Abstract:
There is provided a slit valve, comprising: a first slit valve portion having a first window therethrough, the first window is sized to permit passage of an object through the first window; wherein the first window is surrounded by a first area of the first slit valve portion; a second slit valve portion that comprises a first sealing element and a first positioning module; wherein the first positioning module is arranged to move the first sealing element in relation to the first window; wherein at least one slit valve portion of the first and second slit valve portions comprises at least one first gas opening for emitting pressurized gas so as to assist in a creation of a first gas cushion between the first area and the first sealing element when the first sealing element is placed adjacent to the first window thus creating a seal between the first and second slit valve portions.

Description:
CROSS-REFERENCES TO RELATED APPLICATIONS 
     The present application claims priority to U.S. Provisional Patent Application No. 61/865,129, filed Aug. 12, 2013. The contents of this application are hereby incorporated by reference. 
    
    
     FIELD OF THE INVENTION 
     Slit valves and processing systems that include at least one chamber. 
     BACKGROUND OF THE INVENTION 
     Slit valves may be used as interfaces between different chambers of semiconductor substrates. 
     Slit valves are required to selectively seal windows formed in the different chambers without contaminating these different chambers. In addition, these slit valves are required to exhibit maximum resistance from dynamic mechanical wear and chemical attack. 
     Conventional slit valves have elastic O-shaped rings that seal gaps between parts of the slit valves. These O-shaped rings may contaminate any chamber in which they are positioned. In addition, O-shaped rings that are expected to operate at high temperature environments are very costly. 
     There is a growing need to provide low contamination and effective sealing solutions. 
     BRIEF SUMMARY OF THE INVENTION 
     According to an embodiment of the invention, there is provided a slit valve, comprising: a first slit valve portion having a first window therethrough, the first window is sized to permit passage of an object through the first window; wherein the first window is surrounded by a first area of the first slit valve portion; a second slit valve portion that comprises a first sealing element and a first positioning module; wherein the first positioning module is arranged to move the first sealing element in relation to the first window; wherein at least one slit valve portion of the first and second slit valve portions comprises at least one first gas opening for emitting pressurized gas so as to assist in a creation of a first gas cushion between the first area and the first sealing element when the first sealing element is placed adjacent to the first window thus creating a seal between the first and second slit valve portions. According to an embodiment of the invention, the chamber wall first slit valve portion includes the gas openings. According to another embodiment of the invention, the gas openings are provided within the seal element. According to an embodiment of the invention, one or more slit valve portions of the first and second slit valve portions comprises at least one first vacuum opening for sucking at least a portion of the pressurized gas so as to assist in a prevention of a propagation of the pressurized gas outside a vicinity of the first and second slit valve portions. According to an embodiment of the invention, the Slit valve may include vacuum openings for reducing the propagation of the pressurized gas outside the slit valve. According to yet another embodiment of the invention, one or more slit valve portions of the first and second slit valve portions comprises a first group and a second group of first vacuum openings for sucking at least a portion of the pressurized gas so as to reduce a propagation of the pressurized gas outside a vicinity of the first and second slit valve portions; wherein the first gas opening is positioned between the first and second groups of the first vacuum openings (e.g. Air bearing between vacuum grooves). According to an embodiment of the invention, the first group of first vacuum openings is positioned between the at least one first gas opening and the first window (e.g. Vacuum grooves between window and first gas opening). According to an embodiment of the invention, one or more slit valve portions of the first and second slit valve portions comprises multiple first vacuum openings for applying a differential pressure sucking scheme for sucking at least a portion of the pressurized gas so as to assist in a prevention of a propagation of the pressurized gas outside a vicinity of the first and second slit valve portions. According to an embodiment of the invention, the first sealing plate comprises the at least one first gas opening for emitting pressurized gas (e.g. sealing plate has gas openings). According to an embodiment of the invention, the at least one first gas opening comprises a first gas groove that surrounds the window. According to an embodiment of the invention, the at least one gas opening comprises multiple grooves that are spaced apart from each other, each groove surrounds the window. According to an embodiment of the invention, the slit valve further comprises sealing elements for sealing at least one portion of the positioning module. According to an embodiment of the invention, the first slit valve portion is integrated with a sidewall of an object processing chamber. According to an embodiment of the invention, the slit valve further comprises a third slit valve portion having a second window therethrough, the second window is sized to permit passage of the object through the second window; wherein the second window is surrounded by a second area of the third slit valve portion; a fourth slit valve portion that comprises a second sealing element and a second positioning module; wherein the second positioning module is arranged to move the second sealing element in relation to the second window; and wherein the slit valve is arranged to seal the second window with the second sealing element. According to an embodiment of the invention, the at least one slit valve portion of the third and fourth slit valve portions comprises at least one second gas opening for emitting another pressurized gas so as to assist in a creation of a second gas cushion between the second area and the second sealing element when the second sealing element is placed adjacent to the second window thus creating a seal between the third and fourth slit valve portions. According to an embodiment of the invention, the one or more slit valve portions of the third and fourth slit valve portions comprises at least one second vacuum opening for sucking at least a portion of the other pressurized gas so as to assist in a prevention of a propagation of the other pressurized gas outside a vicinity of the second and third slit valve portions. 
     According to an embodiment of the invention, there is provided an processing system, comprising: a first chamber, comprising a first chamber wall defining a first window therethrough, the first window is sized to permit passage of an object through the first window; wherein the first window is surrounded by a first area of the first chamber wall; a slit valve portion that comprises a first sealing element and a first positioning module; wherein the first positioning module is arranged to move the first sealing element in relation to the first window; wherein at least one of the first chamber wall and the slit valve portion comprises at least one first gas opening for emitting pressurized gas so as to assist in a creation of a first gas cushion between the first area and the first sealing element when the first sealing element is placed adjacent to the first window thus creating a seal between the first chamber wall and the slit valve portion. According to an embodiment of the invention, the object processing system further comprises: a second chamber, comprising a second chamber wall defining a second window therethrough, the second window is sized to permit passage of an object through the second window; wherein the second window is surrounded by a second area of the second chamber wall; another slit valve portion that comprises a second sealing element and a second positioning module; wherein the second positioning module is arranged to move the second sealing element in relation to the second window. 
    
    
     
       BRIEF DESCRIPTION OF THE DRAWINGS 
       Further details, aspects and embodiments of the invention will be described, by way of example only, with reference to the drawings. In the drawings, like reference numbers are used to identify like or functionally similar elements. Elements in the figures are illustrated for simplicity and clarity and have not necessarily been drawn to scale. 
         FIG. 1  is a top view of an object processing tool according to an embodiment of the invention; 
         FIG. 2  is a schematic diagram of an external slit valve when the external slit valve is at the open position, according to an embodiment of the invention; 
         FIG. 3  is a cross sectional view of an external slit valve taken across a vertical plane denoted A-A in  FIG. 2 , according to an embodiment of the invention; 
         FIG. 4  is a magnified portion of the cross sectional view of an external slit valve taken across the vertical plane denoted A-A in  FIG. 2 , according to an embodiment of the invention; 
         FIG. 5  is a cross sectional view of a portion of an external slit valve according to an embodiment of the invention; 
         FIG. 6  is a cross sectional view of a portion of an external slit valve according to an embodiment of the invention; 
         FIG. 7  is a schematic diagram of the pneumatic actuators according to various embodiments of the invention; 
         FIG. 8  illustrates an internal single slit valve when the sealing plate of the internal single slit valve is at the open position, according to an embodiment of the invention; 
         FIG. 9  is a cross sectional view of an internal single slit valve along vertical plane A-A of  FIG. 8 , according to an embodiment of the invention; 
         FIG. 10  is a magnified cross sectional view of a portion of an internal single slit valve taken along vertical plane A-A of  FIG. 8 , according to an embodiment of the invention; 
         FIG. 11  is a front view of a portion of an internal dual slit valve according to an embodiment of the invention; and 
         FIG. 12  is a cross sectional view of a portion of an internal dual slit valve taken along a vertical plane denoted A-A in  FIG. 11  according to an embodiment of the invention; 
         FIG. 13  is a cross sectional view of the portion of an internal dual slit valve taken along a horizontal plane denoted B-B in  FIG. 11  according to an embodiment of the invention; and 
         FIG. 14  is a magnified portion of the cross sectional view of an internal dual slit valve taken along the vertical plane denoted A-A in  FIG. 11  according to an embodiment of the invention; and 
         FIG. 15  is a cross sectional view of the portion of the internal dual slit valve taken along a horizontal plane according to another embodiment of the invention. 
     
    
    
     It will be appreciated that for simplicity and clarity of illustration, elements shown in the figures have not necessarily been drawn to scale. For example, the dimensions of some of the elements may be exaggerated relative to other elements for clarity. Further, where considered appropriate, reference numerals may be repeated among the figures to indicate corresponding or analogous elements. 
     DETAILED DESCRIPTION OF THE INVENTION 
     In the following detailed description, numerous specific details are set forth in order to provide a thorough understanding of the invention. However, it will be understood by those skilled in the art that the present invention may be practiced without these specific details. In other instances, well-known methods, procedures, and components have not been described in detail so as not to obscure the present invention. 
     The subject matter regarded as the invention is particularly pointed out and distinctly claimed in the concluding portion of the specification. The invention, however, both as to organization and method of operation, together with objects, features, and advantages thereof, may best be understood by reference to the following detailed description when read with the accompanying drawings. 
     It will be appreciated that for simplicity and clarity of illustration, elements shown in the figures have not necessarily been drawn to scale. For example, the dimensions of some of the elements may be exaggerated relative to other elements for clarity. Further, where considered appropriate, reference numerals may be repeated among the figures to indicate corresponding or analogous elements. 
     Because the illustrated embodiments of the present invention may for the most part, be implemented using electronic components and circuits known to those skilled in the art, details will not be explained in any greater extent than that considered necessary as illustrated above, for the understanding and appreciation of the underlying concepts of the present invention and in order not to obfuscate or distract from the teachings of the present invention. 
     In the following figures various slit valves are shown. All of these slit valves are illustrated as having a first slit valve portion that is static and a second slit valve portion that moves in relation to the first slit valve portion. In all the following figures the first slit valve portion is shown as including pressurized gas and vacuum gas openings. It is noted that the pressurized gas openings and, additionally or alternatively, the vacuum gas openings can be included in the second slit valve portion or in both slit vale portions. 
     The first slit valve portion may be integrated with a sidewall of a chamber, may be coupled to the sidewall of the chamber or may form a part of the sidewall of the chamber. 
       FIG. 1  is a top view of an object processing tool  20  according to an embodiment of the invention. 
     The object processing tool  20  includes (a) a load port  1  in which there are cassettes  2  with substrates  3 , (b) a factory interface  4  with an external robot  5 , (c) a load lock  7 , (d) an external slit valve  6 , (e) an internal single slit valve  8 , (f) a transfer chamber  9  that includes an internal robot  10 , (g) multiple process chambers  11 , and (h) internal dual slit valves  12 . 
     The internal single slit valve  8  provides an interface between the load lock  7  and the transfer chamber  9 . Internal dual slit valves  12  provide interfaces between the transfer chamber  9  and the process chambers  11 . 
     The operating conditions of the different slit calves differ from each other, and this affects their design. 
     The first type of slit valve is the external slit valve  6  that operates in atmospheric environment and seals the load lock  7  where may be either slight overpressure or vacuum. Sealing the transfer chamber  9  is required when the pumping process and vacuum environment exists in the transfer chamber. In this condition the force between atmospheric pressure and vacuum is pressing the sealing plate to the valve body and air bearing contra force is balancing this force. 
     The second type of slit valve is internal single slit valve  8  that separates the load lock  7  and the transfer chamber  9  where there is always vacuum condition, so the sealing should be performed for two scenarios:
         a. The load lock  7  maintains an atmosphere pressure and the transfer chamber maintains vacuum.   b. Both load lock  7  and transfer chamber  9  maintain vacuum.       

     In the first scenario the internal single slit valve  8  faces the same conditions as the external slit valve  6 . 
     In the second scenario there is no force that presses the sealing plate to the valve housing—as there is no difference in the pressure level obtained on both sides of the slit valve. Accordingly—there should be provides a force for pressing the sealing plate towards the valve housing. This may achieved by applying a mechanical force. 
     In addition—there may be an additional difference that may be attributes to the need to maintain vacuum and a clean environment on both sides of the slit valve—so that any pressurized gas that is released to form the air bearing (or air cushion) should be pumped away. 
     The third type of slit valve is the internal dual slit valve  12 , which operates always in vacuum-vacuum conditions—as vacuum is maintained within the transfer chamber  9  and within the process chambers  11 . 
     External Slit Valve  6   
     The main operation condition of the external slit valve  6  is atmosphere-vacuum (the external slit valve  6  is exposed to an atmospheric pressure level from one side and to a vacuum pressure level on the other side, and it may include vacuum openings between an air bearing area and load lock  7 . 
       FIG. 2  is a schematic diagram of the external slit valve  6  when the external slit valve  6  is at the open position, according to an embodiment of the invention. 
       FIG. 3  is a cross sectional view of the external slit valve  6  taken across a vertical plane denoted A-A in  FIG. 2 , according to an embodiment of the invention. 
       FIG. 4  is a magnified portion of the cross sectional view of the external slit valve  6  taken across the vertical plane denoted A-A in  FIG. 2 , according to an embodiment of the invention. 
     External slit valve  6  may include a housing  101 , a window  102  for transfer of substrates, an air bearing area  103 , a groove  104  for providing pressurized gas of an atmospheric pressure  104  and three grooves  105 ,  106  and  107  for pumping vacuum. 
     The housing  101  may be integrated with a wall of the load lock  7  or may be coupled to the wall of the load lock  7 . This housing  101  defined the window through which substrates can be transferred between the load lock  7  and the factory interface  4 . 
     The three grooves  105 ,  106  and  107  can apply a differential pumping scheme in which the pressure levels decrease with the distance from groove  104 . 
     On the base plate  108  two subsystems are mounted. A first subsystem may include two horizontal actuators  109  and  110  of the sealing plate  126 . 
     A second subsystem provides a guiding mechanism for the sealing plate  126  and may include of one master slide  111  for example, slide bushing and two slave slides  112  and  113 . 
     The actuator module of the base plate  108  may introduce a vertical motion between the window and the sealing plate  126 . The actuator module may include a module housing  114 , a guiding unit with one master slide  115  and one slave slide  116 . 
     Two rods  117  and  118  have channels  119  and  120  in order to supply compressed gas to the two horizontal actuators  109  and  110  via a control solenoid valve. 
     A vertical pneumatic cylinder  121  with piston  122  and rod  123  may provide a vertical motion of the base plate  108 . Yoke  124  synchronizes the vertical motion of two rods  117  and  118 . Part  125  is cover of the actuator module of the base plate  108 . 
       FIG. 4  is a cross sectional view of a portion of the external slit valve  6  of  FIG. 2  where the base plate  108  is at an upper position and the sealing plate  126  is at the right end position, according to an embodiment of the invention. 
       FIG. 4  illustrates a gap (Δ) formed between housing  101  and the sealing plate  126 . This gap can be about 5-7 mm and is too big for the formation of the air bearing. 
     The external slit valve  6  can be closed by performing the following steps (and the air bearing may be activated to output pressurized gas during the execution of the following stages):
         a. Elevating the base plate  108  by vertical pneumatic cylinder  121  with two guiding rods  117  and  118 . The adjustment of upper position of the base plate  108  may be performed by hard stop (not shown). In this position the gap between housing  101  and the sealing plate  126  may be about 5-7 mm.   b. After the vertical pneumatic cylinder  121  reach the upper position, the two horizontal actuators  109  and  110  are activated. Each horizontal actuator  109  and  110  has a bellows  302  which is mounted on the bellows actuator base  301 . When the gap between the sealing plate  126  and housing  101  reaches a desired valve (which may be between 150 till 300 microns) the force balance between actuator force and force of two springs  205  is obtained.   c. The vacuum seal does not operate with such gaps and there is a need to reduce the gap. This is achieved by introducing a pressure difference so that the load lock  7  and vacuum grooves  105 ,  106  and  107  are placed at a lower pressure level than the environment of the load lock  7 . This can include introducing vacuum into the load lock  7 —pumping gas from the load lock while maintaining the environment outside the sealing plate  126  at an atmospheric pressure level. At the end of this process the gap between the housing  101  and sealing plate  126  is small enough to enable the vacuum seal to operate. The gap Δ can be about 5-7 microns. At this condition there is provided a force balance between the force of bellows actuators  109  and  110 , air bearing  103 , vacuum force in the load lock  7  chamber and differential vacuum grooves  105 ,  106  and  107 ; and also force of the atmospheric pressure are settled.       

     The sliding subsystem of the sealing plate  126  may include a master slide  111  and two slave slides  112  and  113 . Basically, the master slide  111  may include the slide housing  201 , thrust bearing  202 , slide bushing  203  and rod  204 . Slide housing  201  and thrust bearing  202  form the spherical kinematic joint that allows reaching the high level parallelism around 3-4 microns between surfaces of the sealing plate  126  and housing  201 . This adjustment should be performed at an initialization step. 
       FIG. 5  is a cross sectional view of a portion of the external slit valve according to an embodiment of the invention. 
     Each plenum, annular grooves  104 ,  105 ,  106  and  107  and its isolating land may act to remove residual pressurized gas from the air bearing annular groove  103  until the required level of isolation outside the vicinity of the slit valve is achieved. 
     Gas opening  402  is maintained at atmospheric pressure. Vacuum openings such as exhaust conduits  403 ,  404  and  405 , which may be similar to the exhaust ports in the gas exhaust system disclosed in the commonly assigned U.S. Pat. No. 6,163,033, are coupled to each plenum to remove the residual gas. The conduits may be connected to vacuum pumps (not shown). The vacuum pumps may be operated separately, or under the control of the system controller. The necessary number of plenum stages depends upon the level of vacuum required and the pumping rate of the vacuum pumps in conjunction with the precision of the air bearing gap. 
       FIG. 6  is a cross sectional view of a portion of the external slit valve according to an embodiment of the invention. 
     In this case the labyrinth seals  127  are situated between annular grooves  104 ,  105 ,  106  and  107 . This configuration may reduce the amount of pressurized gas that may escape the vicinity of the gas and vacuum openings and may increase the vacuum level in the load lock  7 . 
       FIG. 7  is a schematic diagram of the pneumatic actuators according to various embodiments of the invention. 
     Two bellows actuators  503  and  504  are mounted on the base plate  502  and they move the sealing plate  501  in horizontal direction. Sliding unit  505  provides the precise motion. Pneumatic cylinder  506  moves the base plate  502  with all its components in vertical direction. Solenoid valve  507  5/2-way type is intended for control of the pneumatic cylinder  506  and 3/2-way solenoid valve  508  may be used for control of two bellows actuators  503  and  504  which operate together. Unit  509  is compressed air service unit 
     The parallelism between the sealing plate  126  and housing  101  may require an adjustment process. The value of the parallelism should be around 3-4 microns at that the flatness of corresponding surfaces of the plate and housing is about 1-2 microns. In this case the material of the sealing plate  126  may be ceramic (for example, alumina) and housing  101  may be made of aluminum (for example, AL6061T651). 
     The adjustment process may include the following steps:
         a. Move the sealing plate  126  in the upper position where the gap (of certain value) between sealing plate  126  and housing  101  is in the range of 5-7 mm.   b. Release the three screws  207  on each slide bushing  203  that clamp the spherical kinematic joints.   c. Move the sealing plate  126  to the tight contact with housing  101  using two pneumatic bellows actuators  503  and  504 .   d. Tighten all screws  207  on each slide bushing  203  that perform the clamping of the three spherical kinematic joints between the slide housing  201  and the thrust bearing  202 .   e. Return the sealing plate  126  at the position where the gap between sealing plate  126  and housing  101  is of the certain value.   f. Check the parallelism between sealing plate  126  and housing  101 , which should be around 3-4 microns. For this connect two pneumatic bellows actuators with atmospheric pressure.   g. Repeat the above procedure if the parallelism between sealing plate  126  and housing  101  doesn&#39;t lie in the desired range.       

     Internal Single Slit Valve 
     The internal single slit valve and the internal dual slit valve may operate under vacuum-vacuum conditions in which both sides of these internal slit valves are at vacuum—as vacuum is maintained within the process chambers  11 , the transfer chamber  9  and the load lock  7 . 
     The positioning module of these internal slit valves and especially all moving parts of the positioning module are operating under vacuum and should be sealed by means of bellows, which ensures a good seal and prevent contamination of the particles. 
       FIG. 8  illustrates an internal single slit valve  8  when the sealing plate of the internal single slit valve  8  is at the open position, according to an embodiment of the invention. 
       FIG. 9  is a cross sectional view of the internal single slit valve  8  along vertical plane A-A of  FIG. 8 , according to an embodiment of the invention. 
       FIG. 10  is a magnified cross sectional view of a portion of the internal single slit valve taken along vertical plane A-A of  FIG. 8 , according to an embodiment of the invention. 
     The internal single slit valve  8  may include a rear interface plate  601 , a housing  602  and a front interface plate  603 . Two windows  622  and  623  are intended for transfer of substrates. The actuating module of the vertical motion has body  604  and cover  605 . 
     The sealing plate  606  moves in a horizontal direction by two bellows pneumatic actuators  609  and  610  that are mounted on the base plate  607 . Two bellows  611  and  612  are sealed by two rods  613  and  614 . These rods have channels  617  and  618  in order to supply compressed air to the two actuators  609  and  610  via a control solenoid valve not shown here. 
     The guiding unit of the valve vertical motion may include of a master slide  615  and one slave slide  616 . Pneumatic cylinder  608  with piston  619  and rod  620  provides the vertical motion of the base plate  607 . Yoke  621  synchronizes the vertical motion of two rods  613  and  614 . Part  605  is a cover of the vertical actuator module. 
       FIG. 10  is a cross section view of a portion of the internal single slit valve  8  where the base plate  607  is on upper position and the sealing plate  606  is on the right end position according to an embodiment of the invention. In this case the gap between rear interface plate  601  and the sealing plate  606  is in the range of 5-7 mm. 
     Two pneumatic actuators  609  and  610  may provide the horizontal motion of the sealing plate  606 . Each actuator may include a base  801 , a housing  803 , and bellows  807 . 
     The sliding subsystem of the each horizontal actuator may include slide  804 , slide rod  805  and opposing spring  808 . Slide  804  is mounted into actuator housing  802  and slide rod  805  is installed on the rod holder  806  that is mounted on the sealing plate  606 . 
     The opposing spring  808  is mounted around the slide rod  805  between slide housing  802  and spring support  809 . The sliding subsystem is installed within the horizontal pneumatic actuator that provides the full protection from the particle contaminations. 
     Compressed gas is supplied to the horizontal pneumatic actuator via PTFE Teflon flexible tube  811  and two hose nipples. First nipple is mounted on the actuator cover  810  and second one is installed on the base  801 . 
     Each pneumatic actuator may include the spherical kinematic joint between thrust bearing plate  802  and housing  803 . The thrust bearing plate  802  is connected to the base plate  607  by four screws  624 , and the slide housing  803  is connected to the thrust bearing plate  802  by fore screws  625  that have the spherical washers. Such design allows reaching the high level parallelism around 1-3 microns between surfaces of the sealing plate  606  and the rear interface plate  601 . This adjustment should be performed at an initialization step. 
       FIGS. 9 and 10  are schematic diagrams of the air bearing and differential vacuum seal portion according to various embodiment of the invention. 
     Basically, such internal slit valve has two differential vacuum seal portions that are built around the air bearing area  705 . Each plenum, annular grooves  701 ,  702 ,  703 ,  704 ,  706 ,  707 ,  708  and  709  and its isolating land act to remove residual gas from the air bearing annular groove  705  until the required level of isolation is achieved at the seal interface here the grooves  704  and  709  are the atmospheric pressure grooves. Exhaust conduits  701 ,  702 ,  703 ,  706 ,  707  and  708  which may be similar to the exhaust ports in the gas exhaust system disclosed in the commonly assigned U.S. Pat. No. 6,163,033, are coupled to each plenum to remove the residual gas. The conduits are connected to vacuum pumps not shown. 
     The vacuum pumps may be operated separately, or under the control of the system controller. The necessary number of plenum stages depends upon the level of vacuum required and the pumping rate of the vacuum pumps in conjunction with the precision of the air bearing gap. 
     The slit valve can be closed by performing the following steps:
         a. Initial conditions are the following: air bearing is disconnected from the source of compressed air, both the atmospheric channel groove  704  and  709  blocked, and all another annular grooves are connected to the vacuum pumps.   b. Elevating the base plate  607  and sealing plate  606  by pneumatic cylinder  608  with two guiding rods  613  and  614 . The adjustment of upper position of the sealing plate  606  is performed by hard stop not shown. In this position the gap between rear interface plate  601  and the sealing plate  606  is about 5-7 mm.   c. After the sealing plate  606  reaches the upper position two horizontal motion pneumatic actuators  609  and  610  are activated. Each bellows is expanded and moves the sealing plate  606  towards to rear interface plate  601 . When the gap between sealing plate  606  and rear interface plate  601  reaches a desired value, which may be between 150 till 300 microns, the force balance between actuator force and force of spring  808  is got. The adjustment can be performed at an initialization step by changing of the pressure level of the compressed air.   d. At the final phase the air bearing  705  is connected to the compressed air source, two grooves  704  and  709  are connected to the atmosphere. This lead to a new force balance between two opposing springs  808 , air bearing  705  and two pneumatic actuators  609  and  610 . In this case, the gap between sealing plate  606  and rear interface plate  601  is about 4-7 microns.       

     Adjustment procedure of the parallelism between sealing plate and housing may be similar to that applied for the external slit valve. 
     Internal Dual Slit Valve 
     According to an embodiment of the invention there may be provided a dual slit valve that may be operative to selectively seal two windows formed in two different sidewalls of different chambers. Thus, a first window may be formed in an external sidewall of a transfer chamber and a parallel window may be formed in an internal sidewall of a process chamber. In this case a dual slit valve can be arranged to seal both windows, one window at a time to leave both windows open. 
     When positioning a dual slit valve between the transfer chamber and the process chamber cross contamination should be taken into account and there is a need to prevent contamination from the process chamber from entering the transfer chamber and to prevent contamination from the transfer chamber from entering the process chamber. 
       FIG. 11  is a front view of a portion of the internal dual slit valve according to an embodiment of the invention. 
       FIG. 12  is a cross sectional view of the portion of the internal dual slit valve taken along a vertical plane denoted A-A in  FIG. 11  according to an embodiment of the invention. 
       FIG. 13  is a cross sectional view of the portion of the internal dual slit valve taken along a horizontal plane denoted B-B in  FIG. 11  according to an embodiment of the invention. 
       FIG. 14  is a magnified portion of the cross sectional view of the internal dual slit valve taken along the vertical plane denoted A-A in  FIG. 11  according to an embodiment of the invention. 
     The internal dual slit valve may include a rear interface plate  901 , housing  902  and front interface plate  903 . The actuating module of the vertical motion has body  904  and cover  905 . Three covers  906 ,  907  and  908  are intended to adjustment and service of two sealing plates  913  and  914 . The sealing plate  914  moves in a horizontal direction by two bellows pneumatic actuators  926  and  929  that are mounted on the base plate  912 . The second sealing plate  913  moves in a horizontal direction by two bellows pneumatic actuators  927  and  928  that are mounted on the base plate  911 . 
     Both the base plate  911  and  912  are mounted on the base  910  that moves in vertical direction by vertical actuating module that contains two bellows  915  and  916 , which are sealed two rods  917  and  918 . These rods have channels  921  and  922  in order to supply compressed air to the four horizontal actuators. 
     The guiding unit of the valve vertical motion may include of one master slide  919  and one slave slide  920  for example, top ball bushing. Pneumatic cylinder  909  with piston  923  and rod  924  provide the vertical motion of the base  910 . Yoke  925  synchronizes the vertical motion of two rods  917  and  918 . Part  905  is cover of the vertical actuator module. 
     Two pneumatic actuators  926  and  929  provide the horizontal motion of the sealing plate  914 . Another two pneumatic actuators  927  and  928  provide the horizontal motion of the sealing plate  913 . Each pair of actuators is controlled by solenoid valve not shown. 
     Compressed air is supplied to the horizontal pneumatic actuators via PTFE Teflon flexible tube (not shown). Two nipples  932  and  935  are connected to the nipple  936 , and two other nipples  933  and  934  are connected to the nipple  937 . 
     The each pneumatic actuator contains the spherical kinematic joint between thrust bearing plate  1108  and housing  1101 . The thrust bearing plate  1108  is connected to the base plate  912  by four screws  1109 , and the slide housing  1101  is connected to the thrust bearing plate  1108  by four screws  1110  that have the spherical washers. Such design allows reaching the high level parallelism around 1-3 microns between surfaces of the sealing plate  914  and the rear interface plate  901 . This adjustment should be performed at an initialization step. 
     Each actuator may include of the housing  1101 , cover  1102 , and bellows  1106 . The sliding subsystem of the each horizontal actuator may include slide  1103 , slide rod  1104  and opposing spring  1107 . Slide  1103  is mounted into actuator housing  1101  and slide rod  1104  is installed on the rod holder  1105  that is mounted on the sealing plate  914 . The opposing spring  1107  is mounted around the slide rod  1104  between housing  1101  and spring support  1111 . The sliding subsystem is installed within the horizontal pneumatic actuator that provides the full protection from the particle contaminations. 
     As shown in  FIG. 12  and  FIG. 13  the rear interface plate  901  and the front interface plate  903  has two differential vacuum seal portions that are built around the air bearing area  1005  and  1014 . The rear interface plate  901  has plenum, annular grooves  1001 ,  1002 ,  1003 ,  1004 ,  1006 ,  1007 ,  1008  and  1009 . The front interface plate  903  has plenum, annular grooves  1010 ,  1011 ,  1012 ,  1013 ,  1015 ,  1016 ,  1017  and  1018 . Annular groves and their isolating lands act to remove residual gas from the air bearing annular grooves until the required level of isolation. Exhaust conduits which may be similar to the exhaust ports in the gas exhaust system disclosed in the commonly assigned U.S. Pat. No. 6,163,033, are coupled to each plenum to remove the residual gas. The conduits are connected to vacuum pumps not shown. 
     The vacuum pumps may be operated separately, or under the control of the system controller. The necessary number of plenum stages depends upon the level of vacuum required and the pumping rate of the vacuum pumps in conjunction with the precision of the air bearing gap. 
     The dual slit valve can be closed by performing the following steps same to the type A slit valve:
         a. Initial conditions are the following: air bearing is disconnected from the source of compressed air, the atmospheric channels grooves  1004 ,  1009 ,  1013  and  1018  blocked, and all another annular grooves are connected to the vacuum pumps.   b. Elevating the base  910  and two sealing plates  913  and  914  by pneumatic cylinder  909  with two guiding rods  917  and  918 . The adjustment of upper position of the sealing plates  913  and  914  is performed by hard stop not shown. In this position the gap between rear interface plate  901  and the sealing plate  914 , and between front interface plate  903  and the sealing plate  913  is in the range between 5 and 7 mm.   c. After the sealing plates reach the upper position four horizontal motion pneumatic actuators  926 ,  927 ,  928  and  929  are activated. Each bellows is expanded and moves two sealing plates towards to interface plates. When the gap between each sealing plate and its interface plate reaches a desired value, which may be between 150 till 300 microns, the force balance between actuator force and force of opposing springs is got. The adjustment can be performed at an initialization step by changing of the pressure level of the compressed air.   d. At the final phase the air bearings  1005  and  1014  are connected to the compressed air source, four grooves  1004 ,  1009 ,  1013  and  1018  are connected to the atmosphere. This lead to a new force balance between pair of opposing springs, air bearing and pair of pneumatic actuators. In this case, the gap between each sealing plate and corresponding interface plate is about 4-7 microns.       

     Basically, in the normal sealing mode the valve internal volume may be connected to the standalone vacuum pump or to the vacuum pump of the groove  1001  or  1010 . In the cases where the ventilation procedure performs in the process chamber or in the transfer chamber the valve internal volume is connected to the ventilated chamber. In this case, the valve operates as the single slit valve slit valve type “A”. 
     Adjustment procedure of the parallelism between sealing plate and housing is similar to that of the external slit valve. 
       FIG. 15  illustrates a cross sectional view of a dual slit valve according to another embodiment in the invention. 
     The internal dual slit valve is mounted between the process chamber  1301  and the transfer chamber  1302 . It situates within an intermediate chamber  1303 . 
     The main valve has the insert  1304  for providing of the pressurized gas bearing and differential pumping channels. Pressurized gas bearing area  1310  and two grooves of the differential pumping  1309  and  1311  are connected to the compressed gas line  1308  and two vacuum lines  1306  and  1307  accordingly. The front surface of the sealing plate  1312  and also front surface of the insert  1304  must have high level of flatness 1 around 1-2 microns. The sealing plate  1312  has four corner bumpers  1320  on its front surface area. There are contact pads at all four corners that provide low contact area in the case the slit valve insert  1304  is not coplanar to slit valve sealing plate  1312 . Such contacts would only be made before gas bearing pressure builds and sealing plate  1312  floats. 
     Floating gap between the insert  1304  and sealing plate  1312  is in the range from 4 to 10 microns. Mounting gimbals  1315  have two axis of rotation to enable planarity of the sealing plate  1312  to slit valve insert  1304 . “L” motion actuator shaft  1313  has two axis linear motions: first one is vertical to raise or lower the sealing plate  1312 , and second motion is horizontal to seal the valve opening. The bellows  1314  is sealed the actuator shaft  1313 . 
     The service valve may include of insert  1305  with front side sealing surface, sealing plate  1316  with “O”-ring  1317 . 
     Mounting gimbals  1320  have two axis of rotation to enable planarity of the sealing plate  1316  to insert  1305 . “L” motion actuator shaft  1318  has two axis linear motions: first one is vertical to raise or lower the sealing plate  1316 , and second motion is horizontal to seal the valve opening. The bellows  1319  is sealed the actuator shaft  1318 . 
     The service valve may be only closed when the process  1301  or transfer  1302  chamber is vented. 
     The service valve may be used to eliminate the requirement for the primary valve between the process chamber and transfer chamber to seal against the full pressure differential of atmosphere. Eliminating this requirement significantly reduces the force the valve needs to provide and therefore the pressurized gas level. 
     The required force may drop by a factor of around 1000. 
     As the pressurized gas levels are reduced, the leak rate of the pressurized bearing gas into the vacuum chambers is also reduced. This enables the valve to have a very low leak rate even with only 1 simple stage of differential vacuum pumping. Meeting the leak rate requirement with 1 stage of differential pumping would be preferred to a 2 or 3 stage differential pumping solution from size and cost of pumping basis. 
     The dual slit valve may provide a double sealing area two sealing plate provides “zero” cross contamination property and provides a simple and a reliable seal during vented procedure of the process or transfer chamber. 
     In the foregoing specification, the invention has been described with reference to specific examples of embodiments of the invention. It will, however, be evident that various modifications and changes may be made therein without departing from the broader spirit and scope of the invention as set forth in the appended claims. 
     Moreover, the terms “front,” “back,” “top,” “bottom,” “over,” “under” and the like in the description and in the claims, if any, are used for descriptive purposes and not necessarily for describing permanent relative positions. It is understood that the terms so used are interchangeable under appropriate circumstances such that the embodiments of the invention described herein are, for example, capable of operation in other orientations than those illustrated or otherwise described herein. 
     The connections as discussed herein may be any type of connection suitable to transfer signals from or to the respective nodes, units or devices, for example via intermediate devices. Accordingly, unless implied or stated otherwise, the connections may for example be direct connections or indirect connections. The connections may be illustrated or described in reference to being a single connection, a plurality of connections, unidirectional connections, or bidirectional connections. However, different embodiments may vary the implementation of the connections. For example, separate unidirectional connections may be used rather than bidirectional connections and vice versa. Also, plurality of connections may be replaced with a single connection that transfers multiple signals serially or in a time multiplexed manner. Likewise, single connections carrying multiple signals may be separated out into various different connections carrying subsets of these signals. Therefore, many options exist for transferring signals. 
     Although specific conductivity types or polarity of potentials have been described in the examples, it will be appreciated that conductivity types and polarities of potentials may be reversed. 
     Each signal described herein may be designed as positive or negative logic. In the case of a negative logic signal, the signal is active low where the logically true state corresponds to a logic level zero. In the case of a positive logic signal, the signal is active high where the logically true state corresponds to a logic level one. Note that any of the signals described herein can be designed as either negative or positive logic signals. Therefore, in alternate embodiments, those signals described as positive logic signals may be implemented as negative logic signals, and those signals described as negative logic signals may be implemented as positive logic signals. 
     Furthermore, the terms “assert” or “set” and “negate” (or “deassert” or “clear”) are used herein when referring to the rendering of a signal, status bit, or similar apparatus into its logically true or logically false state, respectively. If the logically true state is a logic level one, the logically false state is a logic level zero. And if the logically true state is a logic level zero, the logically false state is a logic level one. 
     Those skilled in the art will recognize that the boundaries between logic blocks are merely illustrative and that alternative embodiments may merge logic blocks or circuit elements or impose an alternate decomposition of functionality upon various logic blocks or circuit elements. Thus, it is to be understood that the architectures depicted herein are merely exemplary, and that in fact many other architectures can be implemented which achieve the same functionality. 
     Any arrangement of components to achieve the same functionality is effectively “associated” such that the desired functionality is achieved. Hence, any two components herein combined to achieve a particular functionality can be seen as “associated with” each other such that the desired functionality is achieved, irrespective of architectures or intermedial components. Likewise, any two components so associated can also be viewed as being “operably connected,” or “operably coupled,” to each other to achieve the desired functionality. 
     Furthermore, those skilled in the art will recognize that boundaries between the above described operations merely illustrative. The multiple operations may be combined into a single operation, a single operation may be distributed in additional operations and operations may be executed at least partially overlapping in time. Moreover, alternative embodiments may include multiple instances of a particular operation, and the order of operations may be altered in various other embodiments. 
     Also for example, in one embodiment, the illustrated examples may be implemented as circuitry located on a single integrated circuit or within a same device. Alternatively, the examples may be implemented as any number of separate integrated circuits or separate devices interconnected with each other in a suitable manner. 
     Also for example, the examples, or portions thereof, may implemented as soft or code representations of physical circuitry or of logical representations convertible into physical circuitry, such as in a hardware description language of any appropriate type. 
     Also, the invention is not limited to physical devices or units implemented in non-programmable hardware but can also be applied in programmable devices or units able to perform the desired device functions by operating in accordance with suitable program code, such as mainframes, minicomputers, servers, workstations, personal computers, notepads, personal digital assistants, electronic games, automotive and other embedded systems, cell phones and various other wireless devices, commonly denoted in this application as ‘computer systems’. 
     However, other modifications, variations and alternatives are also possible. The specifications and drawings are, accordingly, to be regarded in an illustrative rather than in a restrictive sense. 
     In the claims, any reference signs placed between parentheses shall not be construed as limiting the claim. The word ‘comprising’ does not exclude the presence of other elements or steps then those listed in a claim. Furthermore, the terms “a” or “an,” as used herein, are defined as one or more than one. Also, the use of introductory phrases such as “at least one” and “one or more” in the claims should not be construed to imply that the introduction of another claim element by the indefinite articles “a” or “an” limits any particular claim containing such introduced claim element to inventions containing only one such element, even when the same claim includes the introductory phrases “one or more” or “at least one” and indefinite articles such as “a” or “an.” The same holds true for the use of definite articles. Unless stated otherwise, terms such as “first” and “second” are used to arbitrarily distinguish between the elements such terms describe. Thus, these terms are not necessarily intended to indicate temporal or other prioritization of such elements. The mere fact that certain measures are recited in mutually different claims does not indicate that a combination of these measures cannot be used to advantage. 
     While certain features of the invention have been illustrated and described herein, many modifications, substitutions, changes, and equivalents will now occur to those of ordinary skill in the art. It is, therefore, to be understood that the appended claims are intended to cover all such modifications and changes as fall within the true spirit of the invention.