Abstract:
The present invention provides an apparatus and a method of handling and transferring substrate in reduced particle contamination and thermal stress, as well as increased speed. One embodiment of the present invention provides an apparatus for handling a substrate. The apparatus comprises a support plate, and at least one pad protruding an upper surface of the support plate. The pad is configured to support a backside of the substrate so that the backside of the substrate is a first distance away from the upper surface of the support plate. The thermal resistance of the pad is substantially equal to the thermal resistance of the medium between the substrate and the upper surface.

Description:
CROSS-REFERENCE TO RELATED APPLICATIONS  
       [0001]     This application is continuation in part of U.S. patent application Ser. No. 11/111,155, filed on Apr. 20, 2005, entitled “Purged Vacuum Chuck with Proximity Pins”, which is herein incorporated by reference. 
     
    
     BACKGROUND OF THE INVENTION  
       [0002]     1. Field of the Invention  
         [0003]     Embodiments of the present invention generally relate to apparatus and method for handling semiconductor substrates.  
         [0004]     2. Description of the Related Art  
         [0005]     In modern semiconductor processing, multilayered features are fabricated on semiconductor substrates in a cleanroom environment using specific processing recipes having many processing steps. A semiconductor process system may include single process chambers and cluster tools which integrate a number of process chambers to perform a sequential processing steps without removing substrates from a highly controlled processing environment. The process chambers may include, for example, substrate preconditioning chambers, cleaning chambers, bake chambers, chill chambers, chemical vapor deposition chambers, physical vapor deposition chambers, etch chambers, electrochemical plating chambers, and the like. The substrates being processed are generally handled and transferred from one chamber to another by robots or other substrate handling devices. The transferring and handling steps are critical to process quality and throughput.  
         [0006]     As the semiconductor industry develops, the size of substrates becomes larger and larger; the size of features becomes smaller and smaller; at the same time, the requirement for throughput becomes higher and higher. As a result, there is a demand for substrate handling and transferring tools of higher precision, increased speed, less particle contamination, and less mechanical and/or thermal stress.  
         [0007]     To address the issue of particle contamination generated from contact, contact area is decreased as much as possible, and friction between substrate and substrate support has been decreased too. For example, substrates are usually supported on the backside by as few as three pins. However, since the substrate is only supported by a few pins, the substrate is likely to deform because of gravity and the support pressure is increased which may lead back to particle generation. Additionally, decreased friction introduces a problem of slippage, where a substrate will slide over a substrate support during transferring losing the precise positioning crucial to the semiconductor process. In some cases, vacuum chucks and mechanical gripping systems are added to substrate handling devices to avoid slippage. Consequently, the system becomes more complicated and contact area becomes larger and more particle contaminations are introduced.  
         [0008]     Thermal stress also becomes a problem especially handling a substrate after a process performed in an elevated temperature. In the one hand, the substrate is not cooled down uniformly because the thermal resistance of the contact area is generally different from where there is no contact. In the other hand, the substrate may shrink in size while cooling down, thus introducing friction, slippage, and deformation, especially for substrates of large size.  
         [0009]      FIG. 1  illustrates a schematic view of an exemplary integrated thermal unit  10  where substrate handling and transferring requires low particle contamination, reduced thermal stress and increased speed is required. A detailed description of an integrated thermal unit may be found in United States Patent Application entitled “Integrated Thermal Unit Having Bake and Chill Plates”, attorney docket number A9999/T60600, which is herein incorporated by reference.  
         [0010]     The integrated thermal unit  10  comprises an enclosed housing  40  on which shutters  34   a  and  34   b  are disposed and configured for transferring substrates into and out of the integrated thermal unit  10  respectively. A bake station  12  for baking substrates, a chill station  14  for precisely chilling substrates, and a shuttle station  16  for transferring substrates between the bake station  12  and the chill station  14  as needed are disposed inside the enclosed housing  40  in a linear arrangement.  
         [0011]     The shuttle station  16  comprises a shuttle plate  18  configured to move along a track  48  and transfer a substrate among the bake station  12 , the chill station  14 , and the shuttle station  16 . A lift pin assembly  36  is configured to pick-up a substrate from the shuttle plate  18  or load a substrate on the shuttle plate  18 .  
         [0012]     The bake station  12  comprises a bake plate  20 , a clam shell enclosure  22 , a chill base  24 , and a lift pin assembly  38 . The bake plate  20  is movable between a loading position (shown in  FIG. 1 ) and a heating position in which the bake plate  20  is urged into the clam shell enclosure  22  by a motorized lift  28 . The chill base  24  is configured to cool the bake plate  20  rapidly from a higher, bake temperature to a lower, substrate receiving temperature after a bake step. The lift pin assembly  38  is configured to load/unload substrates to/from the shuttle plate  18  and the bake plate  20 .  
         [0013]     The chill station  14  comprises a precision chill base  30  and a lift pin assembly  37  configured to load/unload substrates to/from the shuttle plate  18  and the precision chill base  30 .  
         [0014]     An exemplary processing sequence for the integrated thermal unit  10  may include: loading a substrate onto the lift pin assembly  36  through shutter  34   a , picking up the substrate by the shuttle plate  18 , transferring the substrate to the bake station  12  by the shuttle plate  18 , picking up the substrate by the lift pin assembly  38 , returning the shuttle plate  18  to the shuttle station  16 , raising the bake plate  20  and moving the substrate into the clam shell enclosure  22 , baking the substrate, lowering the bake plate  20 , raising the lift pin assembly  38  to pick up the baked substrate, moving the shuttle plate  18  to the bake station  12 , loading baked substrate on the shuttle plate  18 , transferring the baked substrate to the chill station  14 ; rising the lift pin assembly  37  to pick up the baked substrate, returning the shuttle plate  18  to the shuttle station  16 , loading the baked substrate on the precision chill plate  30  by lowering the lift pin assembly  37 , raising the lift pin assembly  37  to pick up the chilled substrate, transferring the substrate out of the thermal unit  10  via the shutter  34   b.    
         [0015]      FIGS. 2A-2B  illustrate a shuttle plate  80  of prior art which may be used in place of the shuttle plate  18  in the integrated thermal unit  10  of  FIG. 1 . The shuttle plate  80  includes a plate body  81  and an adapter  83  configured to coupled the plate body  81  to a movement mechanism. Two slots  84  and  85  are formed in the plate body  81  and configured to accommodate lift pins for loading and unloading a substrate. A plurality of proximity pins  82  are disposed on an upper surface of the plate body  81  and are configured to support a substrate  88  thereon (as shown in  FIG. 2B ) to reduce contact area and particle generation. Suitable material for the proximity pins  82  is not easily abraded by the interaction with the backside of the substrate. The proximity pins  82  are usually made of sapphire, or other suitable material such as diamond, diamond-like carbon, silicon dioxide, silicon, a metal, and a polymeric material. However, the friction between the proximity pins  82  and the substrate  88  is generally not large enough to keep the substrate  88  from sliding especially when the shuttle plate  80  is accelerating or deaccelerating horizontally. Therefore, a plurality of pocket pins  87  are disposed around a receiving area  86  to keep the substrate  88  from sliding out of position. The pocket pins  87 , however, contact the side of the substrate  88  which may cause extra particle contamination. When the substrate is substantially smaller than the receiving area  86 , the substrate may slide a good length before hitting the pocket pins  87  and controlling the position of the substrate becomes difficult.  
         [0016]     As described in the exemplary processing sequence, the shuttle plate  18  also transfers the baked substrate to the chill station  14 . Since the environment is cooler than the baked substrate, the baked substrate is being cooled down while transferred by the shuttle plate  18 . For a shuttle plate constructed like the shuttle plate  80 , a baked substrate may not cool down evenly between the areas contacting the proximity pins and the areas exposed directly to the environment, thus causing thermal or even mechanical stress.  
         [0017]     In conclusion, a shuttle plate of prior art are susceptible to thermal stress, particle contamination and slippage.  
         [0018]     Therefore, there exists a need for apparatus and method of handling and transferring substrate in reduced particle contamination and thermal stress, as well as increased speed.  
       SUMMARY OF THE INVENTION  
       [0019]     Embodiment of the present invention generally provide an apparatus and a method for handling semiconductor substrates.  
         [0020]     One embodiment of the present invention provides an apparatus for handling a substrate. The apparatus comprises a support plate, and at least one pad protruding an upper surface of the support plate wherein the pad is configured to support a backside of the substrate so that the backside of the substrate is a first distance away from the upper surface of the support plate, and a thermal resistance of the pad is substantially equal to a thermal resistance of a medium between the substrate and the upper surface.  
         [0021]     Another embodiment of the present invention provides an apparatus for supporting and handling a substrate. The apparatus comprises a support plate and a plurality of pads formed on an upper surface of the support plate and configured to support the substrate, wherein the plurality of pads are made of an elastomer having fluorine as a major constituent.  
         [0022]     Yet another embodiment of the present invention provides a method for handling a substrate. The method comprises providing a support plate having at least one pad formed an upper surface and a substantially uniform thermal resistance across the upper surface, positioning the substrate on the at least one pad, and transferring the substrate by moving the support plate.  
     
    
     BRIEF DESCRIPTION OF THE DRAWINGS  
       [0023]     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.  
         [0024]      FIG. 1  illustrates a schematic view of an exemplary integrated thermal unit that requires substrate handling and transferring.  
         [0025]      FIG. 2A  illustrates a shuttle plate of prior art for transferring a substrate.  
         [0026]      FIG. 2B  illustrates a partial sectional view of the shuttle plate shown in  FIG. 2A .  
         [0027]      FIG. 3  is a schematic view of one embodiment of a shuttle plate of the present invention.  
         [0028]      FIG. 4A  illustrates a sectional view of the shuttle plate of  FIG. 3  in accordance with a lift pin assembly.  
         [0029]      FIG. 4B  is an enlarged view of the shuttle plate of  FIG. 4A .  
         [0030]      FIG. 5A -D illustrate an exemplary embodiment of manufacturing substrate pads of the present invention.  
         [0031]      FIG. 6  illustrates one embodiment of a shuttle plate of the present invention.  
         [0032]      FIG. 7  illustrate one embodiment of a shuttle plate of the present invention.  
         [0033]      FIG. 8  illustrates a top view of the shuttle plate of  FIG. 7 .  
         [0034]      FIG. 9  illustrates one embodiment of a shuttle plate of the present invention. 
     
    
     DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENT  
       [0035]     Embodiments of the invention generally provide a substrate support plate having thin pads of elastomer which has high static friction coefficient and affords lack of residue. The thin pads are configured to keep a substrate from touching the substrate support plate. The thickness of the thin pads are designed such that the thermal resistance of the thin pads are substantially equal to the thermal resistance of the air gap between the substrate support plate and the substrate supported by the thin pads. Thus, the substrate support plate of the present invention provides high friction between the substrate and the supporting surface, low particle generation, and substantially uniform heat transfer property.  
         [0036]      FIG. 3  is a schematic view of one embodiment of a shuttle plate  100  of the present invention. The shuttle plate  100  is configured to support and transfer a substrate in a semiconductor processing system, such as the integrated thermal unit  10  shown in  FIG. 1 .  
         [0037]     The shuttle plate  100  generally comprises a plate body  101  coupled to an adaptor  102 . The adapter  102  is configured to transfer motions to the plate body  101 . A plurality of substrate pads  103  protrude by the same level of height from an upper surface  105  of the plate body  101 . In one embodiment, each of the plurality of substrate pads  103  has a circular upper surface of between 0.3 mm and 3 mm in diameter. The plurality of substrate pads  103  are configured to support a substrate  110  above the upper surface  105  as shown in  FIG. 4A , which is a sectional view of the shuttle plate of  FIG. 3  in accordance with a lift pin assembly  120 . Referring back to  FIG. 3 , two pairs of slots  104  are formed on the plate body  101 , opening to two opposite sides of the plate body  101 . The slots  104  are configured to accommodate lift pins  121  of the lift pin assembly  120 , as shown in  FIG. 4A . The two pairs of slots  104  enable the shuttle plate  100  be compatible with lift pins located at two sides of the shuttle plate  100 .  
         [0038]     The plate body  101  may be made of aluminum coated with a polymer, for example Teflon® polymer manufactured by Dupont of Wilmington, Del., or Tufram® polymer manufactured by General Magnaplate Corporations of Linden, N.J. In alternative embodiments, the plate body  101  may be fabricated from stainless steel, silicon carbide, copper, graphite, aluminum nitride, aluminum oxide, boron nitride or combination/laminates of these materials.  
         [0039]     In one embodiment, the substrate pads  103  are generally made from an elastomeric polymer having fluorine as a major constituent. Flourine provides high static and dynamic friction coefficient to an elastomer. Sapphire balls or similar low contact surface used in the state-of-the-art substrate handling systems provide low particle contamination during contact. However, sapphire balls and similar materials have relatively low friction coefficients. For example, sapphire has a static friction coefficient of about 0.4 against silicon and a dynamic friction coefficient of about 0.01. In many situations, vacuum or electrostatic attraction is needed to secure the substrate supported by these low friction materials, thus, increasing system complexity. Fluorinated elastomer generally has similar low particle properties as sapphire, and a static friction coefficient of about 1.66(dry)/2.49(wet) and a dynamic friction coefficient of about 0.42(dry)/0.41(wet). Therefore, the substrate pads  103  of present invention provides about 40 times more dynamic friction and about a factor of 4 for static friction to a substrate supported thereon compared to the state-of-the-art substrate contact surfaces. In one aspect, the shuttle plate  100  of the present invention is capable of accelerating or deaccelerating a substrate at a rate of about 0.5 g to 0.8 g via the friction from the substrate pads  103  only. Extra securing mechanism, such as vacuum, electrostatic attraction, and mechanical gripping, may be eliminated from the system, therefore, increases reliability of the system.  
         [0040]     In another embodiment, the substrate pads  103  are made from an elastomeric polymer having fluorine as a major constituent and with no inorganic or non-fluoridated filler. Elastomeric material used in supporting substrates typically has an inorganic filler, such as silica, barium sulphate, or titanium dioxide. These fillers are micron sized or larger particles, hence leading to a particle source. The elstomeric polymer used to form the substrate pads  103  generally has a nanometer sized organic filler which essentially eliminates a particle source. Therefore, the contact area between the substrate and the substrate pads  103  may be increased and the pressure of contact decreased. A suitable material for the substrate pads  103  may be a perfluoroelastomer, which has a backbone comprises long chains of carbon atoms covalently bonded to fluorine atoms, and totally organic and fully fluoridated nanofillers, for example G67P from Perlast®.  
         [0041]      FIG. 4B  is an enlarged view the shuttle plate of  FIG. 4A . As shown in  FIG. 4B , each of the substrate pads  103  is positioned inside a recess  106  having a height of h 1  formed on the upper surface  105  of the plate body  101 . The substrate pads  103  protrude the upper surface  105  by a height of h 2  so that there is a gap of h 2  between the upper surface  105  and a back side  111  of the substrate  110  supported thereon. The total height h 3  of the substrate pads  103  is the summation of h 1  and h 2 .  
         [0042]     Since the air is generally a better insulator for heat than the materials used to build substrate pads in a substrate support, the substrate pads may be designed to have a substantially equal thermal resistance as that of the air gap by choosing a sufficient thickness for the substrate pads, wherein the thermal resistance of a structure is defined as temperature difference across the structure when a unit of heat energy flows through unit area of the structure in unit time. Therefore, a uniform heat transfer across a substrate being supported may be achieved by choosing a sufficient thickness for the substrate pads, which are mostly recessed into the support structure. The state-of-the-art approaches do not compensate for the differences in thermal conductivity of the pad material and the air, therefore, the substrate pads need to have a very low contact area to minimize the heat transfer between a substrate and the substrate pads. By using an equivalent thermal resistance to air, the contact area of the substrate pads may be greatly increased, which reduces pressure and therefore particle production.  
         [0043]     In one embodiment, the total height h 3  is chosen in a way that the thermal resistance of the substrate pads  103  substantially equals the thermal resistance of the air gap having a thickness of h 2 . The thermal resistance of the substrate pads  103  may be calculated from the total height h 3  and thermal conductivity of the material from which the substrate pads  103  are made. The thermal resistance of the air gap may be calculated from the thickness h 2  and the thermal conductivity of air. Therefore, the total height h 3  of the substrate pads  103  may be chosen using the following equation:  
         h   ⁢           ⁢   3     =         K   pad       K   air       ⁢   h   ⁢           ⁢   2         
 
 wherein K pad  and K air  are thermal conductivity of the pad material and the air respectively. It should be noted that the thermal conductivity of air may be replaced by thermal conductivity of other medium that fills between the substrate  110  and the plate  101 . 
 
         [0044]     In one embodiment, the air gap thickness h 2  is about 0.1 mm, and the total height h 3  is about 1.0 mm for substrate pads made from a perflouroelastomer.  
         [0045]      FIG. 5A -D illustrate an exemplary embodiment of manufacturing substrate pads of the present invention. As illustrated in  FIG. 3A , recesses  206  configured to accommodate substrate pads are formed in an upper surface  205  of a plate body  201 . The recesses  206  may be formed using an end-mill. After the recesses  206  are formed, the plate body  201  may be cleaned to get rid of any particles. Surfaces of the recesses  206  may be optionally roughed. An optional layer of adhesive may be applied on the surfaces of the recesses  206  for better adhesion. As shown in  FIG. 5B , a mold  220  having recesses  221  matching the recesses  206  of the plate body  201  is provided. In one aspect, the mold  220  may have a ridge of about 4 to 10 microns near the periphery. Each of the recesses  221  has a small tunnel  222  opening to an opposite side of the mold  220 . The small tunnels  222  are configured for injecting elastomer materials into the recesses  221 . The mold  220  may be generally pushed down against the plate body  201  near the periphery so that the recesses  221  match the respective recesses  206  on the plate body  201 . In one embodiment, a slight seal may be used between the mold  220  and the plate body  201  to prevent flash formed from squeezed out mold material. In another embodiment, laser elation may be used to remove the flash. As shown in  FIG. 5C , elastomer is injected and filled to the recesses  206 / 221  via the small tunnels  222 , forming a substrate pad  203 . The mold  220  may be removed after the injected elastomer being cured for about 4 to 10 minutes at temperature of about 180° C. to 230° C.  
         [0046]      FIGS. 6-9  illustrate several embodiment of substrate support plate having substrate pads similar to the substrate pads  103  of  FIG. 3 .  
         [0047]      FIG. 6  illustrates schematic view of another embodiment of a shuttle plate  300  of the present invention. The shuttle plate  300  generally comprises a plate body  301  having a substrate pad  303  protruding from an upper surface  305  of the plate body  301 . Two slots  304  are generally formed on the plate body  310  configured for accommodating lifting pins. The substrate pad  303  is configured to support a substrate near the center of gravity. The shuttle plate  300  may be made from the same materials as the shuttle plate  100  of  FIG. 3 . The shuttle plate  300  is desirable when a substrate may encounter relatively large shrinkage, for example due to large temperature drop, while being supported or transferred by the shuttle plate  300 .  
         [0048]      FIG. 7  illustrates a schematic sectional view of another embodiment of a shuttle plate  400  of the present invention. The shuttle plate  400  comprises a plate body  401  and a plurality of substrate pads  403  protruding from an upper surface  405  of the plate body  401 . Slots  404  are formed on the plate body  401  and configured to house lift pins  421 . The plate body  401  further has a plurality of vacuum ports  406  opening at the upper surface  405  and connected to a vacuum source  408 . The vacuum ports  406  are configured to hold a substrate  410  in combination with the substrate pads  403 .  FIG. 8  illustrates a top view of the shuttle plate  400  of FIG.  7 . In one embodiment, the vacuum ports  406  form a circle inside a substrate receiving area  407 .  
         [0049]      FIG. 9  illustrates yet another embodiment of a shuttle plate  500  of the present invention. The shuttle plate  500  comprises a single substrate pad  503  positioned near a center of a substrate receiving area  507 . A plurality of vacuum ports  506  are distributed near a periphery of the substrate receiving area  507 .  
         [0050]     Embodiments of the present invention is generally related apparatus and method for supporting a semiconductor substrate during semiconductor processing operations. The method and apparatus for supporting a substrate of the present invention may be used in handling substrates in various situations, such as in a bake station, a chill station, a cleaning station, a substrate boat in a batch chamber, a chemical vapor deposition chamber, a robot in a cluster tool, and other situations where low contamination, high precision and/or high throughput is desired. One of ordinary skills in the art will appreciate that various components may be combined with substrate supporting apparatus of the present invention, for example vacuum and/or purge ports, electrodes for electrostatic chucking, heat exchange elements, lift pin holes, etc, for purposes related to the process.  
         [0051]     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.