Abstract:
Substrate support methods and apparatus include vertically aligned lift pins that have bearing surfaces that engage friction plates and/or magnetic fields to maintain the vertical orientation of the lift pins during substrate lifting. In some embodiments, a magnetic field and/or weighting may alternatively or additionally be used to control the vertical orientation of the lift pins, limit the angle of the lift pins, and/or prevent the lift pins from unintentionally binding in a susceptor as the susceptor is raised and prevent the resulting uneven support of the substrate.

Description:
[0001]     The present application claims priority to U.S. Provisional Patent Application Ser. No. 60/575,869, filed Jun. 1, 2004 and to U.S. Provisional Patent Application Ser. No. 60/587,294, filed Jul. 12, 2004, both of which are hereby incorporated by reference herein in their entirety for all purposes. 
     
    
     FIELD OF THE INVENTION  
       [0002]     The present invention relates to methods and apparatus for handling substrates in flat panel display and/or electronic device processing systems. More specifically, the present invention relates to controlling lift pins used to raise substrates such as glass substrates, polymer substrates, semiconductor wafers, etc., off of a surface.  
       BACKGROUND  
       [0003]     As depicted in  FIG. 1 , a prior art substrate support  100  includes a conventional vertical lift pin  102  that relies on a bushing  106  or collar mounted in a susceptor  104  to provide horizontal support near the top of the lift pin  102  to maintain the pin  102  in a vertical position and limit the angle that the pin  102  can vary from a vertical orientation. An intentionally low friction ceramic skid plate  110  is provided to contact the rounded bottom of the conventional lift pin  102 . The conventional lift pin  102  itself typically has a smooth radius bearing surface  108  for contacting the skid plate  110 . The ceramic skid plate  110  is mounted on an aluminum plug  112  that is inserted into an opening in the bottom wall  114  of a process chamber. The plug  112  includes an O-ring  116  to maintain the seal of the chamber. Thus, the bushing  106  provides the only horizontal force on the lift pin  102  to guide it as the pin  102  is raised or lowered. The lower end of the lift pin  102  is free to slip on the skid plate  110 .  
         [0004]     In operation, the susceptor  104  is lowered toward the bottom wall  114  of the chamber which causes the lower bearing surface  108  of multiple lift pins  102  to contact multiple skid plates  110 . As the susceptor  104  is further lowered the lift pins rise relative to the susceptor  104  and lift the substrate (not pictured) off of the susceptor  104 . Once the substrate has been lifted, a substrate blade (not pictured) such as an end effector may be inserted below the substrate to remove the substrate from the chamber.  
         [0005]     In conventional substrate supports, as the bushing  106  wears from guiding the lift pin  102 , play may develop in the horizontal position of the lift pin  102  and the bushing&#39;s ability to maintain a precise vertical orientation of the lift pin  102  may become compromised. In addition, the lift pin  102  may not travel smoothly through a worn bushing  106  which may affect substrate positioning. Further, the more surface area of a bushing that contacts a lift pin, the more likely it is that potentially contaminating particles may be generated.  
         [0006]     An additional problem with conventional lift pins  102  is that they have a tendency to bind in the bushings  106  due to friction such that some lift pins  102  may remain raised above the top surface of the susceptor  104  even as the susceptor  104  is raised. This results in the substrate being lifted unevenly and, in some circumstances, the substrate may be damaged either by a bound lift pin  102  piercing the substrate or suddenly becoming unbound and dropping the substrate. Thus, what is needed is substrate lifting methods and apparatus that are not subject to such problems.  
       SUMMARY  
       [0007]     In some embodiments, the present invention provides a substrate support with lift pins that do not rely solely on bushings to maintain the pins in a vertical orientation or to limit the angle of the pins as they travel. In some embodiments, the present invention uses friction applied at the lower end of the lift pins to maintain the vertical orientation of the lift pins. In some embodiments, the present invention uses magnetic force or a combination of friction and magnetic force to maintain the lift pins&#39; orientation. The present invention applies friction and/or magnetic force to the lower bearing surface of the lift pins such that the lift pins are restricted from horizontal movement by both the friction and/or magnetic force applied at the bottom of the lift pins as well as by reduced contact area bushings at the top of the lift pins.  
         [0008]     In some embodiments, a weight and/or a permanent magnet are used to prevent lift pins from binding in their bushings. As the susceptor is raised, the weight and/or permanent magnet attached to each lift pin pulls the lift pins through their bushings such that any binding friction is overcome by the force of the weight and/or permanent magnet and thus, the lift pins move smoothly through the susceptor.  
         [0009]     Numerous other aspects are provided, as are systems and apparatus in accordance with these and other aspects of the invention. These and the other aspects and features of the present invention will be more fully understood with reference to the attached drawings and the following detailed description. 
     
    
     DRAWINGS  
       [0010]      FIG. 1  illustrates a conventional bushing-controlled substrate support.  
         [0011]      FIG. 2  illustrates a first example embodiment of a substrate support according to the present invention.  
         [0012]      FIG. 3  illustrates a portion of the first example embodiment of a substrate support according to the present invention.  
         [0013]      FIG. 4  illustrates a second example embodiment of a substrate support according to the present invention.  
         [0014]      FIG. 5  is a flowchart illustrating an example method according to the present invention.  
         [0015]      FIG. 6  illustrates a third example embodiment of a substrate support according to the present invention.  
         [0016]      FIGS. 7A and 7B  illustrate operation of a fourth example embodiment of a substrate support according to the present invention.  
         [0017]      FIG. 8  depicts front, side, top, and bottom detailed views of the fourth example embodiment of a substrate support according to the present invention.  
         [0018]      FIG. 9  illustrates a fifth example embodiment of a substrate support according to the present invention. 
     
    
     DETAILED DESCRIPTION  
       [0019]     Turning to  FIG. 2 , the present invention provides an improved substrate support  200 . In the illustrated embodiment, a lift pin  202  is held in a vertical orientation by a pointed bearing surface  208  (or “point bearing  208 ”) in contact with a friction plate  210  made of ceramic or other suitable material. Note that a bushing  206  mounted in the susceptor  204  is “wide open” or “free” as compared with the “tight” bushing  106  used in the conventional substrate support  100 . Also note that in the conventional substrate support  100 , the vertical orientation (angle) of the lift pin  102  is maintained or controlled by the tight bushing  106 , while in the substrate support  200  of the present invention, the vertical orientation of the lift pin  102  is maintained or controlled primarily by the friction plate  210  engaging the pointed bearing surface  208  at the lower end. It is further noted that, while conventional substrate support  100  may contact the lift pin  102  simultaneously at multiple points, the wide open bushing  206  generally will not.  
         [0020]     The friction plate  210  may be mounted on a plug  212  that is inserted into an opening in the bottom wall  214  of a process chamber (not separately shown). The plug  212  may be made from aluminum (or other suitable material) and may include an O-ring  216  or other sealing surface to maintain the seal of the chamber.  
         [0021]     Turning to  FIG. 3 , details of the pointed bearing surface  208  of the lift pin  202  and a portion of the friction plate  210  are depicted. Although the drawing is not to scale, note that the pointed bearing surface  208  can engage the friction plate  210  by settling into one of the valleys between the pyramid-shaped protrusions on the surface of the friction plate  210 . The pyramid-shaped protrusions may be formed on the surface of the friction plate  210 , for example, by cutting intersecting rows of V-shaped grooves into the surface of the friction plate  210 . In some embodiments, the recesses in the surface of the friction plate  210  may be sized to match the dimensions of the pointed bearing surface  208  of the lift pin  202  such that the two precisely mate when engaged. In some embodiments, other friction plate textures and/or bearing shapes may be used (e.g., to create a high friction interlock upon engagement). For example, the friction plate  210  may include rows of tightly spaced cone-shaped recesses or cylinder-shaped recesses to receive a pointed bearing surface. In some embodiments, the bearing surface may, for example, include an inverted pyramid shape, or a series of inverted pyramid points, to mate with the pyramid-shapes on the friction plate depicted in  FIG. 3 .  
         [0022]     A pyramid friction plate  210  and a pointed bearing surface  208  may accommodate thermal expansion and at the same time ensure that the vertical position of the pin is maintained.  
         [0023]     Turning to  FIG. 4 , a second example embodiment of an improved substrate support  400  is depicted. Although not shown, wide open bushings in the susceptor such as those depicted in  FIG. 2 , may be used with the embodiment depicted in  FIG. 4 . In such embodiments, a pin  418  or other connecting mechanism may be used to hold a pointed bearing  408  in a recess of a shaft of the lift pin  402 . In some embodiments, the pointed bearing  408  may comprise steel coated with aluminum. In general, the pointed bearing  408  may comprise any ferromagnetic material or suitably coated ferromagnetic material.  
         [0024]     A ceramic (or other suitable material) friction plate  410  may be mounted on the top of a plug  412  that is inserted into an opening in the bottom wall  414  of a process chamber. Note that the plug  412  may include and O-ring  416  to help seal the chamber. Also note that the plug  412  may be made from aluminum or any suitable material.  
         [0025]     An electromagnet  426  formed from, for example, an iron core  424  wrapped with a coil  422  charged by an alternating current source  420 , may be inserted into an opening of the plug  412  and may be used to attract the pointed bearing  408 . Thus, an electromagnet  426  may be used to vertically align the lift pin  402  as the lift pin approaches the friction plate  410  when the lift pin is lowered along with the susceptor (not shown). The electromagnet  426  may also be used to enhance the engagement between the pointed bearing  408  and the friction plate  410 . The stronger the magnetic field, the more the friction between the pin  402  and plate  410 . Note that a friction plate  410  like the ones described above with reference to  FIG. 3 , may be used with the example embodiment depicted in  FIG. 4 .  
         [0026]     Turning to  FIG. 5 , a flowchart depicting an example method of the present invention is provided. In Step S 1 , the susceptor is fully raised in the process chamber. The heads of lift pins  402  are flush within recesses of the susceptor. Any number of different processes and heating may be applied to the substrate on the susceptor. The electromagnet  426  associated with each lift pin  402  is off.  
         [0027]     In Step S 2 , after the substrate processing is complete, the electromagnets  426  are energized and the susceptor is lowered. As the susceptor is lowered, the lift pin point bearings  408  engage the friction plates  410  mounted on plugs  412  in the bottom of the process chamber. The energized electromagnets  426  create magnetic fields that attract the point bearings  408  of the lift pins  402  and pull the lift pins  402 , effectively forcing them to maintain their vertical alignment.  
         [0028]     In Step S 3 , the susceptor is fully lowered and the lift pins  402  are fully raised. The substrate, which is supported by the heads of the lift pins  402 , is fully elevated so that a robotic arm or other device may exchange the processed substrate for a new, unprocessed substrate. During the exchange, the electromagnets  426  may remain energized.  
         [0029]     In Step S 4 , after the exchange is complete, the susceptor is raised. While the susceptor is raised and the lift pins  402  are lowered, the lift pin vertical alignment for each lift pin  402  is maintained by the friction plate  410  and point bearing  408  engagement as well as by the energized electromagnet  426 .  
         [0030]     In Step S 5 , the susceptor continues to rise and the lift pins  402  disengage the friction plates  410  as the lift pin heads are seated in recesses in the susceptor. The electromagnets  426  turn off upon disengagement to prevent any unintended effects that an electromagnetic field may have upon the substrate processes. Flow continues to Step S 1  where the method may repeat.  
         [0031]     In a third embodiment of an improved substrate support  600 , a relatively large bearing foot  608  may be attached to the lower end of the lift pin  602  using a pin  618  or other connecting mechanism as depicted in  FIG. 6 . In some embodiments, the bearing foot  608  may be large enough to maintain the vertical alignment of the lift pin  602  without any horizontal support from the “wide open” or “reduced contact area” bushing  606  in the susceptor  604 . The bearing foot  608  may engage a slide plate  610  mounted on a plug  612  filling an opening in the lower wall  614  of the process chamber. The slide plate  610  may be made of ceramic or any other suitable material.  
         [0032]     In some embodiments a vertical magnetic field may be applied to the bearing foot  608  and/or lift pin  602  to help maintain the vertical alignment of the lift pin  602 . In such embodiments, a bushing  606  may not be used at all. In some embodiments the bushing  606  may be a magnetic bushing that does not contact the lift pin  602 , but applies a magnetic field to further help maintain the alignment of the lift pin  602  which may include a ferromagnetic core (not pictured).  
         [0033]     In some embodiments, the plug  612 , which may be made of aluminum or other suitable material, may not fill the entire opening in the lower wall  614  of the chamber so as to create a recess to receive the bearing foot  608  as depicted in  FIG. 6 . Note that the plug  612  may include an O-ring  516  or other sealing surface to help seal the chamber. Also note that the opening in the lower wall  614  of the chamber may include a lip  620  on the edge of the opening inside the chamber. In some embodiments, the lip  620  may be used to secure the slide plate  610  to the plug  612 .  
         [0034]     Turning to both  FIGS. 7A and 7B , operation of a fourth exemplary embodiment is described.  FIG. 7A  depicts an embodiment of a substrate support in a raised position  700 A and  FIG. 7B  depicts the same embodiment of the substrate support in a lowered position  700 B. In the raised position  700 A, the lift pin  702  substrate bearing surface is above the susceptor  704  ready to receive a substrate. As the susceptor  704  is raised, the lift pin  702  remains stationary despite upward forces due to friction from the bushing  706 . In accordance with some embodiments of the present invention, a weight and/or permanent magnet  708  attached to the lower end of the lift pin  702  pulls the lift pin  702  downwardly toward the chamber bottom  710  with more force than the upward friction force. Thus, binding of the lift pin  702  in the bushing  706  is avoided and the lift pin  702  does not move up as the susceptor  704  is raised until the top of the lift pin  702  is fully seated into the susceptor  704 . Although not pictured, the susceptor  704  may be elevated further such that the lift pin  702  no longer contacts the bottom of the chamber  710 .  
         [0035]     In some embodiments that use a permanent magnet  708  attached to the lift pin  702 , a protective cover  712  and magnetically susceptible plate  714  may be attached to a plug  716  in the chamber bottom  710 . The protective cover  712  may be made from ceramic, aluminum, or any suitable inert material. The magnetically susceptible plate  714  may be made from steel or any suitable magnetically susceptible material.  
         [0036]     When a substrate is to be removed from the chamber, the susceptor  704  is lowered such that the lift pins  702  once again contact the bottom of the chamber  710  and are ultimately pushed up through the bushings  706 . Before contact however, as the lift pin  702  approaches the magnetically susceptible plate  714  when the susceptor is being lowered, the lower end of the lift pin  702  is pulled downward toward the magnetically susceptible plate  714 . This pull helps maintain the vertical orientation of the lift pin  702 .  
         [0037]     It may be preferable to use a magnet in, or attached to, the lift pins in some embodiments as opposed to other embodiments wherein a magnetic field generated by an electromagnet  426  ( FIG. 4 ) acts on magnetically susceptible lift pins  408 . This is because a magnetic field may not be uniform over the entire horizontal area that the lift pin  402  may range due to thermal expansion and other forces. In other words, thermal expansion of the susceptor relative to the chamber wall  414  (where the electromagnet  426  is mounted) may affect the vertical orientation of the lift pin  402  since the lift pin  402  will tend to be pulled toward the center of the magnetic field. If the lift pin  402  does not remain precisely over the center of the magnetic field, as is likely given the high probability that there may be a differential thermal expansion between the susceptor lift pin position and the bottom of the chamber, the lift pin  402  may be pulled out of vertical alignment by a horizontal component force of the magnetic field.  
         [0038]     By putting a permanent magnet  708  in, or on, the lift pin  702  and not using an electromagnet mounted in the chamber bottom, the magnet  708  will be drawn directly downward towards the magnetically susceptible plate  714  at the point of closest approach. In other words, assuming the magnetically susceptible plate  714  is large enough to cover the horizontal range of the lift pin relative to the chamber bottom, thermal expansion of the susceptor relative to the chamber body (where the magnetically susceptible plate  714  is mounted) will not affect the tendency of the lift pin to be pulled straight downward by the magnetic force of the permanent magnet  708 , regardless of the amount of differential thermal expansion that has occurred between the susceptor lift pin position and the bottom of the chamber.  
         [0039]     However, in some electromagnet embodiments, a large enough magnetic field may be generated to create sufficient uniformity over the entire horizontal range of the lift pin such that the magnetically susceptible lift pin will not experience any horizontal component force from the magnetic field as it is lowered toward the electromagnet. In some embodiments, the plug in the chamber bottom may include a permanent magnet that creates a magnetic field to attract a magnetically susceptible lift pin. As with the electromagnet embodiment discussed above, it may be preferable to insure that the permanent magnet in the plug creates a field large enough to be substantially uniform over the entire horizontal area in which the lift pin may range due to thermal expansion or other forces.  
         [0040]      FIG. 8  depicts an illustration of four views  800 A,  800 B,  800 C,  800 D of an example embodiment of a substrate support  800  that uses weight and/or permanent magnet  804  attached to a lift pin  802 . View  800 A is a front view that illustrates the lift pin  802  passes through the center of an inverted “U”-shaped weight and/or permanent magnet  804 . Thus, as depicted, in some embodiments a “horseshoe” shaped magnet maybe used. View  800 B is a side view that illustrates the weight and/or permanent magnet  804  rotated ninety degrees from the front view  800 A. View  800 C is a top view and view  800 D is a bottom view that illustrates a pin  806  through the lift pin  802  that may be used to secure the weight and/or permanent magnet  804  to the lift pin  802 . Any suitable method of attaching the weight and/or permanent magnet  804  to the lift pin  802  may be used.  
         [0041]     In some embodiments, a weight may be sufficient to overcome any friction that may cause the shaft of a lift pin  702  ( FIG. 7A ) to bind-up or otherwise get stuck in a straight-bore bushing  706  of a susceptor  704 . In some embodiments where it may be desirable to avoid any possibility of the shaft of the lift pin  702  binding-up in the bushing  706 , a permanent magnet, such as one made of neodymium, iron, and boron (NIB); aluminum, nickel, and cobalt (Alnico); and/or cobalt and samarium (C-S), that has the benefit of both gravitational and magnetic forces pulling directly downward, may be employed.  
         [0042]     In some embodiments, a bushing with a tapered bore or other profile may be used. A tapered bore may include an expanded inner diameter down the length of the bushing to further reduce the likelihood of the lift pin binding. In such embodiments, methods described herein that maintain the vertical orientation of the lift pin may be employed as practicable.  
         [0043]     Turning to  FIG. 9 , an example embodiment of a substrate support  900  that uses weight and/or permanent magnet  902  encapsulated in a lift pin  904  is depicted. In some embodiments, the weight and/or permanent magnet  902  may be held in a cap  906  that attaches to the end of a lift pin  904 . Although not pictured, in some embodiments, the cap  906  may attach to the lift pin  904  using a pin through both the cap  906  and the lift pin  904 . In some embodiments, the inside of the cap  906  may include threads that match threading on the end of the lift pin  904  such that the cap  906  may simply be screwed onto the end of the lift pin  904 . Other suitable methods of attaching the cap  906  to the lift pin  904  may be employed. In some embodiments the cap  906  may be made from aluminum, ceramic, or other suitable inert material. In operation, a lift pin  904  with an encapsulated weight and/or permanent magnet  902  may function in the same manner as described above with regard to the weight and/or permanent magnet  708  attached to the lift pin  702 .  
         [0044]     Accordingly, while the present invention has been disclosed in connection with exemplary embodiments thereof, it should be understood that other embodiments may fall within the spirit and scope of the invention, as defined by the following claims.