Abstract:
A system for controlling an axial movement of an article is presented. The system comprises a support stage assembly and a spring suspension arrangement mounted on the support stage assembly. The spring suspension arrangement comprises first and second assemblies arranged in a coaxial relationship one inside the other. The first assembly is attached to the support stage assembly. The second assembly serves for supporting an article-carrying member and is driven for movement along the axis with respect to the first assembly. The outer one of the first and second assemblies is configured to define two spaced-apart parallel planes perpendicular to said axis. The first and second assemblies are attached to each other by first and second membrane-like members arranged in a spaced-apart parallel relationship along said axis.

Description:
FIELD OF THE INVENTION  
       [0001]     This invention relates to an article transfer system, particularly useful in applications where precise positioning of an article with respect to a processing or metrology tool is required.  
       BACKGROUND OF THE INVENTION  
       [0002]     Various applications, such as article inspection and measurements, as well as lithography processing, require precise movement of the article with respect to a processing tool along a vertical axis (Z-axis). For example, in the manufacture of semiconductor devices, as well as testing of circuits on semiconductor wafers, the wafer is typically supported on a stage mounted for a Z-axis movement (Z-stage) and sometimes also for rotation (Z/Theta stage).  
         [0003]     U.S. Pat. No. 5,150,040 discloses a dual mode Z/Theta stage for supporting and moving a workpiece, such as a semiconductor wafer, for positioning during testing. The Z/Theta stage has a peripheral four-point elevator drive. The elevating suspension comprises parallel, vertically oriented, rigid lift pins, which bear the weight of a top-plate. The lift pins are located about the periphery of the stage to provide stability of the support. The top plate essentially floats on the lift pins so that virtually no frictional forces are translated to lift pins. The lift pins are elevated together by the force of four matched pin lift levers, crank arms. The crank arms are driven by downward force from a vertically translating air piston, which is in contact with the crank arms. The air piston provides a gentle force moderated by pneumatic pressure, which can moderate the full force of a stepping motor that drives it.  
       SUMMARY OF THE INVENTION  
       [0004]     There is a need in the art to facilitate processing of articles by supporting an article on an article transfer system enabling precise movement of the article along a vertical axis. Here, the term “processing” signifies also measurement or inspection of articles.  
         [0005]     The system of the present invention has a simple construction allowing precise movement of an article along a vertical axis (Z-axis) within a limited range of distances, and preferably also rotation of the article about the Z-axis.  
         [0006]     The main idea of the present invention consists of utilizing a spring suspension arrangement for supporting an article-carrying member. The spring suspension arrangement is formed by two assemblies arranged in a coaxial relationship, one inside the other, wherein the outer assembly is configured to define two spaced-apart parallel planes perpendicular to the vertical axis. The arrangement is such that the first assembly is kept at a fixed position, and the second assembly, which is intended for supporting an article-carrying member, is driven for movement along a vertical axis with respect to the first assembly, while the assemblies are attached to each other by first and second membrane-like members arranged in a spaced-apart parallel relationship along the vertical axis. The vertical movement of the second assembly causes the deformation of the membrane-like members, thereby limiting the movement of the second assembly (and consequently the article-carrying member) by the deformability of membranes.  
         [0007]     Thus, according to a broad aspect of the present invention, there is provided a system for controlling an axial movement of an article, the system comprising: 
        a support stage assembly;     a spring suspension arrangement mounted on said support stage assembly and comprising first and second assemblies arranged in a coaxial relationship one inside the other, the first assembly being attached to said support stage assembly and the second assembly serving for supporting an article-carrying member and being driven for movement along said axis with respect to the first assembly, the outer one of the first and second assemblies being configured to define two spaced-apart parallel planes perpendicular to said axis, said first and second assemblies being attached to each other by first and second membrane-like members arranged in a spaced-apart parallel relationship along said axis.        
 
         [0010]     According to one embodiment of the invention, the outer assembly is composed of at least three spaced-apart pin-like members kept at a fixed position with respect to one another, and the inner assembly is composed of at least one pin-like member. According to another preferred embodiment of the invention, the outer and inner assemblies are configured as cylinders or prisms, of preferably substantially the same height. The inner assembly at its top and bottom is attached to the top and bottom of the outer assembly by said first and second membrane-like members, respectively. The membrane-like members are preferably of annular geometry, and may be clamped to the opposite sides of each of the outer and inner assemblies via clamping rings.  
         [0011]     According to another aspect of the invention, there is provided a system for controlling movement of an article along at least a vertical axis, the system comprising: 
        a support stage assembly;     a spring suspension arrangement mounted on said support stage assembly and comprising first and second vertically oriented cylindrical assemblies arranged in a coaxial relationship one inside the other, the first assembly being attached to said support stage assembly and the second assembly serving for supporting an article-carrying member and being driven for movement along the vertical axis with respect to the first assembly, the inner cylindrical assembly at its top and bottom being attached to the top and bottom of the outer cylindrical assembly by, respectively, first and second membrane-like members thereby arranged in a spaced-apart parallel relationship along the vertical axis.        
 
         [0014]     According to yet another aspect of the invention, there is provided a system for controlling movement of an article along at least a vertical axis, the system comprising: 
        a support stage assembly;     a spring suspension arrangement mounted on said support stage assembly and comprising first and second vertically oriented cylindrical assemblies arranged in a coaxial relationship one inside the other, the outer cylindrical assembly being attached to said support stage assembly and the inner cylindrical assembly serving for supporting an article-carrying member and being driven for movement along the vertical axis with respect to the outer assembly, the inner cylindrical assembly at its top and bottom being attached to the top and bottom of the outer cylindrical assembly by, respectively, first and second membrane-like members being thereby arranged in a spaced-apart parallel relationship along the vertical axis,     a drive assembly associated with said inner cylindrical assembly and operable to provide said movement thereof.        
 
         [0018]     The article-carrying member mounted on the second assembly may be driven for rotation with respect to said second assembly in a plane perpendicular to said axis of movement of the second assembly. The support stage assembly may be driven for movement in a plane perpendicular to said axis of movement of the second assembly. Considering a disk-like article, the support stage assembly is preferably movable along at least one perpendicular axis for a distance of at least a radius of the article The system may thus be operable as a Z-Theta-stage, R-Z-Theta-stage or X-Y-Z-Theta-stage.  
         [0019]     Thus, according to yet another aspects of the invention, there are provided an R-Theta-Z system and an X-Y-Theta-Z system for controlling movement of an article including the above-described spring suspension arrangement.  
         [0020]     The system of the present invention has a simple (and low cost) construction, which can be operable by a simple servo-control mechanism and provides for smoothness of the article movement with high precision. These features are of great importance for such applications as processing/inspection/measurements of semiconductor wafer structures. Generally, the system of the present invention can advantageously be used in optical measurements (precise focusing), electrical measurements (e.g., in four point probe measurements), near field measurements (e.g., eddy current based resistivity measurements), etc. 
     
    
     BRIEF DESCRIPTION OF THE DRAWINGS  
       [0021]     In order to understand the invention and to see how it may be carried out in practice, a preferred embodiment will now be described, by way of non-limiting example only, with reference to the accompanying drawings, in which:  
         [0022]      FIGS. 1A and 1B  schematically illustrate the main constructional and operational principles of an article transfer and positioning system according to the invention, where  FIG. 1A  shows the system in an initial, non-deformated state of membranes of a spring suspension arrangement, and  FIG. 1B  shows the system in an operative state with the membranes being deformated.  
         [0023]      FIG. 2  exemplifies a specific implementation of the system of the present the invention;  
         [0024]      FIG. 3  more specifically illustrates a part of the system of  FIG. 2  configured to provide rotation of an article supporting element about the Z-axis; and  
         [0025]      FIG. 4A  schematically illustrates a Z-R-Theta-system of the present invention; and  
         [0026]      FIG. 4B  shows an exploded view of the Z-R-Theta-system of  FIG. 4A . 
     
    
     DETAILED DESCRIPTION OF THE INVENTION  
       [0027]     The present invention provides an article transfer and positioning system configured and operable to enable precise movement of the article along a vertical axis (Z-axis), and preferable also rotation about the Z-axis.  
         [0028]      FIGS. 1A and 1B  schematically illustrate the main constructional and operational principles of a system  10  according to the invention. The system  10  includes such main constructional parts as a support stage assembly  12  and a spring arrangement  11  mounted on the support stage assembly  12 . The stage  12  may be driven for movement in a horizontal plane, presenting the so-called X-Y-stage or alternatively R-Theta stage.  
         [0029]     The spring arrangement  11  includes inner and outer assemblies  14 A and  14 B, wherein one of these assemblies—the outer assembly  14 A in the present example—is attached to the stage  12  and define upper and lower horizontal planes P 1  and P 2 . The other assembly—inner assembly  14 B in the present example—is attached to the assembly  14 A in a manner to be vertically movable with respect to the assembly  14 A within a limited range of distances. This is achieved by attaching the assemblies  14 A and  14 B to each other via two membrane-like members M 1  and M 2 . Thus, driving of the inner assembly  14 B for movement along the Z-axis would result in the simultaneous deformation of the membranes M 1  and M 2  ( FIG. 1B ), the limits of the Z-movement being defined by the deformability of the membranes and their dimensions. As shown in the figure in dashed lines, an article-carrying member  18  is mounted on the inner assembly  14 B, and would thus be movable together with the assembly  14 B. The membranes are preferably identical and are centered at the central axis CA of the inner assembly  14 B.  
         [0030]     It should be understood that, alternatively, the same effect could be achieved by attaching the inner assembly  14 B to the stage  12 , rather than the outer assembly  14 A, and driving the outer assembly  14 A for movement along the Z-axis in a similar manner.  
         [0031]     Driving of the inner assembly  14 B (or outer assembly, as the case may be) along the Z-axis can generally be achieved by associating this assembly with any suitable linear driver  20 .  
         [0032]     It should also be understood that, generally, in order to define the upper and lower planes for the membranes&#39; location (in their non-deformable position), the outer assembly  14 A can be formed by at least three spaced-apart members (e.g. rods or struts) N 1 -N 3 , preferably arranged so as to form a regular polygon (equilateral triangle in the present example) that are fixed to the stage  12  and are kept at a fixed position with respect to one another. As for the inner assembly, it may be in the form of a member (e.g. rod-shaped) N 4  located at the center of this polygon. Preferably, the assemblies  14 A and  14 B are configured as outer and inner prisms or cylinders.  
         [0033]     Referring to  FIG. 2 , there is illustrated a specific, but non-limiting, example of implementation of a system  100  according to the invention for use in transferring and positioning of articles. The system  100  is configured as a Z-stage, and preferably also as an R-Theta-stage. The system  100  comprises a spring suspension arrangement  110  mounted on a stage assembly  112 . The stage  112  can be mounted for movement in a horizontal plane along one or two perpendicular axes (X-Y plane), i.e., presents an X-stage.  
         [0034]     The spring arrangement  110  is formed by outer and inner cylinder-like assemblies (drums)  114 A and  114 B. The outer drum  114 A is formed with openings, generally at  115 , the provision of which is optional and is aimed at decreasing the weight of the entire construction and also at allowing access to the inner parts of the construction (e.g., for maintenance purposes). The drums  114 A and  114 B are attached to each other by top and bottom membrane-like members M 1  and M 2  (for example made of a stainless steel and having a thickness of 0.5 mm). The membranes M 1  and M 2  have an annular shape and are clamped to the drums by means of clamping rings  117 A and  117 B, respectively, and bolts  119 A and  119 B.  
         [0035]     Further provided in the system  100  is a drive assembly  116  configured and operated for providing a movement of the drum  114 B along the Z-axis. In the present example, the drive assembly  116  comprises a mechanical pair formed by a roller bearing  116 A mounted on a central axis (shaft) CA of the inner drum  114 B and a wedge element  116 B supporting the bearing  116 A on its inclined surface. A linear motor  116 C is provided being connected to the wedge element  116 B for moving it along the X-axis. Thus, when the wedge  116 A is driven for a back and forward movement along the X-axis, the roller bearing  116 B drives the inner assembly  114 B for movement along the Z-axis. The inner drum  114 B serves for supporting an article holding assembly  118 . In the present example, where measurements/inspection/processing of semiconductor wafers is considered, the wafer supporting assembly  118  includes a chuck unit  120  preferably mounted for rotation in the horizontal plane. Considering rotation of the chuck carrying a disk-like article (e.g., semiconductor wafer), the stage  112  is movable along the X-axis within the range defined by the radius of the article (of at least the wafer&#39;s radius). The system  100  thus presents the Z-R-Theta stage. It should be understood that, generally, the system  100  might utilize X-Y-movement of the stage  112  with and without a rotation of the chuck unit  120 .  
         [0036]      FIG. 3 , which is a cross-sectional view of a part of the system  100 , more specifically illustrates the chuck unit  120  mounted on the inner drum  114 B. As shown, the chuck unit  120  is mounted on a rotor-part  124 A of a motor  124 , whose stator-part  124 B is attached to the inner drum  114 B. As further shown in  FIGS. 2 and 3 , the chuck unit  120  is mounted on a shaft of the rotor-part  124 A via a pair of spherical washers  125 A (male) and  125 B (female) facing each other by their concave and convex surfaces and a bolt  126 , e.g. spherical washers DIN 6319 commercially available from Ganter Griff. While mounting the chuck, its precise horizontal positioning can be regulated by displacing the washers with respect to each other.  
         [0037]     Reference is now made to  FIGS. 4A and 4B  showing the entire construction of the system  100  being used for supporting an article, e.g., wafer W (300 mm diameter). The configuration of the system  100  presents an accurate R-Theta-Z-system that can be operable as an integrated or stand-alone wafer stage platform. In the present example, the system  100  is used for auto-focusing purposes to control the wafer&#39;s in-focus position relative to an optical measuring module located above the wafer (not shown).  
         [0038]     Wafer W is hold by a buffer unit (frame)  130 . The construction and operation of the buffer unit  130  does not form a part of the present invention and therefore need not be specifically described. The preferred implementation of the buffer unit  130  is disclosed in co-pending U.S. application Ser. No. 10/232,384 assigned to the assignee of the present application. The buffer unit  130  is mounted on the stage  112  and associated with a drive mechanism (not shown) to be movable along the Z-axis with respect to the stage  112 , and consequently with respect to the chuck unit  120 , which is mounted on the inner drum  114 B of the spring suspension arrangement. The chuck  120  is typically provided with openings for vacuum holding of the wafer. Considering the use of such a buffer unit for gripping and holding a wafer (load/unload station), the diameter of the chuck  120  is smaller than the diameter of the wafer. The chuck  120  is movable along the Z-axis (due to the movement of the drum of spring suspension arrangement) within a 1 mm-distance at a 0.1 μm precision, and is 360-degree rotatable. In the present example, also mounted on the stage  112  is an optical system  132  serving as the so-called “notch finder” for identifying a wafer located on the chuck and/or providing angular positioning of the wafer with respect to a processing tool (measurement, inspection, etc. tool).  
         [0039]     Those skilled in the art will readily appreciate that various modifications and changes can be applied to the embodiments of the invention as hereinbefore described without departing from its scope as defined in and by the appended claims.