Abstract:
Embodiments of the present invention generally relate to a substrate transferring system. One embodiment of the present invention provides a substrate holder comprising a pedestal plate, a basin wall extending from a top surface of the pedestal plate, wherein the basin wall has a substantially leveled top surface, the basin wall and the pedestal plate define a basin configured to retain a liquid therein, and a liquid port opening to the basin, wherein the liquid port is configured to flow a liquid to the basin and allow the liquid to overflow from the basin wall, and a top surface of the overflow liquid in the basin is configured to support a substrate without contacting the basin wall or the pedestal plate.

Description:
BACKGROUND OF THE INVENTION 
     1. Field of the Invention 
     Embodiments of the present invention generally relate to an apparatus and a method for transferring a substrate during processing. More particularly, embodiments of the present invention provide apparatus and method for supporting a substrate during loading and unloading. 
     2. Description of the Related Art 
     Sub-micron multi-level metallization is one of the key technologies for the next generation of ultra large-scale integration (ULSI). The multilevel interconnects that lie at the heart of this technology require planarization of interconnect features formed in high aspect ratio apertures, including contacts, vias, trenches and other features. 
     Planarization is generally performed using Chemical Mechanical Polishing (CMP) and/or Electro-Chemical Mechanical Deposition (ECMP). A planarization method typically requires that a substrate be mounted in a carrier head, with the surface to be polished exposed. The substrate supported by the carrier head is then placed against a rotating polishing pad. The carrier head holding the substrate may also rotate, to provide additional motion between the substrate and the polishing pad surface. A polishing solution is usually supplied to the rotating polishing surface to assist the planarization process. 
     During the planarization process, the substrate is generally secured on the carrier head from the backside of the substrate, for example by forming vacuum cups between a membrane on the carrier head and the backside of the substrate. Prior to or after the planarization process, a load cup is generally used for substrate transferring to and from a carrier head. 
     In the state of the art load cup may have a substrate supporting means, for example, support fingers, configured to hold a substrate and transfer the substrate to and from the carrier head. When unloading a substrate from a carrier head, the membrane is usually inflated to release the vacuum cups between the membrane and the backside of the substrate. The substrate will then fall off the carrier head to a load cup underneath under the effect of gravity.  FIG. 1  schematically illustrates a substrate holder used in the state of the art load cup. A carrier head  10  having a membrane  11  configured to secure a substrate  12  thereon. The membrane  11  is inflated so that the substrate  12  is no longer drawn to the carrier head  10  by suction. A substrate holder  15  having a plurality of support fingers  14  is positioned underneath the carrier head  10  to catch the substrate  12  once the substrate  12  falls off the carrier head  10  under the effect of gravity. During this transferring process, a processed surface  13  of the substrate  12  is exposed to air or other process environment. The processed surface  13  is generally wet from polishing solutions on polishing stations. Structures, such as copper structures, easily corroded when exposing to air in a wet condition. 
     The state of the art load cup has several limitations. First, the time requires to load/unload a substrate from a carrier head is relatively long and unpredictable since the load cup passively waits for gravity to take effect. Second, a substrate to be loaded/unloaded is generally wet and exposed to atmosphere during unloading resulting in corrosion on the processed surface. 
     Therefore, there is a need for apparatus and method to transfer a substrate at an increased and predictable rate and with decreased corrosion. 
     SUMMARY OF THE INVENTION 
     The present invention generally relates to a substrate transferring system. Particularly, the present invention relates to a load cup for transferring a substrate with reduced corrosion and increased speed. 
     One embodiment of the present invention provides a substrate holder comprising a pedestal plate, a basin wall extending from a top surface of the pedestal plate, wherein the basin wall has a substantially leveled top surface, the basin wall and the pedestal plate define a basin configured to retain a liquid therein, and a liquid port opening to the basin, wherein the liquid port is configured to flow a liquid to the basin and allow the liquid to overflow from the basin wall, and a top surface of the overflow liquid in the basin is configured to support a substrate without contacting the basin wall or the pedestal plate. 
     Another embodiment of the present invention provides a method for transferring a substrate comprising holding the substrate using a first substrate holder, filling a basin in a second substrate holder with a liquid to form a liquid surface over a basin wall of the second substrate holder, maintaining a flow of the liquid to the basin to allow the liquid overflow from the basin wall without disturbing the liquid surface, and releasing the substrate from the first substrate holder to the liquid surface, wherein the substrate is supported on the liquid surface. 
     Yet another embodiment of the present invention relates to a method for transferring a substrate comprising maintaining a flow of the liquid to a basin of a load cup to form a liquid support surface for supporting a substrate and to allow the liquid overflow from walls of the basin without disturbing the liquid support surface, aligning a first substrate handler with the load cup, wherein the substrate is secured by the first substrate handler, releasing the substrate to the load cup, wherein the substrate is supported by the liquid support surface, aligning a second substrate handler with the load cup, loading the substrate to the second substrate handler, and draining the liquid from the basin of the load cup. 
    
    
     
       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  (prior art) schematically illustrates a substrate holder used in the state of the art load cup. 
         FIG. 2  schematically illustrates a planarization system in accordance with one embodiment of the present invention. 
         FIG. 3  schematically illustrates a substrate holder in accordance with one embodiment of the present invention. 
         FIGS. 4A-4F  schematically illustrate substrate unloading/loading process in accordance with one embodiment of the present invention. 
         FIG. 5  is a flow chart showing a substrate loading method in accordance with one embodiment of the present invention. 
         FIG. 6  is a flow chart showing a substrate unloading method in accordance with one embodiment of the present invention. 
         FIGS. 7A-7E  schematically illustrate a substrate holder in accordance with one embodiment of the present invention. 
     
    
    
     To facilitate understanding, identical reference numerals have been used, where possible, to designate identical elements that are common to the figures. It is contemplated that elements disclosed in one embodiment may be beneficially utilized on other embodiments without specific recitation. 
     DETAILED DESCRIPTION 
     The present invention generally relates to an apparatus and a method for transferring a substrate, particularly relates to supporting a substrate in a chemical mechanical polishing (CMP) system or electrochemical mechanical polishing (ECMP) system. 
       FIG. 2  illustrates a partial sectional view of a polishing system  100 . The polishing system  100  comprises a polishing station  102 , a carrier head  104  and a load cup  110 . The polishing station  102  comprises a rotatable platen  106  having a polishing material  116  disposed thereon. The carrier head  104  is supported above the polishing station  102  coupled to a base  126  by a transfer mechanism  118 . 
     The transfer mechanism  118  is adapted to position the carrier head  104  selectively over the polishing material  116  or over the load cup  110  (shown in dotted lines). The carrier head  104  comprises a membrane  150  configured to hold a substrate  146  thereon. A detailed description of the carrier head  104  may be found in U.S. Pat. No. 6,183,354, entitled “Carrier Head with a Flexible Membrane for a Chemical Mechanical Polishing”, and U.S. patent application Ser. No. 11/054,128 filed on Feb. 8, 2005 now U.S. Pat. No. 7,001,257, entitled “Multi-chamber Carrier Head with a Flexible Membrane”, which are herein incorporated as reference. 
     The load cup  110  generally includes a pedestal assembly  128  configured to support a substrate  146  on a liquid surface. The pedestal assembly  128  is supported by a shaft  136  which is coupled to an actuator  133 . When transferring a substrate between the load cup  110  and the carrier head  104 , the carrier head  104  is generally rotated to above the load cup  110 , as shown in the dotted lines. The membrane  150  may be inflated to release the substrate  150  which is then grabbed by the load cup  110 . 
     In one embodiment, the pedestal assembly  128  defines a shallow basin configured to retain liquid, such as deionized (DI) water, and to support the substrate  146  on a top surface of the retained liquid in the shallow basin. 
       FIG. 3  schematically illustrates a non-contact substrate holder  200  in accordance with one embodiment of the present invention. The non-contact substrate holder  200  is configured to support a substrate on a liquid support surface formed in a basin, wherein the substrate does not contact the non-contact substrate holder  200  other than the liquid support surface. The non-contact substrate holder  200  may be used as the pedestal assembly  128  of the polishing system  100  of  FIG. 2 . 
     The non-contact substrate holder  200  comprises a pedestal  201  having a basin wall  202  extended thereon. The basin wall  202  and an inner surface  203  of the pedestal  201  form a basin  204 . The basin  204  is configured to retain a liquid and form a liquid support surface to support a substrate thereon. 
     A liquid port  209  is formed on the pedestal  201  near a center of the inner surface  203 . The liquid port  209  is in fluid communication with a liquid source  205  and is configured to fill the basin  204  and to provide a liquid flow to the basin  204  during operation. After the basin  204  has been filled, a liquid flow from the liquid port  209  will cause the liquid to over flow out of the basin wall  202 . The liquid flow is configured to provide a force to the liquid support surface for supporting a substrate thereon without disturbing the liquid support surface. 
     In one embodiment, the liquid port  209  is also connected to a collecting pen  206  to which liquid in the basin  204  may be drained. Shut off valves  207 ,  210  may be used to switch the basin  204  between the liquid source  205  and the collecting pen  206 . In another embodiment, an output port may be formed on the pedestal  201  to drain the basin  202 . 
     The non-contact substrate holder  200  is configured to support a substrate on a liquid support surface over the basin  201 . The basin  201  may have a surface area smaller than a substrate. In one embodiment, at least three blocking pins  208  may extend from the pedestal  201  outside the basin wall  202 . The blocking pins  208  are higher than the basin wall  202  and are configured to keep a substrate supported on the liquid support surface from drifting away. 
       FIGS. 4A-4E  schematically illustrate substrate unloading/loading process in accordance with one embodiment of the present invention using the non-contact substrate holder  200  of  FIG. 3 . 
       FIG. 4A  schematically illustrates the non-contact substrate holder  200  in a receiving state. A liquid flow  212  is provided continuously to the basin  204  through the liquid port  209  forming a liquid support surface  214  and causing liquid to over flow over the basin wall  202 . Flow rate of the liquid flow  212  is set such that the force of over flowing liquid is large enough to support a substrate over the liquid support surface  214  without generating disturbance, such as bubbles, on the liquid support surface  214 . 
     As shown in  FIG. 4B , a substrate  213  may be lowered towards the liquid support surface  214  to be loaded on the non-contact substrate holder  200 . The substrate  213  may be lowered to the liquid support surface  214  by any a substrate handler, such as a robot or a polishing head. The liquid support surface  214  may have a slightly domed shape due to the liquid flow  212  entering near a center of the basin  202 . As a result of the domed shape of the liquid support surface  214 , center areas of a surface  211  of the substrate  213  usually contacts the liquid support surface  214  first. As the substrate  213  continue to lower, contact areas between the surface  211  the liquid support surface  214  gradually increase from center outwards to a complete contact. 
     As shown in  FIG. 4C , the substrate  213  is held by the non-contact substrate holder  200  over the liquid support surface  214 . Gravity G of the substrate  213  is countered by upward force F from upward liquid flow  212  and surface tension of the liquid support surface  214 . In one embodiment, the liquid is DI water. In one embodiment, the liquid flow has a flow rate of about 2 liter/minute to about 6 liter/minute for supporting a substrate on the liquid support surface  214 . 
     The substrate  213  may be held in  FIG. 4C  waiting to be transferred to another substrate handler, for example a robot or a polishing head. A substrate handler, which secures a substrate by an edge of the substrate, may grab the substrate  213  by edge while the substrate  213  is supported by the liquid support surface  214 . Once, the substrate handler has a secure handle of the substrate  213 , the liquid flow  212  may be stopped and basin  202  drained for the substrate  213  to be lifted away. 
     Polishing heads used in chemical mechanical polishing generally hold substrates from backside by vacuum.  FIGS. 4D-4E  schematically illustrate transferring of the substrate  213  from the non-contact substrate holder  200  to a polishing head  250 . 
     The polishing head  250  comprises a support plate  252  surrounded by a membrane  251  configured to be in contact with a backside of a substrate. The support plate  252  has a planar surface  252   a  and a plurality of recesses  253  are formed on the support plate  252 . A pumping system is generally connected to the space between the support plate  252  and the membrane  251  to inflate and deflate the membrane  251 . To load a substrate, the support plate  252  may be used to push the membrane  251  against a backside of the substrate. The membrane  251  is then deflated generating vacuum pouches between the membrane  251  and the substrate when portions of the membrane  251  retreat into the plurality of recesses  253  formed on the support plate  252 . 
     A detailed description of similar polishing head and method for loading/unloading substrates using such polishing head may be found in the U.S. patent application Ser. No. 11/757,069, filed Jun. 1, 2007, entitled “Fast Substrate Loading on Polishing Head without Membrane Inflation Step”, which is incorporated by reference. 
     As shown in  FIG. 4D , the polishing head  250  approaches the non-contact substrate holder  200  and presses the membrane  251  against the substrate  213  supported on the liquid support surface  214 . The pressing allows the membrane  251  to make solid contact with the substrate  213 . The pressing force of the polishing head  250  and gravity of the substrate  213  is countered by upward force F from upward liquid flow  212  and surface tension of the liquid support surface  214 . 
     In one embodiment, the flow rate of the liquid flow  212  may be increased to support the substrate  213  while the polishing head  250  presses against the substrate  250 . In one embodiment, the liquid flow has a flow rate of about 2 liter/minute to about 6 liter/minute during pressing of the polishing head  250 . 
     As shown in  FIG. 4E , after the membrane  251  makes full contact with the substrate  213 , the membrane  251  is then deflated to form a plurality of vacuum pouches  255  between the substrate  213  and the membrane  251  within the plurality of recesses  253 . The substrate  213  is now secured to the polishing head  250 . 
     Once the substrate  213  is secured attached to the polishing head  250 , the liquid flow  212  may be stopped and basin  202  drained for the substrate  213  to be transferred to the polishing head  250 , as shown in  FIG. 4F . In another embodiment, the liquid flow  212  may be increased to push the substrate  213  towards the polishing head  250 . 
       FIG. 5  is a flow chart showing a method  300  for loading a substrate to a load cup in accordance with one embodiment of the present invention. 
     In step  310 , a liquid flow is provided to a load cup having a basin to fill the basin and maintain an overflow from the basin. The liquid flow is configured to form a liquid surface over the basin for supporting a substrate thereon. In one embodiment, the liquid flow may have a constant flow rate. 
     In step  320 , a substrate is lowered toward the liquid support surface by a substrate handler, such as a robot or a polishing head. 
     In step  330 , the substrate is released from the substrate handler to the load cup on the liquid support surface. The liquid flow allows the substrate stay afloat on the liquid support surface. 
       FIG. 6  is a flow chart showing a method  350  for unloading a substrate from a load cup in accordance with one embodiment of the present invention. 
     In step  360 , a substrate holder, such as a robot or a polishing head, is aligned with a substrate supported on a liquid surface of a load cup. The alignment may be completed using alignment pins disposed on the load cup. 
     In step  370 , the substrate holder pushes the substrate against the liquid support surface to load the substrate on the substrate holder. 
     In step  380 , the load cup is drained or the liquid flow rate is increased to release the substrate from the liquid surface of the load cup. 
       FIGS. 7A-7E  schematically illustrate a substrate holder  400  in accordance with one embodiment of the present invention.  FIG. 7A  is a schematic top view of the substrate holder  400  and  FIG. 7B  is a schematic side view of the substrate holder  400 . 
     The substrate holder  400  comprises a pedestal body  401 . A basin wall  402  extends from the pedestal body  401 . The basin wall  402  and a top surface  403  of the pedestal body  401  form a basin  404 . In one embodiment, the basin  404  is substantially circular and configured to support a circular substrate. 
     A liquid port  405  is formed on the pedestal body  401  near a center of the basin  404 . A port  408  is formed within the liquid port  405 . The port  408  may be adapted to a liquid source or a drain. The port  408  is substantially smaller in diameter than the recess and has a side opening  409  opens to a buffering basin  410 . The liquid port  405  has a shoulder  405   a  configured to support a cover  406  thereon. The cover  406  has a plurality of openings  407  between the buffering basin  410  and the basin  404 . 
       FIG. 7C  schematically illustrates the substrate holder  400  supporting a substrate  418  thereon. A liquid flow  417  enters of the port  408  maintains an overflow off the basin wall  402  allowing the substrate  418  to be supported on a liquid surface  416  within the basin  404 . 
     The cover  406  covers the port  408  directing flow of a liquid along a path from the port  408  through the side opening  409  to the buffering basin  410 , then through the plurality of openings  407  to the basin  404 , as shown in  FIG. 7C . This configuration reduces turbulence to a liquid surface  416  from the incoming liquid flow  417  from the port  408  to achieve a smooth liquid surface  416 . The smooth liquid surface of the present invention reduces air bubbles between the liquid surface  416  and the substrate supported thereon, thus reduces corrosion. The smooth liquid surface all so reduces damages to structures on the substrate from the liquid flow. During draining, the liquid flows a reversed direction as shown in  FIG. 7C . 
     Returning to  FIGS. 7A-7B , the substrate holder  400  further comprises a plurality of blocking pins  414  extending from the pedestal body  401  outside the basin wall  402 . Each of the plurality of blocking pins  414  is retractable. In an extended position, the blocking pin  414  is taller than the basin wall  402  thus prevents a substrate supported on the liquid surface  416  from drifting away. In one embodiment, the plurality of blocking pins  414  are evenly distributed alone a perimeter of the basin wall  402 . The blocking pins  414  may be pressed to retract during transferring of a substrate between a polishing head and the substrate holder  400 , as shown in  FIG. 7D . 
     The substrate holder  400  further comprises one or more aligning pin  415 . As shown in  FIG. 7B , the aligning pins  415  extend from the pedestal body  401  outside the basin wall  402 . Each aligning pin  415  has a coned shape to form an extended circle around the basin wall  402 . The aligning pins  415  are configured to gradually align with the substrate  418  during dropping off the substrate  418 . The coned shape of the aligning pins  415  gradually guides the substrate  418  towards the basin wall  402  as the substrate  418  moves vertically downward. The aligning pins  415  may be pressed to retract during transferring of a substrate between a polishing head and the substrate holder  400 , as shown in  FIG. 7D . 
     The substrate holder  400  further comprises one or more head aligning pin  419 . As shown in  FIG. 7B , the head aligning pins  419  extend from the pedestal body  401  outside the basin wall  402 . The head aligning pins  419  is configured to align the substrate holder  400  with the polishing head  450  when the polishing head  450  approaches the substrate holder  400 , as shown in  FIG. 7D . 
     The substrate holder  400  further comprises a plurality of spraying nozzles  412  disposed in recesses  411  formed under the top surface  403  of the pedestal body  401  inside the basin  404 . The spraying nozzles  412  are configured to spray cleaning solution to a polishing head as shown in  FIG. 7E . The spraying nozzles  412  may also be used to clean substrates prior to or after loading. The spraying nozzles  412  are formed in the recesses  411  to avoid contact with the substrate. 
     The substrate holders of the present invention use a smooth liquid surface to support a substrate. As a result, very small impact is applied to the substrate from the liquid during operation, thus, reduces damages to delicate features formed on the substrate. The liquid contact of the substrate holders of the present invention reduces contacts between the substrate surface and the air, thus reducing erosion and contamination. 
     Even though a planarization process is described with the non-contact substrate holder of the present invention, a person skilled in the art can apply the non-contact substrate holder for holding and transferring substrates in any suitable processes, such as wet cleaning, electroplating, and electroless plating. 
     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.