Abstract:
A method and arrangement for lifting lowering and centering a substrate on a surface employs lift pins have conical tips. A capture range is provided by the conical tips to capture and center misaligned wafers. One or more of the pins are inclined in certain embodiments to enhance the alignment capability of the lift pins. The inclined lift pins, when retracting into a support member at an angle, move a supported substrate horizontally into proper alignment.

Description:
This is a divisional of application Ser. No. 09/097,006 filed Jun. 12, 1998, now U.S. Pat. No. 6,146,463. 
    
    
     FIELD OF THE INVENTION 
     The present invention relates to the field of semiconductor substrate processing equipment. More particularly, the present invention relates to an apparatus and method for aligning a workpiece, such as on a support member. 
     BACKGROUND OF THE RELATED ART 
     In the fabrication of integrated circuits, equipment has been developed to automate substrate processing by performing several sequences of processing steps without removing the substrate from a vacuum environment, thereby reducing transfer times and contamination of substrates. Such a system has been disclosed for example by Maydan et al., U.S. Pat. No. 4,951,601, in which a plurality of processing chambers are connected to a transfer chamber. A robot in a central transfer chamber passes substrates through slit valves in the various connected processing chambers and retrieves them after processing in the chambers is complete. 
     The processing steps carried out in the vacuum chambers typically require the deposition or etching of multiple metal, dielectric and semiconductor film layers on the surface of a substrate. Examples of such processes include chemical vapor deposition (CVD), physical vapor deposition (PVD), and etching processes. Although the present invention pertains primarily to CVD processes, it may have application to other processes as well. 
     CVD vacuum chambers are employed to deposit thin films on semiconductor substrates. Typically, a precursor gas is charged to a vacuum chamber through a gas manifold plate situated above a substrate. The substrate is heated to process temperatures. The precursor gas reacts on the heated substrate surface to deposit a thin layer of material thereon. In a typical process chamber, a support member on which a substrate is mounted during processing is movable vertically in the chamber by means of a vertically movable support member. A plurality of lift pins are also vertically movable by an elevator and extend through the support member to facilitate transfer to the substrate from a robot blade onto the support member. 
     A number of problems associated with the deposition of the film or material on the substrate are at least partially attributed to improper alignment and shielding of the substrate. One such related problem occurs when the material deposits on the edge and back side surfaces of the substrate. Typically, these edge and back side surfaces are rougher than the highly polished top surface and are not coated with the adhesive layer covering the top surface. Therefore, material deposited on these surfaces tends to flake off the substrate and create particles. Generation of particles within the chamber is to be avoided as the particles may contaminate the substrates being processed and, thereby reduce the yield of good devices, and may damage the chamber components. Another problem occurs when the material deposits on the back side of the substrate causing the substrate to stick to the support member. Sticking may lead to particle generation when the deposited material adhering the substrate to the support member is broken away during removal of the substrate from the chamber. 
     An additional concern relating to the alignment and shielding pertains to the industry demands for film uniformity and edge exclusion. As the desire for greater throughput and efficiency has increased, the standards governing the placement and thickness of the deposited film at the substrate edge have continually become more stringent. Ideally, the deposited film has a uniform thickness across the entire area of the substrate with the edges of the film dropping off rapidly so that the zone of exclusion has little or no deposition thereon. Further, there is ideally no deposition on the beveled edges of the substrate. Industry practice has moved toward this ideal goal so that the current industry standards demand no film deposition on the beveled edge of the substrate and a film thickness at a point 3 mm from the edge of the substrate that is 90 percent or more of the film thickness at the center of the substrate with a thickness uniformity of less than 3 percent, excluding the area within 1 mm from the substrate edge. To achieve these requirements, the substrate must be properly aligned on the support member with the edges properly shielded. 
     In an effort to overcome the abovementioned problems, various devices and methods have been developed to shield the edge and back side surfaces of the substrate and to provide proper alignment of the substrate relative to the support member and other chamber components. Included among these devices are shadow rings, shielding purge gases and their delivery systems, and alignment mechanisms, such as guide pins. Shadow rings and purge gases are used to prevent deposition of the material on the edge and back side surfaces of the substrate; whereas, guide pins have been used to align the substrate on the support member. 
     The shielding purge gas is directed about the periphery of the substrate and exerts a positive pressure that reduces the chance that processing gas will reach the edge and back side surfaces of the substrate. To provide the purge gas to the full periphery of the substrate, the support member typically includes an annular gas groove that has an inner diameter that is less than the outer diameter of the substrate and an outer diameter that is greater than the outer diameter of the substrate so that a properly aligned substrate resting on the upper surface of the substrate overhangs the gas groove about the full periphery of the substrate. It has been found that the combination of a shadow ring and a purge gas further enhances edge performance. 
     As depicted schematically in FIGS. 11 and 12, one type of alignment mechanism employs a plurality of guide pins  90  extending upwardly from the upper surface of the support member  92 . The guide pins  90  are equally spaced about the periphery of the support member  92  and have an inner angled surface that flares outwardly toward their upper ends. The guide pins  90  are sufficiently spaced so that they can receive a substrate therebetween. The guide pins  90  act as a funnel that centers the substrate on the support member  92  as the support member  92  moves to receive the substrate thereon. So that the substrate is properly positioned with its full peripheral edge overhanging the gas groove  94 , the guide pins  90  extend from the outer periphery of the gas groove  94  and partially overhang the gas groove  94 . In this way, the lower end of the funnel defined by the plurality of guide pins  90  has a diameter that is intermediate the inner and outer diameters of the gas groove  94  and that is larger than the outer diameter of the substrate. Accordingly, as the support member  92  moves upwardly to receive the substrate thereon, the angled walls of the guide pins  90  force the substrate laterally into alignment and so that it overhangs the gas groove  94  about the full periphery of the substrate. 
     However, the guide pins  90  used to force the substrate laterally into alignment necessarily abut the edge of the substrate to obtain this alignment and remain in abutment therewith when the substrate rests upon the upper surface of the support member  92 . The purge gas flowing from the gas groove  94  cannot flow between the guide pins  90 , which are attached to the upper surface of the support member  92 , and the substrate when the substrate and guide pins  90  are in abutment with one another. Therefore, the contact between the guide pins  90  and the substrate prevents the purge gas from shielding the edge of the substrate proximal the guide pins  90  in abutment with the substrate and permits deposition of the film in the vicinity of the abutting guide pins  90 . Thus, the blockage caused by contact between the guide pins  90  and the substrate edge allows the film to deposit in the exclusionary zone and on the beveled edge near the guide pins  90  creating a danger of flaking and particle generation and preventing compliance with the industry requirements for edge exclusion. Furthermore, the lift pins  96  employed to lift the wafer from the surface of the support member are typically located radially interior to the gas groove  94 . This requires more complicated routing of gas channels in the surface of the support member  92 . Hence, the prior art arrangement uses different sets of pins, as depicted in the top view of FIG. 12, to provide the separate functions of lifting the substrate and centering the substrate. This complicates the arrangement and increases the costs of the arrangement. 
     Thus, despite the use of all the prior art features, there remains a need for increasing proper alignment between a substrate, a support member, and a shadow ring. Additionally, there is a need for an alignment mechanism that does not adversely affect the flow of purge gas at the substrate edge, nor require routing around lift pins on the surface of the support member. 
     SUMMARY OF THE INVENTION 
     These and other needs are met by embodiments of the present invention which provide an arrangement for raising, lowering and horizontally positioning a workpiece with respect to a surface. A plurality of pins are provided, with each pin having a substantially horizontal workpiece support surface that extends radially from the pin, and a post that extends vertically from the workpiece support surface. The post forms one end of the pin. A plurality of pin guides are spaced from one another. Each of these pin guides is configured to receive and guide one of the pins substantially vertically. At least one of these pin guides is angled to guide one of the pins at a non-zero angle with respect to vertical. A lift mechanism is coupled to the pins to raise and lower the pins through the pin guides. In certain embodiments of the invention, a support member is provided onto which the workpiece is lowered and positioned by the lift pins and on which the workpiece is supported during processing of the workpiece. The pin guides are formed within the support member. 
     The guidance of at least one of the pins at a non-zero angle with respect to vertical allows alignment to be performed during the lowering of the workpiece to the support member. When the pins are extended, the distance between the distal end of the at least one pin that is angled from the distal ends of the remaining lift pins is greater than when the pins are retracted into the pin guides. As the pins are lowered, with at least one of the pins being inclined, the distance between the pins is reduced. If a workpiece being supported by the pins is misaligned, the inclined pin will move the misaligned workpiece back into alignment as the pins are retracted. 
     The earlier stated needs are also met by another aspect of the present invention which provides a workpiece processing apparatus comprising a chamber in which the processing of the workpiece is performed. A support member in the chamber supports the workpiece during the processing of the workpiece. Pins are provided that receive a workpiece above the support member and lower and simultaneously center a workpiece on the support member. The workpiece processing apparatus, which is a chemical vapor deposition (CVD) apparatus, for example, may be used to process a workpiece such as a semiconductor wafer substrate. In such instances, it is often vital to precisely align the workpiece on the support member. The use of pins that receive the workpiece, and lower and simultaneously center the workpiece on the support member, eliminates the need for both lift pins and guide pins. Instead, the lifting and guiding functions normally provided by separate sets of pins are combined into a single set of pins. The pins can be either inclined or all guided vertically with respect to the workpiece, according to different embodiments of the invention. The configuration of the pins is taken advantage of to align the workpiece when the pins are guided vertically, in accordance with an embodiment of the present invention. 
     In another aspect of the present invention, a method of centering a workpiece on a support member is provided in which the workpiece is received on a plurality of pins that are extended above the support member. The pins are lowered to lower the workpiece onto the support member, with at least one of these pins being inclined at a non-zero angle with respect to vertical. The workpiece is moved horizontally with the pins during the step of lowering the pins, to there by center the workpiece on the support member. According to this aspect of the present invention, the workpiece is moved horizontally by the pins merely by the action of lowering the pins, so that the centering and lowering functions are accomplished simultaneously and may be performed by a single set of pins. 
     According to another aspect of the present invention, a lift pin for wafer processing apparatus is provided with an elongate portion and a wafer support section at one end of the elongate portion. The wafer support section has a substantially horizontal wafer support surface that extends circumferentially from the elongate portion. The cone extends vertically from this wafer support section. 
     The lift pin of the present invention provides alignment of a workpiece as the shape of the cone is advantageously employed to provide a capture range to capture misaligned wafers. Hence, a wafer received on the cones of a plurality of pins may be misaligned, but upon sliding down the cones to the wafer support section, the wafer will be moved horizontally and into proper alignment. This feature is useful in embodiments which employ all vertical lift pins, all inclined lift pins, or a combination of vertical and inclined lift pins. 
     The earlier stated needs are also met by an embodiment of the present invention which provides an arrangement for horizontally positioning a workpiece on a surface. The arrangement includes a plurality of pins arranged to receive a workpiece at first pin ends and lower and raise the workpiece to and from the surface. Guides are configured to receive and guide movement of the pins so that in a receiving position in which the pins receive the workpiece, the first pins ends are separated from one another in the horizontal plane to define a first perimeter. In a delivery position in which the workpiece is on the surface, the first pin ends are separated from one another in the horizontal plane define a second perimeter that is smaller than the first perimeter. Since the separation of the pin ends from one another becomes smaller when the workpiece is in a delivery position on the surface, an initially misaligned workpiece will become aligned when the pins are moved from the receiving position to the delivery position. 
     The foregoing and other features, aspects and advantages of the present invention will become apparent from the following detailed description of the present invention when taken in conjunction with the accompanying drawings. 
    
    
     BRIEF DESCRIPTION OF THE DRAWINGS 
     FIG. 1 is a partial cross-sectional side elevational view of a process chamber constructed in accordance with an embodiment of the present invention. 
     FIG. 2 is a side view of a support member and lift pins constructed in accordance with an embodiment of the present invention depicting the pins in an extended position. 
     FIG. 3 is a side view of a support member and lift pins constructed in accordance with an embodiment of the present invention depicting the pins in a retracted position. 
     FIG. 4 is a top view of a support member constructed in accordance with an embodiment of the present invention. 
     FIG. 5 is a side cross-sectional view of a support member and lift pins constructed in accordance with another embodiment of the present invention. 
     FIG. 6 is a side cross-sectional view of a support member and lift pins constructed in accordance with a further embodiment of the present invention. 
     FIG. 7 depicts an embodiment of a lift pin in accordance with the present invention to be used in an inclined pin guide. 
     FIG. 8 is an enlarged view of one end of the lift pin of FIG.  7 . 
     FIG. 9 depicts a lift pin constructed in accordance with the embodiment of the present invention that is to be guided vertically. 
     FIG. 10 is an enlarged view of one end of the lift pin of FIG.  9 . 
     FIG. 10 a  is a top schematic view of a pin arrangement. 
     FIG. 11 is a schematic cross-sectional view of a prior art support member, lift pin and guide pin arrangement. 
     FIG. 12 is a schematic top view of the prior art arrangement of FIG.  11 . 
    
    
     DETAILED DESCRIPTION OF EXEMPLARY EMBODIMENTS 
     The present invention provides an alignment arrangement for aligning a substrate  20  relative to a support member  12  in a process chamber  10 . The alignment apparatus as described herein is particularly useful in CVD (chemical vapor deposition) processing chambers and the following description refers primarily to the CVD processes to facilitate description and understanding. However, it is understood that the present invention may have application to other processes, process chambers, and apparatus, such as PVD and etch processes, and is therefore not limited to the precise form described. 
     FIG. 1 shows a typical process chamber  10  defined by an outer body  11 . The chamber  10  may be part of a vacuum processing system having a plurality of process chambers  10  connected to a central transfer chamber. The process chamber  10  houses a support member  12  that may take the form of a pedestal or susceptor mounted on a generally vertically oriented shaft  26 . The support member  12  serves to support a substrate  20  on its flat upper surface  22 . The support member  12  has a number of lift pins  14  disposed between pin guides  16 . Only a single pin  14  and pin guide  16  are depicted in FIG. 1 for illustration purposes. The lift pins  14  of the present invention support the substrate  20  during the substrate exchange with the robot. As will be described, the lift pins  14  of the present invention also center the substrate  20  on the support member  12 . The lift pins  14  lift the substrate  20  clear of the upper surface  22  of the support member  12  after the processing period. The removal of the substrate  20  is achieved by a conventional process chamber robot arm (not shown) which enters the process chamber  10  through a slit valve opening  18 . The same robot arm is also used to insert the substrate  20  into the process chamber  10 . The lift pins  14  are movable substantially vertically under action of a lift mechanism of which only the lift ring  24  is depicted in FIG. 1 between a receiving position in which the lift pins  14  receive the substrate  20  and a delivery position in which the substrate  20  is on the surface of the support member  12 . 
     Typically, the support member  12  comprises a block of metal, e.g., aluminum, that has a single coil resistance heater embedded therein. However, the support member  12  may be formed of other materials such as ceramic. In order to provide uniform heating of the support member  12  and to uniformly heat the substrate  20  mounted thereon, the coil must be in contact with the bulk of the support member  12  on all sides. Alternatively, the support member  12  may include cooling channels to cool some region of substrate  20  to improve temperature uniformity. A motion actuator (not shown) interconnected to the shaft  26  of the support member  12  is adapted to move the support member  12  vertically within the process chamber  10  alternatively, between a first, lowered position, and a second, raised position where a process step is performed. 
     FIG. 2 is a side view of an embodiment of a support member  12  having a single inclined pin guide. The remaining components of the process chamber are not depicted in FIG.  2 . In the embodiment of FIG. 2, a single pin guide  16   a  is inclined from the vertical by an angle α of approximately 3°. This causes the lift pin  14   a  that is guided within the pin guide  16   a  to be also inclined at an angle α of approximately 3°. This pin  14   a  will henceforth be referred to as an inclined pin. In this embodiment the remaining pin guides  16   b  are vertical so that lift pins  14   b  are guided vertically as they extend from and retract into the support member  12 . A second vertical lift pin  14   b  and pin guide  16   b  are provided in this embodiment, but is not depicted in FIG.  2 . An exemplary arrangement of the lift pins  14   a - 14   b  is provided in a top view of the support member  12  of FIG.  4 . 
     Referring to FIG. 2, the inclined lift pin  14   a  and the vertical lift pins  14   b  are hown in their extended positions in which substrate  20 , shown in FIG.  1  and not shown in FIG. 2, is captured during transfer of the substrate  20  from a robot arm (not shown). When in the extended position, lift pins  14   a  and  14   b  have their distal ends separated from one another by a distance slightly larger than the diameter of the substrate  20 . This difference between the distance separating the distal ends of the lift pins  14   a  and  14   b  and the diameter of the wafer is provided with reference numeral X in FIG.  2  and is referred to as the capture range. In an exemplary embodiment in which the wafer diameter is approximately 7.882″ in diameter at 475° C., the capture range is approximately 0.057″. This assumes that the angle of inclination α of the inclined pin  14   a  is approximately 3° and that the lift pins  14   a  and  14   b  have been extended approximately 0.660″ from the top surface  22  of the support member  12 . 
     The capture range provided in the embodiment of FIG. 2 due to the inclination of one of the lift pins  14   a  through the angling of a pin guide  16   a  provides a number of advantages. A relatively inexpensive robot mechanism that is not as precise as more expensive robot mechanisms may be used to carry the substrate into the chamber  10  and exchange it with the lift pins  14   a ,  14   b . Furthermore, since the lift pins  14   a ,  14   b  perform the function of centering the substrate  20  onto the top surface  22  of the support member  12  in precise alignment within the workpiece area  44 , separate sets of lift pins and guide pins are unnecessary. Additionally, the lift pins  14   a ,  14   b  may be positioned outside of the workpiece area  44  so that the gas grooves within the workpiece area  44  do not have to be routed around the lift pins  14   a ,  14   b , as in the prior art. 
     FIG. 3 is a side view of the support member  12  with the lift pins  14   a ,  14   b  in a retracted position. As made apparent by this figure, a misaligned substrate  20  (shown in phantom) has been horizontally positioned (e.g. centered) upon the retraction of the lift pin  14   a ,  14   b  into their respective pin guides  16   a ,  16   b . In preferred embodiments, the horizontal positioning of the substrate  20  causes the substrate  20  to be centered on the support member  12  within a ring groove  46  shown in FIG.  4 . When correctly positioned within the workpiece area  44  shown in FIG. 4, the edges of the substrate  20  will be entirely within the ring groove  46  (i.e. partially overhang) so that the purged gas may properly flow over the edge of the substrate  20  during substrate processing. 
     The angle of inclination α of the inclined lift pin  14   a  is approximately 3° in the embodiment of FIG.  2 . However, the angle from vertical may range from approximately 1° to approximately 10° to provide the alignment advantages of the invention. In addition to the inclined orientation of the inclined lift pin  14   a , the horizontal positioning of the substrate  20  is further enhanced by the design of the lift pin  14   a ,  14   b  themselves. This will be described in more detail with respect to the embodiments of FIG.  6  and the pins of FIGS. 7-10. 
     In an alternate embodiment of the present invention, depicted in FIG. 5, a plurality of the lift pins  14   a  are guided at an inclined angle by their angled pin guides  16   a . For example, all three pin guides  16   a  may be angled so that all of the pins  14   a  will be inclined when they are extended. While this embodiment provides a larger potential capture range for a given angle of inclination of the lift pins  14   a , the embodiment of FIG. 2 is presently preferred since only a single axis of uncertainty is present. In other words, upon lifting up the substrate  20  by the lift pins  14   a  for retrieval by the robot arm, the substrate  20  may only move along one axis of the embodiment of FIG. 2 since only one of the pins is inclined. By contrast, in the embodiment of FIG. 5 the substrate  20  may move in any horizontal direction during the lifting process. This makes the exchange with the robot arm potentially more difficult. However, the embodiment of FIG. 5 is still useful in centering a workpiece on a support member since it performs the centering and the lifting functions without the need for separate guide pins. 
     FIG. 6 depicts a further embodiment of the present invention in which none of the pins are inclined at an angle with respect to vertical. In this case, all three (or more) pin guides  16   b  are substantially vertical so that they have a zero angle of inclination with respect to vertical. The lift pins  14   b  are therefore guided in a substantially vertical fashion by the pin guides  16   b  as will be made clear by the following description and reference to FIGS. 9 and 10. As with the earlier described embodiments of FIGS. 2 and 5, it is desired that the lift pins  14   b  capture a misaligned substrate  20  during an exchange with a robot arm. Since the relative distances between the pins remains invariant during retraction and extension on the pins  14   b , in the embodiment of FIG. 6, another arrangement for providing a capture range is required. This is accomplished through the shape of the vertical lift pins  14   b , as depicted in FIGS. 9 and 10. Each vertical lift pin  14   b  has an elongate portion  48  with a first, distal end  49  forming the substrate receiving end. The second end  51  contacts the lift ring  24  so that the vertical lift pin  14   b  is lifted up and down by movement of the lift ring  24 . 
     At the distal end  49  of the elongate rod  48 , a wafer support section  50  is provided. The wafer support section  50 , for each of the vertical lift pins in FIG. 6, as well as the vertical lift pins  14   b  used in the embodiment of FIG. 2, have a flat workpiece support surface  60  on the top of the wafer support section  50 . A substrate  20  is supported at its edge on the workpiece support surface  60 . 
     A cone  55  is provided at the distal end  49  of the vertical lift pin  14   b  and extends vertically from the workpiece support section  50 . The cone  55  has a cone tip  58  and base section  56  connected at the workpiece support section  50 . The tip of the cone  55  is conically shaped and may generally have an angle of between 0° and approximately 90°. However, it is preferred that the angle γ formed by the sides of the cone tip section  58  is between approximately 25° to approximately 40°. 
     The shape of the cones  55  is such that the diameter of the cones at the tips  55  is less than the diameter of the cones  55  at the bases  56 . Hence, the distance between the tips  58  of two vertical lift pins  14   b  will be greater than the distance between the bases  56  of those pins. As can be seen in a top view of the pins in FIG. 10 a , in a single horizontal plane, the perimeter defined by the tips  58  of the cones  55  is larger than the diameter defined by the bases  56 . Accordingly, the lift pins  14   b , even when all vertically arranged as in the embodiment of FIG. 6, has a capture range which allows a misaligned wafer or substrate  20  to be captured within the tips  58  of the cones  14   b . After capture, the substrate  20  will then become horizontally positioned (e.g. centered) by sliding down the cones  55  to rest against the base sections  56  and on the flat horizontal workpiece support surface  60  of the workpiece support section  50 . 
     An exemplary embodiment of the inclined lift pins  14   a , used in the embodiments of FIGS. 2 and 5, shares many of the same features with the vertical lift pins of FIGS. 9 and 10. For example, each inclined lift pin  14   a  has an elongate section  48 , a workpiece support section  50 , and a cone  55  with a tip  58  and base section  56 . As with the vertical lift pins  14   b , the inclined lift pin  14   a  also has the sides of the cone tip  58  angled between 0 and 90° angle with a preferred range of between about 25° and 40°. Unlike the vertical lift pins  14   b , however, the inclined lift pin  14   a  has either an angle or curved workpiece support surface  52  at the workpiece support section  50 . In the preferred embodiment in which the workpiece support surface  52  is flat, the surface  52  is angled at an angle β that is at least as much as the angle of inclination a of the pin guide  16   a  (and therefore the angle of inclination of the pin  14   a ). As an example, if the pin guide  16   a  is angled at approximately 3°, the angle β of the workpiece support section with respect to the center axis of the inclined work pin  14   a  is at least equal to 3°. It is preferred that the angle of inclination β workpiece support surface  52  be between approximately 2° and 5°. The workpiece support section  52  can also be angled at an angle greater than the angle of inclination α. 
     One reason for the angling of the workpiece support surface  52  of inclined lift pin  14   a  is to provide a flat support surface for the substrate  20  at that lift pin  14   a . If a vertical lift pin of FIG. 9 with a flat workpiece support surface  60  were used instead of the inclined lift pin of FIG. 8 in an angled pin guide  16   a , then only one edge of the workpiece support surface  60  would contact the substrate  20 . This would cause mechanical stresses on the substrate  20 . 
     Although it is advantageous to provide a larger effective support surface for the substrate  20 , this also has a slight disadvantage in that the inclined lift pin  14   b  will tend to pull a substrate  20  in the direction of arrow A so that the once-aligned substrate  20  will again become misaligned upon the extension of the lift pins  14   a ,  14   b . To overcome this concern, the angle β may be made greater than the angle of inclination a so that the substrate  20  does not rest flatly on the workpiece support section  52 , but rather at a slight angle to the workpiece support section  52 . Alternatively, instead of a flat workpiece section  52 , a slight curve in the surface may be provided to prevent two flat surfaces from being in intimate contact with each other. In certain embodiments of the invention, the workpiece support section  52  is made of a material having a very low coefficient friction so that the substrate  20  will slide easily on the workpiece support surface  52 . 
     The lift pins  14   a ,  14   b  may be made of any suitable material, taking into account the specific conditions the lift pins  14   a ,  14   b  will be exposed to within the process chamber  10 . It is desirable that the pins be non-reactive with the processes taking place within the chamber  10 . Ceramic materials such as alumina are suitable for many processes such as chemical vapor deposition. 
     The embodiments of the present invention provide methods and arrangements that use a single set of pins to both center and lift and raise a substrate, such as that of semiconductor wafer. This is accomplished by inclining one or more of the lift pins and/or configuring the lift pins with conical tips so that misaligned substrates will be misaligned when placed on the tips. 
     Although the present invention has been described and illustrated in detail, it is to be clearly understood that the same is by way of illustration and example only and is not to be taken by way of limitation, the spirit and scope of the present invention being limited only by the terms of the appended claims.