SYSTEM AND METHOD FOR CLAMP COMPENSATION - Patent application

Abstract

To provide a system and a method for operating a positioning system including a clamp element such as a piezoelectric element.SOLUTION: A method includes: applying a clamp element drive signal to a drive unit clamp element such that a clamp element of a positioning system 200 moves in a first direction toward mover elements 242, 244; and applying a shear element drive signal to a drive unit shear element such that the shear element moves in a second direction to compensate at least in part for misalignment between the drive unit clamp element and the mover element. The shear element drive signal can compensate at least in part for motion of the mover elements due to an angle at which the drive unit clamp element contacts the mover element.SELECTED DRAWING: Figure 2A

Description

[Technical field]

[0001] The present disclosure relates to systems and methods for operating a positioning system that includes a clamping element, such as a piezoelectric element. [Background technology]

[0002] High resolution imaging and / or device processing can be accomplished using one or more instruments, such as a scanning electron microscope (SEM), a transmission electron microscope (TEM), an ion column, a laser, and / or other beam generating instruments. Such instruments may require precise positioning of a workpiece to capture an image or process a desired area. Generally, a positioning system includes a carrier element on which the workpiece (or specimen to be imaged) can be mounted, and a set of actuators, such as motors, arranged to move the carrier element.

[0003] Some existing positioning systems operate using piezoelectric motors or actuators, e.g., walking piezo actuators. However, the stroke of the piezo actuator may be limited, which can result in choppy motion. To achieve high quality images and accurate processing, disturbance of the workpiece must be minimized. While useful, existing positioning systems suffer from significant position and velocity impairments that can prevent accurate positioning. Thus, an improved system for positioning the workpiece is needed. Summary of the Invention

[0004] Described herein are embodiments of drive units for positioning systems, and systems and methods for improving the movement of such devices. In an exemplary embodiment, the method can include applying a clamp element drive signal to a drive unit clamp element such that the clamp element moves in a first direction toward a mover element, and applying a shear element drive signal to a drive unit shear element such that the shear element moves in a second direction to at least partially compensate for misalignment between the drive unit clamp element and the mover element.

[0005] In any or all of the disclosed embodiments, the shear element drive signal can at least partially compensate for movement of the mover element due to the angle at which the drive unit clamping element contacts the mover element.

[0006] In any or all of the disclosed embodiments, the shear element drive signal can be based at least in part on a displacement of the mover element caused by contact between the drive unit clamping element and the mover element.

[0007] In any or all of the disclosed embodiments, the drive unit clamping element and the drive unit shear element may be piezoelectric elements.

[0008] In any or all of the disclosed embodiments, applying the shear element drive signal may include applying an initial shear element drive signal and a compensation signal.

[0009] In any or all of the disclosed embodiments, the method may further include determining a modified shear element drive signal by, at least in part, determining a first displacement of the mover element in response to contact with the drive unit clamping element, and determining a first compensation signal based at least in part on a product of the first displacement of the mover element and a reverse shear constant of the drive unit shear element.

[0010] In any or all of the disclosed embodiments, determining the modified shear element drive signal may further include determining a second displacement of the mover element in response to application of the first compensation signal, and determining the second compensation signal based at least in part on the second displacement of the mover element.

[0011] In any or all of the disclosed embodiments, the method may further include combining the second compensation signal with the initial shear element drive signal to obtain a modified shear element drive signal.

[0012] In any or all of the disclosed embodiments, the shear element drive signal can at least partially compensate for misalignment of the drive unit clamping element by moving the drive unit shear element in a direction opposite to the direction of movement of the mover element caused by contact with the mover drive unit clamping element.

[0013] In another representative embodiment, the method can include applying a clamping element drive signal to a drive unit clamping element to engage a moving body element, determining a first displacement of the moving body element, and determining a first compensation signal applied to one or more drive unit shear elements based at least in part on the first displacement. The method can further include applying the first compensation signal to one or more drive unit shear elements and applying the clamping element drive signal to the drive unit clamping element, determining a second displacement of the moving body element in response to the first compensation signal and the clamping element drive signal, and comparing the second displacement to a preselected threshold. For a second displacement less than the preselected threshold, the method can include combining the first compensation signal with the initial shear element drive signal to generate a modified shear element drive signal, and for a second displacement greater than the preselected threshold, determining a second compensation signal applied to one or more drive unit shear elements.

[0014] In any or all of the disclosed embodiments, the method may further include applying the modified shear element drive signal to the one or more drive-unit shear elements while applying a clamp element drive signal to a drive-unit clamp element.

[0015] In any or all of the disclosed embodiments, determining the compensation signal may include multiplying the displacement of the mover element by an inverse shear constant of one or more shear elements.

[0016] In any or all of the disclosed embodiments, the method may further include applying the first compensation signal and the second compensation signal to one or more drive unit shear elements and applying a clamp element drive signal to the drive unit clamp element, determining a third displacement of the mover element, and comparing the third displacement to a preselected threshold. For a third displacement less than the preselected threshold, the method may include combining the second compensation signal with the initial shear element drive signal to generate a modified shear element drive signal, and for a third displacement greater than the preselected threshold, determining a third compensation signal to be applied to the one or more drive unit shear elements.

[0017] In any or all of the disclosed embodiments, the compensation signal may be a first compensation signal, and determining the second compensation signal may include multiplying said second displacement of the moving body element by an inverse shear constant of one or more shear elements and subtracting the result from the first compensation signal.

[0018] In any or all of the disclosed embodiments, determining the displacement of the moving element includes measuring the displacement of the moving element with a position encoder.

[0019] In any or all of the disclosed embodiments, the displacement of the mover element is caused at least in part by a misalignment between the drive unit clamp element and the mover element.

[0020] In an exemplary embodiment, the positioning system may comprise a control unit including a shear signal generator configured to generate a modified shear element drive signal, the modified shear element drive signal including an initial shear element drive signal and a compensation signal.

[0021] In any or all of the disclosed embodiments, the control unit further comprises a clamp signal generator configured to generate the clamp element drive signal.

[0022] In any or all of the disclosed embodiments, the positioning unit further includes a drive unit including a clamping element and one or more shearing elements, and a mover element coupled to the carrier for holding the workpiece, engaged with the drive unit, and movable relative to the drive unit.

[0023] In any or all of the disclosed embodiments, the control unit further comprises a processor configured to generate a compensation signal based at least in part on the displacement of the mover element.

[0024] The positioning system described in any or all of the disclosed embodiments may be included in a system for electron microscopy that may include a scanning transmission electron microscope (STEM) and a positioning system that may be arranged to selectively position a workpiece for imaging with the STEM.

[0025] In any or all of the disclosed embodiments, the STEM can be configured to image the workpiece while the workpiece is being moved by the positioning system.

[0026] In any or all of the disclosed embodiments, the control unit may further comprise a look-up table (LUT) containing a plurality of pre-calculated compensation signals.

[0027] The foregoing and other objects, features, and advantages of the present disclosure will become more apparent with reference to the following detailed description and accompanying drawings. [Brief description of the drawings]

[0028] [Figure 1] 1 illustrates an exemplary embodiment of a multi-beam system. [Figure 2A] FIG. 1 shows a schematic cross-sectional side view of an exemplary embodiment of a positioning system mounted to the side of an electron microscope system. [Figure 2B] 2B shows the system of FIG. 2A with the workpiece displaced along the z-axis. [Diagram 3] 1 shows a schematic diagram of a position encoder according to one embodiment; [Figure 4A] FIG. 1 is a schematic diagram illustrating a front view of a drive unit engaging with a mover element according to one embodiment. [Figure 4B] FIG. 4C is a schematic diagram showing a side view of the drive unit of FIG. 4B. [Figure 5A] FIG. 2 is a perspective view of an exemplary embodiment of a longitudinal piezo element. [Figure 5B] FIG. 2 is a perspective view of an exemplary embodiment of a longitudinal piezo element. [Figure 6A] FIG. 2 is a perspective view of an exemplary embodiment of a shear piezo element. [Figure 6B] FIG. 2 is a perspective view of an exemplary embodiment of a shear piezo element. [Figure 7A] 1 illustrates an exemplary drive cycle of one embodiment of a drive unit engaging with a moving element. [Figure 7B] 1 illustrates an exemplary drive cycle of one embodiment of a drive unit engaging with a moving element. [Figure 7C] 1 illustrates an exemplary drive cycle of one embodiment of a drive unit engaging with a moving element. [Figure 7D] 1 illustrates an exemplary drive cycle of one embodiment of a drive unit engaging with a moving element. [Figure 8A] 7A-7D are graphs of representative drive signals for clamping elements of the drive units of FIGS. [Figure 8B] 7A-7D are graphs of representative drive signals for shear elements of the drive units of FIGS. [Figure 9] 1 shows a side elevation view of an exemplary embodiment of a drive unit engaging with a mover element, where the clamping surface of the clamping element is parallel to the surface of the mover element. [Figure 10] 13A is a side view of an embodiment of a drive unit engaging with a mover element, where the surface of the clamping element is inclined relative to the surface of the mover element. FIG. [Figure 11] FIG. 1 is a schematic block diagram of an exemplary embodiment of an open loop control system. [Figure 12A] 1 is a graph of the position of a clamping element over time at a drive frequency of 1 Hz. [Figure 12B] 1 is a graph of the velocity of a clamping element over time at a drive frequency of 1 Hz. [Figure 13A] 4 is a graph of a representative signal of one or more clamping elements of a drive unit. [Figure 13B] 1 is a representative graph of velocity as a function of time for clamp measurements. [Figure 13C] 1 is a representative graph of velocity as a function of time with open loop control. [Figure 14] 13 is a representative graph of velocity signals of 1 Hz and -1 Hz drive signals corrected with a clamped velocity signal. [Figure 15A] 4 is a graph of a representative drive signal for one or more clamping elements of a drive unit. [Figure 15B] 4 is a graph of a representative compensated drive signal for one or more shear elements of a drive unit. [Figure 16] 11 is a graph showing the position of a mover element as a function of commutation angle where the drive signal is modified by successive implementations of an iterative learning control scheme to compensate for misalignment of the clamping element. [Figure 17A] 4 is a graph of a representative drive signal for one or more clamping elements of a drive unit. [Figure 17B] 4 is a graph of a representative compensated drive signal for one or more shear elements of a drive unit. [Figure 18A] 4 is a graph showing the position of a mover element as a function of commutation angle for compensated and uncompensated drive signals. [Figure 18B] 4 is a graph showing the velocity of a moving element as a function of commutation angle for compensated and uncompensated drive signals. [Figure 19] FIG. 1 is a schematic block diagram of an exemplary closed-loop iterative learning based control system. [Figure 20] FIG. 1 is a process flow diagram of an exemplary method for positioning a mover element using a drive unit. [Figure 21] FIG. 2 is a process flow diagram of an exemplary method for determining a compensation signal for a drive unit. [Figure 22] FIG. 2 is a process flow diagram of an exemplary method for determining a compensation signal for a drive unit. [Figure 23] 1 illustrates a representative computer control system for use in implementing the disclosed methods and apparatus. [Figure 24] 1 illustrates an exemplary control system for use in implementing the disclosed methods and apparatus. [Diagram 25] 1 illustrates an exemplary control system for use in implementing the disclosed methods and apparatus. DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENTS

[0029] Introduction The present disclosure relates to systems and methods for moving carrier elements, such as wafer stage assemblies, along, for example, linear and / or curved guides or axes. The systems described herein may enable a workpiece, such as a semiconductor wafer, to be precisely positioned relative to one or more tools (e.g., scanning electron microscope (SEM), transmission electron microscope (TEM), ion column, laser beam, etc.) within a process chamber (e.g., vacuum chamber) where the tools and / or workpieces may be positioned at various angles according to the needs of the system. The following systems and methods are described in some examples with reference to semiconductor processing applications, however, the position systems and control methodologies described herein are also applicable to other fields where precise positioning and / or imaging is used, such as the preparation or analysis of biological samples.

[0030] Example 1 1, in an exemplary embodiment, the multi-beam system may be configured as a dual beam system 100 including a scanning electron microscope (SEM), generally designated 102, and an ion beam column, generally designated 104. The SEM 102 may include one or more charged particle beam (CPB) lenses, such as a condenser lens 116 and an objective lens 106. In some embodiments, the one or more CPB lenses may be magnetic lenses, and in particular, the objective lens 106 may be a magnetic objective lens. The ion beam column is arranged to provide a focused ion beam (FIB) to a workpiece W, and the SEM 102 is positioned to generate an image of the workpiece W.

[0031] The SEM 102 and ion beam column 104 may be mounted in a vacuum chamber 108 that houses a movable positioning system 110 for holding a workpiece W. The vacuum chamber 108 may be evacuated using a vacuum pump (not shown). As discussed in more detail below, the positioning system 110 is movable along an X-axis, a Y-axis, and / or a Z-axis, as shown with respect to a coordinate system 150, with the Y-axis being perpendicular to the plane of the page.

[0032] In some embodiments, the SEM 102 may be disposed vertically above the workpiece W and may be used to image the workpiece W, and the ion beam column 104 may be disposed at an angle and may be used to machine and / or treat the workpiece W. Figure 1 shows an exemplary orientation of the SEM 102 and the ion beam column 104.

[0033] The SEM 102 may include an electron source 112 and may be configured to manipulate a "raw" radiation beam from the electron source 112 and perform operations thereon, such as focusing, aberration reduction, trimming (using an aperture), filtering, etc. The SEM 102 may generate a beam 114 of input charged particles (e.g., an electron beam) propagating along a particle-optical axis 115. The SEM 102 may generally include one or more lenses, such as a condenser lens 116 and an objective lens 106 (e.g., a CPB lens), for focusing the beam 115 onto a workpiece W. In some embodiments, the SEM 102 may include a deflection unit 118 that may be configured to steer the beam 115. For example, the beam 114 may be steered in a scanning motion (e.g., a raster or vector scan) across a sample being investigated or a workpiece to be processed.

[0034] The dual beam system 100 may further comprise a computer processor and / or controller 128 for, among other things, controlling the deflection unit 118, the charged particle beam (CPB) lenses 106, 116, and the detector (not shown), and for displaying information collected from the detector on a display unit. In some cases, a control computer 130 is provided for establishing various excitations, recording image data, and generally controlling the operation of both the SEM and the FIB.

[0035] 1, the ion beam column 104 may include an ion source (e.g., plasma source 120) and ion beam optics 122. In the illustrated embodiment, the ion beam column 104 is a plasma focused ion beam (PFIB), but in other embodiments, the ion beam column 104 may be a standard focused ion beam (FIB) with a liquid metal ion source (LMIS) or other ion source compatible with a focused ion beam column. The ion beam column 104 may generate and / or direct an ion beam 124 along an ion optical axis 125. As described above, the ion column 104 may be used to perform imaging, processing, and / or machining operations on a workpiece, such as cutting, milling, etching, deposition, and the like.

[0036] In embodiments in which the ion beam is a PFIB, the ion source 120 may be fluidly coupled to multiple gases via a gas manifold 165 that includes gas sources coupled to the ion source 120 by respective valves. During operation of the ion source 120, gases may be introduced where they are charged or ionized, thereby forming a plasma. Ions extracted from the plasma may then be accelerated through the ion beam column 104 and become an ion beam. In other embodiments, the system 100 may include one or more lasers, or other types of milling or diagnostic tools.

[0037] As described above, such a multi-beam system may include a positioning system (e.g., a stage) configured to hold and position the workpiece W. The positioning system may position / move the carrier element with multiple degrees of freedom, including linear motion (e.g., to select a particular area of ​​the workpiece for analysis) and / or angular or rotational motion (e.g., to achieve a selected angle of the workpiece relative to the instrument). The positioning system may include one or more piezoelectric actuators that may employ the disclosed clamp compensation systems and methods.

[0038] Additional details of the piezo motors, stages, and beam systems described herein can be found in applications entitled "Systems and Methods of Hysteresis Compensation," filed herein and referenced by Attorney Reference Number 9748-102338-01, and in applications entitled "Electron Microscope Stage," filed herein and referenced by Attorney Reference Number 9748-102714-01, each of which is incorporated herein by reference in its entirety.

[0039] Example 2 2A and 2B show a cross-sectional view of an exemplary positioning system 200 coupled to a beam system configured as a charged particle microscope (CPM), generally designated 208. The positioning system 200 may comprise one or more drive units. For example, in the illustrated embodiment, the system may comprise three drive units, two of which, drive units 202 and 204, can be seen in FIG. 2. In the illustrated embodiment, the drive units 202, 204 are configured as walking or stepping piezo drive units, such as Hainmade Piezo Stepper (HMPS) actuators available from Hainmade BV. However, in other embodiments, the drive units may comprise other types of actuators, such as other types of piezo actuators, voice coil motors, rack and pinion systems, linear motors, etc.

[0040] The first and second drive units 202, 204 can be configured to position the workpiece W along at least the X and Z axes of a coordinate system 206 defined with respect to the beam system 208. As noted above, the positioning system can include three or more drive units, enabling movement of the workpiece along the X, Y, and Z axes. In some specific embodiments, the positioning system can include three drive units oriented such that each drive unit is offset 120 degrees from the other drive units.

[0041] As mentioned above, the positioning system 200 can be used with a multi-beam system, such as the CPM 208. The CPM 208 can be, for example, a combination of a scanning electron microscope (SEM), a transmission electron microscope (TEM), or a scanning transmission electron microscope (STEM). The CPM 208 can include a beam source 210, an upper pole objective lens 212, a lower pole objective lens 214, and a detector 216 (e.g., a camera, a photomultiplier tube, a photodiode, a CMOS detector, a CCD detector, a photocell, etc.). The components can be positioned at least partially within a vacuum chamber 218. A carrier element 220 including a workpiece W positioned thereon is shown extending from the positioning system 200 into the vacuum chamber 218.

[0042] The positioning system 200 may include a frame or housing 222 attached to an exterior surface 224 of the CPM 208 (e.g., an exterior surface of the vacuum chamber 218). The housing 222 may be attached to the surface 224 using one or more bearings 226, which allows the housing 222 to tilt or rotate (e.g., about the x-axis) relative to the surface 224. In some embodiments, the bearings 226 may be coupled to a mounting element 228 disposed on the surface 224 of the CPM 208, as shown in FIG.

[0043] The housing 222 can be positioned such that a portion of the housing, including a carrier element 220 for holding the workpiece W, can extend through an opening in a side of the CPM 208 and at least partially into the vacuum chamber 218. The positioning system 200 can be configured to adjust the position of the workpiece W relative to the beam 230 by adjusting the position of the carrier element 220 using drive units (e.g., first and second drive units 202, 204), as described in more detail below.

[0044] The carrier element 220 can be coupled to first and second guides 232, 234. Each guide 232, 234 can be further coupled to a respective strut member 238, 240 via a respective joint 236 (e.g., a hinge, knuckle joint, ball joint, etc.). The strut 238 can be pivotally coupled to a mover element or member 242 at a pivot joint 239, and the strut 240 can be pivotally coupled to a mover element or member 244 at a pivot joint 241. The first and second drive units 202, 204 can be configured to engage the mover elements 242 and 244, respectively. The drive unit 202 can be configured to move the mover element 242 along its axis toward and away from a rear wall 243 of the housing 222 in a series of step movements, as described in more detail below. The drive unit 204, like the mover element 242, can be configured to move the mover element 244 along its axis toward and away from the rear wall 245 of the housing 222. The struts 238, 240 (together with the mover elements and drive units) can be positioned at an angle relative to one another such that movement of the mover element 242 away from the rear wall 243, together with movement of the mover element 244 toward the rear wall 245, can tilt the carrier element 220 out of the XY plane, as shown in FIG. 2B. Simultaneous movement of the mover elements 242 and 244 away from the walls 243 and 245 toward the CPM 208 can move the carrier element 200 along the X-axis. In the illustrated embodiment, the mover elements 242 and 244 are positioned at an angle of 90° relative to one another. In a particular embodiment, three drive units and corresponding mover elements can be arranged around the axis of the carrier element 220 at angular intervals of 120°.

[0045] Each mover element 242, 244 may include a respective encoder scale 246. First and second position encoders 248 and 250 (e.g., optical encoders) mounted to the housing 222 may be configured to determine the position of each mover element 242, 244, respectively, based on the encoder scale 246. The encoder scale 246 may be coupled to or integrally formed with the movers 242, 244.

[0046] 3 shows a schematic diagram of an exemplary position encoder 300. An encoder scale 302 is attached to a moving body that may be positioned between a light source 304 and a detector 306. In certain embodiments, the light source and detector may be mounted to a housing of the positioning system.

[0047] As shown, a beam 308 produced by a light source 304 is split into two beams 310, 312 as it passes through the encoder scale 302. Two mirrors 314, 316 are used to recombine the beams and direct the combined beam 318 towards the detector 306.

[0048] 2A , each encoder 248, 250 can be configured to determine a position of a respective mover element 242, 244. The location data generated by the encoders 248, 250 can be used by a controller 252 to operate the actuators 202, 204 to position the mover elements 242, 244 at selected positions, thereby positioning the workpiece W at a selected position, as described in more detail below. The positioning system can include one or more piezoelectric actuators that can employ the disclosed clamp compensation systems and methods.

[0049] Example 3 4A and 4B show an exemplary drive unit 400 in more detail, which may be configured for use with a positioning system as either drive unit 202 or 204. Drive unit 400 may engage a mover member or element 402. As described above, mover element 402 may be coupled to a carrier element and thus may position a workpiece W relative to a CPM 208 or other instrument within vacuum chamber 218. In the illustrated embodiment, drive unit 400 may be a piezo drive unit comprising two sets of actuators 404, 406 housed within first and second frame or housing portions 408, 410.

[0050] For example, in the illustrated embodiment, each actuator set may comprise three movable members, referred to herein as actuators. Each actuator, in turn, may comprise one or more actuator elements, such as shear elements, clamping elements, or various combinations thereof. Each of the actuator elements may be independently movable and / or controllable. In other embodiments, the actuator sets may comprise a greater or lesser number of actuators. Further, while in the illustrated embodiment, each set of actuators comprises the same number of actuators, in other embodiments, one set of actuators comprises more or less actuators than the other. For example, a first set of actuators may comprise three actuators, a second set of actuators may comprise four actuators, and so on.

[0051] Returning to FIG. 4A , the first set of actuators 404 may include a first actuator 404a disposed adjacent a first surface 412 of the mover element 402, and second and third actuators 404b, 404c disposed on opposite sides of the mover element 402 adjacent a second surface 414 of the mover element. In the illustrated embodiment, the first actuator 404a includes a shear element 420 and a clamp element 422, and the second and third actuators 404b, 404c include shear elements. As described in more detail below, the clamp and / or shear elements may frictionally engage the mover element 402 to move the mover element 402 in a selected direction.

[0052] The second set of actuators 406 may include a first actuator 406a disposed adjacent to the second surface 414 of the mover element 402, and second and third actuators 406b, 406c disposed adjacent to the first surface 412 of the mover element 402. In the illustrated embodiment, the first actuator 406a includes a shear element 424 and a clamp element 426, and the second and third actuators 406b, 406c include shear elements.

[0053] The two sets of actuators 404, 406 can be operated in an alternating, stepping, or "walking" motion such that when the first set of actuators 404 engages and exerts a force on the moving body elements 402, it disengages or releases the second set of elements 406, and vice versa. There can be a short period between steps when both sets of actuators 404 and 406 are in contact with the moving body 402. This is called a "handover" state when one set of actuators "takes over" from the other set of actuators. This configuration, where one actuator of the set engages a first surface of the moving body elements and the second and third actuators of the set engage a second surface of the moving body elements, can help reduce distortion during operation and provide smoother movement of the moving body elements. The alternating handover action between the two sets of actuators advantageously minimizes slippage between the actuators and the moving body elements. Furthermore, this configuration allows the stroke length of the drive unit to be extended without affecting stiffness or operational performance.

[0054] When actuated, the shear elements can be displaced along the Z axis, as shown with respect to coordinate system 416, which is perpendicular to the plane of the page of Fig. 4A and parallel to the plane of the page of Fig. 4B. The clamping elements can be displaced along the Y axis. By alternating actuation of sets of actuators, large travel strokes can be achieved.

[0055] In some embodiments, the first frame portion 408 can be coupled to a biasing member 418 (e.g., a spring) that allows the first frame portion 408 to move relative to the mover element 402. In use, when the actuator element is energized in an extended position (e.g., clamp element 420 of FIG. 4A), the first frame portion 408 moves relative to the mover element 402, thereby compressing the biasing member 418. In some embodiments, the biasing member 418 can be biased to the extended position to maintain frictional contact between the actuator housed in the first portion of the frame 408 and the mover element 402.

[0056] In some embodiments, the ends of the actuators (e.g., the portions adjacent the mover elements) can be coated with aluminum oxide to reduce wear on the actuators and extend the life of the drive unit. In other embodiments, each of the clamps and / or shear elements can include a wear resistant plate configured to reduce damage to the clamps and / or shear elements due to frictional engagement with the mover.

[0057] Example 4 Figures 5A-5B show an exemplary embodiment of a clamping element 500, and Figures 6A-6B show an exemplary embodiment of a shearing element 600. In the illustrated embodiment, the clamping element and the shearing element comprise piezoelectric elements.

[0058] In certain embodiments, the clamping element 500 can be a longitudinal piezo element and the shearing element 600 can be a shearing piezo element. As described in more detail below, the longitudinal piezo element 500 can be configured to deform or elongate axially when a voltage is applied, and the shearing piezo element 600 can be configured to displace one end laterally relative to the opposite end when a voltage is applied. As shown in Figures 5B and 6B, in some embodiments, each element 500, 600 can comprise multiple piezoelectric members 502, 602 disposed adjacent to one another. In other embodiments, the clamping and shearing elements 500, 600 can be single layer piezo elements or monolithic multi-layer piezo elements, also referred to as monolithic co-fired piezo elements. In certain embodiments, the displacement of the clamping and / or shearing elements can be linearly related to the applied voltage. Depending on how the piezo member 502, 602 is polarized, it can be considered a longitudinal element or a shearing element. The clamping element can move between a first, or neutral, configuration, a second, elongated configuration (e.g., when energized by applying a positive voltage), and / or a third, shortened configuration (e.g., when energized by applying a negative voltage).

[0059] For example, as shown in FIG. 5A, an electric field (indicated by arrow 506) may be applied parallel to the direction of polarization (indicated by arrow 504). In some embodiments, as shown in FIG. 5B, the clamping element may include eight piezo layers, although in other embodiments, the clamping element may include a greater or lesser number of layers. In some specific embodiments, the clamping element may include three piezo layers. In some embodiments, the voltage applied to the clamping element may be, for example, between −30V and 60V.

[0060] When energized (e.g., by applying a positive or negative voltage), the clamping element 500 can expand and / or contract longitudinally, i.e., in the direction indicated by arrow 508. With reference to FIG. 5A, the clamping element 500 can have a first or neutral configuration having a first or natural length L1 when no voltage is applied to the voltage clamping element, a second or expanded configuration having a first or second length L2 when a first or positive power is applied to the element, and a third or contracted configuration having a third length L3 when a second or negative voltage is applied to the element. The second length L2 can be greater than the first length L1, and the first length L1 can be greater than the third length L3. The lengths can be based at least in part on the magnitude of the applied voltage.

[0061] 6A and 6B show an exemplary shear piezo element 600. As shown in FIG. 6A, an electric field (indicated by arrow 606) is applied orthogonal to the direction of polarization (indicated by arrow 604). In some embodiments, as shown in FIG. 6B, the shear element 600 may comprise eight layers of piezo members. However, in other embodiments, the shear element may comprise a greater or lesser number of layers. In some particular embodiments, the shear element 600 may comprise four layers of piezo members. In some embodiments, the voltage applied to the shear actuator may be between -250V and 250V, for example.

[0062] When energized (e.g., by applying a positive or negative voltage), a portion of the shear element 600 can shear or move laterally in a selected direction, as indicated by arrow 608. For example, the shear motion causes a displacement of a first surface 610 of the shear piezo element relative to an opposite second surface 612 of the shear element. The shear element can have a first offset position where the first surface is displaced from the second surface in a first direction by a first displacement length D1 when a positive voltage is applied, and a second offset position where the first surface is displaced from the second surface in a second direction (e.g., opposite the first direction) by a second displacement length D2 when a negative voltage is applied. The displacement lengths D1 and D2 can be based at least in part on the magnitude of the applied voltage.

[0063] The piezoelectric members 502 and 602 may include, but are not limited to, ceramics (including natural and synthetic ceramics), crystals (including natural and synthetic crystals), Group III-V and II-VI semiconductors, polymers, organic nanostructures, or any combination thereof. In some particular embodiments, the piezoelectric elements may include lead zirconate titanate (PZT). Such piezoelectric elements may expand when a positive voltage is applied and contract when a negative voltage is applied. The magnitude and rate of contraction, expansion, and / or shear displacement may depend on the magnitude of the voltage applied to the piezoelectric members.

[0064] Example 6 7A-7D show the positions of actuators of an exemplary drive unit 700 (which may be configured similarly to drive unit 400) throughout a drive cycle. Drive unit 700 is configured to engage mover element 702. Drive unit 700 includes two sets of actuators 704 and 706. Each actuator set may be comprised of three actuators. For example, actuator set 704 may include actuators 704a, 704b, and 704c, and actuator set 706 may include actuators 706a, 706b, and 706c. The actuators may include shear elements, clamp elements, and / or combinations thereof. For example, in the illustrated embodiment, actuators 704b, 704c, 706b, and 706c include shear elements. Actuator 704a may include shear element 714 and clamp element 716, and actuator 706a may include shear element 718 and clamp element 720. The actuators can be housed in first and second frame portions 708, 710. In certain embodiments, the displacement of the actuators can be linearly related to the applied voltage. Because there are two sets of actuators 704, 706, and each set can comprise two types of elements (clamp and shear), four drive signals can be used to move the sets of actuators 704, 706 in alternating fashion. In some embodiments, the drive signals can be configured as waveforms (e.g., voltage waveforms) for the alternating or repetitive nature of the walking motion.

[0065] In this example, actuators 704a and 706a have equal lengths, but in other examples, actuators 704a and 706a can have different lengths. In this example, there are two clamping elements 716 and 720, and six shearing elements 704b, 704c, 714, 706b, 706c, 718. However, in other examples, the drive unit can include a greater or lesser number of clamping and shearing elements.

[0066] 8A and 8B show the drive signals for the drive cycles shown in FIGS. 7A-7D. The drive signals may depend on a commutation angle α and may be periodic with a period of 2π. The commutation angle α may be defined using the following equation:

number

[0067] FIG. 8A illustrates an example drive or voltage signal for the clamping elements of the first and second sets of actuators, and FIG. 8B illustrates an example drive or voltage signal for the shear elements of the first and second sets of actuators. Referring now to FIG. 8A, a first voltage signal 800 can be applied to the clamping elements 716 of the first actuator set 704, and a second voltage signal 802 can be applied to the clamping elements 720 of the second actuator set 706. The voltage signals in FIG. 8A rise and fall at a constant rate between −30V and 60V. The drive signal for the clamping elements 716 can be π rad out of phase with the drive signal for the clamping elements 720 such that when the voltage applied to the clamping elements 716 is 60V, the voltage applied to the clamping elements 720 is −30V, and vice versa. The period, maximum, and minimum values ​​of both signals are the same. However, in other embodiments, the drive signal for the clamping elements 716 can be different from the drive signal for the clamping elements 720.

[0068] The voltage signals 804 and 806 in Figure 8B can increase or rise at a first rate from -250V to 250V through an angle of 3π / 2 rad and decrease or rise at a second rate from 250V to -250V at an angle of π / 2 rad as in a sawtooth waveform. The signals in Figure 8B can also be out of phase or phase shifted by π rad.

[0069] FIG. 7A shows the drive unit 700 in a first or starting position of the drive cycle where the commutation angle is zero. This position corresponds to the drive signal value at a commutation angle of 0 rad in FIGS. 8A and 8B, indicated by the reference letter a. As shown in FIG. 8A, the voltages applied to the clamping elements 716 and 720 of the actuators 704a and 706a are equal at 0 rad such that both actuators have equal lengths L1, engaging and clamping the mover element 702 between them. With reference to FIG. 8B, the voltages applied to the shear elements of the actuators 704b and 704c, as well as the shear element 714 of the actuator 704a, may be −200V. The voltages applied to the shear elements 706b and 706c, as well as the shear element 720 of the actuator 706a, may be 200V. Thus, the actuators 704b, 704c, 706b, and 706c are also in contact with the mover element 702. The actuator positions in Figure 7A may correspond to a take-over motion where all elements of both sets of actuators 704, 706 are in equilibrium with each other and in contact with the mover 702. The derivatives of the shear voltages of the shear elements of both shear groups with respect to the commutation angle may be equal. Thus, both shear groups may move at the same speed.

[0070] FIG. 7B illustrates the drive unit in a second exemplary position in the drive cycle, corresponding to the portion of the drive signal indicated by reference letters b-c in FIGS. 8A and 8B. The clamp element 716 of the actuator 704a of the first set of actuators 704 is energized with a maximum voltage, thus moving the actuator 704a from the first length L1 to an extended length L2 that is greater than L1. As illustrated in FIG. 8A, the voltage applied to the clamp element 716 of the actuator 704a may be 60V, and the voltage applied to the clamp element 720 of the actuator 706a may be −30V. The extended length L2 of the actuator 704a moves the first frame portion 708 relative to the mover element 702 such that the actuators 706b and 706c no longer engage the mover element 702. The first frame portion 708 may be coupled to a biasing element 712.

[0071] The biasing element 712 (e.g., a spring) can compress to allow movement of the first frame portion 708 relative to the mover element 702. Meanwhile, the clamping element 720 of the actuator 706a is energized at its minimum voltage (e.g., −30V), thus moving the actuator 706a from the first length L1 to a contracted configuration having a length L3 less than length L1 such that the actuator 706a is no longer engaged with the mover element 702. The actuators 706b and 706c are in position for the next “takeover” movement, while the actuators 704b, 704c, and 714 move, displace, or drive the mover element 702 relative to the drive unit 700 under the influence of the increasing drive voltage of FIG. 8B. As shown in FIG. 8B, the voltage applied to shear elements 718, 706b, and 706c can be stepped down from 250V to −250V, and the voltage applied to shear elements 714, 704b, and 704c can be stepped up from −250V to 250V.

[0072] FIG. 7C shows the actuators in a third exemplary position in the drive cycle, corresponding to the portion of the drive signal indicated by reference letter d in FIGS. 8A and 8B. The third exemplary position is a second "handover" motion similar to the handover motion described above with respect to FIG. 7A, where all of the actuators are in contact with the mover element 702. As shown in FIG. 8A, the voltages applied to the clamping elements 716 and 720 of actuators 704a and 706a are equal at 0 rad such that both actuators have equal lengths L1, engaging and clamping the mover element 702 between them. With reference to FIG. 8B, the voltages applied to the shear elements of actuators 704b and 704c and the shear element 714 of actuator 704a may be 200V. The voltages applied to the shear actuators 706b and 706c and the shear element 718 of actuator 706a may be -200V.

[0073] FIG. 7D illustrates the actuators in a fourth exemplary position in the drive cycle, corresponding to the portion of the drive signal indicated by reference letters ef in FIGS. 8A and 8B. This position is similar to the position illustrated in FIG. 7B, except that the second set of actuators 706 are engaged with the mover elements 702 and the first set of actuators 704 are disengaged. The clamping element 720 of actuator 706a is energized with a maximum voltage, thus moving actuator 706a from a length L1 to an extended configuration having a length L2 greater than L1. As illustrated in FIG. 8A, the voltage applied to the clamping element 720 of actuator 706a may be 60V, and the voltage applied to the clamping element 716 of actuator 704a may be −30V. The expanded configuration of actuator 706a can move mover element 702 (and thereby elements 704a, 706b, 706c and first frame portion 708) relative to (e.g., away from) second frame portion 710 such that actuators 704b and 704c no longer engage mover element 702. Clamp element 716 is energized with a minimum voltage (e.g., −30V), thus moving actuator 704a from a first length L1 to a contracted configuration having a length L3 less than length L1 such that actuator 704a no longer engages mover element 702. Actuators 704b and 704c are in position for the next “takeover” movement while actuators 706b and 706c drive or displace mover element 702 due to the increase in drive voltage in FIG. 8B. As shown in FIG. 8B, the voltage applied to shear elements 718, 706b, and 706c can rise from -250V to 250V, and the voltage applied to shear elements 714, 704b, and 704c can fall from 250V to -250V.

[0074] Because the selected drive signals of the actuator sets are periodic, the configuration of the drive unit corresponding to the portion of the drive signal indicated by reference letter g in Figures 8A and 8B is the same as the configuration shown in Figure 7A. This combination of piezo elements and drive signals enables the drive unit to move the mover element 702 in a series of steps reminiscent of a walking motion. This drive cycle can be repeated as necessary to move the mover element 702 to a selected position. The direction of the drive signal can also be reversed to move the mover element in the opposite direction.

[0075] Example 7 As mentioned above, the drive unit(s) can be used to move the mover(s) so that the workpiece W can be positioned relative to a charged particle microscope (CPM), e.g., a STEM. Disturbances in the position and velocity of the workpiece W can be undesirable for tracking the point-to-point movement of the workpiece W moving at a constant velocity. For example, the disturbances can cause the guidance system to lose track of the position of the workpiece and / or the selected area of ​​the workpiece that is intended to be imaged. In some embodiments, the CPM can be configured to image the workpiece W while the workpiece is moving. In such embodiments, it is particularly advantageous to have a smooth and consistent movement of the workpiece W.

[0076] As shown in Fig. 9, the actuators 902, 904 of the drive unit 900 are typically positioned such that they are perpendicular to the mover element 906. For example, the actuators 902, 904 can be positioned such that an axis 908 extending longitudinally through the actuators 902, 904 forms a 90° angle with the surface of the mover element 906. The surface of the actuators 902, 904 that contacts the contact surface 910 of the mover element is parallel to the mover element 906, and the actuators move perpendicular to the surface of the mover. In use, this configuration allows the actuators with clamping elements to engage the mover element without affecting the position of the mover element.

[0077] Example 8 However, as shown in FIG. 10, in some embodiments, one or both of the actuators 1002, 1004 of the drive unit 1000 may be positioned at an angle (e.g., tilted) relative to the mover element 1006. This may be referred to as "clamping element misalignment." In such embodiments, the surface of the actuator that contacts the mover element of the contact surface 1012 is not parallel to the surface 1012, and the actuator moves at a non-perpendicular angle relative to the mover element. For example, practical limitations on the dimensional and / or positional tolerances of components in the system may result in one or both of the actuators 1002, 1004 being angled or tilted relative to the mover element 1006. This is illustrated by lines 1008, 1010 that extend axially through the actuators 1002 and 1004, respectively, and form angles β, φ with the contact surface 1012 with the mover element 1006. The angled actuators 1002, 1004 can result in a change (e.g., an addition or subtraction) in the velocity of the shear elements, thereby causing a perturbation in the position and velocity of the workpiece W. For example, the angled actuator elements can contact the surface of the mover at a commutation angle α in front of where the vertical actuator would expect to contact. This can push the mover forward or backward as the actuator continues to extend, depending on the direction of the misalignment.

[0078] Example 9 The disturbances caused by the tilted actuators can be quantified, for example, using open-loop clamp measurements. An exemplary control architecture 1100 for such open-loop measurements is shown in FIG. 11. The control system 1100 can include an integrator tool or module 1102 and a signal generator module 1104. The drive unit is represented by block 1106. Blocks 1102, 1104, and 1106 are grouped together in block 1108, which represents a physical system G (which can include, for example, a carrier unit, a drive unit, a position encoder, etc.). In the illustrated embodiment, the drive frequency f α may be input to an integrator module 1102. The integrator module 1102 may output the commutation angle α to a signal generator 1104, which may provide a plurality (e.g., four) output signals u to a drive unit 1106. i Because the illustrated embodiment has two types of piezo elements (e.g., shears and clamps) and two sets of piezo actuators (see, e.g., FIGS. 7A-7D), the signal generator can generate four signals or voltage functions u i to move the drive unit in a selected manner. In one exemplary embodiment, the clamping elements can be energized with a clamping element drive signal while the shearing elements remain stationary. m By measuring the position of the moving element x m As the open loop measurement progresses, the displacement of the moving body element can be determined.

[0079] In the particular open loop measurement described above, a drive signal can be used to energize the clamping elements of the actuator while the shear elements of the actuator remain stationary at 0 V. By measuring the position of the moving element at a constant drive frequency, the effect of the tilted clamping element on the position of the moving element can be determined.

[0080] 12A-12B show example position and velocity measurements determined using open-loop measurements, with FIG. 12A showing the position and velocity measurements determined using a constant drive frequency f of 1 Hz. α 12B shows an example position estimation using a constant drive frequency f of 1 Hz. α 12A and 12B show an example velocity estimation using the velocity signal and, therefore, the disturbances in the position signal are repetitive.

[0081] Example 10 In certain embodiments, the velocity, and therefore the position disturbance, may be related to the drive signal applied to the clamping element, and the directional dependence of the open loop response, as shown in Figures 13A-13C. For moments in the drive cycle where the voltage applied to the clamping element of the actuator is constant, the velocity may be zero. Figure 13A shows a typical drive signal applied to the clamping element of the actuator. Figure 13B shows the normalized velocity change of the clamp measurement with a drive frequency of 1 Hz. Figure 13C shows the normalized velocity change of the clamp measurement with a drive frequency of 1 Hz. α 13B shows the normalized velocity evolution of the clamping element driven by the open loop control system 1100 at {-1, 1} Hz. With reference to FIG. 13B, it can be seen that for the drive cycle movement where the voltage applied to the clamping element is constant, the velocity of the clamp measurement is zero. As the clamping element begins to contract (e.g., at α=0.71π rad and α=1.71π rad), the velocity of the clamping element increases to an approximately constant speed or level. As shown in FIG. 13C, f α The speed of the clamping element at f = 1 Hz increases, α =-1Hz the speed of the clamping elements is decreased.

[0082] Similar disturbances occur before certain clamping phases (e.g., α=0.28π rad and α=1.28π rad). Just before and just after certain clamping phases, only one clamping element is in contact with the moving body (e.g., the clamping element of the first set of actuators or the clamping element of the second set of actuators). Thus, velocity increases and decreases can be the result of tilted clamping elements.

[0083] Disturbances caused by one or more tilted clamping elements of the actuator can be at least partially counteracted or mitigated by actuating a shearing element to compensate for the tilt or misalignment of the clamping element. More specifically, the angled clamping elements can be at least partially compensated for by modifying the waveform of the drive signal(s) of the shearing element to provide a modified drive signal (e.g., a signal comprising an initial shearing signal combined with a compensation signal) to the shearing elements of the actuator. An exemplary compensation signal can be generated by superposition of velocities resulting from clamped and open-loop measurements. FIG. 14 shows normalized open-loop velocity signals at 1 Hz and −1 Hz corrected with a clamped velocity signal based on the superposition of shear and clamped velocities. From FIG. 14, it can be seen that the minimum at α∈{0.1π, 1.15π}rad decreases to about 0 m / s. Thus, in certain embodiments, at least negative velocities can be avoided using the tilt compensation algorithm described herein.

[0084] Example 11 Misalignment, displacement, and / or tilt of the clamping element relative to the mover element can be at least partially compensated for by modifying the motion of the shear element. The displacement trajectory of the shear element can be determined based at least in part on the observed displacement of the mover element when the clamping element is acted upon. In a particular embodiment, the shear element has a displacement of about 3.0×10 when a voltage signal having an amplitude of 250 V is applied. -6 m. Thus, the voltage required to produce a particular shear displacement can be approximated by the model shown below in Equations 1 and 2. The inverse shear constant TIFF0007600493000002.tif28170 relates the applied voltage to the shear displacement of the shear piezo element.

number

number

[0085] In equations 2 and 3, TIFF0007600493000005.tif28170 is the reverse shear constant [V / m], u is the applied voltage [V], and x m is the position of the moving element [m].

[0086] Ideally, the displacement of the mover element when clamped by the clamping element should be 0 m. Therefore, in a particular embodiment, the shear compensation signal or waveform can be generated using an iterative learning control (ILC) scheme and an inverse shear model, as shown in Equation 3.

number

[0087] In Equation 3, u j+1 is the adjustment compensation signal [V], and u j is the initial correction signal [V], TIFF0007600493000007.tif28170 is the reverse shear constant [V / m], and x mは is the displacement of the moving body [m].

[0088] Example 12 15A and 15B show clamping elements and initial voltage waveforms for the shearing elements that can be used with the ILC system to adjust the shearing element drive signal. FIG. 15A shows a typical drive signal applied to the clamping element of the actuator during operation of the drive unit to move the clamping element in a first direction (e.g., toward or away from the moving body element), and FIG. 15B shows an initial drive signal, referred to herein as a compensation signal or waveform, applied to the shearing element of the actuator to move the shearing element in a second direction (e.g., opposite to the direction of movement of the moving body element). In certain embodiments, the signal shown in FIG. 15B can be obtained at least in part based on the path or position of the moving body element during a clamping operation in which the clamping element is actuated with the signal shown in FIG. 15A. In other words, the initial voltage signal for the shearing element can be at least in part based on the path of the moving body element during a clamping operation without misalignment compensation. For example, a first voltage waveform for driving the shearing element is applied to the moving body x m The position of the inverse shear constant JPEG0007600493000008.jpg23 and subtracting the resulting amount from the initial uncorrected shear element voltage signal according to Equation 3 above. The clamp can then be actuated again and the shear element can be driven with the waveform resulting from Equation 3. The shear element can be moved in a second direction (e.g., opposite to the direction of movement of the mover element) to at least partially compensate for the misalignment between the clamp element and the mover element. The displacement, position, or path of the mover element can be determined (e.g., using a position encoder) and the difference between the measured displacement and the target displacement can be measured throughout the drive cycle (e.g., α=0 to α=2π). This difference may be referred to as the error. The sum of the errors can be compared to the target displacement or path (e.g., 0 m, or no movement). If the displacement exceeds a preselected threshold (e.g., 1 μm, 100 nm, 10 nm, etc.), the voltage signal of the second shear element can be determined based at least in part on the difference between the measured displacement and the target displacement of the mover element. In certain embodiments, the retraction motion of the shear elements can be oriented such that this group does not contact the mover element during clamping, meaning that changes in the position of the mover element can be caused by misalignment of the clamping element.

[0089] The shear element drive signal (e.g., voltage applied to the shear element) can be iteratively modified by repeating the above process to reduce the movement of the mover element during clamping by the clamping element. This process can be repeated until the displacement of the mover element converges to or approaches the target displacement. FIG. 16 shows the change in the drive signal over eight iterations of the ILC scheme. For each trial, the shear element drive signal is modified to reduce the change in the position of the mover element. In certain embodiments, it is possible to reduce the displacement of the mover element by a factor of 60 or more compared to the operation of the drive unit without compensating for clamp misalignment. A shear element waveform that results in zero displacement, near zero displacement, or a preselected displacement of the mover element is referred to herein as a compensation waveform or compensation drive signal.

[0090] Example 13 To apply tilt compensation during operation, a compensation drive signal, such as the compensation drive signal associated with FIG. 16, can be combined with the initial or unmodified shear element drive signal (see, for example, FIG. 8B). In some specific embodiments, the amplitude of the initial waveform is reduced to 150V because the maximum voltage to the shear element cannot exceed 250V due to practical limitations of the system. The resulting drive signals are shown in FIGS. 17A-17B. FIG. 17A shows the drive signal applied to the clamping element, and FIG. 17B shows the modified or compensated shear element drive signal resulting from combining the compensation waveform with the initial shear drive signal. The resulting modified drive signal shown in FIG. 17B is configured to move the mover element to a target position (or a selected distance per cycle) while mitigating movement of the mover element caused by misalignment of the clamping element.

[0091] Example 14 FIG. 18A shows the uncompensated and compensated position evolutions of a drive unit. The frequency of the drive signal may be 1 Hz. The uncompensated drive signal may be similar to the drive signal shown in FIGS. 8A and 8B, and the compensated drive signal may be similar to the drive signal shown in FIGS. 17A and 17B. The compensated position evolution 1802 is smoother and less perturbed than the uncompensated position evolution 1800. FIG. 18B shows the uncompensated and compensated velocities over one drive signal cycle. The compensated velocity 1804 has no negative velocity and is smoother and has shallower changes than the uncompensated velocity 1806. The use of slope compensation reduces the minimum change in velocity.

number

[0092] Example 15 FIG. 19 illustrates an exemplary control system 1900 for closed loop processing used to implement the processes described herein. The control system 1900 can include an integrator tool or module 1902 and a signal generator module 1904. A drive unit is represented by block 1906. Blocks 1902, 1904, and 1906 are grouped together in block 1908, which represents a physical system G (e.g., carrier unit, drive unit, position encoder, etc.). In the illustrated embodiment, the summing junction is connected to a preselected threshold r (e.g., between 10 nm and 100 nm) and x m (the displacements of the moving body elements) to yield an error value e. The error value can be calculated using the following formula: e=rx m

[0093] The error value can then be input to the controller 1910. The controller 1910 controls the drive frequency f α , which may be input to an integrator module 1902. The integrator module 1902 may output the commutation angle α to a signal generator 1904, which may generate multiple (e.g., four) output voltage signals u i to the drive unit 1906, resulting in a position change x m In certain embodiments, the output signal to the shear element generated by the waveform generator 1904 may be a compensated drive signal based at least in part on a predetermined movement of the mover element during clamping.

[0094] Example 16 20, an exemplary method 2000 for positioning a mover element of a positioning system using a drive unit includes applying a first drive signal to a clamping element of the drive unit such that the clamping element moves in a first direction toward the mover element, at 2002. At 2004, a second drive signal can be applied to at least one shearing element of the drive unit such that the shearing element moves in a second direction to compensate for misalignment between the clamping element and the mover element.

[0095] Example 17 Referring to FIG. 21 , an exemplary method 2100 for generating a compensated drive signal of a drive unit includes, at 2102, applying a clamp element drive signal to a clamp element of the drive unit, the clamp element configured to engage a mover element. At 2104, a displacement of the mover element is determined. At 2106, a compensation signal to be applied to one or more shear elements of the drive unit is determined based at least in part on the displacement of the mover element. At 2108, the compensation signal is applied to the one or more shear elements and the clamp element drive signal is applied to the clamp element. At 2110, a second displacement of the mover element is determined. At 2112, if the second displacement is below a preselected threshold (e.g., 10 nm to 100 nm), the compensation signal is combined with the initial shear element drive signal to generate a modified or compensated shear element drive signal.

[0096] Example 18 Referring to FIG. 22, an exemplary method 2200 for determining a modified shear element drive signal includes applying a clamp element drive signal to a clamp element at 2202. At 2204, a displacement of the mover element can be measured (e.g., using a position encoder). At 2206, the displacement can be used to determine a compensation signal. At 2208, the clamp element drive signal can be applied to the clamp element, and the compensation signal can be applied to one or more shear elements. At 2210, the displacement of the mover element can be measured again. At 2212, if the displacement of the mover element is below a preselected threshold (e.g., if the displacement is below a value of 10 nm to 100 nm), the compensation signal can be combined with the initial shear element drive signal to generate a modified shear element drive signal at 2214. At 2216, the modified shear element drive signal can be applied to one or more shear elements, and the clamp element drive signal can be applied to the clamp element. Referring again to 2212, if the displacement is not below the preselected threshold (e.g., if the displacement is greater than a value between 10 nm and 100 nm), then the displacement of the mover element can be used to determine an additional compensation signal in 2206. Operations 2206 through 2212 can be repeated until the displacement of the mover element is below the preselected threshold.

[0097] Example 19 23 and the following discussion are intended to provide a brief, general description of an exemplary computing environment in which the disclosed technology may be implemented. For example, the controller 252 may be configured similarly to the computing environment described below. Additionally, the disclosed technology may be implemented in other computer system configurations including handheld devices, digital signal processors (DSPs), multiprocessor systems, microprocessor-based or programmable consumer electronics, network PCs, minicomputers, mainframe computers, and the like. The disclosed technology may also be practiced in distributed computing environments where tasks are performed by remote processing devices that are linked through a communications network.

[0098] 23, an exemplary system implementing the disclosed technology includes a general purpose controller in the form of an exemplary general purpose PC 2300, including one or more processing units 2302, a system memory 2304, and a system bus 2306 coupling various system components including the system memory 2304 to the one or more processing units 2302. The system bus 2306 may be any of several bus structures including a memory bus or memory controller, a peripheral bus, and a local bus using any of a variety of bus architectures. The exemplary system memory 2304 includes a read only memory (ROM) 2308 and a random access memory (RAM) 2310. The ROM 2308 contains a basic input / output system (BIOS) 2312 containing the basic routines that help to transfer information between elements within the PC 2300. In the example of FIG. 23, data and processor-executable instructions for controlling the movement of the SEM and FIB positioning systems, imaging, processing, and other operational modes are stored in memory 2310A, and data and processor-executable instructions for identifying and quantifying beam components are stored in memory 2310A.

[0099] The exemplary PC 2300 further includes one or more storage devices 2330, such as a hard disk drive for reading from and writing to a hard disk, a magnetic disk drive for reading from and writing to a removable magnetic disk, and an optical disk drive. Such storage devices may be connected to the system bus 2306 by a hard disk drive interface, a magnetic disk drive interface, and an optical drive interface, respectively. The drives and associated computer-readable media provide non-volatile storage of computer-readable instructions, data structures, program modules, and other data for the PC 2300. Other types of computer-readable media may store data accessible by a PC, such as magnetic cassettes, flash memory cards, digital video disks, etc.

[0100] A number of program modules may be stored on storage device 2330, including an operating system, one or more application programs, other program modules, and program data. A user may enter commands and information into the PC 2300 through one or more input devices 2340, such as a keyboard, and a pointing device, such as a mouse. A monitor 2346 or other type of display device is also connected to the system bus 2306 via an interface, such as a video adapter.

[0101] The PC 2300 can operate in a networked environment using logical connections to one or more remote computers, such as a remote computer 2360. In some examples, one or more network or communication connections 2350 are included. The remote computer 2360 may be another PC, a server, a router, a network PC, or a peer device or other common network node, and typically includes many or all of the elements described above with respect to the PC 2300, although only a storage device 2362 is illustrated in FIG. 23. The personal computer 2300 and / or the remote computer 2360 can be connected to logical local area networks (LANs) and wide area networks (WANs).

[0102] Example 20 24 illustrates an exemplary embodiment of a control system 2400 for implementing the above-described process. The control system may include a clamp signal generator 2402, a shear signal generator 2404, and a look-up table (LUT) 2406.

[0103] The clamp signal generator can be configured to generate one or more clamp element drive signal(s) that are applied to one or more clamp elements of the drive unit 2408. For example, the clamp signal generator 2402 can generate a first clamp element drive signal 2410 that can drive a first clamp element (e.g., element 716 in FIGS. 7A-7D) and a second clamp element drive signal 2412 that can drive a second clamp element (e.g., clamp element 720 in FIGS. 7A-7D). In some embodiments, the clamp signal generator can also include a clamp LUT. The clamp LUT can receive the commutation angle α as an input and generate the clamp drive signal(s) (such as a voltage) as an output. In some embodiments, the first and second clamp element drive signals 2410, 2412 can be converted from digital to analog signals using a digital-to-analog converter (DAC).

[0104] The shear signal generator can be configured to generate one or more initial shear element drive signal(s) 2414. The LUT 2406 can include an array of compensation or error correction signals 2416. The LUTs can be pre-calculated and stored in static program storage, calculated as part of the control system initialization phase, or stored in application specific platform hardware. In use, the control system 2400 can select one or more compensation signal(s) 2416 from the LUT based on system requirements. The compensation signal 2416 can be converted from a digital to an analog signal using a digital to analog converter (DAC) 2418. The converted signal(s) 2420 can be combined with the initial shear element signal(s) 2414 at a summing junction 2422 to generate one or more modified shear element drive signals. For example, in the illustrated embodiment, there are two modified shear element drive signals 2424 and 2426. The first shear element drive signal 2424 can drive a first set of shear elements (e.g., elements 704b, 704c, and 714 in FIGS. 7A-7D), and the second shear element drive signal 2426 can drive a second set of shear elements (e.g., elements 706b, 706c, and 718 in FIGS. 7A-7D).

[0105] In other embodiments, the compensation signal 2416 and the initial shear element drive signal(s) 2141 can be combined in a summing junction 2422 as digital signals, and the modified shear element drive signals 2424 and 2426 can be converted to analog signals using a DAC.

[0106] The clamping element drive signal(s) and the modified shear element drive signal(s) can be applied to the drive unit 2408 to generate movement of the drive unit. The signals, e.g., the clamping element drive signal(s), the initial shear element drive signal(s), the compensation signal(s), and the modified shear element drive signal(s), are fed to the control system 2400 at a frequency f α can function independently.

[0107] Example 21 25 illustrates another exemplary embodiment of a control system 2500 for implementing the above-described process. The control system 2500 can include a clamp signal generator 2502, a shear signal generator 2504, and a processor 2506 with a memory unit 2508.

[0108] The clamp signal generator can be configured to generate one or more clamp element drive signal(s) that are applied to one or more clamp elements of the drive unit 2510. For example, the clamp signal generator 2502 can generate a first clamp element drive signal 2512 that can drive a first clamp element (e.g., element 716 in FIGS. 7A-7D) and a second clamp element drive signal 2514 that can drive a second clamp element (e.g., clamp element 720 in FIGS. 7A-7D). In some embodiments, the clamp signal generator can also include a clamp LUT. The clamp LUT can receive the commutation angle α as an input and generate the clamp drive signal(s) (such as a voltage) as an output. In some embodiments, the first and second clamp element drive signals 2512, 2514 can be converted from digital to analog signals using a digital-to-analog converter (DAC).

[0109] The shear signal generator can be configured to generate one or more initial shear element drive signal(s) 2516. The processor 2506 can be configured to generate one or more error correction or compensation signal(s) 2518. The compensation signal 2518 can be converted from a digital signal to an analog signal using a digital-to-analog converter (DAC) 2520. The converted signal(s) 2522 can be combined with the initial shear element signal(s) 2516 at a summing junction 2524 to generate one or more modified shear element drive signals. For example, in the illustrated embodiment, there are two modified shear element drive signals 2526 and 2528. The first shear element drive signal 2424 can drive a first set of shear elements (e.g., elements 704b, 704c, and 714 in FIGS. 7A-7D), and the second shear element drive signal 2426 can drive a second set of shear elements (e.g., elements 706b, 706c, and 718 in FIGS. 7A-7D).

[0110] The clamping element drive signal and the modified shear element drive signal(s) can be applied to the drive unit 2510 to generate a movement (e.g., a displacement) of the mover element x relative to the drive unit 2510. m The displacement of x can be measured using a position encoder 2530 (similar to the position encoders 248 and 250 described above). m 2518 and / or select a pre-calculated compensation signal from memory 2508. For example, the processor 2506 may m The compensation signal can be calculated based on the product of the inverse shear constant and the clamping element drive signal(s), the initial shear element drive signal(s), the compensation signal(s), and the modified shear element drive signal(s) at a frequency f α can function independently.

[0111] Although the principles of the disclosure have been described and illustrated with reference to exemplary embodiments, it will be recognized that the exemplary embodiments may be modified in arrangement and detail without departing from such principles. For example, elements of the exemplary embodiments shown in software may be implemented in hardware and vice versa. Also, techniques from any example may be combined with techniques described in any one or more of the other examples.

[0112] General Considerations For the purpose of this description, certain aspects, advantages, and novel features of the disclosed embodiments are described herein. The disclosed methods, devices, and systems should not be construed as limiting in any manner. Rather, the present disclosure is directed to all novel and non-obvious aspects and aspects of the various disclosed embodiments, alone and in various combinations and subcombinations with each other. The disclosed methods, devices, and systems are not limited to any particular aspect or feature or combination thereof, nor do they require any one or more particular advantages to exist or problems to be solved.

[0113] Although some operations of the disclosed methods are described in a particular order for convenience, it is to be understood that this method of description encompasses reordering, unless a particular order is required by specific language described below. For example, operations described in order may in some cases be reordered or performed simultaneously. Furthermore, for simplicity, the accompanying drawings may not show the various ways in which the disclosed methods may be used in conjunction with other methods. In addition, the description may use terms such as "provide" and "achieve" to describe the disclosed methods. These terms are high-level abstractions of actual operations that are performed. The actual operations that correspond to these terms may vary depending on the particular implementation and are readily discernible to those skilled in the art.

[0114] All features described herein are independent of one another and can be used in combination with any other feature described herein, except where structurally impossible.

[0115] As used in this application and the claims, the singular forms "a," "an," and "the" include the plural forms unless the context clearly dictates otherwise. Additionally, the term "include" means "comprise." Additionally, the terms "coupled" and "associated" generally mean electrically, electromagnetically, and / or physically (e.g., mechanically or chemically) coupled or linked and do not exclude the presence of intermediate elements between coupled or associated items unless specifically stated to the contrary.

[0116] In the following description, certain terms may be used, such as "up," "down," "upper," "lower," "horizontal," "vertical," "left," and "right." These terms are used for clarity of explanation when dealing with relative relationships, where applicable. However, these terms are not intended to imply absolute relationships, positions, and / or orientations. For example, with respect to an object, a "top" surface can become a "bottom" surface simply by flipping the object over. Nevertheless, it is still the same object.

[0117] Unless otherwise stated, all numerical values ​​expressing amounts of materials, angles, pressures, molecular weights, percentages, temperatures, times, etc., used in the specification or claims should be understood as modified by the term "about". Thus, unless otherwise stated, implicitly or explicitly, the numerical parameters recited are approximations that may depend on the desired properties and / or detection limits sought under testing conditions / methods well known to those skilled in the art. When directly and explicitly distinguishing the embodiments from the prior art discussed, the numbers of the embodiments are not approximate unless the word "about" is recited. Moreover, not all options described herein are equivalent.

[0118] In view of the many possible embodiments to which the principles of this disclosure may be applied, it should be recognized that the illustrated embodiments are preferred examples only and should not be construed as limiting the scope of the disclosure. Rather, the scope of the disclosure is at least as broad as the following claims. Accordingly, we claim all that comes within the scope and spirit of those claims.

Claims

1. applying a clamp element drive signal to the drive unit clamp element such that the clamp element moves in a first direction towards the mover element; applying a shear element drive signal to a drive-unit shear element such that the shear element moves in a second direction to at least partially compensate for a misalignment between the drive unit clamp element and the mover element, the misalignment being such that the drive unit clamp element is disposed at an angle relative to the mover element.

2. The method of claim 1 , wherein the shear element drive signal at least partially compensates for movement of the mover element due to an angle at which the drive unit clamping element contacts the mover element.

3. The method of claim 1 , wherein the shear element drive signal is based at least in part on a displacement of the mover element caused by contact between the drive unit clamping element and the mover element.

4. The method of claim 1 , wherein the drive unit clamping element and the drive unit shear element are piezoelectric elements.

5. The method of claim 1 , wherein applying the shear element drive signal comprises applying an initial shear element drive signal and a compensation signal.

6. At least in part, determining a first displacement of the mover element in response to contact with the drive unit clamping element; 2. The method of claim 1, further comprising: determining a modified shear element drive signal by: determining a first compensation signal based at least in part on a product of the first displacement of the mover element and a back shear constant of the drive unit shear element.

7. Determining the modified shear element drive signal comprises: determining a second displacement of the mover element in response to application of the first compensation signal; The method of claim 6 , further comprising: determining a second compensation signal based at least in part on the second displacement of the mover element.

8. The method of claim 7 , further comprising combining the second compensation signal with an initial shear element drive signal to obtain the modified shear element drive signal.

9. 2. The method of claim 1, wherein the shear element drive signal at least partially compensates for the misalignment of the drive unit clamping element by moving the drive unit shear element in a direction opposite to a direction of movement of the mover element caused by contact with the drive unit clamping element.

10. applying a clamp element drive signal to a drive unit clamp element to engage the mover element; Determining a first displacement of the mover element; determining a first compensation signal to be applied to one or more drive unit shear elements to at least partially compensate for a misalignment between the drive unit clamping element and the mover element based at least in part on the first displacement; applying the first compensation signal to the one or more drive unit shear elements and applying the clamp element drive signal to the drive unit clamp element; determining a second displacement of the mover element in response to the first compensation signal and the clamp element drive signal; comparing the second displacement to a preselected threshold; for a second displacement less than the preselected threshold, combining the first compensation signal with an initial shear element drive signal to generate a modified shear element drive signal; and for a second displacement greater than the preselected threshold, determining a second compensation signal to be applied to the one or more drive unit shear elements to at least partially compensate for a misalignment between the drive unit clamping element and the mover element; The method, wherein the misalignment is a condition in which the drive unit clamping element is disposed at an angle relative to the mover element.

11. The method of claim 10 , further comprising applying the modified shear element drive signal to the one or more drive unit shear elements while applying the clamp element drive signal to the drive unit clamp element.

12. 11. The method of claim 10, wherein determining the first compensation signal and / or determining the second compensation signal comprises multiplying the displacement of the mover element by an inverse shear constant of the one or more shear elements.

13. applying the first compensation signal and the second compensation signal to the one or more drive unit shear elements and applying the clamp element drive signal to the drive unit clamp element; determining a third displacement of the mover element; comparing the third displacement to the preselected threshold; for a third displacement less than the preselected threshold, combining the second compensation signal with the initial shear element drive signal to generate a modified shear element drive signal; The method of claim 10 , further comprising: determining a third compensation signal to be applied to the one or more drive unit shear elements for a third displacement greater than the preselected threshold.

14. The method described in claim 13, wherein determining the second compensation signal comprises multiplying the second displacement of the moving element by an inverse shear constant of the one or more shear elements and subtracting the result from the first compensation signal.

15. The method of claim 10 , wherein determining the displacement of the moving element comprises measuring the displacement of the moving element with a position encoder.

16. The method of claim 10 , wherein the displacement of the mover element is caused at least in part by the misalignment between the drive unit clamp element and the mover element.

17. 1. A positioning system comprising: a control unit including a shear signal generator configured to generate a modified shear element drive signal, the modified shear element drive signal including an initial shear element drive signal and a compensation signal; a drive unit including a clamping element and one or more shear elements; a mover element coupled to a carrier for holding a workpiece, the mover element engaging with the drive unit and movable relative to the drive unit; A positioning system, wherein the compensation signal is for at least partially compensating for a misalignment between the drive unit and the moving element, the misalignment being a state in which the drive unit is disposed at an angle relative to the moving element.

18. The positioning system of claim 17 , wherein the control unit further comprises a clamp signal generator configured to generate a clamp element drive signal.

19. The positioning system of claim 17 , wherein the control unit further comprises a processor configured to generate the compensation signal based at least in part on a displacement of the mobile element.

20. A scanning transmission electron microscope (STEM); 20. A system for electron microscopy comprising: a positioning system according to claim 17 arranged to selectively position a workpiece for imaging with the STEM.

21. The system of claim 20 , wherein the STEM is configured to image the workpiece while the workpiece is being moved by the positioning system.

22. The positioning system of claim 17, wherein the control unit further comprises a look-up table (LUT) containing a plurality of pre-calculated compensation signals.

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