Abstract:
A pin stop and method of implementation suitable for use lift pin assemblies used in semiconductor process environments is provided. The pin stop includes a pin shaft and a circular pin head with soft stop and hard stop features defined thereon. The soft stop feature is defined in a grove in the pin head surface and is configured to impact a stopping surface slowing movement of a lift pin assembly. The hard stop then impacts the stopping surface providing a constant, reliable and repeatable position of a wafer positioned on the lift pin assembly.

Description:
BACKGROUND OF THE INVENTION 
     1. Field of the Invention 
     The present invention relates generally to the preparation of substrates such as those used in semiconductor fabrication as well as in the manufacture of hard disk drives, and more particularly to a stop for pin lifter devices configured to raise and lower substrates. 
     2. Description of the Related Art 
     In the fabrication of semiconductor devices, there is a need to perform a variety of substrate preparation and fabrication operations in which substrates such as silicon wafers are manipulated within a process environment such as a process chamber. A common method of substrate manipulation is the use of lift pins that are configured to contact a wafer, typically on a back side or non-active surface of the substrate, and with a minimum of surface area contact. In the plurality of fabrication processes that may be performed in a process chamber, the substrate may be raised or lowered as required for both manipulation within the process chamber as well as in preparation for insertion into and removal from the process chamber. 
     In the prior art, lift pins are configured to raise and lower a substrate between constant, fixed positions in a processing environment such as a process chamber. FIG. 1A shows a typical lift pin assembly  10  within a process chamber. Lift pins  16  are attached to a yoke  20 , and travel through a support chuck  14  to a back side of a wafer  12 . When a wafer is to be lifted, the lift pins  16  are configured to contact the back side of the wafer  12  in at least three points to raise the wafer  12  off the support chuck  14 . The lift pins  16  then withdraw through the support chuck  14  and lower the wafer  12  on to the support chuck  14 . As is known, when a wafer  12  is disposed on the support chuck  14 , there is no contact between the lift pins  16  and the wafer  12 . Bellows  18  are configured around each of the lift pins  16  between the support chuck  14  and the yoke  20  enclosing the lift pins  16  and preventing any contamination of the portion of the lift pin that travels through the support chuck  14 . 
     The yoke  20  is attached to a shaft  22  which is raised and lowered by an actuator  24 . The actuator is typically pneumatic, and can also be electrical. The raising and lowering of shaft  22  raises and lowers the yoke  20  which raises and lowers the lift pins  16  in contact with the wafer  12 . The actuator  24  receives pneumatic supply, or electrical power and control through cable  26 . 
     The lower portion of the lift pin assembly  10  includes the lift pin stops  30 ,  32 . An upper pin stop  30  is inserted through an upper pin stop housing plate  28 . The upper pin stop housing plate is connected to shaft  22 . Contact between the upper pin stop  30  and an upper pin stop plate  35  halts upward travel of the shaft  22  and raising of the lift pins  16 . 
     A lower pin stop  32  is inserted through a lower pin stop housing plate  34 . Contact between the upper pin stop housing plate  28  and the lower pin stop  32  halts downward travel of the shaft  22  and lowering of the lift pins  16 . 
     FIG. 1B shows a closer view of upper pin stop  30  shown in FIG.  1 A. As described in reference to FIG. 1A, the upper pin stop housing plate  28  is attached to shaft  22  (not shown in FIG.  1 B). As the lift pin assembly  10  lifts the wafer  12 , upper pin stop housing  28  travels upward closing a gap  38  between upper pin stop housing plate  28  and upper pin stop plate  35 . Upward travel of upper pin stop housing plate  28  is halted by contact between a tip  36  of upper pin stop  30  and upper pin stop plate  35 . Upper pin stop  30  thus stops the raising of lift pins  16  and the wafer  12 . 
     FIG. 1B shows that upper pin stop  30  is configured through upper pin stop housing plate  28 . Typically, pin stops  30  and  32  are threaded to provide for adjustment of the pin stop  30 ,  32  position in housing plates  28 ,  34 . The position of the upper pin stop  30  is therefore adjustable by raising or lowering the upper pin stop  30  in upper pin stop housing plate  28 . Adjustment of upper pin stop  30  sets the upper extent of the lift pin assembly  10  by establishing the point at which upper travel of upper pin stop housing plate  28  is halted. In a similar manner, the lower pin stop  32  (See FIG. 1A) sets the lower extent of the lift pin assembly  10 . 
     As can be seen in FIG. 1B, the contact between the tip  36  of upper pin stop  30  and the upper pin stop plate  35  that halts upward travel is a direct, surface to surface contact. In some prior art applications, the material from which the upper pin stop plate  35  is constructed is metal, and the material from which the upper pin stop  30  is constructed is metal, and so the resulting contact is metal to metal contact. In some prior art applications, the upper pin stop  30  has been constructed of a hard plastic, and so the resulting contact is hard plastic to metal. Additionally, some prior art applications incorporate hard plastic layers over the contact areas, also known as stopping surfaces, of upper pin stop housing plate  28  (See FIG. 1A) and upper pin stop plate  35 . 
     Each of the above described types of contact used in a pin stop assembly  10  result in problems with prior art pin stops. In the configuration where a metal pin stop  30 , contacts a metal upper pin stop plate  35 , the result is an abrupt, hard stop. An abrupt, hard stop is a rapid deceleration caused by hard surface to surface contact typically causing lift pin  16  vibration, bounce, or noise. The metal to metal hard stop can be so abrupt and hard that wafer  12  shifting on the lift pins  16  can result, and in some cases, wafer  12  fracture. Wafer  12  shifting, however slight, can be detrimental to process operations. By way of example, in plasma etching operations, wafer shifting introduces intolerable variance into the process. 
     The use of hard plastic pin stops or the use of hard plastic layers over the stopping surfaces and resulting hard plastic to metal contact can dampen an abrupt hard stop, but introduces inaccuracies in wafer  12  positioning. Over time, hard plastic exhibits deformation. The deformation results in a change in wafer  12  positioning, and a known requirement in wafer processing is constant, predictable wafer  12  positioning. Hard plastic deformation can result from repeated impact and contact in accordance with pin stop function and design, and can be exacerbated by heat. The deformation of hard plastic used in a hard plastic to metal contact configuration introduces an unacceptable variance. 
     One approach, as described above, to mitigating the problems associated with hard stops is to re-configure the metal to metal contact by, for example, introducing a hard plastic alternative. It has been found that hard plastic is generally unacceptable, as already described. Another approach to the hard stop problems is to mechanically dampen the movement of the shaft  22  (See FIG. 1A) at the actuator  24  (See FIG.  1 A). Unfortunately, known mechanical dampening techniques require more space than is available within a process chamber, and tend to contribute unacceptable cost to design and manufacture. 
     In view of the foregoing, there is a need to develop and implement a pin stop that can be easily and inexpensively utilized in all manner of substrate lift pin assemblies. The pin stop design should be able to be implemented in existing lift pin assemblies such as those within semiconductor wafer process chambers with a minimum of available space. The pin stop should reduce or eliminate the prior art problems caused by hard stops resulting in wafer shifting or breakage. 
     SUMMARY OF THE INVENTION 
     Broadly speaking, the present invention fills these needs by providing a simple pin stop that is easily integrated into existing systems and assemblies, and produces a consistent, repeatable, and reliable pin stop while minimizing and eliminating unacceptable wafer shifting or breakage. The present invention can be implemented in numerous ways, including as a process, an apparatus, a system, a device, or a method. Several embodiments of the present invention are described below. 
     In one embodiment, a yoke having a plurality of lift pins for the lifting and lowering of a substrate and connected to a pin stop housing plate is provided. The pin stop housing plate includes a pin stop having a head. In the head of the pin stop is a face in which is configured a contact surface that is designed to halt movement of the yoke when the contact surface abuts a stop surface. The contact surface includes a hard stop and a soft stop. The soft stop is configured to compress against the stop surface until the stop surface meets the hard stop. 
     In another embodiment, an apparatus for stopping movement of a yoke used in a wafer processing system is provided. The apparatus includes a pin shaft and a head connected to the pin shaft. The head has a contact surface that is defined by a hard stop and a soft stop. The hard stop and the soft stop are configured to impact a stopping surface to halt movement of the yoke. The head also has a recess for receiving the soft stop. The soft stop is configured to compress against the stopping surface until the hard stop meets the stopping surface. 
     In still a further embodiment, a pin stop for stopping movement of a lift pin assembly is provided. The lift pin assembly has a yoke with a set of lift pins and a shaft that moves the yoke into a down position and an up position. The shaft has a yoke connection end connecting the shaft to the yoke, and a stop connection end connecting the shaft to a pin shaft. The pin shaft has a head which has a hard stop and a soft stop. The hard stop and the soft stop are configured to impact a stopping surface and halt the movement of the shaft. The soft stop is configured to compress against the stopping surface until the hard stop contacts the stopping surface. 
     In yet another embodiment, a method for controlling an abrupt stopping motion of a shaft is provided. The method includes moving a contact surface toward a stopping surface and then absorbing an initial impact between the contact surface and the stopping surface. The absorbing is designed to compress a soft stop component of the contact surface. The method then provides for halting the movement of the contact surface when a hard stop component of the contact surface meets the stopping surface. 
     The advantages of the present invention are numerous. One notable benefit and advantage of the invention is the elimination of unacceptable wafer shifting or breakage resulting from current hard stop apparatus. By combining the dampening effects of a soft stop with the constant, repeatable and reliable wafer positioning of a hard stop, a lift pin stop is provided that is simple in design and easily implemented to increase reliability of substrate processing and handling. 
     Another significant advantage is the simplicity of design of the present invention. Although mechanical dampening of the pin stop might produce desirable results, such dampening implementations require space and complexity for various apparatus that are not feasible for process chamber applications. The present invention provides a simple design that is easily implemented in existing and future applications without requiring additional space or complexity. Space considerations are particularly stringent requirements in process chamber applications, and the present invention provides the notable advantage of being easily implemented in process chambers. Additionally, the present invention provides a notable cost savings by being economical to manufacture and install, and by reducing cost of manufacture by reducing or eliminating wafer shifting or breakage and resulting scrap losses. 
    
    
     Other advantages of the invention will become apparent from the following detailed description, taken in conjunction with the accompanying drawings, illustrating by way of example the principles of the invention. 
     BRIEF DESCRIPTION OF THE DRAWINGS 
     The present invention will be readily understood by the following detailed description in conjunction with the accompanying drawings, wherein like reference numerals designate like structural elements. 
     FIG. 1A shows a typical lift pin assembly within a process chamber. 
     FIG. 1B shows a closer view of the lower pin stop shown in FIG.  1 A. 
     FIG. 2 illustrates a combination pin stop in accordance with one embodiment of the present invention. 
     FIG. 3A illustrates a cross-section of combination pin stop in accordance with one embodiment of the present invention. 
     FIG. 3B shows a combination pin stop configured in a housing plate in accordance with an embodiment of the invention. 
     FIG. 4 shows a pin stop assembly implementing a combination pin stop in accordance with one embodiment of the present invention. 
     FIG. 5A is a graph of acceleration over time of a pin stop using a typical hard stop. 
     FIG. 5B shows a graph of acceleration over time of a pin stop using a combination pin stop in accordance with an embodiment of the present invention. 
    
    
     DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENTS 
     An invention for a pin stop for use in lift pin assemblies is disclosed. In preferred embodiments, the pin stop includes a flat head and a combination of a soft stop for dampened deceleration and a hard stop for constant, repeatable, and reliable stop positioning. In the following description, numerous specific details are set forth in order to provide a thorough understanding of the present invention. It will be understood, however, to one skilled in the art, that the present invention may be practiced without some or all of these specific details. In other instances, well known process operations have not been described in detail in order not to unnecessarily obscure the present invention. 
     FIG. 2 illustrates a combination pin stop  100  in accordance with one embodiment of the present invention. The combination pin stop  100  includes a head  102 , center shaft  104 , and base  106 . The center shaft  104  is also known as a pin shaft and pin post. In one embodiment, the center shaft  104  is threaded (not shown) to provide combination pin stop  100  positional adjustment within a mounting. 
     The head  102  of combination pin stop  100  includes a flat face  108  having a soft stop component  110  and a hard stop component  112  configured therein. The soft stop component  110  includes such structures as a washer, bushing, o-ring, or other similar structures to provide an initial soft stop dampened deceleration feature to the combination pin stop  100 . The washer, bushing, o-ring or other similar structure that is the soft stop component  110  can be constructed of any generally flexible and elastic material such as rubber, fiber, polystyrene, and the like. Additional desired properties include strength, resilience, and resistance to heat. In a preferred embodiment of the present invention, the soft stop component is constructed of viton or fluorosilicon. 
     The hard stop component  112  configured on the flat face  108  of the combination pin stop  100  is constructed of generally hard, unforgiving material such a metal. The hard stop component  112  is configured to provide the combination pin stop  100  with the repeatable, reliable stop position characteristic, and therefore is designed to provide a hard and constant surface. Any material suitable for process chamber operation that provides strength, light weight, hardness, and low particulate generation such as stainless steel can be used for the hard stop component. 
     The base  106  is generally configured to provide a feature with which to adjust the position of the combination pin stop  100  within a pin stop housing. As described above, center shaft  104  includes threads in one embodiment for position adjustment within a pin stop housing. Base  106  provides a surface upon which to act with necessary force, such as torsion, to adjust the position of the combination pin stop  100 . 
     FIG. 3A illustrates a cross-section of combination pin stop  100  in accordance with one embodiment of the present invention. As can be seen in FIG. 3A, head  102  of combination pin stop  100  incorporates features providing both soft stop  110  and hard stop  112  components. In one embodiment, groove  109  is configured in head  102  which is open in face  108 . Soft stop  110  is configured to be inserted in groove  109  such that a portion of soft stop  110  is below the plane of face  108  in groove  109  in head  102 , and a portion of soft stop  110  is above the surface of the plane of face  108 , and above the plane of the hard stop  112 . Groove  109  is configured to provide a region into which soft stop  110  can be forced as pressure is applied to a surface of soft stop  110 . In one embodiment of the present invention, the surface to surface contact corresponding to that contact described in reference to FIGS. 1A and 1B correlates to soft stop  110  and hard stop  112  contacting a stopping surface (not shown in FIG.  3 A). Face  108  is configured to contain soft stop  110  and hard stop  112  features, but does not contact the stopping surface. Soft stop  110  absorbs first contact and begins deceleration of the pin stop  100 . As pressure between surfaces of soft stop  110  and the stopping surface increases, soft stop  110  is compressed and forced further into groove  109 . As described above, soft stop  110  is constructed of flexible and elastic materials to allow for absorbing and compressing, as well as return to original shape and volume when pressure is removed. 
     Attachment  113  is provided to attach head  102  to center shaft  104 . Combination pin stop  100  is configured to be compatible with existing pin stop structures. In order to insert a combination pin stop  100  in a housing plate (not shown in FIG.  3 A), it is necessary to remove head  102 . In prior art pin stop structures, the head feature is substantially the same size as the shaft. In one embodiment of the present invention, head  106  is large enough to accommodate a face  108  in which is configured a groove  109  for holding a soft stop  110 . A hard stop  112  is configured substantially over the shaft  104  on face  108 . Because head  102  is generally larger than shaft  104 , attachment  113  is provided to allow shaft  104  to be inserted into a housing plate (not shown in FIG.  3 A), and then head  102  to be attached to center shaft  104  after center shaft  104  is positioned in a housing plate. 
     FIG. 3B shows a combination pin stop  100  configured in a housing plate  150  in accordance with an embodiment of the invention. Threads  114  are provided on shaft  104  in order to fix and adjust the position of the combination pin stop  100  in housing plate  150 . Corresponding threads (not shown) are provided in housing plate  150 . Base  106  can be used to raise and lower the combination pin stop  100  with applied torsion to advance or retract the threaded shaft  114  along the threaded housing plate  150 . Knurled nuts  115  secure the combination pin stop at a desired position within the housing plate  150 . 
     FIG. 3B further illustrates a soft stop  110  configured in groove  109  in face  108  of head  102 . Hard stop  112  is configured in the center of face  108  substantially over shaft  104 . Attachment  113  is shown providing attachment for head  102  to shaft  104 . Attachment  113  is of known mechanical configuration including threaded attachment, slotted attachment, pinned attachment, and the like. 
     FIG. 4 shows a pin stop assembly  130  implementing a combination pin stop  100  in accordance with one embodiment of the present invention. The illustrated pin stop assembly  130  includes an upper pin stop plate  134 , an upper pin stop housing plate  150 , an upper combination pin stop  100   a , a lower pin stop housing plate  152 , and a lower combination pin stop  100   b . Shaft  132  is connected to upper pin stop housing plate  150  at a stop connection end  133 . Shaft  132  is ultimately connected to a yoke at a yoke connection end, and the yoke is configured to hold lift pins (not shown in FIG.  4 ). 
     Movement of shaft  132  in directions shown by directional arrow  136  corresponds to the raising and lowering of lift pins (not shown in FIG.  4 ). The raising of the lift pins includes a movement in an upward direction of shaft  132 . As can be seen in FIG. 4, as shaft  132  moves in an upward direction, upper pin stop housing plate  150  moves upward with shaft  132 , the upper pin stop housing plate  150  being connected to shaft  132  at stop connection end  133 . As upper pin stop housing plate  150  travels upward, upper combination pin stop  100   a  travels upward approaching upper pin stop plate  134 . Upward travel is first slowed when soft stop  110  abuts a stopping surface on an under surface of upper pin stop plate  134 . Upward travel is then halted when the hard stop  112  of upper combination pin stop  100   a  contacts a stopping surface on an under surface of upper pin stop plate  134  as is described in greater detail below. 
     The lowering of the lift pins includes a movement in a downward direction of shaft  136 . As shaft  136  moves in a downward direction, upper pin stop housing plate  150  moves downward with shaft  132 . The upper pin stop housing plate  150  thus moves downward toward lower combination pin stop  100   b . Downward travel is halted when the hard stop  112  of lower combination pin stop  100   b  contacts a stopping surface on an under surface of upper pin stop housing plate  150 . 
     As can be appreciated, when shaft  132  travels downward and therefore lowers the lift pins (not shown in FIG.  4 ), contact between the hard stop  112  of lower combination pin stop  100   b  and a stopping surface on an under surface of upper pin stop housing plate  150  halts downward travel. As described in reference to FIG. 1A, the lowering of the lift pins withdraws the lift pins into a support chuck and positions a wafer on the support chuck. With the wafer positioned on the support chuck, there is no contact between the wafer and the lift pins and it is therefore of little consequence how hard or soft the stop is when the lift pins are lowered. When raising the lift pins, however, a wafer is positioned on at least three lift pins, and the halting of the upward travel of the lift pins by upper pin stop  100   a  contributes to the occurrence or non-occurrence of the undesirable wafer shifting, jumping, or breakage. The embodiments of the present invention are configured to reduce and eliminate such undesirable consequences. In a preferred embodiment, the combination pin stop  100   a  need only be configured to the upper pin stop position, and FIG. 4 is shown with combination pin stops  100   a ,  100   b  in both the upper and lower pin stop positions in accordance with an alternative embodiment. 
     Referring once again to the detail of FIG. 3B, it should be appreciated that as upper combination pin stop  100   a  approaches the under surface of upper pin stop plate  134 , contact first occurs when soft stop  110  abuts the stopping surface. As upward travel continues, soft stop  110  is compressed and slows upward travel until hard stop  112  contacts the under surface of the upper pin stop plate  134 . Hard stop  112  provides a constant, repeatable, and reliable stop point for the lift pins (not shown). Upward travel is halted, and the lift pins are positioned in the same position each and every time. 
     As described above in reference to FIG. 2, one embodiment of the present invention uses viton as a soft stop  110 . As is known, viton is available in different rated degrees of hardness called durameters. The lower the durameter number, the higher the degree of softness or sponginess. In one embodiment of the present invention, the viton rating can range between about 40 durameters and about 90 durameters, with an optimal rating at about 60 to 70 durameters. The durameter of the selected material for soft stop  110  can be varied according to the specific process and environment. By way of example, a large or heavy substrate may support a higher durameter rating than a smaller or lighter substrate. Additional factors such as temperature or pressure in the processing environment, and in the vicinity of the pin stops, may indicate variation in the durameter of the selected material for a soft stop. In one embodiment, the soft stop  110  functions to dampen the deceleration of the pin stop  100  without insulating or preventing the hard stop  112  from producing a constant, reliable, and repeatable stop. 
     FIGS. 5A and 5B present a graphical representation of the effect of the combination of soft and hard stops in one combination pin stop. FIG. 5A is a graph  160  of acceleration over time of a pin stop using a typical hard stop. Acceleration “g” is denoted on the vertical axis, and time “t” is denoted on the horizontal axis so that the graph  160  shows the variance of acceleration over time. Point  162  represents time  0  when the action of the lift pin is initiated. The pin stop accelerates to a point  164  at which time it achieves constant velocity. At point  166 , the hard stop contacts the pin stop surface resulting in immediate and abrupt deceleration (negative acceleration)  168 . The abrupt, hard stop results in vibration or noise shown in region  170  before returning to steady state at  172 . It is during the region shown as  170  that undesirable wafer shifting or breakage occurs. 
     FIG. 5B shows a graph  174  of acceleration over time of a pin stop using a combination pin stop in accordance with an embodiment of the present invention. As in FIG. 5A, acceleration “g” is denoted on the vertical axis, and time “t” is denoted on the horizontal axis so that the graph  174  shows the variance of acceleration over time. Point  162  represents time  0  when the action of the lift pin is initiated. The pin stop accelerates to a point  164  at which time it achieves constant velocity. At point  176 , the soft stop contacts the pin stopping surface resulting in a gradual deceleration until the hard stop contacts the pin stop surface at point  177 . After the hard stop halts travel at the constant, repeatable and reliable position, there is some resulting noise  178  prior to steady state  172 , but it is much less pronounced than with a typical hard stop, and much less likely to produce wafer shifting or breakage. 
     Thus configured, the combination pin stop dampens the deceleration of the pin stop while maintaining a constant, reliable, and repeatable pin stop and wafer positioning. The present invention provides an effective pin stop without increasing the complexity of the design and adjustment of lift pin assemblies, and is configurable to existing lift pin assembly applications. The present invention provides for reducing or eliminating wafer shifting and wafer breakage. 
     Although the foregoing invention has been described in some detail for purposes of clarity of understanding, it will be apparent that certain changes and modifications may be practiced within the scope of the appended claims. Accordingly, the present embodiments are to be considered as illustrative and not restrictive, and the invention is not to be limited to the details given herein, but may be modified within the scope and equivalents of the appended claims.