Abstract:
An apparatus and method for maintaining or adjusting the orientation of a large area substrate is disclosed by using multiple support plates disposed below a susceptor adapted to support the large area substrate. The multiple support plates are supported by a plurality of support shafts that are coupled to at least one actuator. The apparatus is designed to selectively adjust the horizontal cross-sectional profile of the susceptor to promote even and uniform processing. The horizontal profile may be one of planar, concave, or convex. The apparatus allows any adjustment to be made before, during, or after processing.

Description:
CROSS REFERENCE TO RELATED APPLICATIONS:  
       [0001]     This application claims benefit of U.S. Provisional Patent Application No. 60/610,634, filed Sep. 15, 2004 (APPM/009635L), which is incorporated herein by reference to the extent it is not inconsistent with this application. 
     
    
     BACKGROUND OF THE INVENTION  
       [0002]     1. Field of the Invention  
         [0003]     Embodiments of the present invention generally relate to a substrate processing system in the electronics industry. More specifically, the invention relates to a system and method for supporting large area substrates in flat panel display manufacture.  
         [0004]     2. Description of the Related Art  
         [0005]     Flat panel displays typically employ an active matrix of electronic devices, such as insulators, conductors, and thin film transistors (TFT&#39;s) to produce flat panel screens used in a variety of devices such as television monitors and computer screens. Generally, these flat panel displays are manufactured on large area substrates which may comprise two thin plates made of glass, a polymeric material, or other suitable material capable of having an electronic device formed thereon. Layers of a liquid crystal material or a matrix of metallic contacts, a semiconductor active layer, and a dielectric layer are deposited through sequential steps and sandwiched between the two thin plates. At least one of the plates will include a conductive film that will be coupled to a power supply which will change the orientation of the crystal material and create a patterned display on the screen face.  
         [0006]     These processes typically require the large area substrate to undergo a plurality of processing steps that deposit the active matrix material. Chemical vapor deposition (CVD) and plasma enhanced chemical vapor deposition (PECVD) are some of the well known processes for this deposition. These processes require that the large area substrate, supported in the deposition chamber by a susceptor, be maintained in a fixed position relative to the deposition apparatus during deposition to ensure uniformity in the deposited layers.  
         [0007]     Flat panel displays and the substrates the displays are formed on have increased dramatically in size over recent years due to market acceptance of this technology. Previous generation large substrates had sizes of about 500 mm by 650 mm and have increased in size to about 1800 mm by about 2200 mm (or larger). The processes employed are time intensive and profitable production relies on high throughput resulting in usable and operable flat panel displays. Therefore, producers cannot afford to produce one inoperable unit, much less, a plurality of unusable units caused by non-uniform deposition.  
         [0008]     The CVD and PECVD processes that are performed on these substrates generate large amounts of heat. The susceptors that are used to support the large area substrates are typically heated to heat the large area substrate and enhance the deposition process. In order to maintain a fixed position between the gas distribution plate and the susceptor during these processes, a susceptor is typically supported by a susceptor support that is resistant to heat, and expansion and contraction. The susceptor support is typically a ceramic and generally spans a length and/or width of the susceptor in monolithic strips that have suitable width and breadth to accomplish its intended purpose of maintaining a desired cross-sectional horizontal profile of the susceptor.  
         [0009]     Susceptors have increased in size in relation to the larger substrate sizes. The susceptor support must also increase in size in relation to the susceptor so the susceptor may be suitably supported. This increase in size in the ceramic material used to support the susceptor is increasingly expensive. Therefore, there exists a need to redesign the susceptor support used for large area substrates, in order to accommodate larger substrates and keep material costs at a minimum. There is also a need in the art to manipulate a susceptor to conform to a desired shape within the deposition chamber.  
         [0010]      FIG. 1A  is a schematic side view of a chamber  2 , having a lid  8 , a bottom  4 , and sidewalls  6 . The chamber  2  also includes a substrate support or susceptor  14  which is used to support a large area substrate  16  during processing in the chamber  2 , and a gas distribution plate or diffuser  10 . The susceptor is supported by a susceptor support plate assembly  12 , which consists of a plurality of parallel branch plates  24   a - 24   d  sandwiched below the susceptor  14 , and a center plate  22 . The center plate  22  is disposed on and supported by a support shaft  33 , disposed on a lift plate  30 , which is coupled to a vertical lifting mechanism  18  that provides vertical movement to the substrate support  14  in the direction indicated by arrow  20 .  
         [0011]      FIG. 1B  is a schematic top view of the susceptor support plate assembly  12  shown in  FIG. 1A . The substrate support  14  is shown by a dashed line in order to show the layout of the susceptor support plate assembly  12 . The branch plates  24   a - 24   d  and the center plate  22  are large monolithic strips made of a ceramic material that are configured to support the substrate support  14 .  
         [0012]     An efficient and successful deposition process requires the substrate  16  to remain in a desired position within the chamber  2  during processing. As mentioned earlier, significant amounts of heat are produced during the PECVD process. The large area substrate  16  may reach a near molten state and, as a result, may be very pliable. The planarity of the large area substrate  16  is dependent upon the planarity and rigidity of the susceptor  14  and, in turn, the planarity of the susceptor  14  is dependent on the rigidity and planarity of the susceptor support plate assembly  12 . In order for the susceptor  14  to function as a cathode in the RF excitation scheme, it is preferably made of an electrically conductive material, such as aluminum, which is vulnerable to thermal and gravitational forces that may cause a sag or bowing that will translate to the large area substrate  16 . These forces are counteracted by the susceptor support plate assembly  12  by maintaining the desired cross-sectional horizontal profile of the susceptor  14  and, in turn, the cross-sectional horizontal profile of the large area substrate  16  supported thereon.  
       SUMMARY OF THE INVENTION  
       [0013]     The present invention generally provides a solution to the problems encountered by using large ceramic monoliths to support a large area susceptor by replacing the currently used support assembly with a plurality of smaller support plates positioned to maintain a desired cross-sectional horizontal profile and reduce warping of the susceptor, which translates to a conforming large area substrate.  
         [0014]     In one embodiment, a susceptor support apparatus is described having a plurality of support plates adapted to support a susceptor in a deposition chamber, wherein at least four of the plurality of support plates are adapted to couple to at least two support shafts which extend outside the deposition chamber.  
         [0015]     In another embodiment, an apparatus for supporting a large area substrate in a deposition chamber is described having a susceptor adapted to support the large area substrate, a plurality of susceptor support plates positioned below the susceptor, and a plurality of support shafts coupled to one or more actuators positioned below the plurality of support plates, wherein at least two of the plurality of support shafts positioned below the plurality of support plates extend outside the deposition chamber.  
         [0016]     In another embodiment, an apparatus for adjusting the planarity of a large area substrate is described which includes a chamber having a top, a bottom, and a sidewall a susceptor disposed within the chamber adapted to support the large area substrate, and at least two support shafts that extend outside of the chamber, the at least two support shafts adapted to support the susceptor.  
         [0017]     In another embodiment, an apparatus for supporting a large area susceptor in a deposition chamber is described having at least one support truss located outside the deposition chamber, and a plurality of support shafts coupled to the at least one support truss adapted to support the susceptor.  
         [0018]     In another embodiment, a method of supporting a susceptor in a deposition chamber is described including supporting a center region of the susceptor with at least one support shaft, and supporting a perimeter of the susceptor with a plurality of support shafts, wherein the at least one support shaft and the plurality of support shafts extend outside the chamber and are coupled to at least one vertical actuator. 
     
    
     BRIEF DESCRIPTION OF THE DRAWINGS  
       [0019]     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.  
         [0020]      FIG. 1A  (Prior Art) is a schematic cross-sectional view of chamber having a susceptor support plate assembly.  
         [0021]      FIG. 1B  (Prior Art) is a schematic top view of the susceptor support plate assembly shown in  FIG. 1A .  
         [0022]      FIG. 2A  is a schematic cross-sectional view of one embodiment of a plasma chamber.  
         [0023]      FIG. 2B  is a schematic top view of one embodiment of a susceptor support assembly.  
         [0024]      FIG. 3A  is a schematic cross-sectional view of another embodiment of a plasma chamber.  
         [0025]      FIG. 3B  is a schematic top view of another embodiment of a susceptor support assembly.  
         [0026]      FIG. 4  is a schematic top view of another embodiment of a susceptor support assembly.  
         [0027]      FIG. 5  is a schematic top view of another embodiment of a susceptor support assembly.  
         [0028]      FIG. 6  is a schematic top view of another embodiment of a susceptor support assembly.  
         [0029]      FIG. 7  is a schematic top view of another embodiment of a susceptor support assembly.  
         [0030]      FIG. 8  is a schematic top view of another embodiment of a susceptor support assembly. 
     
    
     DETAILED DESCRIPTION  
       [0031]     The present invention generally provides an apparatus and method of supporting a large substrate that minimizes bowing or deflection caused by thermal and gravitational forces and provides a substantially planar surface where a susceptor or substrate support may be supported which, in turn, may support a substrate in a planar or level orientation. Some aspects also provide for isolated lifting points for counteracting substrate support deformation or end sag, or manipulating the susceptor via these lifting points to produce a desired horizontal profile in the susceptor. References made to the horizontal profile and/or the horizontal orientation of various elements depicted in the Figures refers to horizontal cross-sectional views of the particular elements as shown in the Figures.  
         [0032]     Embodiments described herein are configured to replace the susceptor support plate assembly  12  shown in  FIGS. 1A, 1B  by employing a susceptor support assembly having smaller ceramic support plates to support the susceptor. This is advantageous because the chambers adapted to receive the susceptor support plate assemblies do not require major redesign and the volume within the chamber that is subject to vacuum remains substantially equal to the volume of the chamber as depicted in  FIG. 1A . The support plates may be less expensive to manufacture as compared to the susceptor support plate assembly  12  of  FIGS. 1A  and  1 B. To prevent confusion, common reference numerals referring to similar elements in the drawings are duplicated, where possible.  
         [0033]      FIG. 2A  is a schematic cross-sectional view of one embodiment of a plasma chamber  22  having a susceptor support assembly  200  configured to produce and maintain a desired horizontal profile in the susceptor. The desired horizontal profile may be one of planar, concave, or convex. The chamber  22  may be any size capable of accommodating any known or unknown dimensions of large area substrates. The chamber  22  includes a top  28 , sidewalls  26 , and a bottom  24  defining an interior region  250 . The interior region  250  includes a gas distribution plate or diffuser  10  coupled to the chamber  22  above a susceptor  214 . The chamber  22  is in communication with a gas source  217  that is adapted to couple to a gas inlet  213  that provides a process gas to the interior region  250 . The chamber is coupled to a radio frequency power source  215  that excites the process gas into a plasma to form a plasma area  17  below the diffuser  10 . The susceptor  214  may be heated by a resistive heater embedded or coupled to the susceptor  214 , or the susceptor  214  may be heated by heat lamps, or some other form of thermal energy adapted to heat the susceptor. The chamber  22  is coupled to a vacuum source to evacuate the interior region  250  of the chamber. A plurality of lift pins  3  are also shown disposed in the susceptor  214  and are adapted to facilitate transfer of a large area substrate (not shown) by being movably disposed in suitable holes in the susceptor  214 . In operation, the large area substrate is placed on an upper surface of the lift pins  3  by a robot (not shown). The susceptor  214  is then raised vertically to allow the lift pins  3  to retract to place the substrate on an upper surface of the susceptor  214 . The susceptor  214 , with the large area substrate thereon, is then raised to the plasma area  17  for processing.  
         [0034]     The susceptor  214  is supported by a plurality of susceptor support plates  29 , which are supported by a plurality of support shafts  234  and a single support shaft  233  which extend outside (i.e. ambient environment) the chamber  22  through bores in the chamber bottom  24 . The size, number, and shape of the susceptor support plates  29  are configured to produce and maintain a desired horizontal profile in the susceptor  214 . The desired horizontal profile may be one of planar, convex, or concave. Seals  232 , such as flexible bellows, provide a vacuum tight seal isolating the chamber  22  from ambient environment in areas around the support shafts  233 ,  234 . A susceptor support truss  231  provides support to the plurality of support shafts  234  and the support plates  29 .  
         [0035]     In one embodiment, a single vertical actuator  218  provides vertical movement which is translated to a moving block  230  which is in communication with the support truss  231  and the support truss  231  is coupled to all support shafts  233 ,  234 . In another embodiment (not shown), the support shafts  234  may be coupled to two support trusses  231 , each support truss in communication with at least one vertical actuator, while the support shaft  233  is coupled to the moving block  230  or coupled directly to the vertical actuator  218 . In this embodiment, the susceptor  214  is supported adjacent a perimeter  260  of the susceptor  214  by a plurality of support shafts  234  coupled to at least two support trusses in communication with at least one vertical actuator, while the center region  265  of the susceptor  214  is supported by the support shaft  233  in direct, or indirect, communication with the vertical actuator  218 . In another embodiment (not shown), the perimeter  260  of the susceptor  214  may be supported by a support truss formed in the pattern of support shafts  234  as seen from a top view, while the center region  265  of the susceptor  214  is supported by the support shaft  233  in direct, or indirect, communication with the vertical actuator  218 . In this embodiment, the support truss could be formed in a rectangular pattern (as seen from a top view) having the support shafts  234  coupled thereto and adapted to contact and support the perimeter  260  of the susceptor  214 . Other shapes of support trusses are contemplated, such as an X pattern, or a star pattern. Any heat from the susceptor  214  and the chamber  22  that may be absorbed by the shafts  233  and  234  may be absorbed by the moving block  230  prior to any heat being transferred to the actuator  218 . Alternatively, cooling blocks  221  may be added below the seals  232 , to aid in minimizing any thermal migration that may damage the actuator  218 . The shafts  233  and  234  may also be manufactured to include interior cooling channels (not shown). The actuator  218  may be any actuator capable of providing vertical movement and may be powered by air, hydraulics, electrical power, or other mechanical power. When the actuator  218  is energized, the susceptor  214  is urged upward or downward in the direction of arrow  20  via the mechanical teaming of the moving block  230 , the truss  231 , the support shafts  233  and  234 , and the support plates  29 .  
         [0036]      FIG. 2B  is a schematic top view of the susceptor support assembly  200  shown in  FIG. 2A . The susceptor  214  is shown in dashed lines to show the layout of the support plates  29  and corresponding susceptor lift points  5 . Each of the support points  5  depict the location of the support shafts  233  and  234  below the support plates  29 . Any number of susceptor support points  5  and corresponding support plates  29  may be added to the layout shown, in order to prohibit or counteract any gravitational and thermal forces that may alter the desired horizontal profile of the susceptor  214 . The number of susceptor support points  5  may also be reduced by varying the size of the support plates  29 . Shapes of the support plates  29  may also be varied to provide support to the susceptor  214 . In one embodiment, the support plates  29  are annular and, in another embodiment, the support plates  29  are circular. In other embodiments, the support plates  29  may be polygonal shapes, such as rectangles, trapezoids, hexagons, octagons, or triangles. The susceptor support  200  may also comprise support plates  29  that may be a combination of these shapes. In another embodiment, a spacer or shim (not shown) may be placed between the support plate  29  and the shaft  233  or  234 , and/or between the support plate  29  and the susceptor  214  in order to provide further adjustment and support to the susceptor  214 .  
         [0037]      FIG. 3A  is a schematic view of another embodiment of a plasma chamber  32  having a susceptor support assembly  300  configured to produce and maintain a desired horizontal profile in a susceptor  314 . The desired horizontal profile may be one of planar, concave, or convex. The chamber  32  is similar to the chamber  22  shown in  FIG. 2A  with the exception of the susceptor support assembly  300 . Also, the plasma area and support pins are not shown in for clarity. In this embodiment, the susceptor  314  is supported by susceptor support plates  39 , which are supported by parallel branch plates  324   a - 324   c.  Outer parallel branch plates  324   a  and  324   c  are supported by a plurality of support shafts  334 , extending outside the chamber  32 , while branch plate  324   b  is supported by a single support shaft  333  also extending outside the chamber  32  through the chamber bottom  34 . A moving block  330  is disposed below single support shaft  333  while the support shafts  334  are in direct communication with a vertical actuator  318 . Alternatively, the single support shaft  333  may be in direct communication with the vertical actuator  318 . The vertical actuators  318  may be any actuator capable of vertical movement and may be commonly or independently controlled. The size, number, and shape of the susceptor support plates  39  are configured to produce and maintain a desired horizontal profile in the susceptor  314 . In one embodiment, the support plates  39  are annular and, in another embodiment, the support plates  39  are circular. In other embodiments, the support plates  39  may be polygonal shapes, such as rectangles, trapezoids, hexagons, octagons, or triangles. The susceptor support  300  may also comprise support plates  39  that may be a combination of these shapes. Seals  332 , such as flexible bellows, provide a vacuum tight seal isolating the chamber  32  from ambient environment in areas around the support shafts  333 ,  334 . Any heat absorbed by the shafts  333  and  334  may be absorbed by the shafts  333  and  334 , and moving block  330  prior to any heat being transferred to the vertical actuators  18 . Alternatively, cooling blocks  321  may be added below the seals  332 , to aid in minimizing any thermal migration that may damage the actuators  318 . The shafts  333  and  334  may also be manufactured to include interior cooling channels (not shown).  
         [0038]     In this embodiment, the vertical actuators  318  may be commonly or independently controlled. A perimeter  360  of the susceptor  314  may be supported by a plurality of support plates  39  while a center area  365  of the susceptor  314  is supported by a separate plurality of support plates  39 . The vertical actuators may be powered electrically, hydraulically, pneumatically, or combinations thereof. All of the vertical actuators  318  may operate similarly, or the vertical actuators  318  may be any combination of actuators, wherein, for example, some of the vertical actuators are pneumatically operated and the others are electrically operated. In operation, the vertical actuators  318  are energized either alone or in combination to provide vertical movement to the susceptor  314 . These vertical actuators  18  may remain in the same position during processing or may be energized during processing to adjust the horizontal profile of the susceptor  314 .  
         [0039]      FIG. 3B  is a schematic top view of the susceptor support assembly  300  shown in  FIG. 3A . The susceptor  314  is shown in dashed lines to show the layout of the support plates  39  and the corresponding susceptor lift points  5 . Any number, shape, or size of support plates  39  may be added to, or subtracted from, the layout shown, in order to prohibit or counteract any gravitational and thermal forces that may alter the desired horizontal profile of the susceptor  314 . Lift points  5  can be seen below parallel branch plates  324   a - 324   c  and the corresponding support plates  39  overlying branch plates  324   a  and  324   c.  The lift points  5  are intended to show the placement of the support shafts  334  (under branch plates  324   a  and  324   c ) and the single support shaft  333  (under branch plate  324   b ). Also shown are a plurality of support points  7  that define areas of contact between the support plates  39  and the susceptor  314 . The use of a shims or spacer  26  can be used with the parallel branch plates  324   a - 324   c  between the branch plates  324   a - 324   c  and the support plates  39  to further adjust the planarity of the susceptor  314 .  
         [0040]     Although three vertical actuators  318  have been used in this embodiment, any number or combination and type of vertical actuators  318  may be used. Vertical actuators  318  may be added under each susceptor support point  7  that may negate the use of parallel branch plates  324   a - 324   c.  Additional vertical actuators  318 , or larger and differently shaped susceptor support plates  39  may also be employed to create additional susceptor support points  7 .  
         [0041]      FIG. 4  is a schematic top view of the susceptor support assembly  400  configured to produce and maintain a desired horizontal profile in a susceptor  414 . The desired horizontal profile may be one of planar, concave, or convex. The susceptor  414  is shown in dashed lines in order to show the layout of a plurality of support plates  49   a - 49   d,  a plurality of branch plates  424   e,    424   f,  and lift points  5 , which correspond to an upper surface of the support shafts (not shown) located below the susceptor  414 . In this embodiment, a perimeter  460  and a center area  465  of the susceptor  414  is supported by a combination of the branch plates  424   e,    424   f,  and support plates  49   d.  Support points  7  are also shown in the areas where the susceptor  414  and the support plates are in contact. Although the embodiment shown includes seven lift points  5 , any number of lift points  5  may be added or subtracted by employing more or less vertical actuators. The support shafts may be coupled to a support truss as shown in  FIG. 2A , or be in direct communication with an actuator as shown in  FIG. 3A . Likewise, any number of support points  7  may be added to the layout shown by the addition of support plates and/or actuators in order to prohibit or counteract any gravitational and thermal forces that may alter the desired horizontal profile of the susceptor  414 . Additional support plates may be added, for example, along the upper surface of the branch plates  424   e  and  424   f.  Any shape or combination of shapes, branch members, and vertical actuators may be used to create a desired support structure beneath the susceptor  414 . Also, the use of a shim or spacer  26  can be used alone, or in combination with branch plates  424   e  and  424   f  and the support plates  49   a - 49   d.  Other spacers (not shown) may be used between the support shafts  433 ,  434  and the support plates  49   a - 49   d,  or between the support shafts and the branch plates  424   e,    424   f.    
         [0042]      FIG. 5  is a schematic top view of a susceptor support assembly  500  configured to produce and maintain a desired horizontal profile in a susceptor  514 . The desired horizontal profile may be one of planar, concave, or convex. The susceptor  514  is shown in dashed lines to show the layout of the support plates  59  and the corresponding susceptor lift points  5  each of which denote an upper surface of a support shaft (not shown). Although thirteen lift points  5  are shown in this view, any number of lift points  5  may be added or subtracted to produce and maintain the desired horizontal profile of the susceptor  514 . In one embodiment, a plurality of support plates  59  are used to support the susceptor  514 . In another embodiment, the susceptor  514  is in direct communication with the support shafts without the use of support plates  59 . In yet another embodiment, a combination of direct support by support shafts and support plates  59  is used to support the susceptor  514 . A plurality of support points  7  is also shown to define the areas of the susceptor  514  in contact with the support plates  59 . Any number of support points  7  may be added or removed from the layout shown, in order to prohibit or counteract any gravitational and thermal forces that may alter the desired horizontal profile of the susceptor  514 . The shapes and sizes of the support plates  59  may be also be alternated to produce and maintain the desired horizontal profile of the susceptor  514 .  
         [0043]      FIG. 6  is a schematic top view of a susceptor support assembly  600  configured to produce and maintain a desired horizontal profile of a susceptor  614 . The desired horizontal profile may be one of planar, concave, or convex. The susceptor  614  is shown in dashed lines to show the layout of the support plates  69  and the corresponding lift points  5 , which denote the location of support shafts (not shown) below a plurality of branch plates  624   a - 624   e.  In this embodiment, the five lift points  5  are supported by five support shafts coupled to at least one vertical actuator. The support shafts may be coupled to a support truss as shown in  FIG. 2A , or in direct communication with a vertical actuator as shown in  FIG. 3A . Although five lift points  5  are shown, any number of lift points may be added or subtracted from the layout shown. Also shown is a plurality of support points  7  defining areas of contact between the support plates  79  and the susceptor  614 . Any number of support points  7  may be added to the layout shown, in order to prohibit or counteract any gravitational and thermal forces that may alter the desired horizontal profile of the susceptor  614 . As in other embodiments, the support plates  69  may be of any shape, or combinations of shapes, such as circular and rectangular, and may be of any size that is configured to support the susceptor  614  in the desired horizontal profile.  
         [0044]      FIG. 7  is a schematic top view of a susceptor support assembly  700  configured to produce and maintain a desired horizontal profile of a susceptor  714 . The desired horizontal profile may be one of planar, concave, or convex. The susceptor  714  is shown in dashed lines to show the layout of the support plates  79  and the corresponding susceptor lift points  5 , which correspond to an upper surface of a plurality of support shafts (not shown) located below the susceptor  714  and a plurality of support plates  79 . The support assembly  700  includes a base structure  770  which includes a longitudinal support member  724   a  and two transverse support members  724   b  coupled thereto, configured to support a center area  765  of the susceptor  714 . A perimeter  760  is supported by a plurality of support shafts denoted by lift points  5  below the plurality of support plates  79 . In this embodiment, the base structure  770  is coupled to a vertical actuator while the support plates  79  on the perimeter  760  are coupled to at least one vertical actuator by a support truss as described in  FIG. 2A , or in direct communication with a vertical actuator as described in  FIG. 3A . Any number, shape, or size of support plates  79  may be added to, or subtracted from, the layout shown, in order to prohibit or counteract any gravitational and thermal forces that may alter the desired horizontal profile of the susceptor  714 . The support points  7 , denoting the location of areas of contact between the susceptor  714 , and the support plates  79  and the branch plates  724   b,  are also shown. Any corrections made to the susceptor  714  may also employ the use of a shim or spacer  26 . It is also noted that in this embodiment or others, any number of support points  7  may be created under the susceptor  714 , whether in direct communication with the support shafts, or in indirect communication with support shafts by the use of support plates  79 .  
         [0045]      FIG. 8  is a schematic top view of a susceptor support assembly  800  configured to produce and maintain a desired horizontal profile in a susceptor  814 . The desired horizontal profile may be one of planar, concave, or convex. The susceptor  814  is shown in dashed lines to show the layout of a plurality of support plates  89  and the corresponding lift points  5 , which correspond to an upper surface of a plurality of support shafts (not shown) located below the susceptor  814 . In this embodiment, a center plate  822  is shown supporting a center area  865  of the susceptor  814  and a plurality of support plates  89  support a perimeter  860  of the susceptor  814 . The center plate  822  may be coupled to a vertical actuator while the support plates  89  on the perimeter may be coupled to a support truss as described in  FIG. 2A , or coupled directly to a plurality of actuators as described in  FIG. 3A . The lift points  5  around the perimeter  860  may include support plates  89  as shown, or may be in direct communication with a support shaft without the use of support plates  89 . If support plates  89  are used, any number, shape, or size of support plates  89  may be added to, or subtracted from, the layout shown, in order to prohibit or counteract any gravitational and thermal forces that may alter the desired horizontal profile of the susceptor  814 . The support points  7 , which denote areas of contact between the susceptor  814 , and support plates  89  and center plate  822 , are also shown. In one embodiment, the center plate  822  is rectangular and is parallel to the edges of the susceptor  814 . In another embodiment, the center plate  822  is not parallel to the perimeter of susceptor  814 . For example, the center plate  822  may be rotated 45° in order to provide support for areas between the outer corners of the susceptor  814 . Alternatively, the center plate  822  may take another shape such as a cross, or a star-like shape. Any number of support points  7  may be added or subtracted by adding or removing vertical actuators, or changing the size, location, and/or shape of the susceptor support points  5 , or alternatively using different numbers and shapes of support plates  89 . It is also noted that in this embodiment or others, any number of support points  7  may be created under the susceptor  814 , whether the susceptor  814  is in direct, or indirect, communication with the support shafts.  
         [0046]     While the foregoing has described an apparatus and method of producing and maintaining a desired horizontal profile in a susceptor, a further method of encouraging thermal expansion in the susceptor, or pre-loading the susceptor will be described. The susceptor support assemblies described above may be manufactured from a ceramic material, but in smaller sizes and varying shapes and the susceptor is typically manufactured from an aluminum material. These two materials have different coefficients of expansion and a pre-loading of the susceptor may be necessary to allow the susceptor to expand unhindered by the support plates and/or the support shafts. This is accomplished by vertically positioning the susceptor in the chamber to a position where the support pins are not in contact with the chamber.  
         [0047]     In one embodiment, the vertical actuator that supports the center region of the susceptor is then held static and any support shafts along the perimeter of the susceptor are vertically lowered to discontinue contact between any perimeter support plates and/or support shafts by actuating at least one other vertical actuator. In another embodiment, the perimeter support shafts are held static and the center support shaft is vertically raised. In both embodiments, the susceptor may be suspended and supported at the center by a single support shaft and no other part, such as support shafts or support plates, contact the susceptor, and the lift pins disposed in the susceptor do not contact the chamber at any point. A small gap, such as between about 0.125 inches to about 1.0 inches, between the susceptor and the support plates and/or the support shafts may be created to allow the susceptor to expand radially from the center region. Heat from a heat source, such as an embedded resistive heater in the susceptor, heat lamps, or other heat source coupled to the susceptor or chamber, may be applied to promote this thermal expansion. The susceptor may be heated by this heat source to a temperature of about 100° C. to about 250° C. to facilitate this expansion.  
         [0048]     Once the thermal expansion of the susceptor has been completed, the support shafts and/or support plates adapted to support the perimeter of the susceptor may be placed into contact with the susceptor by lowering the support shaft supporting the center region of the susceptor, or raising the support shafts adapted to support the perimeter of the susceptor. The susceptor may then be lowered by all support shafts to place a lower surface of the lift pins, which are movably disposed in the susceptor, in contact with an upper surface of the chamber bottom, thereby raising an upper surface of the support pins above the upper surface of the susceptor. A large area substrate may be introduced into the chamber through a slit valve  228  (shown in  FIG. 2A ) by a robot and placed above the susceptor on the upper surface of the lift pins. The robot may then be retracted and the slit valve may be closed. The chamber may be pumped down to a suitable pressure and the susceptor may be vertically raised from this transfer position by all support shafts. When the susceptor is raised, the lift pins will move away from the chamber bottom, allowing the substrate to come into contact with and lie flat on the upper surface of the susceptor. The susceptor may further be heated at this time and subsequently raised to the plasma area  17  ( FIG. 2A ) for processing. Once the substrate has been processed, the susceptor is lowered to the transfer position, the processed substrate is removed, and a new substrate may be introduced and processed. The susceptor, having been pre-heated by this method, may maintain its expanded orientation unless processing is halted and the susceptor is allowed to cool.  
         [0049]     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.