Wafer Chuck Assembly

Abstract

To provide a wafer chuck assembly that prevents eccentricity and misalignment during wafer rotation in an EBR process for forming a bevel at an edge portion of a wafer.SOLUTION: A wafer chuck assembly 100 includes a chuck hub, and a centering hub 102 disposed inside the chuck hub. An engagement device operates between an engagement position and a non-engagement position to support a wafer 112 and prevent displacement during processing. A plurality of hollow chuck arms 118 are attached to the chuck hub, and each hollow chuck arm extends radially between a proximal end adjacent the chuck hub and a distal end remote therefrom. Each of a plurality of centering cams 110 is mounted at or toward the tip of the chuck arm and is operable to engage or disengage the wafer in response to rotational movement of the centering hub relative to the chuck hub.SELECTED DRAWING: Figure 3

Description

[Technical field]

[0001] [Priority claim] This application claims the benefit of priority to U.S. Provisional Patent Application No. 62 / 667,190, filed May 4, 2018, and U.S. Patent Application No. 16 / 215,608, filed December 10, 2018, both of which are incorporated by reference in their entireties.

[0002] The present disclosure generally relates to chuck technology for supporting a semiconductor wafer during processing. In one embodiment, a vacuum wafer chuck for edge bevel removal (EBR) is provided. In a more specific aspect, the present disclosure relates to a post-electrofill module (PEM) chuck for removing unwanted metal, such as a plating film or seed layer, from the outer edge of a wafer during EBR. [Background technology]

[0003] The discussion of the background art provided herein is intended to present the contents of the present disclosure generally, and the inventions of the presently named inventors are not admitted expressly or impliedly as prior art to the present disclosure to the extent that they are described in this Background section and in a manner that is not prior art at the time of filing.

[0004] EBR is typically performed by applying chemical fluids through a nozzle aimed near the wafer edge while the wafer is rotated. To produce uniform EBR results, the wafer must be properly centered on the chuck or must be concentric with the chuck. Existing chucks that use friction pads or passive centering means may not actively center the wafer before the EBR process. This can lead to poor EBR results. Poor EBR results can cause further errors, for example, when the transfer of the wafer to the PEM by a robot is not precise.

[0005] An additional problem occurs when the etchant used in the EBR process bounces off around the wafer support means, such as the vertical alignment pin (VAP) surface. The bounced liquid can interfere with the EBR process and contribute to poor EBR results. This effect can become more evident as the edge exclusion (EE) area decreases. EE usually refers to the amount of material removed about the wafer edge.

[0006] In a further example, a wafer may slip off a conventional chuck support during rotation, again leading to poor centering and poor EBR results. Wafer presence detection using external sensors is not always reliable and can be affected, for example, by wafer droplet splash. Splash can occur as described above or in other ways during wafer cleaning. A slipped wafer can cut harmful grooves into the cams of chucks that have centrifugal centering cams. This can shorten the life of the chuck and can also cause the grooved cams to press against the wafer edge. Summary of the Invention

[0007] In some examples, a wafer chuck assembly for supporting a wafer includes a chuck hub, a centering hub disposed within the chuck hub, an engagement device movable between an engaged position and a disengaged position, respectively, for engaging the chuck hub with the centering hub to prevent or allow relative movement therebetween in either a clockwise or counterclockwise rotational direction, a chuck motor for selectively rotating the chuck hub and / or the centering hub during wafer processing and wafer centering operations based on the engaged or disengaged position of the engagement device, a plurality of chuck arms attached to the chuck hub, each chuck arm extending radially between a proximal end adjacent the chuck hub and a distal end remote therefrom, and a plurality of centering cams attached at or toward the distal end of the chuck arm and movable radially inward or outward relative to the centering hub to engage or disengage an edge of a supported wafer in response to rotational movement of the centering hub relative to the chuck hub.

[0008] In some examples, the chuck motor is configured to impart relative rotational motion between the centering hub and the chuck hub during a wafer centering operation. In some examples, the centering hub is fixed to the chuck motor during the wafer centering operation, and the chuck motor is configured to rotate the chuck hub in a first rotational direction during the wafer centering operation.

[0009] In some examples, the chuck motor is configured to rotate the centering hub and the chuck hub together in a same rotational direction during the wafer processing operation, hi some examples, the same rotational direction of the centering hub and the chuck hub during the wafer processing operation is opposite to a first rotational direction of the chuck hub during the wafer centering operation.

[0010] In some examples, the centering hub includes at least one cam surface on its outer surface. In some examples, each chuck arm includes a respective elongated actuation rod operatively disposed between the at least one cam surface of the centering hub and a centering cam disposed at a distal end of the respective chuck arm. Each elongated actuation rod may include a bearing surface at a proximal end thereof for engaging the at least one cam surface of the centering hub. In some examples, each elongated actuation rod includes a coupling at a distal end thereof with a respective centering cam of the respective chuck arm. In some examples, rotational movement of the centering hub causes the respective cam surface of the centering hub to urge the respective elongated actuation rod radially outward to actuate the respective centering cam via the coupling.

[0011] In some examples, the wafer chuck assembly further comprises at least one vacuum pad for supporting a wafer during wafer centering operations and / or wafer processing operations. In some examples, the at least one vacuum pad is configured to maintain the wafer in a centered position on the wafer chuck assembly at least during wafer processing operations when the wafer is released onto the plurality of centering cams. In some examples, at least one of the plurality of chuck arms is provided with at least one vacuum pad. Each of the plurality of chuck arms may comprise a vacuum line for supplying vacuum pressure to the at least one vacuum pad. In some examples, the presence or absence of vacuum pressure at the at least one vacuum pad is detected and correlated to the presence or absence of a wafer or the presence of a defective wafer in the wafer chuck assembly.

[0012] In some examples, the centering cams are biased toward an open, wafer-releasing configuration. In some examples, each centering cam of the plurality of centering cams is operable between a first wafer centering position and a second storage position, the second storage position being disposed below a top surface of a wafer supported in the wafer chuck assembly.

[0013] In some examples, the wafer chuck assembly further comprises control means for detecting a torque of the chuck motor and correlating the detected chuck motor torque with at least a first wafer centering position of the plurality of centering cams. In some examples, the wafer chuck assembly further comprises control means for detecting a torque of the chuck motor and correlating the detected chuck motor torque with a centered position of a wafer held on the wafer chuck assembly. In some examples, the wafer chuck assembly further comprises control means for detecting a torque of the chuck motor and correlating the detected chuck motor torque with a diameter of a wafer held on the wafer chuck assembly.

[0014] In another embodiment, a vacuum wafer chuck assembly is provided that includes a chuck hub, a centering hub disposed within the chuck hub, a plurality of chuck arms attached to the chuck hub, each chuck arm extending radially between a proximal end adjacent the chuck hub and a distal end remote therefrom, a plurality of centering cams, each mounted at or toward a distal end of the chuck arm and movable radially inwardly or outwardly relative to the centering hub to engage or release an edge of a supported wafer in response to a rotational movement of the chuck hub, and at least one vacuum pad for supporting a wafer during a wafer centering or wafer processing operation.

[0015] In some examples, the wafer chuck assembly further includes an engagement device operable between an engaged position and a disengaged position to engage the chuck hub with the centering hub to prevent relative movement therebetween in either a clockwise or counterclockwise rotational direction, or to allow relative movement therebetween in either a clockwise or counterclockwise rotational direction, respectively, and a chuck motor for selectively rotating the chuck hub and / or the centering hub based on the engaged or disengaged position of the engagement device during wafer processing and wafer centering operations.

[0016] In some examples, the chuck motor is configured to impart relative rotational motion between the centering hub and the chuck hub during a wafer centering operation. In some examples, the centering hub is fixed to the chuck motor during the wafer centering operation, and the chuck motor is configured to rotate the chuck hub in a first rotational direction during the wafer centering operation.

[0017] In some examples, the chuck motor is configured to rotate the centering hub and the chuck hub together in a same rotational direction during the wafer processing operation, hi some examples, the same rotational direction of the centering hub and the chuck hub during the wafer processing operation is opposite to a first rotational direction of the chuck hub during the wafer centering operation.

[0018] In some examples, the centering hub includes at least one cam surface on its outer surface. In some examples, each chuck arm includes a respective elongated actuation rod operatively disposed between the at least one cam surface of the centering hub and a centering cam disposed at a distal end of each chuck arm of the plurality of centering cams. In some examples, each elongated actuation rod includes a bearing surface at a proximal end thereof for engaging the at least one cam surface of the centering hub. In some examples, each elongated actuation rod includes a coupling portion at a distal end thereof with a respective centering cam of a respective chuck arm.

[0019] In some examples, rotational movement of the centering hub causes respective cam surfaces on the centering hub to urge respective elongated actuating rods radially outwardly, thereby actuating respective centering cams via the linkages.

[0020] In some examples, the at least one vacuum pad is configured to maintain the wafer in a centered position on the wafer chuck assembly at least during wafer processing operations when the wafer is released onto the plurality of centering cams. In some examples, the at least one vacuum pad is provided on at least one of the plurality of chuck arms. In some examples, each of the plurality of chuck arms includes a vacuum line for supplying vacuum pressure to the at least one vacuum pad. In some examples, the presence or absence of vacuum pressure at the at least one vacuum pad is detected and correlated to the presence or absence of a wafer or the presence of a defective wafer in the wafer chuck assembly.

[0021] In some examples, the centering cams are biased toward an open, wafer-releasing configuration. In some examples, each centering cam of the plurality of centering cams is operable between a first wafer centering position and a second storage position, the second storage position being disposed below a top surface of a wafer supported in the wafer chuck assembly.

[0022] In some examples, the wafer chuck assembly further comprises control means for detecting a torque of the chuck motor and correlating the detected chuck motor torque with at least a first wafer centering position of the plurality of centering cams. In some examples, the wafer chuck assembly further comprises control means for detecting a torque of the chuck motor and correlating the detected chuck motor torque with a centered position of a wafer held on the wafer chuck assembly. In some examples, the wafer chuck assembly further comprises control means for detecting a torque of the chuck motor and correlating the detected chuck motor torque with a diameter of a wafer held on the wafer chuck assembly.

[0023] In another embodiment, a wafer chuck assembly for supporting a wafer is provided. An exemplary wafer chuck assembly includes a chuck hub, a centering hub disposed within the chuck hub, a chuck motor for selectively rotating the chuck hub or the centering hub during wafer processing and wafer centering operations, a plurality of chuck arms attached to the chuck hub, each chuck arm extending radially between a proximal end adjacent the chuck hub and a distal end remote therefrom, a plurality of centering cams, each centering cam mounted at or toward a distal end of the chuck arm and movable radially inwardly or outwardly relative to the centering hub to engage or disengage an edge of a supported wafer in response to rotational movement of the centering hub relative to the chuck hub, and control means for detecting torque of the chuck motor and correlating the detected chuck motor torque with at least a first wafer centering position of the plurality of centering cams.

[0024] In some examples, the wafer chuck assembly further includes an engagement device operable between an engaged position and a disengaged position to engage the chuck hub with the centering hub to prevent relative movement therebetween in either a clockwise or counterclockwise rotational direction, or to allow relative movement therebetween in either a clockwise or counterclockwise rotational direction, respectively, and the chuck motor selectively rotates the chuck hub or the centering hub based on the engaged or disengaged position of the engagement device during wafer processing and wafer centering operations.

[0025] In some examples, the control means detects the torque of the chuck motor and correlates the detected chuck motor torque with a centered position of a wafer held on the wafer chuck assembly. In some examples, the control means detects the torque of the chuck motor and correlates the detected chuck motor torque with a diameter of a wafer held on the wafer chuck assembly. [Brief description of the drawings]

[0026] Certain embodiments are illustrated by way of example and not limitation in the accompanying drawings.

[0027] [Figure 1A] 1 is a schematic cross-sectional view of an aspect of a chuck assembly in accordance with an exemplary embodiment; [Figure 1B] 1 is a schematic cross-sectional view of an aspect of a chuck assembly in accordance with an exemplary embodiment;

[0028] [Diagram 2] 1 is an illustration of a centering hub in accordance with an exemplary embodiment;

[0029] [Diagram 3] 1 is an illustration of a chuck assembly attached to a spindle assembly in accordance with an illustrative embodiment;

[0030] [Figure 4A] 2 is an illustration of a chuck spindle assembly and vacuum supply components in accordance with an illustrative embodiment; [Figure 4B] 2 is an illustration of a chuck spindle assembly and vacuum supply components in accordance with an illustrative embodiment;

[0031] [Diagram 5] 1 is an illustration of a top side view of a chuck assembly in accordance with an exemplary embodiment;

[0032] [Figure 6] 1 is an underside view of a chuck assembly for holding a wafer in accordance with an exemplary embodiment.

[0033] [Figure 7] 4 is a pictorial diagram of a centering hub and associated components of a chuck assembly in accordance with an exemplary embodiment;

[0034] [Figure 8]FIG. 2 is a cross-sectional view of a chuck assembly secured to a head portion of a chuck spindle assembly according to an exemplary embodiment;

[0035] [Figure 9] 11 is a pictorial diagram illustrating an arrangement of engagement fins and locking pins according to an exemplary embodiment;

[0036] [Figure 10] FIG. 13 is a cross-sectional view of a chuck assembly with a retracted stop pin and a cam in a lowered position according to an exemplary embodiment.

[0037] [Figure 11] FIG. 11 is a cross-sectional view of the example chuck assembly of FIG. 10 with the locking pin up and cam up or wafer centering position according to an example embodiment.

[0038] [Figure 12A] 1 is a pictorial diagram of a conventional chuck component in accordance with an exemplary embodiment; [Figure 12B] 1 is a pictorial diagram of a conventional chuck component in accordance with an exemplary embodiment;

[0039] [Figure 12C] 1 is a pictorial diagram of a chuck assembly and associated components in accordance with an exemplary embodiment;

[0040] [Figure 13] 11A-11C are tables and graphs of exemplary EBR measurement results according to some exemplary embodiments.

[0041] [Figure 14] 5 illustrates a torque profile of a chuck motor during a centering operation according to an exemplary embodiment.

[0042] [Figure 15] FIG. 1 is a block diagram representing an example machine upon which one or more example embodiments may be implemented or controlled.

[0043] [Figure 16] 4 is a flow chart illustrating the operation of a method according to an example embodiment. DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENTS

[0044] The following description includes systems, methods, techniques, instruction sequences, and computer program products embodying exemplary embodiments of the present disclosure. In the following description, for purposes of explanation, numerous specific details are set forth to provide a thorough understanding of the exemplary embodiments. However, it will be apparent to those skilled in the art that the subject matter of the present invention may be practiced without these specific details.

[0045] A portion of the disclosure of this patent document contains material that may be subject to copyright protection. The copyright owner has no objection to any facsimile of the patent document or patent disclosure as it appears in the Patent and Trademark Office patent file or records, and reserves all copyrights therein. The following notice applies to any material shown in the drawings that form a part of this document, as identified below:Copyright Lam Research Corporation, 2018-19 Reproduction without permission is prohibited.

[0046] In one example, a centering chuck assembly is provided. The chuck assembly includes a retractable gripping cam (or clamp) for centering a wafer held by the chuck assembly, described in more detail below. Some exemplary wafer chuck assemblies include vacuum pads for improved gripping force and engagement flexibility of the wafer in the chuck. The chuck assembly may actively center the wafer after it is placed on it. The wafer may be placed on the chuck assembly by a robot prior to processing, for example, in an EBR process. Centering of the wafer is possible in other applications as well.

[0047] As noted above, accurate and reliable centering of the wafer on the chuck assembly (also referred to herein as the chuck, where applicable) can be important to achieving high EBR quality. In some examples of the present disclosure, the chuck assembly includes a vacuum pad to which a vacuum can be applied to secure an element such as a substrate or wafer. In some examples, the chuck assembly further includes a centering cam that retracts horizontally below the top surface of the wafer mounted on the chuck assembly while a vacuum is applied to the vacuum pad to hold the wafer in place. The lack of a surrounding structure with the retracting cam eliminates a splash surface that can cause EBR chemicals or water to splash onto the wafer surface. This arrangement thus substantially eliminates a major contributor to the poor EBR results and disadvantages described above.

[0048] In some examples of the present chuck assemblies, high wafer gripping forces can be generated. In some examples, a wafer can be vacuum gripped in place with six or more times the gripping force of a conventional friction pad having the same diameter. In some examples, the presence or position of a wafer in the chuck assembly is detected or measured in conjunction with a vacuum clamp. For example, the backside of a mounted wafer can seal against a vacuum pad in the chuck, allowing a gradual or stepwise vacuum to be developed or applied to the wafer. The fact that a vacuum can be applied can indicate that a wafer is present in the chuck. In other examples, low vacuum pressure can indicate that a wafer is not present in the chuck or is somehow improperly mounted. High vacuum pressure can indicate correct wafer mounting.

[0049] Reference is now made to Figures 1A-1B, which include schematic cross-sectional views of an exemplary chuck assembly 100. A centering hub 102 is disposed within a chuck hub 104. The centering hub 102 can rotate independently of the chuck hub 104, but rotates in the same direction as the chuck hub 104 under normal rotational motion, e.g., during wafer processing. The normal rotational motion can be, for example, clockwise. An illustration of an exemplary centering hub 102 is shown in Figure 2. As shown, the centering hub 102 includes a series of cam surfaces 114 that abut the ends of an actuation push rod 116, which will be described in more detail below.

[0050] In a wafer centering operation, the centering hub 102 is locked to the chuck spindle 106 by a locking pin 108 that can be pressed upward into a recess 109 of the centering hub 102. Thus, the centering hub 102 becomes a fixture, so to speak. The chuck assembly 100 can then be rotated in the opposite direction (e.g., counterclockwise) to create a relative rotational movement between the centering hub 102 and the chuck hub 104. The relative rotational movement between the centering hub 102 and the chuck hub 104 at a slow speed causes the cam surface 114 of the centering hub 102 to urge the actuation push rod 116 outwardly to rotate the cam 110 as shown in FIG. 1B. In some examples, the actuation push rod 116 is movably mounted within a hollow chuck arm 118. In some examples, the cam 110 is kinematically coupled to accommodate wafers 112 of different diameters. Although three cams 110 are shown, other numbers and configurations of cams are possible.

[0051] In some examples, the motor torque of the chuck spindle 106 is monitored and a spike in the motor torque indicates that the cam 110 has fully closed against the edge of the wafer 112 to indicate that the wafer 112 has been centered. The centering hub 102 may be spring loaded radially as shown to release the cam 110 and remove the wafer 112 when rotation stops or when the chuck assembly 100 slows down. In some examples, the chuck hub 104 is positioned to remain stationary during centering of the wafer and the centering hub 102 rotates therein to operate the cam 110. In other examples, neither the centering hub 102 nor the chuck hub 104 are stationary during centering, yet counter-rotating motion between these components is provided so that the cam 110 remains operable and can open and close. In some examples, one or more sensors monitor the position of the locking pin 108. The motor of the chuck spindle 106 may be used for both rotation and centering.

[0052] Some examples of the chuck assembly 100 include a vacuum supply line 120. In Figure 1A, the vacuum supply line 120 provides a vacuum (or negative pressure) to a vacuum pad 122 that supports the wafer 112. In some examples, the hollow chuck arm 118 is radially aligned with the vacuum supply line 120 to minimize obscurity and reduce the possibility of rinse agent splashback during EBR.

[0053] 3 includes an illustration of the chuck assembly 100 with some internal components shown in ghost lines. Components corresponding to those described above are numbered the same. Generally shown are the chuck assembly 100, chuck spindle 106, spindle motor 126, and vacuum supply 124 relative to the rotating union (visible in FIG. 4A).

[0054] 4A-B further illustrate pictorial views of the chuck spindle 106 assembly and vacuum supply. The illustrated rotary union 128 passes vacuum to the chuck vacuum lines in a manner somewhat similar to how slip rings pass current to the coils of an electric motor, and a correspondingly sized O-ring 130 seals the vacuum circuit to the chuck assembly 100. The view of FIG. 4A also shows the locking pin 108 in an up or locked position, which engages the centering hub 102 with the chuck spindle 106. In FIG. 4B, the pneumatic supply 107 for the drive cylinder 132 that drives the locking pin 108 is shown.

[0055] In some examples, the chuck spindle motor 126 has an encoder or index feed capability so that the exact rotational position of the motor or a component secured thereto can be ascertained. In some examples, the motor or chuck has a 20-bit encoder capable of 1.04 million position detections per revolution. The encoded information, along with the motor torque information, can be used to perform self-diagnostic tests, which are described in more detail below. For example, a motor torque spike at an unexpected rotational position may indicate that a centering error has occurred. Alternatively, the cam 110 stops moving and resists when it contacts the outer circumference of the wafer 112, so that the diameter of the wafer 112 may be derived based on the occurrence or location of the torque spike of the spindle motor 126. A window of acceptable torque spikes may be established.

[0056] In some examples, the angle at which the cam 110 at the outer end of the chuck arm 118 grips the edge of the wafer 112 is proportional to the degree to which the centering hub 102 has rotated to induce rotation of the cam 110. The rotational position of the centering hub 102 may be derived and measured based on a corresponding indexed rotational position of the spindle motor 126. The cam 110 and the centering hub 102 are directly interconnected via the actuation push rod 116. In some examples, the rotational position of the centering hub 102 is correlated with the radial or clamp position of the cam 110. The change in rotational position, or motor position, is detected by an encoder and derived accordingly, which is then mapped to the radial position of the centering clamp.

[0057] In some examples, a motor torque spike may be expected at the moment the cam 110 engages the edge of the wafer 112 placed between the cams 110, so that the diameter of the wafer 112 placed on the chuck cams 110 is set from the encoded rotational position of the spindle motor 126. The rotational position of the centering hub 102 at which the motor spike is detected is related to the radial position of the cam 110 (or all three cams) and when that radial position corresponds to the outer edge of the wafer 112, the diameter of the wafer 112 gripped between the cams is derived. In some examples of the present chuck, calculated or measured correlations between aspects such as motor torque, encoder position, presence or absence of a wafer, diameter of the wafer, and vacuum pressure (or lack thereof) are used in certain method embodiments discussed further below.

[0058] 5 includes an illustration of the top side of the chuck assembly 100 according to an exemplary embodiment. Components corresponding to those described above are labeled with corresponding numbers. When activated, the vacuum pad 122 can grip a wafer placed on the chuck assembly 100, either in cooperation with the cam 110 or without the cam 110. The cam 110 can center the wafer as described above. A cylindrical chuck arm 118 houses a push rod 116 for actuating the cam 110. A vacuum supply line 120 conveys vacuum from the rotating union to the vacuum pad 122, e.g., as described above.

[0059] Figure 6 includes an image of the underside of the exemplary chuck assembly 100 shown in Figure 5. In this view, the centering hub abutments or fins 134 are visible. In the illustrated example, the fins 134 are integrally formed with the centering hub 102, although other arrangements are possible. The fins 134 can be selectively engaged by the locking pins 108 to initiate the wafer centering operation described above.

[0060] An initial relative rotational motion in one direction between the illustrated chuck hub 104 (e.g., stationary in this example) and centering hub 102 drives the cam 110 closer to the center, causing the cam 110 to grip the wafer 112 gripped therebetween. Once the cam 110 closes, no further relative rotational motion is possible between the centering hub 102 and the chuck hub 104, the torque of the spindle motor 126 spikes to indicate centering and clamping of the wafer 112, and then both the hub and chuck are driven by the chuck spindle 106 to speed up in the opposite direction to the operating rotational speed. At high process speeds, it is important that the wafer 112 is reliably held concentrically in the chuck assembly 100 due to the high centripetal forces generated and the precision typically required.

[0061] FIG. 7 shows further details of the exemplary chuck assembly 100. Here, the centering hub 102 is again shown. When the centering hub 102 is rotated, the cam surface 114 of the centering hub 102 acts on a spring-loaded ball plunger 136 located at the lower end of each push rod 116. The upper end of each push rod 116 actuates a rotating cam 110 which rotates accordingly to grip the wafer 112 placed therebetween. In the illustration, a vacuum pad 122 is shown adjacent to the cam 110. The push rods 116 move radially outward when urged in that direction by the cam surface 114 of the rotating centering hub 102 moving, for example, in a clockwise direction as shown. The push rods 116 can be retracted by the centering hub 102 rotating in the other direction such that the cams 110 are retracted.

[0062] As the push rods 116 move outward, they rotate respective cams 110 located at the upper ends of each push rod 116, thereby causing the cams 110 to grip and center the wafer 112 held in the chuck. When the vacuum source is activated, the vacuum pads 122 grip the backside of the wafer 112, and the cams 110 may be retracted accordingly when the wafer 112 is still held securely in place by the vacuum pads 122. With the vacuum pads 122 holding the wafer 112 in place, the cams 110 may be retracted completely below the top surface of the wafer 112 so that the top surface of the wafer 112 remains clean and unobstructed during an EBR procedure or other processing. The ability of the cams 110 to retract completely can provide at least some of the advantages discussed above.

[0063] In the illustrated example, the push rod 116 is biased inwardly by a spring 138, which biases the cam 110 open until it is closed by the outward movement of the push rod 116. When the centering hub 102 is rotated counterclockwise relative to the chuck hub 104, the biased open spring load of the illustrated chuck assembly 100 allows the cam 110 to retract and release the wafer 112. This arrangement does not have a wafer release feature.

[0064] 8 includes a cross-sectional view of the chuck assembly 100 secured to the head of the chuck spindle 106 assembly. In this view, the locking pin 108 is seen in an up or locked position. When the locking pin 108 is up and the chuck hub 104 is rotated counterclockwise as viewed from above, the abutments or fins 134 of the centering hub engage the side walls of the locking pin 108. Rotational movement of the centering hub 102 is prevented by the locking pin 108, allowing relative rotational movement between the chuck hub 104 (which supports the push rod 116) and the locked centering hub 102. The camming action induced by the relative rotational movement between the chuck hub 104 and the centering hub 102 moves the push rod 116 outward, closing the cam 110 as described above.

[0065] In FIG. 9, an illustration of an exemplary centering hub fin 134 disposed on the underside of an exemplary centering hub 102 is shown. When the locking pin 108 is extended (upward), the locking pin 108 engages the fin 134. When the locking pin 108 is retracted (downward), the centering hub 102 is free to rotate in either direction, but will most likely rotate in a direction typically used for very high speed rotation during wafer processing. The locking pin 108 is actuated by the locking drive cylinder 132, as described above. The locking pin 108 and the drive cylinder 132 are non-rotating fixtures. When the locking pin 108 is extended (upward), the locking pin 108 engages the centering hub fin 134, locking the centering hub 102 against rotational movement in the locking direction. Thus, the centering hub 102 is fixed to the ground against rotational movement in at least the direction blocked by the locking pin 108. As the chuck hub 104 is rotated counter-rotatingly by the spindle motor 126 over the stationary centering hub 102 mounted below the chuck hub 104, the actuation push rod 116 carried by the chuck hub 104 is pushed by the cam surface 114, actuating the cam 110 to center the wafer 112 held therebetween in the manner described above. A vacuum is applied to the vacuum pad 122 which grips the backside of the wafer 112 in the centered position. The locking pin 108 may then be retracted to allow the spindle motor 126 to rotate the chuck hub 104 in the direction opposite the locking direction up to processing (operating) speed.

[0066] FIG. 10 includes a cross-sectional view of the chuck assembly 100 rotating at operating speed. The illustrated chuck assembly configuration is known as the "home state." In this embodiment, the cams 110 of the chuck assembly 100 are in a retracted or lowered position as shown. The wafer 112 is held in place by (negative) vacuum pressure applied through the vacuum pads 122. The locking pins 108 are in a retracted or lowered position as shown. A bearing abutment 140 is provided at the lower end of each actuation push rod 116. In the illustrated embodiment, the bearing abutments 140 are located at the "deepest" (innermost) position of the cam surface 114 of the centering hub 102 against which the bearing abutments 140 act in use. FIG. 11 includes a similar cross-sectional view of the chuck assembly 100, but in this case the cams 110 are in an extended or upper position for centering the wafer 112 held therebetween. In the illustrated embodiment, the bearing abutment 140 is located at the "shallowest" (outermost) position of the cam surface 114 of the centering hub 102 over which the bearing abutment 140 operates in use.

[0067] The series of figures in Figures 12A-12C are intended to provide a convenient visual comparison of certain aspects of the present chuck assembly 100 shown in Figure 12C with certain aspects of a conventional chuck assembly 1200 shown in Figures 12A-12B. The chuck assembly 1200 shown in Figure 12A includes a centrifugal or passive type centrifugal cam 200 as opposed to an active or positive type cam of the present disclosure. Figure 12B includes an enlarged view of a VAP 202 of the centrifugal cam 200. As discussed in more detail in the Background above, the presence of such a VAP 202 may be ineffective, for example, during EBR or when cleaning the wafer 112. Friction (non-vacuum) pads 204 can be seen adjacent to each cam 200.

[0068] In contrast, FIG. 12C pictorially depicts an exemplary chuck assembly 100 according to an exemplary embodiment of the present disclosure. In the illustrated example, three cam-carrying arms 119 are disposed radially equally spaced about a central chuck hub 104. Each arm 119 carries a respective cam 110. As shown, three non-cam-carrying arms 121 are disposed between the cam-carrying arms 119. Each cam-carrying arm 119 and each non-cam-carrying arm 121 includes a vacuum pad 122 disposed toward the outer end of the arm. In some examples, the vacuum pad 122 is configured by or includes a vacuum cup. Vacuum pressure is applied to the vacuum pad 122 to attract or secure the wafer to the vacuum pad under the negative pressure of the applied vacuum. In the illustrated example, six vacuum pads 122 are provided. Each cam-carrying arm 119 includes a vacuum supply line 120 and a hollow chuck arm 118 including a push rod 116 in the manner described above. Other arm arrangements or configurations are possible.

[0069] An exemplary chuck assembly 100 of the type shown in FIG. 12C can actively center a wafer after it is handed over to the chuck assembly 100 from a robot. The ability to center the wafer after placement can eliminate, or at least greatly reduce, the need for precise robotic wafer placement in the chuck assembly. Different centering configurations can be employed depending on the wafer diameter. Concentricity can be maintained by stable centering and elimination of VAP from the wafer edge. The illustrated chuck assembly 100 can also minimize streaking and taper width by using a higher rpm EBR process and can provide supplemental wafer detection using, for example, vacuum gripping levels.

[0070] Comparative results were obtained that support the validity of the above-mentioned features. For example, FIG. 13 shows exemplary plot results of EBR measurements observed within a particular edge exclusion (EE) wafer range (here, 1.7 mm and 2.3 mm) and measured at 360 points on a test wafer. The EBR results of the conventional point of reference (POR) chuck show significant deformational manifestations of streaks or notches as indicated by the sharply descending spikes in the graph at three different points 1301, 1303, and 1305 around the test wafer. These points correspond to the presence of VAP.

[0071] In comparison, wafers supported by the present chucks exhibit little, if any, such deformation, as shown, for example, by the top line 1307 of the present vacuum (VAC) chuck (2.3 mm) in the graph of FIG. 13. Similar flat results can be seen with the present VAC chuck (1.7 mm). Note that for the conventional POR chuck, the downward spike is more pronounced as EE (y-axis) decreases in the graph. This is believed to represent an increased effect of VAP at each point. The 1.7 mm point is closer to the outer edge of the wafer than the 2.3 mm point and is more susceptible to negative edge effects. The comparative range of measured deformation values ​​can be seen in the columns marked with rectangles in the table at the bottom right of the figure.

[0072] Certain embodiments of the present disclosure include methods, embodiments, or processes. In some examples, the methods include processes of wafer centering, wafer gripping, and fluid disturbance mitigation to provide superior EBR. An exemplary method may include at least the following operations or aspects described below. The method may be performed, for example, in conjunction with one or more of the present chuck assemblies described herein (e.g., chuck assembly 100 having cam 110 and vacuum pad 122 shown in FIG. 12C).

[0073] 16, a method 1600 may include, at 1602, placing a wafer on the chuck assembly 100. The wafer is centered at 1604 by the centering cam 110 as described above. Once the centered position of the wafer is found at 1606 (e.g., detected by an increase in spindle motor torque), the wafer is vacuum clamped at 1608 by the vacuum pad 122 on which the wafer is placed. Vacuum continues to be applied at 1610 and the centering cam 110 is retracted to keep the wafer precisely in place and concentric.

[0074] If the wafer is deformed by the movement of the centering cams, the vacuum pads may leak. If the wafer is not vacuum clamped properly, the method 1600 is aborted, since failure to properly vacuum clamp the wafer may indicate a broken, cracked, missing, or improperly placed wafer, and may indicate that the wafer is not resting on all of the vacuum pads 122.

[0075] Assuming the vacuum is maintained, centering cam 110 is maintained in a stowed position below the top surface of the wafer during wafer processing steps (EBR, cleaning, drying, etc.) Because centering cam 110 is below the wafer surface, there is no obstruction to bouncing EBR chemicals away from the wafer edge due to centrifugation.

[0076] In another example, a method for vacuum gripping a wafer in a wet process chamber is provided that may include at least the following acts or address certain aspects as follows:

[0077] In some instances, gripping the backside of the wafer in a wet process chamber can be difficult. For example, there can be a large pressure differential across the surface or edge of the vacuum pad, which can result in some degree of fluid leakage that causes liquid to be drawn into the vacuum circuit. Liquid that enters the vacuum circuit later exits the vacuum circuit and is deposited on the backside of the wafer by centrifugal action at the end of the EBR process. As a result, it can be very important to successful wafer processing that there is no liquid leakage past the edge or edge of the vacuum pad 122.

[0078] Thus, in some instances, a vacuum pad or cup shape is selected that does not leave wet watering or allow leakage. Different rubber formulations or hardness are possible to provide a proper seal and not leave any stains on the backside of the wafer.

[0079] In some examples, a method is provided for determining a wafer center independent of the wafer diameter using monitored motor torque, which may include at least the following operations or may address certain aspects as follows:

[0080] As mentioned above, motor torque and encoder position may be co-dependent and may be measured together to ascertain centering or concentricity of the wafer on the wafer chuck. In a chuck assembly 100 of the type described above (e.g., with respect to FIG. 3), when the centering cam 110 clamps the wafer edge, the spindle motor torque spikes and a high torque is seen which indicates the clamped position of the wafer. In some examples, the associated motor encoder position is within a known window which indicates the chuck has clamped onto a 300 mm wafer (for example) when the torque spike occurs.

[0081] In another example, a method is provided for preventing EBR deviation using chuck self-diagnostics. The method may include at least the following operations or address certain aspects as follows: Here, motor torque measurements and encoder readback allow for detection of inherent errors in checking centering. For example, if the motor torque spikes and the encoder position is outside of an acceptable range, it indicates a centering error. Some example situations that may cause a centering error include a broken cam, a broken wafer, a broken or frozen component, or a motor or encoder failure. Utilizing aspects such as the codependence of motor torque and encoder allows for centering errors to be detected on the first or early wafers of a series of wafers, rather than on subsequent wafers. Early corrective action can be taken to prevent EBR deviation on subsequent wafers, avoiding significant waste and avoiding significant economic and time losses.

[0082] In another example, a method is described for measuring the wafer diameter during centering and providing automatic adjustment of EBR. The method may include at least the following operations or may address certain aspects as follows: The wafer diameter may be estimated from an encoder readback of the spindle motor torque spike during the wafer centering routine. The wafer diameter may vary, which may affect the edge exclusion area parameter. Further variations may include measuring the edge exclusion area from the wafer edge to the copper etched by the EBR process, regardless of the actual wafer diameter. Thus, small variations in the wafer diameter allowed by a given specification may result in a change in the measured edge exclusion area.

[0083] If the wafer is measured to be unusually under or oversized despite this variability, the wafer diameter can be transferred to the EBR system, which in some examples can be configured to automatically adjust the position of the EBR nozzle to maintain the desired edge exclusion area based on applicable criteria of the EBR parameters.

[0084] In another example, a method for a center reference for edge detection is provided. The method may include at least the following operations or may address certain aspects as follows: In some examples, it is desirable to ensure that the diameter of the copper plating film on the wafer is the same from wafer to wafer in a batch regardless of edge exclusion area. In some examples, the chuck measures the wafer diameter during a centering routine. The EBR metrology measures the edge exclusion area after EBR. If the EBR metrology detects a change in the edge exclusion area, the wafer diameter can be determined from the chuck to see if the change is due to a process issue or a change in wafer diameter. If the edge exclusion area is caused by a change in wafer diameter, it can be determined that the center reference for edge detection has not changed. Based on the determination, it is concluded that the copper plating diameter has not changed.

[0085] In another example, fixture diagnostics and safety features are provided. Some examples use multi-position vacuum gripping sensors distributed across the backside of the wafer to detect wafer breakage or improper placement. The method may include the following operations or aspects.

[0086] By way of background, the wafers selected for processing may be defective. For example, one wafer may be chipped (e.g., having a sliced ​​shape like a pizza). The remainder of the wafer may contain a notch and not be gripped by a chuck assembly that has, for example, only three vacuum cups spaced 120° apart around the circumference of the chuck. In this unstable condition, the wafer may disintegrate violently and completely, or may fly off at high speeds. Increasing the number of vacuum pads or vacuum cups improves detection of smaller chipped portions.

[0087] 14, the motor torque detection routine of the exemplary chuck assembly 100 will now be described with respect to graph 1400. During centering, the chuck hub of the chuck assembly 100 is moved in a negative direction (e.g., counterclockwise when viewed from above) by the spindle motor over the internal, temporarily stationary centering hub to activate the centering cam, as described above. The negative rotational direction of the spindle motor may be contrasted with the positive rotational direction (e.g., clockwise) employed during a process such as an EBR process. The spindle motor moves in a negative direction to indicate a negative torque value. The negative values ​​are shown on the y-axis of graph 1400. A "high" negative torque would have a large negative value and be seen lower on graph 1400.

[0088] Graph 1400 of FIG. 14 includes an example torque profile of the spindle motor during the centering process described above. Referring to graph 1400, in phase 1402, the chuck assembly is rotating and the torque is very low (-5% of rated torque) before the centering hub fins 134 (described above) reach the locking pin 108. At point 1404, the locking pin 108 engages the fins 134 and the (negative) torque increases. The result in the figure shows an overshoot and undershoot torque profile at point 1406 and just after point 1406. The spindle motor torque then remains stable and approximately constant until point 1408, when the cam 110 begins to engage the wafer 112, moving the wafer 112 to the desired center position. The motor torque then spikes, implying that the wafer 112 is no longer moving, and reaches a slightly compressed centering position where it begins to resist the centering cam 110. An exemplary motor torque spike is shown at point 1410.

[0089] The magnitude of the centering torque may vary from chuck to chuck due to component variability, tolerance differences, spring constants, etc. These variability may be accommodated by calibrating the chuck to determine the torque required to center a 300 mm wafer. For example, the cutoff torque in the phase from point 1410 to point 1412 may be set appropriately to ensure that a given wafer is not overstressed or damaged during centering. In phase 1414, the chuck arm spring extends while the cam 110 retracts. After phase 1414 when the centering hub fins 134 lose contact with the locking pin 108, an undershoot and overshoot spike 1416 occurs.

[0090] FIG. 15 is a block diagram illustrating an example machine 1500 on which one or more example method embodiments described herein may be implemented or controlled. In another embodiment, the machine 1500 may operate as a stand-alone device or may be coupled (e.g., networked) to other machines. In a networked arrangement, the machine 1500 may operate as a server machine, a client machine, or both in a server-client network environment. In one example, the machine 1500 may function as a peer machine in a peer-to-peer (P2P) (or other distributed) network environment. Furthermore, although only one machine 1500 is shown, the term "machine" should also be construed to include a group of machines that individually or cooperatively execute a set (or multiple sets) of instructions to implement one or more methodologies discussed herein (such as through cloud computing, software as a service (SaaS), or other computer cluster configurations).

[0091] The examples described herein may include or operate with logic, multiple components, or mechanisms. An electric circuit is a circuit implemented in a tangible object that includes hardware (e.g., simple circuits, gates, logic, etc.). Electrical circuit elements may be flexible over time and with respect to changes in the underlying hardware. An electric circuit includes elements that, when in operation, may perform a specific operation alone or in cooperation. In one example, the hardware of an electric circuit may be invariably designed to perform a specific operation (e.g., an operation by the hardware). In one example, the hardware of an electric circuit may include variably connected physical components (e.g., execution units, transistors, simple circuits, etc.) that include a computer-readable medium that is physically adjusted (e.g., magnetically, electrically, by a movable arrangement of invariant dense particles, etc.) to encode instructions for a specific operation. When connecting the physical components, the underlying electrical properties of the hardware components are changed (e.g., from insulator to conductor, or vice versa). The instructions enable the embedded hardware (e.g., execution unit or loading mechanism) to form electrical circuit elements in the hardware by variable coupling to perform some of the specific operations when in operation. Accordingly, the computer-readable medium is communicatively coupled to other components of the electrical circuit when the device is in operation. In one example, any of the physical components may be used in one or more elements of one or more electrical circuits. For example, the execution unit may be used in a first circuit of a first electrical circuit at a point in time during operation, and used again in a second circuit of the first electrical circuit or in a third circuit of the second electrical circuit at a different time.

[0092] The machine (e.g., a computer system) 1500 may include a hardware processor 1502 (e.g., a central processing unit (CPU), a hardware processor core, or a combination thereof), a graphics processing unit (GPU) 1503, a main memory 1504, and a static memory 1506, some or all of which may communicate with each other through an interlink (e.g., a bus) 1508. The machine 1500 may further include a display device 1510, an alphanumeric input device 1512 (e.g., a keyboard), and a user interface (UI) navigation device 1514 (e.g., a mouse). In one example, the display device 1510, the alphanumeric input device 1512, and the UI navigation device 1514 may be touch screen displays. The machine 1500 may further include a mass storage device (e.g., a drive unit) 1516, a signal generating device 1518 (e.g., a speaker), a network interface device 1520, and one or more sensors 1521 (such as a Global Positioning System (GPS) sensor, a compass, an accelerometer, or other sensor). The machine 1500 may include an output controller 1528, such as a serial connection (e.g., Universal Serial Bus (USB)), a parallel connection, or other wired or wireless (e.g., infrared (IR), near field communication (NFC)) connection, for communicating with or controlling one or more peripheral devices (e.g., a printer, a card reader, etc.).

[0093] The mass storage device 1516 may include a machine-readable medium 1522 on which is stored one or more sets of data structures or instructions 1524 (e.g., software) embodied or used by any one or more of the techniques or functions described herein. The instructions 1524 may reside, completely or at least partially, within the main memory 1504, within the static memory 1506, within the hardware processor 1502, or within the GPU 1503 during execution by the machine 1500. In one example, one or any combination of the hardware processor 1502, the GPU 1503, the main memory 1504, the static memory 1506, and the mass storage device 1516 may constitute a machine-readable medium.

[0094] Although the machine-readable medium 1522 is illustrated as a single medium, the term “machine-readable medium” may include a single medium or multiple media (e.g., a centralized or distributed database, and / or associated caches and associated servers) configured to store one or more instructions 1524.

[0095] The term "machine-readable medium" may include any medium capable of storing, encoding, or transmitting instructions 1524 for execution by the machine 1500, and any medium that causes the machine 1500 to perform one or more techniques of the present disclosure, or any medium capable of storing, encoding, or transmitting data structures used by or associated with the instructions 1524. Non-limiting examples of machine-readable media may include solid-state storage devices, as well as optical and magnetic media. In one example, a mass machine-readable medium includes a machine-readable medium 1522 that comprises a plurality of particles having a fixed (e.g., stationary) mass. Thus, a mass machine-readable medium is not a transitory propagating signal. Specific examples of mass machine-readable media may include non-volatile memory (such as semiconductor storage devices (e.g., electrically programmable read-only memory (EPROM), electrically erasable programmable read-only memory (EEPROM)) and flash memory devices), magnetic disks (such as internal hard disks and removable disks), magneto-optical disks, and CD-ROM and DVD-ROM disks. The instructions 1524 may further be transmitted or received over a communications network 1526 using a transmission medium via the network interface device 1520 .

[0096] Although the embodiments have been described with reference to certain exemplary embodiments, it will be apparent that various modifications and changes may be made to these embodiments without departing from the broad scope of the inventive subject matter. Thus, the specification and drawings should be taken in an illustrative and not a restrictive sense. The accompanying drawings, which form a part of this application, show by way of illustration, and not by way of limitation, specific embodiments in which the subject matter may be practiced. The illustrated embodiments are described in sufficient detail to enable those skilled in the art to practice the teachings disclosed herein. Other embodiments may be used or derived therefrom, such that structural and logical substitutions and changes may be made without departing from the scope of the present disclosure. Thus, the above description should not be taken in a limiting sense, and the scope of the various embodiments is defined only by the appended claims, along with the full scope of equivalents to which such claims are entitled.

[0097] Such embodiments of the subject matter of the present invention may be referred to individually and / or collectively under the term "invention" for convenience, without any intention of intentionally limiting the scope of the present application to a single invention or inventive concept, when in fact more than one is disclosed. Thus, even if specific embodiments are shown and described herein, it should be recognized that any arrangement designed to achieve the same purpose may be substituted for the specific embodiment shown. The present disclosure is intended to include all adaptations or variations of the various embodiments. Combinations of the above embodiments with other embodiments not specifically described herein will be apparent to one of ordinary skill in the art upon reviewing the above description. The present disclosure includes the following application examples: [Application example 1] 1. A wafer chuck assembly for supporting a wafer, comprising: Chuck hub and a centering hub disposed within the chuck hub; an engagement device movable between an engaged position and a disengaged position to engage the chuck hub with the centering hub to prevent relative movement therebetween in a clockwise or counterclockwise rotational direction, or to allow relative movement therebetween in either rotational direction; a chuck motor for selectively rotating the chuck hub and / or the centering hub based on the engaged or disengaged position of the engagement device during wafer processing and centering operations; a plurality of chuck arms attached to the chuck hub, each chuck arm extending radially between a proximal end adjacent the chuck hub and a distal end remote therefrom; a plurality of centering cams, each mounted at or toward a distal end of a chuck arm and movable radially inwardly or outwardly relative to the centering hub to engage or disengage an edge of a supported wafer in response to rotational movement of the centering hub relative to the chuck hub; A wafer chuck assembly comprising: [Application example 2] The wafer chuck assembly according to application example 1, The chuck motor is configured to impart relative rotational motion between the centering hub and the chuck hub during the wafer centering operation. [Application example 3] The wafer chuck assembly according to application example 2, a wafer chuck assembly, the centering hub being fixed to the chuck motor during the wafer centering operation, the chuck motor being configured to rotate the chuck hub in a first rotational direction during the wafer centering operation. [Application example 4] The wafer chuck assembly according to Application Example 3, The wafer chuck assembly, wherein the chuck motor is configured to rotate the centering hub and the chuck hub together in the same rotational direction during the wafer processing operations. [Application example 5] The wafer chuck assembly according to application example 4, a wafer chuck assembly, wherein the same rotational direction of the centering hub and the chuck hub during the wafer processing operation is opposite to the first rotational direction of the chuck hub during the wafer centering operation. [Application Example 6] The wafer chuck assembly according to application example 1, The centering hub includes at least one cam surface on an outer surface thereof. [Application Example 7] The wafer chuck assembly according to application example 6, a wafer chuck assembly, wherein each chuck arm includes a respective elongated actuation rod operatively disposed between the at least one cam surface of the centering hub and a centering cam disposed at an end of each chuck arm of the plurality of centering cams. [Application Example 8] The wafer chuck assembly according to application example 7, each elongated actuation rod including a bearing surface at a proximal end thereof for engaging the at least one cam surface of the centering hub; [Application Example 9] The wafer chuck assembly according to application example 7, A wafer chuck assembly, wherein each elongated actuation rod has at its tip a connection with a respective centering cam of a respective chuck arm. [Example 10] The wafer chuck assembly according to Application Example 9, a wafer chuck assembly, wherein rotational movement of the centering hub causes respective cam surfaces of the centering hub to urge respective elongated actuation rods radially outward, thereby actuating respective centering cams via the connections. [Application Example 11] The wafer chuck assembly according to application example 1, further comprising: A wafer chuck assembly comprising at least one vacuum pad for supporting the wafer during the wafer centering operation and / or the wafer processing operation. [Application Example 12] The wafer chuck assembly according to application example 11, the at least one vacuum pad is configured to maintain the wafer in a centered position on the wafer chuck assembly at least during the wafer processing operation when the wafer is released onto the plurality of centering cams. [Application Example 13] The wafer chuck assembly according to application example 11, A wafer chuck assembly, wherein the at least one vacuum pad is provided on at least one of the plurality of chuck arms. [Example 14] The wafer chuck assembly according to application example 11, A wafer chuck assembly, wherein each of the plurality of chuck arms includes a vacuum line for supplying vacuum pressure to the at least one vacuum pad. [Example 15] The wafer chuck assembly according to application example 14, A wafer chuck assembly, wherein the presence or absence of vacuum pressure at the at least one vacuum pad is detected and correlated to the presence or absence of the wafer in the wafer chuck assembly, or the presence of a defective wafer.

Claims

1. 1. A vacuum wafer chuck assembly for supporting a wafer, comprising: Chuck hub and a centering hub disposed within the chuck hub; a plurality of chuck arms attached to the chuck hub, each chuck arm extending radially between a proximal end adjacent the chuck hub and a distal end remote therefrom; a plurality of centering cams, each mounted at or toward a distal end of the chuck arm and movable radially inwardly or outwardly relative to the centering hub to engage or disengage an edge of a supported wafer in response to rotational movement of the centering hub; at least one vacuum pad for supporting the wafer during wafer centering or wafer processing operations; an engagement device movable between an engaged position and a disengaged position to engage the chuck hub with the centering hub to prevent relative movement therebetween in a clockwise or counterclockwise rotational direction, or to allow relative movement therebetween in either rotational direction; a chuck motor for selectively rotating the chuck hub and / or the centering hub based on the engaged or disengaged position of the engagement device during wafer processing and centering operations; A vacuum wafer chuck assembly comprising:

2. 2. The wafer chuck assembly of claim 1, The chuck motor is configured to impart relative rotational motion between the centering hub and the chuck hub during the wafer centering operation.

3. 3. The wafer chuck assembly of claim 2, further comprising: a wafer chuck assembly, the centering hub being fixed to the chuck motor during the wafer centering operation, the chuck motor being configured to rotate the chuck hub in a first rotational direction during the wafer centering operation.

4. 4. The wafer chuck assembly of claim 3, The wafer chuck assembly, wherein the chuck motor is configured to rotate the centering hub and the chuck hub together in the same rotational direction during the wafer processing operations.

5. 5. The wafer chuck assembly of claim 4, a first rotational direction of the chuck hub during the wafer centering operation and a second rotational direction of the chuck hub during the wafer processing operation, the first rotational direction being opposite to the first rotational direction of the chuck hub during the wafer centering operation.

6. 2. The wafer chuck assembly of claim 1, The centering hub includes at least one cam surface on an outer surface thereof.

7. 7. The wafer chuck assembly of claim 6, each chuck arm includes a respective elongated actuation rod operatively disposed between the at least one cam surface of the centering hub and a centering cam disposed at a distal end of each chuck arm of the plurality of centering cams.

8. 8. The wafer chuck assembly of claim 7, each elongated actuation rod including a bearing surface at a proximal end thereof for engaging the at least one cam surface of the centering hub;

9. 9. The wafer chuck assembly of claim 8, A wafer chuck assembly, wherein each elongated actuation rod has at its tip a connection with a respective centering cam of a respective chuck arm.

10. 10. The wafer chuck assembly of claim 9, a wafer chuck assembly, wherein rotational movement of the centering hub causes respective cam surfaces of the centering hub to urge respective elongated actuation rods radially outward, thereby actuating respective centering cams via the connections.

11. 2. The wafer chuck assembly of claim 1, the at least one vacuum pad is configured to maintain the wafer in a centered position on the wafer chuck assembly at least during the wafer processing operation when the wafer is released onto the plurality of centering cams.

12. 2. The wafer chuck assembly of claim 1, The at least one vacuum pad is provided on at least one of the plurality of chuck arms.

13. 2. The wafer chuck assembly of claim 1, A wafer chuck assembly, wherein each of the plurality of chuck arms includes a vacuum line for supplying vacuum pressure to the at least one vacuum pad.

14. 14. The wafer chuck assembly of claim 13, A wafer chuck assembly, wherein the presence or absence of vacuum pressure at the at least one vacuum pad is detected and correlated to the presence or absence of the wafer in the wafer chuck assembly, or the presence of a defective wafer.

15. 2. The wafer chuck assembly of claim 1, The plurality of centering cams are biased toward an open wafer release configuration.

16. 2. The wafer chuck assembly of claim 1, a wafer chuck assembly, wherein each centering cam of the plurality of centering cams is movable between a first wafer centering position and a second storage position, the second storage position being disposed below an upper surface of the wafer supported in the wafer chuck assembly.

17. 17. The wafer chuck assembly of claim 16, further comprising: a control means for detecting a torque of the chuck motor and correlating the detected chuck motor torque with at least the first wafer centering position of the plurality of centering cams.

18. 10. The wafer chuck assembly of claim 1, further comprising: a wafer chuck assembly comprising: a control means for detecting a torque of the chuck motor and correlating the detected chuck motor torque with a centered position of the wafer held on the wafer chuck assembly.

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