Abstract:
An integrated thermal unit comprises a bake station comprising a bake plate configured to hold and heat a substrate; a chill station comprising a chill plate configured to hold and cool a substrate; and a substrate transfer shuttle configured to transfer substrates from the bake plate to the chill plate along a horizontally linear path within the thermal unit and raise and lower substrates along a vertical path within the integrated thermal unit.

Description:
CROSS-REFERENCES TO RELATED APPLICATIONS  
       [0001]     This application claims priority to U.S. Provisional Application No. 60/674,018, filed Apr. 21, 2005, the disclosure of which is hereby incorporated by reference in its entirety.  
         [0002]     This application is related to U.S. Pat. No. ______, filed ______(Attorney Docket No. A9999/T60610); and to U.S. Pat. No. ______, filed ______ (Attorney Docket No. A9999.3/T60630); and to U.S. Pat. No. ______, filed ______ (Attorney Docket No. A9999.4/T60900). Each of the applications listed above are assigned to Applied Materials, Inc., the assignee of the present invention and are hereby incorporated by reference. 
     
    
     BACKGROUND OF THE INVENTION  
       [0003]     The present invention relates generally to the field of substrate processing equipment. More particularly, the present invention relates to a method and apparatus for controlling the temperature of substrates, such as semiconductor substrates, used in the formation of integrated circuits.  
         [0004]     Modern integrated circuits contain millions of individual elements that are formed by patterning the materials, such as silicon, metal and/or dielectric layers, that make up the integrated circuit to sizes that are small fractions of a micrometer. The technique used throughout the industry for forming such patterns is photolithography. A typical photolithography process sequence generally includes depositing one or more uniform photoresist (resist) layers on the surface of a substrate, drying and curing the deposited layers, patterning the substrate by exposing the photoresist layer to electromagnetic radiation that is suitable for modifying the exposed layer and then developing the patterned photoresist layer.  
         [0005]     It is common in the semiconductor industry for many of the steps associated with the photolithography process to be performed in a multi-chamber processing system (e.g., a cluster tool) that has the capability to sequentially process semiconductor wafers in a controlled manner. One example of a cluster tool that is used to deposit (i.e., coat) and develop a photoresist material is commonly referred to as a track lithography tool.  
         [0006]     Track lithography tools typically include a mainframe that houses multiple chambers (which are sometimes referred to herein as stations) dedicated to performing the various tasks associated with pre- and post-lithography processing. There are typically both wet and dry processing chambers within track lithography tools. Wet chambers include coat and/or develop bowls, while dry chambers include thermal control units that house bake and/or chill plates. Track lithography tools also frequently include one or more pod/cassette mounting devices, such as an industry standard FOUP (front opening unified pod), to receive substrates from and return substrates to the clean room, multiple substrate transfer robots to transfer substrates between the various chambers/stations of the track tool and an interface that allows the tool to be operatively coupled to a lithography exposure tool in order to transfer substrates into the exposure tool and receive substrates from the exposure tool after the substrates are processed within the exposure tool.  
         [0007]     Over the years there has been a strong push within the semiconductor industry to shrink the size of semiconductor devices. The reduced feature sizes have caused the industry&#39;s tolerance to process variability to shrink, which in turn, has resulted in semiconductor manufacturing specifications having more stringent requirements for process uniformity and repeatability. An important factor in minimizing process variability during track lithography processing sequences is to ensure that every substrate processed within the track lithography tool for a particular application has the same “wafer history.” A substrate&#39;s wafer history is generally monitored and controlled by process engineers to ensure that all of the device fabrication processing variables that may later affect a device&#39;s performance are controlled, so that all substrates in the same batch are always processed the same way.  
         [0008]     To ensure that each substrate has the same “wafer history” requires that each substrate experiences the same repeatable substrate processing steps (e.g., consistent coating process, consistent hard bake process, consistent chill process, etc.) and the timing between the various processing steps is the same for each substrate. Lithography type device fabrication processes can be especially sensitive to variations in process recipe variables and the timing between the recipe steps, which directly affects process variability and ultimately device performance.  
         [0009]     In view of these requirements, the semiconductor industry is continuously researching methods and developing tools and techniques that can improve the uniformity in wafer history for track lithography and other types of cluster tools.  
       BRIEF SUMMARY OF THE INVENTION  
       [0010]     According to the present invention, methods and apparatus related to semiconductor manufacturing equipment are provided. More particularly, embodiments of the present invention relate to a method and apparatus for heating and/or cooling a substrate in a highly controllable manner. Embodiments of the invention contemplate multiple substrates being processed according to the same heating and cooling sequence in a highly controllable manner thus helping to ensure a consistent wafer history for each substrate. While some embodiments of the invention are particularly useful in heating and/or cooling substrates in a chamber or station of a track lithography tool, other embodiments of the invention can be used in other applications where it is desirable to heat and cool substrates in a highly controllable manner.  
         [0011]     Certain embodiments of the invention pertain to an integrated thermal unit. According to one such embodiment, an integrated thermal unit comprises a bake plate configured to heat a substrate supported on a surface of the bake plate; a chill plate configured to cool a substrate supported on a surface of the chill plate; and a substrate transfer shuttle configured to transfer substrates from the bake plate to the cool plate, the substrate transfer shuttle having a temperature controlled substrate holding surface that is capable of cooling a substrate heated by the bake plate.  
         [0012]     According to another embodiment of the invention, an integrated thermal unit comprises a bake station comprising a bake plate configured to hold and heat a substrate; a chill station comprising a chill plate configured to hold and cool a substrate; and a substrate transfer shuttle configured to transfer substrates from the bake plate to the chill plate along a horizontally linear path within the thermal unit and raise and lower substrates along a vertical path within the integrated thermal unit.  
         [0013]     According to another embodiment of the invention, an integrated thermal unit comprises a bake plate having a substrate holding surface configured to hold and heat a substrate in a baking position; and a chill plate having a substrate holding surface configured to hold and cool a substrate in a cooling position where the substrate holding surface of the bake plate is positioned in a first substantially horizontal plane when the bake plate is in the baking position and the substrate holding surface of the chill plate is positioned in a second substantially horizontal plane that is below the first plane when the chill plate is in a cooling position.  
         [0014]     According to still another embodiment of the invention, a bake station is provided. The bake station comprises a bake plate adapted to heat a substrate supported on an upper surface of the bake plate, the bake plate vertically moveable between an upper baking position and a lower cooling position; and a plurality of heat sinks adapted to be engageably coupled to a lower surface of the bake plate when the bake plate is in the lower cooling position.  
         [0015]     Certain other embodiments of the invention pertain to a track lithography tool comprising a plurality of pod assemblies adapted to accept one or more cassettes of wafers and one or more robots adapted to transfer wafers from the one or more pod assemblies to processing modules within the track lithography tool, wherein at least one of the processing modules includes an integrated thermal unit according to one of the embodiments described above.  
         [0016]     Still other embodiments of the invention pertain to methods of processing a substrate in an integrated thermal unit. According to one such embodiment, a method of processing a substrate in a integrated thermal unit having a bake plate and a chill plate comprises transferring a substrate having a liquid resist material applied thereon into the integrated thermal unit; positioning the substrate on the bake plate; heating the substrate with the bake plate; transferring the substrate from the bake plate to the chill plate with a shuttle having a temperature controlled surface; cooling the substrate with the chill plate; and transferring the substrate out of the integrated thermal unit.  
         [0017]     According to another embodiment, a method of processing a substrate in a integrated thermal unit having a bake plate and a chill plate comprises transferring a substrate having a liquid resist material applied thereon into the integrated thermal unit; positioning the substrate on the bake plate; heating the substrate with the bake plate; transferring the substrate from the bake plate to the chill plate, wherein the transferring includes moving, within the integrated thermal unit, the substrate along a horizontally linear path and along a vertical path with a substrate transfer shuttle; cooling the substrate with the chill plate; and transferring the substrate out of the integrated thermal unit.  
         [0018]     According to another embodiment, a method of processing a substrate in a integrated thermal unit having a bake plate and a chill plate comprises transferring a substrate having a liquid resist material applied thereon into the integrated thermal unit; positioning the substrate on the bake plate; heating the substrate with the bake plate; transferring the substrate from the bake plate to the chill plate with a shuttle having a temperature controlled surface; cooling the substrate with the chill plate; and transferring the substrate out of the integrated thermal unit.  
         [0019]     According to still another embodiment of the invention a method of rapidly reducing a set point temperature of a bake plate is provided. This embodiment comprises, after using the bake plate to heat a substrate disposed on an upper surface of the bake plate while the bake plate is in a baking position, vertically moving the bake plate to a lower position in which a lower surface of the bake plate contacts a plurality of heat sinks adapted to be engageably coupled to the lower surface of the bake plate.  
         [0020]     Many benefits are achieved by way of the present invention over conventional techniques. For example, including bake and chill plates in one integrated unit minimizes the delay associated with transferring a baked wafer to the chill plate. Also, the inclusion of a shuttle having a temperature controlled substrate holding surface that transfers wafers between the bake and chill plates provides an additional degree of control over each wafer&#39;s thermal history thus enabling a more uniform thermal history among multiple wafers. Moreover, embodiments of the invention increase chamber throughput by decreasing the load on the main, central robot(s) of a track lithography tool and provide a safe haven for post-bake wafers in case of a malfunction of a main, central robot. Other embodiments increase wafer throughput by decreasing the amount of time it take to change the set point temperature of a bake plate from a first temperature to a second temperature lower than the first temperature. Depending upon the embodiment, one or more of these benefits, as well as other benefits, may be achieved. These and other benefits will be described in more detail throughout the present specification and more particularly below in conjunction with the following drawings. 
     
    
     BRIEF DESCRIPTION OF THE DRAWINGS  
       [0021]      FIG. 1  is a conceptual view of one embodiment of an integrated thermal unit according to the present invention;  
         [0022]      FIG. 2A  is a simplified perspective view of the integrated thermal unit depicted in  FIG. 1 ;  
         [0023]      FIG. 2B  is a simplified perspective view of integrated thermal unit  10  depicted in  FIG. 2A  with the top of the unit removed;  
         [0024]      FIG. 3  is a block diagram that illustrates a sequence of events that are performed according to one embodiment of the method of the present invention;  
         [0025]      FIG. 4  is a cross-sectional view of bake station  12  and chill station  14  shown in  FIG. 2B ;  
         [0026]      FIG. 5  is a perspective view of chill shuttle  18  shown  FIG. 2B  according to one embodiment of the invention;  
         [0027]      FIG. 6  is a perspective view of a portion of the integrated thermal unit shown in  FIG. 2B  having bake station  12  and chill station  14  removed;  
         [0028]      FIG. 7  is a perspective view of chill plate  30  shown  FIG. 2B  according to one embodiment of the invention;  
         [0029]      FIG. 8  is perspective view of bake plate  20  shown  FIG. 2B  according to one embodiment of the invention;  
         [0030]      FIG. 9  is a perspective view of a cross-section of bake plate  20  shown  FIG. 8 ;  
         [0031]      FIG. 10  is a cross-sectional view of bake plate  20  shown in  FIGS. 8 and 9 ;  
         [0032]      FIG. 11  is bottom perspective view of bake station  12  shown  FIG. 8 ;  
         [0033]      FIG. 12  is a simplified cross-sectional view of an engageable heat sink  140  shown in  FIG. 11 ;  
         [0034]      FIG. 13  is a conceptual view of an alternative embodiment of an integrated thermal unit according to the present invention;  
         [0035]      FIG. 14  is a plan view of one embodiment of a track lithography tool according to one embodiment of the present invention; and  
         [0036]      FIG. 15  is a flowchart illustrating an exemplary processing sequence for a semiconductor substrate processed by the track lithography tool shown in  FIG. 14 . 
     
    
     DETAILED DESCRIPTION OF THE INVENTION  
       [0037]     The present invention generally provides a method and apparatus for heating and cooling substrates in a highly controllable manner. While it is to be recognized that embodiments of the invention are particularly useful in helping to ensure a consistent wafer history for each substrate in a plurality of substrates that are heated and cooled according a particular thermal recipe within a track lithography tool, other embodiments of the invention can be used in other applications where it is desirable to heat and cool substrates in a highly controllable manner.  
         [0038]      FIG. 1  is a simplified conceptual view of one embodiment of an integrated thermal unit  10  according to the present invention. Integrated thermal unit  10  includes a bake station  12 , a chill station  14  and a shuttle station  16  all within an enclosed housing  40 . Chill station  16  includes a shuttle  18  for transferring substrates between the bake and chill stations as needed. Bake station  12  includes a bake plate  20 , an enclosure  22  and a chill base  24 . Bake plate  20  is moveable between a wafer loading position (shown in  FIG. 1 ), a closed heating position in which the bake plate is urged towards and within clam shell enclosure  22  by a motorized lift  28  and a cooling position in which the bake plate contacts chill base  24 . Chill base  24  is engageably coupled to bake plate chill to enable the set point temperature of the bake plate to be rapidly changed from a relatively high, bake temperature to a lower bake temperature when, for example, switching to a new thermal recipe.  
         [0039]     Chill station  14  includes a chill plate  30  and a particle shield  32  that protects a wafer situated on chill plate  30  from possible particle contamination when shuttle  18  passes over the chill station to transfer a wafer to or from bake station  12 . Substrates can be transferred into and out of thermal unit  10  through elongated openings that are operatively coupled to shutters  34   a  and  34   b , respectively.  
         [0040]     As shown in  FIG. 2A , which is a simplified perspective view of integrated thermal unit  10  depicted in  FIG. 1 , thermal unit  10  includes an exterior housing  40  made of aluminum or another suitable material. Housing  40  is long relative to its height in order to allow bake station  12 , chill station  14  and shuttle station  16  to be laterally adjacent to each other and to allow multiple integrated thermal units to be stacked on top of each other in a track lithography tool as described below with respect to  FIG. 14 . In one particular embodiment, housing  40  is just 20 centimeters high.  
         [0041]     Housing  40  includes side pieces  40   a , a top piece  40   b  and a bottom piece  40   c . Front side piece  40   a  includes two elongated openings  41   a ,  41   b  that allow substrates to be transferred into and out of the thermal unit. Opening  41   a  is operatively coupled to be closed and sealed by shutter  34   a  (not shown) and opening  41   b  is operatively coupled to be closed and sealed by shutter  34   b  (also not shown). Top piece  40   b  of housing  40  includes coolant channels  42  that allow a coolant fluid to be circulated through the channels in order to control the temperature of top piece  40   b  when an appropriate plate (not shown) is attached to top piece  40   b  via screw holes  44 . Similar coolant channels are formed in the lower surface of bottom piece  40   c.    
         [0042]     Also shown in  FIG. 2A  is various control circuitry  46   a - 46   d  which controls the precision baking operation of bake station  12  and the precision cooling operation of chill station  14 ; and tracks  48  and  49  that enable shuttle  18  (not visible within  FIG. 2A ) to move linearly along the length of the thermal unit and vertically within the thermal unit as discussed in more detail below. In one embodiment, control circuitry  46   a - 46   b  is positioned near stations  12  and  14  (e.g., within three feet) in order to enable more accurate and responsive control of temperature adjusting mechanisms associated with each station.  
         [0043]      FIG. 2B  is a simplified perspective view of integrated thermal unit  10  as seen with top  40   b  and particle shield  32  (shown in  FIG. 1 ) removed. In  FIG. 2B , shuttle  18 , chill plate  30  and clam shell enclosure  22  of bake station  12  are visible. Also visible is a space  47  between rear support piece  90  of housing  40  and bottom piece  40   c . Space  47 , which is also visible in  FIG. 5 , extends along much of the length of integrated thermal unit  10  to allow shuttle  18  to transfer wafers between stations  12 ,  14  and  16  as discussed in detail below.  
         [0044]     In order to better appreciate and understand the general operation of integrated thermal unit  10 , reference is now made to  FIG. 3  along with  FIGS. 1 and 2 B.  FIG. 3  is a simplified block diagram that illustrates a sequence of events that is performed by thermal unit  10  to thermally treat wafers according to one embodiment of the method of the present invention. A wafer may be treated in accordance with the process set forth in  FIG. 3  after, for example, having a photoresist layer deposited over the wafer at an appropriate coating station of a track lithography tool. While the discussion below focuses on treating a single wafer within unit  10 , a person of skill in the art will appreciate that thermal unit  10  will often be used to simultaneously process two wafers. For example, while one wafer is being heated on bake plate  20 , thermal unit  10  can be in the process of cooling another wafer on chill plate  30  or transferring another wafer out of the thermal unit at the completion of its thermal treatment.  
         [0045]     As shown in  FIG. 3 , a wafer&#39;s history in thermal unit  10  starts by transferring the wafer into the thermal unit  10  through wafer transfer slot  41   b  and placing the wafer onto stationary lift pins  36  ( FIG. 1 ) at shuttle station  16  ( FIG. 3 , step  50 ). The wafer may be transferred into thermal unit  10  by, for example, a central robot that services both wafer transfer slots  41   a  and  41   b  as well as one or more coating or developing stations in a track lithography tool (not shown). Typically wafer transfer slot  41   b  is closed by shutter  34   b , thus step  50  also includes moving shutter  34   b  to open slot  41   b . During step  50  shuttle  18  is in a wafer receiving position at station  16  where lift pins  36  extend through slots  19   a  and  19   b  of the shuttle  18 . After the wafer is properly positioned on lift pins  36 , the robot arm recedes out of the thermal unit and chill shuttle  18  is raised to lift the wafer off of stationary lift pins  36  ( FIG. 3 , step  51 ) and then moved linearly along the length of the thermal unit to transfer the wafer to bake station  12  ( FIG. 3 , step  52 ). The path to bake station  12  takes shuttle  18  over particle shield  32  at chill station  14 .  
         [0046]     At bake station  12 , the wafer is placed on lift pins  38  and shuttle  18  is free to handle another task or return to its home position at shuttle station  16  ( FIG. 3 , step  53 ). While the shuttle is being returned to home position, bake plate  20  is raised by motorized lift  28  thereby picking the wafer up off of stationary lift pins  38  and bringing the wafer into its bake position within clam shell enclosure  22  ( FIG. 3 , step  54 ). Once inside claim shell enclosure  22  the wafer is heated or baked according to a desired thermal recipe ( FIG. 3 , step  55 ).  
         [0047]     After completion of bake step  55 , the bake plate  20  is lowered to its wafer receiving position dropping the wafer off on lift pins  38  ( FIG. 3 , step  56 ). Next, shuttle  18  returns to bake station  12  and picks the wafer up off of lift pins  38  ( FIG. 3 , step  57 ) and brings the wafer to chill station  14  ( FIG. 3 , step  58 ). The path to chill station  14  takes shuttle over particle shield  32  to shuttle station  16  where shuttle  18  is lowered and then moved towards chill station  14 . Once at chill station  14 , lift pins  37  are raised by a pneumatic lift to lift the wafer off of the shuttle ( FIG. 3 , step  59 ). Shuttle  18  is then free to handle another task or return to its home position at station  16  ( FIG. 3 , step  60 ) and lift pins  37  are lowered to drop the wafer of onto chill plate  30  ( FIG. 3 , step  61 ).  
         [0048]     The wafer is then cooled on chill plate  30  according to a predetermined thermal recipe ( FIG. 3 , step  62 ). After completion of the cooling process, lift pins  37  are raised to pick the wafer up off of the chill plate ( FIG. 3 , step  63 ) and the wafer is transferred out of the integrated thermal unit through elongated slot  41   a  ( FIG. 3 , step  64 ) by, for example, being picked up by the same central robot that transferred the wafer into the thermal unit in step  50 . Typically, elongated slot  41   a  is closed by shutter  34   a , thus step  64  also includes opening shutter  34   a  to open slot  41   a.    
         [0049]     Embodiments of the invention allow a process such as that described above to be carried out in a highly controllable and highly repeatable manner. Thus, embodiments of the invention help ensure an extremely high degree of uniformity in the thermal treatment of each wafer that is processed within integrated thermal unit  10  according to a particular thermal recipe. As discussed in more detail below, a number of specific aspects of the present invention can be used independent from each other or in combination to help achieve such a repeatable, uniform wafer history.  
         [0050]     One such aspect is the placement of hot plate  20  with respect to chill plate  30 . Specifically, in some embodiments of the invention hot plate  20  is positioned within integrated thermal unit  10  at a position that is higher than the position of chill plate  30 . Because heat generated from bake plate  20  generally rises to an upper portion of thermal unit  10 , such positioning helps minimize thermal cross-talk between the bake station and chill station that may otherwise lead to discrepancies in the thermal treatment of wafers over time.  
         [0051]     This aspect of the invention is illustrated in  FIG. 4 , which is a simplified cross-sectional view of a portion of integrated thermal unit  10  showing bake plate  20  and chill plate  30 . As shown in  FIG. 4 , when hot plate  20  is within claim shell enclosure  22  at a baking position  71 , wafer support surface  70  lies in a horizontal plane A that is well above the horizontal plane C that wafer support surface  72  of chill plate  30  lies in. In some embodiments plane A is at least 4 cm above plane C and in one particular embodiment plane A is 6 cm above plane C. Furthermore, in some embodiments of the invention even when the bake plate is engaged with heat sinks  140  (described below) while in a wafer receiving position, upper surface  70  of the bake plate lies in a horizontal plane B that is above the upper surface  72  of the chill plate (plane C). In some embodiments plane B is at least 2 cm above plane C and in one particular embodiments plane B is 2.5 cm above plane C. Also, in some embodiments the upper surface of particle shield  32  also lies in or substantially closed to plane B.  
         [0052]     Maintaining such a height difference in the positions of bake plate  20  and chill plate  30  helps minimize thermal cross-talk between the two stations and helps ensure a highly controlled, repeatable thermal treatment among multiple wafers.  
         [0053]     Another aspect of the present invention that helps ensure an extremely high degree of uniformity in the thermal treatment of each wafer is the design of shuttle  18 . As shown in  FIG. 5 , which is a simplified perspective view of shuttle  18 , the shuttle includes a wafer receiving area  74  upon which a semiconductor wafer is placed while the shuttle is transferring the wafer from one station to another. In one embodiment, shuttle  18  is made from aluminum and wafer receiving area  74  and other portions of an upper surface  75  of the shuttle are actively cooled by a coolant (e.g., deionized water) that flows through coolant passages (shown in  FIG. 4  as passages  75 ) in the shuttle.  
         [0054]     The coolant is delivered to passages  75  by tubes that connect to inlets/outlets  76 , which in turn connect to a manifold (not shown) within portion  79  of shuttle  18  that helps distribute the fluid evenly throughout the shuttle. The fluid tubes are at least partially supported by fingers  78  of tube support mechanism  77  as shuttle  18  traverses the length of the integrated thermal unit. Actively cooling wafer receiving surface  74  helps maintain precise thermal control of wafer temperature during all times while the wafer is within thermal unit  10 . Actively cooling shuttle  18  also starts the wafer cooling process sooner than it would otherwise be initiated if such active cooling did not occur until the wafer is transferred to a dedicated chill station, which in turn reduces the overall thermal budget of the wafer.  
         [0055]     Also shown in  FIG. 5  are slots  19   a ,  19   b , wafer pocket buttons  80  and small contact area proximity pins  82  and slots  19   a ,  19   b . Slots  19   a ,  19   b  allow the shuttle to be positioned or moved under a wafer being held by lift pins. For example, in chill station  14  a wafer is held above the chill plate prior to and after chill step  63  on a set of three lift pins arranged in a triangular formation (see  FIG. 7  showing holes  84  that allow the lift pins to extend through chill plate  30 ). Slot  19   a  is aligned to allow shuttle  18  to slide past two of the three lift pins and slot  19   b  is aligned to allow the shuttle to slide pass the third lift pin. Pocket buttons  80  screw into threaded holes in the upper surface of shuttle  18  and extend above the surface to help center a wafer within wafer receiving area  74 . Pocket buttons  80  can be made from any appropriately soft material, such as a thermoplastic material, that exhibits strong fatigue resistance and thermal stability. In one embodiment, buttons  80  are made from polyetheretherketone, which is also known as PEEK.  
         [0056]     Proximity pins  82  are distributed across upper surface  74  of shuttle  18  and are fabricated from a material with a low coefficient of friction, such as sapphire. Proximity pins  82  allow the wafer being transported by shuttle  18  to be brought into very close proximity of temperature controlled surface  74 . The small space between the wafer and temperature controlled surface  74  helps create uniform cooling across the entire surface area of the wafer while at the same time minimizing contact between the underside of the wafer and the shuttle thus reducing the likelihood that particles or contaminants may be generated from such contact. Further details of proximity pins  82  are set forth in U.S. application Ser. No. 11/111,155, entitled “Purged Vacuum Chuck with Proximity Pins” filed on Apr. 20, 2005 (Attorney Docket No.: A9871/T60200), which is hereby incorporated by reference for all purposes. In one particular embodiment shuttle  18  includes four pocket buttons  80  and seventeen proximity pins  82 .  
         [0057]     Shuttle  18  also includes an elongated U-shaped support bracket  86  that allows the shuttle to be mounted to a support plate  88  shown in  FIG. 6 , which is a perspective view of a portion of integrated thermal unit  10  having bake station  12  and chill station  14  removed. As seen in  FIG. 6 , support plate  88  loops under and around rear support piece  90 , which is mounted to bottom plate  40   c , through slot  47 . Plate  88  (and thus shuttle  18 ) can be moved linearly along a track  48  (horizontal path X). Plate  88  also slides vertically along track  49  allowing shuttle  18  to be raised and lowered (vertical path Z) in order to pick up and/or drop off wafers at a particular station.  
         [0058]     Referring now to  FIG. 7 , which is a perspective view of chill plate  30  according to one embodiment of the invention, chill plate  30  includes a coolant inlet  95  and outlet  96  that allow a coolant liquid, such as deionized water, to be circulated through coolant channels (not shown) to cool a wafer supported on wafer support surface  72 . Chill plate  30  also includes a number of wafer pocket buttons  85  and small contact area proximity pins  83  that are similar to buttons  80  and proximity pins  82  described above with respect to  FIG. 5 . In one particular embodiment, chill plate  30  includes eight pocket buttons  85  and seventeen proximity pins  83 . Also, while not shown in  FIG. 7 , chill plate  30  may include a plurality of vacuum ports and be operatively coupled to a vacuum chuck to secure a wafer to the chill plate during the cooling process.  
         [0059]     Also not shown in  FIG. 7 , a particle shield  32  (shown in  FIG. 1 ) is positioned above chill plate  30  in order to protect the chill plate, and any wafer positioned on the chill plate, from possible particle contamination when shuttle  18  traverses between bake station  12  and shuttle station  16  over chill plate  30 . Particle shield  32  is connected to bottom housing piece  40   c  between bake station  12  and chill station  14  (see  FIG. 4 ) and front side piece  40   a  of housing  40  in a manner that allows shuttle  18  to pass under the particle shield and access chill plate  30  as needed. In one particular embodiment, particle shield  32  is made from stainless steel.  
         [0060]     Reference is now made to  FIGS. 8, 9  and  10  where  FIG. 8  is a perspective view of bake station  12  shown  FIG. 2B  according to one embodiment of the invention;  FIG. 9  is a perspective view of a cross-section of bake station  12  shown  FIG. 8  and  FIG. 10  is a cross-sectional view of the bake station. As shown in  FIGS. 8-10 , bake station  12  has three separate isothermal heating elements: bake plate  20 , top heat plate  110  and side heat plate  112 , each of which is manufactured from a material exhibiting high heat conductivity, such as aluminum or other appropriate material. Each plate  20 ,  110 ,  112  has a heating element, for example, resistive heating elements, embedded within the plate. Bake station  12  also includes side top and bottom heat shields  116  and  118 , respectively, as well as a bottom cup  119  that surrounds bake plate  20  and a lid  120  (shown in  FIG. 10  only). Each of heat shields  116 ,  118 , cup  119  and lid  120  are made from aluminum. Lid  120  is attached to top heat plate  110  by eight screws that are threaded through threaded holes  115 .  
         [0061]     Bake plate  20  is operatively coupled to a motorized lift  26  so that the bake plate can be raised into a clam shell enclosure  22  and lowered into a wafer receiving position. Typically, wafers are heated on bake plate  20  when it is raised to a baking position as shown in  FIG. 4 , position  71 . When in the baking position, cup  119  encircles a bottom portion of side heat plate  112  forming a clam shell arrangement that helps confine heat generated by bake plate  20  within an inner cavity formed by the bake plate and enclosure  22 . In one embodiment the upper surface of bake plate  20  includes 8 wafer pocket buttons and 17 proximity pins similar to those described with respect to shuttle  18  and chill plate  30 . Also, in one embodiment bake plate  20  includes a plurality of vacuum ports and be operatively coupled to a vacuum chuck to secure a wafer to the bake plate during the baking process.  
         [0062]     During the baking process, a faceplate  122  is positioned just above and opposite wafer support surface  70  of bake plate  20 . Faceplate  122  can be made from aluminum as well as other suitable materials and includes a plurality of holes or channels  122   a  that allow gases and contaminants baked off the surface of a wafer being baked on bake plate  20  to drift through faceplate  122  and into a radially inward gas flow  124  that is created between faceplate  122  and top heat plate  110 .  
         [0063]     Gas from radially inward gas flow  124  is initially introduced into bake station  12  at an annular gas manifold  126  that encircles the outer portion of top heat plate  110  by a gas inlet line  127 . Gas manifold  126  includes numerous small gas inlets  130  ( 128  inlets in one embodiment) that allow gas to flow from manifold  126  into the cavity  132  between the lower surface of top heat plate  110  and the upper surface of faceplate  122 . The gas flows radially inward towards the center of the station through a diffusion plate  134  that includes a plurality of gas outlet holes  136 . After flowing through diffusion plate  134 , gas exits bake station  12  through gas outlet line  128 .  
         [0064]     An aspect of the invention that helps minimize any delay associated with switching from one thermal recipe to another thermal recipe an thus helps ensure high wafer throughput through integrated thermal unit  10  is discussed below with respect to  FIGS. 11 and 12 .  FIG. 11  is a bottom perspective view of bake station  12  shown  FIGS. 8-10 . As shown in  FIG. 11 , in one embodiment of the invention bake station  12  includes a plurality of engageable heat sinks  140 . Each engageable heat sink  140  is made from an appropriate heat sink material, such as aluminum, copper, stainless steel or other metal.  
         [0065]     As previously mentioned, bake plate  20  heats a wafer according to a particular thermal recipe. One component of the thermal recipe is typically a set point temperature at which the bake plate is set to heat the wafer. During the baking process, the temperature of the wafer is routinely measured and one or more zones of the bake plate can be adjusted to ensure uniform heating of the substrate. Typically bake plate is heated to the desired set point temperature while a large batch of wafers are processed according to the same thermal recipe. Thus, for example, if a particular thermal recipe calls for a set point temperature of 175° C. and that recipe is to be implemented on  100  consecutive wafers, bake plate  20  will be heated to 175° C. during the length of time it takes to process the 100 consecutive wafers. If, however, a subsequent batch of 200 wafers is to be processed according to a different thermal recipe that, for example, requires a set point temperature of 130° C., the set point temperature of bake plate  20  needs to be rapidly changed from 175° C. to 130° C. between processing the 100th and 101st wafers.  
         [0066]     Embodiments of the present invention enable a rapid reduction in the set point temperature of bake plate  20  by lowering the bake plate with motor  26  into a lower cooling position that is below the wafer receiving position. In the cooling position a bottom surface  73  of the bake plate contacts an upper surface  142  of each heat sink  140 . Contact between the heat sinks and bake plate is possible because bottom cup  119  includes a plurality of holes  138  that correspond to the plurality of heat sinks  140  allowing the heat sinks to extend through bottom cup  119  to contact bake plate  20 .  
         [0067]      FIG. 12  is a simplified cross-sectional view of an engageable heat sink  140 . As shown in  FIG. 12 , each engageable heat sink  140  includes a lower base portion  144  that has a larger diameter than the main body of the heat sink. Lower base portion  144  fits within a cavity  152  that is defined by bottom base plate  40   c  and an aluminum plate  150 . Base portion  144  of the heat sink engages a lip  154  of the bottom base plate and is pressed against the lip by a spring  145  positioned between aluminum plate  150  and base portion  144 .  
         [0068]     When bake plate  20  is lowered into the cooling position, spring  145  causes heat sink  140  to press upon lower surface of  73  of the bake plate. The combined thermal mass of all heat sinks  140  allows bake plate  20  to be rapidly cooled from one set point temperature to a lower set point temperature as may be required, for example, when transitioning to a new thermal recipe.  
         [0069]     While heat sink  140  shown in  FIGS. 11 and 12  is shown to be cylindrical in shape, many other shapes and sizes can be used. Also, in some embodiments, each heat sink  140  can be actively cooled by forming one or more coolant channels within the body of the heat sink. Also in some embodiments, heat sink  140  includes a thermal pad on its upper surface  142  that provides for smooth contact between the heat sink and bake plate during the engaging process.  
         [0070]      FIG. 13  is a conceptual view of an alternative embodiment of an integrated thermal unit  150  according to the present invention. One primary difference between the embodiment of the invention shown in  FIG. 13  and the embodiment shown in  FIG. 1  is the placement of the bake, chill and shuttle stations  12 ,  14  and  16 , respectively. In  FIG. 13 , the shuttle (shuttle  152  as compared to shuttle  18 ) has been moved to a central position between the bake station and chill station. Such an arrangement provides a benefit in further reducing thermal cross-talk between the bake and chill stations and also alleviates the need for particle shield  32  to be positioned over chill plate  30  because shuttle  18  does not need to “fly over” the chill plate to deliver a wafer to bake plate  20 . One benefit of the arrangement of  FIG. 1  as compared to that of  FIG. 13  is the separation of shuttle  18  from bake plate  20  when the shuttle is in a position to receive wafers passed into the integrated thermal unit.  
         [0071]     Also, shuttle  152  in  FIG. 13  is operatively configured to move linearly along a X-axis (horizontal path) along the length of housing  40  but is not configured to be moveable vertically. This difference requires moveable lift pins at each of the bake, chill and shuttle stations in order to properly exchange wafers between shuttle  152  and the station.  
         [0072]      FIG. 14  is a plan view of one embodiment of a track lithography tool  200  in which the embodiments of the present invention may be used. As illustrated in  FIG. 14 , track lithography  200  contains a front end module  210  (sometimes referred to as a factory interface)  210 , a central module  212 , and a rear module  214  (sometimes referred to as a scanner interface). Front end module  210  generally contains one or more pod assemblies or FOUPS (e.g., items  216 A-D), a front end robot  218 , and front end processing racks  220 A,  220 B. The one or more pod assemblies  216 A-D are generally adapted to accept one or more cassettes  230  that may contain one or more substrates “W”, or wafers, that are to be processed in track lithography tool  200 .  
         [0073]     Central module  212  generally contains a first central processing rack  222 A, a second central processing rack  222 B, and a central robot  224 . Rear module  214  generally contains first and second rear processing racks  226 A,  226 B and a back end robot  228 . Front end robot  218  is adapted to access processing modules in front end processing racks  220 A,  220 B; central robot  224  is adapted to access processing modules in front end processing racks  220 A,  220 B, first central processing rack  222 A, second central processing rack  222 B and/or rear processing racks  226 A,  226 B; and back end robot  228  is adapted to access processing modules in the rear processing racks  226 A,  226 B and in some cases exchange substrates with a stepper/scanner  5 .  
         [0074]     The stepper/scanner  5 , which may be purchased from Canon USA, Inc. of San Jose, Calif., Nikon Precision Inc. of Belmont, Calif., or ASML US, Inc. of Tempe Ariz., is a lithographic projection apparatus used, for example, in the manufacture of integrated circuits (ICs). The scanner/stepper tool  5  exposes a photosensitive material (resist), deposited on the substrate in the cluster tool, to some form of electromagnetic radiation to generate a circuit pattern corresponding to an individual layer of the integrated circuit (IC) device to be formed on the substrate surface.  
         [0075]     Each of the processing racks  220 A,  220 B;  222 A,  222 B and  226 A,  226 B contain multiple processing modules in a vertically stacked arrangement. That is, each of the processing racks may contain multiple stacked integrated thermal units  10 , multiple stacked coater modules  232 , multiple stacked coater/developer modules with shared dispense  234  or other modules that are adapted to perform the various processing steps required of a track photolithography tool. As examples, coater modules  232  may deposit a bottom antireflective coating (BARC); coater/developer modules  234  may be used to deposit and/or develop photoresist layers and integrated thermal units  10  may perform bake and chill operations associated with hardening BARC and/or photoresist layers.  
         [0076]     In one embodiment, a system controller  240  is used to control all of the components and processes performed in the cluster tool  200 . The controller  240  is generally adapted to communicate with the stepper/scanner  5 , monitor and control aspects of the processes performed in the cluster tool  200 , and is adapted to control all aspects of the complete substrate processing sequence. In some instances, controller  240  works in conjunction with other controllers, such as controllers  46 A- 46 D, which control hot plate  20  and chill plate  30  of integrated thermal unit  10 , to control certain aspects of the processing sequence. The controller  240 , which is typically a microprocessor-based controller, is configured to receive inputs from a user and/or various sensors in one of the processing chambers and appropriately control the processing chamber components in accordance with the various inputs and software instructions retained in the controller&#39;s memory. The controller  240  generally contains memory and a CPU (not shown) which are utilized by the controller to retain various programs, process the programs, and execute the programs when necessary. The memory (not shown) is connected to the CPU, and may be one or more of a readily available memory, such as random access memory (RAM), read only memory (ROM), floppy disk, hard disk, or any other form of digital storage, local or remote. Software instructions and data can be coded and stored within the memory for instructing the CPU. The support circuits (not shown) are also connected to the CPU for supporting the processor in a conventional manner. The support circuits may include cache, power supplies, clock circuits, input/output circuitry, subsystems, and the like all well known in the art. A program (or computer instructions) readable by the controller  240  determines which tasks are performable in the processing chamber(s). Preferably, the program is software readable by the controller  240  and includes instructions to monitor and control the process based on defined rules and input data.  
         [0077]     It is to be understood that embodiments of the invention are not limited to use with a track lithography tool such as that depicted in  FIG. 14 . Instead, embodiments of the invention may be used in any track lithography tool including the many different tool configurations described in U.S. application Ser. No. 11/112,281 entitled “Cluster Tool Architecture for Processing a Substrate” filed on Apr. 22, 2005 (Attorney Docket No. AMAT/9540), which is hereby incorporated by reference for all purposes and including configurations not described in the 11,112,281 application.  
         [0078]      FIG. 15  is a flowchart illustrating an exemplary processing sequence for a semiconductor substrate processed within track lithography tool  200 . A person of skill in the art will appreciate that the various process steps discussed below with respect to  FIG. 15  present a number of different opportunities for the methods of the present inventions to be employed. The skilled artisan will also appreciate that various embodiments of the methods of the invention are not limited to the particular processing sequence set forth in  FIG. 15  and can instead be used in any sequence of process steps or any application where it is desirable to exhibit a high degree of control over the thermal processing (and in particular complimentary bake and chill steps) of a plurality of substrates according to a particular process recipe.  
         [0079]      FIG. 15  illustrates one embodiment of a series of method steps  300  that may be used to deposit, expose and develop a photoresist material layer formed on a substrate surface. The lithographic process may generally contain the following: a transfer substrate to coat module step  310 , a bottom anti-reflective coating (BARC) coat step  312 , a post BARC bake step  314 , a post BARC chill step  316 , a photoresist coat step  318 , a post photoresist bake step  320 , a post photoresist chill step  322 , an optical edge bead removal (OEBR) step  324 , an exposure step  326 , a post exposure bake (PEB) step  328 , a post exposure bake chill step  330 , a develop step  332 , a substrate rinse step  334 , a post develop chill step  336  and a transfer substrate to pod step  338 . In other embodiments, the sequence of the method steps  300  may be rearranged, altered, one or more steps may be removed, additional steps added or two or more steps may be combined into a single step with out varying from the basic scope of the invention.  
         [0080]     In step  310 , a semiconductor substrate is transferred to a coat module.  
         [0081]     Referring to  FIG. 14 , the step of transferring the substrate to the coat module  310  is generally defined as the process of having front end robot  218  remove a substrate from a cassette  230  resting in one of the pod assemblies  216 . A cassette  230 , containing one or more substrates “W”, is placed on the pod assembly  216  by the user or some external device (not shown) so that the substrates can be processed in the cluster tool  200  by a user-defined substrate processing sequence controlled by software retained in the system controller  240 .  
         [0082]     The BARC coat step  310  is a step used to deposit an organic material over a surface of the substrate. The BARC layer is typically an organic coating that is applied onto the substrate prior to the photoresist layer to absorb light that otherwise would be reflected from the surface of the substrate back into the resist during the exposure step  326  performed in the stepper/scanner  5 . If these reflections are not prevented, standing waves will be established in the resist layer, which cause feature size to vary from one location to another depending on the local thickness of the resist layer. The BARC layer may also be used to level (or planarize) the substrate surface topography, which is generally present after completing multiple electronic device fabrication steps. The BARC material fills around and over the features to create a flatter surface for photoresist application and reduces local variations in resist thickness.  
         [0083]     BARC coat step  310  is typically performed using a conventional spin-on resist dispense process in which an amount of the BARC material is deposited on the surface of the substrate while the substrate is being rotated which causes a solvent in the BARC material to evaporate and thus causes the material properties of the deposited BARC material to change. The air flow and exhaust flow rate in the BARC processing chamber is often controlled to control the solvent vaporization process and the properties of the layer formed on the substrate surface.  
         [0084]     Post BARC bake step  314 , is a step used to assure that all of the solvent is removed from the deposited BARC layer in BARC coat step  312 , and in some cases to promote adhesion of the BARC layer to the surface of the substrate. The temperature of post BARC bake step  314  is dependent on the type of BARC material deposited on the surface of the substrate, but will generally be less than about 250° C. The time required to complete post BARC bake step  314  will depend on the temperature of the substrate during the post BARC bake step, but will generally be less than about 60 seconds.  
         [0085]     Post BARC chill step  316 , is a step used to control and assure that the time the substrate is above ambient temperature is consistent so that every substrate sees the same time-temperature profile and thus process variability is minimized. Variations in the BARC process time-temperature profile, which is a component of a substrates wafer history, can have an effect on the properties of the deposited film layer and thus is often controlled to minimize process variability. Post BARC chill step  316 , is typically used to cool the substrate after post BARC bake step  314  to a temperature at or near ambient temperature. The time required to complete post BARC chill step  316  will depend on the temperature of the substrate exiting the post BARC bake step, but will generally be less than about 30 seconds.  
         [0086]     Photoresist coat step  318 , is a step used to deposit a photoresist layer over a surface of the substrate. The photoresist layer deposited during the photoresist coat step  318  is typically a light sensitive organic coating that are applied onto the substrate and is later exposed in the stepper/scanner  5  to form the patterned features on the surface of the substrate. Photoresist coat step  318  is a typically performed using conventional spin-on resist dispense process in which an amount of the photoresist material is deposited on the surface of the substrate while the substrate is being rotated which causes a solvent in the photoresist material to evaporate and thus causes the material properties of the deposited photoresist layer to change. The air flow and exhaust flow rate in the photoresist processing chamber is controlled to control the solvent vaporization process and the properties of the layer formed on the substrate surface. In some cases it may be necessary to control the partial pressure of the solvent over the substrate surface to control the vaporization of the solvent from the resist during the photoresist coat step by controlling the exhaust flow rate and/or by injecting a solvent near the substrate surface. Referring to  FIG. 14 , in an exemplary photoresist coating process, the substrate is first positioned on a wafer chuck in coater/developer module  234 . A motor rotates the wafer chuck and substrate while the photoresist is dispensed onto the center of the substrate. The rotation imparts an angular torque onto the photoresist, which forces the photoresist out in a radial direction, to ultimately covering the substrate.  
         [0087]     Photoresist bake step  320 , is a step used to assure that all of the solvent is removed from the deposited photoresist layer in photoresist coat step  318 , and in some cases to promote adhesion of the photoresist layer to the BARC layer. The temperature of post photoresist bake step  320  is dependent on the type of photoresist material deposited on the surface of the substrate, but will generally be less than about 350° C.  
         [0088]     The time required to complete post photoresist bake step  320  will depend on the temperature of the substrate during the post photoresist bake step, but will generally be less than about 60 seconds.  
         [0089]     Post photoresist chill step  322 , is a step used to control the time the substrate is at a temperature above ambient temperature so that every substrate sees the same time-temperature profile and thus process variability is minimized. Variations in the time-temperature profile can have an effect on properties of the deposited film layer and thus is often controlled to minimize process variability. The temperature of post photoresist chill step  322 , is thus used to cool the substrate after post photoresist bake step  320  to a temperature at or near ambient temperature. The time required to complete post photoresist chill step  322  will depend on the temperature of the substrate exiting the post photoresist bake step, but will generally be less than about 30 seconds.  
         [0090]     Optical edge bead removal (OEBR) step  324 , is a process used to expose the deposited light sensitive photoresist layer(s), such as, the layers formed during photoresist coat step  318  and the BARC layer formed during BARC coat step  312 , to a radiation source (not shown) so that either or both layers can be removed from the edge of the substrate and the edge exclusion of the deposited layers can be more uniformly controlled. The wavelength and intensity of the radiation used to expose the surface of the substrate will depend on the type of BARC and photoresist layers deposited on the surface of the substrate. An OEBR tool can be purchased, for example, from USHIO America, Inc. Cypress, Calif.  
         [0091]     Exposure step  326 , is a lithographic projection step applied by a lithographic projection apparatus (e.g., stepper scanner  5 ) to form a pattern which is used to manufacture integrated circuits (ICs). The exposure step  326  forms a circuit pattern corresponding to an individual layer of the integrated circuit (IC) device on the substrate surface, by exposing the photosensitive materials, such as, the photoresist layer formed during photoresist coat step  318  and the BARC layer formed during the BARC coat step  312  of some form of electromagnetic radiation.  
         [0092]     Post exposure bake (PEB) step  328 , is a step used to heat a substrate immediately after exposure step  326  in order to stimulate diffusion of the photoactive compound(s) and reduce the effects of standing waves in the resist layer. For a chemically amplified resist, the PEB step also causes a catalyzed chemical reaction that changes the solubility of the resist. The control of the temperature during the PEB is typically critical to critical dimension (CD) control. The temperature of PEB step  328  is dependent on the type of photoresist material deposited on the surface of the substrate, but will generally be less than about 250° C. The time required to complete PEB step  328  will depend on the temperature of the substrate during the PEB step, but will generally be less than about 60 seconds.  
         [0093]     Post exposure bake (PEB) chill step  330 , is a step used to control the assure that the time the substrate is at a temperature above ambient temperature is controlled so that every substrate sees the same time-temperature profile and thus process variability is minimized. Variations in the PEB process time-temperature profile can have an effect on properties of the deposited film layer and thus is often controlled to minimize process variability. The temperature of PEB chill step  330 , is thus used to cool the substrate after PEB step  328  to a temperature at or near ambient temperature. The time required to complete PEB chill step  330  will depend on the temperature of the substrate exiting the PEB step, but will generally be less than about 30 seconds.  
         [0094]     Develop step  332 , is a process in which a solvent is used to cause a chemical or physical change to the exposed or unexposed photoresist and BARC layers to expose the pattern formed during exposure process step  326 . The develop process may be a spray or immersion or puddle type process that is used to dispense the developer solvent. In some develop processes, the substrate is coated with a fluid layer, typically deionized water, prior to application of the developer solution and spun during the development process. Subsequent application of the developer solution results in uniform coating of the developer on the substrate surface. In step  334 , a rinse solution is provided to surface of the substrate, terminating the develop process. Merely by way of example, the rinse solution may be deionized water. In alternative embodiments, a rinse solution of deionized water combined with a surfactant is provided. One of ordinary skill in the art would recognize many variations, modifications, and alternatives.  
         [0095]     In step  336 , the substrate is cooled after the develop and rinse stets  332  and  334 . In step  338 , the substrate is transferred to the pod, thus completing the processing sequence. Transferring the substrate to the pod in step  338  generally entails the process of having the front end robot  218  return the substrate to a cassette  230  resting in one of the pod assemblies  216 .  
         [0096]     Based on the description of the present invention herein, a person of skill in the art will appreciate that embodiments of the invention may be beneficially used to heat and/or cool a substrate during, among other steps not described in  FIG. 15 , post BARC bake step  314  and post BARC chill step  316 , during post PR bake step  320  and post PR chill step  322 , during post exposure bake step  328  and post exposure chill step  330  and during post develop chill step  336 . A skilled artisan will also appreciate some of the various bake and chill sequences set just described have differing bake and or chill requirements. Thus, the skilled artisan will appreciate that the functional specifications of a particular bake plate  20  and/or chill plate  30  incorporated into the integrated thermal unit will depend on the material the bake and/or chill plate are intended to heat and cool, respectively. For example, BARC materials may be adequately heated with a low temperature, low precision bake plate (e.g., a maximum 250° C., single zone heater) while photoresist materials may require a high temperature, mid-precision bake plate (e.g., a maximum 350° C., three zone heater) and the post exposure bake process may require a low temperature, high precision bake plate (e.g., a maximum 250° C., fifteen zone heater). Thus, embodiments of the invention are not limited to any particular type of or configuration of bake plate  20  or chill plate  30 . Instead, generally each of bake plate  20  and chill plate  30  is designed to particular performance standards as required by the application for which the bake plate and chill plate will be used as can be determined by a person of skill in the art.  
         [0097]     While the present invention has been described with respect to particular embodiments and specific examples thereof, it should be understood that other embodiments may fall within the spirit and scope of the invention. The scope of the invention should, therefore, be determined with reference to the appended claims along with their full scope of equivalents.