Improved Automatic Wafer Centering System and Its Technology

Abstract

Systems and techniques for determining and correcting inter-wafer misalignment in a stack of wafers handled by a wafer handling robot are discussed. An improved automatic wafer centering system is provided that can be used to determine the minimum circle associated with the wafers of the stack, which can then be used to determine whether the wafers of the stack meet various process requirements and / or whether centering correction can be performed to better align the wafers with an acceptance station coordinate system.

Description

[0001] Incorporated by reference

[0002] The PCT application form is filed simultaneously with this specification as part of this application. Each application for which this application claims the benefit or priority thereof as identified in the PCT application form filed simultaneously herewith is incorporated herein by reference in its entirety and for all purposes. Background Art

[0003] Semiconductor processing tools typically use wafer handling robots to move circular wafers (which have a nominally circular shape but may have notches or flats at one or more locations to enable rotational indexing or determination of rotational position) between stations or apparatuses within the semiconductor processing tool. Some wafer handling robots are equipped with "blade" - type end effectors, similar to spatulas, which are designed to lift and support the wafer from below. The wafers supported by such blade - type end effectors are typically held in place by friction and can be displaced or moved relative to the end effector by applying sufficient lateral force to the wafer (e.g., which may be applied to the wafer due to a collision with another object or by inertial effects). For example, if the end effector undergoes an acceleration such that the frictional force holding the wafer in place is overcome, there may be slippage between the wafer and the end effector. Wafers may also sometimes be misaligned on the end effector, resulting in an initial "slip" effect, e.g., when the wafer is not properly centered. Summary of the Invention

[0004] Details of one or more embodiments of the subject matter described in this specification are set forth in the accompanying drawings and the following description. Other features, aspects, and advantages will become apparent from the description, the drawings, and the claims.

[0005] In some implementations, a device for handling one or more wafers having a nominal diameter of D1 is provided. The device may include: a wafer handling robot configured to support the one or more wafers having a nominal diameter of D 1 when placed thereon, of the nominal diameter of D 1one or more wafers; a first edge detection system; and a controller including one or more processors and one or more memory devices. The one or more processors, the one or more memory devices, the wafer handling robot, and the first edge detection system may be operatively connected to each other, and the one or more memory devices may store computer-executable instructions for controlling the one or more processors to: a) obtain information about a first reference point of the wafer handling robot; b) determine that a first group of one or more wafers is supported by the wafer handling robot, the first group of one or more wafers defining a profile edge in a horizontal plane when viewed along a vertical axis; c) cause the first edge detection system to obtain information indicating first horizontal coordinates of at least five points along the profile edge of the first group of one or more wafers relative to the first reference point; d) for the first group of one or more wafers, determine a minimum circle circumscribing the first horizontal coordinates of the at least five points determined in (c) when viewed along the vertical axis; e) for the first group of one or more wafers, determine a first center deviation by determining information indicating the length and direction of a first reference line segment extending from the center of the minimum circle for the first group of one or more wafers to the first reference point; f) determine a first sliding amount of the first group of one or more wafers based on a difference between the diameter of the minimum circle and D 1 ; and g) determine whether the first sliding amount of the first group of one or more wafers exceeds a first threshold amount.

[0006] In some implementations of the device, the first edge detection system may include three first through-beam optical sensors, and each first through-beam optical sensor may: be configured to emit a corresponding vertically directed beam when activated, be positioned such that a farthest horizontal distance between any of the beams is less than D 1 when the first through-beam optical sensor is activated, and be configured to register when the beam emitted by it intersects an edge of an object when the first through-beam optical sensor is activated.

[0007] In some implementations of the device, the first edge detection system may include a machine vision system, and the machine vision system may be configured to obtain the information indicating the first horizontal coordinates of the at least five points along the profile edge of the first group of one or more wafers relative to the first reference point.

[0008] In some implementations of the device, the first edge detection system includes one or more of the following: a set of three or more direct-through beam optical sensors, a set of three or more reflective-through beam optical sensors, a machine vision measurement system, or a set of three or more capacitive sensors.

[0009] In some implementations of the device, the wafer handling robot may include an end effector having N blades, the first group of one or more wafers may include N or fewer wafers, and each blade may be configured to support one of the wafers having a nominal diameter of D 1 and N may be greater than 1.

[0010] In some implementations of the device, the N blades may include a first group of N - 1 blades fixed relative to each other, the first group of N - 1 blades may be configured to move as a unit relative to the portion of the wafer handling robot to which the first group of N - 1 blades is attached, and the blade of the end effector that is not in the first group of N - 1 blades may be configured to move independently of the first group of N - 1 blades and relative to the portion of the wafer handling robot to which the first group of N - 1 blades is attached.

[0011] In some such implementations, N may be equal to 5.

[0012] In some implementations of the device, the wafer handling robot may include an end effector having only one blade and the first group of one or more wafers may include only one wafer.

[0013] In some implementations of the device, the device may further include: a first wafer container including one or more first wafer supports configured to receive the first group of one or more wafers. In some such implementations, each of the one or more first wafer supports may be configured to support a wafer placed thereon and within a boundary region envelope associated with the first wafer container and having a minimum horizontal dimension D 2 where D 2 is at least the first threshold amount greater than D 1 In some such implementations of the device, the first wafer container may further include a second edge detection system configured to register when an edge of an object intersects one or more second horizontal positions monitored by the second edge detection system when the second edge detection system is activated.

[0014] In some implementations of the device, the one or more memory devices may also store computer-executable instructions for further controlling the one or more processors to perform the following operations: causing the wafer handling robot to place at least some of the one or more wafers in the first set of wafers into the first wafer container at least in part in response to determining that the first slip amount of the one or more wafers in the first set is less than the first threshold amount.

[0015] In some additional implementations of the device, the one or more memory devices may also store computer-executable instructions for further controlling the one or more processors to perform the following operations: determining a first wafer offset of the one or more wafers in the first set based on information indicating the length and orientation of the first reference line segment for the one or more wafers in the first set; and during one or more operations in which the one or more wafers in the first set are supported by the wafer handling robot, causing the wafer handling robot to operate to place at least some of the one or more wafers in the first set into the first wafer container according to the first wafer offset.

[0016] In some implementations of the device, the one or more memory devices may also store computer-executable instructions for further controlling the one or more processors to perform the following operations: causing the wafer handling robot to place the wafers in the one or more wafers in the first set into a second wafer container at least in part in response to determining that the first slip amount of the one or more wafers in the first set is greater than the first threshold amount; and thereafter and during a second time period, for each wafer in the first set of wafers, causing the wafer handling robot to: retrieve the wafer from the second wafer container, while the wafer is supported by the wafer handling robot, causing the first edge detection system to obtain information indicating at least three second horizontal coordinates along the contour edge of the wafer relative to the first reference point, using the at least three second horizontal coordinates, determining an estimated center point of the wafer relative to the first reference point, by determining information indicating the length and direction of a second reference line segment extending from the estimated center point of the wafer to the first reference point, determining a second center deviation, determining a second wafer offset for the wafer based on information indicating the length and orientation of the second reference line segment for the wafer, and during one or more operations in which the wafer is supported by the wafer handling robot, causing the wafer handling robot to operate to place the wafer into the first wafer container according to the second wafer offset.

[0017] In some implementations, a device for handling wafers having a nominal diameter of D may be provided 1A method for one or more wafers. The method may include: a) Using a wafer handling robot, retrieving one or more wafers of a first set having a nominal diameter of D 1 of the first set, the wafer handling robot being configured to support the one or more wafers of the first set when the one or more wafers of the first set are placed thereon, the one or more wafers of the first set defining a profile edge in a horizontal plane when viewed along a vertical axis; b) Using the first edge detection system, obtaining information about a first reference point of the wafer handling robot; c) Using the first edge detection system, obtaining information indicating first horizontal coordinates of at least five points along the profile edge of the one or more wafers of the first set relative to the first reference point; d) For the one or more wafers of the first set, determining a smallest circle circumscribing the first horizontal coordinates of the at least five points determined in (c) when viewed along the vertical axis; e) For the one or more wafers of the first set, determining a first center deviation by determining information indicating the length and direction of a first reference line segment extending from the center of the smallest circle of the one or more wafers of the first set to the first reference point; f) Determining a first sliding amount of the one or more wafers of the first set based on the difference between the diameter of the smallest circle and D 1 ; and g) Determining whether the first sliding amount of the one or more wafers of the first set exceeds a first threshold amount.

[0018] In some implementations of the method, the first edge detection system may include three first through-beam optical sensors, and each first through-beam optical sensor may: be configured to emit a corresponding vertically directed beam when activated, be positioned such that the farthest horizontal distance between any of the beams is less than D 1 when the first through-beam optical sensor is activated, and be configured to register when the beam emitted by it intersects the edge of an object when the first through-beam optical sensor is activated. In such an implementation, (c) may be performed by obtaining a horizontal coordinate each time the profile edge of the one or more wafers of the first set intersects one of the beams emitted by one of the first through-beam optical sensors.

[0019] In some implementations of the method, the first edge detection system may include a machine vision system configured to obtain the information indicating the first horizontal coordinates of the at least five points along the profile edge of the one or more wafers of the first set relative to the first reference point; and (c) may be performed by using the machine vision system to obtain the horizontal coordinates of the at least five points.

[0020] In some implementations of the method, the first edge detection system may include one or more objects selected from the group consisting of a set of three or more direct-through beam optical sensors, a set of three or more reflective-through beam optical sensors, a machine vision measurement system, and a set of three or more capacitance sensors.

[0021] In some implementations of the method, the wafer handling robot may include an end effector having N blades, the first group of one or more wafers may include N or fewer wafers, and each blade may be configured to support one of the wafers having a nominal diameter of D 1 and N may be greater than 1.

[0022] In some further implementations of the method, the N blades may include a first set of N - 1 blades fixed relative to each other, the first set of N - 1 blades may be configured to move as a unit relative to the portion of the wafer handling robot to which the first set of N - 1 blades is attached, and the blade of the end effector that is not in the first set of N - 1 blades may be configured to move independently of the first set of N - 1 blades and relative to the portion of the wafer handling robot to which the first set of N - 1 blades is attached. In some such implementations of the method, N may be equal to 5.

[0023] In some implementations of the method, the wafer handling robot may include an end effector having only one blade, and the first group of one or more wafers may include only one wafer.

[0024] In some implementations of the method, D 1 may be at least the first threshold amount smaller than D 2 where D 2 may be the minimum horizontal dimension of the bounding region envelope associated with a first wafer container that includes one or more first wafer supports configured to receive the first group of one or more wafers, and each of the one or more first wafer supports may be configured to support a wafer placed thereon and within the bounding region envelope.

[0025] In some such implementations, the first wafer container may further include a second edge detection system configured to register when an edge of an object intersects one or more second horizontal positions monitored by the second edge detection system when the second edge detection system is activated.

[0026] In some implementations of the method, the method may further include: in (g), determining that the first slide amount of one or more wafers of the first group is less than the first threshold amount, and (h) causing the wafer handling robot to place at least some of the one or more wafers in the first group into the first wafer container at least in part in response to determining that the first slide amount of the one or more wafers of the first group is less than the first threshold amount. In some such implementations of the method, the method may further include: (i) determining a first wafer offset of the one or more wafers of the first group based on information indicating the length and orientation of the first reference line segment for the one or more wafers of the first group; and (j) during one or more operations in which the one or more wafers of the first group are supported by the wafer handling robot, causing the wafer handling robot to operate to place at least some of the one or more wafers in the first group into the first wafer container according to the first wafer offset.

[0027] In some implementations of the method, the method may further include: (h) causing the wafer handling robot to place the wafers in the one or more wafers of the first group into a second wafer container at least in part in response to determining that the first slide amount of the one or more wafers of the first group is greater than the first threshold amount; and (i) after (h) and during a second time period, for each wafer in the first group of wafers, causing the wafer handling robot to: retrieve the wafer from the second wafer container, while the wafer is supported by the wafer handling robot, causing the first edge detection system to obtain information indicating at least three second horizontal coordinates along the profile edge of the wafer relative to the first reference point, using the at least three second horizontal coordinates, determining an estimated center point of the wafer relative to the first reference point, by determining information indicating the length and direction of a second reference line segment extending from the estimated center point of the wafer to the first reference point, determining a second center deviation, based on information indicating the length and orientation of the second reference line segment for the wafer, determining a second wafer offset for the wafer, and during one or more operations in which the wafer is supported by the wafer handling robot, causing the wafer handling robot to operate to place the wafer into the first wafer container according to the second wafer offset.

[0028] In some implementations, a non-transitory computer-readable medium may be provided, having stored thereon computer-executable instructions for controlling one or more processors to: (a) using a wafer handling robot, place a wafer having a nominal diameter of D 1retrieving one or more wafers of the first group, the wafer handling manipulator being configured to support the one or more wafers of the first group when the one or more wafers of the first group are placed thereon, the one or more wafers of the first group defining a profile edge in a horizontal plane when viewed along a vertical axis; b) using the first edge detection system, obtaining information about a first reference point of the wafer handling manipulator; c) using the first edge detection system, obtaining information indicating first horizontal coordinates of at least five points along the profile edge of the one or more wafers of the first group relative to the first reference point; d) for the one or more wafers of the first group, determining a smallest circle circumscribing the first horizontal coordinates of the at least five points determined in (c) when viewed along the vertical axis; e) for the one or more wafers of the first group, determining a first center deviation by determining information indicating the length and direction of a first reference line segment extending from the center of the smallest circle for the one or more wafers of the first group to the first reference point; f) determining a first sliding amount of the one or more wafers of the first group based on a difference between the diameter of the smallest circle and D 1 ; and g) determining whether the first sliding amount of the one or more wafers of the first group exceeds a first threshold amount.

[0029] In some implementations of the non-transitory computer-readable medium, the first edge detection system may include three first through-beam optical sensors, each of the first through-beam optical sensors: being configured to emit a corresponding vertically-directed beam when activated, being positioned such that a farthest horizontal distance between any of the beams is less than D 1 , and being configured to register when the beam emitted by it intersects an edge of an object when the first through-beam optical sensor is activated. In such an implementation, the non-transitory computer-readable medium may also store instructions for: controlling the one or more processors to operate the three first through-beam optical sensors such that the horizontal coordinates of (c) are obtained each time an edge of the profile of the one or more wafers of the first group intersects one of the beams emitted by one of the first through-beam optical sensors.

[0030] In some implementations of the non - transitory computer - readable medium, the first edge detection system may include a machine vision system, and the machine vision system is configured to obtain the information of the first horizontal coordinates of at least five points indicating the profile edges of one or more wafers of the first group relative to the first reference point; and the non - transitory computer - readable medium may further store operation instructions for: controlling the one or more processors to connect to the machine vision system and use the machine vision system to obtain the horizontal coordinates in (c).

[0031] In some implementations of the non - transitory computer - readable medium, the first edge detection system may include one or more of the following items and the non - transitory computer - readable medium further stores instructions for causing the one or more processors to connect and communicate with one or more of the following items: a set of three or more direct - through beam optical sensors, a set of three or more reflective - through beam optical sensors, a machine vision measurement system, or a set of three or more capacitive sensors.

[0032] In some implementations of the non - transitory computer - readable medium, D 1 may be smaller than D 2 by at least the first threshold amount, and D 2 may be the minimum horizontal dimension of a bounding - region envelope associated with a first wafer container that includes one or more first wafer carriers configured to receive one or more wafers of the first group, and the one or more first wafer carriers may each be configured to support a wafer placed thereon and within the bounding - region envelope.

[0033] In some implementations of the non - transitory computer - readable medium, the non - transitory computer - readable medium may further store instructions for controlling the one or more processors to perform the following operations: in (g), determining that the first sliding amount of one or more wafers of the first group is less than the first threshold amount, and in (h), causing the wafer handling manipulator to place at least some of the one or more wafers in the first group of wafers into the first wafer container at least in response to determining that the first sliding amount of one or more wafers of the first group is less than the first threshold amount.

[0034] In some such implementations of the non-transitory computer-readable medium, the non-transitory computer-readable medium may also store instructions for controlling the one or more processors to perform the following operations: i) determining a first wafer offset of the one or more wafers of the first group based on information indicating the length and orientation of the first reference line segment for the one or more wafers of the first group; and j) during one or more operations in which the one or more wafers of the first group are supported by the wafer handling robot, causing the wafer handling robot to operate to place at least some of the wafers in the one or more wafers of the first group into the first wafer container according to the first wafer offset.

[0035] In some implementations of the non-transitory computer-readable medium, the non-transitory computer-readable medium may also store instructions for controlling the one or more processors to perform the following operations: h) causing the wafer handling robot to place the wafer in the one or more wafers of the first group into a second wafer container at least in part in response to determining that the first sliding amount of the one or more wafers of the first group is greater than the first threshold amount; and i) after (h) and during a second time period, for each wafer in the first group of wafers, causing the wafer handling robot to: retrieve the wafer from the second wafer container, while the wafer is supported by the wafer handling robot, causing the first edge detection system to obtain information indicating at least three second horizontal coordinates along the profile edge of the wafer relative to the first reference point, using the at least three second horizontal coordinates, determining an estimated center point of the wafer relative to the first reference point, by determining information indicating the length and direction of a second reference line segment extending from the estimated center point of the wafer to the first reference point, determining a second center deviation, based on information indicating the length and orientation of the second reference line segment for the wafer, determining a second wafer offset for the wafer, and during one or more operations in which the wafer is supported by the wafer handling robot, causing the wafer handling robot to operate to place the wafer into the first wafer container according to the second wafer offset. BRIEF DESCRIPTION OF THE DRAWINGS

[0036] The various embodiments disclosed herein are depicted in the figures of the drawings by way of example and not limitation, where like reference numerals refer to like elements.

[0037] Figure 1A and 1B A wafer stack experiencing inter-wafer misalignment is depicted.

[0038] Figures 2A to 2GDepicts a graph of a calibration wafer that is being translated through the beams of three through-beam optical sensors that are part of an improved AWC system.

[0039] Figure 2H Depicts the potential positions of the through-beam optical sensors based on calibration measurements.

[0040] Figure 3 Depicts a flowchart of a technique that uses an improved AWC system.

[0041] Figures 4 to 13 Depicts an example portion of a semiconductor processing tool that includes an improved AWC system in various operating states.

[0042] Figures 14A to 14G Depicts a top view of a wafer stack that has been placed on an end effector and is being translated through a set of three through-beam optical sensors.

[0043] Figure 15 Depicts Tables 1 and 2.

[0044] Figure 16 Depicts an exemplary minimum circle for a multi-wafer profile edge.

[0045] Figure 17 Depicts Figure 16 the minimum circle of, but with the profile edge removed.

[0046] The figures here are generally not drawn to scale, but aspects of the figures, as explored below, may be drawn to scale. Specific embodiments

[0047] Wafer handling robots are typically equipped with high-precision positioning sensors that monitor, for example, the amount of rotation in each robotic arm joint. By measuring this rotation and knowing the distances between the centers of rotation of the various links in the robotic arm, the wafer handling robot can very precisely track the position of any point on the robotic arm (including the end effector) relative to the robotic arm base and the world coordinate system.

[0048] However, the wafer handling robot must interact with other objects in the semiconductor processing tool, such as load locks, front-opening unified pods (FOUPs), wafer buffers, etc. Such other components may be installed in various different positions in the semiconductor processing tool, and due to assembly tolerances and other factors, may vary somewhat in how they are assembled relative to other components and / or the wafer handling robot. Once the wafer handling robot is installed in the tool (and periodically thereafter, e.g., after the equipment has been removed for maintenance and then reinstalled or replaced), it can be trained to "learn" the exact positions of each potential wafer pick-up and drop-off location (or "station").

[0049] For example, this training can be performed by placing the robotic arm in a free movement mode, in which the robotic arm can be freely repositioned by applying an external force to the robotic arm linkages and then positioning the end effector of the robotic arm relative to each wafer station at a desired position. In most applications, this involves aligning the nominal center point of the end effector, i.e., the position of the end effector that coincides with the center line of the wafer considered to be optimally supported by the end effector (e.g., centered between the wafer support pads of the end effector or centered along the center line of the end effector) with the axis of the station, which will ideally intersect the center of the wafer perfectly placed on the station. The positioning of the end effector relative to each wafer station can be achieved by using a fixture that can be fixed in place relative to the wafer station and / or the end effector and is designed such that the end effector can be accurately positioned. Once this relative positioning has been set, the wafer handling robot can be made to "learn" the station position. For example, the wafer handling robot can determine the location of the station position based on feedback from wafer handling robot position sensors and other information (such as the distance between the centers of rotation of the robotic arm joints). Once the wafer handling robot has learned all the station positions, the robot can then be made to return to any of the learned station positions based on the learned position information.

[0050] Although the robotic arm can be made to navigate accurately and repetitively between various different learned station positions during operation through its position sensors, if there is slippage between the wafer and the end effector, the wafer will be off-center relative to the ideal or target position for the station when placed in the station. To correct for this potential misalignment, a technique called automatic wafer centering can be used.

[0051] In a device with automatic wafer centering (AWC) technology, each station that requires precise wafer placement can be equipped with a pair of through-beam optical sensors; each through-beam optical sensor can be configured to provide a vertically directed beam. Such sensors are typically set at the entrance of the station such that when the wafer is translated through the entrance to the station by the wafer handling robot, the wafer edge intersects each vertically directed beam twice (once at the leading edge of the wafer and once at the trailing edge of the wafer). Each time the wafer edge intersects one of the beams, the through-beam optical sensor can send a signal to the robotic arm controller. If the XY position of the through-beam optical sensor and the XY position of the nominal center point of the end effector are known when the through-beam optical sensor detects an intersection with the edge of the corresponding beam, the XY position of the edge intersection relative to the nominal center point can be determined.

[0052] Before normal operation of the AWC system, a calibration wafer can be attached to the end effector at a default position to center it relative to the end effector at a specific location, such as the previously discussed nominal center point, using one or more pins or other fixing devices to fix the calibration wafer in place relative to the end effector in a repeatable and safe manner, thereby preventing lateral sliding of the calibration wafer. The calibration wafer can be a precision-machined circular disk with a known diameter (e.g., 300 mm). The calibration wafer can then be linearly translated through the through-beam optical sensor pair of the AWC system such that each through-beam optical sensor detects the edge of the calibration wafer twice (once when the calibration wafer enters the beam and a second time when the calibration wafer exits the beam), and the XY coordinates of the nominal center point of the end effector can be determined using the beam of each through-beam optical sensor for each intersection with the edge of the calibration wafer. The XY coordinates of each through-beam optical sensor can be determined by using the nominal center point coordinates associated with the two edge intersections detected by the through-beam optical sensor and the known radius of the calibration wafer. For example, the position of the optical center of the through-beam and the two nominal center point coordinates can form a triangle with one side extending between the two nominal center point coordinates (the length of which can be calculated based on the XY distance between the two coordinates), and the remaining two sides having lengths equal to the radius of the calibration wafer. Based on this information, two possible positions of the optical center of the through-beam can be identified (one on each side of the nominal center point). The most likely candidate of the two possible positions can then be selected (for example, there may be a predefined spatial envelope within which the position of the through-beam optical sensor can be expected; one solution may fall within the envelope and the other may be outside the envelope - the solution within the envelope can be selected as the actual position).

[0053] After calibration and determination of the position of the through-beam optical sensors, the AWC system can be used to scan regular wafers that may experience slippage relative to the end effector. When a regular wafer (e.g., a wafer being processed in a semiconductor processing tool) is placed on the end effector and then moved through the AWC system, XY positions can be obtained for each position where the edge of the wafer intersects the beam of one of the through-beam optical sensors (in effect, the XY position of the through-beam optical sensor that detects the edge intersection). At the same time, based on the XY coordinates of each such intersection point and the associated XY coordinates of the nominal center point of the end effector, the XY position of the edge intersection point relative to the nominal center point can be determined. Since all four edge intersection points lie on the edge of a circular wafer of known diameter, the position of the wafer center relative to the nominal center point of the end effector can be determined using any three of the four coordinates. In a typical system, four sets of three points can be evaluated to determine circles of substantially equal size that share the same center point (since they all measure the same circular wafer); if one of these circles is determined to be too small, the determination of that circle can be ignored because it may be an edge intersection point where the position of the intersection with the wafer edge does not lie on the circular edge, such as a one-degree notch in the circular edge. In a perfectly centered wafer, the center point of the wafer and the nominal center point of the end effector will coincide with each other in the XY plane. However, if there is misalignment between the two, the X offset and Y offset between the nominal center point and the wafer center point can be determined and then used by the robotic arm controller to adjust the final placement of the wafer at the target position of the station to recenter the wafer at the target position.

[0054] The inventors of the present case have determined that for high-capacity end effectors, i.e., end effectors that can transport multiple wafers simultaneously in a stacked configuration, traditional AWC techniques will be infeasible. For example, some end effectors may include multiple (e.g., five) blades configured in a vertical stacked form, with each blade configured to support a wafer from below. During the movement of a wafer handling robotic arm equipped with such a high-capacity end effector, each wafer thus supported may experience different degrees (and even in different directions) of slippage, depending on multiple factors such as contact pad wear variability, wafer variability, and other parameters. An example of such a misaligned wafer stack is shown in Figure 1A and Figure 1B ; as can be seen, there are five wafers 102 placed in the stack 104. The wafers are shown as isolated, but in reality they would be supported by several other structures in such a stacked configuration, such as an end effector or a wafer container, such as a FOUP. Due to such misalignment, the wafer stack supported by the end effector may not have a circular silhouette edge when viewed in the XY plane.

[0055] As used herein, the term "contour edge" means the outline defined by the outermost edges of an aggregate of objects when orthogonally projected onto a plane perpendicular to an axis. For example, if two 3-inch squares are stacked on top of each other and their centers are offset from each other by a distance of 1 inch along an axis parallel to one of the sides of the squares, then in a plane parallel to the plane of such squares, the contour edge of such a configuration would be a 3-inch by 4-inch rectangle.

[0056] Accordingly, traditional AWC techniques do not provide sufficiently accurate results to allow their use in the case of stacked wafers. The inventors of the present case have conceived of an AWC system in which, in addition to the two through-beam optical sensors typically used, there is at least a third through-beam optical sensor. In such an improved AWC system, each wafer transfer through the through-beam optical sensors results in at least six XY coordinates instead of the usual four XY coordinates. More than six of these coordinates are then initially used in the improved AWC system in a manner different from the four coordinates in a typical AWC system. For example, in a typical AWC system, it is assumed that the wafer has a circular contour edge of a given diameter. In the improved AWC system described in more detail below, there are no explicit assumptions about the diameter of the wafer and the circularity of the contour edge in the case of processing a wafer stack. Instead, it is determined in accordance with the circle of the smallest diameter that circumscribes the six coordinates (or more, if even more through-beam optical sensors are used) (herein also simply referred to as the "smallest circle"). This smallest circle is then used as an approximation of the boundary of the wafer stack.

[0057] Although the above discussion and the examples explored elsewhere in this case focus on through-beam optical sensors, the techniques explored herein can be implemented using any suitable edge detection system configured to obtain information indicative of horizontal coordinates associated with the intersection of the edges of an object (e.g., a semiconductor wafer) at various predefined positions. For example, the edge detection system can include more than one sensor configured to obtain such measurements. For example, some edge detection systems can utilize sensors such as through-beam optical sensors, e.g., sensors that include a beam emitter configured to emit a beam and a light detector positioned to receive the emitted beam; when an object intersects the beam and interrupts it, this can be regarded as the intersection of the object edge at a predefined position (which coincides with the beam). Other edge detection systems can use other types of sensors, for example, capacitance, ultrasonic, or capable of obtaining information indicative of horizontal coordinates associated with the intersection of the edges of an object at a predefined position. In some embodiments, the edge detection system can use a single sensor, such as an image sensor. In an edge detection system based on an image sensor, machine vision algorithms can be used to monitor various edge detection positions.

[0058] As used herein, the term "circumscribe" is used in its general sense as it pertains to geometric figures, i.e., to describe a figure that touches the figure it circumscribes but does not cut through it. In the example of a set of points, a geometric figure that circumscribes the set of points will, for each point in the set of points, (a) coincide with or touch the point or (b) enclose the point within the figure, i.e., none of the points in the set will lie outside the figure (although some or all of them may lie on the outer boundary of the figure).

[0059] Once the minimum circle has been determined as described above, the center deviation of the minimum circle relative to the nominal center point can be obtained by determining the XY coordinates of the center of the minimum circle relative to the nominal center point of the end effector. This center deviation can be used as described above for a typical automatic wafer centering system.

[0060] In some embodiments, the improved AWC system also makes a determination in accordance with information indicating the diameter of the minimum circle and then, for example, compares this information with a corresponding threshold amount such as a cylindrical stay - out zone. If the comparison indicates that the minimum circle is larger than the stay - out zone, an error condition can be enabled, which indicates that the wafer stack is sufficiently misaligned such that correction based on the center deviation will not be sufficient to meet the process requirements. This error condition triggers additional operations that can be used to address the problem.

[0061] Although it is not necessary to understand the operation of the improved AWC system as described herein, Figures 2A to 2G a figure is depicted in which a calibration wafer is translated through the beams of three through - beam optical sensors that are part of the improved AWC system. This operation can be used to enable the robotic arm control system to determine the positions of more than three through - beam optical sensors used in each improved AWC system.

[0062] In Figure 2AIn this case, a calibration wafer 206 with a radius R (e.g., 150 mm for a 300 mm wafer system) is supported by a blade 208 of an end effector (not shown) and is latched in place relative to the blade 208 by a pin 210 or other clamping assembly. The calibration wafer 206 is latched such that it has a center point aligned with the nominal center point 214 of the blade 208 (and the end effector of which the blade 208 is a part). More than three (this example uses three) through-beam optical sensors 212 are spaced at different intervals, and the beams they emit travel in a vertically oriented direction (perpendicular to the page of the figure). In this example, the through-beam optical sensors 212 are unevenly spaced such that at any one time only one through-beam optical sensor 212 intersects the edge of the calibration wafer 206 substantially (given the general direction of travel of the blade 208), thus providing a form of time-division multiplexing that can enable a single channel to be used to receive signals from the through-beam optical sensors 212. In other embodiments, the through-beam optical sensors 212 may each be connected to their own dedicated channels such that the output of each through-beam optical sensor can be monitored independently without using time-division multiplexing. The through-beam optical sensors 212 may generally be distributed in a manner that results in a distribution of measurement points over most of the wafer (e.g., more than 80% to 90% of the wafer diameter) to provide a widely distributed set of measurement points, thereby enabling more accurate determination of position information. In the example discussed herein, there are three through-beam optical sensors located at -132 mm, 60 mm, and 142 mm from a reference axis, which, for example, corresponds to an axis along which the nominal center point of the end effector would translate when passing through the improved AWC system. Of course, it should be understood that other spacings (and even additional through-beam optical sensors) may be used based on the particular constraints of a given semiconductor processing tool. For example, if the blade of the end effector is 130 mm wide, the through-beam optical sensor located 60 mm from the reference frame discussed above may only be able to detect the leading edge of the wafer; the line of sight to the trailing edge from the sensor would be blocked by the blade (although this could be avoided by including a notch or other opening in the end effector near where the expected wafer edge intersects the beam). For example, shifting this through-beam optical sensor outwards by 10 or 15 mm would be able to avoid this blockage.

[0063] Figures 2B to 2G Figure 206 depicts the calibration wafer 206 during translation in a direction perpendicular to the line along which the through-beam optical sensors 212 are arranged, but it should be understood that the calibration wafer may also be translated through the through-beam optical sensors 212 in other directions that are not necessarily orthogonal to the plane defined by the beams of the through-beam optical sensors 212 with a similar effect. In Figures 2B to 2GIn [the figure], the calibration wafer 206 and the blade 208 are shown as stationary, while the three through-beam optical sensors 212 translate along the translation axis, but this is merely a convention for convenience in fitting the illustration on fewer pages - in reality, the through-beam optical sensors 212 would be static while the calibration wafer 206 and the blade 208 would be moving.

[0064] As the calibration wafer 206 translates through the beams of the through-beam optical sensors 212, the position of the nominal center point 214 (or some other reference point fixed relative to the end effector) can be identified at each moment when the edge of the calibration wafer intersects one of the through-beam optical sensors. Thus, in Figure 2B when the middle through-beam optical sensor 212 registers that the edge of the calibration wafer 206 has intersected the beam of this through-beam optical sensor 212 at point A, the position of the nominal center point 214 (as shown by the circular dotted crosshair A) can be recorded. Similar nominal wafer center positions can be recorded for other intersections of the edge of the calibration wafer 206 with one of the beams of the through-beam optical sensors 212, for example, as shown for the intersection / nominal center point 214 positions B, C, D, E, and F in Figures 2C to 2G After such data capture, the captured nominal center point positions and the radius R of the calibration wafer 206 can be used to determine the actual positions of the through-beam optical sensors 212. For example, the positions A and F of the nominal center point 214 should each be a distance R from the middle through-beam optical sensor, as

[0065] shown; in other words, if circles of radius R are centered at each of positions A and F, the two circles will intersect each other twice - each intersection point can be a possible position of the associated through-beam optical sensor 212 (in Figure 2H a line of length R connects positions A and F, B and E, and C and D to their respective potential through-beam optical sensor positions - solid lines are used to indicate "actual" positions, while dotted lines are used to indicate "phantom" positions). Once these two positions are determined, the one that is closest to the theoretical position of the through-beam optical sensor 212 position (e.g., as defined in engineering drawings) can be considered the actual position of the through-beam optical sensor 212 (the actual position of the through-beam optical sensor 212 will deviate from those theoretical positions due to factors such as production tolerances, assembly misalignment, thermal expansion, etc. (such differences, although significant relative to wafer misalignment, should not cause the through-beam optical sensor to migrate so far as to be closer to the "phantom" position compared to the "true" position)). Figure 2H

[0066] ​Once the actual position of the through-beam optical sensor 212 has been obtained, the improved AWC system can be made ready for use. The foregoing examples for determining the actual position of the through-beam optical sensor 212 are merely representative; other techniques may also be suitable. Additionally, the actual position of the through-beam optical sensor 212 can be re-evaluated periodically, such as after a predefined time period or after a maintenance operation has been performed that may cause a change in the alignment or position of the device.

[0067] Figure 3 A flowchart depicting an exemplary technique for using the improved AWC system is shown. In block 302, the nominal center point of the end effector of the wafer handling manipulator and the positions of more than three through-beam optical sensors can be determined, for example, by calibrating the use of the wafer as previously described.

[0068] At Figure 3 various different points during the Figures 4 to 13 discussion, reference may be made to Figure 3 which depicts an exemplary portion of a semiconductor processing tool incorporating the improved AWC system in various different operating states. Before discussing the Figure 4 exemplary technique of

[0069] Figure 4 An isometric view of multiple portions of a semiconductor processing tool is shown, particularly, portions related to wafer handling. As Figure 4 shown, a wafer handling manipulator 418 is provided, which includes a base 422, multiple linkages 420, and an end effector 424. In this example, the end effector 424 actually consists of two end effectors: a stack end effector 426 and a single end effector 428. In this example, the stack end effector 426 includes four blades 408; the single end effector 428 includes a single blade 408. As will be seen later, the stack end effector 426 and the single end effector 428 may be independently movable, such that the single end effector 428 can be used individually to move a single wafer 402 at a time. When the stack end effector 426 and the single end effector 428 are aligned with each other, the entire stack 404 of wafers 402 can be supported and held together. The end effector 424 has a nominal center point 414, which generally coincides with the center point of the wafer 402 (of course, as described above, the wafer 402 may experience misalignment with the nominal center point 414).

[0070] At Figure 4Also shown is a first wafer container 430A having a plurality of support racks 432 (equivalent structures may be referred to herein simply as "wafer supports"); for example, the first wafer container 430A may represent a buffer station for storing a plurality of wafers, a load lock for transferring wafers into and out of a vacuum environment, or any number of other types of equipment. A second wafer container 430B is also depicted and may be constructed in a substantially similar manner to the first wafer container 430A, for example, having a plurality of support racks 432 and being configured to simultaneously receive a plurality of wafers. The second wafer container 430B may be, for example, a FOUP or other type of wafer receiving device. The support racks 432 in the first wafer container 430A and the second wafer container 430B (and other wafer receiving structures) may each be used as one of the stations in a semiconductor processing tool of which the depicted equipment is a part. In this example, the first wafer container 430A may be equipped with an improved AWC system 434, including three or more through-beam optical sensors 412, which emit vertically oriented light beams 436. The second wafer container 430B in this example does not include the improved AWC system 434, but in some embodiments, the improved AWC system may be included in a manner similar to that discussed above with respect to the first wafer container 430A.

[0071] exist Figure 4 Also visible in the figure is a controller 450, which may have one or more processors 452 and one or more memory devices 454. The controller 450 may be operatively connected to the wafer handling robot 418 and the improved AWC system 434 so that it can control the operation of the wafer handling robot 418 and receive data from the improved AWC system 434. For example, the wafer handling robot 418 may include one or more position sensors 448, which may, for example, provide feedback to the controller 450 of the position of the links 420 and end effectors 424. For example, this feedback may be used to determine the angular orientation of the links 420 and end effectors 424 relative to the base 422 and to each other, which may be used in conjunction with the distances between the centers of rotation of the various rotational joints in the wafer handling robot 418 to determine the position of any point (e.g., the nominal center point 414) on the wafer handling robot 418 at any time. In some embodiments, the controller 450 may also be operatively connected to a plurality of protrusion sensors 440, which may be vertically oriented through-beam optical sensors similar to those used in the improved AWC system 434. Many of the various systems and components discussed in this section are described in detail in the accompanying drawings. Figures 5 to 13 Not shown or indicated.

[0072] The discussion now returns to Figure 3。After the positions of more than three through-beam optical sensors 212 are determined, the technique can proceed to block 304, where the following determination can be made: one or more wafers of the first group are supported by the end effector (or should be on the end effector according to the current wafer handling stage), and one or more wafers of the first group should be inspected for positioning and alignment relative to the end effector 424. For the purposes of the discussion herein, it will be assumed that one or more wafers of the first group are a group of five wafers, as depicted in Figures 4 to 13 As depicted. However, it should be understood that one or more wafers of the first subgroup can contain a different number of wafers. In some extreme examples, one or more wafers of the first subgroup can contain only a single wafer. In such an example, since there is only one wafer present, there will be no inter-wafer slippage. A standard AWC system can be used in such an example, but the improved AWC techniques discussed herein can be used to provide more accurate placement for a single wafer, for example, of a different size than the calibration wafer. Such a system can be used when wafers 402 of the same nominal size can be handled by the wafer handling robot 418 when in different physical states (for example, the same wafer 402 may have a different diameter at an elevated temperature compared to at room temperature or some lower temperature). For example, when the wafer 402 is removed from the processing chamber after processing, it may be at several hundred degrees Celsius compared to, for example, approximately 20°C when last handled by the wafer handling robot 418. For example, a standard 300 mm semiconductor wafer can increase in size by nearly 0.3 mm when at a temperature of 400°C compared to room temperature. Although this increase in size may be considered quite small, the standard tolerance for the wafer diameter of a 300 mm wafer is typically only ±0.5 mm, so this thermal expansion would be significant in terms of the expected tolerance.

[0073] In block 306, the stack 404 of wafers 402 can be translated through the improved AWC system 434 during a first time period, as Figure 5 Shown. As the stack 404 is translated through the beams 436, the through-beam optical sensors 412 associated with each beam 436 can register when the profile edges of the stack 404 of wafers 402 intersect each beam 436. In block 308, the coordinates of each such intersection are determined; these coordinates can be determined relative to the nominal center point 414 of the end effector 424, as previously discussed.

[0074] Figures 14A to 14G Depicts a top view of a stack of wafers 1402 placed on the end effector 1408 as it is translated through a set of three through-beam optical sensors in order to obtain such coordinates; for purposes of discussion, it can be assumed that the components shown in Figures 14A to 14G Are similar to Figure 4 And 5corresponding components therein. Similar components in the two sets of figures have the same last two digits in their reference numerals.

[0075] As seen in Figure 14A , three through-beam optical sensors 1412 are disposed at various different intervals across the travel path of the end effector support blade 1408, which in turn supports a stack of wafers 1402. In this example, the wafers 1402 have undergone observable misalignment such that their centers 1403 are clustered in a small cloud around the nominal center point 1414 of the end effector / blade 1408. The outlines of all five wafers 1402 in this example have been depicted, and the contour edge 1438 of the stack of wafers 1402 has been indicated with a thick dotted line to assist in the illustration. In Figures 14B to 14G , the individual wafers 1402 are not shown, but instead the contour edge 1438 is shown separately.

[0076] In Figure 14B , the stack of wafers 1402 has been translated past the rightmost through-beam optical sensor 1412, causing the robotic arm controller to receive a signal from the rightmost through-beam optical sensor 1412 indicating that the contour edge 1438 has intersected the beam of that through-beam optical sensor 1412. In response to receiving this signal, the controller can then determine and store the intersection point (x 1 , y 1 ) XY position relative to the nominal center point 1414. For example, this can be accomplished by simple coordinate translation and subtraction. For example, the XY position of the through-beam optical sensor in this world coordinate system and the XY position of the nominal center point 1414 in the same coordinate system can both be determined, and the final position of the intersection point (x 1 , y 1 ) relative to the nominal center point 1414 can then be determined by subtracting the respective world coordinates of the nominal center point 1414 from the corresponding world coordinates of the intersection point (x 1 , y 1 ). At some point, a transformation can be made such that the coordinates of the intersection point (x 1 , y 1 ) relative to the nominal center point 1414 can be defined relative to a coordinate system that is fixed relative to the end effector (or other reference frame). For ease of reference, the exemplary coordinates of the intersection point (x 1 , y 1 ) relative to the nominal center point 1414 are indicated by the values shown on two orthogonal dash-dot-dash lines in Figure 14B . Thus, in this example, the intersection point (x 1 , y 1) will have coordinates (60, 143.4) mm.

[0077] This procedure can be repeated for each subsequent intersection event, for example, separately for the points (x Figure 14C , 14D , 14E, 14F, and 14G at (x 2 , y 2 ); (x 3 , y 3 ); (x 4 , y 4 ); (x 5 , y 5 ); and (x 6 , y 6 ) as shown. Once all six coordinates have been obtained, in block 310, the smallest circle enclosing all the obtained coordinates can be determined. Any suitable technique for making this determination can be used. For example, in at least some embodiments, a "brute force" approach can be implemented, where all potential triples of coordinates are evaluated to determine the parameters of the circle passing through all the coordinates in the triple. The resulting circle can then be evaluated to determine a) the circle size and b) whether there are any coordinates that are not on or enclosed by the circle. The smallest of such circles enclosing all the coordinate points can then be confirmed and selected as the smallest circle.

[0078] For example, for each coordinate triple (x 1 , y 1 ); (x 2 , y 2 ); and (x 3 , y 3 ) (where the subscripts are simply used to distinguish within the triple and are not necessarily related to the subscripts for the six exemplary coordinate points above), the center coordinates (x c , y c ) and radius r of the circle defined by the coordinate triple can be determined according to the following equations:

[0079]

[0080] In the last equation for r, of course, either of the other two coordinate points in the triple can substitute for (x 1 , y 1 ).

[0081] Figure 15Depicts Tables 1 and 2. Table 1 outlines the (x,y) coordinate data for the above example; the coordinate systems of the respective intersection points relative to the nominal center point 1414 are listed. Table 2 lists all twenty possible three - tuples of the six coordinates from Table 1. Tables 1 and 2 provide data in millimeters. Thus, for example, the data in the fourth row of Table 2 is for coordinate 1 (60,143.4), coordinate 2 (-132,80.2), and coordinate 6 (60,-144.9). The first column indicates the relevant coordinate triple for each row, the second through seventh columns list the XY coordinate data for that triple, and the eighth through tenth columns list the calculated center coordinates and radius of the circle that fits the coordinate triple for each row. Finally, the last column indicates whether all six coordinates from Table 1 are circumscribed by the circle with the parameters of each row. As can be seen, only four of the twenty coordinate triples define a circle that circumscribes all the coordinates from Table 1. Among these four, the sixth circle, i.e., the one listed in the sixth row of data in Table 2, has the smallest value and will represent the minimum circle as discussed above. It should be understood that the circle diameter / center point position values listed in Table 2 have been rounded, and thus there is an impression that the circles for the 1, 3, 5 triple and the 3, 5, 6 triple have the same size, i.e., there are two minimum circles that enclose all the points, but in reality, only one of them is truly the smallest (in this example, the circle for the 1, 3, 5 triple defines a radius of 156.402 mm, while the circle for the 3, 5, 6 triple defines a radius of 156.428 mm). Figure 16 Depicts the exemplary minimum circle discussed above. In Figure 16 it, the contour edge 1638 of the wafer stack is shown with internal diagonal hatching so that it can be easily distinguished from the minimum circle 1642 defined as in the sixth row of Table 2( Figure 16 is not drawn to a 1:1 scale relative to the dimensions listed in Tables 1 and 2, but it is drawn to scale at approximately 55%). All six coordinate systems from Table 1 are shown. As can be seen, each coordinate lies on the minimum circle 1642 (e.g., points 1, 3, and 5) or within the minimum circle 1642. It should be understood that although this example uses six coordinate measurements, satisfactory accuracy can be obtained through minimum circle determination using as few as a set of five measurements (of course, more than six coordinate measurements can also be used to further increase accuracy).

[0082] This minimum circle thus serves as a proxy for the entire stack of wafers. It should be noted that this minimum circle is not 100% accurate, i.e., a minimum circle can be defined that circumscribes all the measured coordinate points along the contour edge of the wafer stack but it does not actually circumscribe the entire stacked wafer. Figure 17 Describes this example. Figure 17 Depicts Figure 16The smallest circle, but the contour edge 1638 has been removed. In addition, the wafer 1602 has been added to the figure. As can be seen, the wafer has an outermost edge that intersects with the coordinates (x 1 , y 1 ) and (x 2 , y 2 ). Therefore, it is in a position that does not change any of the coordinate measurements listed in Table 1. However, as can be observed, the outermost peripheral edge of the wafer 1602 slightly extends beyond the smallest circle. Nevertheless, this protrusion is minor and can be accommodated in subsequent operations by the use of appropriate tolerances or thresholds. In the simulation, compared to the same evaluation performed with, for example, one hundred coordinate measurements, the maximum error of the sliding amount (expressed as the minimum circle radius minus the nominal wafer radius) and the center deviation (expressed as the displacement distance, regardless of direction) using the combination of triples from six coordinate measurements is approximately ±10%. This error can be easily adjusted by selecting a threshold amount that allows for this potential error.

[0083] Once the smallest circle is determined in block 310, the sliding amount for one or more wafers of the first group can be determined in block 312. The sliding amount is an indication of the magnitude of the relative sliding between different wafers in one or more wafers of the group (in the example of a single wafer, since there is only one wafer, there is of course no relative sliding; however, if desired, this parameter can still be calculated to provide other information, such as an indication of how much the wafer size has changed due to thermal expansion or contraction). A zero sliding amount can indicate that the wafers in the stack are approximately perfectly aligned. A non-zero sliding amount can indicate that at least some of the wafers are misaligned. In some examples, depending on the placement requirements for a given station in a semiconductor processing tool, several misalignment amounts may be acceptable, but typically there is a threshold sliding amount that, if exceeded, will result in an error condition or require remedial action to be taken.

[0084] The sliding amount can be a metric based on the dimensional difference between the nominal wafer diameter (e.g., 300 mm) and the diameter of the smallest circle. For example, the sliding amount can be evaluated based on the diameter difference (or, if desired, the radius difference, or the ratio between two diameters or radii) between the nominal wafer diameter and the diameter of the smallest circle.

[0085] Another parameter that can be obtained once the smallest circle is determined (as indicated in block 314) is the center deviation, which means the deviation between the nominal center point of the end effector and the center point of the smallest circle. In Figure 16 and 17 , the center deviation is defined by the X offset 1644 (in this example, -0.2 mm) and the Y offset 1646 (in this example, -0.9 mm).

[0086] For one or both of the center deviation and the slip amount of a given wafer stack, it can be evaluated by the robotic arm controller and then used to affect the handling of the wafer. For example, in block 316, it is determined whether the slip amount is greater than a predetermined threshold amount. For example, this amount can be preselected based on the specifications of the equipment equipped with the improved AWC system. For example, the buffer station may require that all 300 mm wafers stored therein fit within a cylindrical bounding region envelope of 305 mm. In practice, this requirement can be evaluated by checking several predetermined positions around the cylindrical bounding region envelope to see if any wafer intersects such a position. For example, the buffer station may have three, four, or more vertically oriented through-beam optical sensors (independent of the through-beam optical sensors used in the improved AWC system; for clarity, in this text, the "first through-beam optical sensor" as part of the improved AWC system and the "second through-beam optical sensor" that can be used as a protrusion sensor in the wafer container will be mentioned), for example, the protrusion sensor 440 from Figure 4 is placed at different positions along a circumference that is at least greater than the wafer diameter of the wafers expected to be accommodated by the buffer station (however, it should be understood that the protrusion sensors are not necessarily arranged along the circumference, other peripheral shapes can also be used, and the bounding region envelope does not even need to be cylindrical, other shapes can also be used if appropriate). If the wafer intersects the beam of any of these through-beam optical sensors, it will trigger an error condition. Although it may be possible to attempt to manipulate the wafer stack within the station at this time so that no beam of the through-beam optical sensors intersects the wafer, if the slip amount is too large, it is not possible to move the stack as a whole to achieve this goal (except by completely removing it). By using the slip amount and an appropriately set threshold, once the measurement of the wafer stack using the improved AWC system is completed, it can be determined whether the wafer stack can be placed within the station without causing an error condition.

[0087] If the slide amount is less than the threshold, i.e., it is possible to position and hold the wafer stack within the station within acceptable operating tolerances, the technique can proceed to block 318, where wafer centering correction can be performed. For example, the wafer handling robot 418 can be controlled to move the nominal center point 414 to the target position for the nominal center point 414 of the station associated with the improved AWC system, e.g., the center of the first wafer container 430A in this example. If there is a center deviation, the wafer handling robot 418 can be controlled to adjust the placement of the wafer by an amount that will effectively offset this center deviation, e.g., adjust the placement of the wafer with respect to the target destination by the X offset and Y offset discussed earlier. This adjustment will cause the center of the smallest circle of the stack 404 of wafers 402 to be aligned with the target position in the first wafer container 430A, rather than with the nominal center point 414 of the end effector. As a result, the stack 404 of wafers 402 will be substantially centered within the cylindrical envelope discussed earlier, thereby reducing the chance that the wafers may be detected as having crossed the boundaries of the cylindrical envelope.

[0088] Once the stack 404 of wafers 402 has been adjusted to center the smallest circle on the target point in the first wafer container 430A, in block 320 the wafer handling robot 418 can be caused to lower the stack 404 of wafers 402 onto the support frame 432 without causing further XY translation. In block 322, the wafer handling operation can be completed, and the wafer handling robot 418 can then continue to perform other operations as needed.

[0089] If in block 316 the slide amount is determined to be greater than the threshold amount, the technique can proceed to block 324, where the wafer can be withdrawn from the first wafer container 430A and placed in a temporary storage location, e.g., into a FOUP, buffer, or some other container configured to support the wafers 402 individually when the wafer handling robot 418 transfers the wafers 402 to the first wafer container 430A during a second time period after a first time period. In this example, the temporary storage location is the second wafer container 430B. Although the wafer containers 430A and 430B are shown here as being generally identical in structure, it should be understood that in actual implementation the wafer containers 430A and 430B may be different structurally and / or functionally. Figure 6 Depicted is the wafer handling robot 418 and the wafer 402 after the wafer 402 has been withdrawn from the first wafer container 430A and just before the wafer 402 is inserted into the second wafer container 430B. In Figure 7 , the wafer handling robot 418 has placed the wafer 402 into the second wafer container 430B.

[0090] At block 326, the wafer handling robot 418 can retrieve a single wafer from among the first set of one or more wafers from the second wafer container 430B. To do so, in some embodiments, it may be necessary to reconfigure the end effector 424 of the wafer handling robot 418 (or use a different robotic arm having an end effector configured to pick up only one wafer at a time). In this example, as previously discussed, the end effector 424 has two parts: a single end effector 428 and a stacked end effector 426. The single end effector 428 can include only a single blade 408 and is configured to lift only a single wafer 402 at a time. The stacked end effector 426 can include N - 1 blades, where N is the number of wafers in the first set of one or more wafers. In this example, there are five wafers 402 in the first set of one or more wafers 402, so N = 5 and 5 - 1 = 4 blades 408 are part of the stacked end effector 426. The single end effector 428 and the stacked end effector 426 may be movable relative to each other. For example, the stacked end effector 426 can be rotated so that the blades 408 of the stacked end effector 426 do not engage the wafers 402 in the first set of one or more wafers 402 when the single end effector 428 is used to retrieve a wafer 402 from the first set of one or more wafers 402.

[0091] This is shown in Figure 8 and 9 In Figure 8 , the wafer handling robot 418 has been withdrawn from the second wafer container 430B, and the wafer 402 has been temporarily placed in the second wafer container 430B. Once out of the second wafer container 430B, the stacked end effector 426 can be rotated to a position that is, for example, 180° out of phase relative to the single end effector 428, as shown in Figure 9 . Other mechanisms and techniques for staggering the stacked end effector 426 from the single end effector 428 can also be used or used in place of the illustrated embodiment.

[0092] Once the wafer handling robot 418 has been reconfigured for single wafer retrieval / handling, at block 326, the wafer handling robot 418 can be controlled to retrieve a single wafer 402 before proceeding to block 328, as shown in Figure 10 and 11 . At block 328, the wafer handling robot 418 can be controlled to send the single wafer 402 back to the first wafer container 430A and again through the improved AWC system 434, as shown in Figure 12 and 13 . In Figure 12 versus 13During the transition between the positions shown, the transmissive beam optical sensor 412 can be used to obtain an indication of when the edge of the wafer 402 intersects the beam 436 emitted by the transmissive beam optical sensor 412. At block 330, at each intersection, the XY coordinate system of the nominal center point 414 is determined and used together with the XY position of the transmissive beam optical sensor 412 to determine the position of the edge intersection point relative to the nominal center point. This procedure is similarly used for the previous XY determinations made for the minimum circle. Although the same number of coordinates can be determined as when making the determination for the minimum circle determination, since only a single wafer is present, this technique can also be performed using as few as two transmissive beam optical sensors 412. Since only a single wafer is present, there is no need to determine a slide amount, but the minimum circle technique can still be performed if desired to accurately position the center of the wafer 402, for example, if the wafer diameter (e.g., due to thermal effects) is different from the expected wafer diameter.

[0093] Once the edge position of the wafer 402 relative to the nominal center point 414 has been determined, at block 332, the position of the center of the wafer 402 relative to the nominal center point 414 of the end effector can be determined. As mentioned above, this determination can be made using the techniques discussed earlier with respect to the minimum circle determination. If desired, a simpler technique can be used where, assuming the wafer 402 has the appropriate diameter and any three of the relative coordinates can be used to determine a circle that is assumed to represent the wafer and is centered on the wafer 402. The calculated X offset and Y offset between the center of the wafer and the nominal center point 414 can be used to determine the center deviation of the single wafer 402 and then, when the wafer 402 is placed in the first wafer container 430A, to adjust the placement of the wafer 402 so that the center of the wafer 402 is aligned with the target position in the first wafer container 430A.

[0094] At block 336, it can be determined whether any additional wafers in the first set of one or more wafers remain in the second wafer container 430B. If so, the technique can return to block 326 and the procedure can be repeated until all of the wafers in the first set of one or more wafers have been transferred to the first wafer container 430A. Since the wafers 402 are all transferred individually to the first wafer container 430A, this provides the opportunity to independently correct the placement of each wafer 402, thereby allowing the displacement between wafers in the wafer stack to be eliminated (or at least significantly reduced). However, transferring the wafers one by one will take a significantly longer time compared to transferring multiple wafers in a batch simultaneously.

[0095] Once it has been determined that all of the wafers 402 in the first set of one or more wafers 402 have been transferred to the first wafer container 430A, the technique can proceed to block 338, where the wafer handling manipulator can be used to perform other operations.

[0096] As described above, in some embodiments, the controller may be included as part of the above system, or may be used to cause some or all of the above techniques to be performed.

[0097] Such systems may include semiconductor processing equipment, which includes one or more processing tools, one or more chambers, one or more platforms for processing, and / or specific processing components (wafer pedestals, gas flow systems, etc.) and other parts not specifically discussed herein. These systems may be integrated with electronics for controlling their operation before, during, and after the processing of semiconductor wafers or substrates. These electronics may be referred to as "controllers", which may control various components or sub-components of one or more systems. Depending on the processing requirements and / or the type of system, the controller may be programmed to cause any of the techniques discussed herein to be performed, such as, including controlling a wafer handling robot to perform wafer transfer operations in accordance with the concepts discussed herein, wafer scanning by an improved AWC system, and then potentially causing subsequent corrective actions to be performed, such as singly placing a wafer into a wafer container and / or re-centering the placed wafer prior to wafer placement.

[0098] Broadly speaking, a controller may be defined as an electronic device having various integrated circuits, logic, memory, and / or software for receiving instructions, issuing instructions, controlling operations, controlling the operation of various operatively connected device components, and so on. The integrated circuits may include chips in the form of firmware storing program instructions, digital signal processors (DSPs), chips defined as application specific integrated circuits (ASICs), and / or one or more microprocessors, or microcontrollers that execute program instructions (e.g., software). The program instructions may be instructions sent to the controller in the form of various individual settings (or program files), which define operation parameters for performing a specific wafer handling process on a semiconductor wafer. In some embodiments, the operation parameters may include, for example, aspects such as nominal wafer size, robotic arm parameters, placement envelopes, and so on.

[0099] In some embodiments, the controller can be part of or coupled to a computer that is integrated with, coupled to, otherwise networked to, or a combination of the system. For example, the controller can be in the "cloud" or be all or part of a wafer fab host system, which can allow remote access to the wafer processing system. The computer can enable remote access to the system to monitor the current progress of a manufacturing operation, review the history of past manufacturing operations, review trends or performance criteria for multiple manufacturing operations, change the parameters of the current process, set processing steps to follow the current process, or initiate a new process. In some examples, a remote computer (e.g., a server) can provide a processing recipe to the system via a network, which can include a local network or the Internet. The remote computer can include a user interface that enables the input or programming of parameters and / or settings, which are then sent from the remote computer to the system. In some examples, the controller receives instructions in the form of data that specify the parameters for each processing step to be performed during one or more operations, such as parameters for managing wafer handling operations. It should be understood that the parameters can be specific to the type of wafer transfer process to be performed and the type of tool that the controller is configured to interface with or control. Thus, as described above, the controller can be distributed, for example, by including one or more discrete controllers that are networked together and work towards a common purpose, such as the processing and control described herein. An example of a distributed controller for such a purpose is one or more integrated circuits in a semiconductor processing tool that communicate with one or more integrated circuits remote (e.g., at the platform level or as part of a remote computer), which are combined to control the wafer handling process.

[0100] Without limitation, an exemplary semiconductor processing tool having an AWC system and a wafer handling robot with the improvements described herein can include additional components, such as one or more plasma etch chambers or modules, deposition chambers or modules, spin-rinse chambers or modules, metal plating chambers or modules, cleaning chambers or modules, bevel etch chambers or modules, physical vapor deposition (PVD) chambers or modules, chemical vapor deposition (CVD) chambers or modules, atomic layer deposition (ALD) chambers or modules, atomic layer etch (ALE) chambers or modules, ion implantation chambers or modules, track chambers or modules, and any other semiconductor processing systems that can be associated with or used in the processing and / or production of semiconductor wafers.

[0101] As described above, depending on the one or more processing steps to be performed by the tool, the controller can communicate with one or more other tool circuits or modules, other tool components, cluster tools, other tool interfaces, adjacent tools, neighboring tools, tools located throughout the factory, a host computer, another controller, or tools used in the material transport that shuttles wafer containers to and from tool locations and / or load ports in a semiconductor manufacturing facility.

[0102] If the phrase "for each <thing> in one or more <things>" is used herein, it should be understood to include both single-thing groups and multi-thing groups, i.e., the phrase "for each of..." is used to mean, as used in a programming language, for each thing in any group of things being referred to. For example, if the group of things being referred to is a single thing, "each" will only mean that single thing (although the dictionary definition of "each" would generally define the term to mean "each of two or more things") and does not imply that there must be at least two of those things.

[0103] It should also be understood that the terms "stack" or "stack configuration", when used herein, include not only multi-thing configurations but also single-thing configurations. Thus, for example, "one or more stacked things" will include this single thing (a "stacked" single thing) as well as multiple instances of such things that are stacked. Similarly, "one or more things placed in a stack configuration" will include a single thing as well as multiple such things that are stacked, e.g., on top of one another. It should also be understood that reference to "one or more things" generally includes singular-type examples (e.g., reference to the use of a single such thing) or plural-type examples (e.g., reference to multiple such things).

[0104] The term "light beam" is used herein to mean light that can be emitted from a light source or emitter; a light source can emit multiple light beams simultaneously in different directions. For example, an omnidirectional light source can emit light beams simultaneously in all or nearly all directions. In such a light source, light beams emitted generally upward and downward can be characterized as vertically directed light beams, while light beams emitted horizontally can be characterized as horizontally directed light beams. For a light emitter or light source that emits collimated light beams, there may be only a limited number of light beams emitted. However, the vast majority of the light energy released by that emitter or light source can be concentrated in a single light beam (or a cluster of light beams within a very limited angular range, e.g., in the case of a laser or a similar light source). Thus, a laser emitted along a vertical axis and an omnidirectional light that emits at least some light along a vertical axis can both be described as emitting vertically directed light beams.

[0105] The term "wafer" as used herein can mean a semiconductor wafer or substrate or other similar types of wafers or substrates.

[0106] It should also be understood that the use of designators such as (a), (b), (c), etc. herein is for organizational purposes only and is not intended to impart any particular order or significance to the items associated with each sequential designator. For example, "(a) obtaining speed-related information and (b) obtaining position-related information" will include obtaining position-related information before obtaining speed-related information, obtaining speed-related information before obtaining position-related information, and obtaining position-related information simultaneously with obtaining speed-related information. However, there may be some cases where some of the items associated with the sequential designators may inherently require a particular order, such as "(a) obtaining speed-related information, (b) determining a first acceleration based on the speed-related information, and (c) obtaining position-related information"; in this example, since (b) depends on the information obtained in (a), (a) must be performed before (b), however, (c) may be performed before or after either (a) or (b).

[0107] Various modifications to the embodiments described in this disclosure may be apparent to those skilled in the art, and the general principles defined herein may be applied in other embodiments without departing from the spirit and scope of the disclosure. Therefore, the claims are not intended to be limited to the embodiments shown herein, but rather to the broadest scope consistent with this disclosure, the principles disclosed herein, and novel features.

[0108] Several features described in the context of multiple independent embodiments in this specification may also be implemented in combination in a single embodiment. Conversely, various features described in the context of a single embodiment may also be implemented independently or in any suitable sub-combination in multiple embodiments. Additionally, although multiple features may be described above as being implemented in certain combinations and even claimed as such from the start, one or more features from the claimed combination may in some instances be excised from that combination, and the claimed combination may be directed to a sub-combination or a variation of a sub-combination.

[0109] Similarly, although multiple operations are depicted in the drawings in a particular order, this should not be construed as: such operations are to be performed in the particular order shown or in a sequential order, or that all of the recited operations are to be performed to achieve the desired result. Additionally, the drawings may schematically depict one or more exemplary procedures in a flowchart form. However, other operations not depicted may be incorporated into the exemplary procedures so schematically depicted. For example, one or more additional operations may be performed before, after, concurrently with, or between any of the operations depicted. In some cases, multitasking and parallel processing may be advantageous. Further, the separation of various system components in the above-described embodiments should not be construed as requiring such separation in all embodiments, and it should be understood that the program components and systems can generally be integrated together or packaged into multiple program products in a single program product. Additionally, other embodiments are within the scope of the following claims. In some examples, the acts described in the claims can be performed in a different order and still achieve the desired result.

Claims

1. An apparatus for handling one or more wafers having a nominal diameter of D 1 , the apparatus comprising: A wafer transfer robot, which is configured to support one or more wafers having a nominal diameter of D when one or more wafers having a nominal diameter of D are placed thereon; 1 when one or more wafers having a nominal diameter of D are placed thereon; 1 one or more wafers having a nominal diameter of D; First edge detection system ； and a controller including one or more processors and one or more memory devices, wherein: the one or more processors, the one or more memory devices, the wafer handling robot, and the first edge detection system are operably connected to each other, and the one or more memory devices store computer-executable instructions for controlling the one or more processors to: a) obtain information about a first reference point of the wafer handling robot; b) determine that a first group of one or more wafers is supported by the wafer handling robot, the first group of one or more wafers defining a profile edge in a horizontal plane when viewed along a vertical axis; c) cause the first edge detection system to obtain information indicating first horizontal coordinates of at least five points of the profile edge along the first group of one or more wafers relative to the first reference point; d) for the first group of one or more wafers, determine a minimum circle circumscribing the first horizontal coordinates of the at least five points determined in (c) when viewed along the vertical axis; e) for the first group of one or more wafers, determine a first center deviation by determining information indicating the length and direction of a first reference line segment extending from the center of the minimum circle for the first group of one or more wafers to the first reference point; f) Determine a first sliding amount of one or more wafers of the first group based on a difference between a diameter of the minimum circle and D 1 ; and g) determine whether at least one of the first sliding amount of the first group of one or more wafers and the first center deviation of the first group of one or more wafers represents a wafer alignment error condition.

2. The apparatus according to claim 1, wherein the first edge detection system includes three first through-beam optical sensors, and each of the first through-beam optical sensors: is configured to emit a corresponding vertically directed beam when activated, positioned such that when the first through-beam optical sensor is activated, the furthest horizontal distance between any of the beams is less than D 1 , and is configured to register when the beam emitted by it intersects the edge of an object when the first through-beam optical sensor is activated.

3. The apparatus according to claim 1, wherein the first edge detection system includes a machine vision system, and the machine vision system is configured to obtain the information indicating the first horizontal coordinates of the at least five points of the profile edge along the first group of one or more wafers relative to the first reference point.

4. The apparatus according to claim 1, wherein the first edge detection system includes one or more members selected from the group consisting of: a group of three or more direct through-beam optical sensors, a group of three or more reflective through-beam optical sensors, a machine vision measurement system, and a group of three or more capacitance sensors.

5. The apparatus according to claim 1, wherein: the wafer handling robot includes an end effector having N blades, the first group of one or more wafers includes N or fewer wafers, Each blade is configured to support one of the wafers having a nominal diameter of D 1 and N>1。 6. The apparatus according to claim 5, wherein: the N blades include a first group of N - 1 blades fixed relative to each other, The N-1 blades of the first group are configured to move as a unit relative to the portion to which the N-1 blades of the first group of the wafer handling manipulator are attached, and The blades of the end effector that are not among the N-1 blades of the first group are configured to be movable independently of the N-1 blades of the first group and relative to the portion to which the N-1 blades of the first group of the wafer handling manipulator are attached.

7. The apparatus according to claim 6, wherein N = 5.

8. The apparatus according to claim 1, wherein the wafer handling manipulator includes an end effector having only one blade and the one or more wafers of the first group include only one wafer.

9. The apparatus according to claim 1, further comprising: A first wafer container including one or more first wafer supports configured to receive one or more wafers of the first group, wherein each of the one or more first wafer supports is configured to support a wafer placed thereon and within a boundary region envelope associated with the first wafer container and having a minimum horizontal dimension D 2 , where D 2 is at least a first threshold amount greater than D 1 .

10. The apparatus according to claim 9, wherein the first wafer container further includes a second edge detection system configured to register when an edge of an object intersects one or more second horizontal positions monitored by the second edge detection system when the second edge detection system is activated.

11. The apparatus according to claim 9, wherein the one or more memory devices further store computer-executable instructions for further controlling the one or more processors to perform the following operations: h) Cause the wafer handling manipulator to place at least some of the one or more wafers in the first group of wafers into the first wafer container at least in part in response to determining that the first sliding amount of the one or more wafers in the first group is less than the first threshold amount.

12. The apparatus according to claim 11, wherein the one or more memory devices further store computer-executable instructions for further controlling the one or more processors to perform the following operations: i) Determine a first wafer offset of the one or more wafers in the first group based on information indicating the length and orientation of the first reference line segment for the one or more wafers in the first group; and j) During one or more operations in which the one or more wafers in the first group are supported by the wafer handling manipulator, cause the wafer handling manipulator to operate to place at least some of the one or more wafers in the first group into the first wafer container according to the first wafer offset.

13. The apparatus according to claim 9, wherein the one or more memory devices further store computer-executable instructions for further controlling the one or more processors to perform the following operations: h) Cause the wafer handling manipulator to place the wafers in the first group of wafers into a second wafer container at least in part in response to determining that the first sliding amount of the one or more wafers in the first group is greater than the first threshold amount; and i) After (h) and during a second time period, for each wafer in the first group of wafers, cause the wafer handling manipulator to: Retrieve the wafer from the second wafer container, When the wafer is supported by the wafer handling robot, cause the first edge detection system to obtain information indicating at least three second horizontal coordinates along the profile edge of the wafer relative to the first reference point. Using the at least three second horizontal coordinates, determine an estimated center point of the wafer relative to the first reference point. Determine a second center deviation by determining information indicating the length and direction of a second reference line segment extending from the estimated center point of the wafer to the first reference point. Based on the information indicating the length and orientation of the second reference line segment for the wafer, determine a second wafer offset for the wafer, and During one or more operations in which the wafer is supported by the wafer handling robot, cause the wafer handling robot to operate to place the wafer into the first wafer container according to the second wafer offset.

14. A method for handling one or more wafers having a nominal diameter of D 1 comprising: a) Using a wafer handling robot, retrieve one or more wafers of a first set having a nominal diameter of D 1 wherein the wafer handling robot is configured to support the one or more wafers of the first set when the one or more wafers of the first set are placed thereon, and the one or more wafers of the first set define a profile edge in a horizontal plane when viewed along a vertical axis; b) Using a first edge detection system, obtain information about a first reference point of the wafer handling robot; c) Using the first edge detection system, obtain information indicating first horizontal coordinates of at least five points along the profile edge of the one or more wafers of the first group relative to the first reference point; d) For the one or more wafers of the first group, determine a smallest circle circumscribing the first horizontal coordinates of the at least five points determined in (c) when viewed along a vertical axis; e) For the one or more wafers of the first group, determine a first center deviation by determining information indicating the length and direction of a first reference line segment extending from the center of the smallest circle of the one or more wafers of the first group to the first reference point; f) Determine a first sliding amount of one or more wafers of the first set based on a difference between a diameter of the smallest circle and D 1 ; and g) Determine whether at least one of the first sliding amount of the one or more wafers of the first group and the first center deviation of the one or more wafers of the first group indicates a wafer alignment error condition.

15. The method according to claim 14, wherein: The first edge detection system includes three first through-beam optical sensors, Each first through-beam optical sensor: is configured to emit a corresponding vertically directed beam when activated, positioned such that the farthest horizontal distance between any of said beams is less than D when said first through-beam optical sensor is activated 1 , and is configured to register when the beam emitted by it when the first through-beam optical sensor is activated intersects the edge of an object; and c) is performed by obtaining a horizontal coordinate each time the profile edge of the one or more wafers of the first group intersects one of the beams emitted by one of the first through-beam optical sensors.

16. The method according to claim 14, wherein: The first edge detection system includes a machine vision system, and the machine vision system is configured to obtain the information indicating the first horizontal coordinates of the at least five points along the profile edge of the one or more wafers of the first group relative to the first reference point; and c) is performed by using the machine vision system to obtain the horizontal coordinates of the at least five points.

17. The method according to claim 14, wherein the first edge detection system comprises one or more members selected from the group consisting of: a set of three or more direct-through beam optical sensors, a set of three or more reflective-through beam optical sensors, a machine vision measurement system, and a set of three or more capacitance sensors.

18. The method according to claim 14, wherein: the wafer handling robot comprises an end effector having N blades, the one or more wafers of the first group comprise N or fewer wafers, Each blade is configured to support one of the wafers having a nominal diameter of D 1 and N>1。 19. The method according to claim 18, wherein: the N blades comprise a first set of N - 1 blades fixed relative to each other, the first set of N - 1 blades of the wafer handling robot are configured to move as a unit relative to the portion to which the first set of N - 1 blades of the wafer handling robot are attached, and the blade of the end effector that is not in the first set of N - 1 blades is configured to move independently of the first set of N - 1 blades and relative to the portion to which the first set of N - 1 blades of the wafer handling robot are attached.

20. The method according to claim 19, wherein N = 5.

21. The method according to claim 14, wherein the wafer handling robot comprises an end effector having only one blade and the one or more wafers of the first group comprise only one wafer.

22. The method according to claim 14, wherein: D 1 less than D 2 by at least a first threshold amount, D 2 is the minimum horizontal dimension of the boundary region envelope associated with the first wafer container, the first wafer container including one or more first wafer carriers configured to receive one or more wafers of the first group, and each of the one or more first wafer supports is configured to support a wafer placed thereon and within the envelope of the boundary region.

23. The method according to claim 22, wherein the first wafer container further comprises a second edge detection system configured to register when an edge of an object intersects one or more second horizontal positions monitored by the second edge detection system when the second edge detection system is activated.

24. The method according to claim 22, further comprising: in (g), determining that the first sliding amount of the one or more wafers of the first group is less than the first threshold amount, and h) causing the wafer handling robot to place at least some of the wafers in the one or more wafers of the first group into the first wafer container at least in part in response to determining that the first sliding amount of the one or more wafers of the first group is less than the first threshold amount.

25. The method according to claim 24, further comprising: i) determining a first wafer offset of the one or more wafers of the first group based on information indicating the length and orientation of the first reference line segment for the one or more wafers of the first group; and j) during one or more operations in which the one or more wafers of the first group are supported by the wafer handling robot, causing the wafer handling robot to operate to place at least some of the wafers in the one or more wafers of the first group into the first wafer container according to the first wafer offset.

26. The method according to claim 22, further comprising: h) cause the wafer handling robot to place the wafer in one or more wafers of the first group into a second wafer container at least in part in response to determining that the first sliding amount of the one or more wafers of the first group is greater than the first threshold amount; and i) after (h) and during a second time period, for each wafer in the one or more wafers of the first group, cause the wafer handling robot to: retrieve the wafer from the second wafer container, while the wafer is supported by the wafer handling robot, cause the first edge detection system to obtain information indicating at least three second horizontal coordinates along the contour edge of the wafer relative to the first reference point, using the at least three second horizontal coordinates, determine an estimated center point of the wafer relative to the first reference point, by determining information indicating the length and direction of a second reference line segment extending from the estimated center point of the wafer to the first reference point, determine a second center deviation, based on the information indicating the length and orientation of the second reference line segment for the wafer, determine a second wafer offset for the wafer, and during one or more operations in which the wafer is supported by the wafer handling robot, cause the wafer handling robot to operate to place the wafer into the first wafer container according to the second wafer offset.

27. A non-transitory computer-readable medium having computer-executable instructions stored thereon for controlling one or more processors to: a) Using a wafer handling robot, one or more wafers of a first group having a nominal diameter of D 1 are retrieved, the wafer handling robot being configured to support the one or more wafers of the first group when the one or more wafers of the first group are placed thereon, the one or more wafers of the first group defining a profile edge in a horizontal plane when viewed along a vertical axis; b) using a first edge detection system, obtain information about a first reference point of the wafer handling robot; c) using the first edge detection system, obtain information indicating first horizontal coordinates of at least five points along the contour edge of the one or more wafers of the first group relative to the first reference point; d) for the one or more wafers of the first group, determine a smallest circle circumscribing the first horizontal coordinates of the at least five points determined in (c) when viewed along a vertical axis; e) for the one or more wafers of the first group, by determining information indicating the length and direction of a first reference line segment extending from the center of the smallest circle for the one or more wafers of the first group to the first reference point, determine a first center deviation; f) Determine a first sliding amount of one or more wafers of the first set based on a difference between a diameter of the smallest circle and D 1 ; and g) determine whether at least one of the first sliding amount of the one or more wafers of the first group and the first center deviation of the one or more wafers of the first group indicates a wafer misalignment condition.

28. The non-transitory computer-readable medium according to claim 27, wherein: the first edge detection system includes three first through-beam optical sensors, each first through-beam optical sensor: is configured to emit a corresponding vertically directed beam when activated, Positioned such that when the first through-beam optical sensor is activated, the farthest horizontal distance between any of the beams is less than D 1 , and is configured to register when the beam emitted by it when the first through-beam optical sensor is activated intersects the edge of an object; and The non-transitory computer-readable medium also stores instructions for the following operations: controlling the one or more processors to operate the three first through-beam optical sensors such that each time the contour edge of one or more wafers of the first group intersects one of the light beams emitted by one of the first through-beam optical sensors, the horizontal coordinate of (c) is obtained.

29. The non-transitory computer-readable medium according to claim 27, wherein: the first edge detection system includes a machine vision system, and the machine vision system is configured to obtain the information indicating the first horizontal coordinates of at least five points of the contour edge of one or more wafers of the first group relative to the first reference point; and the non-transitory computer-readable medium also stores instructions for the following operations: controlling the one or more processors to connect to the machine vision system and use the machine vision system to obtain the horizontal coordinate of (c).

30. The non-transitory computer-readable medium according to claim 27, wherein the first edge detection system includes one or more members selected from the group consisting of the following items and the non-transitory computer-readable medium also stores instructions for causing the one or more processors to connect and communicate with one or more members selected from the group consisting of the following items: a group of three or more direct through-beam optical sensors, a group of three or more reflective through-beam optical sensors, a machine vision measurement system, and a group of three or more capacitance sensors.

31. The non-transitory computer-readable medium according to claim 27, wherein: D 1 less than D 2 by at least a first threshold amount D 2 is the minimum horizontal dimension of the boundary region envelope associated with the first wafer container, the first wafer container including one or more first wafer carriers configured to receive one or more wafers of the first group, and each of the one or more first wafer carriers is configured to support a wafer placed thereon and located within the envelope of the boundary region.

32. The non-transitory computer-readable medium according to claim 31, wherein the non-transitory computer-readable medium also stores instructions for controlling the one or more processors to perform the following operations: in (g), determining that the first sliding amount of one or more wafers of the first group is less than the first threshold amount, and h) causing the wafer handling robot to place at least some of the wafers in the one or more wafers of the first group into the first wafer container at least partially in response to determining that the first sliding amount of one or more wafers of the first group is less than the first threshold amount.

33. The non-transitory computer-readable medium according to claim 32, wherein the non-transitory computer-readable medium also stores instructions for controlling the one or more processors to perform the following operations: i) determining a first wafer offset of one or more wafers of the first group based on the information indicating the length and orientation of the first reference line segment for the one or more wafers of the first group; and j) During one or more operations in which one or more wafers of the first group are supported by the wafer handling robot, operate the wafer handling robot to place at least some of the one or more wafers in the first group of wafers into the first wafer container according to the first wafer offset.

34. The non-transitory computer-readable medium according to claim 31, wherein the non-transitory computer-readable medium further stores instructions for controlling the one or more processors to perform the following operations: h) Cause the wafer handling robot to place the wafer in the one or more wafers in the first group into a second wafer container at least in part in response to determining that the first sliding amount of the one or more wafers in the first group is greater than the first threshold amount; and i) After (h) and during a second time period, for each wafer in the first group of wafers, cause the wafer handling robot to: Retrieve the wafer from the second wafer container, When the wafer is supported by the wafer handling robot, cause the first edge detection system to obtain information indicating at least three second horizontal coordinates along the profile edge of the wafer relative to the first reference point, Use the at least three second horizontal coordinates to determine an estimated center point of the wafer relative to the first reference point, Determine a second center deviation by determining information indicating the length and direction of a second reference line segment extending from the estimated center point of the wafer to the first reference point, Determine a second wafer offset for the wafer based on the information indicating the length and orientation of the second reference line segment for the wafer, and During one or more operations in which the wafer is supported by the wafer handling robot, operate the wafer handling robot to place the wafer into the first wafer container according to the second wafer offset.

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