Abstract:
Substrate handling apparatus and methods are described. In one aspect, the substrate handling apparatus includes a clamping member having an extended condition wherein substrate movement relative to the transfer arm is substantially restricted and a retracted condition wherein substrate movement relative to the transfer arm is substantially free. The substrate handling apparatus further includes a sense mechanism (e.g., a vacuum sensor) constructed to determine whether a substrate is properly positioned on the support arm and to trigger the mode of operation of the clamping member between extended and retracted conditions. The sense mechanism also provides information relating to the operating condition of the clamping member.

Description:
BACKGROUND OF THE INVENTION 
     The invention relates to apparatus and methods for handling a substrate. 
     Apparatus and methods for handling substrates are used in a variety of applications. For example, in semiconductor processing applications, a substrate may be handled by an automated transfer mechanism, such as a transfer robot, which transfers substrates into and out of one or more semiconductor processing stations. Automated transfer mechanisms often include a substrate support in which a substrate may have limited freedom of movement in at least one dimension. Such movement may result in the generation of particles and the misalignment of the substrate with respect to a processing system in which the substrate is placed. Significant substrate misalignment may reduce the number of devices that can be formed on a particular substrate or may cause the substrate to produce particles or even break inside the vacuum chamber. When a substrate breaks inside a vacuum chamber or when a substantial amount of particle contamination has accumulated inside the chamber, the chamber must be opened and exposed to ambient pressure; the chamber must be cleaned; and the chamber must be pumped back down to a sub-ambient pressure suitable for processing. In high vacuum processing applications, such a procedure may take up to twenty-four hours to complete, significantly delaying the time during which the system can be used to process substrates. 
     SUMMARY OF THE INVENTION 
     In one aspect, the invention features an apparatus for handling a substrate, comprising: a contact surface constructed to contact the substrate; a sensor constructed to detect contact between the substrate and the contact surface; and a clamping member having an extended condition wherein substrate movement relative to the contact surface is substantially restricted and a retracted condition wherein substrate movement relative to the contact surface is substantially free. 
     In another aspect, the invention features an apparatus for handling a substrate, comprising: a movable transfer arm having a support surface constructed to carry the substrate; a contact surface coupled to the transfer arm constructed to contact the substrate; and a vacuum sensor constructed to detect contact between the substrate and the contact surface. 
     The sensor may include a pressure transducer. The contact surface may define a channel opening. A housing defining a channel may be provided to couple the channel opening to a vacuum source. A controller may be provided for operating the clamping member between the extended condition and the retracted condition in response to signals received from the sensor. The contact surface may define a channel opening. 
     An edge restraint may be provided to contact a first peripheral edge portion of the substrate to limit substrate movement toward the edge restraint. In this embodiment, the extended condition of the clamping member may be characterized by the application of force by the clamping member against a second peripheral edge portion of the substrate urging the first peripheral edge portion of the substrate against the edge restraint. The extended condition of the clamping member may be further characterized by the application of force by the clamping member against the second peripheral edge portion of the substrate urging the substrate against the contact surface. The clamping member may comprise a pusher for contacting the second peripheral edge portion of the substrate, and a biasing member coupled to the pusher for biasing the pusher into the extended condition. The contact surface may be adapted to contact the bottom substrate surface, and the pusher may be adapted to contact only the top substrate surface along the second peripheral edge portion of the substrate. 
     In yet another aspect, the invention features a substrate handling apparatus comprising: a contact surface constructed to contact the substrate and to define a channel opening; a pusher constructed to contact the substrate; a biasing member having a first end coupled to the pusher and having a second end; and a housing defining a first channel wherein the pusher and the biasing member are disposed, with the second end of the biasing member being coupled to the housing and the pusher being free to move within the first housing channel, the housing further defining a second channel constructed to couple the channel opening to a vacuum source. 
     The housing may define a third channel through which the first housing channel is exposed to ambient pressure when the pusher extends out of the first housing channel beyond a fixed distance. An edge restraint may be provided for contacting a first peripheral edge portion of the substrate and thereby to limit substrate movement toward the edge restraint, wherein the biasing member biases the pusher against a second peripheral edge portion of the substrate urging the first peripheral edge portion of the substrate against the edge restraint, the third housing channel being closed by the pusher when the substrate is clamped between the edge restraint and the pusher. The housing may define a fourth channel through which the first housing channel is exposed to ambient pressure for determining when the pusher is unable to retract with the first housing channel beyond a fixed distance. The pusher may cut off the second channel from the vacuum source when the pusher is retracted within the first housing channel beyond a fixed distance. 
     In another aspect of the invention, the substrate handling apparatus comprises: a contact surface constructed to contact the substrate; an edge restraint adapted to contact the first peripheral edge portion of the substrate to limit substrate movement toward the edge restraint; and a clamping member coupled to the contact surface and biased to extend toward the second peripheral edge portion of the substrate thereby to urge the first peripheral edge potion of the substrate against the edge restraint, the clamping member being adapted to retract away from the second peripheral edge portion of the substrate when coupled to an energy source. 
     The clamping member may be adapted to retract away from the second peripheral edge portion of the substrate when coupled to a vacuum source. The clamping member may be adapted to retract away from the second peripheral edge portion of the substrate when coupled to an energy source independently of the position of the contact surface within a processing environment. 
     In yet another aspect of the invention, the substrate handling apparatus comprises: a movable transfer arm having a support surface constructed to carry the substrate; an edge restraint adapted to contact a first peripheral edge portion of the substrate to limit substrate movement toward the edge restraint; a contact surface constructed to contact the substrate and to define a channel opening; a pusher constructed to contact a second peripheral edge portion of the substrate; a biasing member having a first end coupled to the pusher and having a second end; and a housing defining a first channel wherein the pusher and the biasing member are disposed, with the second end of the biasing member being coupled to the housing and the pusher being free to move within the first housing channel, the housing further defining a second channel for coupling the channel opening to a vacuum source. 
     A sensor (e.g., a pressure transducer) may be provided for detecting contact between the substrate and the contact surface. A vacuum source may be coupled to the second housing channel. A flow restrictor may be coupled to the vacuum source, and a valve may be provided for selectively coupling the second housing channel to the vacuum source directly or through the flow restrictor. 
     In another aspect, the invention features a method of handling a substrate, comprising: providing a transfer arm having a contact surface constructed to contact the substrate and to define a channel opening, the channel opening being coupled to a first channel; coupling the first channel to a vacuum source; monitoring the pressure inside the first channel; and positioning the substrate on the transfer arm in contact with the contact surface. 
     A clamping member may be coupled to the contact surface and may have an extended condition wherein substrate movement relative to the contact surface is substantially restricted and a retracted condition wherein substrate movement relative to the contact surface is substantially free. Prior to positioning the substrate on the transfer arm, vacuum pressure may be applied to the first channel to place the clamping member in the retracted position. The vacuum applied to the first channel may be decreased in response to a decrease in the monitored first channel pressure upon the positioning of the substrate on the transfer arm, the decrease in applied vacuum being sufficient to place the clamping member in the extended condition. After the applied vacuum is decreased, the substrate may be re-positioned on the transfer arm when the monitored first channel pressure is higher than a predetermined maximum value. 
     The clamping member that is provided may comprise a second channel through which the first channel is exposed to ambient pressure when the clamping member extends beyond a fixed distance. After the applied vacuum is decreased, the substrate may be re-positioned on the transfer arm when the monitored first channel pressure is higher than a predetermined maximum value. After the applied vacuum is decreased, the vacuum applied to the first channel may be increased to place the clamping member in the retracted position. 
     The clamping member that is provided may comprise a second channel through which the first channel is exposed to ambient pressure when the clamping member extends beyond a threshold distance. After the applied vacuum is increased, the clamping member may be examined when the monitored first channel pressure is higher than a predetermined minimum value. 
     In another aspect, the invention features a method of handling a substrate, comprising: providing a transfer arm comprising a clamping member biased to extend toward the substrate and thereby restrain the substrate from moving relative to the transfer arm, the clamping member being adapted to retract away from the substrate when energized; energizing the clamping member sufficiently to retract the clamping member away from the substrate; and after energizing the clamping member, positioning the substrate on the transfer arm. 
     The clamping member may be energized by coupling the clamping member to a vacuum source. After the substrate is positioned on the transfer arm, the clamping member may be de-energized sufficiently to enable the clamping member to extend toward the substrate and thereby restrain the substrate from moving relative to the transfer arm. 
     Among the advantages of the invention are the following. 
     It has been realized that substrate movement relative to the transfer arm during substrate handling can generate particles and can result in substrate misalignment which prevents the substrate from being precisely and reliably positioned inside the processing stations. This problem has been addressed by providing a substrate handling apparatus that includes a clamping member having an extended condition for limiting substrate movement relative to the transfer arm and a retracted condition for freeing substrate movement relative to the transfer arm. The substrate handling apparatus further includes a sense mechanism for determining whether a substrate is properly positioned on the support arm and for triggering the mode of operation of the clamping member between extended and retracted conditions. The sense mechanism also provides information relating to the operating condition of the clamping member. 
     Other features and advantages will become apparent from the following description, including the drawings and claims. 
    
    
     BRIEF DESCRIPTION OF THE DRAWINGS 
     FIG. 1 is a diagrammatic top view of a substrate processing system that includes an apparatus for handling a substrate. 
     FIG. 2A a diagrammatic side view of a transfer head of the substrate handling apparatus shown in FIG.  1 . 
     FIG. 2B is a diagrammatic top view of the transfer head of FIG.  2 A. 
     FIG. 3 is a diagrammatic cross-sectional, side view of a clamping member coupled to a sensor, a three-way valve, and an energizing source. 
     FIG. 4 is a flow diagram of a method of handling a substrate. 
     FIG. 5A is a time plot of vacuum pressure applied to a clamping member during the handling of a substrate. 
     FIG. 5B is a time plot of monitored pressure during the handling of a substrate. 
    
    
     DETAILED DESCRIPTION 
     Referring to FIG. 1, in one embodiment, a substrate processing system  10  includes a substrate handling apparatus  12  for transferring substrates  14 ,  16  between a substrate load station  18  and one or more processing stations  20 - 26 . Substrate handling apparatus  12  includes a transfer arm  28  that is mounted on a rotatable table  30  within a transfer chamber  32 . In operation, load station  18  is at ambient pressure and each of the processing chambers  20 - 26  and transfer chamber  32  are maintained at a sub-ambient pressure. A load lock chamber  34  is disposed between transfer chamber  32  and load station  18 . Load lock chamber  34  is at ambient pressure when a substrate is being transferred to or from load station  18 , and it is at a sub-ambient pressure when a substrate is being transferred between transfer chamber  32  and one or more processing stations  20 - 26 . Transfer arm  28  can rotate about an axis  35  and can extend into and out of load station  18  and processing stations  20 - 26  to controllably position a substrate into and out of a processing chamber with high accuracy. The position and orientation of transfer arm  28  is recorded and controlled by microprocessor-based controller (not shown). 
     Referring to FIGS. 2A and 2B, transfer arm  28  includes a transfer head  40  which has a seat portion  42  for receiving a substrate  46  (shown by dashed lines) and a base portion  44 . Transfer head  40  may be formed from stainless steel. Seat portion  42  includes a support blade  48 , with a substantially planar surface  49  and four support surfaces  50 - 56 , bounded by two edge restraints  58 ,  60 . Support surfaces  50 - 56  are inclined with respect to planar surface  49  at an angle φ (phi) (FIG.  2 A), which preferably has a value of about 135-175 degrees. When properly aligned, substrate  46  is supported on support surfaces  50 - 56  above planar surface  49  and against edge restraints  58 ,  60 . The backside of substrate  46  remains substantially particle-free and contamination-free because substrate  46  makes only limited contact with transfer head  40 . 
     Base portion  44  of transfer arm  28  includes a flange  62  which has a slot  64  for receiving a clamping member  66 , which may be selectively actuated to limit substrate movement relative to transfer arm  28 . Clamping member  66  includes a vacuum fitting  74  for coupling to a vacuum source and a housing  68 , which is bolted to flange  62  and contains a pusher  70  and a biasing member  72  (e.g., a spring). Housing  68  may be formed from stainless steel. Pusher  70  includes a cylindrical housing  76  and a face plate  78  which is mounted to cylindrical housing  76  by a screw  79 . Pusher  70  and face plate  78  may be formed from a TEFLON® (DuPont) resin, a DELRIN® (DuPont) resins, or other material that has a low coefficient of friction. Face plate  78  has a front surface  80  that lies in a plane which is oriented to intersect the top planar surface of the substrate at an angle θ (theta) (FIGS.  2 A), and  3  which preferably has a value of about 75 to 85 degrees. With this orientation, front surface  80  contacts the top of the peripheral edge of substrate  46  and thereby applies to substrate  46  a downward force component toward planar surface  49  of support blade  48 . This feature tends to prevent pusher  70  from applying to substrate  46  an upward force component that would lift substrate  46  off of the one or more of support surfaces  50 - 56 . 
     As shown diagrammatically in FIG. 3, clamping member  66  may be coupled to a vacuum source  90  (e.g., a pump) through a three-way valve  92 . Valve  92  selectively couples clamping member  66  to vacuum source  90  directly at a port  92   a  (a high vacuum condition), indirectly through a flow restrictor  94  at a port  92   b  (a low vacuum condition), or breaks the connection between clamping member  66  and vacuum source  90  at port  92   c  (no vacuum condition). A sensor  96  (e.g., a pressure transducer) monitors the pressure applied to clamping member  66 . 
     Clamping member housing  68  defines a central channel  98  through which pusher  70  slides back-and-forth. Housing  68  further defines a detection channel  100  which extends from central channel  98  to a contact surface  102  against which substrate  46  makes contact when properly seated on transfer head  40 . Housing  68  also includes proximal and distal pusher sensing channels  104 ,  106 , respectively, which extend from central channel  98  to the exterior surface of housing  68 . The operation and function of channels  100 ,  104  and  106  are explained below. 
     In operation, when three-way valve  92  couples clamping member  66  directly to vacuum source  90 , the resulting vacuum produced in central channel  98  is sufficient to overcome the force applied by biasing member  72  and thereby withdraw pusher  70  within central channel  98 . In this mode of operation (retracted condition), substrate  46  may be unloaded from or loaded onto transfer head  40 . When three-way valve  92  couples clamping member  66  indirectly to vacuum source  90  through flow restrictor  94 , the resulting vacuum in central channel  98  is insufficient to overcome the force applied by biasing member  72 . In this mode of operation (extended condition), front surface  80  of face plate  78  contacts the top peripheral edge of substrate  46  and urges substrate against edge restraints  58 ,  60  (FIG.  2 B), thereby clamping substrate  46  and limiting substrate movement relative to transfer head  40 . Valve  92  is connected at port  92   c  (no vacuum condition) when vacuum source  90  is turned off. 
     Referring to FIG. 4, in accordance with one method, a substrate may be handled as follows. Clamping member  66  is coupled to vacuum source  90  (step  110 ). Sufficient vacuum pressure is applied to place clamping member  66  in the retracted condition (step  112 ; three-way valve is in the high vacuum position). The substrate is positioned on transfer arm  28  in contact with contact surface  102  (step  114 ). The pressure is monitored (step  116 ). If the pressure monitored by sensor  96  is higher than a first threshold (step  118 ), the substrate is not properly positioned. Sufficient vacuum pressure is then reapplied to place clamping member  66  in the retracted condition (step  112 ), and the substrate is re-positioned on the transfer arm (step  114 ). If the monitored pressure is lower than the first threshold, the vacuum pressure is decreased in response to a decrease in the monitored pressure resulting from the fact that channel  100  is closed by the substrate and that channels  104 ,  106  are closed by pusher  70  (step  120 ; three-way valve in the low vacuum position). If the monitored pressure is higher than a second threshold (step  122 ), pusher  70  has missed the substrate and is over-extended. In this case, pusher sensing channels  104  and  106  will be open. Sufficient vacuum pressure is then reapplied to place clamping member  66  in the retracted position (step  112 ), and the substrate is re-positioned on the transfer arm (step  114 ). If the monitored pressure is lower than the second threshold (step  122 ), the substrate is properly clamped onto the transfer arm and the substrate now may be transferred for processing (step  124 ). After the substrate has been transferred, the substrate may be handled as follows. Sufficient vacuum pressure is applied to place clamping member  66  in the retracted position (step  126 ). If the monitored pressure is higher than a third threshold (step  128 ), the clamping member is not fully retracted and pusher sensing channel  106  will remain open. In this situation, pusher  70  should be examined (step  130 ). If the monitored pressure is lower than the third threshold, the substrate may be removed from transfer arm  28  (step  132 ). 
     The vacuum pressure applied and the vacuum pressure monitored during the handling method of FIG. 4 are plotted in FIGS.  5 A and SB, respectively. When clamping member  66  is in the retracted condition (Time 0), the applied pressure drops to a minimum value  220  (FIG.  5 A). The monitored pressure, on the other hand, drops to a first intermediate value  222  because detection channel  100  is open as there is no substrate blocking detection channel  100  (FIG.  5 B). When a substrate is loaded onto support head  40  and contacts surface  102  (Time 1), detection channel  100  is closed and the monitored pressure drops to a minimum value  224 . If the substrate fails to properly contact surface  102  the monitored pressure will remain at intermediate value  222  (shown by dashed line  225 ). When clamping member  66  is placed in the extended condition (Time 2), the applied pressure rises to a maximum value  226  (FIG.  5 A). In this mode of operation, if the substrate is properly clamped, the monitored pressure will rise to a second intermediate value  228  because only pusher sensing channel  106  will remain open. If the substrate is not properly clamped, however, the monitored pressure will increase to a maximum value  130  because pusher  70  would be over-extended (e.g., because substrate  46  has been pushed over edge restraints  58 ,  60 ) and detection channel  100  and pusher sensing channels  104 ,  106  would be all open. To release the substrate (Time 3), clamping member is placed in the retracted condition by reducing the applied pressure to minimum value  220 , which is sufficient to overcome the force applied by biasing member  72 . If pusher  70  fully retracts within housing  68 , pusher sensing channels  104 ,  106  will be closed and the monitored pressure will drop to the minimum value  224 . If, on the other hand, pusher  70  fails to fully retract within housing  68  (e.g., if contamination prevents the pusher from freely moving in central channel  98 ), the monitored pressure would drop to a third intermediate value  232  because pusher sensing channel  106  would remain open and sensing channel  104  would be closed. When the substrate is unloaded from transfer head  40  (Time 4), the monitored pressure will rise again to first intermediate value  222  because only detection channel  100  will be open. If pusher  70  fails to fully retract, however, the monitored pressure will rise to a fourth intermediate value  234  because both detection channel  100  and pusher sensing channel  106  will remain open. 
     In the method of FIG. 4, the first and third thresholds are preferably has a value that is slightly greater than the minimum monitored pressure value  224  (FIG.  5 B), and the second threshold is preferably has a value that is slightly greater than the second intermediate pressure value  128  (FIG.  5 B). 
     Other embodiments are within the scope of the claims. The principles described above may be used to provide substrate handling systems designed to handle a variety of substrates, such as, semiconductor wafers, rectangular or square glass sheets for flat panel displays, printed circuit boards, or master disks used in the manufacture of compact disks. Such systems can be also designed to handle substrates in a variety of ways. For example, a handling apparatus may be designed to transfer substrates between a load station and one or more processing stations under ambient and sub-ambient conditions, as described above, or may be designed to move substrates within a processing environment.