Abstract:
A system and method for supporting and transferring a substrate relative to a plurality of testing columns are provided. The system includes a testing table adapted to support and move the substrate relative to the plurality of testing columns. The testing table may include an end effector disposed therein to transfer the substrate relative to an upper surface of the testing table. The method includes transferring the substrate to the testing table and moving the substrate relative to the plurality of testing columns. Signals indicative of electronic device performance are sensed to determine operability of the devices on the substrate.

Description:
CROSS-REFERENCE TO RELATED APPLICATIONS 
     This application is a divisional of U.S. patent application Ser. No. 11/018,236, filed Dec. 21, 2004, which issued as U.S. Pat. No. 7,330,021 on Feb. 12, 2008, which is a divisional of U.S. patent application Ser. No. 10/778,982, filed Feb. 12, 2004, which issued as U.S. Pat. No. 6,833,717 on Dec. 21, 2004. The aforementioned related patent applications are herein incorporated by reference. 
    
    
     BACKGROUND OF THE INVENTION 
     1. Field of the Invention 
     Embodiments of the present invention generally relate to an integrated electron beam testing system for glass panel substrates. 
     2. Description of the Related Art 
     Active matrix liquid crystal displays (LCDs) are commonly used for applications such as computer and television monitors, cell phone displays, personal digital assistants (PDAs), and an increasing number of other devices. Generally, an active matrix LCD comprises two glass plates having a layer of liquid crystal materials sandwiched therebetween. One of the glass plates typically includes a conductive film disposed thereon. The other glass plate typically includes an array of thin film transistors (TFTs) coupled to an electrical power source. Each TFT may be switched on or off to generate an electrical field between a TFT and the conductive film. The electrical field changes the orientation of the liquid crystal material, creating a pattern on the LCD. 
     The demand for larger displays, increased production and lower manufacturing costs has created a need for new manufacturing systems that can accommodate larger substrate sizes. Current TFT LCD processing equipment is generally configured to accommodate substrates up to about 1.5×1.8 meters. However, processing equipment configured to accommodate substrate sizes up to and exceeding 1.9×2.2 meters is envisioned in the immediate future. Therefore, the size of the processing equipment as well as the process throughput time is a great concern to TFT LCD manufacturers, both from a financial standpoint and a design standpoint. 
     For quality control and profitability reasons, TFT LCD manufacturers are increasingly turning toward device testing to monitor and correct defects during processing. Electron beam testing (EBT) can be used to monitor and troubleshoot defects during the manufacturing process, thereby increasing yield and reducing manufacturing costs. In a typical EBT process, TFT response is monitored to provide defect information. For example, EBT can be used to sense TFT voltages in response to a voltage applied across the TFT. Alternatively, a TFT may be driven by an electron beam and the resulting voltage generated by the TFT may be measured. 
     During testing, each TFT is positioned under an electron beam. This is accomplished by positioning a substrate on a table positioned below the beam and moving the table to sequentially position each TFT on the substrate below the electron beam test device. 
     As flat panels increase in size, so does the table and associated equipment used for the testing. Larger equipment requires more space, i.e., a larger footprint per processing unit throughput, resulting in a higher cost of ownership. The large size of the equipment also increases the cost of shipping and may, in some cases, restrict the means and locales to which such equipment may be transported. 
     Therefore, there is a need for a compact testing system for flat panel displays that conserves clean room space and that can reliably position flat panels under an EBT device. 
     SUMMARY OF THE INVENTION 
     Embodiments described herein generally provide a method and apparatus for testing a substrate, such as a large area substrate having electronic devices located thereon. In one embodiment, a method for testing a substrate is described. The method includes transferring the substrate to a testing table, positioning a prober to contact a plurality of electronic devices located on the substrate, moving the substrate relative to a plurality of testing columns, and sensing signals indicative of performance of the plurality of electronic devices as the substrate is moved relative to the testing columns. 
     In another embodiment, a method for testing a substrate is described. The method includes transferring the substrate having a plurality of electronic devices located thereon to a testing table, moving the substrate between a plurality of testing columns and the testing table, sensing signals indicative of performance of the plurality of electronic devices as the substrate is moved between the plurality of testing columns and the testing table, and transferring the substrate from the testing table. 
     In another embodiment, a method for testing a substrate is described. The method includes transferring the substrate having a plurality of electronic devices located thereon to a testing table disposed in a chamber, moving the substrate between a plurality of testing columns and the testing table, sensing signals from the substrate indicative of performance of the plurality of electronic devices as the substrate is moved between the plurality of testing columns and the testing table, and transferring the substrate from the testing table after the substrate has moved beyond the plurality of testing columns. 
     In another embodiment, a test system is described. The test system includes a testing table having an end effector disposed therein to transfer the substrate relative to an upper surface of the testing table, a plurality of testing columns disposed adjacent and in a position to view a portion of the testing table, a prober having a plurality of electrical contact pads, and a controller coupled to the prober. 
     In another embodiment, a test system is described. The test system includes a testing table having an end effector disposed therein and movable relative to the testing table, a plurality of testing columns disposed adjacent and in a position to view a portion of the testing table, a prober having a plurality of electrical contact pads in communication a plurality of electronic devices located on the substrate, and a controller coupled to the prober. 
    
    
     
       BRIEF DESCRIPTION OF THE DRAWINGS 
       So that the manner in which the above recited features of the present invention can be understood in detail, a more particular description of the invention, 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. 
         FIG. 1  is a schematic view of one embodiment of an integrated electron beam test assembly as described herein. 
         FIG. 2  is a schematic plan view of one embodiment of a prober transfer assembly. 
         FIG. 3  is an enlarged schematic view of one embodiment of a load lock chamber. 
         FIG. 4  is a partial cross section view of the load lock chamber and the testing chamber. 
         FIG. 5  is an enlarged cross section view of the embodiment of the testing chamber shown in  FIG. 4 . 
         FIGS. 6A and 6B  are enlarged schematic views of the drive systems according to one embodiment described herein. 
         FIG. 7  is a schematic plan view of one embodiment of an end effector shown in an extended position from the substrate table. 
         FIG. 8  is an enlarged partial cross section view of the testing chamber shown in  FIG. 5 . 
         FIG. 9  is another enlarged cross section view of the testing chamber of  FIG. 5 . 
         FIG. 10  is a basic schematic plan view of the embodiment of the transfer module as it is shown in cross section in  FIG. 9 . 
         FIG. 10A  shows an exemplary testing pattern showing twelve different test locations. 
         FIGS. 11-20  are partial cross section views of the embodiment of the load lock chamber and the testing chamber illustrating the sequence of operation of a transfer module disposed within the testing chamber. 
     
    
    
     DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENT 
       FIG. 1  shows a schematic view of an electron beam test system  100 . The electron beam test system  100  is an integrated system requiring minimum space, and is capable of testing large glass panel substrates, up to and exceeding 1.9 meters by 2.2 meters. As will be described below, the electron beam test system  100  provides stable substrate handling, reduces both substrate and prober alignment time, reduces unwanted particle generation, and provides improved test accuracy, reliability and repeatability. 
     Referring to  FIG. 1 , the electron beam test system  100  includes a prober storage assembly  200 , a prober transfer assembly  300 , a load lock chamber  400 , and a testing chamber  500 . The prober storage assembly  200  houses one or more probers  205  proximal the test chamber  500  for easy use and retrieval. Preferably, the prober storage assembly  200  is disposed beneath the test chamber  500  as shown in  FIG. 1 , reducing the clean room space needed for a contaminant free and efficient operation. The prober storage assembly  200  preferably has dimensions approximating those of the testing chamber  500  and is disposed on a mainframe  210  supporting the testing chamber  500 . The prober storage assembly  200  includes a shelf  220  disposed about the mainframe  210  to provide a support for the one of more probers  205 . The prober storage assembly  200  may further include a retractable door  230  that can seal off the storage area and protect the stored probers  205  when not in use. 
       FIG. 2  shows a schematic plan view of the prober transfer assembly  300 . The prober transfer assembly  300  is a modular unit disposable near the testing chamber  500  for transferring a prober  205  between the prober storage assembly  200  and the test chamber  500 . The prober transfer assembly  300  includes a base  305  connected to two or more vertical support members  310 A,  310 B (two are shown). Wheels or casters  315  may be arranged on a bottom surface of the base  305  to easily maneuver the assembly  300  when desired. 
     The prober transfer assembly  300  further includes a lift arm  320  that is attached at one end thereof to the support members  310 A,  310 B. The support members  310 A,  310 B each include a recessed track  312  (one is shown in this view) for mating engagement with the lift arm  320 . The recessed tracks  312 , one or both, may house a linear actuator, a pneumatic cylinder, a hydraulic cylinder, a magnetic drive, a stepper or servo motor, or other type of motion device (not shown). The recessed tracks  312  working in conjunction with the motion device (not shown) guide and facilitate the vertical movement of the lift arm  320 . A second motion device (not shown) or pair of motion devices (also not shown) may be coupled to the lift arm  320  to move the lift arm  320  in a horizontal direction. This horizontal movement facilitates the insertion of the lift arm  320  having the prober  205  disposed thereon within the testing chamber  500  or within the storage assembly  200  to deliver the prober  205 , as explained in more detail below. Likewise, the horizontal movement of the lift  320  facilitates the retrieval of a prober  205  from the testing chamber  500  or from the storage assembly  200 . These above mentioned horizontally and vertically actuated motors may be combined into a single motor capable of moving the lift arm  320  in both directions. Such a combined motor may be located in one or both of the recessed tracks  312  or coupled to the lift arm  312 . 
     In operation, the lift arm  320  supports the prober  205  on an upper surface thereof, and is raised or lowered by the linear motors (not shown) disposed within the recessed tracks  312  to align the prober  205  at the elevation of the testing chamber  500  or the storage assembly  200 . The lift arm  320  is then extended or retracted by the horizontal linear motor to transfer the prober  205  in or out of the testing chamber  500  or storage assembly  200 . 
     Referring again to  FIG. 1 , the load lock chamber  400  is disposed adjacent and connected to the testing chamber  500 . These chambers  400 ,  500  share a common environment which is typically maintained at vacuum conditions by a pump (not shown) coupled through the testing chamber  500 . The load lock chamber  400  transfers substrates between the transfer chamber  500  and the outside which is typically a clean room at atmospheric pressure. The load lock chamber  400  may function as an isolated processing environment that is capable of being heated or cooled as well as pressurized or de-pressurized, depending on system requirements. Consequently, load lock chamber  400  enables the transfer of substrates into and out of the testing chamber  500  without exposure to outside contaminants. 
       FIG. 3  shows an enlarged schematic view of one embodiment of a load lock chamber  400  having a dual slot substrate support. The load lock chamber  400  includes a chamber body  402  and a dual slot substrate support  422  disposed therein. The chamber body  402  includes at least a first sealable port  404  and a second sealable port  406  formed through sidewalls  408 ,  410  thereof as shown. Each port  404 ,  406  is selectively sealable by a slit valve (not shown) to isolate an interior environment of the chamber body  402 . The first port  404  typically couples the load lock chamber  400  to a factory interface (substrate queuing system), a processing system or other device (not shown). The second port  406  is typically disposed between the load lock chamber  400  and the testing chamber  500  to facilitate substrate transfer therebetween. 
     A pumping system (not shown), coupled to the load lock chamber  400  through a pumping port (also not shown for simplicity purposes), allows pressure within the load lock chamber  400  to be decreased or increased to a level substantially equal to that of the pressure within the testing chamber  500 . A vent (not shown), having a flow control valve (not shown) in communication therewith, is formed through the chamber body  402  of the load lock chamber  400 . The control valve may be selectively opened to deliver filtered gas into the load lock chamber  400 , thereby raising or lowering the pressure within the load lock chamber  400  to a level substantially equal to the pressure in the device (not shown) coupled to the load lock chamber  400  through the first port  406 . 
     The dual slot support  422  is disposed on a shaft (not shown) connected to a lift mechanism (also not shown). The lift mechanism allows the dual slot support  422  to move vertically within the chamber body  402  to facilitate substrate transfer to and from the load lock chamber  400 . The dual slot support  422  includes a first substrate support tray  424  and a second substrate support tray  426  that are maintained in a stacked, spaced-apart relationship by a pair of vertical supports  428 . 
     The load lock chamber  400  may include a heater and/or cooler disposed therein to control the temperature of the substrates positioned within the load lock chamber  400 . For example, one or more heating plates and one or cooling plates (not shown) may be attached to the substrate support trays  424 ,  426 . Also for example, a heat exchanger (not shown) may be disposed within the sidewalls of the chamber body  402 . Alternatively, a non-reactive gas, such as nitrogen for example, may be passed through the load lock chamber  400  to transfer heat in and out of the chamber  400 . 
     Each tray  424 ,  426  is configured to support a substrate thereon (not shown). Typically, one or more support pins  429  are coupled to an upper surface of each substrate support tray  424 ,  426  or at least partially disposed therethrough to support a substrate. The support pins  429  may be of any height, and provide a pre-determined spacing or gap between a lower surface of the substrate and the upper surface of the substrate support tray  424  or  426 . The gap prevents direct contact between the substrate support trays  424 ,  426  and the substrates, which might damage the substrates or result in contaminants being transferred from the substrate support trays  424 ,  426  to the substrates. 
     In one aspect, the support pins  429  have a rounded upper portion that contacts a substrate disposed thereon. The rounded surface reduces surface area in contact with the substrate thereby reducing the chances of breaking or chipping the substrate disposed thereon. In one embodiment, the rounded surface resembles a hemispherical, ellipsoidal, or parabolic shape. The rounded surface may have either a machined or polished finish or other suitable finish of adequate smoothness. In a preferred embodiment, the rounded surface has a surface roughness no greater than 4 micro inches. In another aspect, the rounded upper portion of the support pin  429  is coated with a chemically inert material to reduce or eliminate chemical reactions between the support pin  429  and the substrate supported thereon. Additionally, the coating material may minimize friction with the substrate to reduce breakage or chipping. Suitable coatings include nitride materials, such as silicon nitride, titanium nitride, and tantalum nitride, for example. A more detailed description of such support pins and coatings may be found in U.S. Pat. No. 6,528,767. 
     In another aspect, the support pins  429  may be a two piece system comprising a mounting pin disposed on an upper surface of the support tray  422 ,  426 , and a cap disposable on the mounting pin. The mounting pin is preferably made of a ceramic material. The cap includes a hollow body to receive the mounting pin. The upper portion of the cap may be rounded and smoothed as discussed above. Similarly, the cap may be coated as described above. A more detailed description of such a two piece system may also be found in U.S. Pat. No. 6,528,767. 
     In yet another aspect, an upper portion of the support pins  429  may include a socket that retains a ball moveable within the socket. The ball makes contact with and supports the substrate disposed thereon. The ball is allowed to rotate and spin, much like a ball bearing, within the socket allowing the substrate to move across the ball without scratching. The ball is generally constructed of either metallic or non-metallic materials that provide friction reduction and/or inhibit chemical reaction between the ball and the substrate. For example, the ball may include a metal or metal alloy, quartz, sapphire, silicon nitride or other suitable non-metallic materials. Preferably, the ball has a surface finish of 4 micro-inches or smoother. The ball may further include the coating describe above. A more detailed description of such a support pin may be found in U.S. Pat. No. 6,528,767. 
     Alternatively, the support pins  429  may be a two piece system comprising a mounting pin disposed on an upper surface of the support tray  422  or  426 , and a cap disposable on the mounting pin, whereby the cap includes the socket and ball configuration described above. A more detailed description of such a ball and socket may be found in co-pending U.S. patent application Ser. No. 09/982,406, as well as Ser. No. 10/376,857, both entitled “Substrate Support”, and both assigned to Applied Materials, Inc. 
     Further, the support pins  429  may include a housing having one or more roller assemblies and a support shaft at least partially disposed therein. The support shaft is able to move axially through the housing as well as rotate within the housing to reduce wear and tear on the pin head during loading and unloading of a substrate supported thereon. The support pins  429  may also include a housing having one or more ball assemblies and a support shaft at least partially disposed therein. The ball assemblies include one or more spherical members that are held into place by a sleeve that is at least partially disposed about the housing. The one or more spherical members contact the shaft and allow the shaft to move axially as well as radially within the housing. This also reduces wear and tear on the pin head during loading and unloading of a substrate supported thereon. A more detailed description of such support pins may be found in commonly assigned and co-pending U.S. patent application Ser. No. 10/779,130 entitled “Support Bushing for Flat Panel Substrates.” 
       FIG. 4  shows a partial cross section view of the load lock chamber  400  and the testing chamber  500 . The testing chamber  500  includes a housing  505 , one or more electron beam testing (EBT) columns  525 A/B (two are shown in this view), a base  535 , and a substrate table  550 . Four EBT columns  525  A, B, C, D are shown in  FIG. 1 . The EBT columns  525 A/B/C/D are disposed on an upper surface of the housing  505  and are coupled to the housing  505  via a port  526 A/B formed through the upper surface thereof. The housing  505  provides a particle free environment and encloses the substrate table  550  and the base  535 . The base  535  is fixed at the bottom of the housing  505  and supports the substrate table  550 . 
     Considering the substrate table  550  in more detail,  FIG. 5  shows an enlarged cross section view of the testing chamber  500  shown in  FIG. 4 . The substrate table  550  includes a first stage  555 , a second stage  560 , and third stage  565 . The three stages  555 ,  560 , and  565  are planar monoliths or substantially planar monoliths, and are stacked on one another. In one aspect, each of the three stages  555 ,  560 ,  565  independently move along orthogonal axes or dimensions. For simplicity and ease of description, the first stage  555  will be further described below as representing the stage that moves along the X-axis and will be referred to as the lower stage  555 . The second stage  560  will be further described below as representing the stage that moves along the Y-axis and will be referred to as the upper stage  560 . The third stage  565  will be further described below as representing the stage that moves along the Z-axis and will be referred to as the Z-stage  565 . 
     The lower stage  555  and the upper stage  560  each may move side to side or forward and backward, depending on the orientation of the testing chamber  500 . In other words, the lower stage  555  and the upper stage  560  both move linearly on the same horizontal plane, but move in a direction orthogonal to one another. In contrast, the Z-stage  565  moves in a vertical direction or the “Z direction.” For example, the lower stage  555  moves side to side in the “X direction”, the upper stage  560  moves forward and backward in the “Y direction and the Z-stage  565  moves up and down in the “Z direction.” 
     The lower stage  555  is coupled to the base  535  through a first drive system (not shown in this view). The first drive system moves the lower stage  555  linearly along the X axis. Similarly, the upper stage  560  is coupled to the lower stage  555  through a second drive system, (not shown in this view) which moves the upper stage  560  linearly along the Y axis. The first drive system is capable of moving the substrate table  550  in the X direction or dimension by at least 50 percent of the width of the substrate. Likewise, the second drive system is capable of moving the substrate table  550  in the Y direction or dimension by at least 50 percent of the length of the substrate. 
       FIGS. 6A and 6B  show an enlarged schematic view of these drive systems. Referring to  FIG. 6A , the first drive system  722  generally includes a pair of linear rails  702 A coupled to the base  535 . A plurality of guides  706 A are movably engaged with the rails  702 A and are coupled to a first side  704 A of the lower stage  555  (not shown in this view). The guides  706 A move along the rails  702 A, thereby allowing the lower stage  555  to move over the base  535  in a first direction, i.e., along the X-axis. Linear motor  708 A, such as a ball screw and motor, is coupled between the lower stage  555  and the base  535  to control the position of the guides  706 A. The lower stage  555  is coupled to each of the guides  706 A, allowing the lower stage  555  to move in response to the actuator  708 A. In addition to linear actuators, other types of motion devices may be used as well, such as a pneumatic cylinder, a hydraulic cylinder, a magnetic drive, or a stepper or servo motor, for example. 
     Referring to  FIG. 6B , the upper stage  560  is coupled to the lower stage  555  via the second drive system  726 . The second drive system  726  is configured similar to the first drive system  722  except the second drive system  726  is oriented in a direction orthogonal to the first drive system  722 . Similar to the lower stage  555  above, a lower surface of the upper stage  560  is coupled to each of the guides  706 B, allowing the upper stage  560  to move in response to the linear motor  708 B. Generally, the drive systems  722 ,  726  have a range of motion that allows all of the surface area of a substrate disposed within the testing chamber  500  to be moved beneath the EBT columns  525  during testing. 
     Referring back to  FIG. 5 , the testing chamber  500  further includes an end effector  570  to transfer a substrate  585  in and out of the testing chamber  500 . In operation, the end effector  570  may be extended from the testing chamber  500  into the load lock chamber  400  to load a substrate. Likewise, the end effector  570  having a substrate loaded thereon may be extended from the testing chamber  500  into the load lock chamber  400  to transfer the substrate to the load lock chamber  400 . A motion device, such as a linear actuator, a pneumatic cylinder, a hydraulic cylinder, a magnetic drive, or a stepper or servo motor, for example may be coupled to the end effector  570  to assist this transfer. In one aspect, the end effector  570  includes a pair of bearing blocks  572  that permit the end effector  570  to move in and out of the testing chamber  500 . 
     The end effector  570  has a planar or substantially planar upper surface on which the substrate  585  may be supported. In one embodiment, the end effector  570  is a slotted monolith that rests on an upper surface of the upper stage  560 .  FIG. 5  shows one embodiment of the end effector  570  having four fingers that are evenly spaced, which contact and support the substrate  585  when placed thereon. The actual number of fingers is a matter of design and is well within the skill of one in the art to determine the appropriate number of fingers needed for the size of substrate to be manipulated. 
     The Z-stage  565  is disposed on an upper surface of the upper stage  560 . The Z-stage  565  has a planar or substantially planar upper surface to contact and support the substrate  585  within the testing chamber  500 . The Z-stage  565  is slotted or segmented such that each segment of the Z-stage  565  sits adjacent the fingers of the end effector  570 . As such the Z-stage  565  and the end effector  570  can be interdigitated on the same horizontal plane. This configuration allows the Z-stage  565  to move above and below the end effector  570 . Accordingly, the spacing between the segments of the Z-stage  565  corresponds to the width of the fingers of the end effector  570  plus some additional measure to assure clearance. Although five segments are shown in the cross section view of  FIG. 5 , the Z-stage may have any number of segments. 
     Still referring to  FIG. 5 , one or more Z-stage lifts  575  is coupled to the back side of each of the segments making up the Z-stage  565 . Each Z-stage lift  575  is disposed within a channel  576  formed in the upper stage  560 , and a bellows  577  is arranged about each Z-stage lift  575  to reduce particle contamination within the testing chamber  500 . The Z-stage lift  575  moves up and down vertically and may be actuated pneumatically or electrically. The bellows  577  compress and expand in response to the movement of the lift  575 . 
       FIG. 7  shows a schematic plan view of the end effector  570  shown in an extended position from the substrate table  550 . The end effector  570  extends from the testing chamber  500  (not shown) to the load lock chamber  400  (not shown) to transfer substrates therebetween. The sequence of which is described in more detail below. As shown in  FIG. 7 , the end effector includes four fingers  571 A-D that have extended away from the five segments  566 A-E of the Z-stage  565 . The substrate  585  is disposed on and supported by the fingers  571 A-D. The fingers  571 A-D move in and out of the Z-stage  565  such that the fingers  571 A-D interdigitate with the segments.  566 A-E when the end effector  570  is disposed in substantially the same plane as the Z-stage  565 . This configuration allows the end effector  570  to freely extend and retract. As will be described below, the Z-stage  565  is capable of elevating above the end effector  570  to load and un-load the substrate  585  between the end effector  570  and the Z-stage  565 . 
       FIG. 8  shows an enlarged partial cross section view of the testing chamber  500  shown in  FIG. 5 . The Z-stage lift  575  is activated to move the Z-stage  565  vertically up and down. As shown, the Z-stage  565  is in a lowered or “substrate transfer” position. In this position, the substrate  585  rests on the upper surfaces of the fingers of the end effector  570 , and does not contact the lower surface of the prober  205 . Also, the lift  575  is located at the bottom of the channel  576  and the bellows  577  are extended. 
     Still referring to  FIG. 8 , as shown, the prober  205  rests on a collar  579  disposed on an upper surface of the upper stage  560  and is secured to the collar  579  using a pin assembly  580 . The pin assembly  580  may include a spring loaded pin  581  disposed within a recess  582  formed in the collar  579 . The pin  581  extends into a matching receptacle  583  machined into the perimeter of the prober  205 , securing the prober  205  to the upper stage  560 . 
       FIG. 9  shows another enlarged cross section view of the testing chamber  500 . In this view, the Z-stage  565  is shown in a raised or “substrate testing” position. In the testing position, the Z-stage lift  575  is activated, moving the Z-stage  565  vertically upward in the “Z direction.” The Z-stage  565  travels upward, traversing the fingers of the end effector  570  and lifting the substrate  585  off the end effector  570 . The Z-stage  565  continues to move upward until the substrate  585  sits against the backside of the prober  205  to make an electrical connection between the prober  205  and the substrate  585 . This allows the prober  205  to directly contact the substrate  585  and facilitate the electron beam test methods as described below. As shown in  FIG. 9 , the Z-stage lifts  575  have moved to an upward portion of the channel  576 , and the bellows  577  are compressed. 
     For further understanding,  FIG. 10  shows a basic schematic plan view of the substrate table  550  as it is shown in cross section in  FIG. 9 . The housing  505  has been removed to more easily visualize the components of the substrate table  550  in relation to the EBT testing columns  525 A-D. The substrate table  550  is shown such that side  550 A would be adjacent the prober transfer assembly  300  disposed toward the X direction and the side  550 B would be adjacent the load lock chamber  400  disposed toward the Y direction. 
     As shown in this perspective, the lower stage  555  is disposed on the base  535  and moves along rails  702 A. The upper stage  560  is disposed on the lower stage  555  and moves along rails  702 B. The Z-stage  565  is disposed on the upper stage  560  and the end effector  570  (not shown) is disposed therebetween. The substrate  585  is resting on the upper surface of the Z-stage  565  and abuts the lower surface of the prober  205 . 
     In operation, the substrate table  550  positions the substrate  585  and the prober  205  so that the columns  525 A-D may interact with discrete portions of the substrate  585 . Each column  525 A-D is an electron beam generator that detects voltage levels of the devices formed on the substrate  585 . 
     The prober  205  generally has a picture frame configuration, having sides at least partially defining at least one window or display  206  through which the columns  525 A-D interact with the substrate  585 . Each window  206  is positioned to allow a predefined field of pixels (or other device) formed on the substrate  585  to be exposed to the electron beam generated by the columns  525 A-D. Accordingly, the number, size and positions of the windows  206  in a particular prober  205  are chosen based upon the layout of the substrate  585  and the devices on the substrate  585  to be tested. 
     A face of the prober  205  contacting the substrate  585  generally includes a plurality of electrical contact pads that are coupled to a controller (not shown). The electrical contact pads are positioned to provide electrical connection between a predetermined pixel (or other device formed on the substrate  585 ) and the controller. Thus, as the substrate  585  is urged against the prober  205 , electrical contact between the controller and the devices on the substrate  585  are made through the contact pads on the prober  205 . This allows the controller to apply a voltage to a selected pixel or to monitor each pixel for changes in attributes, such as voltage, during testing. 
     In one embodiment, the substrate is tested by sequentially impinging at least one electron beam emitted from the columns  525 A-D on discrete portions or pixels composing the thin film transistor matrix. After a pixel is tested, the substrate table  550  moves the substrate  585  to another discrete position within the testing chamber  500  so that another pixel on the substrate  585  surface may be tested. 
       FIG. 10A  shows an exemplary testing pattern showing twelve different test locations. The discrete portions of the substrate surface under each column  525 A-D represents one test location. As shown, the substrate  585  is moved along the X-axis as shown by arrow  1001  and tested in four locations under columns  525 A,  525 B,  525 C, and  525 D. The substrate  585  is then moved along the Y-axis as shown by arrow  1002  and tested in four different locations. The substrate  585  is then moved and tested as shown by arrows  1003  and  1004  until the entire surface of the substrate  585  or the desired portions of the substrate surface have been tested using the desired electron beam test method. 
     Electron beam testing may employ several test methods. For example, the electron beam may be utilized to sense pixel voltages in response to the voltage applied across the pixels or the pixel through the electrical connections in the prober  205 . Alternatively, a pixel or a plurality of pixels may be driven by the electron beam which provides a current to charge up the pixel(s). The pixel response to the current may be monitored by the controller (not shown) that is coupled across the pixel by the prober  205  to provide defect information. Examples of electron beam testing are described in U.S. Pat. No. 5,369,359, issued Nov. 29, 1994 to Schmitt; U.S. Pat. No. 5,414,374, issued May 9, 1995 to Brunner et al.; U.S. Pat. No. 5,258,706, issued Nov. 2, 1993 to Brunner et al.; U.S. Pat. No. 4,985,681, issued Jan. 15, 1991 to Brunner et al.; and U.S. Pat. No. 5,371,459, issued Dec. 6, 1994 to Brunner et al. The electron beam may also be electromagnetically deflected to allow a greater number of pixels to be tested at a given substrate table  550  position. 
       FIGS. 11-20  show partial cross section views of the load lock chamber  400  and the testing chamber  500  to illustrate the sequence of operation of the substrate table  550 .  FIG. 11  shows the Z-stage  565  in the “testing position.” As shown, the slit valve  1101  between the load lock chamber  400  and the testing chamber  500  is closed. The substrate  585 A is disposed on the upper surface of the Z-stage  565 . The Z-stage  565  is raised above the fingers of the end effector  570 , holding the substrate  585 A against the prober  205 . As described above but not shown in these cross sections, the lower stage  555  and the upper stage  560  move linearly in their respective directions to place discrete portions of the substrate  585 A beneath at least one of the testing columns  525 A-D. Once testing is complete, the tested substrate  585 A is transferred from the testing chamber  500  and an untested substrate  585 B from the load lock chamber  400  is inserted into the testing chamber  500 . 
       FIGS. 12 through 16  illustrate the transfer of the tested substrate  585 A from the testing chamber  500  to the load lock chamber  400 . To facilitate this transfer, the slit valve  1101  is opened as shown in  FIG. 12 . The Z-stage  565  is lowered transferring to the substrate  585 A to the end effector  570  as shown in  FIG. 13 . The end effector  570  having the substrate  585 A disposed thereon extends through the slit valve  1101  above the lower tray  424  of the dual substrate support  422 , as shown in  FIG. 14 . The substrate support  422  is then raised to unload the substrate  585 A from the end effector  570 . The substrate  585 A is disposed on and held by the pins  429 , as shown in  FIG. 15 . The end effector  570  then retracts to the testing chamber  500 , completing the exchange of the tested substrate  585 A to the load lock chamber  400 , as shown in  FIG. 16 . 
       FIGS. 17-20  illustrate the transfer sequence of an untested substrate  585 B to the testing chamber  500 . To initiate this transfer, the dual substrate support  422  lowers to align the substrate  585 B with the slit valve  1101 , as shown in  FIG. 17 . The end effector  570  extends into the load lock chamber  400  as shown in  FIG. 18 , and the dual substrate support  422  lowers even further to load the substrate  585 B onto the end effector  570  as shown in  FIG. 19 . The end effector  577  having the substrate  585 B disposed thereon retracts into the test chamber  500  and the slit valve  1101  is closed, thereby completing the transfer of the untested substrate  585 B from the load lock chamber  400  to the testing chamber  500 , as shown in  FIG. 20 . 
     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. Further, all patents, publications, and other documents cited in this application are fully incorporated by reference to the extent such disclosure is not inconsistent with this application and for all jurisdictions in which such incorporation is permitted.