Abstract:
A robot assembly for transferring substrates includes a central tube assembly oriented along a central axis, perpendicular to a substrate transfer plane, and having an inner surface that forms part of a first enclosure at a first pressure, and an outer surface that forms part of a second enclosure at a second, different pressure. The robot assembly further includes a transfer robot which itself includes multiple rotor assemblies, each configured to rotate parallel to the substrate transfer plane. The various rotor assemblies are organized in pairs, each pair having one rotor fitted with a telescoping support arm/end effector arrangement to support substrates thereon, and the other rotor fitted with inner and outer actuator arms that cooperate to effect radial movement of the corresponding end effector of the paired rotor assembly. Each rotor is controlled to effect the transfer of substrates within a wafer processing system asynchronously and at differing heights.

Description:
RELATED APPLICATIONS 
       [0001]    This application is a non-provisional of and claims the priority benefit of U.S. Provisional Patent Application Nos. 60/847,828, filed 27 Sep. 2006, and 60/890,835, filed 20 Feb. 2007, each of which is incorporated herein by reference. 
     
    
     FIELD OF THE INVENTION 
       [0002]    The present invention relates to the field of wafer handling and transfer systems used in semiconductor manufacturing. 
       BACKGROUND 
       [0003]    In semiconductor processing systems, particularly those operating under high vacuum conditions, semiconductor wafers must be transferred into and out of process modules where steps in the manufacturing process take place. Since the cost of wafer processing is dependent on the throughput of the system, it is imperative that wafers be removed from each process module as soon as each module has completed processing the wafer which was loaded into it. Such transfers to/from processing modules are performed by so-called transfer robots. 
         [0004]    Conventional transfer robots were typically designed to transfer only one wafer at a time, or to transfer two wafers at a time but only simultaneously (i.e., not asynchronously). Typically a number of process modules are mounted around the perimeter of a transfer chamber containing a transfer robot. Hence, for enhanced system throughput, it is common to configure the transfer robot to be capable of transferring wafers into process modules at fixed relative orientations to each other (e.g., side-by-side, or at 180° separation around the transfer chamber perimeter). 
         [0005]      FIG. 39  is adapted from U.S. Pat. No. 5,993,141, and shows a conventional dual wafer robot  3910 , which is limited to wafer handling within a single plane. In the following description, let x represent either a or b in  FIG. 39 . Linear track, section  3912   x  is pivotally mounted to a rotatable stage  3914  by pivot pin  3916   x.  Motorized platen  3918   x  is slidably mounted on linear track section  3912   x  and carries an end effector  3920   x  on a leading (outer) edge. The upper surface of linear track section  3912   x  includes a linear bearing  3922   x,  along each of the longitudinal edges thereof to guide the motorized platen  3918   x.  The central portion of track section  3912   x  includes a plurality of raised metal edges  3924  (preferably formed of a ferromagnetic material), disposed in a spaced, parallel relation to one another and substantially perpendicular to the linear bearings  3922   x.  A plurality of coils (not shown) in motorized platen  3918   x  electromagnetically interact with raised edges  3924  to drive platen  3918   x  along the track section  3912   x.  The extension and retraction motions of end effectors  3920   a  and  3920   b  of this robot may function asynchronously, but are limited to operation with both end effectors  3920   a  and  3920   b  being in the same plane since both linear track sections  3912   a  and  3912   b  are attached to rotatable stage  3914 . 
         [0006]      FIG. 40  is adapted from U.S. Pat. No. 6,071,055, and show&#39;s a portion of a dual wafer robot  4010  that is limited to wafer handling in a tandem configuration with simultaneous motion of both wafers in the same plane. The dual wafer robot  4010  is housed in transfer chamber  4012 , shown with three dual wafer process chambers  4014  attached. Transfer of wafers into/out of process modules  4014  is through vacuum valves  4016 . Note that this dual wafer robot design, with both end effectors locked together in a U-shaped assembly, inherently must transfer both wafers: (1) simultaneously, (2) in the same plane, and (3) only into a single dual-wafer process module  4014 . 
         [0007]      FIG. 41  is adapted from U.S. Pat. No. 5,678,980 and illustrates a dual wafer robot that is limited to single wafer loading and unloading. In this design, end effector  4110  is supported and moved by outer arms  4114  and  4116 . Similarly, end effector  4112  is supported and moved by outer arms  4118  and  4120 . Outer arms  4114 ,  4116 ,  4118  and  4120  are attached to, and moved by, center arras  4122  and  4124 . 
         [0008]    In view (A) of  FIG. 41 , center arm  4124  is rotating (arrow at upper center) counter-clockwise around pivot  4126 , while center arm  4122  is rotating (arrow at lower center) at the same speed clockwise around pivot  4126 . The combined motion of arms  4122  and  4124  causes outer arms  4114  and  4116  to extend end effector  4110  as shown by the left arrow. Simultaneously, outer arms  4118  and  4120  are retracting end effector  4112  as shown by the right arrow. Because the outer arms  4114 ,  4116 ,  4118 , and  4120  are longer than central arms  4122  and  4124 , end effector  4110  moves much farther outwards than end effector  4112  moves inwards. 
         [0009]    In view (B) of  FIG. 41 , center arms  4122  and  4124  are rotating (arrows at center) in the opposite directions from view (A), thus end effector  4112  is extending (right arrow), while end effector  4110  is retracting (left arrow) towards the center. 
         [0010]    In view (C) of  FIG. 41 , center arms  4122  and  4124  are positioned 180° relative to each other, making the radial positions of end effectors  4110  and  4112  the same. Arms  4122  and  4124  are rotating clockwise (arrows at center) at the same speed, causing end effectors  4110  and  4112  to rotate clockwise around pivot  4126  (arrows at left and right). 
         [0011]    Note that in this dual wafer design, the wafers are restricted to a 180° orientation, and only one end effector can be extended at a time (while the other end effector must be retracted). Also, for pick-and-place operation (where a processed wafer is removed and another wafer is immediately placed into a process module), it is necessary to rotate the robot a full 180° to insert a wafer following removal of a processed wafer, thereby decreasing system throughput. 
         [0012]      FIG. 42  is adapted from U.S. Pat. No. 5,794,487 and illustrates a dual wafer robot  4210  that is limited to single wafer loading and unloading (i.e., one which cannot load two wafers simultaneously). Lower arm link  4212  is connected to base  4214  through shoulder  4216 , which enables 360° rotation. Upper arm link  4218  is connected to lower arm link  4212  through elbow  4220 , which enables relative motion between upper arm link  4218  and lower arm link  4212 . Two end effectors  4222  are mounted with a 180° relative orientation on central support  4224 , which contains wrist  4226 . Extension and retraction of end effectors  4222  is effected by changing the angle between upper arm link  4218  and lower arm link  4212 . Thus, in this dual wafer robot, only a single wafer can be loaded or unloaded at a time, since if one of the two end effectors  4222  is extended, the other end effector  4222  is necessarily retracted at the same time. 
         [0013]      FIG. 43  is adapted from U.S. Pat. No. 5,539,266 and illustrates a robot actuator having two motors, each requiring a magnetic air-to-vacuum coupler separate from the robot motors. In particular, this actuator includes two coaxial magnetic couplers for driving the robot mechanism. The coupler mechanism consists of two primary rings  4312  and  4314  of permanent magnets located outside the vacuum chamber wall  4316  (i.e., in air) and mounted for rotation about a common axis  4318 . 
         [0014]    For example, first primary ring  4312  may be mounted on a flanged shaft  4320 , driven by motor M 2   4322 . Second primary ring  4314  may be mounted on a flanged bushing  4324  that is driven by motor M 1   4326 , where flanged bushing  4324  is rotatably mounted on shaft  4320 . Motors M 1   4326  and M 2   4322  are servo motors of conventional design. 
         [0015]    Both primary rings  4312  and  4314  include a large number of permanent magnets oriented radially with alternating N and S poles directed outwards. Flux rings  4328  and  4330  provide flux return paths for the permanent magnets in primary rings  4312  and  4314 , respectively. All components  4312 ,  4314 ,  4320 ,  4322 ,  4324 ,  4326 ,  4328  and  4330 , are mounted outside of vacuum wall  4316  (in air). 
         [0016]    Secondary ring  4332  includes flux return path  4334  and a plurality of permanent magnets (the same number as in primary ring  4312 ). Secondary ring  4336  includes flux return path  4338  and a plurality of permanent magnets (the same number as in primary ring  4314 ). The permanent magnets in secondary rings  4332  and  4336  are attracted through vacuum wall  4316  to the permanent magnets in primary rings  4312  and  4314 , respectively. Angular movements of primary rings  4312  and  4314  are thereby coupled to secondary rings  4332  and  4336 , respectively. Angular movements of secondary rings  4332  and  4336  are coupled to the in-vacuum robot actuation mechanism. 
         [0017]    Note that in this prior art robot drive mechanism, the drive motors are completely separate from the function of coupling motion through vacuum wall  4316 . For each of the two magnetic couplers, two sets of permanent magnets are required: one set directly coupled to the motor (but not part of the motor), and a second set directly coupled to the robot actuator and magnetically coupled to the first set of permanent magnets. 
       SUMMARY OF THE INVENTION 
       [0018]    In various embodiments, the present invention provides a robot assembly for transferring substrates, for example, semiconductor wafers and the like. The robot assembly includes a central tube assembly oriented along a central axis and having an inner surface that forms part of a first enclosure at a first pressure, and an outer surface that forms part of a second enclosure at a second pressure. The second pressure is generally different from said first pressure. A substrate transfer plane is perpendicular to the central axis of the central tube assembly. The robot assembly further includes a first transfer robot which itself includes a first rotor assembly and a second rotor assembly, each of which is configured to rotate parallel to the substrate transfer plane concentrically with the outer surface of the central tube assembly. In one embodiment, the second rotor assembly is positioned above the first rotor assembly. 
         [0019]    The first transfer robot may further include a first support arm, rigidly attached to the first rotor assembly and extending radially outwards therefrom, a first slider, supported by the first support arm and configured to move in a generally radial direction along a length of said first support arm; a first end effector, supported by the first slider and configured to move in a generally radial direction along a length thereof; a first inner actuator arm, having an inner end rigidly attached to said second rotor assembly and also having an outer end; and a first outer actuator arm, having a first end ratably coupled to the outer end of the first inner actuator arm by a first bearing so as to permit rotation of the first outer actuator arm parallel to the substrate transfer plane, and a second end ratably coupled to the first end effector by a second bearing to permit rotation of the first outer actuator arm parallel to the substrate transfer plane. 
         [0020]    In some cases, the first rotor assembly may be mounted on the central tube assembly by first bearing means, and the second rotor assembly may be mounted on the first rotor assembly by second bearing means. Alternatively, the first and second rotor assembles may each be mounted on the central tube assembly by respective first and second bearing means or respective first and second multiplicities of bearing means. In one particular example, the first and second rotor assembles are each mounted on the central tube assembly by two bearing means. 
         [0021]    In some embodiments of the invention, the first rotor assembly of the transfer robot includes a first motor rotor assembly. That first motor rotor assembly may itself include a first multiplicity of permanent magnets attached to a first flux return ring, and arranged in alternating North pole and South pole orientations radially inwards. Likewise, the second rotor assembly may include a second motor rotor assembly, having a second multiplicity of permanent magnets attached to a second flux return ring, and arranged in alternating North pole and South pole orientations radially. 
         [0022]    In some cases, the central tube assembly of the robot assembly includes a first stator positioned generally in a first common plane with the first motor rotor assembly and inside the first enclosure. The first stator may include a first multiplicity of pole faces oriented radially outwards towards the multiplicity of permanent magnets of the first motor rotor. Likewise, a second stator may be positioned generally in a second common plane with the second motor rotor assembly and inside the first enclosure. The second stator may include a second multiplicity of pole faces oriented radially outwards towards the multiplicity of permanent magnets of the second motor rotor. 
         [0023]    To provide control of the robot assembly, the first stator and said second stator may be electrically connected to a motor control system configured to vary magnetic field excitations of (i) the multiplicity of pole faces in said first stator, and (ii) the multiplicity of pole faces in said second stator, thereby to induce rotation of the first rotor assembly and the second rotor assembly, respectively. 
         [0024]    In some embodiments of the invention, the robot assembly may include a first middle actuator arm, having a first end and a second end, wherein the first end of the first middle actuator arm is coupled to the first inner actuator arm at a location on the first inner actuator arm approximately halfway between its inner and outer ends by a third bearing, enabling the first middle actuator arm to rotate around an axis parallel to the substrate transfer plane. Also, a second end of the first middle actuator arm may be coupled to the first slider by a fourth bearing, enabling the first middle actuator arm to rotate around parallel to the substrate transfer plane. 
         [0025]    In still further embodiments of the invention, the robot assembly may include third and fourth rotor assemblies, each configured to rotate parallel to the substrate transfer plane, concentrically with the outer surface of the central tube assembly. In some cases, the fourth rotor assembly may be positioned below said third rotor assembly. Generally, the third rotor assembly may be configured similarly to the first rotor assembly with a second support arm, second slider and second end effector, and the fourth rotor assembly may be configured similarly to the second rotor assembly with a second inner actuator arm and second outer actuator arm. The third and fourth rotor assemblies may be attached to the central tube assembly in any of the same configurations as the first and second rotor assemblies may be so attached. Likewise, similar arrangements of motor rotor assemblies and stators may be used in connection with the third and fourth rotor assemblies as were used for the first and second rotor assemblies, respectively. 
         [0026]    In some cases, the robot assembly may include a bellows, having an upper and a lower end, oriented generally along the central axis of said central tube assembly, wherein the upper end of the bellows is attached with a vacuum seal to the lower end of said central tube assembly, and the lower end of said bellows is attached with a vacuum seal to the second enclosure. 
         [0027]    In addition, a vertical actuator assembly attached to the central tube assembly within the first enclosure may enable vertical motion of the central tube assembly relative to the second enclosure. Thus, this vertical motion enables simultaneous vertical motion of both the first and second end effectors. 
         [0028]    In some cases, first and second rollers may be attached to the outer surface of the central tube assembly. In such cases, a first cam, attached to the first rotor assembly and positioned to be in contact with the first roller, and a second cam attached to the third rotor assembly, and positioned to be in contact with said second roller, may be used to effect the vertical displacement of components of the robot assembly. For example, the first cam may have a profile shaped to vary the vertical position of the first rotor during rotation thereof said, thereby affecting vertical motion of the first end effector. Likewise, the second cam may have a profile shaped to vary the vertical position of the third rotor during rotation thereof, thereby affecting vertical motion of the second end effector. Alternatively, the cams may be attached to the outer surface of central tube assembly. 
         [0029]    Other embodiments, features and advantages of the present invention are discussed in detail below and recited specifically in the claims following said description. 
     
    
     
       BRIEF DESCRIPTION OF THE DRAWINGS 
         [0030]    Other advantages and features of the present invention will be apparent from the following detailed description of the invention when taken in conjunction with the accompanying drawings, in which: 
           [0031]      FIG. 1A  is an isometric view of a four process module cluster tool configured in accordance with an embodiment of the present invention. 
           [0032]      FIG. 1B  is a top view of the four process module cluster tool illustrated in  FIG. 1A . 
           [0033]      FIG. 2A  is an isometric view of a six process module cluster tool configured in accordance with an embodiment of the present invention. 
           [0034]      FIG. 2B  is a top view of the six process module cluster tool shown in  FIG. 2A . 
           [0035]      FIG. 3A  is an isometric view of an eight process module cluster tool configured in accordance with an embodiment of the present invention. 
           [0036]      FIG. 3B  is a top view of the eight process module cluster tool shown in  FIG. 3A . 
           [0037]      FIG. 4A  is an isometric view of a dual wafer robot configured in accordance with one embodiment of the present invention and showing two end effectors (each carrying a single wafer) in an above and below arrangement on one side of the robot&#39;s rotational axis, where both end effectors are fully retracted. 
           [0038]      FIG. 4B  is a top view of the dual wafer robot illustrated in  FIG. 4A . 
           [0039]      FIG. 4C  is a side view of the dual wafer robot illustrated in  FIGS. 4A-B . 
           [0040]      FIG. 5A  is a top view of a dual wafer robot configured in accordance with an embodiment of the present invention and showing two end effectors (each carrying a single wafer) in an above and below arrangement, where both end effectors are fully extended for loading/unloading two wafers into/out of a pass-through chamber. 
           [0041]      FIG. 5B  is a side view of the dual wafer robot shown in  FIG. 5A . 
           [0042]      FIG. 6A  is an isometric view of a dual wafer robot configured in accordance with an embodiment of the present invention and showing two end effectors (each carrying a single wafer) oriented 180° azimuthally opposed to one another around the robot&#39;s rotational axis, where both end effectors are fully retracted. 
           [0043]      FIG. 6B  is a top view of the dual wafer robot shown in  FIG. 6A . 
           [0044]      FIG. 6C  is a side view of the dual wafer robot shown in  FIGS. 6A-B . 
           [0045]      FIG. 7  is a top view of a dual wafer robot configured in accordance with an embodiment of the present invention and showing two end effectors (each carrying a single wafer) oriented 180° azimuthally opposed to one another around the robot&#39;s rotational axis, where both end effectors are fully extended for loading/unloading a wafer into/out of each of two process modules. 
           [0046]      FIG. 8  is a top view of a dual wafer robot configured in accordance with an embodiment of the present invention and showing two end effectors (each carrying a single wafer) in an above and below arrangement, where the upper end effector is fully extended, and the lower end effector is partially extended, illustrating independent (asynchronous) operation of the two end effectors. 
           [0047]      FIG. 9  is a top view of a dual wafer robot configured in accordance with an embodiment of the present invention and showing two end effectors (each carrying a single wafer) oriented 180° azimuthally opposed to one another around the robot&#39;s rotational axis, where the upper end effector is fully extended and the lower end effector is fully retracted, illustrating independent (asynchronous) operation of the two end effectors. 
           [0048]      FIG. 10  is a top view of a dual wafer robot configured in accordance with an embodiment of the present invention and showing two end effectors (each carrying a single wafer) oriented 90° azimuthally around the robot&#39;s rotational axis with respect to one another, where the upper end effector is fully extended, and the lower end effector is fully retracted, illustrating independent operation of the two end effectors. 
           [0049]      FIG. 11  is a top view of a dual wafer robot configured in accordance with an embodiment of the present invention and showing two end effectors (each carrying a single wafer) oriented 90° azimuthally around the robot&#39;s rotational axis with respect to one another, where the upper end effector is partially extended, and the lower end effector is fully extended, illustrating independent operation of the two end effectors. 
           [0050]      FIG. 12  is a schematic top view of a single robot end effector actuator assembly configured in accordance with an embodiment of the present invention and showing the end effector in three positions: (A) fully retracted, (B) partially extended, and (C) fully extended. 
           [0051]      FIG. 13  is a side view of a single robot end effector actuator configured in accordance with an embodiment of the present invention and showing the end effector fully extended, with a cutaway view of an actuator motor. 
           [0052]      FIG. 14  is a side view in partial cutaway of a single robot end effector actuator in accordance with one embodiment showing an actuator motor. 
           [0053]      FIG. 15  is a schematic top view of an actuator motor and angular position encoder configured in accordance with an embodiment of the present invention. 
           [0054]      FIG. 16  is a schematic of a control system for a single robot configured in accordance with an embodiment of the present invention. 
           [0055]      FIG. 17  is an isometric cutaway view of a dual wafer robot configured in accordance with an embodiment of the present invention. 
           [0056]      FIG. 18  is a cutaway side view of a single robot actuator configured in accordance with an embodiment of the present invention. 
           [0057]      FIG. 19  is a schematic side cross-section of a single robot actuator configured in accordance with an embodiment of the present invention. 
           [0058]      FIG. 20  is a schematic illustration of the operation of two height-controlling cams, one for each of the end effectors, in a dual wafer robot configured in accordance with an embodiment of the present invention. 
           [0059]      FIG. 21  is a schematic view of the operation of a collective Z-motion actuator configured in accordance with an embodiment of the present invention. 
           [0060]      FIG. 22  is a schematic illustration of a wafer transfer process in accordance with an embodiment of the present invention. 
           [0061]      FIG. 23  is a schematic illustration of the three phases of the end effector extension process. 
           [0062]      FIG. 24  is a schematic illustration of an end effector rotation process in accordance with an embodiment of the present invention. 
           [0063]      FIG. 25  is a chart plotting end effector extension distance versus the angle of an actuator arm during the process of extending the end effector from a fully retracted position to a fully extended position. 
           [0064]      FIG. 26  is a chart plotting end effector position and velocity versus elapsed time during an end effector extension process. 
           [0065]      FIG. 27  is a chart plotting end effector acceleration and jerk versus elapsed time during an end effector extension process. 
           [0066]      FIG. 28  is a chart plotting angle and angular acceleration of an inner actuator arm versus elapsed time during an end effector extension process. 
           [0067]      FIG. 29  is a chart plotting end effector azimuthal angular position and azimuthal velocity versus elapsed time during a 90° end effector rotation process. 
           [0068]      FIG. 30  is a chart plotting effector azimuthal acceleration and azimuthal jerk versus elapsed time during a 90° end effector rotation process. 
           [0069]      FIG. 31  is a chart plotting end effector radial (centrifugal) acceleration and radial jerk versus elapsed time during a 90° end effector rotation process. 
           [0070]      FIG. 32  is a chart plotting end effector azimuthal, radial, and total accelerations versus elapsed time during a 90° end effector rotation process. 
           [0071]      FIG. 33  is a chart plotting end effector azimuthal angular position and azimuthal velocity versus elapsed time during a 180° end effector rotation process. 
           [0072]      FIG. 34  is a chart plotting end effector azimuthal acceleration and azimuthal jerk versus elapsed time during a 180° end effector rotation process. 
           [0073]      FIG. 35  is a chart plotting end effector radial (centrifugal) acceleration and radial jerk versus elapsed time during a 180° end effector rotation process. 
           [0074]      FIG. 36  is a chart plotting end effector azimuthal, radial, and total accelerations versus elapsed time during a 180° end effector rotation process. 
           [0075]      FIG. 37  is a chart plotting extension or rotation times of an end effector versus maximum acceleration. 
           [0076]      FIG. 38  is a chart plotting combined times for one rotation plus four extensions of an end effector versus maximum acceleration. 
           [0077]      FIG. 39  illustrates an example of a conventional dual wafer robot that is limited to wafer handling within a single plane. 
           [0078]      FIG. 40  illustrates an example of a conventional dual wafer robot that is limited to wafer handling in a tandem configuration with simultaneous motion of both wafers in a single plane. 
           [0079]      FIG. 41  illustrates an example of a conventional dual wafer robot that is limited to single wafer loading and unloading. 
           [0080]      FIG. 42  illustrates an example of a conventional dual wafer robot that is limited to single wafer loading and unloading. 
           [0081]      FIG. 43  illustrates an example of a conventional robot actuator having two motors, each of which requires a magnetic air-to-vacuum coupler separate from the robot motors. 
           [0082]      FIG. 44A  is an isometric view of a dual wafer robot configured in accordance with a further embodiment of the present invention and showing two end effectors (each carrying a single wafer) in an above and below arrangement on one side of the robot&#39;s rotational axis, where both end effectors are fully retracted. 
           [0083]      FIG. 44B  is a top view of the dual wafer robot shown in  FIG. 44A . 
           [0084]      FIG. 44C  is a side view of the dual wafer robot shown in  FIGS. 44A-B . 
           [0085]      FIG. 45A  is a top view of a dual wafer robot configured in accordance with an embodiment of the present invention and showing two end effectors (each carrying a single wafer) in an above and below arrangement, where both end effectors are fully extended for loading/unloading two wafers into/out of a pass-through chamber. 
           [0086]      FIG. 45B  is a side view of the dual wafer robot shown in  FIG. 45A . 
           [0087]      FIG. 46  is a side view of a dual wafer robot configured in accordance with an embodiment of the present invention and showing two end effectors (each carrying a single wafer) oriented 180° azimuthally with respect to one another around the robot&#39;s rotational axis, where both end effectors are fully retracted. 
           [0088]      FIG. 47  is a schematic side cross-sectional view of a single robot actuator configured in accordance with another embodiment of the present invention. 
           [0089]      FIG. 48  is an isometric view of a dual wafer robot configured in accordance with an embodiment of the present invention and showing two end effectors (each carrying a single wafer) in an above and below arrangement on one side of the robot&#39;s rotational axis, where both end effectors are fully retracted, 
           [0090]      FIG. 49  is a schematic side cross-sectional view of a single robot actuator configured in accordance with still another embodiment of the present invention. 
           [0091]      FIG. 50  is a schematic top view of a single robot end effector actuator assembly configured in accordance with yet a further embodiment of the present invention and showing the end effector in three positions: (A) fully retracted, (B) partially extended, and (C) fully extended. 
           [0092]      FIG. 51  is a side view of the single robot end effector actuator shown in  FIG. 50 , showing the end effector fully extended. 
           [0093]      FIG. 52A  is a schematic top view of a single robot dual end effector actuator assembly configured in accordance with still another embodiment of the present invention, wherein the wafer insertion directions are oriented 180° azimuthally with respect to one another, and showing the dual end effector in three positions: (A) fully retracted, (B) partially extended, and (C) fully extended. 
           [0094]      FIG. 52B  is a side view of the single robot dual end effector actuator illustrated in  FIG. 52A  and showing the dual end effector fully extended, with a cutaway view of an actuator motor. 
           [0095]      FIG. 53  is a schematic top view of a single robot dual end effector actuator assembly configured in accordance with a further embodiment of the present invention, wherein the wafer insertion directions are not oriented 180° azimuthally with respect to one another, and showing the dual end effector in three positions: (A) fully retracted. (B) partially extended, and (C) fully extended. 
           [0096]      FIG. 54A  is a schematic top view of a single robot dual end effector actuator assembly configured in accordance with yet a further embodiment of the present invention, wherein the wafer insertion directions are in tandem but where the insertion processes may be asynchronous, and showing the dual end effector in two positions: (A) both fully retracted, and (B) one fully extended while the other is fully retracted. 
           [0097]      FIG. 54B  is a side view of the single robot dual end effector actuator illustrated in  FIG. 54A , showing the wafer positions in view (B) of  FIG. 54A . 
           [0098]      FIG. 55  is a top schematic view of the single robot dual end effector illustrated in  FIGS. 54A-B , showing the robot operation illustrated in view (B) of  FIG. 54A  in a four process chamber system. 
       
    
    
     DETAILED DESCRIPTION 
       [0099]    Aspects of the present invention are discussed in detail below with particular reference to the field of semiconductor wafer processing. The use of the present invention in this field is intended to serve as an illustrative example. The present invention finds application in many other fields as well, such as in systems for fabrication of flat panel displays or solar cells. 
         [0100]    In many instances, processing times for different modules of a wafer processing system may not be exactly the same. Moreover, for optimal system throughput, it may be necessary to load/unload wafers into/out of process modules oriented at arbitrary angular orientations with respect to one other around the perimeter of a transfer chamber. To address these needs, embodiments of the present invention provide for asynchronous wafer removal and insertion into and out of process modules located at arbitrary angular orientations with respect to one other around a transfer chamber of a cluster tool. Unlike transfer robots of the past, which were designed to transfer only one wafer at a time, or to transfer two wafers but only simultaneously (i.e., not asynchronously), transfer robots configured in accordance embodiments of the present invention are capable of transferring two wafers asynchronously into/out of process modules and/or pass-through modules oriented at arbitrary angular orientations with respect to one other around the perimeter of a transfer chamber. 
         [0101]    Accordingly, a wafer processing system arranged in a cluster tool configuration is disclosed herein. This system includes one or more dual wafer robots, each configured for simultaneous and asynchronous wafer handling. One example of such a wafer processing system is a four process module cluster tool, wherein the four process modules (and, optionally, one or more pass-through modules) are located at arbitrary azimuthal orientation with respect to one another around the perimeter of a transfer chamber containing a dual wafer robot. The configuration of the dual wafer robot enables asynchronous loading/unloading of wafers into/out of any of the four process modules (and/or the pass-through module(s), if present), independent of their attachment positions to the transfer chamber, thereby maximizing processing throughput of the system. 
         [0102]    Another example of such a wafer processing system is a six process module cluster tool, wherein a first group of two process modules is located around the perimeter of a first transfer chamber containing a first dual wafer robot and a second group of four process modules is located around the perimeter of a second transfer chamber containing a second dual wafer robot. A pass-through module (which may be configured as wafer pre-heat and/or wafer cool-down chambers) is positioned between the first and second transfer chambers. The configuration of the first dual wafer robot enables asynchronous loading/unloading of wafers into/out of both process modules in the first group. The configuration of the second dual wafer robot enables asynchronous loading/unloading of wafers into/out of any two of the four process modules in the second group, independent of their attachment positions to the second transfer chamber, thereby maximizing processing throughput of the six process module system. Wafer processing systems with other numbers of process modules (e.g., eight) may be configured in similar fashion. 
         [0103]    In the above-described examples of systems configured in accordance with aspects of the present invention, the wafer heights within the process modules may be generally the same. The wafer positions within the pass-through module(s), however, are preferably arranged in an above and below configuration, for example spaced about 12 mm apart vertically. Such displacement is a design choice and is not critical to the present invention. Other displacements may be used. To accommodate these varying heights, the dual wafer robot can be configured with a cam mechanism that varies the heights of the end effectors carrying the wafers being transferred as a function of the azimuthal positions of the end effectors about a central axis of the dual wafer robot. For example, when an end effector is rotated to face a process module, the cam mechanism may position the end effector at the proper height for insertion/removal of a wafer into/from that process module. When an end effector is rotated to face a pass-through module, the end effector is raised or lowered to accommodate loading/unloading of wafers into/from the pass-through module. In other cases, one wafer may be loaded into the pass-through module while another wafer is removed therefrom. 
         [0104]    For many semiconductor manufacturing processes, such as chemical vapor deposition (CVD), if is necessary to heat the wafer to high temperatures (&gt;300° C. in some cases) before beginning the CVD process. For highest system throughput, it is advantageous to pre-heat the wafer prior to introduction into the process module, thereby reducing or eliminating any pre-heating needed within the process chamber. After the high-temperature process is completed, it is necessary to cool-down the wafer to near room temperature prior to loading it back into the loadlock. Again, it is advantageous to perform this cool-down operation outside the process module in order to maximize system throughput. Thus, as alluded to above, the present wafer processing system can be configured with one or more wafer pre-heat and cool-down chambers in order to maximize the use of process modules for wafer processing operations without having to also accommodate lengthy wafer pre-heat and cool-down steps. 
         [0105]    In many cases, the wafer pre-heat and cool-down times, may be longer than the actual wafer processing times. In these cases, it is advantageous for the pre-heat and cool-down chambers to accommodate a large number of wafers, all of which are undergoing simultaneous pre-heating or cooling-down. In order for the dual wafer robot to be able to load/unload wafers into/out of any two slots in such multi-slot pre-heat and cool-down chambers, it is advantageous for the dual wafer robot to have a collective Z-axis (vertical) motion to enable access to any pair of neighboring slots within the pre-heat and cool-down chambers. Accordingly, embodiments of the present dual wafer robot can be configured to be capable of a second type of vertical motion, enabling collective and simultaneous motion of both wafers, (i.e., both end effectors). Note that this collective, synchronous motion is provided via a different mechanism than the asynchronous, non-collective vertical motion provided by the cam mechanism. 
         [0106]    In various embodiments of the present invention, the dual wafer robot is actuated by a set of four rotors, two for each end effector. The rotation of these rotors is enabled by four brushless/frameless motors, each of which is integrated into a single rotor. The integration of the motors with the rotors eliminates the need for separate air-to-vacuum magnetic couplers. Additional advantages of the integrated motor are (1) the elimination of all moving parts in air, and (2) the ability to provide forced air cooling for the motor stators, which is advantageous in CVD tools where wafer temperatures may exceed 300° C. 
         [0107]    To provide advantageous throughput for the wafer processing system, embodiments of the present dual wafer robot are configured with a control system which enables the end effector motion profile (position, velocity, acceleration and jerk) in both extension and rotation to be optimized for minimum jerk within the constraint of a pre-determined maximum allowable acceleration. For rotational motions having both azimuthal and centrifugal (radial) accelerations, the total acceleration is the vector combination of both accelerations—the robot control takes this into account in the velocity and acceleration profiles during rotation. 
         [0108]    Semiconductor wafer fabrication typically requires a large number of processing steps, many of which require the wafer to be in a high vacuum environment. There are at least three main categories of vacuum processing steps, including:
       1. Deposition—where layers of material are deposited on the surface of a wafer. This material is then patterned in subsequent steps to form transistor gates, contacts, vias, metal conductors, etc.   2. Etching—where one or more previously-deposited layers on the wafer are selectively etched through a previously-patterned layer of photoresist.   3. Ion Implantation—where a high energy beam of dopant ions is directed at the wafer surface and is implanted in the wafer within a few micrometers of the surface, thereby defining conducting regions (after annealing). This process is usually performed in a “batch mode”, where a large number of wafers are simultaneously implanted, not in a cluster tool.       
 
         [0112]    In general, the first two types of processing operations are done in “cluster tools”, which are processing systems consisting of a number of “process modules” arranged around the perimeter of one or more transfer chambers, each containing a wafer transfer robot. The entire internal volume of the cluster tool is maintained at high vacuum to maintain cleanliness of the wafer surface and to enable deposition and etching processes to occur. 
         [0113]    The technical performance and economic viability of a semiconductor fabrication process depends on the throughput at which it can be performed. Typical system throughputs are now substantially in excess of 100 wafers per hour (wph), requiring the use of multiple process modules operating in parallel on wafers introduced into the system through a high-speed air-to-vacuum loadlock. With proper system design, throughput is solely a function of the deposition or etching speeds of the process modules, and is not dependent on the speed of the transfer robot. It is therefore desirable to configure a cluster tool such that the speed of the transfer robot is sufficient to ensure that it is never the rate-limiting step in wafer processing. 
         [0114]    For some deposition processes, such as chemical vapor deposition (CVD), the wafer must be heated to high temperature (e.g., on the order of 300° C.), prior to beginning the deposition process, since CVD entails the thermal decomposition of a reactant species on the wafer surface to leave behind the desired material, while simultaneously generating volatile product gases which must be pumped away. The throughput of a CVD process module will be enhanced if wafers can be preheated prior to loading into the CVD module. Preheating is typically performed in a preheating module, but not usually to the full 300° C. temperature required to begin CVD deposition. It is therefore desirable to configure a cluster tool with one or more pass-through modules, each enabling at least two wafers to be simultaneously preheated to temperatures necessary for CVD processing. 
         [0115]    When CVD processing of a wafer is completed, the wafer must be removed from the process module while still near the high processing temperatures, otherwise a substantial overall reduction in tool throughput will occur. It is undesirable or impossible to transfer wafers at these high temperatures directly into an exit loadlock of the cluster tool, thus a wafer cool-down step is required between the time of wafer removal from the CVD process module and its insertion into the exit loadlock. It is therefore desirable to configure a cluster tool with one or more pass-through modules, each permitting at least two wafers to be cooled down to temperatures necessary for insertion into an exit loadlock. 
         [0116]    Maximization of the throughput of the cluster tool configuration described above requires the ability to unload wafers from each of the process modules immediately after the completion of the processing of each wafer, independent of the status of other process modules mounted on the same transfer chamber. Similarly, it is also necessary to be able to load a wafer into each process module as quickly as possible after the completion of processing of the previous wafer. Since typically there may be as many as four or more process modules attached to each of the transfer chambers, it is advantageous to be able to transfer more than one wafer simultaneously with the transfer robot. In addition, it is also advantageous to be able to load/unload wafers into/out of process modules at arbitrary relative positions to each other (i.e., not always exactly on opposite sides of the transfer chamber). Since processing times may vary between process modules, it is also advantageous to be able to load/unload wafers asynchronously, so that no process module need wait for the completion of processing in another module before wafer unloading can begin. It is therefore desirable to provide a dual wafer robot capable of asynchronously loading and unloading wafers into and out of two process modules, where these process modules may be at arbitrary relative locations to each other around the perimeter of the transfer chamber. 
         [0117]    The actuation of wafer transport robots typically involves one or more electric motors, mounted in air, where some form of air-to-vacuum coupler is used to transfer motion from the motor(s) to the in-vacuum mechanisms of the robot. In addition, the motor often operates at high speed with low torque, thus requiring a reduction gear to generate low speed high torque power necessary for the generally low speed robot motions (both extensions and rotations of end effectors carrying wafers). It is therefore desirable to provide a robot actuation mechanism in which the robot drive motor is a low speed high torque motor, and wherein the stator of the motor is mounted in air and the rotor of the motor is integrated with the robot actuation mechanism in vacuum. The needs for a reduction gear and an air-to-vacuum coupler are thereby eliminated. 
         [0118]    The need for maximization of cluster tool throughput leads to a requirement for maximized speed of the robot motion, both during extension and retraction of the end effectors, and during azimuthal rotation thereof within the transfer chamber. This optimization commonly involves the minimization of the integral of the square of the “jerk” function (the derivative of the acceleration) over the full wafer trajectory. This jerk function minimization is subject to the limitation of a pre-defined maximum allowable acceleration of the end effector. This maximum acceleration is usually a function of the coefficient of friction between the back side of the wafer and pads (e.g., three or more pads) on the end effector on which the wafer lies during transfer. 
         [0119]    In the case of high temperature processing (such as CVD at 300° C.), the use of rubber pads is not feasible, and so metal pads are used. Since metal pads have lower coefficients of friction, the allowable maximum wafer acceleration is reduced. If the wafer exceeds the maximum acceleration permitted by these lower coefficients of friction there is a danger of slippage, leading potentially to wafer misalignment or breakage. 
         [0120]    For linear motions, such as extensions and retractions of the end effector to load/unload wafers into/out of process modules and pass-through modules, there exists much literature on the minimum jerk trajectory strategy. For rotational motions, however, there are two components to the acceleration: azimuthal and radial (centrifugal). Thus, the overall acceleration of the wafer on the end effector is the vector combination of these two orthogonal accelerations. The jerk function is then the vector combination of orthogonal azimuthal and radial jerk functions, and finding the minimum jerk trajectory becomes complicated for a real-time trajectory controller. It is thus desirable to control the rotational motion of a dual wafer robot in order to maintain the total wafer acceleration approximately below a pre-determined maximum value, while simultaneously minimizing the integral of the square of the azimuthal jerk function over the full wafer trajectory. 
         [0121]    In a cluster tool, the heights for loading/unloading wafers into/out of process modules are typically the same. The configurations for the pass-through modules containing the pre-heat and/or cool-down chambers involve at least two slots located above and below one another (i.e., spaced along the vertical Z-axis). Assuming for simplicity that the two slots are spaced ±6 mm relative to the wafer height in a process module, transfer of a wafer from a process module to the upper slot of a two-slot pass-through module may involve moving the wafer 6 mm upwards. Conversely., transfer of a wafer from a process module to the lower slot would involve moving the wafer downwards 6 mm. Note that these motions are in opposite directions, but need to occur either simultaneously or asynchronously. This motion differs from that common with other dual wafer robots, where all vertical motion involves both wafers moving the same distance and direction simultaneously. It is therefore desirable to configure a dual wafer robot with the capability for simultaneous or asynchronous Z-axis motion of the end effectors in different directions over distances sufficient to access vertically-spaced slots in a pass-through module. 
         [0122]    The wafer pre-heat operation described above may require a time comparable or longer than the time for deposition in the process modules. Thus it may be necessary to hold a number of wafers in the pre-heat chamber (located in a pass-through module) until the wafers are fully pre-heated. Similarly, the wafer cool-down operation may have the same constraints. These requirements for longer pre-heating and/or cooling times are typically met by providing a larger number of slots (four or more) in the pre-heat and cool-down chambers, thereby enabling wafers to be stored for longer times prior to either insertion into a process module (pre-heat), or transfer to an exit loadlock (cool-down). Enabling the transfer robot to access all of these slots (which are typically spaced about 12 mm apart along the vertical Z-axis) may require a larger Z-motion for the robot than that described in the preceding paragraph. It is therefore desirable to provide a collective Z-motion for the dual wafer robot in which all end effectors move simultaneously with the same speed and direction along the vertical Z-axis. 
         [0123]    Configurations of the Wafer Processing System 
         [0124]      FIG. 1A  is an isometric view of a four process module cluster tool configured in accordance with one embodiment of the present invention. Using an air robot (not shown), a number of wafers  1002  are loaded into entrance loadlock  1001 , which may be configured to perform a wafer pre-heat operation as described above. Loadlock  1001  may be configured with multiple chambers, each with separate pumpdown and venting capability, to ensure that there are wafers available for loading by dual transfer robot  1006  at all times. An entrance valve (not shown) separates entrance loadlock  1001  from transfer chamber  1005 . When the entrance valve is open, dual transfer robot  1006  extends either or both of two end effectors into entrance loadlock  1001  and withdraws one or two wafers  1007 , one per end effector. Assuming two wafers are withdrawn, one carried on each end effector, the two end effectors of robot  1006  then move in opposite azimuthal directions within transfer chamber  1005 , enabling one of wafers  1007  to be inserted into each of two process modules, such as process modules  1008  and  1011 , nearly simultaneously. 
         [0125]    The rotational distance to move a first end effector (and one wafer  1007 ) counter-clockwise from initially facing loadlock  1001  to facing process module  1008  is shown as roughly 45-60°. The rotational distance to move a second end effector (and a second wafer  1007 ) clockwise to face process module  1011  is shown as roughly 90-120°. Thus wafer insertion into process module  1008  may commence slightly before wafer insertion into process module  1011 —this necessitates asynchronous operation of the two end effectors of the dual wafer robot. 
         [0126]    Later sections of this description discuss the cam mechanism used to control the heights of the end effectors to ensure proper insertion of wafers into the process modules. Loading of process modules  1009  and  1010  requires loading third and fourth wafers from loadlock  1001  onto the two end effectors of dual water robot  1006 . Depending on details of the design of loadlock  1001 , which are not critical to the present invention, a collective Z-motion of the dual wafer robot may be necessary as described below. 
         [0127]    In the illustration, a pass-through module  1012  is shown with two chambers in an above/below orientation with respect to one another. In one embodiment of the present invention, one chamber of the pass-through module is configured for wafer pre-heating, and the other chamber for wafer cool-down. In general, a pass-through module may be used in two modes:
       1. As a pass-through module (illustrated for a six-chamber system in  FIGS. 2A-B , or for an eight-chamber system as shown in  FIGS. 3A-B ). In this mode, one or two wafers would be loaded into the pre-heat chamber of pass-through module  1012 , and then after pre-heating, a second robot (illustrated in  FIGS. 2A-3B ) would remove the wafers for insertion into two process modules (not shown—see  FIGS. 2A-3B ). Similarly, after processing, the wafers would be inserted by the second robot (see  FIGS. 2A-3B ) into the cool-down chamber of pass-through module  1012 . After adequate cool-down, the wafers would be removed by robot  1006  and transferred to exit loadlock  1003 .   2. As a module used only for wafer pre-heating and cool-down (i.e., not functioning as a pass-through). In this mode, one or two wafers would be loaded by robot  1006  into the pre-heat chamber of pass-through module  1012 , and then, when adequately pre-heated, the wafers would be removed by robot  1006  and loaded into any of the process modules  1008 - 1011  (one wafer into each process module). Similarly, after processing, the wafers would be removed from the subject process modules  1008 - 1011  by robot  1006  and inserted into the cool-down chamber of pass-through module  1012 . After adequate cool-down, the wafers would be removed by robot  1006  and transferred to exit loadlock  1003 . Pass-through chamber  1005  always functions in this mode for the four process module cluster tool illustrated in  FIGS. 1A-B .       
 
         [0130]      FIG. 1B  is a top view of the four process module cluster tool shown in  FIG. 1A . Prior to processing, wafers  1002  are loaded into the entrance loadlock  1001  by an air robot (not shown). Processed wafers  1004  are loaded into exit loadlock  1003  and, after venting to atmospheric pressure, are subsequently removed by an air robot (not shown). Each process module  1008 - 1011  is enclosed by a frame  1013  that enables mounting of various electronics and power supplies necessary for the operation of process modules  1008 - 1011 . Two wafers  1027  and  1028  (equivalent to wafers  1007  in  FIG. 1A ) are shown loaded on the two end effectors of robot  1006 . 
         [0131]      FIG. 2A  is an isometric view of a six process module cluster tool, configured in accordance with one embodiment of the present invention. In this configuration, loadlock  1101  contains wafers  1102  ready for processing. Loadlock  1103  contains processed wafers  1104 . Loadlocks  1101  and  1103  are connected to transfer chamber  1105 , containing transfer robot  1106 . Two process modules  1114  and  1119  are attached to transfer chamber  1105 . A first pass-through module  1109 , attached to transfer chambers  1105  and  1110 , enables robot  1106  to transfer two wafers  1107  and  1108  simultaneously or asynchronously from loadlock  1101  into a pre-heat chamber in module  1109 . Pass-through module  1109  may function in either or both of the modes described above. After adequate preheating, a second dual wafer robot  1111  removes the two wafers  1112  and  1113 , and transfers each of wafers  1112  and  1113  to one of the process modules  1115 - 1118  (one wafer per module) that are attached to transfer chamber  1110 . A second pass-through module  1120  is shown, functioning in the non-pass-through mode described above. 
         [0132]      FIG. 28  is a top view of the six process module cluster tool shown in  FIG. 2A . Wafer  1107  is in position for loading into process module  1114 , while robot  1106  has also positioned water  1108  for loading into process module  1119 . Note that in this case, the two end effectors of robot  1106  are oriented 180° azimuthally with respect to each other. Robot  1111  is shown holding with two wafers  1112  and  1113 . Processed wafer  1112  has just been removed from process module  1115  and pre-heated wafer  1113  has just been removed from the pre-heat chamber in pass-through module  1120 . The end effector carrying processed wafer  1112  is rotating clockwise towards pass-through module  1109 . The end effector carrying pre-heated wafer  1113  is rotating counter-clockwise, towards process module  1117 . This configuration with multiple pass-through chambers  1109  and  1120  enables wafers to be pre-heated and/or cooled-down in one or both of chambers  1109  and  1120 , depending on the temperatures of the various wafers already in the system (in process modules  1114 - 1119  or pass-through modules  1109  and  1120 ). Each process module  1114 - 1119  is enclosed by a frame  1121  that enables mounting of various electronics and power supplies necessary for the operation of process modules  1114 - 1119 . 
         [0133]      FIG. 3A  is an isometric view of an eight process module cluster tool configured, in accordance with one embodiment of the present invention. In this configuration, loadlock  1201  contains wafers  1202  ready for processing. Loadlock  1203  contains processed wafers  1204 . Loadlocks  1201  and  1203  are connected to transfer chamber  1205 , containing transfer robot  1206 . Two process modules  1220  and  1227  are attached to transfer chamber  1205 . A first pass-through module  1209 , attached to transfer chambers  1205  and  1210 , enables robot  1206  to transfer two wafers  1207  and  1208  simultaneously or asynchronously from loadlock  1201  into a pre-heat chamber in module  1209 . Pass-through module  1209  may function in either or both of the modes described above. 
         [0134]    After adequate pre-heating, a second dual wafer robot  1211  removes the two wafers  1212  and  1213 , and transfers each wafer to one of the process modules  1221  and  1226 , or to pass-through module  1214 , all of which are attached to transfer chamber  1210 . The second pass-through module  1214  may function in either or both of the modes described above. A third pass-through module  1219  is shown, functioning in the non-pass-through mode described above. 
         [0135]    The operation of robot  1211  in transfer chamber  1210  is to transfer wafers  1212  and  1213  into/out of process modules  1221  and  1226 , and into/out of pass-through modules  1209  and  1214 . The operation of robot  1216  in transfer chamber  1215  is to transfer wafers  1217  and  1218  into/out of process modules  1222 - 1225  and into/out of pass-through modules  1214  and  1219 . 
         [0136]      FIG. 3B  is a top view of the eight process module cluster tool shown in  FIG. 3A . Each process module  1220 - 1227  is enclosed by a frame  1228  that enables mounting of various electronics and power supplies necessary for the operation of process modules  1220 - 1227 . 
         [0137]    Dual Wafer Robot at Pass-Through Module 
         [0138]      FIG. 4A  is an isometric view of a dual wafer robot  2001  configured in accordance with one embodiment of the present invention, showing two wafers  2002  and  2004  supported by end effectors  2003  and  2005 , respectively. Wafers  2002  and  2004  have been positioned by end effectors  2003  and  2005 , respectively, in an above and below configuration, suitable for simultaneous loading of wafers  2002  and  2004  into a pass-through module (not shown). Upper end effector  2003  is supported by support arm  2011  attached to rotor  2012  (see  FIGS. 5A-B  for views of slider  2040  which connects support arm  2011  to end effector  2003 ). Actuator arm  2006  is attached to rotor  2007 , and is connected through pivot  2008  to outer arm  2009 . Outer arm  2009  is connected to end effector  2003  through pivot  2010 . 
         [0139]    Lower end effector  2005  is supported by support arm  2020  (see  FIG. 4C ) that is attached to rotor  2018  (see  FIG. 5B  for a view of slider  2049  which connects support arm  2020  to end effector  2005 ). Actuator arm  2013  is attached to rotor  2014 , and is connected through pivot  2015  to outer arm  2016 . Outer arm  2016  is connected to end effector  2005  through pivot  2017 . Details on the extension of the end effectors are provided in connection with a discussion of  FIG. 12 , below. 
         [0140]      FIG. 4A  illustrates the dual wafer robot  2001  with both end effectors fully retracted—this is the configuration in which the end effectors  2003  and  2005  may rotate. The rotors  2007 ,  2012 ,  2014 , and  2018  rotate around the central fixed tube  2019  which forms part of the transfer chamber (not shown—see. e.g., chambers  1105  and  1110  in  FIGS. 2A-B ).  FIG. 4B  is a top view of the dual wafer robot  2001  shown in  FIG. 4A . 
         [0141]      FIG. 4C  is a side view of the dual wafer robot shown in  FIGS. 4A-B . This view shows more clearly how support arms  2011  and  2020  extend downwards and upwards from rotors  2012  and  2018 , respectively, to enable end effectors  2003  and  2005  to position waters  2002  and  2004  for insertion/removal into/out of vertically-spaced slots in a pass-through module. 
         [0142]      FIG. 5A  is a top view of a dual wafer robot configured in accordance with one embodiment of the present invention, showing two wafers  2042  and  2044  in an above/below arrangement, where both robot end effectors are fully extended for loading two wafers  2042  and  2044  simultaneously into a pass-through chamber (not shown). The slide mechanism includes support arm  2011 , slider  2040 , and end effector  2003 . In cases where there is a large difference between the wafer position for robot rotation and the wafer position in the center of a process module, the three-element telescoping arrangement shown here is desirable. In cases with a smaller extension distance, a two element (i.e., support arm and end effector, without the intervening slider) arrangement may be preferred. The actuator arm mechanism includes components  2006 - 2010  and is attached to the end effector in either the two- or three-element telescoping arrangements. 
         [0143]    In the example shown here, slider  2040  is not directly connected to an actuator—the motion of slider  2040  is due to physical stops (not shown) within the bearings connecting support arm  2011  to slider  2040  and the bearings connecting slider  2040  to end effector  2003 . Physical stops within sliding bearings are familiar to those skilled in the art. 
         [0144]      FIG. 5B  is a side view of the dual wafer robot illustrated in  FIG. 5A . The actuator mechanism for end effector  2005  includes actuator arm  2013  attached to rotor  2014  and coupled through pivot  2015  to outer arm  2016 . Outer arm  2016  attaches to end effector  2005  through pivot  2017 . 
         [0145]    Dual Wafer Robot at Process Modules 
         [0146]      FIG. 6A  is an isometric view of a dual wafer robot configured in accordance with one embodiment of the present invention, showing two wafers  2052  and  2054  oriented 180° azimuthally around the robot&#39;s rotational axis. Both end effectors  2003  and  2005  are shown fully retracted. This is the configuration in which the end effectors  2003  and  2005  may rotate. 
         [0147]      FIG. 6B  is a top view and  FIG. 6C  is a side view of the dual wafer robot illustrated in  FIG. 6A . Note that in this configuration, wafers  2052  and  2054  are at the same height, unlike the situation depicted in  FIGS. 4A-5B . This change in height of the wafers, compared with the above/below configuration shown in  FIGS. 4A-5B , is controlled by the cam mechanism discussed with reference to  FIG. 20 , below. 
         [0148]      FIG. 7  is a top view of a dual wafer robot configured in accordance with an embodiment of the present invention, showing two wafers  2062  and  2064  oriented 180° azimuthally with respect to one another around the robot&#39;s rotational axis. Here, both end effectors  2003  and  2005  are fully extended for simultaneously (or nearly simultaneously) loading a wafer into each of two process modules (not shown). The slider mechanism for end effector  2005 , which includes support arm  2020 , slider  2049  and end effector  2005 , can be seen in this view. 
         [0149]    Independent Asynchronous Operation of the End Effectors 
         [0150]      FIGS. 8-11  illustrate the independent operation of the two end effectors  2003  and  2005  of the dual wafer robot, which, as described above, is important for maximizing wafer processing system throughput. 
         [0151]      FIG. 8  is a top view of a dual wafer robot configured in accordance with one embodiment of the present invention, showing two wafers  2072  and  2074  in an above and below arrangement, where the upper end effector  2003  (carrying wafer  2072 ) is fully extended, and the lower end effector  2005  (carrying wafer  2074 ) is partially extended, illustrating the independent operation of end effectors  2003  and  2005  when the end effectors  2003  and  2005  are in an above and below arrangement. 
         [0152]      FIG. 9  is a top view of a dual wafer robot configured in accordance with one embodiment of the present invention, showing two wafers  2082  and  2084  oriented 180° azimuthally with respect to one another around the robot&#39;s rotational axis, where the upper end effector  2003  (carrying wafer  2082 ) is fully extended, and the lower end effector  2005  (carrying wafer  2084 ) is fully retracted, illustrating the independent operation of end effectors  2003  and  2005  when the end effectors  2003  and  2005  are on opposite sides of the robot rotational axis. 
         [0153]      FIG. 10  is a top view of a dual wafer robot configured in accordance with one embodiment of the present invention, showing two wafers  2002  and  2004  oriented 90° azimuthally with respect to one another around the robot&#39;s rotational axis, where the upper end effector  2003  (carrying wafer  2002 ) is fully extended, and the lower end effector  2005  (earning wafer  2004 ) is fully retracted, illustrating the Independent operation of end effectors  2003  and  2005  with respect to both extension and angular position. 
         [0154]      FIG. 11  is a top view of a dual wafer robot configured in accordance with one embodiment of the present invention, showing two wafers  2002  and  2004  oriented 90° azimuthally with respect to one another around the robot&#39;s rotational axis, where the upper end effector  2003  (carrying wafer  2002 ) is partially extended, and the lower end effector  2005  (carrying wafer  2004 ) is fully extended, illustrating the independent operation of end effectors  2003  and  2005  with respect to both extension and angular position. 
         [0155]    Operation of the End Effector Actuator 
         [0156]      FIG. 12  is a schematic top view of a single robot end effector actuator assembly configured in accordance with one embodiment of the present invention, showing the end effector in three positions: (A) fully retracted, (B) partially extended, and (C) fully extended. 
         [0157]    In view (A), end effector  2256 , carrying wafer  2259  (shown in dotted outline so as to reveal the details of the end effector and related components), is fully retracted into the position for rotation of the end effector  2256  and wafer  2259 . End effector  2256  is attached to slider  2257  by a linear bearing (not shown). Slider  2257  is likewise attached to support arm  2258  by a separate linear bearing (not shown). Linear bearings are familiar to those skilled in the art of actuator mechanisms and so will not be described in detail herein. Actuator arm  2252  is attached to rotor  2250  and further coupled to outer arm  2253  through pivot  2254 . Outer arm  2253  is connected to end effector  2256  through pivot  2255 . Rotor  2250  turns around central tube  2251 . Actuator arm  2252  is starting to turn clockwise as shown by arrow  2260 , causing end effector  2256  to begin extending as shown by the arrow on wafer  2259 . 
         [0158]    In view (B), end effector  2256 , carrying wafer  2259 , is shown partially extended. Actuator arm  2252  has rotated clockwise (arrow  2261 ), driving outer arm  2253  to push end effector  2256  radially outwards. During the extension operation, the rotor (not shown) connected to support arm  2258  does not turn. 
         [0159]    In view (C), end effector  2256  is fully extended, positioning wafer  2259  in either a process module or a pass-through module (not shown). Arrow  2262  shows the last increment of rotation of actuator arm  2252 , giving the last increment of motion to end effector  2256  as shown by the arrow on wafer  2259 . 
         [0160]      FIG. 13  is a side view of the single robot end effector actuator shown in  FIG. 12  view (C), showing the end effector  2256  (carrying wafer  2259 ) fully extended. A cutaway view of an actuator motor is also provided (see  FIG. 14  for details of the motor). The rotational axis  2283  for rotors  2250  and  2261  is shown. 
         [0161]    Operation of the Integrated Rotor Drive Motors and the Robot Control System 
         [0162]      FIG. 14  is a side view in partial cutaway of a single robot end effector actuator configured in accordance with one embodiment of the present invention, showing a motor assembly  2281  that includes a stator assembly, a rotor assembly, and an azimuthal (angular) position encoder. The stator assembly for the brushless/frameless motor consists of coils  2232 , pole pieces  2231 , and inner flux return ring  2230 . The stator assembly is rigidly supported by center tube  2330  (see  FIG. 15 , discussed below, which illustrates further details of the motor assembly). 
         [0163]    The rotor assembly includes the moving permanent magnet assembly for the motor: permanent magnets  2237  and outer flux return ring  2236 , rotating around central axis  2283 . Rotor  2250  is positioned on the outer circumference of central tube  2251  by bearings including outer race  2263 , inner race  2264 , and balls  2265 . The particular example of bearings shown here is for illustrative purposes only. The same positioning function for rotor  2251  may be implemented using one or more sets of three rollers each, positioned at approximately equal spacings around the rotor circumference, and configured to roll around the outer wall of central tube  2251 , or, alternatively, around on a track mounted to the outer wall of central tube  2251 . 
         [0164]    Actuator arm  2252  is moved by rotor assembly  2250 , and support arm  2258  is moved by rotor assembly  2261 , which is actuated by a brushless/frameless motor assembly  2282  (details not shown) equivalent to the motor assembly driving rotor  2281 . An encoder ring  2340  is attached to rotor  2250  (and rotating with rotor  2250 ), and encoder read head  2341  is rigidly attached to vacuum wall  2251  and thus does not rotate. The mounting and operation of optical encoders are familiar to those skilled in the art. 
         [0165]      FIG. 15  is a schematic top view of a motor assembly including a stator assembly, a rotor assembly, and an azimuthal (angular) position encoder in accordance with one embodiment of the present invention. The stator assembly includes a large number of electromagnetic pole pieces  2331 ,  2333 , and  2235 , energized by three separate circuits, A, B, and C, respectively. Circuit A energizes pole pieces  2331  by means of coils  2332 . Circuit B energizes pole pieces  2333  by means of coils  2334 . Circuit C energizes pole pieces  2235  (see also  FIG. 14 ) by means of coils  2336  (equivalent to coil  2232  in  FIG. 14 ). Generally, the phases of circuits A-C are separated by 120° to induce rotation of the rotor assembly. 
         [0166]    Permanent magnets  2337  in the rotor assembly are oriented with their North poles directed inwards, towards the stator. Permanent magnets  2338  are mounted with the opposite (South) orientation. Magnets  2337  and  2338  are equivalent to magnet  2237  in  FIG. 14 . As pole pieces  2331 ,  2333 , and  2235  are energized by circuits A-C, respectively, permanent magnets  2337  and  2338  feel an azimuthal force (torque), thereby inducing rotation of the entire rotor assembly around the central axis of the assembly ( 2283  in  FIG. 14 ). 
         [0167]    The azimuthal position of the rotor is determined using an optical encoder, that includes read head  2341  (rigidly attached to vacuum wall  2251 , see  FIG. 14 , and coupled with electrical connections  2342 ) and encoder ring  2340  (attached to rotor  2250 ). The rotation of the rotor assembly is illustrated by bi-directional arrow  2343 . Note that with this motor design, a separate air-to-vacuum coupler is unnecessary, since the stator-to-rotor coupling through the vacuum wall  2251  provides the air-to-vacuum coupling function. 
         [0168]      FIG. 16  is a schematic illustration of a control system for a single robot configured in accordance with one embodiment of the present invention. Each of the two end effectors in a dual wafer robot requires two motor assemblies, each as shown in  FIGS. 15-16 : one motor assembly  2401  for the support arm, and another motor assembly  2411  for the actuator arm. The signal from encoder read head  2407  (measuring the angular position of the rotor in motor assembly  2401 ) is passed via cable  2408  to encoder controller  2409 . Note, in other embodiments other forms of communicative coupling may be used, such as wireless communications from the read head  2407  to the encoder controller  2409 . Similarly, the signal from encoder read head  2417  (measuring the angular position of the rotor in motor assembly  2411 ) is passed via cable  2418  to encoder controller  2419 . 
         [0169]    Motor driver  2404  generates three signals, A-B-C, to drive the electromagnets in the stator of motor assembly  2401 . Motor driver  2414  generates three signals, D-E-F (equivalent to A-B-C), to drive the electromagnets in the stator of motor assembly  2411 . Control lines  2405  and  2410  connect to motor assembly control  2406 . Control lines  2415  and  2420  connect to motor assembly control  2416 . Motor assembly controls  2406  and  2416  are connected to end effector control  2423  through lines  2421  and  2422 , respectively. End effector control  2423  is connected to the transfer chamber controller (which may, for example, be a programmable controller but is not shown in this illustration) through line  2424 . Rotation of the rotor in motor assembly  2401  is illustrated by bi-directional arrow  2402  and rotation of the rotor in motor assembly  2411  is illustrated by bi-directional arrow  2412 . 
         [0170]      FIG. 17  is an isometric cutaway view of a dual wafer robot configured in accordance with one embodiment of the present invention.  FIG. 4A  is a similar view of the dual wafer robot, not in cutaway, for comparison. In  FIG. 17 , rotors  2007 ,  2012 ,  2018 , and  2014  (see  FIG. 4A ) are cutaway to reveal permanent magnets  2510 - 2513  (equivalent to permanent magnets  2337 - 2338  in  FIG. 15 ), respectively. Note that the permanent magnets  2510 - 2513  are shown skewed in orientation—this skewing smooths out the torque transfer between the stator and the motor rotor during rotation. Alternatively, a non-skewed arrangement of the magnets with skewed magnetizations may be used. Skewing of magnets in motors to reduce “cogging” is familiar to those skilled in the art and so will not be described further herein. 
         [0171]      FIG. 18  is a cutaway side view of a single robot actuator configured in accordance with one embodiment of the present invention. A dual rotor assembly includes rotors  2007  and  2012  locked together along the vertical axis (Z-axis) by a bearing assembly that includes roller bearing  2532 , upper clamp  2531 , and lower clamp  2533 . The bearing assembly leaves rotors  2007  and  2012  free to rotate relative to each other in accordance with the requirements for extension of the end effector described above. 
         [0172]    The Z-axis position of the dual rotor assembly is controlled by the cam  2535 , as illustrated in more detail in  FIGS. 19-20 . Encoder ring  2530  is maintained at a constant height, independent of the Z-axis motion of rotor  2007 . Pin  2539  allows rotor  2007  to remain azimuthally locked to encoder ring  2530  while rotor  2007  moves up and down following the profiles of cam  2535 . Rollers  2554  and  2555  (see  FIG. 19 ) cause rotors  2007  and  2012  to move up and down together during rotation, following the profile of cams  2535  and  2534 . It is necessary for the encoder ring  2530  to remain at a constant height while rotor  2007  turns (thereby causing rotor  2007  to move up and down) in order to maintain the required close spacing to encoder read head  2538  which is fixed to the tube  2251  (see  FIG. 15 ). 
         [0173]    Similarly, pin  2536  allows rotor  2012  to remain azimuthally locked to encoder ring  2537  while rotor  2012  moves up and down (vertically locked to rotor  2007 ) following the profile of cam  2535 . Magnets  2510  and  2511  (equivalent to magnets  2337  and  2338  in  FIG. 15 ) are skewed in order to smooth the torque coupling (i.e., to reduce “cogging”) to the rotating magnetic field induced by the stator pole pieces (see  2231 ,  2331 , and  2333  in  FIG. 15 ) as is familiar to those skilled in the art of brushless/frameless motor design. Cam  2535  is mounted on support  2540 . 
         [0174]    Cam-Driven Independent Z-Motions of the End Effectors 
         [0175]      FIG. 19  is a schematic side cross-section of a single robot actuator configured in accordance with one embodiment of the present invention. Upper roller  2554  runs on the top surface of cam  2535 , while lower roller  2555  rotates against the bottom surface of cam  2534 . Lower roller  2554  is rigidly mounted to the wall  2019  of the central tube and thus defines the position of both rotors  2007  and  2012  in the vertical direction since cam  2535  is rigidly attached to rotor  2012  (through support  2540 ), and rotor  2007  is vertically locked to rotor  2012  by ring bearing  2532 . Upper roller  2554  is spring-loaded down against the top surface of cam  2535 , ensuring that lower roller  2555  stays in contact with the bottom surface of cam  2534 , and thus that, rotors  2007  and  2012  do not move upwards due to vibration or other vertical forces. 
         [0176]      FIG. 20  is a schematic illustration of the operation of two height-controlling cams, one for each of the end effectors in the dual wafer robot, in accordance with one embodiment of the present invention. In view (A), transfer chamber  2801  is shown, surrounded by four folded-out side views at azimuthal angles of 0°, 90°, 180°, and 270°, around the perimeter of transfer chamber  2801 . At 0° (at the left), a wafer  2806  is shown at the proper height  2816  for Insertion into process module  2802 . At 90° (at the bottom), two wafers  2807  and  2808  are shown at the proper heights  2817  and  2818 , respectively, for insertion into pass-through module  2803 . At 180° (at the right), a wafer  2809  is shown at the proper height  2819  for Insertion into process module  2804 . At 270° (at the top), two wafers  2810  and  2811  are shown at the proper heights  2820  and  2821 , respectively, for insertion into pass-through module  2805 . 
         [0177]    View ( 8 ) of  FIG. 20  is a folded-out composite view around the perimeter of transfer chamber  2801  at azimuthal angles 0°, 90°, 180°, and 270°, illustrating the up and down motion of the two end effectors as they rotate from facing process modules (such as  2802  and  2804 ) to facing pass-through modules (such as  2803  and  2805 ) and back again. As an example, wafer  2807 , starting from the upper position  2817  in pass-through module  2803 , moves down  2832  about 6 mm as the end effector (not shown—see, for example, end effector  2003  in  FIG. 4A ) carrying wafer  2807  rotates to face process module  2802  (shown as wafer  2806 ) at height  2816 . Wafer  2808 , starting from the lower position  2818  in pass-through module  2803 , moves up  2835  about 6 mm as the end effector (not shown—see, for example, end effector  2005  in  FIG. 4A ) carrying wafer  2808  rotates to face process module  2804  (shown as wafer  2809 ) at height  2819 . Note that these end effector (and wafer) motions in opposite directions may occur simultaneously or asynchronously, as required for optimal system throughput described above. Trajectories  2830 - 2837  enable wafers to be inserted into process chambers which are all at the same height (e.g., 1100 mm from floor level), while being loaded above and below into pass-through modules (e.g., with a vertical spacing of 12 mm). 
         [0178]    Collective Wafer Z-Motion 
         [0179]      FIG. 21  is a schematic view of the operation of the collective Z-motion actuator, in accordance with one embodiment of the present invention. View (A) shows the dual wafer robot  2605  in the lower position, enabling end effectors  2615  and  2616  to load/unload wafers from slots  2613  and  2614 , respectively, in a pass-through module (not shown). The dual wafer robot  2605  slides on two bearings  2618  and  2619  on a central rigid shaft  2620 . Note that only vertical sliding (not rotary) motion of the robot  2605  is allowed—rotary motion of end effectors  2615  and  2616  is accomplished through the methods described above. 
         [0180]    The vacuum seal for the transfer chamber includes lid  2601 , bottom  2602 , upper flange  2606 , and lower flange  2607 , and is maintained during vertical (Z-axis) motion of robot  2605  by two bellows  2603  and  2604 . Actuator rod  2617  pushes robot  2605  up and down along the axis precisely defined by shaft  2620 . 
         [0181]    Since the center of robot  2065 , as well as the centers of bellows  2603 - 2604 , are at air pressure, the dual bellows configuration is not affected by air pressure tending to push the robot assembly up or down. In an alternative embodiment (not shown), only the lower bellows  2604  is used, and the top of dual wafer robot  2605  is sealed off—this has the advantage of eliminating bellows  2603 , at the expense of introducing a large upward force due to air pressure which must be counteracted by actuator rod  2617 . Bearings  2618 - 2619  may be splines with recirculating ball bearings, air bearings, etc., as is familiar to those skilled in the art. An alternative embodiment may employ two or more rigid shafts such as  2620 , as is familiar to those skilled in the art. 
         [0182]    View (B) of  FIG. 21  shows the dual wafer robot  2605  in the upper position, enabling end effectors  2615  and  2616  to load/unload wafers from slots  2611  and  2612 , respectively, in a pass-through module (not shown). 
         [0183]    A third, intermediate, position for dual wafer robot  2605  is possible, enabling end effectors  2615  and  2616  to load/unload wafers from slots  2612  and  2613 , respectively, in a pass-through module (not shown). Although the present invention is illustrated with regard to four slots  2611 - 2614  in a pass-through module, it is possible for a pass-through module to employ either three, or more than four, slots—in these cases, the collective vertical motion of the dual wafer robot illustrated here would enable loading/unloading of two wafers at a time from any two neighboring slots within the pass-throughout module, as is familiar to those skilled in the art. 
         [0184]    Five-Step Wafer Transfer Process 
         [0185]      FIG. 22  is a schematic illustration of a wafer transfer process according to one embodiment of the present invention. A transfer module  3001  is attached to a process module  3002  and a pass-through module  3004 . Assume for sake of this example that a wafer at position  3020  has just completed processing in module  3002  and thus is ready for removal and subsequent transfer to pass-through module  3004 . After the process gases in module  3002  have been evacuated, the valve  3030  connecting module  3002  to transfer chamber  3001  is opened and one of the two end effectors of the dual wafer robot (not shown—see, for example, end effectors  2003  and  2005  in  FIG. 4A ) is extended  3010  into module  3002 . Typically, module  3002  will have some form of lift mechanism which allows the end effector to move in underneath a wafer in position  3020  and lift the wafer up off the lift mechanism (not shown), thereby freeing the wafer in position  3020  to be removed from module  3002 —this procedure is familiar to those skilled in the art and so is not further described herein. Note that since the end effector is empty during insertion step  3010 , there is no danger of a wafer slipping off the end effector, thus the end effector can be accelerated more quickly than if a wafer were being carried—the throughput calculations in  FIG. 38  assume a 0.5 g acceleration (4900 mm/s 2 ) (see the farthest right point on curve  4133  in  FIG. 37 ). 
         [0186]    Retraction  3011  moves the wafer from position  3020  in module  3002  to position  3021  in transfer chamber  3001 . Note that during retraction  3011 , the end effector acceleration must be small enough to ensure that the wafer does not slip off—axis  4141  in  FIG. 38  corresponds to various allowed accelerations for retraction  3011  (see curve  4133  in  FIG. 37 ). 
         [0187]    Rotation  3012  of the end effector moves the wafer from position  3021  to position  3022  on circle  3024 . Note that during rotation  3012  there will be both azimuthal and radial (centrifugal) accelerations of the wafer. These accelerations are orthogonal and combine in quadrature to give the total wafer acceleration (see  FIGS. 29-36 ). 
         [0188]    Extension  3013  moves the wafer from position  3022  in transfer chamber  3001  to position  3023  in pass-through module  3004 . Steps  3011 - 3013  must be done with an acceleration no higher than some pre-determined level, otherwise there is a risk of the wafer sliding off the end effector (see curves  4133 - 4137  in  FIG. 37 ). 
         [0189]    Finally, retraction  3014  pulls the end effector out of pass-through module  3004 , allowing valve  3031  to close. As for extension  3010  above, the end effector can be moved with a higher acceleration for this step since there is no danger of wafer slippage. Axes  3003  and  3005  define the directions for steps  3010 - 3011  and  3013 - 3014 , respectively. The angle between axes  3003  and  3005  may range from approximately 50° to 180°, depending on the number of process modules  3002  and pass-through modules  3004  which are attached to transfer chamber  3001 , as is familiar to those skilled in the art. 
         [0190]    Phases of End Effector Extension and Rotation 
         [0191]      FIG. 23  is a schematic illustration of the three phases of the end effector extension process. Transfer chamber  3101  is shown connected to process module  3102 , with a valve  3108  providing an opening for loading and unloading of wafer  3105 . The wafer position when the end effector is fully retracted is shown as dashed circle  3103 , and the wafer position for processing in module  3102  is shown as dashed circle  3104 . Velocities are shown as single line arrows, such as  3110 , while accelerations are shown as double-line arrows, such as  3115 . The lengths of the velocity ( 3110 - 3112 ) and acceleration ( 3115 - 3116 ) arrows show relative magnitudes. 
         [0192]    In view (A), the wafer being loaded into module  3102  is at position  3105 , just starting to move with velocity  3110  radially outwards from initial position  3103 . The wafer acceleration  3115  is in the same direction as velocity  3110  and is increasing, consistent with minimizing jerk and staying below the maximum allowed acceleration. 
         [0193]    In view (B), the wafer being loaded into module  3102  is at position  3106 , exactly halfway from position  3013  to position  3104 . At this midpoint, velocity  3111  is a maximum (longer arrow), while the acceleration is 0. 
         [0194]    In view (C), the wafer being loaded into module  3102  is at position  3107 , almost all the way out to final position  3104 . The velocity  3112  is lower, and the acceleration  3116  (opposite in direction to velocity  3112 ) is slowing the wafer down, consistent with jerk minimization. 
         [0195]      FIG. 24  is a schematic illustration of the three phases of the end effector rotation process. Rotation is more complex with respect to jerk minimization and keeping the acceleration below a pre-determined maximum because of radial (centrifugal) acceleration, which goes as V 2 /R, where V=the water azimuthal speed (measured at the outer edge of the wafer on the end effector) and R=the radius of rotation of the outer edge of the wafer on the end effector within the transfer chamber. In the example shown, the rotation is the maximum of 180°, however rotation angles ranging from approximately 50° to 180° are possible, as described in  FIG. 22 . Transfer chamber  3101  is shown connected to two modules  3150  and  3151 . Rotation of the robot is around circle  3153 , from initial position  3154  (on axis  3160 ) to final position  3155  (also on axis  3160 ). Axis  3161  shows the 90° rotation point. 
         [0196]    In view (A) of  FIG. 24 , wafer  3156  has just started to rotate from initial position  3154 . Azimuthal acceleration  3171  is increasing the velocity  3170 , consistent with jerk minimization and keeping the total acceleration approximately below a pre-determined maximum. The radial acceleration  3172  is (velocity  3170 ) 2 /(radius of circle  3153 ). The radial jerk is the time-derivative of the radial acceleration  3172 . The total acceleration is the vector combination of the orthogonal accelerations  3171  and  3172 . The total jerk function is the vector combination of the orthogonal time-derivatives of the azimuthal  3171  and radial accelerations  3172 . 
         [0197]    In view (B) of  FIG. 24 , the wafer is at position  3157  (along axis  3161 ), halfway from position  3154  to position  3155 . Velocity  3173  is at a maximum and there is no azimuthal acceleration. The total acceleration is exactly equal to the radial acceleration  3174  at position  3157 . 
         [0198]    In view (C) of  FIG. 24 , the wafer is at position  3158 , almost all the way to final position  3155  (along axis  3160 ). Velocity  3175  is lower than at position  3157  and the azimuthal acceleration  3176  is slowing the rotation further. Since the azimuthal velocity  3175  has decreased, so has the radial acceleration  3177 =(velocity  3175 ) 2 /(radius of circle  3153 ). 
         [0199]    End Effector Extension Process Optimization 
         [0200]      FIG. 25  is a chart of the end effector extension distance  4003  (plotted against axis  4002 ) versus the angle  4001  of arm # 1  (the actuator arm) during the process of extension of an end effector from the fully retracted position  4004  to the fully extended position  4005 . The same curve  4003  applies for both extension and retraction of the end effector. 
         [0201]      FIGS. 26-28  describe the end effector motion during extension from a fully retracted position to a fully extended position. The graphs for end effector retraction would have the labeling reversed on time axes  4011 ,  4021 , and  4031 , with the beginning of retraction at positions  4016 ,  4026 , and  4036 , respectively, and the end of retraction at time=0 s on the axes  4011 ,  4021 , and  4031 . All three graphs are calculated with the assumption of a maximum allowable acceleration of 0.15 g (2940 mm/s 2 ). For minimization of the square of the jerk function during motion, the equation for the position of the wafer center during extension of the end effector is (see Hogan, Neville, “Adaptive control of mechanical impedance by coactivation of antagonist muscles”, IEEE Trans. Automatic. Control AC-29 (1984), pp. 681-690, and Hogan, Neville, “An organizing principle for a class of voluntary movements”, J. Neurosci. 4 (1984), pp. 2745-2754): 
         [0000]        R ( t )= R   i +( R   f   −R   f )[10( t /τ) 3 −15( t /τ) 4 +6( t /τ) 5 ]  (eq. 1) 
         [0000]    where 
         [0202]    R(t)=the position of the wafer center relative to the center of the robot, 
         [0203]    R i =the initial position of the robot at t=0, 
         [0204]    R f =the final position of the robot at t=d, and 
         [0205]    τ=the extension time of the robot from R i  to R f . 
         [0206]    Taking the time derivative of eq. 1 gives the formula for the minimum jerk velocity of the end effector: 
         [0000]        R ′( t )=( R   f   −R   i )[30( t /τ) 2 −60( t /τ) 3 +30( t /τ) 4 ]/τ  (eq. 2) 
         [0000]    where R′(t)=dR(t)/dt. Taking another time derivative gives the minimum jerk acceleration of the end effector: 
         [0000]        R ″( t )=( R   f   −R   i )[60( t /τ)−180( t /τ) 2 +120( t /τ) 3 ]/τ 2    (eq. 3) 
         [0000]    and the minimum jerk function is then: 
         [0000]        R ′″( t )=( R   f   −R   i )[60−360( t /τ)+360( t /τ) 2 ]/τ 3    (eq. 4) 
         [0207]    Now we must consider how to determine the extension time, τ, which is determined by the maximum allowable acceleration a max . The maximum acceleration occurs at 
         [0000]        t=t   max accel  when  dR ″( t )/ dt≡R ′″( t )=0, 
         [0000]    so from equation 4: 
         [0000]        R ′″( t   max accel )=( R   f   −R   i )[60−360( t   max accel /τ)+360( t   max accel /τ) 2 ]/τ 3 ≡0   (eq. 5) 
         [0208]    Solving the quadratic equation gives: 
         [0000]        t   max accel /τ=(1−1/√3)/2≈0.2113   (eq. 6) 
         [0209]    Now this value for t/τ can be substituted into equation 3 to give: 
         [0000]        R ″( t   max accel )=( R   f   −R   i )[60(0.2113)−180(0.2113) 2 +120(0.2113) 3 ]/τ 2 =( R   f   −R   i )(5.7735)/τ 2   =a   max    (eq. 7) 
         [0210]    Solving this equation for τ gives: 
         [0000]      τ=√[( R   f   −R   i )(5.7735)/ a   max ]  (eq. 8) 
         [0211]      FIG. 26  is a chart of the end effector position (eq. 1)  4014  (plotted against axis  4012 ) and velocity (eq. 2)  4015  (plotted against axis  4013 ) versus the elapsed time  4011  from the beginning (0 s) to the end  4016  of the end effector extension. At time=0 s, the end effector is fully retracted in the position for rotation of the robot within the transfer chamber. At time  4016 , the end effector is fully extended for insertion of the wafer into a process module or a pass-through module. The curves  4014  and  4015  result from the process of minimization of the integral of the square of the jerk function (curve  4025  in  FIG. 27 ) over the time interval from time=0 s to time  4026 . 
         [0212]      FIG. 27  is a chart of the end effector acceleration (eq. 3)  4024  (plotted against axis  4022 ) and jerk (eq. 4)  4025  (plotted against axis  4023 ) versus the elapsed time  4021  from the beginning (0 s) to the end  4026  of the end effector extension process. The process of minimization of the square of the jerk function  4025  results in the parabolic curve shown, starting (t=0 in eq. 4) at 60(R f −R i )/τ 3 , dipping down to −30(R f −R i )/τ 3  at the middle (t=τ/2 in eq. 4) of the trajectory, then curving back up to 60(R f −R i )/τ 3  at the end (t=τ in eq. 4). 
         [0213]      FIG. 28  is a chart of angle of arm # 1   4034  (plotted against axis  4032 ) and angular acceleration of arm # 1   4035  (plotted against axis  4033 ) versus the elapsed time  4031  from the beginning (0 s) to the end  4036  of the end effector extension process. The chart for end effector retraction would be the same, but with the time axis reversed and time=0 at position  4005 . The curve  4003  is derived from the optimized (jerk minimization) curve  4014  in  FIG. 26 . The robot controller would implement this optimized curve through proper control of the robot rotor. 
         [0214]    End Effector 90° Rotation Process Optimization 
         [0215]      FIGS. 29-32  describe the end effector motion during rotation through an angle of 90°. All four graphs are calculated with the assumption of a maximum allowable acceleration of 0.15 g (2940 mm/s) The situation for rotational motion is somewhat more complex than for linear motion (such as robot extension and retraction in  FIGS. 26-28 ). The reason for this is that rotational motion induces centrifugal (radial) acceleration in addition to the azimuthal acceleration of the wafer around the are of the robot motion. Thus, the total wafer acceleration will be the vector sum of the radial and azimuthal accelerations, and the total jerk function will be the vector sum of the radial and azimuthal accelerations. The key difference between the azimuthal and radial accelerations is that the azimuthal acceleration is directly controlled by the motor actuator (as for linear motion), while the radial acceleration is purely a function of the wafer azimuthal velocity. Similarly, the azimuthal jerk is also directly controlled by the motor actuator, while the radial jerk is the derivative of the radial acceleration. 
         [0216]    Equations 9-12 below relate to the wafer azimuthal position S(t), and are very similar to equations 1-4 for the robot extension/retraction motion: 
         [0000]        S ( t )=(π R   r /2)[10( t /β) 3 −15( t /β) 4 +6( t /β) 5 ]  (eq. 9) 
         [0000]        S ′( t )=(π R   r /2)[30( t /β) 2 −60( t /β) 3 +30( t /β) 4 ]/β  (eq. 10) 
         [0000]        S ″( t )=(π R   r /2)[60( t /β)−180( t /β) 2 +120( t /β) 3 ]/β 2    (eq. 11) 
         [0000]        S ′″( t )=(π R   r /2)[60−360( t /β)+360( t /β) 2 ]/β 3    (eq. 12) 
         [0000]    where 
         [0217]    S(t)=the position of the wafer along a 90° are (=π/2 radians), a distance=πR r /2 
         [0218]    R r =the retracted position of the robot (constant during rotation), and 
         [0219]    β=the rotation time of the robot through a 90° are 
         [0000]      =√[(π R   r /2)(5.7735)/ a   max ] by analogy with equation 8 with the substitution of (π R   r /2) in place of ( R   f   −R   i ).   (eq. 13) 
         [0220]    From equation 10, the centrifugal (radial) acceleration is then: 
         [0000]        R ″( t )= S ′( t ) 2   /R   r    (eq. 14) 
         [0221]    Giving a radial jerk of 
         [0000]        R ′″( t )= dR ″( t )/ dt= 2  S ′( t ) S ″( t )/ R   r    (eq. 15) 
         [0222]    Note that since the rotational motion is on a constant radius R r , then 
         [0000]        R ( t )= R   r =constant   (eq. 16) 
         [0000]        R ′( t )=0, (eq. 17) 
         [0223]    The seeming inconsistency between R′(t)=0 and R″(t)&gt;0 is explained by the fact that the wafer is in an accelerating (non-inertial) frame. The reason for jerk function minimization is to ensure that the wafer does not get jarred loose from the end effector during motion, thus it is proper to consider the wafer motion in the frame of the end effector even though it is non-inertial (i.e., it is accelerating rotationally). Combining the radial and azimuthal accelerations and jerks quadratically gives the total acceleration and jerk: 
         [0000]        T ″( t )=√[ R ″( t ) 2   +S ″( t ) 2 ]  (eq. 18) 
         [0000]        T ′″( t )=√[ R ′″( t ) 2   +S ′″( t ) 2 ]  (eq. 19) 
         [0224]      FIG. 29  is a chart of the end effector azimuthal angular position (eq. 9)  4054  (plotted against axis  4052 ) and azimuthal velocity (eq. 10)  4055  (plotted against axis  4053 ) versus the elapsed time  4051  from the beginning (0 s) to the end  4056  of an end effector rotation process for the case of the end effector rotating from 0° to 90°. The maximum allowable velocity, S′ max allowed ,  4057  is calculated by setting the radial (centrifugal) acceleration equal to the maximum allowable acceleration: 
         [0000]      S′ max allowed =√[a max  R r ]  (eq. 20) 
         [0225]    The actual maximum velocity achieved during the 90° rotation is determined by setting t=β/2: 
         [0000]        S′   max   =S ′(β/2)=(π R   r /2)(1.875)/β&lt; S′   max allowed    (eq. 21) 
         [0226]    The graph for end effector rotation in the opposite direction (i.e., from 90° to 0°) would have the time axis  4051  labeling reversed, with the beginning of rotation at position  4056 , and the end of rotation at time=0 s on the axis  4051 —this applies to the graphs in  FIGS. 30-32 , also. End effector rotation must occur with the end effector in the fully retracted position. 
         [0227]      FIG. 30  is a chart of the end effector azimuthal acceleration (eq. 11)  4064  (plotted against axis  4062 ) and azimuthal jerk (eq. 12)  4065  (plotted against axis  4063 ) versus the elapsed time  4061  from the beginning (0 s) to the end  4066  of a 90° end effector rotation process. The maximum allowable accelerations, ±a max allowed ,  4067  (in the same direction as velocity  4055  in  FIG. 29) and 4068  (in the opposite direction as velocity  4055  in  FIG. 29 ) are plotted showing that the azimuthal acceleration  4064  is always between the upper ( 4067 ) and lower ( 4068 ) limits. 
         [0228]      FIG. 31  is a chart of the end effector radial acceleration (eq. 14)  4074  (plotted against axis  4072 ) and radial jerk (eq. 15)  4075  (plotted against axis  4073 ) versus the elapsed time  4071  from the beginning (0 s) to the end  4076  of a 90° end effector rotation process. Note that for 90° rotation, the radial acceleration  4074  is always below the maximum allowable acceleration, a max allowed ,  4077 . The radial acceleration  4074  Is the centrifugal acceleration induced by velocity  4055  (see FIG.  29 )—the radial position is constant at a value corresponding to maximum retraction of the end effector, and the radial velocity is always 0 mm/s. 
         [0229]      FIG. 32  is a chart of the end effector azimuthal acceleration (eq. 11)  4083  (=curve  4064  in  FIG. 30 ), radial acceleration (eq. 14)  4084  (=curve  4074  in  FIG. 31 ), and total acceleration (eq. 18)  4085  (=the vector combination of the orthogonal azimuthal  4083  and radial  4084  accelerations) versus the elapsed time  4081  from the beginning (0 s) to the end  4086  of a 90° end effector rotation process. Note that the total acceleration  4085  is always near or below the maximum allowable acceleration, a max allowed ,  4087 . 
         [0230]    End Effector 180° Rotation Process Optimization 
         [0231]      FIGS. 33-36  describe the end effector motion during rotation through an angle of 180°. All four graphs are calculated with the assumption of a maximum allowable acceleration of 0.15 g (=2940 mm/s). The situation for rotational motion through angles &gt;90° is somewhat more complex than for 90° rotations (such as in  FIGS. 29-32 ) because it is necessary to rotate for part of the time with no azimuthal acceleration in order to avoid excessive radial accelerations. As for the 90° described above, the rotational motion induces centrifugal (radial) acceleration in addition to the azimuthal acceleration of the wafer around the are of the robot motion. What is different for all rotations through angles θ&gt;90°, is that the rotation is at constant speed over the interval from 45° to (θ−45°). The rotational motion can be described in three phases: Phase 1 (azimuthal acceleration). Phase 2 (constant azimuthal speed), and Phase 3 (azimuthal deceleration), where the subscripts denote the formula for each of Phases 1-3 for the case of θ=180°: 
         [0000]        S   1 ( t )=(π R   r /2)[10( t /β) 3 −15( t /β) 4 +6( t /β) 5 ] for 0≦ t≦β/ 2   (eq. 22) 
         [0000]        S   2 ( t )= S   1 (β/2)+ S′   max ( t−β/ 2) for β/2&lt; t &lt;(τ−β/2)   (eq. 23) 
         [0000]        S   3 ( t )=(π R   r )− S   1 (τ− t ) for (τ−β/2)≦ t≦τ   (eq. 24) 
         [0000]        S   1 ′( t )=(π R   r /2)[30( t /β) 2 −60( t /β) 3 +30( t /β) 4 ]/β for 0≦ t≦β/ 2   (eq. 25) 
         [0000]        S   2 ′( t )= S   1 ′(β/2)= S′   max  from eq. 21 for β/2&lt; t &lt;(τ−β/2)   (eq. 26) 
         [0000]        S   3 ′( t )= S   1 ′(τ− t ) for (τ−β/2)≦ t≦τ   (eq. 27) 
         [0000]        S   1 ″( t )=(π R   r /2)[60( t /β)−180( t /β) 2 +120( t /β) 3 ]/β 2  for 0≦ t≦β/ 2   (eq. 28) 
         [0000]        S   2 ″( t )=0 for β/2&lt; t &lt;(τ−β/2)   (eq. 29) 
         [0000]        S   3 ″( t )=− S   1 ″(τ− t ) for (τ−β/2)≦ t≦τ   (eq. 30) 
         [0000]        S   1 ′″( t )=(π R   r /2)[60−360( t /β)+360( t /β) 2 ]/β 3  for 0&lt; t&lt;β/ 2   (eq. 31) 
         [0000]        S   2 ′″( t )=0 for β/2&lt; t &lt;(τ−β/2)   (eq. 32) 
         [0000]        S   3 ′″( t )= S   1 ′″(τ− t ) for (τ−β/2)≦ t≦τ   (eq. 33) 
         [0000]    where 
         [0232]    S i (t)=the position of the wafer along a 180° are (=π radians) for phase i, 
         [0233]    R r =the retracted position of the robot (constant during rotation), 
         [0234]    β=the rotation time of the robot through a 90° are from equation 13, 
         [0000]      =√[(π R   r /2)(5.7735)/ a   max ], and 
         [0235]    τ=the rotation time of the robot through a 180° are. 
         [0000]      =(π R   r /2)/ S′   max +β  (eq. 35) 
         [0236]    The radial functions are calculated similarly to those in equations 14-17. From equations 25-27, the centrifugal (radial) acceleration is (for phases i=1 to 3): 
         [0000]        R   i ″( t )= S   i ′( t ) 2   /R   r    (eq. 36) 
         [0000]    Giving a radial jerk of 
         [0000]        R   i ′″( t )= dR   i ″( t )/ dt= 2 S   i ′( t ) S   i ″( t )/ R   r    (eq. 37) 
         [0000]    Note that since the rotational motion is on a constant radius R r , then 
         [0000]        R   i ( t )= R   f =constant   (eq. 38) 
         [0000]        R   i ′( t )=0.   (eq. 39) 
         [0237]    The seeming inconsistency between R′(t)=0 and R″(t)&gt;0 is explained by the fact that the wafer is in an accelerating (non-inertial) frame. The reason for jerk function minimization is to ensure that the wafer does not get jarred loose from the end effector during motion, thus it is proper to consider the wafer motion in the frame of the end effector even though it is non-inertial (i.e., it is accelerating rotationally). Combining the radial and azimuthal accelerations and jerks quadratically gives the total acceleration and jerk: 
         [0000]        T   i ″( t )=√[ R   i ″( t ) 2   +S   i ″( t ) 2 ]  (eq. 40) 
         [0000]        T   i ′″( t )=√[ R   i ′″( t ) 2   +S   i ′″( t ) 2 ]  (eq. 41) 
         [0238]      FIG. 33  is a chart of the end effector azimuthal angular position (eqs. 22-24)  4094  (plotted against axis  4092 ) and azimuthal velocity (eqs. 25-27)  4095  (plotted against axis  4093 }versus the elapsed time  4091  from the beginning (0 s) to the end  4096  of an end effector rotation process for the case of the end effector rotating from 0° to 180°. The maximum allowable velocity  4097  is calculated by setting the radial (centrifugal) acceleration equal to the maximum allowable acceleration. The graph for end effector rotation in the opposite direction (i.e., from 180° to 0°) would have the time axis  4091  labeling reversed, with the beginning of rotation at position  4096 , and the end of rotation at time=0 s on the axis  4091 —this applies to the graphs in  FIGS. 34-36 , also. Note that the middle portion of the rotation (phase 2) is at constant velocity, since the radial (centrifugal) acceleration roughly equals the maximum allowable acceleration and thus no azimuthal acceleration is possible. End effector rotation must occur with the end effector in the fully retracted position, R r . 
         [0239]      FIG. 34  is a chart of the end effector azimuthal acceleration (eqs. 28-30)  4104  (plotted against axis  4102 ) and azimuthal jerk (eqs. 31-33)  4105  (plotted against axis  4103 ) versus the elapsed time  4101  from the beginning (0 s) to the end  4106  of a 180° end effector rotation process. The maximum allowable accelerations  4107  (in the same direction as velocity  4095  in  FIG. 33) and 4108  (in the opposite direction as velocity  4095  in  FIG. 33 ) are plotted showing that the azimuthal acceleration  4104  is always between the upper ( 4107 ) and lower ( 4108 ) acceleration limits, ±a max allowed . Note that the central region (phase 2 from 45° to 135°) has no azimuthal acceleration and no azimuthal jerk. Thus, in phase 2, the end effector is rotating at constant velocity, S′ max ,  4095  (see  FIG. 33 ) and constant radial (centrifugal) acceleration, S′ max   2 /R r ,  4114  (see  FIG. 35 ). 
         [0240]      FIG. 35  is a chart of the end effector radial acceleration (eq. 36)  4114  (plotted against axis  4112 ) and radial jerk (eq. 37)  4115  (plotted against axis  4113 ) versus the elapsed time  4111  from the beginning (0 s) to the end  4116  of a 180° end effector rotation process The maximum allowable acceleration, a max allowed ,  4117  is plotted showing that the radial acceleration  4114  Is always below the limit. Note that this radial acceleration  4114  is the centrifugal acceleration induced by velocity  4095  (see FIG.  33 )—the radial position is constant at a value corresponding to maximum retraction of the end effector, and the radial velocity is always 0 mm/s. In phase 2 (corresponding to rotation from 45° to 135°), the radial (centrifugal) acceleration is constant because the velocity  4095  (see  FIG. 33 ) is constant. Because the radial acceleration  4114  is constant over the central region, the derivative of the radial acceleration  4114  (the jerk function  4115 ) is 0 mm/s 3 . Since in phase 2 both the azimuthal (eqs. 31-33)  4105  (see  FIG. 34 ) and radial (eq. 37)  4115  jerk functions are 0 mm/s 3 , the total jerk function is also 0 mm/s 3 , and there is no contribution to the integral of the total jerk function squared over the central region. 
         [0241]      FIG. 36  is a chart of the end effector azimuthal acceleration (eqs. 28-30)  4123  (=curve  4104  in  FIG. 34 ), radial acceleration (eq. 36)  4124  (=curve  4114  in  FIG. 35 ), and total acceleration (eq. 40)  4125  (=the vector combination of the orthogonal azimuthal  4123  and radial  4124  accelerations) versus the elapsed time  4121  from the beginning (0 s) to the end  4126  of a 180° end effector rotation process. The maximum allowable acceleration, a max allowed ,  4127  is plotted showing that the total acceleration  4125  is always near or below the limit. 
         [0242]    Rotation and Wafer Transfer Times vs. Maximum Acceleration 
         [0243]      FIG. 37  is a chart of the extension times  4133  or rotation times  4134 - 4137  (plotted against axis  4132 ) of the end effector versus the maximum allowable acceleration  4131 . Rotation time curve  4134  corresponds to a 45° rotation, while rotation time curves  4135 - 4137  correspond to rotations 90°, 135°, and 180°, respectively, 
         [0244]      FIG. 38  is a chart of the combined times  4143 - 4146  (plotted against axis  4142 ) for one rotation+four extensions versus the maximum acceleration  4141 . Combined time  4143  corresponds to four extensions+one 45° rotation. Times  4144 - 4146  correspond to four extensions+rotations of 90°, 135°, and 180°, respectively.  FIG. 22  illustrates the wafer transfer process assumed in the generation of this graph—note that the wafer transfer process involves two extensions and two retractions—for  FIG. 38 , the two retractions are considered to be “extensions” since the timing considerations are identical, as discussed in  FIG. 26 . An extension or retraction of an empty end effector is assumed to be done with 50% of g acceleration (far right of  FIG. 37 ), while extensions or retractions of end effectors carrying wafers are assumed to have the accelerations shown on axis  4141  (corresponding to axis  4131  in  FIG. 37 ). In all cases, the rotations of the end effector are assumed to have a wafer, and thus to correspond to axis  4131  in  FIG. 37 . With proper cluster tool process sequencing, any rotations of the end effector without a wafer should occur while wafers are being processed and thus should have no effect on tool throughput. 
         [0245]    Dual Wafer Robot at Pass-Through Module 
         [0246]      FIG. 44A  is an isometric, view of a dual wafer robot  4401  configured in accordance with a further embodiment of the present invention, showing two wafers  4402  and  4404 , supported by end effectors  4403  and  4405 , respectively. The main difference between the dual wafer robot shown in  FIGS. 4A-11  and the robot shown in FIGS  44 A- 47  is the removal of the cam mechanism for independent asynchronous Z-motion of the end effectors ( FIG. 20 ). For the present robot, the only Z-motion of the end effectors which is possible is the collective Z-motion that was described above with reference to  FIG. 21 . 
         [0247]    In  FIG. 44A , wafers  4402  and  4404  have been positioned by end effectors  4403  and  4405 , respectively, in an above and below configuration, suitable for simultaneous (or near simultaneous) loading of wafers  4402  and  4404  into a pass-through module (not shown). Upper end effector  4403  is supported by support arm  4411  attached to rotor  4412  (see  FIG. 45  for a view of slider  4440  which connects support arm  4411  to end effector  4403 ). Actuator arm  4406  is attached to rotor  4407 , and is connected through pivot  4408  to outer arm  4409 . Outer arm  4409  is connected to end effector  4403  through pivot  4410 . Lower end effector  4405  is supported by support arm  4420  that is attached to rotor  4418 . Actuator arm  4413  is attached to rotor  4414 , and is connected through pivot  4415  to outer arm  4416 . Outer arm  4416  is connected to end effector  4405  through a pivot (not shown) which is equivalent to pivot  4410 . Details on the extension of the end effectors are provided in connection with the discussion of  FIG. 12 , above. 
         [0248]      FIG. 44A  and  FIG. 44B , which is a top view of the dual wafer robot  4401  shown in  FIG. 44A , illustrate the dual wafer robot  4401  with both end effectors fully retracted—this is the configuration in which the end effectors  4403  and  4405  may rotate. The rotors  4407 ,  4412 ,  4414 , and  4418  rotate around the central fixed tube  4419  which forms part of the transfer chamber (not shown—see, e.g., chambers  1105  and  1110  in  FIGS. 2A-B ), 
         [0249]      FIG. 44C  is a side view of the dual wafer robot illustrated in  FIGS. 44A-B . This view shows how support arms  4411  and  4420  extend downwards and upwards from rotors  4412  and  4418 , respectively, to enable end effectors  4403  and  4405  to position wafers  4402  and  4404  for insertion/removal into/out of vertically-spaced slots in a pass-through module. 
         [0250]      FIG. 45  is a top view of a dual wafer robot configured in accordance with an embodiment of the present invention, showing two wafers  4442  and  4444  in an above/below arrangement, where both robot end effectors are fully extended for loading two wafers  4442  and  4444  simultaneously (or nearly so) into a pass-through chamber (not shown). The slide mechanism comprising support arm  4411 , slider  4440 , and end effector  4403  can be seen in this view. In cases where there is a large difference between the wafer position for robot rotation and the wafer position in the center of a process module, the three-element telescoping arrangement shown here is preferred. In cases with a smaller extension distance, a two element (i.e., support arm and end effector, without the intervening slider) arrangement may be preferred. 
         [0251]    The actuator arm mechanism, which includes components  4406 - 4410 , is attached to the end effector in either the two- or three-element telescoping arrangements. In the example shown here, slider  4440  is not directly connected to an actuator—the motion of slider  4440  is due to physical stops (not shown) within the bearings connecting support arm  4411  to slider  4440  and the bearings connecting slider  4440  to end effector  4403 . Physical stops within sliding bearings are familiar to those skilled in the art. FIGS  51 A-B, below, illustrate an alternative extension drive mechanism wherein both the end effector and the intervening slider are actively driven by the rotor mechanism. 
         [0252]    Dual Wafer Robot at Process Modules 
         [0253]      FIG. 46  is a side view of the dual wafer robot, shown in  FIGS. 44A-45 . Note that in this embodiment of the present invention, wafers  4452  and  4454  are not at the same height. If the individual process modules require wafer insertion at the same height, then wafer insertion may be asynchronous, with an intervening collective Z-motion (see  FIG. 21 ) to reposition the second end effector to the same height that the first end effector previously had when inserting a wafer. 
         [0254]    Rotors with Independent Ring Bearings 
         [0255]      FIG. 47  is a schematic side cross-sectional view of a single robot actuator configured in accordance with yet another embodiment of the present invention. In this example, as for the example described immediately above, there is no cam-driven mechanism for asynchronous and independent Z-motions (FIG.  20 )—the only Z-motions are collective motions as discussed with reference to  FIG. 21 . 
         [0256]    The difference between the present example and the example discussed immediately above is that in the example discussed above, the two rotors for a single robot actuator were tied together by a ring bearing (see bearing  2532  in  FIG. 19 ), while in this example, each rotor is tied directly to the support tube  4419  and there is no bearing between the two rotors of a single robot actuator. Upper rotor  4407  is supported by ring bearing  4532 . The inner race of ring bearing  4532  is rigidly clamped to the wall  4419  of the central tube. The outer race of ring bearing  4532  is clamped to rotor  4407 . Lower rotor  4412  is supported by ring bearing  4533 . The inner race of ring bearing  4533  is rigidly clamped to the wall  4419  of the central tube. The outer race of ring bearing  4533  is clamped to rotor  4412 . 
         [0257]      FIG. 48  is an isometric view of a dual wafer robot  5401  configured with the features presently being discussed and showing two wafers  5402  and  5404 , supported by end effectors  5403  and  5405 , respectively. Wafers  5402  and  5404  have been positioned by end effectors  5403  and  5405 , respectively, in an above and below configuration, suitable for simultaneous (or near simultaneous) loading of wafers  5402  and  5404  into a pass-through module (not shown). Upper end effector  5403  is supported by support arm  5411  attached to rotor  5412 . Actuator arm  5406  is attached to rotor  5407 , and is connected through pivot  5408  to outer arm  5409 . Outer arm  5409  is connected to end effector  5403  through pivot  5410 . Lower end effector  5405  is supported by support arm  5420  that is attached to rotor  5418 . Actuator arm  5413  is attached to rotor  5414 , and is connected through pivot  5415  to outer arm  5416 . Outer arm  5416  is connected to end effector  5405  through a pivot (not shown) which is equivalent to pivot  5410 . Details on the extension of the end effectors are provided in connection with the discussion of  FIG. 12 , above. 
         [0258]      FIG. 48  illustrates the dual wafer robot  5401  with both end effectors fully retracted—this is the configuration in which the end effectors  5403  and  5405  may rotate. The rotors  5407 ,  5412 ,  5414 , and  5418  rotate around the central fixed tube  5419  which forms part of the transfer chamber (not shown—see, e.g., chambers  1105  and  1110  in  FIGS. 2A-B ). 
         [0259]    Rotors with Two Independent Ring Bearings 
         [0260]      FIG. 49  is a schematic side cross-sectional view of a single robot actuator in accordance still another embodiment of the present invention. In this example, as for the two discussed immediately above, there is no cam-driven mechanism for asynchronous and independent Z-motions (FIG.  20 )—the only Z-motions are collective motions as illustrated in  FIG. 21 . The difference between the immediately preceding example and the present example is that in the former, a single ring bearing guided the rotation of each rotor; in the present case, however, the rotation of each rotor is guided by a pair offing bearings. This arrangement has the advantage of improved rotational stability for each rotor, but at the added cost of a larger number of bearings per robot. 
         [0261]    As shown in the diagram, upper rotor  5806  is supported by ring bearings  5802  and  5805 . The inner races of ring bearings  5802  and  5805  are rigidly clamped to the wall  5830  of the central tube. The outer races of ring bearings  5802  and  5805  are clamped to rotor  5806 . Lower rotor  5816  is supported by ring bearings  5812  and  5815 . The inner races of ring bearings  5812  and  5815  are rigidly clamped to the wall  5830  of the central tube. The outer races of ring bearings  5812  and  5815  are clamped to rotor  5816 . 
         [0262]    Operation of the End Effector Actuator 
         [0263]      FIG. 50  is a schematic top view of a single robot end effector actuator assembly configured in accordance with yet another embodiment of the present invention, showing the end effector in three positions: (A) fully retracted, (B) partially extended, and (C) fully extended. One difference between the end effector actuator described above in connection with  FIG. 12  and the embodiment shown here is the added actuator arm connected to the slider. In the example described with reference to  FIG. 12 , the slider is moved only by contact with the end effector. This has the potential for particle generation during end effector extension and retraction. The example shown in  FIG. 50  avoids this possibility by moving the slider actively (not passively as in the example shown in  FIG. 12 ), thus greatly reducing the potential for vibration or particle generation since there is no impact between the slider and the end effector during the extension and retraction of the end effector. 
         [0264]    In view (A), end effector  6004 , carrying wafer  6001 , is fully retracted into the position for rotation of the end effector  6004  and wafer  6001 . End effector  6004  is attached to slider  6005  by a first linear bearing (not shown). Slider  6005  is attached to support arm  6006  by a second linear bearing (not shown). Linear bearings may be metal or ceramic ball bearings and/or magnetically-levitated bearings, as is familiar to those skilled in the art. 
         [0265]    Actuator arm  6007  is attached to rotor  6002  and coupled to outer arm  6008  through pivot  6011 . Outer arm  6008  is connected to end effector  6004  through pivot  6013 . Actuator arm  6007  is also attached to middle arm  6009  through pivot  6012 . Middle arm  6009  is connected to slider  6005  through pivot  6014 . Rotor  6002  turns around central tube  6003 . Actuator arm  6007  is starting to turn clockwise as shown by the arrow, causing end effector  6004  to begin extending as shown by the arrow on wafer  6001 . 
         [0266]    In view (B), end effector  6004 , carrying wafer  6001 , is shown partially extended. Actuator arm  6007  has rotated clockwise, driving outer arm  6008  to push end effector  6004  outwards. Simultaneously, middle arm  6009  has pushed slider  6005  roughly half as far out as end effector  6004  has moved. During the extension operation, the rotor  6109  (see  FIG. 51 ) connected to support arm  6006  does not turn. 
         [0267]    In view (C), end effector  6004  is fully extended, positioning wafer  6001  in either a process module or a pass-through module (not shown). 
         [0268]      FIG. 51  is a side view of the single robot end effector actuator shown in  FIG. 50  view (C), showing the end effector  6004  (carrying wafer  6001 ) fully extended. The rotor  6109  connected to support arm  6006  can be seen. 
         [0269]    Operation of the Dual End Effector Actuator 
         [0270]      FIG. 52A  is a schematic top view of a single robot dual end effector actuator assembly configured in accordance with still another embodiment of the present invention, showing the dual end effector in three positions: (A) fully retracted, (B) partially extended, and (C) fully extended. One difference between this present example and previously discussed examples is the capability for simultaneous loading/unloading of two wafers with one robot actuator. 
         [0271]    In view (A), end effector  6125  carrying wafer  6101 , and end effector  6128  carrying wafer  6102 , are both fully retracted into the positions for rotation of the end effectors  6125  and  6128 . End effector  6125  is attached to slider  6126  by a first linear bearing (not shown). Slider  6126  is attached to support arm  6127  by a second linear bearing (not shown). End effector  6128  is attached to slider  6129  by a third linear bearing (not shown). Slider  6129  is attached to support arm  6130  by a fourth linear bearing (not shown). Linear bearings may be metal or ceramic ball bearings and/or magnetically-levitated bearings, as is familiar to those skilled in the art. 
         [0272]    Actuator arm  6107  is attached to rotor  6103  and coupled to outer arm  6105  through pivot  6109 . Outer arm  6105  is connected to end effector  6125  through pivot  6111 . Actuator arm  6108  is also attached to rotor  6103  and is coupled to outer arm  6106  through pivot  6110 . Outer arm  6106  is connected to end effector  6128  through pivot  6112 . Rotor  6103  turns around central tube  6104 . Actuator arms  6107  and  6108  are starting to turn clockwise as shown by the curved arrows, causing end effectors  6125  and  6128  to begin extending as shown by the arrows on wafers  6101  and  6102 . 
         [0273]    In view (B), end effectors  6125  and  6128 , carrying wafers  6101  and  6102 , respectively, are shown partially extended. Actuator arm  6107  has rotated clockwise, driving outer arm  6105  to push end effector  6125  radially outwards. Simultaneously, actuator arm  6108  has rotated clockwise, driving outer arm  6106  to push end effector  6128  radially outwards. During the extension operation, the rotor  6132  (see  FIG. 52B ) connected to support arms  6127  and  6130  does not turn. 
         [0274]    In view (C), end effectors  6125  and  6128  are fully extended, positioning wafers  6101  and  6102  in either process modules or pass-through modules (not shown). 
         [0275]      FIG. 52B  is a side view of the single robot dual end effector actuator shown in  FIG. 52A  view (C), showing the end effector  6125  (carrying wafer  6101 ) and the end effector  6128  (carrying wafer  6102 ) both fully extended. Rotor  6132  connected to support arms  6127  and  6130  is shown. 
         [0276]    Operation of the Dual End Effector Actuator 
         [0277]      FIG. 53  is a schematic top view of a single robot end dual effector actuator assembly in accordance with yet a further embodiment of the present invention, showing the dual end effector in three positions: (A) fully retracted, (B) partially extended, and (C) fully extended. One difference between this present embodiment and the embodiment discussed immediately above is the orientation of the end effectors—in the present case, the angle between the end effectors is not 180°. 
         [0278]    In view (A), end effector  6525  carrying wafer  6501 , and end effector  6528  carrying wafer  6502 , are both fully retracted into the positions for rotation of the end effectors  6525  and  6528 —note that in this example, it is not necessary for the support arms  6527  and  6530  to be oriented on directly opposite sides of the central tube  6504 . End effector  6525  is attached to slider  6526  by a first linear bearing (not shown). Slider  6526  is attached to support arm  6527  by a second linear bearing (not shown). End effector  6528  is attached to slider  6529  by a third linear bearing (not shown). Slider  6529  is attached to support arm  6530  by a fourth linear bearing (not shown). Linear bearings may be metal or ceramic ball bearings and/or magnetically-levitated bearings, as is familiar to those skilled in the art. 
         [0279]    Actuator arm  6507  is attached to rotor  6503  and coupled to outer arm  6505  through pivot  6509 . Outer arm  6505  is connected to end effector  6525  through pivot  6511 . Actuator arm  6508  is also attached to rotor  6503  and is coupled to outer arm  6506  through pivot  6510 . Outer arm  6506  is connected to end effector  6528  through pivot  6512 . Rotor  6503  turns around central tube  6504 . Actuator arms  6507  and  6508  are starting to turn clockwise as shown by the curved arrows, causing end effectors  6525  and  6528  to begin extending as shown by the arrows on wafers  6501  and  6502 . 
         [0280]    In view (B), end effectors  6525  and  6528 , carrying wafers  6501  and  6502 , respectively, are shown partially extended. Actuator arm  6507  has rotated clockwise, driving outer arm  6505  to push end effector  6525  radially outwards. Simultaneously, actuator arm  6508  has rotated clockwise, driving outer arm  6506  to push end effector  6528  radially outwards. During the extension operation, the rotor (not shown) connected to support arms  6527  and  6530  does not turn. 
         [0281]    In view (C), end effectors  6525  and  6528  are fully extended, positioning wafers  6501  and  6502  in either process modules or pass-through modules (not shown). 
         [0282]    Operation of the Dual End Effector Actuator 
         [0283]      FIG. 54A  is a schematic top view of a single robot dual end effector actuator assembly  6660  in accordance with still another embodiment of the present invention, wherein the wafer insertion directions are in tandem but where the insertion processes may be asynchronous, showing the dual end effector in two positions: (A) both wafers fully retracted, and (B) one wafer is fully extended while the other wafer is fully retracted. 
         [0284]    In view (A), end effector  6614  carrying wafer  6601 , and end effector  6617  carrying wafer  6602 , are both fully retracted into the positions for rotation of the end effectors  6614  and  6617 . End effector  6614  is attached to slider  6615  by a first linear bearing (not shown). Slider  6615  is attached to support arm  6616  by a second linear bearing (not shown). End effector  6617  is attached to slider  6618  by a third linear bearing (not shown). Slider  6618  is attached to support arm  6619  by a fourth linear bearing (not shown). Linear bearings may be metal, or ceramic ball bearings and/or magnetically-levitated bearings, as is familiar to those skilled In the art. 
         [0285]    Actuator arm  6606  is attached to rotor  6603  and coupled to outer arm  6607  through pivot  6611 . Outer arm  6607  is connected to end effector  6614  through pivot  6610 . Actuator arm  6608  is attached to rotor  6654  (see  FIG. 54B ) and is coupled to outer arm  6609  through pivot  6613 . Outer arm  6609  is connected to end effector  6617  through pivot  6612 . Rotors  6603  and  6654  turn around central tube  6604 . Actuator arm  6606  is starting to turn clockwise as shown by the curved arrow, causing end effector  6614  to begin extending as shown by the arrow on wafer  6601 . Actuator arm  6608  is not rotating, thus end effector  6617  is remaining at the fully retracted position—this demonstrates the fully independent and asynchronous operation of the two end effectors  6614  and  6617 . 
         [0286]    In view (B), end effector  6614 , carrying wafer  6601 , is shown fully extended. Actuator arm  6606  has rotated clockwise, driving outer arm  6607  to push end effector  6614  outwards. Actuator arm  6608  has not moved, thus end effector  6617 , carrying wafer  6602 , remains fully retracted. During the extension operation, the rotor  6653  (see  FIG. 54B ) connected to support arms  6616  and  6619  through cross-member  6605  does not turn. 
         [0287]      FIG. 54B  is a side view of the single robot dual end effector actuator shown in  FIG. 54A  view (B), showing the end effector  6614  (carrying wafer  6601 ) fully extended, and end effector  6617  (carrying wafer  6602 ) fully retracted. Rotor  6653  connected to support arms  66 . 16  and  6619  through cross-member  6605  is shown. Rotor  6654  connected to actuator arm  6608  is at the bottom. 
         [0288]      FIG. 55  is a top schematic view of the single robot dual end effector actuator assembly  6660  shown in  FIGS. 54A-B , showing the robot operation illustrated in view (B) of  FIG. 54A  in a four process chamber system. Central chamber  6682  contains the robot assembly  6660 . Around chamber  6682 , four process modules or loadlocks  6678 - 6681  are connected. There are two wafer positions for processing within each of chambers  6678 - 6681 : positions  6670 - 6671  in chamber  6678 , positions  6672 - 6673  in chamber  6679 , positions  6674 - 6675  in chamber  6680 , and positions  6676 - 6677  in chamber  6681 . The independent and asynchronous operation of the dual end effector robot can be seen in this figure: a wafer has been loaded into position  6671  in chamber  6678 , while the wafer in position  6670  remains unchanged. 
         [0289]    Thus, systems and methods for wafer or other substrate processing, handling and/or transport have been described. Although discussed with reference to certain illustrated embodiments, the present invention should not be limited thereby. For example, in connection with various ones of the examples discussed above the illustrative figures have shown the actuation mechanism with a single outer arm and no middle arm. This need not necessarily be so. In some cases, although shown without such a middle arm, embodiments of the invention may be configured with such a middle arm. The use of such a middle arm provides the advantage of potential reductions in particle generation and lower vibration. The disadvantage of this slightly more complex actuator mechanism is increased cost and complexity. Further, various of the embodiments of the present invention may utilize any of the rotor configurations described above. The potential advantages of the different rotor configurations may, in some cases, simplify the assembly of the robot, actuator mechanism, especially in cases where each rotor is mechanically independent (except for the coupling through the various actuator arms). Hence, the present invention should only be measured in terms of the claims, which follow.