Abstract:
Embodiments disclosed herein generally relate to methods for sealing a processing chamber with a slit valve door. The slit valve door rises from a position below the substrate transfer port for the processing chamber to a raised position. The slit valve door then expands until an o-ring on the door seals against the sealing surface. The slit valve door rises by flowing clean dry air into a vertical air cylinder coupled to the slit valve door. By controlling the rate of air flow venting from the air cylinder using high and low conductance exhaust lines, the speed with which the slit valve door ascends or descends is controlled to ensure that the door gently moves between positions. Thus, the slit valve door may be prevented from moving into position with too great a force that may jolt or shake the processing chamber and produce undesired particles that may contaminate the process.

Description:
BACKGROUND 
       [0001]    1. Field 
         [0002]    Embodiments of the present invention generally relate to a slit valve door and a method for sealing a chamber with a slit valve door. 
         [0003]    2. Description of the Related Art 
         [0004]    In semiconductor, flat panel display, photovoltaic/solar panel, and other substrate processing systems, it is common to arrange vacuum chambers (i.e., load locks, transfer chambers, process chambers) in a cluster, in-line, or a combination of cluster/in-line arrangements to process substrates. These systems may process substrates in single or batch substrate fashion. During processing, substrates may be transferred to and from chambers in which vacuum must be maintained or established. To allow access to the inside of the chamber, and to enable vacuum operation, a substrate transfer port formed through the chamber wall in the shape of a slit is frequently provided to accommodate the substrate being processed. The substrate transfer port is opened and closed (e.g., sealed) by a slit valve assembly. 
         [0005]    The slit valve assembly includes a slit valve door that may be movably actuated to open or close the substrate transfer port. When the slit valve door is clear of the substrate transfer port, one or more substrates may be transferred between the two vacuum chambers through the substrate transfer port. When the slit valve port is closed and sealed by the slit valve door, substrates may not be transferred in or out of vacuum chambers through the substrate transfer port and the vacuum chambers remain sealed. For example, two vacuum chambers connected by a slit valve assembly may include a process or transfer chamber which requires periodic isolation from a load lock chamber in order to maintain vacuum in the process or transfer chamber when the load lock chamber is vented. 
         [0006]    Generally, the operation speed of the slit valve door is important to the throughput of substrate processing system. However, faster door operations result in large shocks or vibrations as the slit valve door opens and closes. The shocks may loosen and disperse particles within the vacuum chambers, which may create defects on the substrate. Additionally, large shocks over time may loosen fasteners and increase wear on the components of the slit valve door. 
         [0007]    Therefore, there is a need for a slit valve door capable of sealing chambers with improved mechanical motion. 
       SUMMARY 
       [0008]    Embodiments disclosed herein generally relate to method and apparatus for sealing a processing chamber with a slit valve door. In one embodiment, a slit valve assembly includes a housing having a substrate transfer port formed in sidewalls of the housing. A slit valve door is disposed within an interior volume of the housing. The slit valve door is coupled to an actuator, which is operable to move the slit valve door between an open position and a closed position within the housing. The slit valve assembly is further coupled to a flow control circuit having an air supply flow path, a high conductance vent flow path, and a low conductance vent flow path selectively coupled to the actuator. 
         [0009]    In one embodiment, a method of sealing a chamber coupled to a slit valve assembly is disclosed. The method includes actuating a slit valve door at a first speed for a first period of time from a first position towards a second position. The slit valve assembly body may have passages formed through walls of the body. The method further includes detecting when the slit valve door nears the second position and, in response to the detecting, actuating the slit valve door at a second speed for a second period of time such that the second speed is less than the first speed. 
     
    
     
       BRIEF DESCRIPTION OF THE DRAWINGS 
         [0010]    So that the manner in which the above recited features of the present disclosure can be understood in detail, a more particular description, briefly summarized above, may be had by reference to embodiments, some of which are illustrated in the appended drawings. It is to be noted, however, that the appended drawings illustrate only typical embodiments of this invention and are therefore not to be considered limiting of its scope, for the invention may admit to other equally effective embodiments. 
           [0011]      FIG. 1  is a schematic sectional view of two chambers connected by a slit valve assembly. 
           [0012]      FIG. 2  is a sectional view of one embodiment of the slit valve assembly of  FIG. 1  having a flow control circuit. 
           [0013]      FIG. 3  is a sectional view of the slit valve assembly of  FIG. 2  having a sealed slit valve door. 
           [0014]      FIG. 4  is a sectional view of the slit valve assembly of  FIG. 2  having a slit valve door in a lowered position. 
           [0015]      FIG. 5  is a schematic view of one embodiment of the flow control circuit of  FIG. 2 . 
           [0016]      FIG. 6  is a flow diagram of a method for closing the slit valve assembly of  FIG. 2  according to embodiments of the invention. 
           [0017]      FIG. 7  is a flow diagram of a method for opening the slit valve assembly of  FIG. 2  according to embodiments of the invention. 
           [0018]      FIGS. 8A and 8B  are graphs illustrating position and shock forces during operation of a slit valve door according to one embodiment of the invention. 
       
    
    
       [0019]    To facilitate understanding, identical reference numerals have been used, where possible, to designate identical elements that are common to the figures. It is contemplated that elements disclosed in one embodiment may be beneficially utilized on other embodiments without specific recitation. 
       DETAILED DESCRIPTION 
       [0020]    Embodiments of the invention generally relate to an apparatus and methods for sealing a vacuum chamber with a slit valve assembly. The slit valve assembly utilizes high and low conductance pneumatic cylinder exhaust lines to control acceleration and deceleration of components to prevent jolting or shaking of the vacuum chamber which may produce undesired particles and process contamination. Embodiments of the invention will be described below in regards to a slit valve assembly and chambers available from AKT America, Inc., a subsidiary of Applied Materials, Inc., Santa Clara, Calif. However, it is to be understood that the invention has utility using other slit valve assemblies and other chambers, including those sold by other manufacturers. 
         [0021]      FIG. 1  is a schematic sectional view of two chambers  102 ,  104  coupled by a slit valve assembly  106 . The vacuum chambers  102 ,  104  have substrate transfer ports  108 ,  110  formed therethrough that permit a substrate to enter and exit the chamber  102 ,  104 . The slit valve assembly  106  is operable to seal the vacuum chambers  102 ,  104  so that the vacuum chambers  102 ,  104  are environmentally isolated from each other. The slit valve assembly  106  includes a door  112  that may be moved between positions that seal the substrate transfer ports  108 ,  110  and allow substrates to pass between the vacuum chambers  102 ,  104  through the substrate transfer ports  108 ,  110 . 
         [0022]    In one embodiment, a flow control circuit  120  is coupled to the various components of the slit valve assembly  106  to facilitate operation of the slit valve door  112 . The flow control circuit  120  is further described in detail below with regards to  FIG. 5 . Additionally, a controller  130 , including a central processing unit (CPU)  136 , a memory  132 , and support circuits  134  for the CPU  136 , is coupled to the flow control circuit  120  and to various components of the slit valve assembly  106  to facilitate control of the slit valve door  112 . To facilitate control of the valve assembly and control circuit as described above, the CPU  136  may be one of any form of general purpose computer processor that can be used in an industrial setting. The memory  132  is coupled to the CPU  136 . The memory  132 , or computer-readable medium, may be one or more of readily available memory such as random access memory (RAM), read only memory (ROM), floppy disk, hard disk, or any other form of digital storage, local or remote. The support circuits  134  are coupled to the CPU  136  for supporting the processor in a conventional manner. These circuits include cache, power supplies, clock circuits, input/output circuitry and subsystems, and the like. A method for controlling the operation of the door, such as described herein, is generally stored in the memory  132  as a software routine. The software routine may also be stored and/or executed by a second CPU (not shown) that is remotely located from the hardware being controlled by the CPU  136 . 
         [0023]      FIGS. 2-4  are sectional front views of one embodiment of a slit valve assembly  106 . The slit valve assembly  106  generally includes a housing  200  having a top  204 , a bottom  206 , and side walls  202  that define an interior volume  208  within the housing  200 . Passages  210  are formed through the side walls  202  to align with the substrate transfer ports  108 ,  110  seen in  FIG. 1 . In one embodiment, the passages  210  are sized to permit substrates to pass through the slit valve assembly  106 . 
         [0024]    The slit valve assembly  106  further includes a slit valve door  112  disposed within the interior volume  208  of the housing  200 . The slit valve door  112  includes a first seal plate  224  and a second seal plate  226  coupled to a base  222 . The first and second seal plates  224 ,  226  are coupled to a seal plate actuator  238 , which is configured to urge the first and second plates  224 ,  226  towards the sidewalls  202 . The seal plates  224 ,  226 , each have a sealing face  228  configured to seal against inside surfaces  230 ,  232  of the side walls  202 . The seal plates  224 ,  226  include o-ring glands  234  which accommodates o-rings  236 . The o-rings  236  provide a seal between the sealing faces  228  and the side walls  202 . 
         [0025]    The slit valve door  112  is coupled to a door actuator  218  by a rod  214  extending through a hole  216  formed through the bottom  206  of the housing  200 . The door actuator  218  may be an air cylinder or a pneumatic cylinder. In the embodiment shown in  FIG. 2 , the door actuator  218  is a vertically-oriented, double-acting air cylinder. A seal  220  may optionally be disposed around the hole  216  to form a seal between the bottom  206  of the housing  200  and the door actuator  218 . 
         [0026]    The door actuator  218  is configured to move the slit valve door  112  to move between a lowered position and a raised position within the interior volume  208  of the housing  200 . In the raised position, as seen in  FIG. 2 , the slit valve door  112  is arranged within the interior volume  208  such that the first and second seal plates  224 ,  226  are aligned with the passages  210 . In the lowered position, as seen in  FIG. 4 , the slit valve door  112  is disposed proximate the bottom of the interior volume  208  of the housing  200  with the seal plates  224 ,  226  clear of the passages  210 , such that a substrate may pass through the slit valve assembly  106  through the passages  210 . As shown in  FIG. 3 , the slit valve door  112  is also configured to seal the passages  210  when in the raised position by sealing the seal plates  224 ,  226  against the sidewalls  202 . 
         [0027]    The slit valve assembly  106  further includes sensors  240  coupled to the controller  130 . The sensors  240  are configured to determine the position of the slit valve door  112  within the interior volume  208 . In one embodiment, the sensors  240  may include flag sensors coupled to the slit valve assembly  106  at locations near the end stroke positions of the door actuator  218 . 
         [0028]    The flow control circuit  120  and the controller  130  are operated to control the slit valve door  112  and the door actuator  218  using a method as further described in  FIG. 6 . Generally, the flow control circuit  120  and controller  130  may use readings from the sensors  240  to determine when the acceleration and deceleration rate and speed of the slit valve door  112  should change so that the slit valve door  112  rapidly and smoothly moves between raised and lowered positions with reduced jolts and shocks. The controller  130  may further control the expansion of the slit valve door  112  such that the seal plates  224 ,  226  smoothly seal against the sidewalls  202  with reduced jolts and shocks. 
         [0029]      FIG. 5  is a schematic diagram of one embodiment of a flow control circuit  120  coupled to a door actuator  218  to selectively raise and lower a slit valve door  112 . As shown in  FIG. 5 , the door actuator  218  is double acting, vertical air cylinder  502  having a piston  504  disposed within an interior volume  506  of the air cylinder and coupled to a slit valve door by a rod  214 . Sensors  240  are located at end positions of the air cylinder  502  to detect when the piston  504  moves proximate the ends of the door actuator&#39;s stroke positions. 
         [0030]    A supply of clean, dry air (CDA)  508  is fluidly coupled to the air cylinder  502  by an air supply valve  510 , a first flow control valve  512 , and a second flow control valve  514  to selectively provide air to the air cylinder  502 . In the embodiment shown, the air supply valve  510  includes a first state that selectively couples the CDA supply  508  to a top end  530  of the air cylinder and selectively couples a bottom end  532  of the air cylinder to vent exhaust. In one embodiment, the air supply valve  510  also includes a second state that selectively couples the CDA supply  508  to the bottom end  532  of the air cylinder and selectively couples the top end  530  of the air cylinder to vent exhaust. The air supply valve  510  may be a diverter valve, a spool valve, a directional control valve, pneumatic valve or a solenoid valve of other suitable valve. The first flow control valve  512  may control the flow rate of air into the top end  530  of the air cylinder  502  while providing a full flow rate out of the top end  530 . Similarly, the second flow control valve  514  may control the flow rate of air into the bottom end  532  of the air cylinder  502  while providing a full flow rate out of the bottom end  532  of the air cylinder. Providing air to the bottom end causes the rod  214  to extend (raising the door  112 ) while providing air to the top and causes the rod  214  to retract (lowering the door  112 ). Controlling the conductance of the exhaust of the air cylinder  502  controls the acceleration and deceleration of the rod  214 , and hence, the level shock caused by movement of the door  112 . 
         [0031]    The flow control circuit  120  further includes a high conductance exhaust line  516  and a low conductance exhaust line  522  fluidly coupled to the air cylinder  502  by a conductance switch  518  to permit air within the interior volume  506  of the air cylinder  502  to vent out to exhaust  524 . The conductance switch  518  selectively couples the high conductance line  516  or the low conductance line  522  to the air cylinder  502  to change the flow rate of exhaust from air cylinder  502 . In one embodiment, the conductance switch  518  may be a diverter valve, a spool valve, a directional control valve, pneumatic valve, a solenoid valve or other suitable valve. The flow control circuit  120  optionally includes a third flow control valve  520  disposed in the low conductance exhaust line  522 . The third flow control valve  520  may control the flow rate through the low conductance exhaust line  522  to exhaust to further reduce the rate of exhaust from the air cylinder  502 . The conductance of the high conductance exhaust line  516  is greater than the conductance of the low conductance exhaust line  522 , for example, at least 80% greater. In one embodiment, the high conductance exhaust line  516  has a flow rate of greater than about 650 L/min to 700 L/min. In one embodiment, the low conductance exhaust line  522  has a flow rate of less than about 75 L/min. 
         [0032]      FIG. 6  is a flow diagram of one embodiment of a method  600  for sealing the slit valve assembly described in  FIGS. 2-4 . It is understood that the method may be practiced utilizing other apparatuses, and it is also understood that the apparatus shown may be utilized with other methods for operating a slit valve assembly. 
         [0033]    The method  600  begins at  602  by raising the slit valve door  112  into a raised position. To move the slit valve door  112  into a raised position, the flow control circuit  120  provides air to the bottom end of the air cylinder  502  of the door actuator  218  to extend the rod  214  and move the slit valve door  112  upwards within the interior volume  208  by a first distance for a first period of time. 
         [0034]    In one embodiment, the air supply switch  510  and second flow control valve  514  are set to a state to fluidly couple the CDA supply  508  to the bottom end  532  of the air cylinder  502 . Clean, dry air is then supplied to the bottom end  532  of the air cylinder  502 . The air pressure from the air filling the interior volume  506  below the piston  504  from the bottom end  532  urges the piston  504  and rod  214  upwards, thereby elevating the slit valve door  112 . Sufficient air is supplied to the air cylinder  502  to move the slit valve door  112  to the raised position proximate to the passages  210 . 
         [0035]    At the same time, air is vented from the top end  530  of the air cylinder  502 . The first control valve  512  permits air to flow out of the top end  530  of the air cylinder  502  at a full flow rate as the piston  504  pushes the air above the piston  504  out of the air cylinder. The conductance switch  518  is set to a state that fluidly couples the air flowing out of the air cylinder  502  to the high conductance exhaust line  516 . The use of the high conductance exhaust line  516  permits a rapid vent from the top of the air cylinder, thereby allowing the slit valve door  112  to accelerate quickly and move rapidly upwards. 
         [0036]    The method  600  continues at  604  by decelerating the slit valve door  112  prior to reaching in the raised position. If the slit valve door  112  stops suddenly from a full speed at the raised position, the slit valve assembly  106  may be jolted, which may cause the creation of particles within the processing chambers that may contaminate the substrate within the chambers. According to one embodiment of the invention, as the slit valve door  112  approaches the raised position, the door actuator  218  decelerates the slit valve door  112  for a second period of time such that slit valve door  112  gently arrives in the raised position and smoothly stops. The door actuator  218  may increase the deceleration of the slit valve door  112  as the slit valve door  112  moves closer to the raised position. 
         [0037]    The slit valve door  112  may be smoothly decelerated by reducing the flow rate of air venting from the door actuator  218 . As the slit valve door  112  reaches the raised position. In one embodiment, the controller  130  determines when the slit valve door  112  has reached a predetermined position proximate to and spaced from the raised position by using the sensors  240  to detect when the piston  504  approaches the end stroke position at the top end  530  of the air cylinder. The controller  130  then activates the conductance switch  518  to change states as to switch the venting end of the air cylinder  502  from the high conductance exhaust line  516  to the low conductance exhaust line  522 , thereby fluidly coupling the top end  530  of the air cylinder to vent exhaust  524  via the low conductance exhaust line  522 . The reduced flow rate of the low conductance line  522  reduces the rate at which air can be vented from the air cylinder  502 , thereby showing the motion of other rod  214  and decelerating the slit valve door  112 . The third flow control valve  520  may be operated to further decrease the flow rate of the low conductance exhaust line  522  to fine-tune the deceleration of the slit valve door  112  at the end of the slit valve door&#39;s upward travel. In other embodiments, a flow restriction through the third control valve  520  is increased after actuating of the conductance switch  518  to decrease the conductance of the low conductance exhaust line  522  while air is venting therethrough. 
         [0038]    The slit valve door  112  smoothly reaches the raised position at a decelerated speed such that the slit valve door  112  does not cause a substantial shock or jolt to the slit valve assembly  106 . In one embodiment, the flow control circuit  120  reduces shock exerted on the slit valve assembly  106  by about 90 percent as compared to conventional single line vented systems. In another embodiment, the slit valve door  112  is decelerated by the flow control circuit  120  such that the slit valve door  112  coming to a stop in the raised position exerts a force of no more than 0.3 g&#39;s on the slit valve assembly  106 . In one embodiment, the total time in which the slit valve door  112  takes to move 142 mm from the lowered position to the raised position is about 0.9 seconds. 
         [0039]    After reaching the raised position, the slit valve door  112  may be operated to close the passages  210 . At  606 , the seal plates  224 ,  226  of the slit valve door  112  expand towards the sidewalls  202  during a third period of time. In one embodiment, a gas may be introduced into the seal plate actuator  238  by a second flow control circuit (not shown) to expand the seal plates  224 ,  226  for a distance just prior to the o-rings  236  initially contacting against the inside surfaces  230 ,  232  of the housing  200 . Although not shown, the second flow circuit may be configured in one embodiment to be identical to the flow control circuit  120 . 
         [0040]    At  608 , the seal plates  224 ,  226  are then decelerated for a fourth period of time prior to contact with the sidewalls  202 . In one embodiment, the controller  130  may control the flow rate of gas entering the seal plate actuator  238  to control the rate of expansion of the slit valve door  112  and the speed at which the first and second seal plates  224 ,  226  contact the inside surfaces  230 ,  232 . When the first and second seal plates  224 ,  226  near the inside surfaces  230 ,  232 , the flow rate of gas may be reduced to decelerate the seal plates  224 ,  226  such that the o-rings  236  smoothly compress against the inside surfaces  230 ,  232 . 
         [0041]      FIG. 7  is a flow diagram of one embodiment of a method  700  for operating the slit valve assembly described in  FIGS. 2-4  to open the slit valve door  112 . The method  700  begins at  702  by contracting the seal plates  224 ,  226  from the sidewalls  202 . In one embodiment, the gas introduced into the seal plate actuator  238  may be vented to atmosphere by the second flow control circuit. The gas may optionally be vented by a vacuum pump coupled to the slit valve door  112 . 
         [0042]    At  704 , the slit valve door  112  is then lowered after the seal plates  224 ,  226  have been retracted clear of the side walls  202 . The door actuator  218  retracts the rod  214  downwards to move the slit valve door  112  to a lowered position. In one embodiment, the air supply valve  510  is set to a first state to fluidly couple the CDA supply  508  to the top end  530  of the air cylinder  502  through the first flow control valve  512 . The first state of the air supply valve  510  also fluidly couples the bottom end  532  of the air cylinder to vent exhaust. The conductance switch  518  is set to a state that fluidly couples the high conductance exhaust line  516  to the air cylinder  502 . 
         [0043]    Clean, dry air is supplied to a top end of the air cylinder  502 . As air fills the interior volume  506  from the top of the air cylinder, the air pressure above the piston  504  urges the piston  504  and rod  214  downwards, thereby lowering the slit valve door  112 . Sufficient air is supplied to the top end of the door actuator  218  to lower the slit valve door  112  to a positioned proximate the bottom of the interior volume  208 . Air flows out of the bottom end  532  of the air cylinder to exhaust through the high conductance exhaust line  516 . The high flow rate of the high conductance exhaust line  516  permits a rapid vent from the bottom of the air cylinder, thereby allowing the slit valve door to move quickly. 
         [0044]    At  706 , the slit valve door is then decelerated to smoothly stop at a lowered position. In one embodiment, the flow control circuit  120  reduces the flow rate of air venting from the air cylinder  502  to smoothly decelerate the slit valve door  112 . When the sensors  240  detect that the piston  504  is approaching the end position at the bottom of the air cylinder  502 , the conductance switch  518  is activated to change to a state that fluidly couples the interior volume of the air cylinder  502  to the low conductance exhaust line  522  from the high conductance exhaust line  516 . The reduced flow rate of the low conductance exhaust line  522  reduces the cylinder speed and, consequently, the speed of the slit valve door  112 . The third flow control valve  520  may be operated to further reduce the flow rate of the low conductance exhaust line  522  and smoothly decelerate the slit valve door  112  into the lowered position. 
         [0045]    In one embodiment, the slit valve door  112  is decelerated by the flow control circuit  120  such that the slit valve door  112  coming to a stop in the lowered position exerts a force of no more than 0.4 g3 s on the slit valve assembly  106 . In one embodiment, the total time in which the slit valve door  112  takes to move 142 mm from the raised position to the lowered position is about 0.8 seconds. 
         [0046]      FIG. 8A  is a graph showing positions and force values during operation of the slit valve door without use of the deceleration method and apparatus described above. When the slit valve door  112  is lowered to a down position at around time  1001 , a corresponding spike in measured shock force as exerted on the slit valve assembly is measured. In some cases, the shock force in conventional systems can be as great as 3.5 g&#39;s of force. Similarly, a corresponding spike in measured shock force is measured when the slit valve door  112  stops at an up position at around time  3501 . In some cases, the shock force in conventional systems felt by the slit valve assembly may reach 3.7 g&#39;s of force. 
         [0047]    In contrast,  FIG. 8B  is a graph showing position and force values during operation of the slit valve door according to embodiments of the invention. When the slit valve door  112  is lowered to the down position, at around time  1001 , the slit valve door is smoothly decelerated to stop at the down position with reduced force. As shown in  FIG. 8B , the shock force of the slit valve door  112  measured upon reaching the down position is less than 0.4 g&#39;s of force. Similarly, when the slit valve door  112  is raised to an up position, at around time  3501 , the slit valve door is smoothly decelerated to stop at the up position. As shown in  FIG. 8B , the shock force measured when the slit valve door  112  reaches the up position is less than 0.3 g&#39;s of force. 
         [0048]    Thus, by utilizing high conductance and low conductance exhaust lines, the slit valve assembly permits a first, fast motion of the slit valve door followed by a second, slower motion as the slit valve door approaches the end of travel. Embodiments of the invention advantageously reduce shocks or jolts during operation of the slit valve door, thereby reducing risk of contamination from particles shaken free during processing while advantageously maintaining fast opening and closing of the slit valve door. Additionally, embodiments of the invention advantageously permits improved operating times of the slit valve door without risking reliability on the mechanical components of the slit valve assembly. Further, the slit valve door assembly advantageously utilizes a single set of valves to control the speed of the vertical air cylinder in both upwards and downwards directions. 
         [0049]    While the foregoing is directed to embodiments of the present invention, other and further embodiments of the invention may be devised without departing from the basic scope thereof, and the scope thereof is determined by the claims that follow.