Wafer chuck assembly

Abstract

To prevent positional deviation of a rotating wafer during EBR processing to form a bevel portion at an edge portion of the wafer.SOLUTION: In a wafer chuck assembly 100 including a chuck hub and a centering hub 102 disposed inside the chuck hub, an engagement device is operable between an engagement position and a disengagement position, and a plurality of hollow chuck arms 118 are attached to the chuck hub, each chuck arm engaging the chuck hub with the centering hub to prevent relative movement in at least a first direction therebetween or allow relative movement therebetween. 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 attached at or toward the tip of the chuck arm and operates to engage or disengage a wafer 112 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 of 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 hereby incorporated by reference in their entireties.

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

Background Art

[0003] The description of the background art herein is for the purpose of generally presenting the content of the present disclosure. The inventions of the presently named inventors are not to be regarded as prior art to the present disclosure, either expressly or implicitly, to the extent that they are described in this background art section and aspects of the description that do not fall within the scope of the prior art at the time of filing.

[0004] EBR is generally performed by applying a chemical solution through a nozzle directed near the wafer edge while the wafer is being rotated. In order to achieve uniform EBR results, the wafer must be properly centered on the chuck or concentric with the chuck. Existing chucks using friction pads or passive centering means may not actively center the wafer prior to 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 by a robot to the PEM is not accurate.

[0005] Further problems occur when the etchant used in the EBR process splashes back from around wafer support means such as the vertically disposed pin (VAP) surface. The splashed liquid can interfere with the EBR process and contribute to poor EBR results. This effect can become more apparent as the edge exclusion (EE) region decreases. EE typically refers to the amount of material removed about the wafer edge.

[0006] In a further example, the wafer may slip off the conventional chuck support during rotation, which can also lead to insufficient centering and poor EBR results. Wafer presence detection using an external sensor is not always reliable and can be affected, for example, by splashing of wafer droplets. Splashing can occur as described above or in another way during wafer cleaning. A slipped wafer can cut harmful grooves in the cam of a chuck having a centrifugal centering cam. This can shorten the life of the chuck and may also cause the grooved cam 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, and an engagement device operable between an engaged position and a disengaged position, the engagement device engaging 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 rotational direction, and a chuck motor for selectively rotating the chuck hub and / or the centering hub during wafer processing operations and during wafer centering operations based on the engaged or disengaged position of the engagement device, and 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, each centering cam being attached to or toward the distal end of a chuck arm and operable 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 centering hub relative to the chuck hub.

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

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

[0010] In some examples, the centering hub comprises at least one cam surface on its outer surface. In some examples, each chuck arm comprises a respective elongated actuating rod operatively disposed between at least one cam surface of the centering hub and a centering cam disposed at the tip of each chuck arm. Each elongated actuating rod may comprise a bearing surface at its proximal end for engaging at least one cam surface of the centering hub. In some examples, each elongated actuating rod comprises a connection portion at its tip with the respective centering cam of each chuck arm. In some examples, by the rotational movement of the centering hub, each cam surface of the centering hub radially outwardly urges the respective elongated actuating rod, thereby actuating the respective centering cam via the connection portion.

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

[0012] In some examples, the plurality of centering cams are biased towards an open wafer release 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 the upper surface of the wafer supported within the wafer chuck assembly.

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

[0014] In other embodiments, a vacuum wafer chuck assembly is provided. An exemplary vacuum wafer chuck assembly 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 centering cam attached to or directed toward the distal end of a chuck arm and operable radially inwardly or outwardly relative to the centering hub to engage or disengage an edge of a supported wafer in response to rotation of the chuck hub, and at least one vacuum pad for supporting the wafer during a wafer centering operation or a 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, the engagement device engaging the chuck hub with the centering hub to prevent relative movement therebetween in either a clockwise or counterclockwise rotational direction, or to enable relative movement therebetween in either rotational direction, 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 a wafer processing operation and a wafer centering operation.

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

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

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

[0019] In some examples, the rotation of the centering hub causes each cam surface of the centering hub to radially outwardly urge each elongated actuating rod, thereby actuating each centering cam via a connecting portion.

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

[0021] In some examples, the plurality of centering cams are biased toward an open wafer release 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, and the second storage position is disposed below the upper surface of the wafer supported within the wafer chuck assembly.

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

[0023] In other embodiments, 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 operations and wafer centering operations, a plurality of chuck arms attached to the chuck hub, each chuck arm extending radially between a proximal end adjacent to the chuck hub and a distal end remote therefrom, a plurality of centering cams, each centering cam being attached to or towards the distal end of a chuck arm and being operable radially inwards or outwards relative to the centering hub to engage or disengage an edge of a supported wafer in response to a rotational movement of the centering hub relative to the chuck hub, and control means for detecting a torque of the chuck motor and associating 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, the engagement device engaging 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 rotational direction, 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 operations and wafer centering operations.

[0025] In some examples, the control means detects a torque of the chuck motor and associates the detected chuck motor torque with a centered position of a wafer held by the wafer chuck assembly. In some examples, the control means detects a torque of the chuck motor and associates the detected chuck motor torque with a diameter of a wafer held by the wafer chuck assembly.

Brief Description of the Drawings

[0026] Some embodiments are shown by way of example and not limitation with reference to the accompanying drawings.

[0027]

FIG. 1A

FIG. 1B

[0028]

FIG. 2

[0029]

FIG. 3

[0030]

FIG. 4A

FIG. 4B

[0031]

FIG. 5

[0032]

FIG. 6

[0033]

FIG. 7

[0034]

FIG. 8

[0035]

FIG. 9

[0036]

FIG. 10

[0037]

FIG. 11

[0038]

FIG. 12A

FIG. 12B

[0039]

FIG. 12C

[0040]

FIG. 13

[0041]

FIG. 14

[0042]

FIG. 15

[0043]

FIG. 16

DETAILED DESCRIPTION OF THE INVENTION

[0044] The following description includes systems, methods, techniques, instruction sequences, and computer program products that embody exemplary embodiments of the present disclosure. In the following description, for purposes of explanation, numerous specific details are set forth in order to provide a thorough understanding of the exemplary embodiments. However, it will be apparent to one of ordinary skill 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 may contain material that is subject to copyright protection. The copyright owner has no objection to the facsimile reproduction by anyone of the patent document or the patent disclosure, as it appears in the Patent and Trademark Office patent file or records, but reserves all copyrights in such facsimile reproduction. The following notice applies to all data shown in any of the drawings that form a part of the text hereof: 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, which is described in more detail below. Some exemplary wafer chuck assemblies include vacuum pads for improving the gripping force and engagement adaptability of the wafer in the chuck. The chuck assembly can actively center the wafer after the wafer is placed. 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 also possible in other applications.

[0047] As described above, accurate and reliable wafer centering in a chuck assembly (referred to herein as a chuck when applicable) can be important for 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 elements such as a substrate or a wafer. In some examples, the chuck assembly further includes a centering cam that is horizontally stored below the upper surface of the wafer placed on the chuck assembly while a vacuum is applied to the vacuum pad to hold the wafer in place. The downwardly stored cam eliminates the deflecting surface that can cause splashing of the EBR chemical or water onto the wafer surface due to the absence of peripheral structures. Thus, this arrangement substantially eliminates the major factors contributing to the poor EBR results and disadvantages described above.

[0048] In some examples of this chuck assembly, a high wafer gripping force can be generated. In some examples, the wafer can be vacuum gripped in place with a gripping force more than six times that of a conventional friction pad having the same diameter. In some examples, the presence or position of the wafer in the chuck assembly is detected or measured in relation to a vacuum clamp. For example, the back surface of the placed wafer can seal the vacuum pad in the chuck, allowing the vacuum to develop gradually or stepwise, or to be applied to the wafer. The fact that a vacuum can be applied may indicate that the wafer is present in the chuck. In other examples, a low vacuum pressure may indicate that the wafer is not present in the chuck or is improperly placed in some way. A high vacuum pressure may mean proper wafer placement.

[0049] Referring now to FIGS. 1A - 1B, these figures include schematic cross - sectional views of an exemplary chuck assembly 100. The centering hub 102 is disposed within the 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, for example, under normal rotational operations during wafer processing. The normal rotational operation can be, for example, clockwise. FIG. 2 shows a drawing of the exemplary centering hub 102. As shown in the figure, the centering hub 102 includes a series of cam surfaces 114 that abut against the end of an actuating push rod 116, which will be described in more detail below.

[0050] During the wafer centering operation, the centering hub 102 is locked to the chuck spindle 106 by a locking pin 108 that can be pushed upward into its recess 109. Thus, the centering hub 102 serves as a fixture. Next, the chuck assembly 100 can be rotated in the reverse direction (e.g., counter - clockwise) such that a relative rotational movement occurs between the centering hub 102 and the chuck hub 104. The relative rotational movement between the slowly rotating centering hub 102 and the chuck hub 104 causes the cam surface 114 of the centering hub 102 to urge the actuating push rod 116 outwardly, rotating the cam 110 as shown in the figure. In some examples, the actuating push rod 116 is movably installed within a hollow chuck arm 118. In some examples, the cam 110 is kinematically coupled to accommodate wafers 112 of different diameters. Three cams 110 are shown, but other numbers and other configurations of cams are possible.

[0051] In some examples, the motor torque of the chuck spindle 106 is monitored, and spikes in the motor torque indicate that the cam 110 is 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-biased 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 remains stationary during wafer centering while the centering hub 102 is arranged to rotate therein to operate the cam 110. In other examples, neither the centering hub 102 nor the chuck hub 104 remains stationary during centering, but still the cam 110 remains operable and reverse rotation movement between these components is provided to be openable and closable. 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 FIG. 1A, the vacuum supply line 120 supplies a vacuum (or negative pressure) to the vacuum pads 122 that support the wafer 112. In some examples, the hollow chuck arm 118 is radially aligned with the vacuum supply line 120 to reduce the likelihood of splashback of the rinse agent during EBR as much as possible.

[0053] FIG. 3 includes a drawing of the chuck assembly 100 with some internal components shown in ghost lines. Those corresponding to the components described above are numbered the same. Generally, the chuck assembly 100, the chuck spindle 106, the spindle motor 126, and the vacuum supply device 124 with respect to the rotary union (which can be seen in FIG. 4A) are shown.

[0054] Figures 4A - 4B further show diagrams of the chuck spindle 106 assembly and the vacuum supply section. The rotary union 128 in the figure passes vacuum through the chuck's vacuum line in a manner somewhat similar to how a slip ring passes current through the coils of an electric motor, and the correspondingly sized O - ring 130 seals the vacuum circuit to the chuck assembly 100. The figure in 4A also shows the locking pin 108 in the upper or locked position that engages the centering hub 102 with the chuck spindle 106. In Figure 4B, an air supply section 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 indexing feed capability so that the exact rotational position of the motor or components fixed thereto can be determined. In some examples, the motor or chuck has a 20 - bit encoder capable of 1,040,000 position detections per revolution. The encoded information, in conjunction with the motor torque information, can be used to perform self - diagnostic tests described in more detail below. For example, if a motor torque spike occurs at an unexpected rotational position, it may indicate that a centering error has occurred. Alternatively, since the cam 110 stops and resists movement when contacting the outer periphery of the wafer 112, the diameter of the wafer 112 may be derived based on the occurrence or position of the torque spike of the spindle motor 126. A window of acceptable torque spikes may be set.

[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 extent to which the centering hub 102 rotates to guide the rotation of the cam 110. The rotational position of the centering hub 102 may be derived and measured based on the corresponding index-fed rotational position of the spindle motor 126. The cam 110 and the centering hub 102 are directly interconnected via the actuating push rod 116. In some examples, the rotational position of the centering hub 102 is associated with the radial position or the clamping position of the cam 110. The change in the rotational position, or the motor position, is detected by an encoder, derived accordingly, and then mapped to the radial position of the centering clamp.

[0057] In some examples, since 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, the diameter of the wafer 112 placed on the chuck cam 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 associated with the radial position of the cam 110 (or all three cams), and when that radial position corresponds to the outer end of the wafer 112, the diameter of the wafer 112 gripped between the cams is derived. In some examples of this chuck, the calculated or measured interrelationships between aspects such as motor torque, encoder position, presence or absence of a wafer, wafer diameter, and vacuum pressure (or not) are used in embodiments of a particular method discussed further below.

[0058] FIG. 5 includes a top view of the chuck assembly 100 according to an exemplary embodiment. Those corresponding to the components described above are denoted by corresponding numerals. The vacuum pad 122, when activated, can grip the wafer placed on the chuck assembly 100 in cooperation with or without the cam 110. The cam 110 can center the wafer as described above. The cylindrical chuck arm 118 houses a push rod 116 for actuating the cam 110. The vacuum supply line 120 conveys vacuum from the rotary union to the vacuum pad 122, for example as described above.

[0059] FIG. 6 includes a bottom view of the exemplary chuck assembly 100 shown in FIG. 5. In this figure, the abutment or fins 134 of the centering hub can be seen. In the example of the figure, the fins 134 are integrally formed with the centering hub 102, but other arrangements are possible. The fins 134 can be selectively engaged by the locking pin 108 to initiate the wafer centering operation described above.

[0060] The one-way initial relative rotational movement between the chuck hub 104 (e.g., in a stationary state in this example) and the centering hub 102 in the figure brings the cam 110 closer to the center and causes the wafer 112 gripped therebetween to be gripped by the cam 110. Once the cam 110 closes, the relative rotational movement between the centering hub 102 and the chuck hub 104 is no longer possible, and the torque of the spindle motor 126 spikes to indicate the centering and fixing of the wafer 112. Next, both the hub and the chuck are driven by the chuck spindle 106 and accelerated in the opposite direction to the operating rotational speed. At high process speeds, it is important that the wafer 112 is securely held concentrically with the chuck assembly 100 in terms of the high centripetal force generated and the accuracy usually required.

[0061] Figure 7 shows further details of the exemplary chuck assembly 100. Here, the centering hub 102 is shown again. When the centering hub 102 is rotated, the cam surface 114 of the centering hub 102 acts on the spring-loaded ball plunger 136 provided at the lower end of each push rod 116. The upper end of each push rod 116 actuates a rotary cam 110 that rotates as appropriate to grip the wafer 112 placed therebetween. In the figure, a vacuum pad 122 is shown adjacent to the cam 110. When the cam surface 114 of the rotating centering hub 102 urges the push rod 116 in that direction, for example, in the clockwise direction in the figure, the push rod 116 moves radially outward. The push rod 116 can be retracted by the centering hub 102 that rotates in the other direction so that the cam 110 is retracted.

[0062] When the push rod 116 moves outward, it rotates each cam 110 disposed at the upper end of each push rod 116, thereby causing the cam 110 to grip and center the wafer 112 held by the chuck. When the vacuum source is activated, the vacuum pad 122 grips the back surface of the wafer 112, and when the wafer 112 is still securely held in place by the vacuum pad 122, the cam 110 may be retracted accordingly. Since the vacuum pad 122 holds the wafer 112 in place, the cam 110 may be fully retracted below the upper surface of the wafer 112 so that the upper surface of the wafer 112 is clean and unobstructed during the EBR process or other processes. The ability of the cam 110 to fully retract can provide at least some of the advantages described above.

[0063] In the example of the figure, the push rod 116 is biased inward by a spring 138, whereby the cam 110 is released and biased until it is closed by the outward movement of the push rod 116. When the centering hub 102 is rotated counterclockwise with respect to the chuck hub 104, the biasing release spring load of the chuck assembly 100 in the figure allows the cam 110 to retract and release the wafer 112. This arrangement does not have a wafer release configuration.

[0064] FIG. 8 includes a cross-sectional view of the chuck assembly 100 fixed to the head portion of the chuck spindle 106 assembly. In this figure, the locking pin 108 is seen in the upper or locked position. When the locking pin 108 is upward and the chuck hub 104 is rotated counterclockwise as viewed from above, the shoulder or fin 134 of the centering hub engages the side wall of the locking pin 108. The rotational movement of the centering hub 102 is blocked by the locking pin 108, and relative rotational movement between the centering hub 102 locked with the chuck hub 104 (supporting the push rod 116) is possible. The cam movement induced by the relative rotational movement between the chuck hub 104 and the centering hub 102 moves the push rod 116 outward and closes the cam 110 as described above.

[0065] FIG. 9 shows a drawing of an exemplary centering hub fin 134 disposed on the back surface of the exemplary centering hub 102. 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 can rotate freely in any direction, but in most cases, it will rotate in the direction normally used when rotating at ultra-high speed 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 fixtures that do not rotate. When the locking pin 108 is extended (upward), the locking pin 108 engages the centering hub fin 134 and locks 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. When the chuck hub 104 rotates counterclockwise at a low speed by the spindle motor 126 over the stationary centering hub 102 installed below the chuck hub 104, the actuating push rod 116 supported by the chuck hub 104 is pushed out by the cam surface 114 to actuate the cam 110 and center the wafer 112 held therebetween in the above-described manner. Vacuum is applied to the vacuum pad 122 that grips the back surface of the wafer 112 at the centered position. Next, the locking pin 108 can be retracted so that the chuck hub 104 can be rotated by the spindle motor 126 to the processing speed (operating speed) in the direction opposite to the locking direction.

[0066] FIG. 10 includes a cross-sectional view of a chuck assembly 100 rotating at an operating speed. The chuck assembly configuration in the figure is known as the "home position." In this mode, the cam 110 of the chuck assembly 100 is in the retracted or lower position as shown in the figure. The wafer 112 is held in place by a (negative) vacuum pressure applied through the vacuum pad 122. The locking pin 108 is in the retracted or lower position as shown in the figure. A bearing contact portion 140 is provided at the lower end of each actuating push rod 116. In the aspect shown in the figure, the bearing contact portion 140 is disposed at the "deepest" (innermost) position of the cam surface 114 of the centering hub 102 where the bearing contact portion 140 operates during use. FIG. 11 includes a similar cross-sectional view of the chuck assembly 100, but in this case, the cam 110 is in the extended or upper position to center the wafer 112 held therebetween. In the aspect shown in the figure, the bearing contact portion 140 is disposed at the "shallowest" (outermost) position of the cam surface 114 of the centering hub 102 where the bearing contact portion 140 operates during use.

[0067] A series of FIGS. 12A - 12C are intended to facilitate a visual comparison of a particular aspect of the present chuck assembly 100 shown in FIG. 12C with a particular aspect of a conventional chuck assembly 1200 shown in FIGS. 12A - 12B. The chuck assembly 1200 shown in FIG. 12A includes a centrifugal or passive centrifugal cam 200 as opposed to the active or positive-acting cams of the present disclosure. FIG. 12B includes an enlarged view of the VAP 202 of the centrifugal cam 200. As described in more detail in the background art above, the presence of such a VAP 202 may not be useful, for example, during EBR or when cleaning the wafer 112. Friction (non-vacuum) pads 204 can be seen adjacent to each cam 200.

[0068] Conversely, FIG. 12C 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 provided equidistantly radially around a central chuck hub 104. Each arm 119 carries a respective cam 110. As shown in the figure, 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 include a vacuum pad 122 disposed towards the outer end of the arm. In some examples, the vacuum pad 122 is constituted by or includes a vacuum cup. A vacuum pressure is applied to the vacuum pad 122, and the wafer is adsorbed or fixed 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 that includes a push rod 116 in the manner described above. Other arm arrangements or arm configurations are possible.

[0069] An exemplary chuck assembly 100 of the type shown in FIG. 12C can actively center a wafer after the wafer is delivered from a robot to the chuck assembly 100. The ability to center the wafer after installation can eliminate or at least significantly reduce the need for precise robotic wafer placement in the chuck assembly. Different centering configurations may be employed depending on the diameter of the wafer. Retention of concentricity can be achieved by stable centering and elimination of VAP from the wafer edge. The chuck assembly 100 of the figure can also minimize streaking and taper width by using a higher rpm EBR process, and can provide supplementary wafer detection, for example, using a vacuum gripping level.

[0070] Comparative results were obtained that support the effectiveness of the above features. For example, FIG. 13 shows an exemplary graphical result of EBR measurements observed within a specific Edge Exclusion (EE) wafer range (here, 1.7 mm and 2.3 mm) and measured at 360 locations on the test wafer. The EBR results of the check of the conventional Point of Reference (POR) show a significant deformation expression of streaks or notches, as indicated by the sharp drop spikes in the graph at three different locations 1301, 1303, and 1305 around the test wafer. These locations correspond to the presence of VAP.

[0071] In comparison, for example, as shown by the uppermost line 1307 of the vacuum (VAC) chuck (2.3 mm) of the present application in the graph of FIG. 13, such deformation shown by the wafer supported by the chuck of the present application is minimal, if any. Similar flat results can also be seen with the VAC chuck (1.7 mm) of the present application. Note that for the conventional POR chuck, the smaller the EE (y-axis) in the graph, the more significant the drop spike. This is said to represent an increase in the effect of VAP at each location. The 1.7 mm location is closer to the outer edge of the wafer than the 2.3 mm location and is more susceptible to negative peripheral effects. The comparison range of the measured deformation values can be seen in the columns marked with rectangles in the table at the lower right of the figure.

[0072] Certain embodiments of the present disclosure include a method, an embodiment, or a process. In some examples, the method includes the processes of wafer centering, wafer gripping, and fluid obstruction mitigation to provide excellent EBR. The exemplary method may include at least the following operations or aspects described below. This method may be implemented in cooperation with, for example, 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] Referring to FIG. 16, method 1600 may include, at 1602, placing a wafer on chuck assembly 100. The wafer is centered by centering cam 110 as described above at 1604. When 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 vacuum pad 122 on which the wafer is placed. The vacuum is continuously applied at 1610 and the centering cam 110 is retracted to maintain the wafer accurately and concentrically in place.

[0074] If the wafer is deformed by the operation of the centering cam, the vacuum pad may leak. The inability to properly vacuum clamp the wafer indicates wafer breakage, cracking, loss, or improper placement, and may indicate that the wafer is not on all of the vacuum pads 122. Therefore, when the wafer is not vacuum clamped, method 1600 is interrupted.

[0075] Assuming the vacuum is maintained, the centering cam 110 is held in a retracted position below the upper surface of the wafer during wafer processing steps (EBR step, cleaning step, dry step, etc.). Since the centering cam 110 is below the wafer surface, there is no obstacle to reflect the EBR chemical solution that moves away from the wafer edge due to centrifugal action.

[0076] In another example, a method for vacuum gripping a wafer in a wet process chamber is provided. This method may include at least the following operations or may address specific aspects as follows.

[0077] In some examples, it can be difficult to grip the backside of a wafer in a wet process chamber. For example, there can be some degree of fluid leakage such that liquid is drawn into the vacuum circuit because of a large pressure differential across the surface or edge of the vacuum pad. Liquid entering 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 for the success of wafer processing that there is no liquid leakage past the edge or rim of the vacuum pad 122.

[0078] Thus, in some examples, a shape of a vacuum pad or vacuum cup is selected that does not leave wet watering or allow leakage. Different rubber formulations or hardnesses are possible to properly seal and not leave contaminants on the backside of the wafer.

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

[0080] As described above, motor torque and encoder position may be co - dependent on each other and may be measured together to confirm the centricity or concentricity of the wafer in 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 indicative of the clamping position of the wafer is observed. In some examples, the associated motor encoder position is within a known window indicating that the chuck has clamped a 300 mm wafer (for example) when the torque spikes.

[0081] In another example, a method for preventing EBR misalignment using chuck self-diagnosis is provided. This method may include at least the following operations, or may address specific aspects as follows. Here, motor torque measurements and encoder feedback enable the detection of inherent errors in centering verification. For example, if the motor torque spikes and the encoder position is outside the acceptable range, it indicates a centering error. Some exemplary situations that can cause centering errors include cam breakage, wafer breakage, breakage or freezing of components, or motor or encoder failure. Utilization of aspects such as the co-dependence of motor torque and encoder enables the detection of centering errors in the first or initial wafer of a series of wafers rather than in subsequent wafers. By taking early corrective measures to prevent EBR misalignment in subsequent wafers, significant waste can be avoided, and large economic losses and time waste can be avoided.

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

[0083] Despite this variability, if the wafer is measured to be abnormally small or large, the wafer diameter may be transferred to the EBR system. The EBR system may be configured in some examples to automatically adjust the position of the EBR nozzle to maintain the desired edge exclusion region based on applicable criteria for EBR parameters.

[0084] In another example, a method for a central criterion regarding edge detection is provided. This method may include at least the following operations or may address specific aspects as follows. In some examples, it is desirable to confirm that the diameter of the copper plating film on the wafer is the same for each wafer in the batch regardless of the edge exclusion region. In some examples, the chuck measures the wafer diameter during the centering routine. The EBR measurement measures the edge exclusion region after EBR. If the EBR measurement detects a change in the edge exclusion region, the wafer diameter can be determined from the chuck to investigate whether the change is due to a process problem or a change in the wafer diameter. If the edge exclusion region is caused by a change in the wafer diameter, it can be determined that the central criterion regarding 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 diagnosis and safety functions are provided. Some examples use vacuum gripping sensors at multiple locations distributed across the entire back surface of the wafer to detect wafer breakage or improper placement. This method may include the following operations or aspects.

[0086] As background, wafers selected for processing may have defects. For example, a single wafer may be chipped (having a shape sliced like a pizza). The remaining portion of the wafer may contain notches and may not be gripped by a chuck assembly having only three vacuum cups spaced 120° apart around the chuck, for example. In this unstable state, the wafer may violently and completely disintegrate or fly off at high speed. Increasing the number of vacuum pads or vacuum cups improves the detection of smaller chipped portions.

[0087] Referring to FIG. 14, the motor torque detection routine of the exemplary chuck assembly 100 is described herein with respect to graph 1400. During centering, the chuck hub of the chuck assembly 100 is moved by the spindle motor in the negative direction (e.g., counterclockwise when viewed from above) on the internal temporarily stationary centering hub as described above, and the centering cam is actuated. The negative rotation direction of the spindle motor may be contrasted with the positive rotation direction (e.g., clockwise) employed during processes such as the EBR process. The spindle motor moves in the negative direction and indicates a negative torque value. The negative value is shown on the y-axis of graph 1400. A "high" negative torque will have a large negative value and will be seen at a lower position on graph 1400.

[0088] The graph 1400 of FIG. 14 includes an exemplary torque profile of the spindle motor during the centering process described above. Referring to graph 1400, in phase 1402, the chuck assembly is rotating before the centering hub fin 134 (described above) reaches the locking pin 108, and the torque is very low (-5% of the rated torque). At point 1404, the locking pin 108 engages the fin 134 and the (negative) torque increases. The result of the figure shows the overshoot and undershoot torque profiles at and immediately after point 1406. Next, while the centering hub 102 is moving relative to the chuck hub 104 to actuate and close the centering cam 110, the spindle motor torque remains stable at a substantially constant value until point 1408. The cam 110 begins to engage the wafer 112 and moves the wafer 112 to the desired center position until point 1408. Next, the motor torque spikes while implying that the wafer 112 is no longer moving, reaches the centering position where it is slightly compressed, and begins to resist the centering cam 110 there. The exemplary motor torque spike is shown at point 1410.

[0089] The magnitude of the centering torque may vary from chuck to chuck depending on the diversity of components, differences in tolerances, spring constants, etc. By calibrating the chuck to determine the torque required to center a 300 mm wafer, these diversities can be accommodated. For example, the cutoff torque in the phase from point 1410 to point 1412 can be appropriately set to ensure that a given wafer is not overcompressed or damaged during centering. In phase 1414, the chuck arm spring extends while the cam 110 is retracted. After phase 1414 when the centering hub fin 134 breaks contact with the locking pin 108, undershoot and overshoot spikes 1416 occur.

[0090] FIG. 15 is a block diagram showing an exemplary machine 1500 in which one or more of the exemplary method embodiments described herein can be implemented or controlled. In another embodiment, the machine 1500 may operate as a stand-alone device or may be coupled (e.g., network-connected) to other machines. In a networked arrangement, the machine 1500 may operate as a server machine, as a client machine, or 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. Further, 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 of the methods discussed herein (such as by cloud computing, software as a service (SaaS), or other computer cluster configurations).

[0091] The examples described in this specification may include, or be operated by, logic, multiple components, or mechanisms. An electrical circuit is a group of circuits implemented in a physical entity 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 electrical circuit includes elements that can perform certain operations, either individually or in cooperation, during operation. In one example, the hardware of an electrical circuit may be designed to be invariant to perform a particular operation (e.g., an operation by the hardware). In one example, the hardware of an electrical circuit includes a physically adjustable (e.g., magnetically, electrically, such as by a movable arrangement of immobile dense particles) computer-readable medium that encodes instructions for a particular operation, and variable-connected physical components (e.g., execution units, transistors, simple circuits, etc.). When connecting physical components, the underlying electrical characteristics of the hardware components are changed (e.g., from an insulator to a conductor, or vice versa). The instructions enable an embedded hardware (e.g., an execution unit or a loading mechanism) to form electrical circuit elements within the hardware by variable connection and perform part of a particular operation during operation. Accordingly, the computer-readable medium is communicatively coupled to other components of the electrical circuit when the device is operating. In one example, any of the physical components may be used in one or more elements of one or more electrical circuits. For example, an execution unit may be used in a first circuit of a first electrical circuit at a point in time during operation, and again in a second circuit of the first electrical circuit, or in a third circuit of a second electrical circuit, at different times.

[0092] A 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 a touch screen. 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 sensors). The machine 1500 may include an output controller 1528, such as a serial connection (e.g., a 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 storing 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 be wholly or at least partially present in the main memory 1504, the static memory 1506, the hardware processor 1502, or 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 shown as one medium, the term "machine-readable medium" may include one or more media (e.g., a centralized database or a 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 that can store, encode, or transmit instructions 1524 for execution by a machine 1500, and any medium that causes a machine 1500 to perform one or more of the techniques of the present disclosure, or any medium that can store, encode, or transmit a data structure used by or associated with the instructions 1524. Examples of non-limiting 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 comprising a plurality of particles having an invariant (e.g., stationary) mass. Thus, a mass machine-readable medium is not a transient propagation signal. Specific examples of mass machine-readable media may include non-volatile memory (such as semiconductor memory 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 disks and DVD-ROM disks. The instructions 1524 may further be transmitted or received through a communication network 1526 using a transmission medium via a network interface device 1520.

[0096] Even though embodiments have been described with reference to specific exemplary embodiments, it will be apparent that various modifications and changes may be made to these embodiments without departing from the broader scope of the inventive subject matter. Accordingly, the specification and drawings are to be regarded in an illustrative rather than a restrictive sense. The accompanying drawings, which form a part of this application, illustrate, for purposes of illustration, specific embodiments in which the subject matter is practiced, and are not intended to limit the subject matter disclosed herein. Embodiments of the figures 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 without departing from the scope of the present disclosure, such that structural and logical substitutions and changes may be made. Thus, the above description should not be taken in a limiting sense, and the scope of various embodiments is defined only by the appended claims and the full scope of equivalents to such claims when they are granted.

[0097] When one or more such embodiments of the subject matter of the present invention are actually disclosed, they may be referred to, for convenience, individually and / or collectively, by the term "invention" without an intention to spontaneously limit the scope of the present application to one invention or inventive concept. Thus, it should be recognized that even if specific embodiments are shown and described herein, arrangements planned to achieve the same purpose may be replaced by the specific embodiments shown. The present disclosure is intended to include all adaptations or diversities of various embodiments. Combinations of the above embodiments and other embodiments not specifically described herein will be apparent to those skilled in the art upon consideration of the above description. The present disclosure includes the following application examples. [Application Example 1] A wafer chuck assembly for supporting a wafer, a chuck hub, a centering hub disposed within the chuck hub, an engagement device operable between an engaged position and a disengaged position, each engaging 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, and a chuck motor for selectively rotating the chuck hub and / or the centering hub based on the engaged position or the disengaged position of the engagement device during a wafer processing operation and a wafer centering operation, 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, each centering cam being attached to or directed toward the distal end of a chuck arm and being operable radially inwardly or outwardly with respect to the centering hub to engage or release an edge of a supported wafer in response to a rotational movement of the centering hub relative to the chuck hub, a wafer chuck assembly comprising the same. [Application Example 2] The wafer chuck assembly according to Application Example 1, wherein the chuck motor is configured to apply a relative rotational movement 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, wherein 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. [Application Example 4] The wafer chuck assembly according to Application Example 3, The chuck motor is configured to rotate the centering hub and the chuck hub together in the same rotational direction during the wafer processing operation, a wafer chuck assembly. [Application Example 5] The wafer chuck assembly according to Application Example 4, 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, a wafer chuck assembly. [Application Example 6] The wafer chuck assembly according to Application Example 1, wherein the centering hub includes at least one cam surface on its outer surface, a wafer chuck assembly. [Application Example 7] The wafer chuck assembly according to Application Example 6, wherein each chuck arm includes a respective elongated operating rod operatively disposed between the at least one cam surface of the centering hub and a centering cam disposed at the tip of each chuck arm of the plurality of centering cams, a wafer chuck assembly. [Application Example 8] The wafer chuck assembly according to Application Example 7, wherein each elongated operating rod includes a bearing surface at its proximal end for engaging the at least one cam surface of the centering hub, a wafer chuck assembly. [Application Example 9] The wafer chuck assembly according to Application Example 7, wherein each elongated operating rod includes a connection portion with the respective centering cam of each chuck arm at its tip, a wafer chuck assembly. [Application Example 10] The wafer chuck assembly according to Application Example 9, wherein by the rotational movement of the centering hub, each cam surface of the centering hub urges the respective elongated operating rod radially outward, thereby operating the respective centering cam via the connection portion, a wafer chuck assembly. [Application Example 11] The wafer chuck assembly according to Application Example 1, and further, includes at least one vacuum pad for supporting the wafer during the wafer centering operation and / or the wafer processing operation, a wafer chuck assembly. [Application Example 12] The wafer chuck assembly according to Application Example 11, The at least one vacuum pad is configured to maintain the wafer at a centered position of the wafer chuck assembly during at least the wafer processing operation when the wafer is released to the plurality of centering cams, wafer chuck assembly. [Application Example 13] A wafer chuck assembly according to Application Example 11, wherein the at least one vacuum pad is provided on at least one of the plurality of chuck arms, wafer chuck assembly. [Application Example 14] A wafer chuck assembly according to Application Example 11, wherein each of the plurality of chuck arms includes a vacuum line for supplying a vacuum pressure to the at least one vacuum pad, wafer chuck assembly. [Application Example 15] A wafer chuck assembly according to Application Example 14, wherein the presence or absence of a vacuum pressure in the at least one vacuum pad is detected and associated with the presence or absence of the wafer within the wafer chuck assembly or the presence of a defective wafer, wafer chuck assembly.

Claims

1. A vacuum chuck assembly for supporting a substrate or a wafer, comprising: A chuck hub; A plurality of chuck arms attached to the chuck hub, each chuck arm extending radially between a proximal end adjacent to the chuck hub and a distal end remote therefrom; A centering hub disposed within the chuck hub; A plurality of centering cams, each centering cam being attached to or directed towards the distal end of a chuck arm and being operable radially inwards or outwards relative to the centering hub to engage or disengage an edge of a supported wafer in response to rotation of the centering hub; A vacuum pad disposed on at least one of the plurality of chuck arms, the vacuum pad supporting and clamping the wafer within the chuck assembly during a wafer centering operation or a wafer processing operation when a vacuum pressure is applied to the vacuum pad; A vacuum sensor for detecting the presence or absence of a vacuum pressure in the vacuum pad during the wafer centering operation or the wafer processing operation, the detection indicating the presence or absence of the wafer within the chuck assembly or the presence of a defective wafer; A vacuum chuck assembly comprising the above.

2. The chuck assembly according to claim 1, further comprising: An engagement device operable between an engaged position and a disengaged position, the engagement device engaging 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 position or the disengaged position of the engagement device during a wafer processing operation and a wafer centering operation. A chuck assembly comprising

3. The chuck assembly according to claim 2, wherein the chuck motor is configured to apply a relative rotational movement between the centering hub and the chuck hub during the wafer centering operation.

4. The chuck assembly according to claim 3, wherein 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.

5. The chuck assembly according to claim 4, 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 operation.

6. The chuck assembly according to claim 5, 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.

7. The chuck assembly according to claim 1, wherein the centering hub includes at least one cam surface on its outer surface.

8. The chuck assembly according to claim 7, each chuck arm comprising an elongated actuating rod operatively disposed between the at least one cam surface of the centering hub and a centering cam disposed at the tip of each chuck arm of the plurality of centering cams.

9. The chuck assembly according to claim 8, wherein each elongated actuating rod is provided, at its proximal end, with a bearing surface for engaging at least one cam surface of the centering hub.

10. The chuck assembly according to claim 9, wherein each elongated actuating rod is provided, at its tip, with a connection portion with a respective centering cam of a respective chuck arm.

11. The chuck assembly according to claim 10, wherein by the rotational movement of the centering hub, each cam surface of the centering hub urges a respective elongated actuating rod radially outward, thereby actuating a respective centering cam via the connection portion.

12. The chuck assembly according to claim 1, wherein the at least one vacuum pad is configured to vacuum clamp the wafer at a centered position of the chuck assembly during at least the wafer processing operation when the wafer is released to the plurality of centering cams.

13. The chuck assembly according to claim 1, wherein each of the plurality of chuck arms is provided with a vacuum line for supplying the vacuum pressure to the vacuum pad.

14. The chuck assembly according to claim 13, wherein the vacuum sensor communicates with the vacuum line.

15. The chuck assembly according to claim 1, wherein the plurality of centering cams are biased towards an open wafer release configuration.

16. The chuck assembly according to claim 2, wherein each centering cam of the plurality of centering cams is operable between a first wafer centering position and a second storage position, and the second storage position is disposed below the upper surface of the wafer supported within the chuck assembly. **Claim 17** The chuck assembly according to claim 16, further comprising control means for detecting the torque of the chuck motor and associating the detected chuck motor torque with at least the first wafer centering position of the plurality of centering cams. **Claim 18** The chuck assembly according to claim 2, further comprising control means for detecting the torque of the chuck motor and associating the detected chuck motor torque with the centered position of the wafer held by the chuck assembly. **Claim 19** A method of detecting the state of a wafer within a vacuum chuck assembly, comprising providing a chuck hub to the chuck assembly; providing a plurality of chuck arms attached to the chuck hub, each chuck arm extending radially between a proximal end adjacent to the chuck hub and a distal end remote therefrom; providing a centering hub disposed within the chuck hub; providing a plurality of centering cams, each centering cam being attached to or directed towards the distal end of a chuck arm and being operable radially inwards or outwards with respect to the centering hub so as to engage or disengage an edge of a supported wafer in response to a rotational movement of the centering hub; Providing a vacuum pad disposed on at least one of the plurality of chuck arms, the vacuum pad supporting and clamping the wafer within the chuck assembly during a wafer centering operation or a wafer processing operation when a vacuum pressure is applied to the vacuum pad; Detecting the presence or absence of a vacuum pressure in the vacuum pad during the wafer centering operation or the wafer processing operation, the detection indicating the presence or absence of the wafer within the chuck assembly or the presence of a defective wafer; A method comprising.

Images