Patent Publication Number: US-11664259-B2

Title: Process apparatus with on-the-fly substrate centering

Description:
CROSS-REFERENCE TO RELATED APPLICATIONS 
     This application is a continuation of U.S. application Ser. No. 15/369,573, filed Dec. 5, 2016, (now U.S. Pat. No. 10,879,101), which is a continuation of U.S. application Ser. No. 14/325,702, filed Jul. 8, 2014, (now U.S. Pat. No. 9,514,974) which is a non-provisional of and claims the benefit of U.S. Provisional Patent Application No. 61/843,685, filed on Jul. 8, 2013, the disclosures of which are incorporated by reference herein in their entireties. 
    
    
     BACKGROUND 
     1. Field 
     The exemplary embodiments generally relate to substrate processing apparatus and, more particularly, substrate processing apparatus with substrate centering. 
     2. Brief Description of Related Developments 
     Typical manufacturing processes for semiconductor integrated circuits may utilize robotic manipulators to cycle substrates, for example, circular silicon wafers (or any other suitable substrates), through pre-determined sequences of operations in fully automated processing equipment. Substrates may be delivered to the substrate processing equipment, also referred to as a tool, in standard transportation cassettes which house a batch of one or more substrates stored in slots. Individual substrates may then be transferred from the cassettes by a specialized pick-place robot which may be integrated into the tool. Typically, the robot holds a substrate by means of frictional force between the backside of the substrate and an end effector. In some applications, the force may be supplemented by a controlled suction-cup gripper or active gripping members disposed on the end effector. 
     As a result of limited, but not negligible, motion of the substrates in the cassettes during transportation, the robot may pick the substrate with undesirable eccentricity or misalignment. The difference between the actual location of the center of the substrate and the specified position on the robot end effector needs to be corrected before the substrate can be processed in the tool. Conventional methods and devices for determination and correction of eccentricity or misalignment of circular substrates may include stationary aligners, aligners built into the robot end effector, and sensors placed externally to or within a chamber through which the substrate is transported by the robot. Placement of the aligners or sensors within the chamber or on the end effector may result in chambers having larger internal volumes to, for example, accommodate the aligners and sensors or the increased size of the end effector. 
     It would be advantageous to provide an on-the-fly substrate centering/alignment system capable of determining eccentricity and/or misalignment of a substrate passing through a chamber while making the internal volume of the chamber as small as possible. 
    
    
     
       BRIEF DESCRIPTION OF THE DRAWINGS 
       The foregoing aspects and other features of the disclosed embodiment are explained in the following description, taken in connection with the accompanying drawings, wherein: 
         FIGS.  1 A- 1 D  are schematic illustrations of substrate processing tools in accordance with aspects of the disclosed embodiment; 
         FIGS.  2 A and  2 B  are schematic illustrations of chambers incorporating aspects of the disclosed embodiment; 
         FIGS.  3  and  4    are schematic illustrations of portions of a slot valve in accordance with aspects of the disclosed embodiment; 
         FIGS.  4 A- 4 D  are schematic illustrations of portions of a slot valve in accordance with aspects of the disclosed embodiment; 
         FIGS.  5 A and  5 B  are schematic illustrations of a chamber incorporating aspects of the disclosed embodiment; 
         FIG.  6    is a schematic illustration of a portion of a substrate processing tool incorporating aspects of the disclosed embodiment; 
         FIGS.  7  and  8    are schematic illustrations of a substrate loading device incorporating aspects of the disclosed embodiments; and 
         FIG.  9    is a flow chart in accordance with aspects of the disclosed embodiment. 
     
    
    
     DETAILED DESCRIPTION 
     In accordance with aspects of the disclosed embodiment, a substrate processing apparatus is provided. The substrate processing apparatus includes one or more slot or isolation valves configured to sense or otherwise detect a substrate passing through the slot valve as will be described in greater detail below for effecting on-the-fly substrate centering/alignment and/or eccentricity (collectively referred to herein as alignment) detection. Locating the alignment sensors within or otherwise on the slot valve allows the internal volume of a chamber to which the slot valve is coupled to be made as small as possible so that only sufficient clearance for the substrate and end effector (and any suitable portion of the robot arm to which the end effector is attached) may be provided within the chamber for the substrate to transit to/from or through the chamber. Although the aspects of the disclosed embodiment will be described with reference to the drawings, it should be understood that the aspects of the disclosed embodiment can be embodied in many forms. In addition, any suitable size, shape or type of elements or materials could be used. 
     Referring to  FIGS.  1 A- 1 D , there are shown schematic views of substrate processing apparatus or tools incorporating the aspects of the disclosed embodiment as disclosed further herein. 
     Referring to  FIGS.  1 A and  1 B , a processing apparatus, such as for example a semiconductor tool station  1090  is shown in accordance with an aspect of the disclosed embodiment. Although a semiconductor tool is shown in the drawings, the aspects of the disclosed embodiment described herein can be applied to any tool station or application employing robotic manipulators. In this example the tool  1090  is shown as a cluster tool, however the aspects of the disclosed embodiment may be applied to any suitable tool station such as, for example, a linear tool station such as that shown in  FIGS.  1 C and  1 D  and described in U.S. Pat. No. 8,398,355, entitled “Linearly Distributed Semiconductor Workpiece Processing Tool,” issued Mar. 19, 2013; U.S. Pat. No. 7,458,763, entitled “Mid-Entry Load Lock for Semiconductor Handling System,” issued Dec. 2, 2008; and U.S. patent application Ser. No. 12/123,329 entitled “Compact Substrate Transport System,” filed on May 19, 2008, the disclosures of which are incorporated by reference herein in their entireties. The tool station  1090  generally includes an atmospheric front end  1000 , a vacuum load lock  1010  and a vacuum back end  1020 . In other aspects, the tool station may have any suitable configuration. The components of each of the front end  1000 , load lock  1010  and back end  1020  may be connected to a controller  1091  which may be part of any suitable control architecture such as, for example, a clustered architecture control. The control system may be a closed loop controller having a master controller, cluster controllers and autonomous remote controllers such as those disclosed in U.S. Pat. No. 7,904,182 entitled “Scalable Motion Control System” issued on Mar. 8, 2011 the disclosure of which is incorporated herein by reference in its entirety. In other aspects, any suitable controller and/or control system may be utilized. 
     In one aspect, the front end  1000  generally includes load port modules  1005  and a mini-environment  1060  such as for example an equipment front end module (EFEM). The load port modules  1005  may be box opener/loader to tool standard (BOLTS) interfaces that conform to SEMI standards E15.1, E47.1, E62, E19.5 or E1.9 for 300 mm load ports, front opening or bottom opening boxes/pods and cassettes. In other aspects, the load port modules may be configured as 200 mm, 300 mm or 450 mm wafer interfaces or any other suitable substrate interfaces such as for example larger or smaller wafers or flat panels for flat panel displays. Although two load port modules are shown in  FIG.  1 A , in other aspects any suitable number of load port modules may be incorporated into the front end  1000 . The load port modules  1005  may be configured to receive substrate carriers or cassettes  1050  from an overhead transport system, automatic guided vehicles, person guided vehicles, rail guided vehicles or from any other suitable transport method. The load port modules  1005  may interface with the mini-environment  1060  through load ports  1040 . The load ports  1040  may allow the passage of substrates between the substrate cassettes  1050  and the mini-environment  1060  or any other suitable chamber having any suitable atmospheric or vacuum atmosphere therein. The mini-environment  1060  generally includes any suitable transfer robot  1013 . In one aspect the robot  1013  may be a track mounted robot such as that described in, for example, U.S. Pat. No. 6,002,840, the disclosure of which is incorporated by reference herein in its entirety. The mini-environment  1060  may provide a controlled, clean zone for substrate transfer between multiple load port modules. 
     The vacuum load lock  1010  may be located between and connected to the mini-environment  1060  and the back end  1020 . It is noted that the term vacuum as used herein may denote an ultra-high vacuum such as 10 −5  Torr or below in which the substrates are processed. The load lock  1010  generally includes atmospheric and vacuum slot valve assemblies  100  (substantially similar to those described herein and generally referred to as valves or slot/isolation valves). The slot valves  100  may provide the environmental isolation employed to evacuate the load lock after loading a substrate from the atmospheric front end and to maintain the vacuum in the transport chamber when venting the lock with an inert gas such as nitrogen. The load lock  1010  may also include an aligner  1011  for aligning a fiducial of the substrate to a desired position for processing. In other aspects, the vacuum load lock may be located in any suitable location of the processing apparatus and have any suitable configuration. 
     The vacuum back end  1020  generally includes a transport chamber  1025 , one or more processing station(s)  1030  and any suitable transfer robot  1014  and may include one or more aspects of the disclosed embodiments described herein. The transfer robot  1014  may be located within the transport chamber  1025  to transport substrates between the load lock  1010  and the various processing stations  1030 . The processing stations  1030  may operate on the substrates through various deposition, etching, or other types of processes to form electrical circuitry or other desired structure on the substrates. Typical processes include but are not limited to thin film processes that use a vacuum such as plasma etch or other etching processes, chemical vapor deposition (CVD), plasma vapor deposition (PVD), implantation such as ion implantation, metrology, rapid thermal processing (RTP), dry strip atomic layer deposition (ALD), oxidation/diffusion, forming of nitrides, vacuum lithography, epitaxy (EPI), wire bonder and evaporation or other thin film processes that use vacuum pressures. The processing stations  1030  are connected to the transport chamber  1025  to allow substrates to be passed from the transport chamber  1025  to the processing stations  1030  and vice versa. 
     Referring now to  FIG.  1 C , a schematic plan view of a linear substrate processing system  2010  is shown where the tool interface section  2012  is mounted to a transport chamber module  3018  so that the interface section  2012  is facing generally towards (e.g. inwards) but is offset from the longitudinal axis X of the transport chamber  3018 . The transport chamber module  3018  may be extended in any suitable direction by attaching other transport chamber modules  3018 A,  3018 I,  3018 J to interfaces  2050 ,  2060 ,  2070  as described in U.S. Pat. No. 8,398,355, previously incorporated herein by reference. It is noted that the interfaces  2050 ,  2060 ,  2070  may include one or more slot valves as described herein to, for example, isolate adjacent modules from one another. Each transport chamber module  3018 ,  3019 A,  3018 I,  3018 J includes any suitable substrate transport  2080  for transporting substrates throughout the processing system  2010  and into and out of, for example, processing modules PM. As may be realized, each chamber module may be capable of holding an isolated or controlled atmosphere (e.g. N2, clean air, vacuum). 
     Referring to  FIG.  1 D , there is shown a schematic elevation view of an exemplary processing tool  410  such as may be taken along longitudinal axis X of the linear transport chamber  416 . In the aspect of the disclosed embodiment shown in  FIG.  1 D , tool interface section  12  may be representatively connected to the transport chamber  416 . In this aspect, interface section  12  may define one end of the tool transport chamber  416 . As seen in  FIG.  1 D , the transport chamber  416  may have another workpiece entry/exit station  412  for example at an opposite end from interface station  12 . In other aspects, other entry/exit stations for inserting/removing workpieces from the transport chamber may be provided. In one aspect, interface section  12  and entry/exit station  412  may allow loading and unloading of workpieces from the tool. In other aspects, workpieces may be loaded into the tool from one end and removed from the other end. In one aspect, the transport chamber  416  may have one or more transfer chamber module(s)  18 B,  18   i . Each chamber module may be capable of holding an isolated or controlled atmosphere (e.g. N2, clean air, vacuum). As noted before, the configuration/arrangement of the transport chamber modules  18 B,  18   i , load lock modules  56 A,  56 B and workpiece stations forming the transport chamber  416  shown in  FIG.  1 D  is merely exemplary, and in other aspects the transport chamber may have more or fewer modules disposed in any desired modular arrangement. In the aspect shown, station  412  may be a load lock. In other aspects, a load lock module may be located between the end entry/exit station (similar to station  412 ) or the adjoining transport chamber module (similar to module  18   i ) may be configured to operate as a load lock. As also noted before, transport chamber modules  18 B,  18   i  have one or more corresponding transport apparatus  26 B,  26   i , which may include one or more aspects of the disclosed embodiment described herein, located therein. The transport apparatus  26 B,  26   i  of the respective transport chamber modules  18 B,  18   i  may cooperate to provide the linearly distributed workpiece transport system  420  in the transport chamber. In this aspect, the transport apparatus  26 B may have a general SCARA arm configuration (though in other aspects the transport arms may have any other desired arrangement such as a frog-leg configuration, telescopic configuration, bi-symmetric configuration, etc.). In the aspect of the disclosed embodiment shown in  FIG.  1 D , the arms of the transport apparatus  26 B may be arranged to provide what may be referred to as fast swap arrangement allowing the transport to quickly swap wafers from a pick/place location. The transport arm  26 B may have a suitable drive section, such as that described below, for providing each arm with any suitable number of degrees of freedom (e.g. independent rotation about shoulder and elbow joints with Z axis motion). As seen in  FIG.  1 D , in this aspect the modules  56 A,  56 ,  30   i  may be located interstitially between transfer chamber modules  18 B,  18   i  and may define suitable processing modules, load lock(s), buffer station(s), metrology station(s) or any other desired station(s). For example the interstitial modules, such as load locks  56 A,  56  and workpiece station  30   i , may each have stationary workpiece supports/shelves  56 S,  56 S 1 ,  56 S 2 ,  30 S 1 ,  30 S 2  that may cooperate with the transport arms to effect transport or workpieces through the length of the transport chamber along linear axis X of the transport chamber. By way of example, workpiece(s) may be loaded into the transport chamber  416  by interface section  12 . The workpiece(s) may be positioned on the support(s) of load lock module  56 A with the transport arm  15  of the interface section. The workpiece(s), in load lock module  56 A, may be moved between load lock module  56 A and load lock module  56  by the transport arm  26 B in module  18 B, and in a similar and consecutive manner between load lock  56  and workpiece station  30   i  with arm  26   i  (in module  18   i ) and between station  30   i  and station  412  with arm  26   i  in module  18   i . This process may be reversed in whole or in part to move the workpiece(s) in the opposite direction. Thus, in one aspect, workpieces may be moved in any direction along axis X and to any position along the transport chamber and may be loaded to and unloaded from any desired module (processing or otherwise) communicating with the transport chamber. In other aspects, interstitial transport chamber modules with static workpiece supports or shelves may not be provided between transport chamber modules  18 B,  18   i . In such aspects, transport arms of adjoining transport chamber modules may pass off workpieces directly from end effector or one transport arm to end effector of another transport arm to move the workpiece through the transport chamber. The processing station modules may operate on the substrates through various deposition, etching, or other types of processes to form electrical circuitry or other desired structure on the substrates. The processing station modules are connected to the transport chamber modules to allow substrates to be passed from the transport chamber to the processing stations and vice versa. A suitable example of a processing tool with similar general features to the processing apparatus depicted in  FIG.  1 D  is described in U.S. Pat. No. 8,398,355, previously incorporated by reference in its entirety. As can be seen in  FIG.  1 A  slot valves  100  may be located between and connect adjacent ones of the interfaces  12 ,  412  and modules  56 A,  18 B,  416 ,  18   i ,  30   i  to selectively seal or otherwise isolate each interface or module from other ones of the interfaces or modules. 
     Referring now to  FIGS.  1 D,  2 A and  2 B , as noted above, the slot valve  100  may be provided ( FIG.  9   , Block  900 ) such that the slot valve is disposed between and connects adjacent modules (or in  FIG.  1 B  be located on one or more sides of load locks  1010 ) so that the modules can be sealed or isolated from other adjacent modules. Each slot valve  100  may include one or more interfaces  100 A,  100 B. Referring also to  FIGS.  2 ,  3  and  4   , each interface  100 A,  100 B may be configured for coupling to any suitable module  200  such as those described herein. In one aspect, one interface  100 A,  100 B may couple the slot valve  100  to an atmospheric environment, such as in an equipment front end module, while the other interface  100 A,  100 B couples the slot valve  100  to a vacuum environment. In other aspects both interfaces  100 A,  100 B may couple the slot valve  100  to atmospheric environments or vacuum environments. The slot valve  100  may include a valve body or housing  100 H that is configured to cover a substrate transport opening of a substrate holding module or chamber to which the valve  100  is attached. The valve may also include a door assembly that includes a door drive  110 , a valve door  120  and at least one sensor element  150  (described in greater detail below). The door drive  110  may be affixed in any suitable manner to the housing  100 H and may be coupled to the valve door  120 . In one aspect the door assembly may be a modular unit that may be removable from the valve housing  100 H as a one piece unit. In another aspect the valve door  120  and the at least one sensing element  150  may be a modular unit that may be removable from the valve housing  100 H as a one piece unit. The door  120  may be disposed within the valve body  100 H and driven by the door drive  110  within the valve body  100 H in any suitable manner and at least in the direction of arrow  250 . The movement of the door  120  within the valve body  100 B by the door drive  110  may be any suitable one or two axis movement sufficient to move the door  120  over an opening  220  in the module  200  so that the opening  220  is sealed by the door  120  for isolating an interior of the module  200 . The movement of the door  120  within the valve body  100 H by the door drive  110  may also be sufficient to move the door  120  away from the opening  220  in the module  200  so that a substrate S carried by, for example, an end effector EE (see  FIG.  1 C ), or any other suitable portion, of a transport robot can pass through the opening  220 . In one aspect the door  120  may be configured to interface with a sealing surface  200 S of the module  200  for sealing the opening  220  while in other aspects, as shown in  FIG.  2 A , the door may be configured to interface with a module insert  210  (on which the sealing surface  200 S is disposed) that can be removed and replaced due to, for example, wear caused interaction between the door  120  and the module insert  210 . In other aspects the slot valve may be integral to at least one of the modules. For example a frame of one of the modules may form the valve body and be configured for coupling to another of the modules such that the valve seals the passage through the valve body in a manner substantially similar to that described above. 
     Referring also to  FIGS.  3  and  4    one or more suitable substrate detection sensor elements  150 A,  150 B (generally referred to as sensor elements  150 ) may be provided or otherwise placed (e.g. located/mounted) on, for example, any suitable side of the door  120  for effecting on-the-fly wafer alignment. In this aspect the sensor elements  150  are illustrated as being mounted on a side  120 T of the door such that the sensor elements are oriented to sense substrates located on a substrate transfer plane WTP ( FIG.  3   ). As seen in  FIGS.  3  and  4    the sensor elements are illustrated on the top side of the door however, in other aspects the sensor elements may be disposed on the lateral sides (e.g. extending between the top and a bottom) of the door (e.g. substantially perpendicular to a substrate transfer plane WTP extending through the valve body), the front side of the door, the back side of the door and/or the bottom (e.g. opposite the top) side of the door. In one aspect the sensor elements may be disposed so they are substantially perpendicular to or otherwise face the substrate transfer plane WTP at any suitable angle. The wafer transfer plane WTP may pass through and be defined by one or more of the valve body  100 H and the opening  220  of the modules to which the valve body is coupled. In this aspect two sensor elements  150 A,  150 B are illustrated as being located on side  120 T but in other aspects more or less than two sensor elements may be provided on the side  120 T. Suitable examples of sensors and sensor arrangements which may be located on the door  120  are described in, for example, U.S. Pat. No. 7,925,378 entitled “Process Apparatus with On-The-Fly Workpiece Centering,” issued on Apr. 12, 2011; U.S. Pat. No. 7,880,155 entitled “Substrate Alignment Apparatus Comprising a Controller to Measure Alignment During Transport,” issued on Feb. 1, 2011; U.S. Pat. No. 7,925,378 entitled “Process Apparatus with On-The-Fly Workpiece Centering,” issued on Apr. 12, 2011; U.S. Pat. No. 6,990,430 entitled “System and Method for On-The-Fly Eccentricity Recognition” issued on Jan. 24, 2006; and U.S. Pat. No. 4,819,167 entitled “System and Method for Detecting the Center of an Integrated Circuit Wafer” issued on Apr. 4, 1989, the disclosures of which are incorporated herein by reference in their entireties. As may be realized, in one aspect the sensor elements  150  may be configured in any suitable manner for operation in a vacuum environment. For example, a view port or any other suitable sealing members may be provided on the door  120  to isolate any suitable portion of the sensing elements from the vacuum environment. In other aspects the sensor elements  150  may be suitably configured for operation within an atmospheric environment. 
     The one or more sensor elements  150  may be any suitable sensor elements such as, for example, optical, capacitive and/or inductive sensor elements. In one aspect each sensor element  150  may include, in the case of at least the optical (or other suitable beam or reflective) sensor elements, an emitter and a receiver pair disposed in a common housing. In another aspect the sensor elements  150 A,  150 B may form a sensor pair such that sensor element  150 A may be an emitter and the sensor element  150 B may be a receiver or vice versa. In still other aspects, there may be one or more corresponding sensor elements  300  (such as emitters, receivers, reflectors, etc.) disposed on an interior surface  100 W (or any other suitable surface) of the valve body  100 H that communicably interface with respective ones of the sensor elements  150  in any suitable manner so that the one or more sensor elements  300  and the respective sensor elements  150  form one or more respective sensor pairs. As may be realized, the sensor elements  300  may, in other aspects, be disposed on an outside surface of the valve body  100 H and communicate with one or more respective sensor elements  150  through a view port or in any other suitable manner. As may also be realized, where sensing elements  300  are positioned on an interior and/or exterior surface of the valve body  100 H to communicably interface with the sensor elements  150 , in one aspect, the sensor elements  150  may be reflectors that reflect an emissive signal from the respective sensing elements  300  back to a receiver of the respective sensing elements  300 . In other aspects the sensor elements  300  may be reflectors that reflect an emissive signal from the respective sensing elements  150  back to a receiver of the sensing elements  150 . 
     Referring still to  FIGS.  2 A and  3   , the door drive  110  may be mechanically and/or electronically configured to position the door  120  so that the one or more sensing elements  150  (e.g. when the door is open) are located in a predetermined sensing position ( FIG.  9   , Block  910 ) for sensing/detecting substrates S passing through the valve body  110 H along the substrate transfer plane WTP ( FIG.  9   , Block  920 ). In other aspects, the door drive  110  may be configured to position the door  120  so that the one or more sensing elements  150  are in a predetermined position relative to the respective sensing elements  300  (e.g. when the door is open) for sensing substrates S passing through the valve body  110 H along the substrate transfer plane WTP. In either aspect, as noted above, the door drive  110  may be, for example, a multi-axis drive configured to, when opening the door, move the door away from the sealing surface  200 S and opening  220  so that opening  220  is unobstructed to allow for the passage of substrates S along the substrate transfer plane WTP. 
     In one aspect, the door drive  110  may include one or more mechanical hard stops  110 S 1 ,  110 S 2  positioned to mechanically arrest or otherwise controllably stop movement of the door  120  along one or more axes of movement for positioning the sensing elements  150  disposed on the door  120  in the predetermined sensing position. In other aspects the door drive  110  may include soft stops for positioning the sensing elements  150  in the predetermined sensing position. For example, the door drive  110  may include one or more suitable encoders  110 E configured to determine, along with any suitable controller such as controller  1091 , the position of the door  120  along one or more axes of movement such that the drive unit  110  stops under the control of the controller and the sensing elements  150  are located at the predetermined sensing position. 
     When disposed at the predetermined sensing position, the one or more sensing elements  150  alone or in combination with sensing elements  300  may detect and effect, along with any suitable controller such as controller  1091  (e.g. the controller receives suitable sensing data from the sensing elements), on-the-fly substrate alignment (e.g. alignment of the substrate with a any suitable substrate holding location) in any suitable manner ( FIG.  9   , Block  930 ) such as, for example, in the manner described in U.S. Pat. Nos. 7,925,378; 7,880,155; 7,925,378; 6,990,430; and/or 4,819,167 the disclosures of which have been previously incorporated herein by reference in their entireties. For example, referring to  FIG.  4 A , one or more sensors  150 AS (e.g. where each of the one or more sensors includes a two sensing elements forming a sensor pair capable of detecting a substrate or a single sensing element capable of detecting a substrate as described above) may be positioned on the door  120  for detecting a substrate S passing along the substrate transfer plane WTP. In this aspect one sensor  150 AS (in other aspects more than one sensing element can be provided) capable of detecting a substrate S is suitably positioned on the door  120  for effecting centering/alignment of the substrate S in a manner substantially similar to that described in U.S. Pat. No. 7,925,378. 
     In another aspect, referring to  FIG.  4 B , one or more sensors  150 CS (e.g. where each of the one or more sensors includes a two sensing elements forming a sensor pair capable of detecting a substrate or a single sensing element capable of detecting a substrate as described above) having any suitable cross section for detecting, for example, any suitable area of a substrate S moving along the substrate transfer plane WTP is provided on the door  120  at any suitable position. Here the sensor  150 CS may be, for example, a beam sensor where the sensor beam has any suitable cross section. Here the sensor beam may have a rectangular cross section but in other aspects the sensor beam may have any suitable distributed shape effecting centering/alignment of the substrate S in a manner substantially similar to that described in U.S. Pat. No. 7,880,155. 
     In yet another aspect, two or more sensors  150 AS,  150 BS (e.g. where each of the one or more sensors includes two sensing elements forming a sensor pair capable of detecting a substrate or a single sensing element capable of detecting a substrate as described above) are provided on the door in any suitable positions for detecting a substrate S moving along the substrate transfer plane WTP. In this aspect the sensors  150 AS,  150 BS may be positioned at any suitable distances DA, DB from, for example, a centerline of the substrate transfer plane WTPCL (e.g. the line along which the center of the substrate S is expected to travel along). Here sensor  150 AS is shown on one side of the centerline WTPCL and the sensor  150 BS is shown on the opposite side of the centerline but in other aspects the sensors  150 AS,  150 BS may be disposed on a common side of the centerline WTPCL. The sensors  150 AS,  150 BS may also be disposed any suitable distance DX from each other along (e.g. relative to) a direction of substrate travel along the substrate transfer plane WTP. In one aspect the distance DX may be substantially zero (e.g. so the sensors are in-line with each other) while in other aspect the distance may be any suitable distance greater than zero. The sensors  150 AS,  150 BS, along with any suitable controller such as controller  1091 , may be configured to effect centering/alignment of the substrate S in a manner substantially similar to that described in U.S. Pat. No. 6,990,430. 
     In still another aspect, three or more sensors  150 AS,  150 BS,  150 DS (e.g. where each of the one or more sensors includes a two sensing elements forming a sensor pair capable of detecting a substrate or a single sensing element capable of detecting a substrate as described above) are provided on the door in any suitable positions for detecting a substrate S moving along the substrate transfer plane WTP. In this aspect the sensors  150 AS,  150 BS,  150 DS are arranged in-line with each other but in other aspects one or more of the sensors may be staggered in a manner similar to that described above with respect to  FIG.  4 C . Here the sensors  150 AS,  150 BS,  150 DS along with any suitable controller such as controller  1091 , may be configured to effect centering/alignment of the substrate S in a manner substantially similar to that described in U.S. Pat. No. 4,819,167. 
     Referring now to  FIGS.  5 A and  5 B , in another aspect chamber  550  may have multiple independently isolatable chambers  550 C 1 ,  550 C 2  within a common housing  550 H. Here the chambers  550 C 1 ,  550 C 2  are illustrated as being stacked above one another but in other aspects the chambers  550 C 1 ,  550 C 2  may be disposed side by side. In still other aspects the chambers may be arranged in a two dimensional array. Each chamber  550 C 1 ,  550 C 2  may be substantially similar to those described above in that each chamber includes one or more openings  220  for allowing substrate S passage to and from an interior environment of the chamber  550 C 1 ,  550 C 2 . Each opening  220  is provided with a respective slot valve  500 A,  500 B (the slot valve bodies are omitted in  FIGS.  5 A and  5 B ) substantially similar to those described above. In this aspect, the slot valves  500 A,  500 B for the vertically arranged chambers  550 C 1 ,  550 C 2  are illustrated as being opposed to one another so that when opening the slot valve doors  520 A,  520 B move away from each other. Suitable arrangements of opposed slot valves (and their door drives which may include door positioning stops/sensors as described herein for allowing the placement of the door sensors in the predetermined sensing position) are described in, for example, U.S. Pat. No. 8,272,825 the disclosure of which has been previously incorporated by reference herein in its entirety. 
     In this aspect, each door  520 A,  520 B may include one or more sensing elements  150  (e.g. that form one or more sensors capable of detecting a substrate) as described above. As may be realized, in one aspect each of the sensing elements  150  for the doors  520 A,  520 B may be configured so that the one or more sensing elements  150  of door  520 A are capable of sensing substrates, in a manner substantially similar to that described above, independent of the sensing elements  150  of door  520 B. In other aspects, the sensing elements  150  of door  520 A may communicably interface with the sensing elements  150  of door  520 B in a manner substantially similar to that described above with respect to sensor elements  300 . For example, one or more sensing elements  150  of door  520 A may form a sensor pair with respective sensing elements  150  of door  520 A such that, for example, an emitter is located on door  520 A and a receiver is located on door  520 B or vice versa. In other aspects, an emitter/receiver may be located on door  520 A and a corresponding reflector may be located on door  520 B or vice versa. 
     In still another aspect of the disclosed embodiment, referring to  FIG.  6   , the valve  100 ′ may include a housing  100 H′, a door  120 ′ and a door drive  110 ′. The valve  100 ′ may be substantially similar to the valves described above however, in this aspect the door  120 ′ and/or the door drive may be oriented at any suitable angle ANG relative to, for example, the substrate transfer plane WTP or any other suitable reference datum within the housing  100 H′ and/or the substrate holding module  200 . In this aspect the at least one substrate sensor element  150  may be located on a side of the door  120 T′ so that when the door is in an open position (e.g. so that substrates can pass through the opening  220 ) the at least one substrate sensor element  150  is capable of sensing substrates located on the substrate transfer plane WTP while the substrates are substantially within the substrate holding module  200 . In this aspect the at least one substrate sensor element may be configured to, for example, detect at least the leading edge of the substrate. In one aspect, such as where the at least one substrate sensor element  150  includes a beam emitter and receiver the beam may be scattered by the edge of the substrate (such as at a corner or other transition between, e.g., a bottom of the substrate and a side of the substrate spanning between the bottom and a top of the substrate) where the scattered light is received by the receiver. 
     In other aspects, the alignment sensors/system described herein may be employed in any suitable substrate station, such as a load port, so that one or more sensors are disposed on the load port door in a manner substantially similar to that described above with respect to the slot valve  100 . For example, referring now to  FIGS.  7  and  8    the load port  1005  described above is illustrated in greater detail. Here the load port  1005  is connected in any suitable manner to any suitable chamber  700  which may be substantially similar to those described above (e.g. an EFEM, load lock, transfer chamber, processing chamber, etc.). The load port  1005  may include a substrate cassette table  710  configured to hold one or more substrate cassettes  1050 . The substrate cassette table  710  may be movable to effect sealing of the cassette  1050  against any suitable sealing surface of the load port  1005  such as, for example, shield  790 . The shield  790  may have an aperture  770  for loading and unloading substrates to/from the cassette  1050 . Aperture  770  may be surrounded by a seal  775 , against which a cassette opening  1051  may sealingly abut. When cassette opening  1051  is in abutting relationship with seal  775 , aperture  770  may be aligned with cassette opening  1051 . 
     The load port  1050  may have a cassette door drive  735 , shown in a retracted position, for sealing aperture  770  when cassette opening  1051  is not abutting seal  775 , and for coupling to and removing cassette door  1015  when cassette opening  1051  is abutting seal  775 . Cassette door drive  735  includes an aperture closure or door  730  mounted on an extendable member  780  which is operated for both translation and pivoting movement by cassette door drive  735 . When in an extended position the aperture closure  730  seals aperture  770 . The aperture closure  730  includes a door transport  785  for operating any suitable door latch operating mechanism so as to lock or release cassette door  1015  from cassette  1050  and to the support cassette door  1015  during translation and pivoting movements. Door transport  785  includes selectively operable door supports (not shown) which are engageable with cassette door  1015  when cassette opening  1051  is in abutting relationship with seal  775 . Substrate station  1050 , as noted above, also includes provisions for interfacing to an isolation valve  740 , which may be substantially similar to the isolation valves described above, for coupling load port  1050  to chamber  700 . Isolation valve  740  is positioned to allow substrates S to be transported along a substrate transfer plane WTP between the cassette  1050  and chamber  700 . 
     The load port  1050  may include any suitable substrate mapper  745  and be configured for mapping the locations of the substrates within the cassette  1050  in a manner substantially similar to that described in U.S. Pat. No. 7,109,509 entitled “Device for the Detection of Substrates Stacked with a Specific Spacing” issued on Sep. 19, 2006; U.S. Pat. No. 7,255,524 entitled “Substrate Cassette Mapper” issued on Aug. 14, 2007; and U.S. Pat. No. 7,677,859 entitled “Substrate Loading and Uploading Station with Buffer” issued on Mar. 16, 2010, the disclosures of which are incorporated herein by reference in their entireties. The load port may also include one or more substrate sensor elements  150 . Here the substrate sensor elements  150  may be disposed on a surface of the aperture closure  730  facing the substrate transfer plane WTP in a manner substantially similar to that described above with respect to valve door  120 . In a manner substantially similar to that described above, the cassette door drive  735  may include any suitable hard stops  735 S or soft stops (including one or more encoders  735 E) for stopping the aperture closure  730  and positioning the sensor elements  150  in a predetermined sensing position for detecting and effecting alignment, along with any suitable controller such as controller  1091 , of substrates S being transferred to and/or from the cassette  1050  in a manner substantially similar to that described above, such as with respect to  FIGS.  4 A- 4 D . 
     In accordance with one or more aspects of the disclosed embodiment, a substrate processing apparatus is provided. The substrate processing apparatus includes a frame defining a chamber with a substrate transport opening and a substrate transfer plane defined therein and a valve mounted to the frame and being configured to seal an atmosphere of the chamber when closed, the valve having a door movably disposed to open and close the substrate transport opening. At least one substrate sensor element disposed on a side of the door and oriented to sense substrates located on the substrate transfer plane. 
     In accordance with one or more aspects of the disclosed embodiment the at least one sensor element is facing the substrate transfer plane. 
     In accordance with one or more aspects of the disclosed embodiment the valve includes a housing with the substrate transfer plane being disposed therethrough. 
     In accordance with one or more aspects of the disclosed embodiment the valve includes a door drive configured to position the door relative to the wafer transfer plane so that the at least one substrate sensor element is located at a predetermined sensing position for sensing substrates located on the substrate transfer plane. 
     In accordance with one or more aspects of the disclosed embodiment the door drive includes mechanical stops configured to position the door within the housing so that the at least one substrate sensor element is located at a predetermined sensing position. 
     In accordance with one or more aspects of the disclosed embodiment substrate processing apparatus includes a controller communicably connected to the door drive where the door drive includes at least one encoder configured to effect, along with the controller, positioning the door within the housing so that the at least one substrate sensor element is located at a predetermined sensing position. 
     In accordance with one or more aspects of the disclosed embodiment, the at least one substrate sensor element includes one or more of an optical beam sensor element, an optical reflective sensor element, an inductive sensor element, or a capacitive sensor element. 
     In accordance with one or more aspects of the disclosed embodiment the at least one substrate sensor element comprises a first sensor element disposed on the side of the door and a second sensor element disposed on the housing to form a sensor pair configured to sense the substrates travelling along the substrate transfer plane. 
     In accordance with one or more aspects of the disclosed embodiment the first sensor element is a reflector and the second sensor element comprises at least one of a beam emitter or beam receiver. 
     In accordance with one or more aspects of the disclosed embodiment the second sensor element is a reflector and the first sensor element comprises at least one of a beam emitter or beam receiver. 
     In accordance with one or more aspects of the disclosed embodiment, the substrate processing apparatus comprises a linearly arranged substrate processing tool. 
     In accordance with one or more aspects of the disclosed embodiment, the substrate processing apparatus comprises a cluster substrate processing tool. 
     In accordance with one or more aspects of the disclosed embodiment, the substrate processing apparatus includes a second isolation valve having a second door, wherein the door is opposing arranged with the second door and the at least one substrate sensor element comprises a first sensor element disposed on the side of the door and a second sensor element disposed on a side of the second door facing the substrate transfer plane, the first and second sensor element forming a sensor pair configured to sense the substrates travelling along the substrate transfer plane. 
     In accordance with one or more aspects of the disclosed embodiment the first sensor element is a reflector and the second sensor element comprises at least one of a beam emitter or beam receiver. 
     In accordance with one or more aspects of the disclosed embodiment the second sensor element is a reflector and the first sensor element comprises at least one of a beam emitter or beam receiver. 
     In accordance with one or more aspects of the disclosed embodiment, a method of aligning a substrate in a substrate processing apparatus is provided. The method includes providing an isolation valve having at least one sensing element mounted to a door of the isolation valve, positioning the at least one sensing element with the door so that the at least one sensing element is located in a predetermined sensing position relative to a wafer transfer plane, sensing a substrate located on the wafer transfer plane with the at least one sensing element, and receiving data from the at least one sensing element with a controller for effecting alignment of the substrate relative to a substrate holding location. 
     In accordance with one or more aspects of the disclosed embodiment the method includes positioning the door with mechanical stops so that the at least one substrate sensor element is located at a predetermined sensing position. 
     In accordance with one or more aspects of the disclosed embodiment the method includes electronically positioning the door so that the at least one substrate sensor element is located at a predetermined sensing position. 
     In accordance with one or more aspects of the disclosed embodiment, the at least one substrate sensor element includes one or more of an optical beam sensor element, an optical reflective sensor element, an inductive sensor element, or a capacitive sensor element. 
     In accordance with one or more aspects of the disclosed embodiment, a substrate processing apparatus is provided. The substrate processing apparatus includes a substrate station having an aperture closure for sealing a loading and unloading aperture of the station where the aperture is configured for loading and unloading substrates from a substrate cassette along a substrate transfer plane, an apparatus including a door drive configured to remove a door of the substrate cassette to open the substrate cassette and for operating the aperture closure to open the aperture, and at least one substrate sensing element disposed on a side of the aperture closure and oriented to sense substrates located on the substrate transfer plane. 
     In accordance with one or more aspects of the disclosed embodiment the at least one substrate sensing element is facing the substrate transfer plane. 
     In accordance with one or more aspects of the disclosed embodiment the door drive is configured to position the aperture closure so that the at least one substrate sensor element is located, relative to the substrate transfer plane, at a predetermined sensing position for sensing substrates located on the substrate transfer plane. 
     In accordance with one or more aspects of the disclosed embodiment the door drive includes mechanical stops configured to position the aperture closure so that the at least one substrate sensor element is located at a predetermined sensing position. 
     In accordance with one or more aspects of the disclosed embodiment substrate processing apparatus includes a controller communicably connected to the door drive where the door drive includes at least one encoder configured to effect, along with the controller, positioning the aperture closure so that the at least one substrate sensor element is located as a predetermined sensing position. 
     In accordance with one or more aspects of the disclosed embodiment, the at least one substrate sensor element includes one or more of an optical beam sensor element, an optical reflective sensor element, an inductive sensor element, or a capacitive sensor element. 
     In accordance with one or more aspects of the disclosed embodiment a valve assembly for a substrate processing apparatus is provided. The valve assembly includes a housing configured to cover a substrate transport opening of a substrate holding chamber. The valve assembly further includes a door assembly having a door configured to open and close the substrate transport opening and at least one substrate sensor element located on a side of the door and oriented to sense substrates located on a substrate transfer plane associated with the substrate transport opening. 
     In accordance with one or more aspects of the disclosed embodiment the door assembly includes a door drive configured to position the door so that the at least one substrate sensor element is located, relative to the substrate transfer plane, at a predetermined sensing position for sensing substrates located on the substrate transfer plane. 
     In accordance with one or more aspects of the disclosed embodiment the door and the at least one substrate sensor element are removable as a unit from the valve assembly. 
     In accordance with one or more aspects of the disclosed embodiment the door is configured to seal an atmosphere of the substrate holding chamber when the door is closed where the atmosphere is an ultra-high vacuum. 
     It should be understood that the foregoing description is only illustrative of the aspects of the disclosed embodiment. Various alternatives and modifications can be devised by those skilled in the art without departing from the aspects of the disclosed embodiment. Accordingly, the aspects of the disclosed embodiment are intended to embrace all such alternatives, modifications and variances that fall within the scope of the appended claims. Further, the mere fact that different features are recited in mutually different dependent or independent claims does not indicate that a combination of these features cannot be advantageously used, such a combination remaining within the scope of the aspects of the invention.