  with a single linear array on the wall  20 . 
         [0033]      FIG. 6  is a top view of another arrangement of which may be used as an alignment mechanism. Similar to  FIG. 4 , two sets  600 ,  610  of magnets, respectively, each having an inner linear array  601   a ,  611   a  and an outer linear array  601   b ,  611   b , are disposed on the wall  20 . Similarly, two linear arrays  690   a ,  690   b  of magnets, one on each side, are disposed on the door  45 , as in  FIG. 3 . However, the spatial relationship between the opposing magnets is altered. In this embodiment, the linear arrays  690   a ,  690   b  on the door are aligned directly with the inner pair of linear arrays  601   a ,  611   a  on the wall  20 . The outer linear arrays  601   b ,  611   b  tend to repel each of the linear arrays of magnets  690   a ,  690   b  inward. Since these forces are counter to one another, the door  45  remains aligned. The configuration of  FIG. 6  can be altered so that the magnets  690   a ,  690   b  are aligned with the outer linear arrays  601   b ,  611   b . In this embodiment, the inner linear arrays  601   a ,  611   a  tend to push the linear arrays  690   a ,  690   b  outward. Again, since these forces are in opposition to each other, the door  45  remains aligned. As was described above, it is also possible to have multiple sets of linear arrays on the door  45 , and two linear arrays on the wall  20 , if desired. This configuration of magnets also provides a separation mechanism and an alignment mechanism. 
         [0034]    The process by which the slitvalve  10  is used to close the opening, thereby isolating the environments on the opposing sides of the wall  20  from each other, will be described and is shown in  FIG. 7 . It is assumed that the door  45  is open, which means that the actuator  50  is in its first open position, and the electrically switchable magnets  200  are in their non-magnetic, or passive, state, as shown in step  700  of  FIG. 7 . The actuator  50  is then actuated and causes the shaft  41 , and consequently the door  45 , to move to a second position, as shown in step  710 . This may be achieved through the application of CDA or other methods. In embodiments containing linear arrays of magnets, the door  45  and wall  20  remain separated as the door  45  moves along the first direction  43 , due to the magnetic repulsion between the linear arrays disposed in the door  45  and the linear arrays disposed in the wall  20 . Once the door  45  has reached the second position, the electrically switchable magnet  200  is set to its energized state, as shown in step  720 . This draws the magnetically attracted material  300  disposed on the door  45  toward the wall  20 , thereby sealing the door  45  against the wall  20 . The ability to move in the second direction  47  is due to the use of a mechanism  46  allowing this movement, such as flexure plates, a linear bearing or a shaft and ball slide. At this point, if electrically switchable permanent magnets were used, a loss of power will have no effect on the state of the slitvalve  10 . In this closed position, the environments on opposing sides of the wall  20  are isolated from one another. 
         [0035]    To move the door  45  to the open position, this process is simply reversed. First, the electrically switchable magnet  200  is changed to its non-energized, passive state, as shown in step  730 . This removes the magnetic field and allows the magnetically attracted material  300  to be released from the electrically switchable magnet  200 . The mechanism  46 , such as flexure plates, returns to its non-stretched state. In addition, the linear arrays  210 ,  310  repel each other, which causes the door  45  to separate from the wall  20 . The actuator  50  is then actuated to move the door  45  to its first open position, as shown in step  740 . It is this position where workpieces may be passed through the aperture  30 . 
         [0036]    Thus, in movements that are parallel to the plane of the wall  20 , such as steps  710 ,  740 , CDA may be used to cause the motion. In steps that are normal or perpendicular to the plane of the wall  20 , magnetic force is used to move the door  45 . 
         [0037]    This arrangement has many advantages. First, there is a significant reduction in the amount of CDA required to operate a load lock. In the prior art, CDA may be used to hold the door  45  against the wall, thereby consuming large amounts of CDA to generate the required force. In addition, traditional cantilevered designs require very heavy doors to help provide the necessary force to create an adequate seal. In addition, the seals currently created are uneven, since the lateral force applied by the door against the wall is not equally applied. The use of magnetic fields to seal the door to the wall allows for a much more even seal, where the pressure is spread much more evenly. The actual seals are usually made from Viton, Chemraz, and Kalrez materials. These seal profiles are typically vulcanized to the aluminum or steel door. By using magnets to create the closing force, the force can be spread out along the length of the door so that the seal force on the elastomeric seal is more consistent and the deformation of the door is minimized. This allows the use of a much lighter door, which further reduces the amount of CDA that is required. 
         [0038]    The present disclosure is not to be limited in scope by the specific embodiments described herein. Indeed, other various embodiments of and modifications to the present disclosure, in addition to those described herein, will be apparent to those of ordinary skill in the art from the foregoing description and accompanying drawings. Thus, such other embodiments and modifications are intended to fall within the scope of the present disclosure. Furthermore, although the present disclosure has been described herein in the context of a particular implementation in a particular environment for a particular purpose, those of ordinary skill in the art will recognize that its usefulness is not limited thereto and that the present disclosure may be beneficially implemented in any number of environments for any number of purposes. Accordingly, the claims set forth below should be construed in view of the full breadth and spirit of the present disclosure as described herein.