System and method for focusing charged-particle beam

Abstract

To provide systems and methods for irradiating a sample with a charged-particle beam.SOLUTION: A charged-particle beam system may include a stage that is configured to hold a sample and that is movable in at least one of X, Y, Z axes. The charged-particle beam system may further include: a position sensing system to determine a lateral and vertical displacement of the stage; and a beam deflection controller configured to apply a first signal to deflect a primary charged-particle beam incident on the sample to at least partly compensate for the lateral displacement, and to apply a second signal to adjust a focus of the deflected charged-particle beam incident on the sample to at least partly compensate for the vertical displacement of the stage. The first and second signals may include an electrical signal having a high bandwidth in a range of 10 kHz to 50 kHz, and 50 kHz to 200 kHz, respectively.SELECTED DRAWING: Figure 4

Description

[Technical Field]

[0001] CROSS-REFERENCE TO RELATED APPLICATIONS

[0001] This application claims priority to U.S. patent application Ser. No. 62 / 786,131, filed December 28, 2018, and U.S. patent application Ser. No. 62 / 944,958, filed December 6, 2019, each of which is incorporated by reference in its entirety.

[0002] TECHNICAL FIELD

[0002] The description herein relates to the field of charged particle beam systems, and more particularly to systems and methods for focusing and dynamically compensating for vibrations of a charged particle beam. [Background technology]

[0003]

[0003] In the integrated circuit (IC) manufacturing process, unfinished or completed circuit components are inspected to ensure they are manufactured according to the design and are free of defects. Inspection systems utilizing optical microscopes or charged particle (e.g., electron) beam microscopes, such as scanning electron microscopes (SEMs), can be used. As the physical size of IC components continues to shrink, the accuracy and yield of defect detection become increasingly important. However, the imaging resolution and throughput of inspection tools struggle to keep up with the miniaturization of IC component features. The accuracy, resolution, and throughput of such inspection tools can be limited by a lack of desired precision in the stage motion and control mechanisms.

[0004]

[0004] Thus, prior art systems face limitations in high precision stage motion control mechanisms for charged particle beam inspection systems, for example, in semiconductor manufacturing processes. Further improvements in the art are desirable. Summary of the Invention

[0005]

[0005] Embodiments of the present disclosure provide systems and methods for high-precision three-dimensional stage control for charged particle beam systems. In one aspect of the present disclosure, a charged particle beam system is disclosed. The charged particle beam system includes a stage configured to hold a sample and movable in at least one of an X, Y, and Z axis. The charged particle beam system may further include a position sensing system for determining lateral and vertical displacements of the stage, and a controller configured to apply a first signal to deflect a primary charged particle beam incident on the sample to at least partially compensate for the lateral displacement of the stage, and to apply a second signal to adjust a focus of the deflected charged particle beam incident on the sample to at least partially compensate for the vertical displacement of the stage. The lateral displacement may correspond to a difference between a current position of the stage and a target position of the stage in at least one of the X and Y axes. The first signal may include an electrical signal that affects how the primary charged particle beam is deflected in at least one of the X and Y axes, and the electrical signal may include a signal having a bandwidth in a range of 10 kHz to 50 kHz.

[0006] In some embodiments, the controller may be further configured to dynamically adjust at least one of the first signal or the second signal during a scan of the primary charged particle beam over the sample. The vertical displacement of the stage may correspond to a difference between a current position and a target position of the stage in the Z-axis, and the vertical displacement may vary during a scan of the primary charged particle beam over the sample to at least partially compensate for angular rotation about at least one of the X-axis or the Y-axis. The second signal may include a voltage signal applied to the stage that affects how the deflected charged particle beam incident on the sample is focused in the Z-axis, and the voltage signal may include a signal having a bandwidth in a range of 50 kHz to 200 kHz.

[0007] In some embodiments, the charged particle beam system may include a stage motion controller, the stage motion controller including a plurality of motors configured to be individually controlled by a third signal. Each of the plurality of motors may be individually controlled to adjust leveling of the stage so that the stage is substantially perpendicular to an optical axis of the primary charged particle beam. In some embodiments, adjusting the leveling of the stage may be based on a geometric model of an actuation output of the stage. The third signal may include a plurality of control signals, each of the plurality of control signals corresponding to at least one of the plurality of motors. In some embodiments, the plurality of motors may include at least one of a piezoelectric motor, a piezoelectric actuator, or an ultrasonic piezoelectric motor.

[0008] In some embodiments, the charged particle beam system may further include a first component configured to form an embedded control signal based on the plurality of control signals, and a second component configured to extract at least one of the plurality of control signals from the embedded control signal. The position sensing system of the charged particle beam system may be configured to determine lateral and vertical displacement of the stage using a combination of a laser interferometer and a height sensor. In some embodiments, the laser interferometer may be configured to determine lateral displacement of the stage, and the height sensor may be configured to determine vertical displacement of the stage.

[0009] In another aspect of the present disclosure, a charged particle beam system is disclosed. The charged particle system may include a stage configured to hold a sample and movable in at least the Z-axis. The charged particle beam system may further include a position sensing system configured to determine a vertical displacement of the stage and a controller configured to apply a voltage signal to the stage that affects how a charged particle beam incident on the sample is focused in the Z-axis. The vertical displacement of the stage may correspond to a difference between a current position and a target position of the stage in the Z-axis, and the vertical displacement may vary during a scan of the primary charged particle beam over the sample to at least partially compensate for angular rotation about at least one of the X- or Y-axis. The controller may be further configured to dynamically adjust the voltage signal during a scan of the primary charged particle beam over the sample.

[0010] In another aspect of the present disclosure, a method for irradiating a sample disposed on a stage in a charged particle beam system is disclosed. The method may include generating a primary charged particle beam from a charged particle source; determining a lateral displacement of the stage, the stage being movable in at least one of an X, Y, and Z axis; applying a first signal to deflect the primary charged particle beam incident on the sample to at least partially compensate for the lateral displacement of the stage; and applying a second signal to the stage to adjust a focus of the deflected charged particle beam incident on the sample to at least partially compensate for a vertical displacement of the stage. The lateral displacement may correspond to a difference between a current position of the stage and a target position of the stage in at least one of the X and Y axes. The vertical displacement of the stage may correspond to a difference between the current position of the stage and the target position in the Z axis, and the vertical displacement may vary during scanning of the primary charged particle beam over the sample to at least partially compensate for angular rotation about at least one of the X and Y axes. The controller may be further configured to dynamically adjust at least one of the first signal or the second signal during scanning of the primary charged particle beam over the sample. The first signal may include an electrical signal that affects how the primary charged particle beam is deflected in at least one of the X and Y axes, and the electrical signal may include a signal having a bandwidth in the range of 10 kHz to 50 kHz. The second signal may include a voltage signal applied to the stage that affects how the deflected charged particle beam incident on the sample is focused in the Z axis. The voltage signal may include a signal having a bandwidth in the range of 50 kHz to 200 kHz.

[0011] In some embodiments, the method for irradiating a sample disposed on a stage in a charged particle beam system may further include applying a third signal to a stage motion controller, the stage motion controller including a plurality of motors configured to be individually controlled by the third signal. The method may further include each of the plurality of motors being individually controlled to adjust leveling of the stage so that the stage is substantially perpendicular to an optical axis of the primary charged particle beam. In some embodiments, adjusting the leveling of the stage may be based on a geometric model of an actuation output of the stage. The third signal may include a plurality of control signals, each of the plurality of control signals corresponding to at least one of the plurality of motors. In some embodiments, the plurality of motors may include at least one of a piezoelectric motor, a piezoelectric actuator, or an ultrasonic piezoelectric motor.

[0012] In some embodiments, applying the third signal may include embedding a plurality of control signals to form an embedded control signal by a first component of the control module, and extracting at least one of the plurality of control signals from the embedded control signal by a second component of the control module. The position sensing system of the charged particle beam system may be configured to determine lateral and vertical displacement of the stage using a combination of a laser interferometer and a height sensor. In some embodiments, the laser interferometer may be configured to determine lateral displacement of the stage, and the height sensor may be configured to determine vertical displacement of the stage.

[0013] In yet another aspect of the present disclosure, a method for irradiating a sample disposed on a stage in a charged particle beam system may include generating a primary charged particle beam from a charged particle source, determining a vertical displacement of the stage, the stage being movable in a Z-axis, and applying a voltage signal to the stage to adjust a focus of the deflected charged particle beam incident on the sample to at least partially compensate for the vertical displacement of the stage. The method may further include determining a lateral displacement of the stage, the stage being movable in at least one of an X-axis and a Y-axis, and applying a beam deflection signal to deflect the focused charged particle beam incident on the sample to at least partially compensate for the lateral displacement.

[0014] In some embodiments, the method for irradiating a sample disposed on a stage in a charged particle beam system may further include dynamically adjusting at least one of a voltage signal or a beam deflection signal during scanning of the primary charged particle beam over the sample. In some embodiments, the method may further include applying a control signal to a stage motion controller, the stage motion controller including a plurality of motors configured to be individually controlled by the control signal. Each of the plurality of motors may be individually controlled to adjust leveling of the stage such that the stage is substantially perpendicular to an optical axis of the primary charged particle beam.

[0015]

[0015] In some embodiments, applying the control signal may include embedding a plurality of control signals to form an embedded control signal by a first component of the control module, and extracting at least one of the plurality of control signals from the embedded control signal by a second component of the control module.

[0016] In yet another aspect of the present disclosure, a non-transitory computer-readable medium is disclosed that includes a set of instructions executable by one or more processors of a charged particle beam device to cause the charged particle beam device to perform a method. The method may include determining a lateral displacement of a stage, the stage being movable in at least one of an X-axis and a Y-axis, and instructing a controller to apply a first signal to deflect a primary charged particle beam incident on the sample to at least partially compensate for the lateral displacement. The set of instructions executable by the one or more processors of the device may further cause the device to apply a third signal to a stage motion controller configured to adjust leveling of the stage so that the stage is substantially perpendicular to an optical axis of the primary charged particle beam.

[0017] In yet another aspect of the present disclosure, a method for focusing a charged particle beam on a sample is disclosed. The method may include irradiating a sample disposed on a stage of a charged particle beam system with the charged particle beam, adjusting a location of a first focal point of the charged particle beam relative to the sample using a first component of the charged particle system, and manipulating an electromagnetic field associated with the sample to form a second focal point by adjusting the first focal point of the charged particle beam relative to the sample using a second component, the second component being located downstream from a focusing component of an objective lens of the charged particle system. Adjusting the location of the first focal point may include adjusting a position of the stage in a Z-axis, and adjusting the position of the stage in the Z-axis may include determining a position of the sample in the Z-axis using a height sensor and adjusting the position of the stage in the Z-axis based on the determined position of the sample using a stage motion controller. The first component of the charged particle system may be configured to adjust a focal depth of the charged particle beam relative to the sample. The first component may be located upstream of a focusing component of an objective lens of the charged particle system. The first component may include a charged particle source, an anode of the charged particle source, or a focusing lens, and the first component and the second component may be different. Manipulating the electromagnetic field may include adjusting an electrical signal applied to a second component of the charged particle system. The second component of the charged particle system may include one or more of a control electrode of the objective lens, a sample, or a stage. Manipulating the electromagnetic field may include adjusting a first component of an electrical signal applied to a control electrode of the objective lens or adjusting a second component of an electrical signal applied to the stage. Adjusting the second component of the electrical signal may adjust the landing energy of the charged particle beam on the sample.Adjusting the electrical signal may include adjusting a first component of the electrical signal to a control electrode of the objective lens and adjusting a second component of the electrical signal to the stage. Adjusting the first component of the electrical signal applied to the control electrode may coarsely adjust a first focus of the charged particle beam on the surface of the sample, and adjusting the second component of the electrical signal to the stage may finely adjust the first focus of the charged particle beam on the surface of the sample. The first component of the electrical signal may be determined based on an acceleration voltage and a landing energy of the charged particle beam. Manipulating the electromagnetic field may include adjusting a magnetic field configured to affect characteristics of the charged particle beam. The characteristics of the charged particle beam may include at least one of a path, a direction, a velocity, or an acceleration of the charged particle beam.

[0018] In some embodiments, the landing energy of the charged particle beam can be in the range of 500 eV to 3 keV, the first component of the electrical signal can include a voltage signal in the range of 5 KV to 10 KV, and the second component of the electrical signal can include a voltage signal in the range of −150 V to +150 V.

[0019] In yet another aspect of the present disclosure, a method for focusing a charged particle beam on a sample is disclosed, which may include irradiating the sample disposed on a stage with the charged particle beam, adjusting a location of a first focal point of the charged particle beam relative to the sample using a first component of a charged particle system, and adjusting a first component of an electrical signal applied to a control electrode of an objective lens to manipulate an electromagnetic field associated with the sample to adjust the first focal point of the charged particle beam on the sample to form a second focal point.

[0020] In yet another aspect of the present disclosure, a charged particle beam system is disclosed. The charged particle beam system may include a stage configured to hold a sample and movable along at least one of an X-axis, a Y-axis, or a Z-axis, and a controller having circuitry. The controller may be configured to use a first component of the charged particle system to adjust a location of a first focal point of the charged particle beam relative to the sample, and to use a second component, the second component being downstream of a focusing component of an objective lens of the charged particle system, to manipulate an electromagnetic field associated with the sample to adjust the first focal point of the charged particle beam relative to the sample to form a second focal point. Adjusting the location of the first focal point may include adjusting a position of the stage in the Z-axis. The system may further include a position sensing system configured to determine a position of the sample in the Z-axis. The position sensing system may include a height sensor including a laser diode sensor assembly. The controller may be configured to adjust the position of the stage in the Z-axis based on the position of the sample determined by the position sensing system. The height sensor may be configured to determine a position of the sample in the Z-axis, and the controller may be configured to adjust the position of the stage in the Z-axis to form a first focal point of the charged particle beam on the sample. The first component may be configured to adjust a focal depth of the charged particle beam relative to the sample and may be located upstream of a focusing component of an objective lens of the charged particle system. The first component may include a charged particle source, an anode of the charged particle source, or a focusing lens, and the first and second components of the charged particle system may be different. Manipulating the electromagnetic field may include adjusting an electrical signal applied to a second component of the charged particle system. The second component of the charged particle system may include one or more of a control electrode of the objective lens, the sample, or the stage. Adjusting the electrical signal applied to the second component may adjust the landing energy of the charged particle beam on the sample.Adjusting the electrical signal may include adjusting a first component of the electrical signal applied to a control electrode of the objective lens and adjusting a second component of the electrical signal applied to the stage. The controller may further be configured to manipulate the electromagnetic field by adjusting a magnetic field configured to affect a characteristic of the charged particle beam. The characteristic of the charged particle beam may include at least one of a path, a direction, a velocity, or an acceleration of the charged particle beam. Adjusting the first component of the electrical signal applied to the control electrode may coarsely adjust a first focus of the charged particle beam on the surface of the sample, and adjusting the second component of the electrical signal to the stage may finely adjust the first focus of the charged particle beam on the surface of the sample. The first component of the electrical signal may be determined based on an acceleration voltage and a landing energy of the charged particle beam.

[0021] In some embodiments, the first component of the electrical signal may be determined based on an acceleration voltage and a landing energy of the charged particle beam. The first component of the electrical signal may include a voltage signal in a range of 5 KV to 10 KV, and the second component of the electrical signal may include a voltage signal in a range of −150 V to +150 V. The landing energy of the charged particle beam is in a range of 500 eV to 3 keV.

[0022] In yet another aspect of the present disclosure, a non-transitory computer-readable medium is disclosed that includes a set of instructions executable by one or more processors of the apparatus to cause the apparatus to perform a method. The method may include using a first component of a charged particle system to adjust a location of a first focal point of a charged particle beam relative to a sample, and using a second component, the second component located downstream from a focusing component of an objective lens of the charged particle system, to manipulate an electromagnetic field associated with the sample to adjust the first focal point of the charged particle beam relative to the sample to form a second focal point. The set of instructions executable by the one or more processors of the apparatus may further cause the apparatus to determine a position of the sample in a Z-axis using a height sensor, and adjust a position of a stage in the Z-axis based on the determined position of the sample using a stage motion controller to form the first focal point of the charged particle beam on the sample. The set of instructions executable by the one or more processors of the device may further cause the device to manipulate the electromagnetic field associated with the sample by adjusting a first component of the electrical signal to coarsely adjust a first focus of the charged particle beam on a surface of the sample and adjusting a second component of the electrical signal to the stage to finely adjust the first focus of the charged particle beam on the surface of the sample.

[0023] In yet another aspect of the present disclosure, a method for generating a 3D image of a sample in a charged particle beam device is disclosed. The method may include irradiating a sample disposed on a stage with a charged particle beam, manipulating an electromagnetic field associated with the sample to adjust a focus of the charged particle beam relative to the sample, forming a plurality of focal planes substantially perpendicular to a primary optical axis of the charged particle beam based on the manipulation of the electromagnetic field, generating a plurality of image frames from the plurality of focal planes of the sample, one image frame of the plurality of image frames associated with a corresponding focal plane of the plurality of focal planes, and generating a 3D image of the sample from the plurality of image frames and the corresponding focal plane information. Manipulating the electromagnetic field may include adjusting a first component of an electrical signal applied to a control electrode of the objective lens or adjusting a second component of an electrical signal applied to the stage.

[0024] In some embodiments, the landing energy of the charged particle beam on the sample may be adjusted by adjusting the second component of the electrical signal. Adjusting the landing energy may include adjusting a first component of the electrical signal to coarsely adjust a first focus of the charged particle beam on the surface of the sample and adjusting a second component of the electrical signal to the stage to finely adjust the first focus of the charged particle beam on the surface of the sample. The first component of the electrical signal may be determined based on an acceleration voltage and a landing energy of the charged particle beam. The first component of the electrical signal may include a voltage signal in a range of 5 KV to 10 KV, and the second component of the electrical signal may include a voltage signal in a range of −150 V to +150 V. The landing energy of the charged particle beam is in a range of 500 eV to 3 keV.

[0025] The method may further include forming a first focal plane of the plurality of focal planes that coincides with a top surface of the sample and a second focal plane of the plurality of focal planes that is spaced a distance below the first focal plane. The distance between the first and second focal planes may be dynamically adjusted based on the feature being imaged or the material of the sample. The method may include generating a plurality of image frames at each focal plane of the plurality of focal planes of the sample. Generating the 3D image may include reconstructing the plurality of image frames using a reconstruction algorithm.

[0026]

[0026] In yet another aspect of the present disclosure, a charged particle beam system is disclosed. The charged particle beam system may include a stage configured to hold a sample and movable along at least one of an X-axis, a Y-axis, and a Z-axis, and a controller having circuitry. The controller may be configured to manipulate an electromagnetic field associated with the sample to adjust a focus of the charged particle beam relative to the sample, form a plurality of focal planes substantially perpendicular to a primary optical axis of the charged particle beam based on the manipulation of the electromagnetic field, generate a plurality of image frames from the plurality of focal planes, one image frame of the plurality of image frames associated with a corresponding focal plane of the plurality of focal planes, and generate a 3D image of the sample from the plurality of image frames and the corresponding focal plane information.

[0027]

[0027] Manipulating the electromagnetic field may include adjusting a first component of an electric signal applied to a control electrode of the objective lens or adjusting a second component of an electric signal applied to the stage. Adjusting the second component of the electric signal may include adjusting the landing energy of the charged particle beam on the sample. Adjusting the landing energy may include applying the first component of the electric signal to coarsely adjust the first focus of the charged particle beam on the surface of the sample and applying the second component of the electric signal to the stage to finely adjust the first focus of the charged particle beam on the surface of the sample. The first component of the voltage signal may be determined based on the acceleration voltage and landing energy of the charged particle beam. The first component of the voltage signal may include a voltage signal in the range of 5 kV to 10 kV, and the second component of the voltage signal may include a voltage signal in the range of -150 V to +150 V. The landing energy of the charged particle beam is in the range of 500 eV to 3 keV.

[0028] In some embodiments, the multiple focal planes include a first focal plane that coincides with a top surface of the sample and a second focal plane that is formed a distance below the first focal plane. The distance between the first focal plane and the second focal plane is dynamically adjusted based on the feature being imaged or the material of the sample. The controller may be configured to generate multiple image frames at each focal plane of the multiple focal planes of the sample and generate a 3D image of the sample by reconstructing the multiple image frames using a reconstruction algorithm.

[0029] In yet another aspect of the present disclosure, a non-transitory computer-readable medium is disclosed that includes a set of instructions executable by one or more processors of the apparatus to cause the apparatus to perform a method. The method may include irradiating a sample disposed on a stage with a charged particle beam, manipulating an electromagnetic field associated with the sample to adjust a focus of the charged particle beam relative to the sample, forming a plurality of focal planes substantially perpendicular to a primary optical axis of the charged particle beam based on the manipulation of the electromagnetic field, generating a plurality of image frames from the plurality of focal planes of the sample, one image frame of the plurality of image frames being associated with a corresponding focal plane of the plurality of focal planes, and generating a 3D image of the sample from the plurality of image frames and the corresponding focal plane information.

[0030]

[0030] In some embodiments, the set of instructions executable by one or more processors of the device may further cause the device to form a first focal plane of the plurality of focal planes that coincides with the top surface of the sample, and to form a second focal plane of the plurality of focal planes that is spaced a predetermined distance below the first focal plane.

[0031] In yet another aspect of the present disclosure, a method for determining vibrations of a charged particle beam device is disclosed. The method may include detecting a first vibration of an electro-optical component configured to direct a charged particle beam toward a sample, detecting a second vibration of an electromechanical component configured to hold the sample, and applying a vibration compensation signal to the electro-optical component to compensate for the first vibration and the second vibration based on the determined vibrations of the charged particle beam device. The method may further include adjusting a position of the sample relative to one or more axes, where adjusting the position of the sample causes vibrations of the electro-optical component and the electromechanical component. Detecting the first vibration may include detecting vibrations of the electro-optical component about one or more axes using a first sensor, where the first sensor includes an acceleration sensor mechanically coupled to the electro-optical component.

[0032] The acceleration sensor may include a piezoelectric sensor, a capacitive accelerometer, a microelectromechanical system (MEMS)-based accelerometer, or a piezoresistive accelerometer, where the first sensor is configured to generate a voltage signal based on a frequency of the detected first vibration. Detecting the second vibration may include detecting vibration of the electromechanical component in translational and rotational axes using the second sensor, where the second sensor includes a plurality of position sensors configured to generate a displacement signal based on the frequency of the detected second vibration. A first position sensor of the plurality of position sensors may be configured to detect vibration of the electromechanical component in a translational axis, and a second position sensor of the plurality of position sensors may be configured to detect vibration of the electromechanical component in a rotational axis. The method may further include receiving, by a first controller, the voltage signal and the displacement signal, and determining, using the first controller, a vibration compensation signal based on the received voltage signal and the displacement signal. Determining the vibration compensation signal may include identifying a plurality of vibration modes based on information related to the first vibration and the second vibration, estimating vibrations of the electro-optical component and the electro-mechanical component based on the identified plurality of vibration modes, determining vibrations in a plurality of axes based on the estimated vibrations of the electro-optical component and the electro-mechanical component, and determining a vibration compensation signal based on the determined vibrations in the plurality of axes. The vibration compensation signal may be determined to compensate for the vibration based on an estimation of predicted vibrations for a future time relative to a measurement time of the first vibration and the second vibration.

[0033] Identifying the plurality of vibration modes may include converting the voltage signals into corresponding distance signals. Identifying the plurality of vibration modes may further include decoupling a second vibration of the electromechanical component from a vibration of a housing of the electromechanical component. Estimating the vibration of the electro-optical component and the electromechanical component may include using a simulation model, where the simulation model may include a three-dimensional finite element model (3D-FEM), a finite difference model (FDM), or a mathematical analysis model. The method may further include receiving, by a second controller, the determined vibration compensation signal. The method may further include receiving, by the second controller, a beam scanning signal, and generating, by the second controller, a modified beam scanning signal based on the received beam scanning signal and the received vibration compensation signal. The method may further include generating, by a signal detector, a beam deflection signal based on the modified beam scanning signal, where the beam deflection signal is applied to the electro-optical component and used to adjust a characteristic of the charged particle beam incident on the sample. The beam deflection signal may be applied to a beam deflection controller associated with the electro-optical component, and the characteristics of the charged particle beam may include a beam scan speed, a beam scan frequency, a beam scan duration, or a beam scan range. The plurality of position sensors may be disposed on a surface of a housing of the electro-mechanical component, and the electro-optical component may include a charged particle column, and the electro-mechanical component includes a stage configured to hold the sample and movable in one or more of an X, Y, or Z axis.

[0034] In yet another aspect of the present disclosure, a charged particle beam system is disclosed. The charged particle beam system may include a first sensor configured to detect a first vibration of an electro-optical component of the charged particle beam system, a second sensor configured to detect a second vibration of an electromechanical component of the charged particle beam system, and a first controller including circuitry for generating a vibration compensation signal based on the detected first and second vibrations applied to the electro-optical component. The electro-optical component may include a charged particle column and configured to direct the charged particle beam toward a sample. The electromechanical component may include a stage configured to hold the sample and movable in one or more of the X, Y, or Z axes. Adjusting the position of the sample may cause vibrations of the electro-optical component and the electromechanical component.

[0035] The system may further include a housing configured to accommodate an electromechanical component of the charged particle beam device. The electromechanical component may be mechanically coupled to the housing such that moving the stage causes vibration of the housing. The electro-optical component may be mechanically coupled to the housing such that vibration of the housing causes a first vibration of the electro-optical component. The first sensor may be further configured to detect the first vibration of the electro-optical component about one or more axes. The first sensor includes an acceleration sensor mechanically coupled to the electro-optical component. The acceleration sensor may include a piezoelectric sensor, a capacitive accelerometer, a microelectromechanical system (MEMS)-based accelerometer, or a piezoresistive accelerometer. The first sensor may be configured to generate a voltage signal based on a frequency of the detected first vibration. The second sensor may be configured to detect a second vibration of the electromechanical component about the translational and rotational axes. The second sensor may include a plurality of position sensors configured to generate a displacement signal based on a frequency of the detected second vibration. A first position sensor of the plurality of position sensors may be configured to detect vibration of the electro-mechanical component in a translational axis, and a second position sensor of the plurality of position sensors may be configured to detect vibration of the electro-mechanical component in a rotational axis, and the first position sensor and the second position sensor may be disposed on a surface of a housing of the electro-mechanical component. The first controller may be further configured to receive the voltage signal and the displacement signal and to determine a vibration compensation signal based on the voltage signal and the displacement signal, and the first controller includes circuitry for identifying a plurality of vibration modes based on information related to the first vibration and the second vibration, estimating vibration of the electro-optical component and the electro-mechanical component based on the identified plurality of vibration modes, determining vibration in the plurality of axes based on the estimated vibration of the electro-optical component and the electro-mechanical component, and determining the vibration compensation signal based on the determined vibration in the plurality of axes.

[0036] Identifying the multiple vibration modes may include converting the voltage signals into corresponding distance signals. Identifying the multiple vibration modes may further include decoupling a second vibration of the electromechanical component from a vibration of a housing of the electromechanical component. Estimating the vibration of the electro-optical component and the electromechanical component may include using a simulation model, and the simulation model may include a three-dimensional finite element model (3D-FEM), a finite difference model (FDM), or a mathematical analysis model. The system may further include a second controller including circuitry for receiving the determined vibration compensation signal. The second controller may include circuitry for receiving the beam scanning signal and generating a modified beam scanning signal based on the received beam scanning signal and the vibration compensation signal. The system may further include a signal generator configured to generate a beam deflection signal based on the modified beam scanning signal. The beam deflection signal may be applied to the electro-optical component and may be configured to adjust a characteristic of the charged particle beam incident on the sample. The beam deflection signal may be applied to a beam deflection controller associated with the electro-optical component. The characteristics of the charged particle beam may include a beam scan speed, a beam scan frequency, a beam scan duration, or a beam scan range. The vibration compensation signal may be determined to compensate for the vibration based on an estimate of a predicted vibration for a future time relative to a measurement time of the first vibration and the second vibration.

[0037] In yet another aspect of the present disclosure, a non-transitory computer-readable medium is disclosed that includes a set of instructions executable by one or more processors of the apparatus to cause the apparatus to perform a method for determining vibrations of a charged particle beam device. The method may include detecting a first vibration of an electro-optical component configured to direct a charged particle beam toward a sample, detecting a second vibration of an electro-mechanical component configured to hold the sample, and applying a vibration compensation signal to the electro-optical component to compensate for the first vibration and the second vibration based on the determined vibration of the charged particle beam device.

[0038] The set of instructions executable by the one or more processors of the apparatus may further cause the apparatus to adjust a position of the sample relative to one or more axes, where adjusting the position of the sample causes vibrations of the electro-optical and electromechanical components. The set of instructions executable by the one or more processors of the apparatus may further cause the apparatus to determine a vibration compensation signal based on the voltage signal and the displacement signal. Determining the vibration compensation signal may include identifying a plurality of vibration modes based on information related to the first vibration and the second vibration, estimating vibrations of the electro-optical and electromechanical components based on the identified plurality of vibration modes, determining vibrations in the plurality of axes based on the estimated vibrations of the electro-optical and electromechanical components, and determining the vibration compensation signal based on the determined vibrations in the plurality of axes. The set of instructions executable by the one or more processors of the apparatus may further cause the apparatus to: receive, by the controller, a beam scanning signal; generate a modified beam scanning signal based on the received beam scanning signal and the vibration compensation signal; generate, by a signal generator, a beam deflection signal based on the modified beam scanning signal, the beam deflection signal being applied to an electro-optical component and configured to adjust a characteristic of the charged particle beam incident on the sample; and apply the beam deflection signal to a beam deflection controller associated with the electro-optical component. [Brief explanation of the drawings]

[0039] [Figure 1] FIG. 1 is a schematic diagram illustrating an exemplary electron beam inspection (EBI) system consistent with an embodiment of the present disclosure. [Figure 2]

[0040] FIG. 1 is a schematic diagram illustrating an exemplary imaging system consistent with an embodiment of the present disclosure. [Figure 3]

[0041] 1 is a schematic diagram of an exemplary charged particle beam system consistent with embodiments of the present disclosure. [Figure 4]

[0042] 1 is a schematic diagram of an exemplary charged particle beam system consistent with embodiments of the present disclosure. [Figure 5]

[0043] 1 is a flowchart illustrating an exemplary method of irradiating a sample, consistent with embodiments of the present disclosure. [Figure 6]

[0044] 1 is a flowchart illustrating an exemplary method of irradiating a sample, consistent with embodiments of the present disclosure. [Figure 7]

[0045] 1 is a flowchart illustrating an exemplary method of irradiating a sample, consistent with embodiments of the present disclosure. [Figure 8]

[0046] 1 is a schematic diagram of an exemplary charged particle beam system consistent with embodiments of the present disclosure. [Figure 9A]

[0047] 1 is a flowchart illustrating an exemplary method for focusing a charged particle beam onto a sample, consistent with embodiments of the present disclosure. [Figure 9B]

[0048] 1 is a flowchart illustrating an exemplary method for focusing a charged particle beam onto a sample, consistent with embodiments of the present disclosure. [Figure 10]

[0049] FIG. 1 is a schematic diagram illustrating an example configuration of a charged particle beam system including an electron beam inspection tool, consistent with an embodiment of the present disclosure. [Figure 11-AB]

[0050] 1 illustrates an image frame and corresponding focal plane of a feature on a sample, consistent with an embodiment of the present disclosure. [Figure 11-CD]

[0050] Figure 1 illustrates an image frame and corresponding focal plane of a feature on a sample, consistent with an embodiment of the present disclosure. [Figure 11-EF]

[0050] Figure 1 illustrates an image frame and corresponding focal plane of a feature on a sample, consistent with an embodiment of the present disclosure. [Figure 12]

[0051] FIG. 1 is a schematic diagram of process steps for generating a reconstructed 3D image from image frames captured at multiple focal planes, consistent with an embodiment of the present disclosure. [Figure 13]

[0052] 9 is a flowchart illustrating an exemplary method for generating a 3D image of a sample in the charged particle beam system of FIG. 8, consistent with an embodiment of the present disclosure. [Figure 14]

[0053] FIG. 1 is a schematic diagram illustrating the translation and rotation axes of a sample stage in a charged particle beam system consistent with an embodiment of the present disclosure. [Figure 15]

[0054] FIG. 1 is a schematic diagram illustrating an example configuration of a charged particle beam system including an electron beam inspection tool, consistent with an embodiment of the present disclosure. [Figure 16]

[0055] FIG. 1 is a schematic diagram illustrating steps of an exemplary algorithm for determining a vibration estimation and compensation signal consistent with an embodiment of the present disclosure. [Figure 17]

[0056] 16 is a flowchart illustrating an exemplary method for focusing a charged particle beam onto a sample in the charged particle beam system of FIG. 15, consistent with an embodiment of the present disclosure. DETAILED DESCRIPTION OF THE INVENTION

[0040]

[0057] Reference will now be made in detail to exemplary embodiments, example embodiments of which are illustrated in the accompanying drawings. The following description refers to the accompanying drawings, in which identical numbers in different drawings represent the same or similar elements unless otherwise indicated. The implementations described in the following description of exemplary embodiments do not represent all implementations consistent with the present disclosure. Rather, these implementations are merely examples of apparatus and methods consistent with the subject-related aspects recited in the appended claims. For example, while some embodiments are described in the context of utilizing electron beams, the present disclosure is not so limited. Other types of charged particle beams may be similarly applied. Furthermore, other imaging systems, such as optical imaging, light detection, x-ray detection, etc., may be used.

[0041]

[0058] Improved computing power in electronic devices can be achieved by dramatically increasing the packing density of circuit components such as transistors, capacitors, and diodes on IC chips while simultaneously miniaturizing the device's physical size. For example, in a smartphone, an IC chip (the size of a thumbnail) can contain over 2 billion transistors, each one 1 / 1000th the size of a human hair. Semiconductor IC manufacturing is, of course, a complex process involving hundreds of individual steps. An error in a single step can significantly affect the functionality of the final product. A single "killer defect" can cause device failure. The goal of a manufacturing process is to increase the overall yield of the process. For example, for a 50-step process to achieve a 75% yield, each individual step must have a yield greater than 99.4%; if the yield of an individual step is 95%, the overall process yield drops to 7%.

[0042]

[0059] As geometries shrink and the IC chip industry transitions to three-dimensional (3D) architectures (e.g., NAND gates, Fin field-effect transistors (FinFETs), and advanced dynamic random access memory (DRAM)), defect detection becomes more difficult and expensive at each lower node. While high process yields are desirable in IC chip manufacturing facilities, maintaining high wafer throughput, defined as the number of wafers processed per hour, is also essential. High process yields and high wafer throughput can be affected by the presence of defects, especially when the defects affect the overall device performance and process yield. Therefore, detecting and identifying micro- and nano-sized defects while maintaining high throughput is essential for high yields and low costs. In addition to defect detection and identification, SEM inspection tools can also be used to identify defect sources by providing high-resolution images combined with elemental analysis of the microstructures on the wafer.

[0043]

[0060] Whether identifying or imaging defects for routine in-line inspection with high-resolution SEM imaging, it should be understood that precise stage motion control is extremely important, especially when the dimensions of the inspection features or defects are tens of nanometers or less. In a high-throughput, high-resolution inspection environment, there may be various factors that can cause measurement errors and affect the imaging and defect detection capabilities of the inspection tool, such as instrument maintenance, sensor calibration, specimen tilt, manufacturing tolerances, and machining errors. In practice, the fabrication of very large-scale integrated (VLSI) circuits requires precise overlay of various layers within specified tolerance limits, making sample stage alignment and precise positioning extremely important. In some cases, the overall overlay tolerance required to manufacture modern integrated circuits can be less than 40 nm. For example, aligning a 200 mm wafer to such a tolerance can be equivalent to docking a 50 km iceberg with 1 cm accuracy.

[0044]

[0061] In some cases, a stage can move in six different axes of motion—three translational and three rotational—resulting in potential motion errors in each of the six axes. Pitch effects in the X and Y axes caused by linear stage motion can result in Abbe errors due to offsets between the plane of the measurement axes and the motion axes of the stage. Additionally, existing global and local Z-leveling techniques for stages may not be sufficient or feasible, in part due to reduced geometry and their impact on overall inspection throughput. Some embodiments of the high-precision three-dimensional stage control system proposed in this disclosure may significantly improve the accuracy of stage positioning and motion control by using high-control bandwidth signals and individually controllable piezoelectric actuators for Z-leveling.

[0045]

[0062] One of several ways to focus a charged particle beam (e.g., an electron beam) and thereby improve imaging resolution is by using opto-mechanical means, such as adjusting the stage height with a piezoelectric transducer. However, focusing capabilities using opto-mechanical techniques may be inadequate for some applications in nanofabrication and inspection of nanofabricated devices, for example, due to the constraints and associated errors of precise motion control, or the need to move the stage fast enough to enable real-time 3D imaging or achieve target throughput. Examples of sources of error include, but are not limited to, vibration, temperature gradients, miscalibration, etc. Therefore, it may be desirable to enhance existing focusing capabilities by allowing the system to further fine-tune the focus of the electron beam while addressing such issues.

[0046]

[0063] As the density of devices on IC chips increases, device architectures include vertically stacked components and multiple layers for advanced features. Inspection of such devices may require a greater depth of focus so that the top, bottom, and intermediate layers of features can be imaged simultaneously while extracting useful information. For example, measuring the critical dimensions of metal contact holes or detecting buried defect particles, among other things, may be useful for analyzing defects and developing process conditions based on information obtained from accurate imaging and measurement. Inspecting stacked structures, such as 3D NAND flash devices, using existing techniques may provide limited or inaccurate information, both of which may adversely affect the throughput and quality of manufactured devices. Therefore, it may be desirable to enable existing inspection tools with real-time 3D imaging capabilities to extend the imaging range while maintaining high imaging resolution, such as by adjusting voltages associated with a stage or lens to change the electromagnetic field and subsequently the focal depth of a charged particle beam.

[0047]

[0064] High-throughput wafer inspection in single-beam and multi-beam inspection systems can be facilitated by the ability to move samples very short distances, e.g., on the order of a few nanometers, with high accuracy and high speed. In some applications, vibrations associated with stage or SEM column movement can limit image resolution or inspection throughput, among other things. Existing systems can use vibration compensation methods to compensate for vibration-induced errors, such as compensation methods, which may not be sufficiently accurate due to improper detection of vibration, inaccurate compensation, measurement delays, an inability to accurately correct for vibration in real time, etc.

[0048]

[0065] In conventional charged particle beam inspection systems, position sensing systems are used to determine stage vibration or to position a sample along an axis. The position sensor is located on a chamber wall that is mechanically coupled to the stage so that stage vibration can be transmitted to the chamber. While the position sensor can accurately determine stage vibration relative to the chamber, vibrations of the chamber, the position sensor, or the beam column associated with the chamber may not be detected or may be detected with insufficient accuracy, or the vibration source may not be identified. In addition, the position sensor used may not detect vibration modes in the translational or rotational axes, resulting in under- or over-compensated vibration compensation signals. Therefore, it may be desirable to accurately detect, identify, isolate, and compensate for vibration-induced errors to minimize loss of image resolution. For example, it may be desirable to detect vibration and isolate the vibration component in the z dimension. The detected z vibration component can be analyzed, and z vibrations at future times relative to when the vibration was sensed can be predicted. Voltages associated with the stage or lens can be adjusted to change the electromagnetic field and, in turn, the focal depth of the charged particle beam to compensate for the predicted vibrations at the time the vibrations are predicted, resulting in an improved, accurate image.

[0049]

[0066] In one aspect of the invention, a charged particle beam system may be used to observe a wafer (wafer 203 in FIG. 2 ) disposed on a sample stage (such as stage 201 in FIG. 2 ). A position sensing system (including height sensor 340 and laser interferometer 350 in FIG. 3 ) may determine lateral and vertical displacements of the stage. In response to determining the lateral displacement, a beam control module (such as beam control module 365 in FIG. 3 ) may apply a first high-control bandwidth signal to a beam deflector (such as deflector array 320 in FIG. 3 ) to deflect a primary charged particle beam incident on the wafer along a plane substantially perpendicular to the charged particle beam. And, in response to determining the vertical displacement, the beam control module may apply a second high-control bandwidth signal to the stage to adjust the focus of the deflected charged particle beam along a plane substantially parallel to the charged particle beam. The charged particle beam system may further include a stage control module (such as the stage control module 362 in FIG. 3) for applying a third signal to the stage motion controllers (including the z-axis motion controllers 372_1, 372_2, and 372_3 in FIG. 3). Each of the z-axis motion controllers may be individually controlled to adjust Z-leveling of the stage so that the stage is substantially perpendicular to the optical axis of the primary charged particle beam 314.

[0050]

[0067] In another aspect of the present disclosure, a method for focusing a charged particle beam on a sample is disclosed. The method may include adjusting a location of a first focal point of the charged particle beam relative to the sample using a first component (e.g., an anode of a charged particle source) located upstream of a focusing component of an objective lens of a charged particle system. The location of the first focal point may also be adjusted by adjusting a position of a stage in the Z axis. The method may further include adjusting the first focal point to form a second focal point by adjusting an electromagnetic field of or associated with the sample. The electromagnetic field may be adjusted using a second component (e.g., a control electrode of the objective lens, a stage, or a wafer) located downstream of the focusing component of the objective lens of the charged particle system. Adjusting the second component may include applying a first component of an electrical signal to a control electrode of the objective lens to coarsely adjust the first focal point and a second component of an electrical signal to the stage to finely adjust the first focal point.

[0051]

[0068] In another aspect of the present disclosure, a method for focusing a charged particle beam onto a sample is disclosed. The method includes determining vibrations of a charged particle beam system and applying a vibration compensation signal to a beam column to compensate for the determined vibrations of the charged particle beam system. The method may further include detecting vibrations of the beam column (an electro-optical component) using an acceleration sensor mounted on the beam column and detecting vibrations of a stage (an electro-mechanical component) using a position sensor mounted in a containment chamber of the charged particle beam system. The method may further include identifying vibration modes of the beam column and stage in each of translational and rotational axes, estimating vibrations of the beam column and stage based on the identified vibration modes, and predicting vibrations of the beam column and stage based on the estimated vibrations. The method may further include generating a compensated beam scan signal based on the predicted vibrations and a beam scan signal, and forming a vibration compensation signal to be applied to the beam column of the charged particle beam system.

[0052]

[0069] According to an embodiment of the present disclosure, the X, Y, and Z axes are Cartesian coordinates: the primary optical axis of the charged particle beam device is along the Z axis, and the primary charged particle beam from the charged particle source travels along the Z axis.

[0053]

[0070] The relative dimensions of components in the figures may be exaggerated for clarity. In the following description of the figures, the same or similar reference numbers refer to the same or similar components or entities, and only the differences with respect to individual embodiments are described.

[0054]

[0071] As used herein, unless otherwise specified, the term "or" includes all possible combinations unless impracticable. For example, if it is specified that a database may include A or B, then the database may include A, or B, or A and B, unless otherwise specified or impracticable. As a second example, if it is specified that a database may include A, B, or C, then the database may include A, or B, or C, or A and B, or A and C, or B and C, or A, B, and C, unless otherwise specified or impracticable.

[0055]

[0072] Reference is now made to FIG. 1 , which illustrates an exemplary charged particle beam inspection (EBI) system 100 consistent with embodiments of the present disclosure. The EBI system 100 may be used for imaging. As shown in FIG. 1 , the EBI system 100 includes a main chamber 101, a load / lock chamber 102, an electron beam tool 104, and an equipment front-end module (EFEM) 106. The electron beam tool 104 is located within the main chamber 101. The EFEM 106 includes a first load port 106 a and a second load port 106 b. The EFEM 106 may include additional load port(s). The first load port 106 a and the second load port 106 b receive wafer FOUPs (front opening unified pods) containing wafers (e.g., semiconductor wafers or wafers made of other materials) or samples (wafers and samples may be used interchangeably) to be inspected. Lots containing multiple wafers may be loaded for processing as a batch.

[0056]

[0073] One or more robot arms (not shown) in the EFEM 106 may transfer the wafer to the load / lock chamber 102. The load / lock chamber 102 is connected to a load / lock vacuum pumping system (not shown) that removes gas molecules from the load / lock chamber 102 to reach a first pressure that is lower than atmospheric pressure. After the first pressure is reached, one or more robot arms (not shown) may transfer the wafer from the load / lock chamber 102 to the main chamber 101. The main chamber 101 is connected to a main chamber vacuum pumping system (not shown) that removes gas molecules from the main chamber 101 to reach a second pressure that is lower than the first pressure. After the second pressure is reached, the wafer is subjected to inspection by the electron beam tool 104. The electron beam tool 104 may be a single beam system or a multi-beam system.

[0057]

[0074] The controller 109 is electronically connected to the electron beam tool 104. The controller 109 may be a computer configured to perform various controls of the EBI system 100. Although the controller 109 is shown in FIG. 1 as being external to the structure including the main chamber 101, the load / lock chamber 102, and the EFEM 106, it is understood that the controller 109 may be part of the structure.

[0058]

[0075] FIG. 2 illustrates an exemplary imaging system 200 according to an embodiment of the present disclosure. The electron beam tool 104 of FIG. 2 may be configured for use in the EBI system 100. The electron beam tool 104 may be a single-beam device or a multi-beam device. As shown in FIG. 2, the electron beam tool 104 may include a motorized sample stage 201 and a wafer holder 202 supported by the motorized stage 201 for holding a wafer 203 to be inspected. The electron beam tool 104 further includes an objective lens assembly 204, an electron detector 206 (including electron sensor surfaces 206a and 206b), an objective aperture 208, a condenser lens 210, a beam-limiting aperture 212, a gun aperture 214, an anode 216, and a cathode 218. The objective lens assembly 204, in one embodiment, may include a modified swing objective retardation immersion lens (SORIL) including a pole piece 204a, a control electrode 204b, a deflector 204c, and an excitation coil 204d. The electron beam tool 104 may additionally include an energy dispersive X-ray spectrometer (EDS) detector (not shown) for characterizing materials on the wafer 203.

[0059]

[0076] A primary charged particle beam 220, e.g., an electron beam, may be emitted from the cathode 218 by applying a voltage between the anode 216 and the cathode 218. The primary electron beam 220 passes through a gun aperture 214 and a beam-limiting aperture 212, both of which may determine the size of the electron beam incident on a condenser lens 210, which is below the beam-limiting aperture 212. The condenser lens 210 focuses the primary charged particle beam 220 before the beam enters the objective aperture 208 and sets the size of the primary electron beam before entering the objective lens assembly 204. A deflector 204c deflects the primary electron beam 220 to facilitate beam scanning over the wafer. For example, in a scanning process, the deflector 204c may be controlled to sequentially deflect the primary electron beam 220 to different locations on the top surface of the wafer 203 at different times to provide data for image reconstruction of different portions of the wafer 203. Moreover, the deflector 204c may also be controlled to deflect the primary electron beam 220 to different sides of the wafer 203 at a location at different times to provide data for three-dimensional image reconstruction of the wafer structure at that location. Furthermore, in some embodiments, the anode 216 and the cathode 218 may be configured to generate multiple primary electron beams 220, and the electron beam tool 104 may include multiple deflectors 204c for simultaneously projecting the multiple primary electron beams 220 onto different portions / sides of the wafer 203 to provide data for image reconstruction of the different portions of the wafer 203.

[0060]

[0077] The excitation coil 204d and the pole piece 204a generate a magnetic field that starts at one end of the pole piece 204a and ends at the other end of the pole piece 204a. A portion of the wafer 203 being scanned by the primary electron beam 220 may be immersed in the magnetic field and may become charged, which creates an electric field. The electric field reduces the energy of the primary electron beam 220 that impinges near the surface of the wafer 203 before it impacts the wafer 203. The control electrode 204b is electrically isolated from the pole piece 204a and controls the electric field on the wafer 203 to prevent micro-arching of the wafer 203 and ensure proper beam focus.

[0061]

[0078] Upon receiving the primary electron beam 220, a secondary electron beam 222 may be emitted from a portion of the wafer 203. The secondary electron beam 222 may form a beam spot on the sensor surfaces 206a and 206b of the electron detector 206. The electron detector 206 may generate a signal (e.g., voltage, current, etc.) representing the intensity of the beam spot and provide the signal to the image processing system 250. The intensity of the secondary electron beam 222 and the resulting beam spot may vary depending on the external or internal structure of the wafer 203. Moreover, as described above, the primary electron beam 220 may be projected onto different locations on the top surface of the wafer or onto different sides of the wafer at specific locations to generate secondary electron beams 222 (and resulting beam spots) of different intensities. Therefore, by mapping the intensity of the beam spot to locations on the wafer 203, the image processing system may reconstruct an image reflecting the internal or external structure of the wafer 203.

[0062]

[0079] The imaging system 200 may be used to inspect the wafer 203 on the stage 201 and, as described above, includes the electron beam tool 104. The imaging system 200 may also include an image processing system 250, which includes an image acquirer 260, storage 270, and a controller 109. The image acquirer 260 may include one or more processors. For example, the image acquirer 260 may include a computer, a server, a mainframe host, a terminal, a personal computer, any type of portable computing device, etc., or a combination thereof. The image acquirer 260 may connect to the detector 206 of the electron beam tool 104 via a medium such as an electrical conductor, a fiber optic cable, a portable storage medium, IR, Bluetooth, the Internet, a wireless network, wireless communication, or a combination thereof. The image acquirer 260 may receive signals from the detector 206 and construct an image. Thus, the image acquirer 260 may acquire an image of the wafer 203. The image acquirer 260 may also perform various post-processing functions, such as generating contour lines and overlaying indicators on the acquired image. The image acquirer 260 may be configured to perform adjustments, such as brightness and contrast, on the acquired image. The storage 270 may be a storage medium, such as a hard disk, random access memory (RAM), or other type of computer-readable memory. The storage 270 may be coupled to the image acquirer 260 and may be used to store raw scanned image data as original images and to store processed images. The image acquirer 260 and the storage 270 may be connected to the controller 109. In some embodiments, the image acquirer 260, the storage 270, and the controller 109 may be integrated together as a single control unit.

[0063]

[0080] In some embodiments, the image acquirer 260 may acquire one or more images of the sample based on an imaging signal received from the detector 206. The imaging signal may correspond to a scanning motion for performing charged particle imaging. The acquired image may be a single image including multiple imaging areas. This single image may be stored in the storage 270. This single image may be an original image that may be divided into multiple regions. Each of these regions may include an imaging area that encompasses a feature of the wafer 203.

[0064]

[0081] Reference is now made to FIG. 3 , an exemplary charged particle beam system consistent with embodiments of the present disclosure. In some embodiments, the charged particle beam system 300 includes a charged particle beam column 310, a primary charged particle beam 314 having an optical axis 312, a focusing lens 315 (similar to focusing lens 210 of FIG. 2 ), a deflector array 320 that deflects the primary charged particle beam 314 to form a deflected charged particle beam 330 that irradiates a wafer 203 disposed on a stage 201, a height sensor 340, a laser interferometer 350, a system control module 360 ​​including a stage control module 362 and a beam control module 365, a beam deflection controller 367, a stage motion controller 370 including a z-axis motion controller 372, and an XY-axis motion controller 374. Alternatively, the charged particle beam system 300 can be part of the imaging system 200 of FIG. 2 or the EBI system 100 of FIG. 1 . It should be understood that in the context of this disclosure, charged particles and electrons may be used interchangeably. Similarly, elements of the claimed apparatus or methods that describe charged particle beams may be used interchangeably with electron beams, where appropriate.

[0065]

[0082] In some embodiments, the charged particle beam system 300 may include an electron beam system or an electron beam inspection system. The charged particle beam system 300 may include a charged particle beam column 310, which may house a cathode 218, an anode 216, a gun aperture 214, and a beam-limiting aperture 212, as shown in FIG. 2. The primary charged particle beam 314 may be emitted from the cathode 218 by applying a voltage between the anode 216 and the cathode 218. In some embodiments, the primary charged particle beam 314 may be an electron beam passing through the gun aperture 214 and the beam-limiting aperture 212, both of which may determine the size of the charged particle beam incident on the condenser lens 210 (similar to the condenser lens 315 in FIG. 3 ) located below the beam-limiting aperture 212. The deflector array 320 may deflect the primary charged particle beam 314 to facilitate beam scanning over the wafer 203 .

[0066]

[0083] The deflector array 320 may include a single deflector, multiple deflectors, or an array of deflectors for deflecting the primary charged particle beam 314 from the optical axis 312. The beam deflection may be configured to scan the primary charged particle beam 314 across the wafer 203 during irradiation or inspection. Deflecting the primary charged particle beam 314 from the optical axis 312 may introduce additional aberrations, resulting in pattern distortion. Deflecting the primary charged particle beam 314 may be done electrostatically or magnetically. Magnetic deflectors allow for longer range deflection than electrostatic deflectors, but their frequency response may be limited due to the inductance of the magnetic coils and eddy currents introduced by the magnetic field.

[0067]

[0084] In some embodiments, the charged particle beam system 300 may include a source conversion unit (not shown in FIG. 3). The source conversion unit may include an image forming element array (not shown in FIG. 3), an aberration compensator array, and a beam-limiting aperture array (e.g., including the beam-limiting aperture 212 of FIG. 2). The image forming element array may include multiple micro-deflectors or micro-lenses for forming multiple parallel images (virtual or real images) of multiple beamlets of the primary electron beam 314. The beam-limiting aperture array may limit multiple beamlets. It should be understood that the source conversion unit 120 may be configured to handle any number of beamlets.

[0068]

[0085] The collector lens 315 may be configured to focus the primary charged particle beam 314. In some embodiments, the collector lens 315 may be further configured to adjust the current of the primary beamlets of the primary charged particle beam 314 downstream of the source conversion unit by varying the focusing power of the collector lens 315. Alternatively, the current may be varied by changing the radial size of the beam-limiting apertures 212 in the beam-limiting aperture array corresponding to the individual primary beamlets.

[0069]

[0086] In some embodiments, the charged particle beam system 300 may include a primary projection optical system (not shown in FIG. 3 ). The primary projection optical system may include the objective lens assembly 204, a beam separator, and a deflection scanning unit (e.g., the deflector array 320 shown in FIG. 3 ). The beam separator may be, for example, a Wien filter including electrostatic deflectors that generate an electrostatic dipole field E1 and a magnetic dipole field B1 (both not shown in FIG. 3 ). During operation, the beam separator may be configured to exert an electrostatic force on individual charged particles of the primary charged particle beam 314 by the electrostatic dipole field E1. The electrostatic force is equal in magnitude but opposite in direction to the magnetic force exerted on individual electrons by the magnetic dipole field B1 of the beam separator. Therefore, the primary charged particle beam 314 may pass at least substantially straight through the beam separator with at least substantially zero deflection angle. In some embodiments, the deflection scanning unit, during operation, is configured to deflect the primary charged particle beam 314 and cause the deflected charged particle beam 330 to scan the probe spot over a respective scan area on the wafer 203.

[0070]

[0087] In practice, the wafer 203 may be observed at high magnification in the charged particle beam system 300 or the EBI system 100, and the stage 201 may stably support the wafer 203 and smoothly move along the horizontal XY axes, the vertical Z axis, stage tilt, or stage rotation. Movement in the X and Y axes may be used to select the field of view (FOV), while movement in the Z axis may be required to change the image resolution, depth of focus, etc. The stage 201 may be, for example, a eucentric stage. With a eucentric stage, the observation area and focus on the wafer surface do not shift while tilting the wafer 203.

[0071]

[0088] In some embodiments, a position sensing system (not shown in FIG. 3) may be used to determine the displacement of the stage 201. The position sensing system may include a height sensor 340 and a laser interferometer 350. It should be understood that the position sensing system may also include two or more height sensors 340, two or more laser interferometers 350, and other suitable components, such as signal amplifiers, bandpass filters, data storage units, data processing units, etc.

[0072]

[0089] In some embodiments, the height sensor 340 may be used to determine the longitudinal displacement of the stage 201. As referred to herein, the vertical displacement of the stage 201 may correspond to the difference between the target position and the actual position of the stage 201 in the Z-axis. An optical height sensor, such as the height sensor 340 shown in FIG. 3, may include a laser diode sensor assembly including a one-dimensional position-sensitive detector (1-D PSD), a linear array of photodiodes, or the like. The height sensor 340 may communicate with a system control module 360 ​​(described in more detail below) so that the output of the height sensor 340 may be analyzed and used to further adjust the stage position. In some embodiments, the output data from the height sensor 340 may be used to modify the beam focus by applying a voltage to the stage to create an adjustable electric field at the surface of the sample, by adjusting the current applied to the objective lens assembly 204, or by applying voltages to the stage and the objective lens assembly 204. It will be understood that other suitable means of focusing the incident beam may be used. One or more optical height sensors may be used based on the complexity and accuracy of the height sensing desired, such as height sensor 340. Other height sensing technologies may be used as appropriate.

[0073]

[0090] In some embodiments, the vertical displacement of the stage 201 may be periodically determined for instrument calibration based on height measurements or height sensing of a standard specimen. For example, a wafer 203 containing patterned standard features, such as metal lines, a photoresist layer, a reflective film deposited on the wafer 203, etc., may be used to calibrate an instrument, a sensor, a motor, or a stage.

[0074]

[0091] High-throughput inspection of wafers in production facilities such as wafer fabs may require the stage 201 to move quickly and accurately in a repeating stop-and-go motion. The stop-and-go motion may include multiple cycles of high acceleration, deceleration, and rest of the stage 201, covering distances on the order of a few microns or nanometers. Moving the stage 201 at high speeds and accelerations may generate vibrations due to system dynamics, which in turn may create dynamic resonances within the system, e.g., constructively interfering vibration waves may cause higher amplitude vibrations throughout the charged particle beam system 300. Vibrations generated by the moving stage 201 may result in translation or displacement errors in two or more axes. For example, during inspection of dies on a wafer 203, the moving stage 201 in the X and Y axes may create dynamic resonances with other moving or non-moving components, causing stage vibrations in the Z axis. Accurate positioning of the stage 201 may require precise position measurement techniques, such as optical height sensors using lasers.

[0075]

[0092] In some embodiments, the laser interferometer 350 may be used to measure translational displacements in the X and Y axes and for precise positioning of the stage 201 in the X and Y axes. Laser interferometer displacement measurement techniques are often used as a high precision displacement measurement means for controlling the movement of equipment, such as steppers, and for controlling X and Y stages used in photolithography processes for fabricating semiconductor devices.

[0076]

[0093] In some embodiments, the laser interferometer 350 may be, for example, a homodyne laser interferometer or a heterodyne laser interferometer. A homodyne laser interferometer uses a single-frequency laser source, whereas a heterodyne laser interferometer uses a laser source with two closely spaced frequencies. The laser source may include a He-Ne gas laser emitting laser light at a wavelength of 633 nm. Other laser sources with single or multiple wavelength or frequency emissions may also be used. In some embodiments, two or more laser interferometers may be used. A combination of a homodyne laser interferometer and a heterodyne laser interferometer may be used in the system.

[0077]

[0094] In some embodiments, the laser interferometer 350 may be used to determine the lateral displacement of the stage 201. As referred to herein, the lateral displacement may correspond to the difference between the target position and the actual position of the stage 201 in at least one of the X and Y axes. In practice, two or more laser interferometers (such as the laser interferometer 350 shown in FIG. 3) may be used in the system to determine the lateral displacement. Because the deflection of the primary charged particle beam 314 is limited to a small area, precise mechanical stage positioning may need to be combined with beam deflection to pattern large features by exposing and stitching together multiple deflection fields. This may be achieved by using two laser interferometers (such as the laser interferometer 350) to measure the stage position in the X and Y axes. In some embodiments, the two split laser beams may be directed to a reference mirror and a stage-mounted mirror in each direction, and the interferometer may then compare the position of the stage mirror with the position of the reference mirror to detect and correct any stage position error. For example, one laser interferometer for the X axis and a second laser interferometer for the Y axis. In some embodiments, two or more laser interferometers may be used for a single axis, such as the X or Y axis. Other suitable techniques may also be used.

[0078]

[0095] 3 , the charged particle beam system 300 may include a system control module 360. The system control module 360 ​​may include a stage control module 362 and a beam control module 365. The system control module 360 ​​may be configured to communicate with the height sensor 340, the laser interferometer 350, and the stage motion controller 370. The system control module 360 ​​may be configured to receive signals from the height sensor 340 and process the received signals based on the determined vertical displacement of the stage 201. The system control module 360 ​​may further be configured to receive signals from the laser interferometer 350 and process the received signals based on the determined lateral displacement of the stage 201. In some embodiments, the system control module 360 ​​may include a user interface (not shown) for receiving user input based on the determined lateral and vertical displacement of the stage 201. The user interface may be, for example, a visual touch screen, a screen with user controls, an audio / visual interface, etc.

[0079]

[0096] In some embodiments, system control module 360 ​​may include a stage control module 362 and a beam control module 365. Stage control module 362 may be, for example, a circuit board containing individual circuits for stage positioning and motion control. Other components may also be mounted on the circuit board, including sequencer circuits, timer circuits, signal processing circuits, etc.

[0080]

[0097] In some embodiments, the stage control module 362 of the system control module 360 ​​may include signal processing circuitry. The signal processing circuitry of the stage control module 362 may be configured to receive signals from the height sensor 340 or the laser interferometer 350. In some embodiments, the stage control module 362 may be configured to receive signals from the laser interferometer 350. The signal processing circuitry may determine a degree of vertical displacement of the stage 201 or a degree of lateral displacement of the stage 201 based on the received signals. The received signals may be, for example, optical signals, electrical signals, or a combination thereof.

[0081]

[0098] In some embodiments, the system control module 360 ​​may include a beam control module 365, also referred to herein as a controller, that includes a beam deflection controller 367. In some embodiments, the beam deflection controller 367 may be configured to apply a first signal to deflect the primary charged particle beam 314 incident on the sample (e.g., wafer 203) to at least partially compensate for lateral displacement of the stage 201. The beam deflection controller 367 may be configured to apply a second signal to adjust the focus of the deflected charged particle beam 330 incident on the wafer 203 to at least partially compensate for vertical displacement of the stage.

[0082]

[0099] In some embodiments, the beam deflection controller 367 may be configured to dynamically adjust at least one of the first signal and / or the second signal during the scanning of the primary charged particle beam 314 over the wafer 203. As used herein, dynamically adjusting a signal refers to continuously and repeatedly adjusting a signal while a sample is being scanned or inspected. For example, the position of the stage 201 may be constantly monitored, measured, recorded, and communicated to a controller, such as the beam deflection controller 367. Upon receiving updated position information, including lateral displacement, vertical displacement, and / or pitch and roll error information, the beam deflection controller 367 may adjust the signal to at least partially compensate for the displacement based on the received information. As the scanning of the wafer continues, stage position and displacement information may be continuously collected, exchanged, and used by the beam deflection controller to adjust the signal.

[0083]

[0100] The beam deflection controller 367 may be a control loop feedback mechanism including, for example, a proportional-integral-derivative (PID) controller, a proportional-integral (PI) controller, or a proportional controller (P), etc. In some embodiments, the laser interferometer 350 may be in direct communication with the beam control module 365 or beam deflection controller 367 configured to deflect the primary charged particle beam 314 incident on the wafer 203.

[0084]

[0101] In some embodiments, the laser interferometer 350 may be in communication with the stage control module 362 or the beam control module 365 (not shown in FIG. 3 ). In some embodiments, the laser interferometer 350 may be in communication with the beam control module 365 via the stage control module 362. For example, the laser interferometer 350 may be in communication with signal processing circuitry (not shown) of the stage control module 362 to generate signals that cause the beam control module 365 to deflect an incident beam corresponding to the determined lateral displacement or position of the stage 201. At least partially compensating for lateral displacement of the stage in the X and Y axes is sometimes referred to herein as XY dynamic compensation. Although FIG. 3 illustrates one laser interferometer 350 configured to determine the position or lateral displacement of the stage 201, two or more interferometers may be used, if desired.

[0085]

[0102] In some embodiments, the electrical signals applied by the beam control module 365 to the deflector array 320 may include signals having a control bandwidth in the range of 10 kHz to 50 KHz. As used herein, the bandwidth ω of a control system may be defined as the frequency range over which the magnitude of the closed-loop frequency response is greater than −3 dB in the frequency domain.

[0086]

[0103] Image resolution is directly dependent on the position of the sample or wafer 203. Repeatability and stability of the stage position can be crucial to image quality in addition to resolution. Movement or small vibrations of the stage 201 or wafer 203 during scanning can significantly affect image quality and can adversely affect the defect detection ability of the inspection tool. Image distortion can be avoided if the sample does not drift once the target position is reached. The positioning stage, e.g., stage 201, may need to move smoothly at speeds of several nanometers per second (nm / s).

[0087]

[0104] In some embodiments, the stage motion controller 370 may control the movement of the stage 201 in the X, Y, or Z axis. The stage motion controller 370 may include a Z-axis motion controller 372 for moving the stage 201 in the Z axis and an XY-axis motion controller 374 for moving the stage 201 in at least one of the X and Y axes. The stage motion controller 370 may include, for example, piezoelectric step drives and actuators, ultrasonic piezoelectric motors, piezoelectric motors, piezoelectric actuators, etc. In some embodiments, the stage motion controller 370 may communicate with and receive signals from the stage control module 362 based on the determined vertical or lateral displacement of the stage 201. The Z-axis motion controller 372 may further include two or more piezoelectric drives or actuators, as shown in FIG. 3 . The XY-axis motion controller 374 may also include two or more piezoelectric drives or actuators.

[0088]

[0105] To improve image resolution and contrast, a user may apply beam modifying voltages to decrease or increase the beam energy of the incident beam on the wafer 203. In some embodiments, the stage 201 may be held at a high bias voltage, so that charged particles leaving the charged particle beam column 310 are decelerated before they reach the wafer 203 or the stage 201. For example, in a secondary electron microscope, if the high voltage (the acceleration voltage applied in the column) is −5 kV and the stage bias is −4 kV, electrons are first accelerated to an energy of 5 keV in the column and then decelerated by 4 keV after leaving the column, so that the effective high voltage is −1 kV without beam deceleration. In some embodiments, the stage 201 may be held at a high bias voltage, so that charged particles leaving the charged particle beam column 310 are accelerated before they reach the wafer 203 or the stage 201. Applying a stage bias may be used to modify the beam energy and focus of the incident charged particle beam in the Z-axis. The incident charged particle beam may include the primary charged particle beam 314 or the deflected charged particle beam 330.

[0089]

[0106] In some embodiments, the voltage signal applied to the stage 201 via the stage motion controller 370 may be an alternating current (AC) voltage signal, for example, as illustrated in Figure 3. The applied voltage signal may be based on the determined vertical displacement of the stage 201 to at least partially compensate for the vertical displacement. At least partially compensating for the vertical displacement of the stage in the Z axis may also be referred to herein as Z dynamic compensation.

[0090]

[0107] In some embodiments, the voltage signal may include a signal having a control bandwidth of 50 kHz to 200 kHz, 60 kHz to 180 kHz, 70 kHz to 160 kHz, 80 kHz to 140 kHz, 90 kHz to 120 kHz, 100 kHz to 110 kHz, or any suitable range. In some embodiments, a preferred control bandwidth for the voltage signal applied to stage 201 may be 100 kHz.

[0091]

[0108] In practice, moving the stage 201 in any of the X, Y, and Z axes can result in a pitch effect. In particular, the pitch effect in the X and Y axes can cause an Abbe error, which can result in inaccurate stage positioning if not taken into account. As referred to herein, the pitch effect of the stage 201 in the X axis can be defined as the angular rotation or tilt of the stage 201 about the Y axis, and the pitch effect of the stage 201 in the Y axis can be defined as the angular rotation or tilt of the stage 201 about the X axis. It is understood that angular rotation about the X axis is also referred to as roll. During scanning of a wafer 203 placed on the stage 201, pitch effect compensation in the X and Y axes can require simultaneous and continuous compensation of lateral displacement (X and Y axes) and vertical displacement (Z axis). The vertical displacement can be compensated for by adjusting the focus of the incident beam on the wafer 203 or by adjusting the position of the stage 201 in the Z axis. In some embodiments, the measured x and y coordinates can be corrected based on the Abbe error determined from the pitch effect in the X and Y axes. The corrected x-y coordinates of the stage 201 may include displacement due to pitch effects. The beam deflection controller 367, the beam control module 365, and the stage control module 362 may communicate with one or more laser interferometers to receive updated stage position information.

[0092]

[0109] In some embodiments, a laser interferometer (such as laser interferometer 350 in FIG. 3) may be configured to measure the compensation necessary to account for pitch effects in the X and Y axes. For example, charged particle beam system 300 may include three laser interferometers, each performing a predetermined function. A first laser interferometer may be used to determine lateral displacement in the X axis, a second laser interferometer may be used to determine lateral displacement in the Y axis, and a third laser interferometer may be used to determine pitch effects in the X and Y axes. It should be understood that four or more laser interferometers may be used, as needed.

[0093]

[0110] 4, z-axis motion controller 372 may include three z-axis motion controllers, such as actuators 372_1, 372_2, and 372_3, each configured to individually communicate with stage control module 362. It should be understood that more z-motion controllers may be used as needed. For example, a stage 201 holding a 300 mm wafer may utilize more z-motion controllers compared to a stage holding a 200 mm wafer, or a stage 201 of an inline charged particle beam inspection tool may utilize more z-motion controllers compared to an offline tool. Individual control of each of the z-motion controllers, such as actuators 372_1, 372_2, and 372_3, may support Z-leveling of stage 201.

[0094]

[0111] In some embodiments, precise positioning of the stage 201 may include precise leveling of the stage so that the stage 201, and therefore the wafer 203 disposed on the stage 201, is perpendicular to the optical axis 312 of the charged particle beam system 300. The leveling of the stage 201 may be constantly monitored by height sensor 340. Upon determining that the stage 201 is non-planar based on signals received from the height sensor 340, the stage control module may generate a signal configured to move one or more z-motion controllers (such as actuator 372_1) to correct the stage leveling. Multiple height sensors may be used to monitor the leveling, vertical displacement, and stage position in the Z-axis. The stage control module 362 may be configured to receive signals from each of the multiple height sensors.

[0095]

[0112] In some embodiments, the stage control module 362 further includes signal processing circuitry 410 including one or more components, such as a signal converter 415, configured to convert optical signals into electrical signals before processing the signals to generate output signals. The signal processing circuitry 410 may be, for example, a processor, a microprocessor, a control circuit, an application specific integrated circuit (ASIC), an integrated circuit, a computing device, a computer, a controller, etc. Other suitable devices and modules may also be used.

[0096]

[0113] In some embodiments, the signal processing circuit 410 may include a signal summarization circuit 412 configured to combine multiple signals from the height sensor 340 into a single signal. In some embodiments, the signal summarization circuit 412 may be configured to receive one or more signals from the signal converter 415. In some embodiments, the signal summarization circuit 412 may include a multiplexer circuit configured as a multiple-input, single-output switch. For example, the signal summarization circuit 412 may receive multiple input signals from the height sensor 340, each representing the stage height at a particular spot on the wafer 203. In some embodiments, the signal summarization circuit 412 may receive multiple signals from each of the multiple height sensors and process the received signals to determine whether the stage 201 is leveled. In some embodiments, the multiple signals from the height sensor 340 may be used to determine the vertical displacement or position of the stage 201.

[0097]

[0114] In some embodiments, the signal aggregation circuitry 412 may include a code division multiplexer, a frequency division multiplexer, a time division multiplexer, a wavelength division multiplexer, a statistical multiplexer, etc. In some embodiments, the multiplexer circuitry may include, for example, a 2-to-1 multiplexer, a 4-to-1 multiplexer, an 8-to-1 multiplexer, a 16-to-1 multiplexer, etc. Other types and configurations of signal processing circuitry may also be used.

[0098]

[0115] In some embodiments, the stage motion controller 370 may include a signal separation circuit 414. The signal separation circuit may be, for example, a demultiplexer circuit configured as a single-input, multiple-output switch. The signal separation circuit 414 may be configured to receive a single output signal from the signal aggregation circuit 412 and generate multiple output signals for actuating one or more z-axis motion controllers 372 or XY-axis motion controllers 374. For example, if the control bandwidth of the voltage signal applied to the stage 201 is 100 kHz, the voltage signal may include three separate signals embedded therein, one for each of the three z-axis motion controllers.

[0099]

[0116] In some embodiments, the stage motion controller 370 may be configured to receive signals from the signal summarization circuit 412. The stage motion controller 370 may process the received signals based on the determined lateral or vertical displacement and any necessary compensation.

[0100]

[0117] In some embodiments, each of multiple output signals of the signal separation circuit 414 may control a z-axis motion controller. For example, as illustrated in FIG. 4, each output signal is associated with a respective z-axis motion controller. In some embodiments, two output signals may be combined to control one z-axis motion controller. Alternatively, one output signal from the signal separation circuit 414 may control two z-axis motion controllers. It should be understood that many combinations of output signals associated with z-axis motion controllers may be possible.

[0101]

[0118] In some embodiments, the output signal from the signal isolation circuit 414 may control an XY axis motion controller 374 based on the determined lateral displacement of the stage 201 via the laser interferometer 350. The stage motion controller 370 may include other circuits and components for routing signals, adjusting signal timing, filtering signals, etc.

[0102]

[0119] In some embodiments, the signal summing circuit 412 and the signal separation circuit 414 may include functional logic gates, such as, for example, AND, OR, NAND, NOR, or combinations thereof. The combinational logic gates may interface with one or more of the system control module 360 ​​or the stage operation controller 370.

[0103]

[0120] In some embodiments, Z-axis leveling of the stage 201 may be achieved by controlling the height of a vertical actuator, e.g., a piezoelectric motor, with geometric model information for calculating actuation output. The geometric model may include a mechanical model of the stage, a computer-aided drawing (CAD) of the stage, a simulation of the stage dimensions, and actuation of the stage movement.

[0104]

[0121] FIG. 5 is a flowchart illustrating an exemplary method of irradiating a sample with a charged particle beam using a charged particle beam system consistent with embodiments of the present disclosure. The method of observing a sample may be performed by the charged particle beam system 300 of FIG. 3, the charged particle beam system 800 of FIG. 8 (described below), or the EBI system 100 of FIG. 1. It is understood that the charged particle beam system may be controlled to observe, image, and inspect a wafer (e.g., wafer 203 of FIGS. 2-3) or a region of interest on the wafer. Imaging may include scanning the wafer to image at least a portion of the wafer, a pattern on the wafer, or the wafer itself. Inspecting the wafer may include scanning the wafer to inspect at least a portion of the wafer, a pattern on the wafer, or the wafer itself.

[0105]

[0122] In step 510, a primary charged particle beam (e.g., primary charged particle beam 220 in FIG. 2) is generated from a charged particle source. In some embodiments, a charged particle beam may refer to a spatially localized group of charged particles having approximately the same kinetic energy and direction. The charged particles may include electrons, protons, or ions. The charged particle source may be, for example, thermionic emission of electrons from a tungsten or lanthanum hexaboride (LaB6) cathode or field-induced emission of electrons from a tungsten / zirconium oxide (ZrO2) cathode. The charged particle beam may include charged particles with high kinetic energy due to a high accelerating field that directs the charged particles toward the sample. The kinetic energy of the charged particles may range from 0.2 to 40 keV or more. In some embodiments, the primary charged particle beam may have an optical axis (e.g., optical axis 312) along which the beam travels toward a wafer or a stage (e.g., stage 201 in FIGS. 2-3).

[0106]

[0123] In step 520, a lateral displacement of the stage may be determined. As used herein, lateral displacement may refer to the difference between the current position of the stage and the target position in the X and Y axes. In a charged particle beam system, there may be many factors that cause lateral displacement of the stage, such as mechanical vibrations, electromagnetic interference from stray magnetic fields, temperature changes due to lens heating, errors due to stage tilt, etc.

[0107]

[0124] In some embodiments, the lateral displacement of the stage may be determined using precision optical position sensing technology. A laser interferometer (e.g., laser interferometer 350 in FIG. 3) may be used to determine the lateral displacement of the stage in the XY axes. The one or more laser interferometers may be in direct communication with a beam control module (e.g., beam control module 365 in FIG. 3) or indirectly in communication with the beam control module via a stage control module (e.g., stage control module 362 in FIG. 3). The one or more laser interferometers may be configured to determine the lateral displacement of the stage based on signals detected by photodetectors of the laser interferometers. In some embodiments, the beam control module, the stage, and the laser interferometers may form a closed feedback control loop.

[0108]

[0125] In step 530, upon determining the lateral displacement of the stage, the beam deflection controller of the beam control module may apply a signal to a primary beam deflector (e.g., deflector array 320 of FIG. 3). The applied signal may deflect the primary charged particle beam in the X or Y axis, or both, to at least partially compensate for the lateral displacement of the stage. The applied signal may include an electrical signal having a bandwidth in the range of 10 kHz to 50 kHz. In a preferred embodiment, the bandwidth of the applied signal may be 30 kHz.

[0109]

[0126] 6 is a flowchart illustrating an exemplary method of irradiating a sample with a charged particle beam using a charged particle beam system consistent with embodiments of the present disclosure. The method of observing a sample may be performed by the charged particle beam system 300 of FIG. 3 or the EBI system 100 of FIG. 1.

[0110]

[0127] Similar to step 510, in step 610, a primary charged particle beam (e.g., primary charged particle beam 220 of FIG. 2) is generated from a charged particle source. The primary charged particle beam may be, for example, an electron beam generated from an electron source. The electron source may include, but is not limited to, thermionic emission of electrons from a tungsten filament or LaB6 cathode, or field emission of electrons from a tungsten / ZrO2 cold cathode.

[0111]

[0128] In step 620, the vertical displacement of a stage (e.g., stage 201 in FIGS. 2-3) may be determined. As used herein, vertical displacement may refer to the difference between the current position and the target position of the stage in the Z-axis. In a charged particle beam system, there may be many factors that cause vertical displacement of the stage. For example, mechanical vibrations, electromagnetic interference from stray magnetic fields, stage motion calibration errors, piezoelectric motor calibration errors, etc.

[0112]

[0129] In some embodiments, vertical displacement of the stage may be determined using precision optical position sensing techniques using an optical height sensor (e.g., height sensor 340 in FIG. 3). The height sensor may include a laser diode assembly including a laser source that irradiates laser light having a predetermined emission wavelength onto the stage or onto a wafer (e.g., wafer 203 in FIGS. 2-3) placed on the stage, and a laser detector configured to detect the reflected laser. The height sensor may be in communication with a stage control module (e.g., stage control module 362 in FIG. 3), a beam control module (beam control module 365 in FIG. 3), or both.

[0113]

[0130] In step 630, upon determining the vertical displacement of the stage, the beam deflection controller (e.g., beam deflection controller 367 of FIG. 3) may apply a signal to the stage to move the stage along the Z axis and thereby adjust the position of the focal plane of the primary charged particle beam in the Z axis. In some embodiments, the vertical movement of the stage may be performed, at least in part, using an actuator, such as, for example, a piezoelectric motor, a piezoelectric actuator, or an ultrasonic piezoelectric motor, or a combination thereof. The applied signal may include a voltage signal having a bandwidth in the range of 50 kHz to 200 kHz. In a preferred embodiment, the bandwidth of the applied signal may be 100 kHz.

[0114]

[0131] In some embodiments, the applied signal may decelerate or accelerate the primary charged particle beam towards the stage based on the polarity of the signal, modifying the focus of the primary charged particle beam incident on the wafer.

[0115]

[0132] 7 is a flowchart illustrating an exemplary method of irradiating a sample with a charged particle beam using a charged particle beam system consistent with embodiments of the present disclosure. The method of observing a sample may be performed by the charged particle beam system 300 of FIG. 3 or the EBI system 100 of FIG. 1. It is understood that the charged particle beam device may be controlled to observe, image, and inspect a wafer (e.g., wafer 203 of FIG. 2) or a region of interest on the wafer. Imaging may include scanning the wafer to image at least a portion of the wafer, a pattern on the wafer, or the wafer itself. Inspecting the wafer may include scanning the wafer to inspect at least a portion of the wafer, a pattern on the wafer, or the wafer itself. Observing the wafer may include monitoring the wafer or a region of interest on the wafer for certain characteristics, such as pattern reproducibility and repeatability, among others.

[0116]

[0133] In step 710, similar to steps 510 and 610, a primary charged particle beam (e.g., primary charged particle beam 220 of FIG. 2) is generated from a charged particle source. The primary charged particle beam may be, for example, an electron beam generated from an electron source. The electron source may include, but is not limited to, thermionic emission of electrons from a tungsten filament or LaB6 cathode, or field emission of electrons from a tungsten / ZrO2 cold cathode.

[0117]

[0134] In step 720, a position sensing system including a height sensor (e.g., height sensor 340 in FIG. 3 ) and a laser interferometer (e.g., laser interferometer 350 in FIG. 3 ) may be used to determine the lateral and vertical displacement of a stage (e.g., stage 201 in FIGS. 2-3 ). In some embodiments, one or more optical height sensors may be used to determine the vertical displacement, and one or more laser interferometers may be used to determine the lateral displacement of the stage. In some embodiments, during scanning of a wafer 203 disposed on the stage 201, pitch effect compensation in the X- and Y-axes may require simultaneous and continuous compensation of the lateral displacement (X- and Y-axes) and vertical displacement (Z-axis). The vertical displacement may be compensated by adjusting the focus of the incident beam on the wafer 203 or by adjusting the position of the stage 201 in the Z-axis. In some embodiments, the measured x- and y-coordinates may be corrected based on the Abbe error determined from the pitch effect in the X- and Y-axes. The corrected x- and y-coordinates of the stage 201 may include the displacement due to the pitch effect. The beam deflection controller 367, the beam control module 365, and the stage control module 362 may communicate with one or more laser interferometers to receive updated stage position information. Compensating for pitch effects in the X and Y axes may include determining lateral beam corrections from the measured x-y position coordinates and continuously adjusting the focus of the primary charged particle beam incident on the wafer during scanning to compensate for vertical displacement. In some embodiments, height sensors and laser interferometers may be used to determine stage positioning, stage calibration, and calibration of motors and drives configured to move the stage in one of the X, Y, and Z axes.

[0118]

[0135] In step 730, after determining the lateral displacement of the stage, a beam deflection controller (e.g., beam deflection controller 367 of FIG. 3) may apply a first signal to a primary beam deflector (e.g., deflector array 320 of FIG. 3) to deflect the primary charged particle beam in at least one of the X or Y axes. The applied signal may include a voltage signal having a high control bandwidth in the range of 10 kHz to 50 kHz. The deflected charged particle beam (e.g., deflected charged particle beam 330 of FIG. 3) may at least partially compensate for the determined lateral displacement of the stage.

[0119]

[0136] In step 740, after determining the vertical displacement of the stage, the beam deflection controller may apply a second signal to the stage to adjust the focal point of the deflected charged particle beam in the Z-axis. The applied second signal may include a voltage signal configured to decelerate or accelerate the charged particle beam toward the stage. The deceleration or acceleration voltage of the charged particle beam may correspond to the vertical displacement of the stage and may at least partially compensate for the vertical displacement by modifying the focal point of the incident charged particle beam in the Z-axis. The voltage signal may include a signal having a high control bandwidth in the range of 50 kHz to 200 kHz.

[0120]

[0137] In step 750, upon determining the stage positioning and stage leveling in the Z axis based on signals received from the one or more height sensors, the stage control module (e.g., stage control module 362 in FIG. 3) may apply signals to a stage motion controller (e.g., stage motion controller 370 in FIG. 3). In some embodiments, the signals may include one or more signals for individually controlling z-motion controllers (e.g., actuators 372_1, 372_2, and 372_3 in FIG. 3) to adjust the Z level of the stage so that it is substantially perpendicular to the primary charged particle beam.

[0121]

[0138] Inspection and imaging of three-dimensional (3D) structures, such as contact holes, vias, or interconnects in semiconductor chips, may be performed by adjusting the focal depth of probe charged particles (e.g., electrons in an electron beam inspection tool) relative to the position of the sample, such as by adjusting the landing energy of the electrons on the sample to change the focal depth, among other things. One of several methods for adjusting the focal depth or focal plane of the primary electron beam includes adjusting the magnetic field associated with the objective lens by adjusting the current through the coils of the magnetic objective lens, among other things. Adjusting the magnetic field to change the focal depth can induce delays associated with the response time between changing the current and the resulting adjustment of the magnetic field, slowing the process and thereby adversely affecting inspection throughput.

[0122]

[0139] Another of several ways to adjust the depth of focus or focal plane is to adjust the landing energy of the electrons of the electron beam, such as by adjusting the voltage of the anode (e.g., anode 216), among other things. Adjusting the anode voltage adjusts the velocity or energy of the electrons incident on the surface of the sample, which may adjust the depth of focus, among other things. However, while the depth of focus may be adjusted, the adjusted primary electron beam may rotate about one or more axes due to changes in the electromagnetic fields experienced by the electrons as the beam travels downstream toward the sample. Rotation of the primary electron beam may, among other things, rotate the image formed from the primary electron beam, adversely affecting inspection throughput. Therefore, it may be desirable to provide a method for adjusting the focal plane of the incident primary electrons while maintaining a desired inspection throughput, such as by adjusting the landing energy of the primary electron beam to produce a desired change in the focal plane.

[0123]

[0140] Reference is now made to FIG. 8 , which illustrates an exemplary charged particle beam system 800 consistent with embodiments of the present disclosure. The charged particle beam system 800 may include a charged particle source including a cathode 802 (similar to cathode 218 of FIG. 2 ) configured to generate a charged particle beam (e.g., an electron beam) along a primary optical axis 801, a source supply unit 805, a condenser lens 810 (similar to condenser lens 315 of FIG. 3 ), an electron detector 815 (similar to electron detector 206 of FIG. 2 ), an objective lens assembly 820 (similar to objective lens 204 of FIG. 2 ), and a height sensor 840 configured to determine a position of a wafer 850 disposed on a stage 860. The charged particle beam system 800 may further include a control unit 830 configured to control electrical signals applied to the stage 860 and the objective lens assembly 820. Alternatively, the charged particle beam system 800 (such as an electron beam system) may be part of the imaging system 200 of Figure 2 or the EBI system 100 of Figure 1. Although not explicitly described, it should be understood that the charged particle beam system 800 may include other standard or non-standard components for performing functions, including but not limited to beam focusing, beam deflection, electron detection, beam current limiting, etc.

[0124]

[0141] In some embodiments, the charged particle beam system 800 may be configured to, among other things, generate and focus an electron beam on the wafer 850. Focusing the electron beam may include adjusting the height of the wafer 850 so that the electron beam is focused on a desired plane of the wafer 850. It should be understood that, because the wafer 850 is positioned on the stage 860, adjusting the height of the stage 860 results in adjusting the height of the wafer 850. One of several methods for focusing the electron beam on the wafer 850 may include using a combination of optical and mechanical techniques. For example, using an optical component, such as an optical height sensor, to determine the height of the stage 860 or wafer 850, and a mechanical component, such as a piezoelectric transducer, configured to mechanically move the stage 860 based on the determined height. However, using purely optical-mechanical techniques to focus the electron beam may result in imprecise determinations in some applications, such as the inspection of 3D NAND flash devices that include vertically stacked structures. In such cases, it may be desirable to further fine-tune the focus of the electron beam using the electrical techniques described herein, for example, to increase imaging resolution.

[0125]

[0142] The source supply unit 805 may be configured to supply power to a charged particle source for generating a charged particle beam. In some embodiments, the source supply unit 805 may be configured to generate an electric field between an anode (not shown) (e.g., anode 216 in FIG. 2 ) and the cathode 802 so that a charged particle beam can be emitted from the charged particle source. In some embodiments, the charged particle source may include a field emission source in which charged particles, such as electrons, are emitted from a field emission gun by placing the cathode in a large electric field gradient. The field emission source may optionally utilize two or more anode plates. A first anode plate may be configured to cause extraction or emission of charged particles from the field emitter, and a second anode plate may be configured to cause acceleration of the extracted charged particles toward the wafer 850. The source supply unit 805 may be configured to determine and supply an extraction voltage and an acceleration voltage. In some embodiments, the source supply unit 805 may be an integral part of a beam control module, such as the beam control module 365 of FIG. 3, or a system control module, such as the system control module 360 ​​of FIG. 3, or may be coupled to a system control module.

[0126]

[0143] 8, the charged particle beam system 800 may include a collector lens 810, similar to the collector lens 315 of FIG. 3, and may perform the same or substantially the same function as the collector lens 315. For example, the collector lens 810 may be configured to focus the charged particle beam. In some embodiments, the current of the primary beamlets of the primary charged particle beam may be adjusted by changing the focusing power of the collector lens 810.

[0127]

[0144] The electron detector 815 of the charged particle beam system 800 may be similar to the electron detector 206 of FIG. 2 and may perform the same or substantially similar functions as the electron detector 206. For example, the electron detector 815 may detect secondary electrons emitted from the wafer 850 upon interaction with the electrons of the primary electron beam and generate a signal related to the intensity of the detected secondary electrons. The objective lens assembly 820 of the charged particle beam system 800 may be similar to or substantially similar to the objective lens 204 of FIG. 2. The objective lens assembly 820 may include, among other things, a control electrode 824 similar to the control electrode 204b of FIG. 2 configured to control an electric field associated with the wafer 850. The objective lens assembly 820 may include, without limitation, a beam-focusing component configured to adjust the focus of the primary electron beam directed toward the wafer 850 and an electric field modulation component configured to adjust the electric field to which the primary electron beam may be subjected. In some embodiments, the electric field modulation component may include the control electrode 824. In some embodiments, the electrical excitation of the control electrode 824 may be adjusted by varying the voltage or current to adjust the generated electric field. The charged particle beam system 800 may further include a control unit 830 configured to control voltages applied to the stage 860 and the objective lens assembly 820. In some embodiments, the control unit 830 may be configured to apply a voltage to the control electrode 824 of the objective lens assembly 820.

[0128]

[0145] In the context of this disclosure, opto-mechanical techniques for adjusting the focus of the electron beam refer to adjusting the height of the stage 860 using a combination of electromechanical and optical devices, including, but not limited to, piezoelectric transducers, piezoelectric drives, lasers, interferometers, and photodiodes, among others. In the context of this disclosure, electrical techniques for adjusting the focus of the electron beam refer to manipulating the electromagnetic fields associated with the electron beam by applying electrical signals to control electrodes (e.g., 824 in FIG. 8 ) of the stage 860, wafer 850, or objective lens assembly 820.

[0129]

[0146] As mentioned above, in electron beam inspection tools, such as SEMs, the precision of electron beam focus achieved by purely opto-mechanical techniques may be inadequate for some applications, such as, among other things, vertically stacked structures within an IC chip. It may be desirable to limit the use of mechanical techniques, since they can introduce errors and variations in at least the focus of the electron beam as a result of, among other things, imprecise stage motion control or mechanical vibrations. On the other hand, electrical techniques may provide more precise adjustment of the focal plane of the electron beam incident on the sample by modifying the electric or magnetic field at the sample, and may provide a faster method for adjusting the focal plane.

[0130]

[0147] Reference is now made to FIG. 9A , which illustrates a flowchart illustrating an exemplary method of focusing a charged particle beam on a sample using charged particle beam system 800, consistent with embodiments of the present disclosure. The method of focusing on a sample may be performed by charged particle beam system 300 of FIG. 3 , charged particle beam system 800 of FIG. 8 , or EBI system 100 of FIG. 1 . It is understood that the charged particle beam device may be controlled to observe, image, and inspect a wafer (e.g., wafer 850 of FIG. 8 ) or a region of interest on the wafer. Imaging may include scanning the wafer to image at least a portion of the wafer, a pattern on the wafer, or the wafer itself. Inspecting the wafer may include scanning the wafer to inspect at least a portion of the wafer, a pattern on the wafer, or the wafer itself. Observing the wafer may include monitoring the wafer or a region of interest on the wafer for pattern reproducibility and repeatability.

[0131]

[0148] In step 910A, similar to steps 510, 610, and 710, a primary charged particle beam (e.g., primary charged particle beam 220 of FIG. 2) is generated from a charged particle source. A sample disposed on a stage (e.g., stage 860 of FIG. 8) is irradiated with the primary charged particle beam. In some embodiments, at least a portion of the sample may be irradiated with at least a portion of the primary charged particle beam. The primary charged particle beam may be, for example, an electron beam generated from an electron source. The electron source may include, but is not limited to, thermionic emission of electrons from a tungsten filament or LaB6 cathode, or field emission of electrons from a tungsten / ZrO2 cold cathode.

[0132]

[0149] The sample may be placed directly on the stage. In some embodiments, the sample may be placed on an adapter, such as a sample holder, and placed on and secured to the stage. The geometric centers of the sample, sample holder, and stage may be aligned with each other and with the primary optical axis (e.g., primary optical axis 801 in FIG. 8 ). The sample, sample holder, and stage may be positioned in a plane orthogonal or substantially orthogonal to the primary optical axis. In some embodiments, the sample or stage may be tilted off-axis so that the primary charged particle beam is incident on the sample at an angle less than or greater than 90°. In some embodiments, the sample and stage may be mechanically coupled such that displacement of the stage in any of the X, Y, or Z axes results in a corresponding displacement of the sample. In some embodiments, the sample holder and stage may be electrically coupled such that ohmic contact or an insignificant potential gradient can be established between the sample holder and the stage. In some embodiments, the sample and sample holder may be electrically coupled such that ohmic contact or an insignificant potential gradient can be established between the sample and the sample holder.

[0133]

[0150] In step 920A, the location of the initial focus of the charged particle beam is adjusted relative to the sample using a first component. As used herein, initial focus refers to an approximate point or plane of the focus of the charged particle beam. In some embodiments, adjusting the location of the initial focus may include using a more precise optical position sensing technique, including an optical height sensor (e.g., height sensor 840 in FIG. 8 ), to determine an initial position of the stage in the Z axis based on the determined initial position of the stage and the desired focal plane of the primary charged particle beam, and adjusting the position of the stage so that the initial focus of the primary charged particle beam is formed at or substantially near the surface of the sample. In some embodiments, it may be desirable to form the initial focus on the top surface of the sample.

[0134]

[0151] In some embodiments, the height sensor may include a laser diode assembly including a laser source that irradiates laser light having a predetermined emission wavelength onto the stage or onto a sample (e.g., wafer 850 in FIG. 8 ) disposed on the stage, and a laser detector configured to detect the laser reflected from the surface of the sample. The height sensor may be in communication with a stage control module (e.g., stage control module 362 in FIG. 3 ), a beam control module (e.g., beam control module 365 in FIG. 3 ), or both. In some embodiments, the stage control module and the beam control module may communicate with each other to adjust the height of the stage to focus the primary charged particle beam on the sample.

[0135]

[0152] In step 930A, after forming an initial focal spot on the sample in step 920A, the focal spot of the primary charged particle beam may be further adjusted by manipulating an electromagnetic field associated with the sample using a second component. The second component may include, but is not limited to, a control electrode of the objective lens (e.g., control electrode 824 in FIG. 8 ), a stage, or the sample, among others. In some embodiments, the second component may be located downstream of the focusing component of the objective lens. The electromagnetic field associated with the sample may include an electric field and a magnetic field that affect the sample. Manipulating the electromagnetic field may allow the initial focal spot of the charged particle beam to be further adjusted to form a final focal spot on the sample. The electromagnetic field may be manipulated, for example, by adjusting an electrical signal applied to a control electrode (e.g., control electrode 824 in FIG. 8 ) of the objective lens assembly (e.g., objective lens assembly 820 in FIG. 8 ), adjusting an electrical signal to the stage, or adjusting a magnetic field configured to affect the characteristics of the charged particle beam.

[0136]

[0153] In some embodiments, manipulating the electromagnetic field may include adjusting an electrical signal applied to a control electrode of the objective lens assembly. The initial focus of the charged particle beam may be adjusted along the Z-axis by adjusting the electrical excitation (e.g., voltage) of the control electrode. The initial height adjustment or initial focus of the charged particle beam is achieved in step 920A by adjusting the stage height based on the optical measurement. After the initial focus is formed, the electrical excitation of the control electrode may be changed to adjust the path or energy of the charged particle beam, thereby adjusting the focus. For example, changing the voltage signal applied to the control electrode may manipulate the electric field experienced by the charged particle beam, thereby enabling adjustment of the focus of the charged particle beam on the sample surface. The combination of opto-mechanical and electrical techniques, as described herein, may enable users to obtain high image quality and high resolution.

[0137]

[0154] In some embodiments, manipulating the electromagnetic field may include adjusting an electrical signal applied to the stage. The initial focus of the charged particle beam may be adjusted along the Z-axis by adjusting a voltage signal applied to the stage. The voltage signal applied to the stage may adjust the landing energy of the charged particle beam on the sample surface. As used herein, the landing energy of the charged particle beam may be defined as the energy of the charged particles when they impact the sample, and may be the difference between the acceleration voltage and the stage / sample bias voltage. To improve image resolution and contrast by adjusting the focus of the incident primary charged particle beam, a user may apply a beam energy modification voltage to the stage to decrease or increase the beam energy of the charged particle beam incident on the sample.

[0138]

[0155] In some embodiments, manipulating the electromagnetic field can include adjusting the electrical signal applied to the sample or wafer to decelerate (lower landing energy) or accelerate (higher landing energy) the charged particles before they strike the sample. For example, in an SEM, if the high voltage (acceleration voltage applied within the column) is 12 kV (e.g., created by setting the voltages of the cathode 218 and anode 216 in FIG. 2 to −12 kV and ground, respectively) and the stage / sample bias voltage is −9 kV (relative to ground), electrons are first accelerated to an energy of 12 keV within the column and then decelerated by the 9 kV electric field after leaving the column, resulting in a landing energy of 3 keV for the charged particles in the charged particle beam. Accelerating or decelerating the charged particles striking the sample can change the penetration depth into the sample and can change the focal depth of the beam. At lower landing energies, e.g., below 1 keV, the charged particle beam can interact primarily with the top surface of the sample. Higher landing energies, for example, 1 keV to 6 keV, may provide greater penetration depth and therefore provide information from the bulk of the sample. In some embodiments, the landing energy of the charged particle beam ranges from 250 eV to 6 keV. Lower landing energies may avoid bulk analysis, but the signal intensity of the secondary charged particles generated may be low, thereby adversely affecting the ability to analyze the sample. On the other hand, higher landing energies may be desirable for extracting bulk and subsurface information, but may alter the sample, thereby adversely affecting the ability to analyze the sample. In some embodiments, the landing energy of the charged particle beam ranges from 500 eV to 3 keV, depending on the sample, any requirements, and the associated application.

[0139]

[0156] Adjusting the landing energy of the charged particle beam may include applying one or more electrical signals to the stage. In some embodiments, the electrical signals may include a first component of a voltage signal or a second component of a voltage signal. The first component of the voltage signal may be a voltage applied to the stage or the sample to affect the acceleration of the charged particle beam. In some applications, the focus of the charged particle beam at the initial focus on the sample may be improper, and therefore the charged particle beam may be further focused or adjusted, for example, to achieve better resolution or contrast. In some embodiments, the first component of the voltage signal may be configured to coarsely adjust the initial focus of the charged particle beam on the sample surface. As used herein, coarse adjustment of the initial focus may refer to adjusting the focus along the Z-axis. In some embodiments, the first component of the voltage signal may include a voltage signal in the range of 5 KV to 10 KV.

[0140]

[0157] The second component of the voltage signal may be a voltage applied to the stage or sample to fine-tune the initial focus formed by adjusting the position of the stage in the Z-axis. As used herein, fine-tuning the initial focus may refer to adjusting the focus along the Z-axis to achieve a sharper focus. The second component of the voltage signal may deflect the incident charged particle beam to allow for small positional adjustments along the X, Y, or Z-axis, allowing for a sharper focus. In some embodiments, the second component of the voltage signal may include a voltage signal in the range of −150 V to +150 V. It should be understood that the first or second component of the applied voltage signal may be higher or lower than the ranges stated herein based on factors including, but not limited to, the application, sample, and tool conditions.

[0141]

[0158] In some embodiments, the landing energy of the charged particle beam incident on the sample surface may be adjusted to manipulate the electromagnetic field by applying a single electrical signal. The single electrical signal may include a first component and a second component of a voltage signal. For example, if the first component of the voltage signal for coarse focus adjustment is −9 KV and the second component of the voltage signal for fine focus adjustment is −100 V, the single electrical signal may include a voltage signal of −9.1 KV. Alternatively, if the first component of the voltage signal for coarse focus adjustment is −9 KV and the second component of the voltage signal for fine focus adjustment is +100 V, the single electrical signal may include a voltage signal of −8.9 KV.

[0142]

[0159] In some embodiments, manipulating the electromagnetic field associated with the sample may include adjusting the magnetic field associated with the sample. In some embodiments, adjusting the electric field by applying an electrical signal may result in adjusting the magnetic field. Adjusting the magnetic field with an electrical or magnetic component may affect the properties of the charged particle beam. For example, current passing through the coils of an electromagnetic lens creates a magnetic field within the bore of a pole piece that may be used to focus the charged particle beam. In some embodiments, the properties of the charged particle beam may include, but are not limited to, the path, direction, velocity, or acceleration of the charged particle beam.

[0143]

[0160] Reference is now made to Figure 9B, which illustrates an exemplary method of focusing a charged particle beam onto a sample using charged particle beam system 800, consistent with embodiments of the present disclosure. The method of focusing onto a sample may be performed by charged particle beam system 300 of Figure 3, charged particle beam system 800 of Figure 8, or EBI system 100 of Figure 1.

[0144]

[0161] In step 910B, similar to steps 510, 610, 710, and 910A, a primary charged particle beam (e.g., primary charged particle beam 220 of FIG. 2) is generated from a charged particle source. A sample disposed on a stage (e.g., stage 860 of FIG. 8) is irradiated with the primary charged particle beam. In some embodiments, at least a portion of the sample may be irradiated with at least a portion of the primary charged particle beam. The primary charged particle beam may be, for example, an electron beam generated from an electron source. The electron source may include, but is not limited to, thermionic emission of electrons from a tungsten filament or LaB6 cathode, or field emission of electrons from a tungsten / ZrO2 cold cathode.

[0145]

[0162] The sample may be placed directly on the stage. In some embodiments, the sample may be placed on an adapter, such as a sample holder, and placed on and secured to the stage. The geometric centers of the sample, sample holder, and stage may be aligned with each other and with the primary optical axis (e.g., primary optical axis 801 in FIG. 8 ). The sample, sample holder, and stage may be positioned in a plane that is orthogonal or substantially orthogonal to the primary optical axis. In some embodiments, the sample or stage may be tilted off-axis so that the primary charged particle beam is incident on the sample at an angle less than or greater than 90°. In some embodiments, the sample and stage may be mechanically coupled such that displacement of the stage in any of the X, Y, or Z axes results in a corresponding displacement of the sample. In some embodiments, the sample holder and stage may be electrically coupled such that an ohmic contact or an insignificant potential gradient can be established between the sample holder and the stage.

[0146]

[0163] In step 920B, similar to step 920A, the location of the initial focus of the charged particle beam is adjusted relative to the sample using a first component. As used herein, initial focus refers to an approximate point or plane of the focus of the charged particle beam. In some embodiments, adjusting the location of the initial focus may include using a more precise optical position sensing technique, including an optical height sensor (e.g., height sensor 840 in FIG. 8 ), to determine an initial position of the stage in the Z axis based on the determined initial position of the stage and the desired focal plane of the primary charged particle beam, and adjusting the position of the stage so that the initial focus of the primary charged particle beam is formed at or substantially near the surface of the sample. In some embodiments, it may be desirable to form the initial focus on the top surface of the sample.

[0147]

[0164] In some embodiments, the height sensor may include a laser diode assembly including a laser source that irradiates laser light having a predetermined emission wavelength onto the stage or onto a sample (e.g., wafer 850 in FIG. 8 ) placed on the stage, and a laser detector configured to detect the laser reflected from the surface of the sample. The height sensor may be in communication with a stage control module (e.g., stage control module 362 in FIG. 3 ), a beam control module (beam control module 365 in FIG. 3 ), or both. In some embodiments, the stage control module and the beam control module may communicate with each other to adjust the height of the stage to the focus of the primary charged particle beam on the sample.

[0148]

[0165] In step 930B, after forming the initial focus on the sample in step 920B, the electromagnetic field may be manipulated to form a final focus, for example, by adjusting the electrical signal applied to the control electrode (e.g., control electrode 824 in FIG. 8 or control electrode 204b in FIG. 2) of the objective lens (e.g., objective lens assembly 820 in FIG. 8 or objective lens assembly 204 in FIG. 2). The initial focus of the charged particle beam may be adjusted to form a final focus along the Z-axis by adjusting the electrical excitation of the control electrode. The initial height adjustment or initial focus of the charged particle beam is achieved in step 920B by adjusting the stage height based on the optical measurement. After the initial focus is formed, the electrical excitation of the control electrode may be changed to adjust the path or energy of the charged particle beam, thereby adjusting the focus. For example, by changing the voltage signal applied to the control electrode, the electric field experienced by the charged particle beam may be manipulated, thereby enabling adjustment of the focus of the charged particle beam on the sample surface. The combination of opto-mechanical and electrical techniques, as described herein, may allow users to obtain high imaging resolution.

[0149]

[0166] As mentioned above, one of the challenges encountered during the inspection of IC chips with device architectures including vertically stacked components is inadequate imaging range and resolution. For example, measuring the depth of 4-5 μm deep metal contact holes or detecting buried defect particles at the bottom of a structure can be useful, among other things, for analyzing defects and developing process conditions based on information extracted from imaging and accurate measurements. The wide depth of focus (DOF) of charged particle beam systems, such as SEMs, can enable a wider imaging range so that the top, bottom, and intermediate layers of deep features can be imaged simultaneously and in real time while maintaining high imaging resolution.

[0150]

[0167] Inspecting vertically stacked structures, such as 3D NAND flash devices, using existing techniques can provide limited or inaccurate information, both of which can negatively impact the throughput and quality of manufactured devices. Therefore, it may be desirable to enable existing inspection tools with real-time 3D imaging capabilities, thereby extending the imaging range while maintaining high imaging resolution. The ability to adjust the focus of a charged particle beam along the Z-axis by manipulating the electromagnetic field may be used to enable multiple planes, features, or regions of interest within a sample to be imaged in real time, thereby obtaining accurate 3D morphology.

[0151]

[0168] Reference is now made to Figure 10, which is a schematic diagram illustrating a charged particle beam system 1000 including an electron beam inspection tool 1004, consistent with an embodiment of the present disclosure. As shown in Figure 10, the charged particle beam system 1000 may include an electron beam inspection tool 1004 similar to the electron beam tool 104 of Figure 1, a controller 1009 electrically or electronically connected to the electron beam inspection tool 1004, and an image acquisition system 1060 including a data processor. Although the image acquisition system 1060 is shown external to the controller 1009, it should be understood that the image acquisition system 1060 may be part of the controller 1009.

[0152]

[0169] In some embodiments, the charged particle beam system 1000 may provide mechanisms to support multiple modes of operation. For example, the charged particle beam system 1000 may be configured to operate in a 2D imaging mode to obtain high-resolution planar images of a sample or region of interest, or in a 3D imaging mode to obtain high-resolution morphological images of a sample containing features and structures having 3D shapes. In some embodiments, the charged particle beam system 1000 may be configured to switch modes in an inspection scan based on the desired analysis, the sample being analyzed, or the application, among other things. For example, the charged particle beam system 1000 may first perform an inspection of the region of interest in a 2D imaging mode, which typically provides higher throughput than the 3D imaging mode, and then switch to the 3D imaging mode to perform a high-resolution scan of, for example, detected defects. This may eliminate the need for two tools, thereby improving the overall throughput of the inspection process. In some embodiments, the charged particle beam system 1000 may perform only an inspection scan in the 3D imaging mode to obtain a high-resolution scan of a region of interest predetermined by the user.

[0153]

[0170] In some embodiments, the controller 1009 may include a computer or processor configured to perform various controls of the electron beam inspection tool 1004. The controller 1009 may be electronically connected to the electron beam inspection tool 1004 and may include processing circuitry configured to perform various signal and image processing functions and to generate various control signals for managing the operation of the charged particle beam system 1000. In some embodiments, the controller 1009 may be configured to switch operational modes based on user input. Switching operational modes may include, but is not limited to, activating hardware components, executing software programs, etc. For example, switching the electron beam inspection tool 1004 to a 3D imaging mode may include adjusting a voltage signal applied to a stage, adjusting a voltage signal applied to a control electrode (e.g., control electrode 824 in FIG. 8 ) of an objective lens (e.g., objective lens assembly 820 in FIG. 8 ), moving the stage in the X, Y, or Z axis to adjust the focus of the charged particle beam, instructing the image acquisition system 1060 to acquire an image of the sample at the focus, and executing an algorithm to process the image information, etc. Although image acquisition system 1060 is shown external to controller 1009 , it may be part of controller 1009 .

[0154]

[0171] The image acquisition system 1060 may be substantially similar to the image acquirer 260 of FIG. 2 and may perform similar functions to the image acquirer 260 of FIG. 2. In some embodiments, the image acquisition system 1060 may be configured to acquire images or image frames and may include one or more processors (not shown) configured to perform functions related to imaging or post-processing, and one or more storage units (not shown) configured to store acquired image frames, post-processing information, analysis results, etc. The image acquisition system 1060 may be configured to communicate with the controller 1009. For example, upon determining that a desired focus has been achieved, the controller 1009 may cause the image acquisition system 1060 to acquire one or more image frames at that focus. The image acquisition system 1060 may be operated through the controller 1009 or by a user. In some embodiments, the image acquisition system 1060 may be remotely operated through a computer-executed program, such as software, an algorithm, or a set of instructions.

[0155]

[0172] As mentioned above, the focus achieved using opto-mechanical techniques may be inadequate for high-resolution and wide-area imaging in some applications, and therefore, a finer and larger depth of focus may be desired. A larger depth of focus may enable high-resolution imaging of deep 3D features, such that the top and bottom surfaces of the feature may be simultaneously and clearly imaged. An exemplary method for focusing a charged particle beam onto the surface of a sample using the 3D imaging mode of operation of the charged particle beam system 1000 is described herein. It should be understood that the number and order of steps in the focusing method are exemplary and for illustrative purposes only. Steps may be added, deleted, edited, reordered, and omitted as desired. The 3D imaging mode of operation includes using a combination of opto-mechanical and electrical techniques to enable the charged particle beam to be focused onto multiple focal planes of a sample, thereby enabling a user to clearly image the entire 3D feature.

[0156]

[0173] In the 3D imaging mode, the charged particle beam system 1000 may be configured to perform an initial height adjustment of the stage (e.g., stage 860 in FIG. 8 ) using opto-mechanical techniques so that the focal point of the charged particle beam coincides with or substantially coincides with a desired focal plane of the wafer 850 placed on the stage 860. In some embodiments, the initial height adjustment of the stage 860 may be performed in the 2D imaging mode, and the charged particle beam system 1000 may be switched to operate in the 3D imaging mode once the height of the stage 860 has been adjusted in the 2D imaging mode using optical height sensors and piezoelectric motors.

[0157]

[0174] Once the initial height adjustment is achieved, a controller (e.g., controller 1009 of FIG. 10 ) may cause the electron beam inspection tool 1004 to adjust the initial focus of the charged particle beam by manipulating an electromagnetic field associated with the sample. The electromagnetic field may be manipulated to adjust the focal plane of the charged particle beam along the Z axis, allowing the charged particle beam to be focused at multiple focal planes of the sample, thus providing more accurate 3D topographical information. The electromagnetic field associated with the sample may be manipulated by adjusting the landing energy of the charged particles on the sample, adjusting the electrical excitation of control electrodes of the objective lens, or adjusting a stage bias voltage.

[0158]

[0175] In some embodiments, manipulating the electromagnetic field by adjusting the landing energy may include applying a first component of a voltage signal to coarsely adjust the initial focus of the charged particle beam on the surface of the sample and applying a second component of the voltage signal to the stage to finely adjust the initial focus of the charged particle beam on the surface of the sample. The first component of the voltage signal may be determined based on a desired height adjustment to shift the focal plane a predetermined distance along the Z axis. The landing energy may be varied based on an acceleration voltage applied to accelerate the charged particles toward the sample and the first component of the voltage signal applied to the stage. The second component of the voltage signal may be applied to further finely adjust the focus along the Z axis. The voltage signal may be applied, for example, to a control electrode of the objective lens (e.g., control electrode 824 in FIG. 8 ), a stage (e.g., stage 860 in FIG. 8 ), or other optomechanical component configured to affect the electromagnetic field of the system.

[0159]

[0176] After the charged particle beam is focused using electrical techniques, the controller 1009 may instruct the image acquisition system 1060 to acquire one or more image frames of the feature or structure. The acquired image frames may be recorded and accessed by a user for analysis. In some embodiments, the stored image frames and corresponding focal plane information may be used to reconstruct a 3D image of the structure using, for example, a reconstruction algorithm.

[0160]

[0177] Reference is now made to Figures 11A-11F, which illustrate image frames and corresponding focal planes of a feature on a sample consistent with embodiments of the present disclosure. Figures 11A, 11C, and 11E represent the top, middle, and bottom focal planes, respectively, of a cross-sectional view of a feature such as a metal contact hole, while Figures 11B, 11D, and 11F represent SEM images of the corresponding focal planes. It should be understood that other features may also be imaged, including, but not limited to, interconnects, metal pads, photoresist profiles, etc.

[0161]

[0178] An exemplary feature 1110 on a sample (e.g., wafer 850 in FIG. 8 ) may include a metal contact hole, for example, in a 3D NAND flash memory device. In some embodiments, feature 1110 may have a conical, cylindrical, triangular, or rectangular shape and a circular or elliptical cross-section. As shown in the cross-sectional view of FIG. 11A , for example, feature 1110 may include a conical metal contact hole having a height h1, a top diameter d1 along a top planar surface 1115, a middle diameter d3 along a mid-planar surface (e.g., mid-planar surface 1135 in FIG. 11C ), and a base diameter d5 along a base planar surface (e.g., base planar surface 1155 in FIG. 11E ). In some embodiments, height h1, top diameter d1, and base diameter d5 may comprise critical dimensions of feature 1110. As used herein, critical dimensions of a feature or device may refer to dimensions that may contribute to parasitic capacitance and resistance and thus affect the electrical performance of the device. Those skilled in the art will appreciate that critical dimensions are dimensions that can be adjusted to optimize device performance and manufacturing yield.

[0162]

[0179] 11B shows an image frame 1150 (e.g., an SEM image) of an array of features 1110 as imaged by the focusing method using a combination of the opto-mechanical and electrical techniques described above. The focal plane of the charged particle beam in FIG. 11B is adjusted to coincide with the top plane 1115 of the feature 1110. It should be understood that individual features 1110 of the array may have different dimensions, including height h1, and the focal plane of the charged particle beam may not coincide with the top plane of other features of the array. In such cases, the controller 1009 may be configured to adjust the focal plane of the charged particle beam based on the feature 1110 being investigated and its dimensions.

[0163]

[0180] Reference is now made to FIGS. 11C and 11D, which respectively illustrate schematic diagrams of a feature 1110 having an intermediate plane 1135 and a corresponding image frame 1152. The intermediate plane 1135 is shown to be located midway between the top plane 1115 and the base plane (e.g., the base plane 1155 in FIG. 11E), but may be any plane between the top plane 1115 and the base plane 1155 that is perpendicular to the Z axis. While FIGS. 11A-11F show three planes and corresponding image frames, it should be understood that any number of planes may be imaged as appropriate. In some embodiments, one or more image frames may represent a plane of the feature 1110. For example, the image acquisition system 1060 may acquire two or more image frames of a plane as desired.

[0164]

[0181] 11E and 11F illustrate schematic views of a feature 1110 having a base plane 1155 and a corresponding image frame 1154, respectively. By way of example, the feature 1110 is shown having a conical shape with a tapered diameter along its height h1. In such a case, as shown in FIGS. 11A, 11C, and 11E, the diameter (e.g., d1) of the top plane of the feature 1110 may be larger than the mid-diameter d3, which may be larger than the base diameter d5 of the feature 1110 (d1 > d3 > d5). In image frames 1150, 1152, and 1154 of FIGS. 11B, 11D, and 11F, respectively, the dark circular regions highlighted by dashed lines indicate the planar view of the in-focus plane of the feature 1110. The diffuse bright regions surrounding the dark regions within the dashed lines represent out-of-focus layers of the sample. It is understood that the dashed lines highlighting the plane of focus provide a visual aid and are for illustrative purposes only.

[0165]

[0182] Reference is now made to FIG. 12 , which is a schematic illustration of a process 1200 for generating a reconstructed 3D image from image frames captured at multiple focal planes, consistent with an embodiment of the present disclosure. Feature 1210 may include, for example, a conical metal contact hole whose diameter tapers along height h1 such that top diameter d1 is greater than base diameter d5. As shown in FIG. 12 , top plane 1215 represents the top surface of feature 1210, having top diameter d1, as shown in corresponding top view 1217. Mid-planes 1225, 1235, and 1245 represent mid-planes of feature 1210, having diameters d2, d3, and d4, respectively, as shown in corresponding top views 1227, 1237, and 1247. Base plane 1255 represents the bottom surface of feature 1210, having base diameter d5, as shown in corresponding top view 1257. Image frames 1220 , 1230 , 1240 , 1250 , and 1260 may be reconstructed to generate a 3D image 1270 of feature 1210 .

[0166]

[0183] In some embodiments, in 3D imaging mode, the charged particle beam may be focused on the top surface of the feature 1210 such that the focal plane of the charged particle beam may coincide with the top plane 1215 of the feature 1210. The focal plane coincident with the top plane 1215 may be referred to as the first focal plane. The image acquisition system 1060 may be configured to acquire a first image frame 1220 of the top surface of the feature 1210. The charged particle beam may be focused by first adjusting the height of the stage 860 to form an initial focus of the charged particle beam on the sample by opto-mechanical means, and then adjusting the initial focus by electrical means, including, but not limited to, adjusting the landing energy of the charged particles, adjusting the electrical excitation of a control electrode, or adjusting a stage bias voltage. In some embodiments, the image acquisition system 1060 may acquire two or more image frames at the focal plane. The acquired image frames may be stored in a storage medium (e.g., storage 270 of FIG. 2 ), such as a hard disk, random access memory (RAM), or other type of computer-readable memory. A storage medium may be coupled to the image acquisition system 1060 and may be used to store raw scanned image data as original images and to store processed images. Information related to focal planes, acquisition conditions, tool parameters, etc. may also be stored in the storage medium.

[0167]

[0184] The focus of the charged particle beam may then be adjusted to focus on a second focal plane located a distance below the first focal plane. In the context of this disclosure, “below” the first focal plane refers to a location deeper in the sample. The distance between the first and second focal planes may be predetermined by a user based on the application or requirements. In some embodiments, the distance may be dynamically adjusted based on the feature being imaged or the material of the sample. The image acquisition system 1060 may be configured to acquire a second image frame 1230 of the feature 1210 at a deeper intermediate plane 1225. The focal plane of the charged particle beam may be shifted deeper into the sample by manipulating the electric field, the magnetic field, or both. For example, the landing energy of the charged particles may be adjusted to form a focal plane below the top surface of the sample. In some embodiments, the position of the focal plane may be shifted by adjusting a voltage applied to a control electrode of the objective lens. By adjusting the voltage applied to the control electrodes, the electromagnetic field associated with the sample may be manipulated to affect the path of charged particles incident on the sample. For example, the charged particles may be accelerated, decelerated, deflected, filtered, or focused based on the electrical excitation and the applied voltage signal. The image acquisition system 1060 may be configured to acquire a third image frame 1240 at mid-plane 1235, a fourth image frame 1250 at mid-plane 1245, and a fifth image frame 1260 at base plane 1255. While FIG. 12 illustrates five imaging planes used to reconstruct a 3D image, any number of imaging planes that allows for the depth range of the imaged feature (e.g., feature 1210) may be used to accurately reconstruct the feature.

[0168]

[0185] In some embodiments, image frames 1220, 1230, 1240, 1250, and 1260 may be reconstructed to generate a 3D image 1270 of feature 1210. In some embodiments, at least two image frames and associated focal plane information may be used, for example, to generate 3D image 1270 of feature 1210, extract critical dimension information, determine overlay shifts, etc. The image frames may be reconstructed using a computer-implemented 3D reconstruction algorithm, software program, image processing program, or the like.

[0169]

[0186] Reference is now made to Figure 13, which illustrates a flowchart showing an exemplary method for generating a 3D image of a sample in a charged particle beam system, consistent with embodiments of the present disclosure. The method for generating a 3D image of a sample may be performed by the charged particle beam system 100 of Figure 1, the imaging system 200 of Figure 2, the charged particle beam systems 300, 800, or 1000 of Figures 3, 8, and 10, respectively.

[0170]

[0187] In step 1310, similar to steps 510, 610, 710, and 910A, a primary charged particle beam (e.g., primary charged particle beam 220 of FIG. 2) is generated from a charged particle source. A sample disposed on a stage (e.g., stage 860 of FIG. 8) is irradiated with the primary charged particle beam. In some embodiments, at least a portion of the sample may be irradiated with at least a portion of the primary charged particle beam. The primary charged particle beam may be, for example, an electron beam generated from an electron source. The electron source may include, but is not limited to, thermionic emission of electrons from a tungsten filament or LaB6 cathode, or field emission of electrons from a tungsten / ZrO2 cold cathode.

[0171]

[0188] The sample may be placed directly on the stage. In some embodiments, the sample may be placed on an adapter, such as a sample holder, and placed on and secured to the stage. The geometric centers of the sample, sample holder, and stage may be aligned with each other and with the primary optical axis (e.g., primary optical axis 801 in FIG. 8 ). The sample, sample holder, and stage may be positioned in a plane orthogonal or substantially orthogonal to the primary optical axis. In some embodiments, the sample or stage may be tilted off-axis so that the primary charged particle beam is incident on the sample at an angle less than or greater than 90°. In some embodiments, the sample and stage may be mechanically coupled such that displacement of the stage in any of the X, Y, or Z axes results in a corresponding displacement of the sample. In some embodiments, the sample holder and stage may be electrically coupled such that ohmic contact or an insignificant potential gradient can be established between the sample holder and the stage. In some embodiments, the sample and sample holder may be electrically coupled such that ohmic contact or an insignificant potential gradient can be established between the sample and the sample holder.

[0172]

[0189] In step 1320, the focus of the primary charged particle beam may be further adjusted by manipulating the electromagnetic field associated with the sample. Prior to adjusting the focus, the position of the stage in the Z-axis is adjusted to form an initial focus of the primary charged particle beam at or substantially at the surface of the sample. As used herein, initial focus refers to an approximate point or plane of the focal point of the charged particle beam. In some embodiments, adjusting the position of the stage may include using a precision optical position sensing technique, including an optical height sensor (e.g., height sensor 840 in FIG. 8 ), to determine an initial position of the stage in the Z-axis based on the determined initial position of the stage and a desired focal plane of the primary charged particle beam, and adjusting the position of the stage so that the initial focus of the primary charged particle beam is formed at or substantially near the surface of the sample. In some embodiments, it may be desirable to form the initial focus on the top surface of the sample.

[0173]

[0190] In some embodiments, the height sensor may include a laser diode assembly including a laser source that irradiates laser light having a predetermined emission wavelength onto the stage or onto a sample (e.g., wafer 850 in FIG. 8 ) placed on the stage, and a laser detector configured to detect the laser reflected from the surface of the sample. The height sensor may be in communication with a stage control module (e.g., stage control module 362 in FIG. 3 ), a beam control module (beam control module 365 in FIG. 3 ), or both. In some embodiments, the stage control module and the beam control module may communicate with each other to adjust the height of the stage to the focus of the primary charged particle beam on the sample.

[0174]

[0191] The electromagnetic field associated with the sample may include electric and magnetic fields that affect the sample. Manipulating the electromagnetic field may allow the initial focus of the charged particle beam to be further adjusted to form a final focus on the sample. The electromagnetic field may be manipulated, for example, by adjusting an electrical signal applied to a control electrode (e.g., control electrode 824 in FIG. 8 ) of an objective lens assembly (e.g., objective lens assembly 820 in FIG. 8 ), adjusting an electrical signal to a stage, or adjusting a magnetic field configured to affect the properties of the charged particle beam.

[0175]

[0192] In some embodiments, manipulating the electromagnetic field may include adjusting an electrical signal applied to a control electrode of the objective lens assembly. The initial focus of the charged particle beam may be adjusted along the Z axis by adjusting the electrical excitation of the control electrode. The initial height adjustment or initial focus of the charged particle beam is achieved by adjusting the stage height based on optical measurements. After the initial focus is formed, the electrical excitation of the control electrode may be changed to adjust the path or energy of the charged particle beam, thereby adjusting the focus. For example, changing a voltage signal applied to the control electrode may manipulate the electric field experienced by the charged particle beam, thereby enabling adjustment of the focus of the charged particle beam on the sample surface. The combination of opto-mechanical and electrical techniques, as described herein, may enable users to obtain high imaging resolution.

[0176]

[0193] In some embodiments, manipulating the electromagnetic field may include adjusting an electrical signal applied to the stage. The initial focus of the charged particle beam may be adjusted along the Z-axis by adjusting a voltage signal applied to the stage. The voltage signal applied to the stage may adjust the landing energy of the charged particle beam on the sample surface. As used herein, the landing energy of the charged particle beam may be defined as the energy of the charged particle when it strikes the sample, which is the difference between the acceleration voltage and the stage / sample bias voltage. To improve image resolution and contrast by adjusting the focus of the incident primary charged particle beam, a user may apply a beam energy modification voltage to the stage to decrease or increase the beam energy of the charged particle beam incident on the sample.

[0177]

[0194] In some embodiments, voltages may be applied to the stage or sample to decelerate (lower landing energy) or accelerate (higher landing energy) the charged particles before they enter the sample. For example, in an SEM, if the high voltage (acceleration voltage applied in the column) is 12 kV and the stage / sample bias voltage is −9 kV, electrons are first accelerated to an energy of 12 keV in the column and then decelerated by 9 keV after leaving the column, resulting in an effective high voltage of the incident charged particle beam of 3 kV and a landing energy of the charged particles in the charged particle beam of 3 keV. Accelerating or decelerating the charged particles entering the sample may change the penetration depth into the sample. At lower landing energies, e.g., below 1 keV, the charged particle beam may interact primarily with the top surface of the sample. At higher landing energies, e.g., 1 keV to 6 keV, the penetration depth may be greater, thus providing information from the bulk of the sample. In some embodiments, the landing energy of the charged particle beam ranges from 250 eV to 6 keV. Lower landing energies may avoid bulk analysis, but the signal intensity of the secondary charged particles produced may be low, thereby adversely affecting the ability to analyze the sample. On the other hand, higher landing energies may be desirable for extracting bulk and subsurface information, but may alter the sample, thereby adversely affecting the ability to analyze the sample. In some embodiments, the landing energy of the charged particle beam ranges from 500 eV to 3 keV, depending on the sample, requirements, and application.

[0178]

[0195] Adjusting the landing energy of the charged particle beam may include applying one or more electrical signals to the stage. In some embodiments, the electrical signal may include a first component and a second component of the electrical signal. The first component of the electrical signal may include a voltage applied to the stage or the sample to affect the acceleration of the charged particle beam, thereby fine-tuning the initial focus formed by adjusting the position of the stage in the Z-axis. In some applications, the focus of the charged particle beam at the initial focus on the sample may not be appropriate, and therefore the charged particle beam may be further focused or adjusted, for example, to achieve better resolution and contrast. In some embodiments, the first component of the voltage signal may be configured to coarsely adjust the initial focus of the charged particle beam on the sample surface. As used herein, coarse adjustment of the initial focus may refer to adjusting the focus along the Z-axis. In some embodiments, the first voltage signal may include a voltage signal in the range of 5 KV to 10 KV.

[0179]

[0196] The second component of the electrical signal may be a voltage applied to the stage or sample to fine-tune the initial focus formed by adjusting the position of the stage in the Z-axis. As used herein, fine-tuning the initial focus may refer to adjusting the focus along the Z-axis to achieve a sharper focus. The second component of the voltage signal may deflect the incident charged particle beam to allow for small positional adjustments along the X, Y, or Z-axis, allowing for a sharper focus. In some embodiments, the second component of the voltage signal may include a voltage signal in the range of −150 V to +150 V. It should be understood that the first and second components of the applied voltage signal may be higher or lower than the ranges stated herein based on factors including, but not limited to, the application, sample, and tool conditions.

[0180]

[0197] In some embodiments, the landing energy of the charged particle beam incident on the sample surface may be adjusted to manipulate the electromagnetic field by applying an electrical signal. In some embodiments, the electrical signal may be applied by a single source. The electrical signal may include a voltage signal having one or more components. For example, if a first component of the voltage signal for coarse focus adjustment is −9 KV and a second component of the voltage signal for fine focus adjustment is −100 V, the electrical signal may include a voltage signal of −9.1 KV. Alternatively, if a first component of the voltage signal for coarse focus adjustment is −9 KV and a second component of the voltage signal for fine focus adjustment is +100 V, the electrical signal may include a voltage signal of −8.9 KV. In some embodiments, the first and second components of the voltage signal may comprise a coarse adjustment signal and a fine adjustment signal, respectively, and the electrical signal may be a numerical sum of the first and second components of the voltage signal. It should be understood that the electrical signal may include two or more components, as appropriate.

[0181]

[0198] In some embodiments, manipulating the electromagnetic field associated with the sample may include adjusting the magnetic field associated with the sample. In some embodiments, adjusting the electric field by applying an electrical signal may result in adjusting the magnetic field. Adjusting the magnetic field with an electrical or magnetic component may affect the characteristics of the charged particle beam. For example, current passing through the coils of an electromagnetic lens creates a magnetic field within the bore of a pole piece, which may be used to focus the charged particle beam. In some embodiments, the characteristics of the charged particle beam may include, but are not limited to, the path, direction, velocity, or acceleration of the charged particle beam. In some embodiments, adjusting the electric field using a magnet may result in adjusting the magnetic field. It should be understood that any type of magnet may be used to adjust the magnetic field as appropriate.

[0182]

[0199] In step 1330, multiple focal planes may be formed based on the manipulation of the electromagnetic fields. In a 3D imaging mode, the charged particle beam may be focused on the top surface of the feature (e.g., feature 1210 in FIG. 12 ) such that the focal plane of the charged particle beam may coincide with the top plane of the feature (e.g., top plane 1215 in FIG. 12 ). The focal plane coinciding with the top plane may be referred to as the first focal plane. An image acquisition system (e.g., image acquisition system 1060 in FIG. 10 ) may be configured to acquire a first image frame of the top surface of the feature (e.g., first image frame 1220 in FIG. 12 ). The charged particle beam may be focused, for example, by adjusting the height of the stage to form an initial focus of the charged particle beam on the sample by opto-mechanical means, and by adjusting the initial focus by electrical means, including, but not limited to, adjusting the landing energy of the charged particles, adjusting the electrical excitation of the control electrodes, or adjusting the stage bias voltage.

[0183]

[0200] The focus of the charged particle beam may then be adjusted to focus at a second focal plane (e.g., mid-plane 1225 in FIG. 12 ) located a distance below the first focal plane. The distance between the first and second focal planes may be predetermined by a user based on the application or requirements. In some embodiments, the distance may be dynamically adjusted based on the feature being imaged or the material of the sample. The image acquisition system may be configured to acquire a second image frame of the feature at a deeper mid-plane (e.g., mid-plane 1225 in FIG. 12 ). The focal plane of the charged particle beam may be shifted deeper into the sample by manipulating the electric field, the magnetic field, or both. In some embodiments, the position of the focal plane may be shifted by adjusting a voltage applied to a control electrode of the objective lens. Adjusting the voltage applied to the control electrode may manipulate the electromagnetic field associated with the sample to affect the path of the charged particles incident on the sample. For example, the charged particles may be accelerated, decelerated, deflected, filtered, or focused based on the electrical excitation and the applied voltage signal. Thus, multiple focal planes (e.g., intermediate planes 1225, 1235, 1245, and 1255 in FIG. 12) may be formed based on the manipulation of the electromagnetic field. It should be understood that the number of intermediate focal planes may be adjusted accordingly.

[0184]

[0201] In step 1340, the image acquisition system may generate two or more image frames at the focal plane. In some embodiments, the image acquisition system may generate one image frame corresponding to the focal plane. The image acquisition system may be configured to communicate with a controller (e.g., controller 1009 of FIG. 10 ). For example, after determining that a desired focus has been achieved, the controller may cause the image acquisition system to acquire one or more image frames at that focus. The image acquisition system may be operated through the controller or by a user. In some embodiments, the image acquisition system may be remotely operated through a computer-implemented program, such as software, an algorithm, or a set of instructions. The acquired image frames may be stored in a storage medium and may be used to save the scanned raw image data as an original image and to save processed images. Information related to the focal plane, acquisition conditions, tool parameters, etc. may also be stored in the storage medium.

[0185]

[0202] In step 1350, the image frames and corresponding focal plane information acquired by the image acquisition system may be reconstructed to generate a 3D image (e.g., 3D image 1270 of FIG. 12). In some embodiments, at least two image frames and associated focal plane information may be used, for example, to generate a 3D image of a feature, extract critical dimension information, determine overlay shifts, etc. The image frames may be reconstructed using a computer-implemented 3D reconstruction algorithm, software program, image processing program, or the like.

[0186]

[0203] High-throughput inspection of wafers in production facilities such as wafer fabs can require the stage of an SEM device to move quickly and precisely in a repeating stop-and-go pattern. The stop-and-go motion can involve multiple cycles of high-speed acceleration, high-speed deceleration, and sudden stops of the stage to displace the stage by several microns or nanometers. Moving the stage at high speed and acceleration can generate vibrations due to system dynamics, which in turn can create dynamic resonance within the system; for example, constructively interfering vibration waves can cause higher-amplitude vibrations throughout the charged particle beam system. Vibrations caused by the moving stage can result in translational or displacement errors in two or more axes. For example, inspecting dies on a wafer placed on a stage that moves in the X and Y axes can cause dynamic resonance with other moving or non-moving components, resulting in stage vibration in the Z axis.

[0187]

[0204] Among the challenges encountered are loss of inspection resolution due to vibration and inadequate vibration compensation. In existing charged particle beam systems, the stage is mechanically coupled to the receiving chamber; therefore, vibrations caused by moving the stage can cause vibrations in the receiving chamber and its attached components. For example, stage vibrations can cause vibrations in the receiving chamber, a position sensor attached to a surface of the receiving chamber, and a charged particle beam column attached to the receiving chamber, among other things. However, while a position sensor can be used to determine vibrations in the stage or a wafer placed on the stage, vibrations in the charged particle beam column and the position sensor itself can go undetected or be improperly detected, resulting in inaccurate beam deflection signals applied to the beam controller, thereby resulting in loss of inspection resolution and reduced inspection throughput.

[0188]

[0205] Furthermore, in existing inspection systems, such as SEMs, position sensor measurements from the stage may be asynchronous with the application of actuation signals to beam deflectors to compensate for vibration, resulting in inaccurate compensation of vibration and loss of inspection resolution. One reason for the timing discrepancy is due to delays introduced by digital signal processing of the vibration signal to generate the vibration compensation signal. In addition, currently used vibration detection and compensation techniques may not be configured to properly distinguish between various vibration modes of the stage, such as tilt, twist, and rotation, and therefore vibrations may be undercompensated, overcompensated, or not compensated. Therefore, it may be desirable to provide a system and method that properly identifies vibration modes and compensates for vibration based on the identification, and dynamically predicts vibration to accurately compensate for calculation and measurement delays.

[0189]

[0206] Reference is now made to FIG. 14 , which is a schematic diagram illustrating the translational and rotational axes of a stage 1450 (which may be, for example, stage 201) in a charged particle beam system consistent with embodiments of the present disclosure. In some embodiments, the stage 1450 may include a wafer stage, a wafer chuck, a sample holder, or a calibration unit. A sample, including, but not limited to, a wafer or device to be imaged, may be placed on the stage 1450. The sample may be secured on the stage 1450, for example, via a vacuum-assisted clamping mechanism. In some embodiments, a wafer chuck (not shown) may be secured on the stage 1450, and the sample may be placed on the wafer chuck. In such a configuration, the wafer chuck may be mechanically coupled to the stage 1450, and the sample may be secured on the wafer chuck using, among other things, a mechanical coupling, a vacuum-assisted means, or a combination thereof.

[0190]

[0207] In some embodiments, the stage 1450 may include an adjustable stage having six degrees of freedom. The stage 1450 may be configured to move in one or more linear translational axes, such as the X, Y, or Z axes, or in one or more rotational axes, such as the Rx, Ry, or Rz axes, as depicted in FIG. 14 . In some embodiments, the stage 1450 may be positioned such that the Z axis is substantially parallel to the primary optical axis (e.g., primary optical axis 801 in FIG. 8 ) and the X and Y axes are substantially perpendicular to the primary optical axis. In some embodiments, the stage 1450 may be tilted along one or more of the rotational axes to adjust, including but not limited to, the amount of interaction between the primary charged particle beam and the sample, the region of the sample to be examined, and the desired analysis, among others.

[0191]

[0208] In some embodiments, the motion stage 1450 may produce vibrations about any translational or rotational axis. For example, moving the stage 1450 along the XY plane may produce vibrations of the stage 1450 about the roll axis (Rx axis), pitch axis (Ry axis), or yaw axis (Rz axis), or a combination thereof. In some embodiments, the vibrations of the stage 1450 may have six degrees of freedom of movement, and may include one or more vibration modes, such as rotation, rocking, tilting, or shifting about one or more axes. It may be desirable to detect, isolate, and identify the vibration modes of the stage 1450 in order to compensate for the vibrations with beam deflection signals configured to adjust properties of the incident primary charged particle beam, such as the X / Y position at which the beam impinges on the sample or the focal depth of the beam. While FIG. 14 illustrates the translational and rotational axes of movement and resulting vibration for an exemplary stage 1450, it will be understood that the containment chamber, SEM column, position sensor, etc. may also vibrate about one or more of the translational and rotational axes.

[0192]

[0209] Reference is now made to FIG. 15 , which illustrates a charged particle beam system 1500 consistent with embodiments of the present disclosure. The charged particle beam system 1500 may include a containment chamber 1510, position sensors 1522 and 1524 disposed on the containment chamber 1510, an acceleration sensor 1526, a charged particle beam column 1530 (also referred to herein as an SEM column), and a sample 1550 disposed on a wafer chuck 1562 of a stage 1560 (which may be stage 201 in FIGS. 2-4 ). The charged particle beam system 1500 may further include a control module 1570 configured to receive the vibration signal and generate a vibration compensation signal to compensate for vibrations of one or more components of the charged particle beam system 1500. The control module 1570 may include a signal processor 1572 including a processor 1574 configured to process signals received from the position sensors 1522 and 1524 and the acceleration sensor 1526, a digital image controller 1576 configured to receive a beam scanning signal 1575, and an actuator 1578 configured to generate a beam deflection signal 1580 to be applied to the SEM column 1530. Alternatively, the charged particle beam system 1500 (such as an electron beam system) may be part of the imaging system 200 of FIG. 2 or the EBI system 100 of FIG. 1. Although not explicitly described, it should be understood that the charged particle beam system 1500 may include other standard or non-standard components for performing functions, including, but not limited to, beam focusing, beam deflection, electron detection, beam current limiting, etc. It should be understood that the described components may perform more or fewer functions than those described, as appropriate.

[0193]

[0210] 15, the charged particle beam system 1500 may include a containment chamber 1510 configured to contain components including, but not limited to, a stage 1560, a wafer chuck 1562, a sample 1550, position sensors 1522 and 1524, and a portion of a charged particle beam column 1530, among others. In some embodiments, the containment chamber 1510 may be substantially similar to and perform substantially similar functions as chamber 101 of FIG. 1. While a portion of the charged particle beam column 1530 is illustrated as being contained within the containment chamber 1510, it will be understood that the charged particle beam column 1530 may be contained entirely within the containment chamber 1510.

[0194]

[0211] In some embodiments, the containment chamber 1510 may be configured to contain electromechanical components of the charged particle beam column 1530. In the context of the present disclosure, the electromechanical components of the charged particle beam column 1530 may include, but are not limited to, the stage 1560, the wafer chuck 1562, the sample 1550, stage motion control motors, drives, etc. The containment chamber 1510 may be located on a vibration isolation or vibration damping platform (not shown) to minimize the effects of vibrations on the overall performance and inspection resolution of images obtained by the charged particle beam system 1500.

[0195]

[0212] In some embodiments, the stage 1560 may be configured to move in one or more of the X, Y, Z, Rx, Ry, or Rz axes (such as those described with respect to the stage 1450 of FIG. 14 ). The stage 1560 may include a wafer chuck 1562 disposed and secured thereon. In some embodiments, the stage 1560 may be configured to move in the X and Y axes, and the wafer chuck 1562 may be configured to move in the Z axis. The sample 1550 may be disposed on the wafer chuck 1562 using a mechanical clamp, a vacuum-assisted clamp, or other suitable non-contact clamping mechanism. For example, the wafer chuck 1562 may include a vacuum sample holder configured to hold and secure the sample 1550 while moving it in one or more axes for inspection. In some embodiments, the wafer chuck 1562 may be configured to be electrically charged to, among other things, adjust the landing energy of the incident primary charged particle beam. It should be appreciated that the sample 1550 may be placed directly on a stage 1560 that is capable of adjusting the position of the sample 1550 in one or more axes, thereby eliminating the need for a wafer chuck 1562.

[0196]

[0213] In some embodiments, the stage 1560 may be mechanically coupled to the containment chamber 1510 such that vibration of the stage 1560 may also cause vibration of the containment chamber 1510. In the context of the present disclosure, mechanically coupled refers to being physically attached to or in physical contact with a portion of the containment chamber 1510 (e.g., via multiple intermediate components). The stage 1560 may be mechanically coupled to the containment chamber 1510 using techniques including, but not limited to, heat welding, spot welding, riveting, soldering, adhesive bonding, etc. In some embodiments, the coupling mechanism may rely on the mechanism's effect on the vacuum pressure within the containment chamber 1510. For example, some metallic adhesives may outgas and cause substantial leakage within the containment chamber 1510, which may adversely affect the overall inspection resolution of the charged particle beam system 1500.

[0197]

[0214] The charged particle beam system 1500 may include a charged particle beam column 1530 configured to generate and focus a charged particle beam (e.g., an electron beam) on a sample 1550. In some embodiments, the SEM column 1530 may be referred to as an electro-optical component. The electro-optical component may include a charged particle source configured to generate charged particles and, for example, a plurality of lenses (optical and electromagnetic) and apertures configured to focus the generated charged particle beam on the sample 1550. In some embodiments, the SEM column 1530 may be mechanically coupled to a portion of the containment chamber 1510 such that vibrations of the containment chamber 1510 can cause vibrations of the SEM column 1530.

[0198]

[0215] The charged particle beam system 1500 may include position sensors 1522 and 1524 configured to determine the displacement of the stage 1560. The position sensors 1522 and 1524 may include laser interferometers. It should be understood that the position sensing system of the charged particle beam system 1500 may also include two or more position sensors and other suitable components, such as signal amplifiers, bandpass filters, data storage units, and data processing units, among others.

[0199]

[0216] In some embodiments, the position sensors 1522 and 1524 may include, among other things, a laser diode sensor assembly including a one-dimensional position sensitive detector (1-D PSD), or a linear array of photodiodes. In some embodiments, the position sensors 1522 and 1524 may be configured to determine the lateral displacement of the stage 1560. As referred to herein, the lateral displacement of the stage 1560 may correspond to the difference between a target position and an actual position of the stage 1560 in the X or Y axis.

[0200]

[0217] In some embodiments, position sensors 1522 and 1524 may be configured to detect vibration modes of stage 1560. For example, position sensor 1522 may be configured to detect vibration modes such as twist, tilt, and rotation in the X-axis, and position sensor 1524 may be configured to detect vibration modes such as twist, tilt, and rotation in the Y-axis. In some embodiments, three or more position sensors may be used. For example, a first position sensor for detecting vibrations along the X-axis, a second position sensor for detecting vibrations along the Y-axis, a third sensor for detecting vibrations about the Rx-axis, and a fourth sensor for detecting vibrations about the Ry-axis. It is understood that fewer or more position sensors, such as laser interferometers, may be used based on the desired sensing complexity and accuracy, application, sample, etc. Other position sensing and vibration detection technologies may be used as appropriate.

[0201]

[0218] The exemplary position sensors 1522 and 1524 may be configured to communicate with a control module 1570 (described in more detail below) so that the outputs of the position sensors 1522 and 1524 are analyzed and used to further adjust beam characteristics to compensate for vibrations. The position sensors 1522 and 1524 may also be configured to generate output signals including displacement signals. In some embodiments, output data from one or more position sensors 1522 and 1524 may be used to modify beam focus, beam energy, beam scan speed, beam scan frequency, beam scan duration, or beam scan range by applying beam deflection signals to the charged particle beam system 1500. It will be understood that other suitable means of focusing the incident beam may be used.

[0202]

[0219] In some embodiments, one or more position sensors 1522 and 1524 may be disposed on a surface of the containment chamber 1510. In configurations including laser interferometers as the position sensors 1522 and 1524, a photodetector surface of the laser interferometer may be positioned to receive optical signals representative of the displacement or vibration of the stage 1560 or sample 1550. In some embodiments, the position sensors 1522 and 1524 may be mechanically coupled to or mounted to the containment chamber 1510, as appropriate. In some embodiments, the position sensors 1522 and 1524 may be configured to adjust the position of the stage 1560 or sample 1550 in one or more of the X, Y, Z, Rx, Ry, and Rz axes, and to detect vibrations in one or more of the X, Y, Z, Rx, Ry, and Rz axes.

[0203]

[0220] In some embodiments, position sensors 1522 and 1524 may include, for example, a homodyne laser interferometer or a heterodyne laser interferometer. A homodyne laser interferometer uses a single-frequency laser source, whereas a heterodyne laser interferometer uses a laser source having two closely spaced frequencies. The laser source may include a He-Ne gas laser emitting laser light at a wavelength of 633 nm. It will be understood that other laser sources having single or multiple wavelength or frequency emissions may also be used as appropriate.

[0204]

[0221] As an example, stage positioning or vibration detection using laser interferometers may involve directing two split laser beams to a reference mirror and a mirror mounted on the stage in each direction. The interferometers may compare the position of the stage mirror to the position of the reference mirror to detect and correct any stage position errors. For example, one laser interferometer for the X axis and a second laser interferometer for the Y axis. In some embodiments, two or more laser interferometers may be used for a single axis, such as the X or Y axis. Other suitable techniques may also be used. In some embodiments, additional laser interferometers may be used for vibration detection in the Rx and Ry axes, as shown in FIG. 15.

[0205]

[0222] Among several challenges encountered in charged particle beam systems such as SEMs are loss of inspection resolution due to undetected vibrations and inadequate compensation for detected vibrations. For example, in existing inspection systems, vibrations of the stage 1560 can cause vibrations of the containing chamber 1510, which in turn can cause vibrations of the SEM column 1530. These vibrations of the SEM column 1530 can remain undetected and therefore uncompensated. Therefore, it may be desirable to provide a method or system for detecting, determining, and compensating for vibrations of the SEM column 1530.

[0206]

[0223] The charged particle beam system 1500 may include an acceleration sensor 1526 configured to determine vibration of the SEM column 1530. The acceleration sensor 1526 may be configured to measure the vibration of the SEM column 1530 or the acceleration of the movement of the SEM column 1530. In some embodiments, the acceleration sensor 1526 may include a piezoelectric accelerometer, a capacitive accelerometer, a microelectromechanical systems (MEMS)-based accelerometer, or a piezoresistive accelerometer. In a piezoelectric accelerometer configured to measure vibration, the force caused by the vibration or change in movement (acceleration) causes the mass to "squish" the piezoelectric material, which generates a charge proportional to the force exerted on the piezoelectric material. Because charge is proportional to force and mass is constant, charge is also proportional to acceleration.

[0207]

[0224] In some embodiments, the acceleration sensor 1526 may include a high-impedance charge output accelerometer. In this type of accelerometer, a piezoelectric crystal generates an electric charge that is directly connected to a measuring instrument. In some embodiments, the acceleration sensor 1526 may include a low-impedance output accelerometer. A low-impedance accelerometer includes a charge accelerometer and a microcircuit including a transistor that converts the charge into a low-impedance voltage signal. The low-impedance accelerometer may generate a voltage signal based on the frequency response or sensitivity of the accelerometer. It is understood that other suitable types of accelerometers may also be used, as appropriate.

[0208]

[0225] In some embodiments, the acceleration sensor 1526 may be configured to detect vibrations of the SEM column 1530 and detect vibration modes including, but not limited to, tilt, rotation, twist, shift, etc. In some embodiments, the charged particle beam system 1500 may include two or more acceleration sensors 1526 mounted to the SEM column 1530. The output signal generated by the acceleration sensor 1526 may include an electrical signal, such as a voltage signal. The accelerometer may generate a voltage signal in response to the detected vibrations and based on the frequency of the detected vibrations.

[0209]

[0226] The charged particle beam system 1500 may include a control module 1570 configured to process vibration signals of the charged particle beam system 1500 and apply vibration compensation signals to the SEM column 1530 to compensate for vibrations. In some embodiments, the control module 1570 may include a signal controller 1572, an image controller 1576 configured to receive a beam scanning signal 1575, and an actuator 1578 configured to generate a beam deflection signal 1580 to be applied to the SEM column 1530.

[0210]

[0227] In existing techniques for vibration detection and compensation, a vibration signal generated by a position sensor may be directly added to a beam scanning signal to form a vibration compensation signal. One of several problems with this approach may include inadequate compensation of vibration, resulting in a loss of inspection resolution, because the vibration compensation signal does not take into account vibration modes in all translational and rotational axes. Additionally, because the vibration signal is directly added to the beam scanning signal, the delay between measuring the vibration and applying the vibration compensation may not be taken into account, causing the controller to generate a vibration compensation signal that either under-compensates or over-compensates. Therefore, it may be desirable to provide a method for determining vibration compensation based on identified vibration modes and estimating vibration to compensate for computational and control sampling delays.

[0211]

[0228] In some embodiments, the control module 1570 may be configured to receive signals related to vibration detection from the position sensors 1522 and 1524 and the acceleration sensor 1526. The control module 1570 may include a signal processor 1572 configured to receive signals from the position sensors 1522 and 1524 and the acceleration sensor 1526 and may be further configured to identify vibration modes of the stage 1560 and the SEM column 1530 using the received signals. In some embodiments, the signal processor 1572 may include a field programmable gate array (FPGA)-based controller and may be configured to process vibration signals from the position sensors 1522 and 1524 and the acceleration sensor 1526. In some embodiments, the signal processor 1572, which may be referred to as a digital vibration estimation controller (DVEC), may be configured to identify vibration modes based on input vibration signals from the position sensors 1522 and 1524 and the acceleration sensor 1526.

[0212]

[0229] In some embodiments, signal processor 1572 may be configured to determine a vibration compensation signal based on signals from position sensors 1522 and 1524 and acceleration sensor 1526, for example, using a dynamic vibration estimation algorithm (described in more detail below with reference to FIG. 16 ) executed by processor 1574. Signal processor 1572 may include other associated components (not shown) to support processor 1574 or signal processor 1572, including, but not limited to, a data storage unit, memory, timing control circuitry, among others.

[0213]

[0230] In some embodiments, signal processor 1572 may be configured to determine a predicted vibration signal based on signals from position sensors 1522 and 1524 and acceleration sensor 1526, for example, using a dynamic vibration estimation algorithm executed by processor 1574. The predicted vibration signal may be applied to digital image controller 1576 in combination with beam scan signal 1575. Beam scan signal 1575 may be applied directly to digital image controller 1576 or may be applied to digital image controller 1576 via control module 1570. In some embodiments, beam scan signal 1575 may be generated by a user, a host, or a beam control module (e.g., beam control module 365 of FIG. 3 ), among others. Digital image controller 1576 may be configured to generate a compensated beam scan signal based on beam scan signal 1575 and the predicted vibration signal from signal processor 1572. In some embodiments, although not preferred, the signal processor 1572 may be configured to receive a beam scanning signal 1575 from the host and determine a predicted vibration signal based on signals from the position sensors 1522 and 1524 and the acceleration sensor 1526.

[0214]

[0231] In some embodiments, the control module 1570 may further include an actuator 1578 configured to receive the compensated beam scan signal from the digital image controller 1576 and generate a beam deflection signal 1580 based on the received compensated beam scan signal. In some embodiments, the actuator 1578 may include a digital wave generator configured to generate an electrical waveform using digital signal processing techniques. The beam deflection signal 1580 may be applied to the SEM column 1530. In some embodiments, the beam deflection signal 1580 may be applied to the SEM column 1530 through a beam deflection controller (e.g., beam deflection controller 367 in FIG. 3 ) or a beam control module (e.g., beam control module 365 in FIG. 3 ). The beam deflection signal 1580 may be configured to compensate for vibrations of the charged particle beam system 1500, for example, by adjusting characteristics of the primary charged particle beam based on the detected vibrations. While the signal processor 1572, the digital image controller 1576, and the actuator 1578 are illustrated as components of the control module 1570, it will be understood that one or more of these components may be used as separate elements of the charged particle beam system 1500. For example, the control module 1570 may include the signal processor 1572 and the digital image controller 1576, while independently operating the actuator 1578. It will also be understood that the charged particle beam system 1500 may not include the control module 1570, but instead may include the signal processor 1572, the digital image controller 1576, and the actuator 1578 as separate components.

[0215]

[0232] Reference is now made to FIG. 16 , which illustrates steps of an exemplary algorithm 1600 for determining a vibration estimation and compensation signal consistent with embodiments of the present disclosure. One or more steps of the algorithm 1600 may be performed, for example, by the processor 1574. In some embodiments, the algorithm 1600 may be performed in real time. In the context of the present disclosure, “real time” may refer to the occurrence of events within a very short period of time, on the order of milliseconds or microseconds. In other words, the occurrence of events with negligible delay between events. For example, in the context of the present disclosure, step 1610 may be performed substantially immediately after vibration measurements by the position sensors 1522 and 1524 and the acceleration sensor 1526.

[0216]

[0233] In step 1610 of algorithm 1600, vibration measurement signals from position sensors 1522 and 1524 and acceleration sensor 1526 may be utilized to identify vibration modes of stage 1560 and SEM column 1530, respectively. Signal processor 1572 (DVEC) may be configured to perform the vibration mode identification. In some embodiments, the vibration mode identification may include matching signals from position sensors 1522 and 1524 and acceleration sensor 1526. For example, the vibration measurement signals from acceleration sensor 1526 may include voltage signals, whereas the vibration measurement signals from position sensors 1522 and 1524 may include distance or displacement signals. In some embodiments, signal processor 1572 may be configured to convert the voltage signals from acceleration sensor 1526 into corresponding displacement signals, such that input signals for vibration mode identification from stage 1560 and SEM column 1530 are matched.

[0217]

[0234] In some embodiments, identifying the vibration modes may further include forming a vibration mode identification matrix of vibration measurements from six degrees of freedom for the stage 1560 and the SEM column 1530 based on the fitted vibration measurement signals. The vibration mode identification matrix may include measurements of vibration in each direction (X, Y, Z, Rx, Ry, and Rz). In this step, the vibration modes of the SEM column 1530 may be identified with reference to the stage 1560.

[0218]

[0235] Identifying the vibration modes in step 1610 may further include using vibration measurements from the acceleration sensor 1526 to decouple vibrations of the position sensors 1522 and 1524 from vibrations of the stage 1560. Because the position sensors 1522 and 1524 may be mounted or mechanically coupled to the containment chamber 1510, vibrations of the containment chamber 1510 may result in vibrations of the position sensors 1522 and 1524. The vibration measurements obtained by the position sensors 1522 and 1524 may include vibrations and vibration modes of the position sensors 1522 and 1524 in addition to vibrations of the stage 1560. Therefore, it may be desirable to decouple and isolate vibrations of the stage 1560 from vibrations of the position sensors 1522 and 1524.

[0219]

[0236] Based on the vibration mode identification matrix, the vibration modes of the SEM column 1530 and the stage 1560 may be determined, and corresponding output signals may be generated.

[0220]

[0237] In step 1620, the identified vibration modes from step 1610 may be used to estimate, using a simulation model or a mathematical model, the vibrations of the SEM column 1530 and stage 1560. In some embodiments, a three-dimensional finite element analysis model (3D-FEM) may be used to estimate the vibrations of the SEM column 1530 and stage 1560 along any or all of the X, Y, Z, Rx, Ry, and Rz axes.

[0221]

[0238] In step 1630, vibrations of the SEM column 1530 and stage 1560 may be predicted based on the estimated vibrations from step 1620. One of several problems encountered with digital signal processing techniques involves computation and measurement delays, also known as "one sample delays." To mitigate the adverse effects of signal processing delays, it may be desirable to determine and apply a "predicted" vibration signal to compensate for the vibrations.

[0222]

[0239] In this context, a one-sample delay may refer to the delay between measuring the vibration and applying the actuation signal or beam deflection signal 1580. For example, the vibration measurement may be performed at a first timestamp, and the correction signal or beam deflection signal to compensate for the measured vibration may be performed at a second timestamp, with the time difference between the first and second timestamps being the amount of time required to process the measured vibration signal to generate the vibration compensation signal. Due to the time delay, the measured vibration and the applied compensation signal are asynchronous, thereby resulting in inaccurate vibration compensation.

[0223]

[0240] To compensate for digital signal processing delays, vibrations may be predicted and forecast based on the estimated vibrations of the SEM column 1530 and stage 1560 at the second timestamp so that vibration measurements and application of the compensation signal can be synchronized.

[0224]

[0241] In some embodiments, the steps of algorithm 1600 may be implemented to predict vibrations of the SEM column 1530 and stage 1560 in one or more of the X-axis, Y-axis, or Rz-axis. One of several ways to compensate for vibrations in the Z-axis, Rx-axis, or Ry-axis may include adjusting the focal depth of the incident primary charged particle beam by adjusting the landing energy, among other things.

[0225]

[0242] Reference is now made to FIG. 17 , which illustrates a flowchart showing an exemplary method 1700 of focusing a charged particle beam (e.g., an electron beam) on a sample in a charged particle beam system, consistent with embodiments of the present disclosure. The method of focusing an electron beam on a sample may be performed by the charged particle EBI system 100 of FIG. 1 , the imaging system 200 of FIG. 2 , or the charged particle beam system 1500. It is understood that the charged particle beam system 1500 may be controlled to observe, image, and inspect a sample (e.g., sample 1550 of FIG. 15 ) or a region of interest on the sample. Imaging may include scanning the sample to image at least a portion of the sample, a pattern on the sample, or the sample itself. Inspecting the sample may include scanning the sample to inspect at least a portion of the sample, a pattern on the sample, or the sample itself. Observing the sample may include monitoring the sample or a region of interest on the sample for reproducibility and repeatability of a pattern.

[0226]

[0243] A primary charged particle beam (e.g., primary charged particle beam 220 in FIG. 2) is generated from a charged particle source. A sample disposed on a stage (e.g., stage 201 in FIGS. 2-4, stage 1560 in FIG. 15) is irradiated with the primary charged particle beam. In some embodiments, at least a portion of the sample may be irradiated with at least a portion of the primary charged particle beam. The primary charged particle beam may be, for example, an electron beam generated from an electron source. The electron source may include, but is not limited to, thermionic emission of electrons from a tungsten filament or LaB6 cathode, or field emission of electrons from a tungsten / ZrO2 cold cathode.

[0227]

[0244] The sample may be placed directly on the stage. In some embodiments, the sample may be placed on an adapter, such as a sample holder (e.g., wafer chuck 1562 in FIG. 15 ), which may be placed on and secured to the stage. The geometric centers of the sample, sample holder, and stage may be aligned with each other and with the primary optical axis (e.g., primary optical axis 801 in FIG. 8 ). The sample, sample holder, and stage may be positioned in a plane that is orthogonal or substantially orthogonal to the primary optical axis. In some embodiments, the sample or stage may be tilted off-axis so that the primary charged particle beam is incident on the sample at an angle less than or greater than 90°. In some embodiments, the sample and stage may be mechanically coupled such that displacement of the stage in any of the X, Y, or Z axes results in a corresponding displacement of the sample.

[0228]

[0245] The stage may be mechanically coupled to the containing chamber (e.g., containing chamber 1510 in FIG. 15 ) such that vibration of the stage can also cause vibration of the containing chamber. The stage may be mechanically coupled to the containing chamber using techniques including, but not limited to, heat welding, spot welding, riveting, soldering, adhesive bonding, etc. The containing chamber may be configured to house electromechanical components of the charged particle beam column. In the context of this disclosure, electromechanical components of the charged particle beam column may refer to parts or elements including, but not limited to, the stage, wafer chuck, sample, stage motion control motors, drives, etc. The containing chamber may be located on a vibration-isolated or vibration-damped platform to minimize the effects of vibration on the overall performance and inspection resolution of the obtained images. In some embodiments, the SEM column (e.g., charged particle beam column 1530 in FIG. 15 ) may be referred to as an electro-optical component. The electro-optical components may include a charged particle source configured to generate charged particles and, for example, a plurality of lenses (optical and electromagnetic) and apertures configured to focus the generated charged particle beam onto the sample. The SEM column may be mechanically coupled to a portion of the containment chamber such that vibrations of the containment chamber can cause vibrations of the SEM column.

[0229]

[0246] In step 1710, an acceleration sensor (e.g., acceleration sensor 1526 in FIG. 15) may be used to detect vibration of an electro-optical component of the charged particle beam system. The electro-optical component may include an SEM column. The acceleration sensor may be configured to measure vibration of the SEM column or acceleration of the SEM column's motion. The acceleration sensor may include a piezoelectric accelerometer, a capacitive accelerometer, a microelectromechanical system (MEMS)-based accelerometer, or a piezoresistive accelerometer. In a piezoelectric accelerometer configured to measure vibration, the force caused by the vibration or change in motion (acceleration) generates a charge proportional to the applied force. Since charge is proportional to force and mass is constant, charge is also proportional to acceleration. The acceleration sensor may include a high-impedance charge output accelerometer or a low-impedance output accelerometer configured to generate a voltage signal in response to detected vibration and based on the frequency of the detected vibration. The acceleration sensor detects vibration of the SEM column and may detect vibration modes including, but not limited to, tilt, rotation, twist, shift, etc. The charged particle beam system may include two or more acceleration sensors mounted on the SEM column. The output signal generated by the acceleration sensors may include an electrical signal, such as a voltage signal.

[0230]

[0247] In step 1720, a position sensor (e.g., position sensor 1522 in FIG. 15 ) may be used to detect vibrations of electromechanical components of the charged particle beam system. The electromechanical components of the charged particle beam system may include a stage, a wafer chuck, a sample, a stage motion control motor, a drive, etc. One or more position sensors may be used to detect vibrations and vibration modes of the stage in the X or Y axis. The position sensor may include, among other things, a laser diode sensor assembly including a one-dimensional position sensitive detector (1-D PSD) or a linear array of photodiodes. The position sensor may be configured to determine lateral displacement of the stage and to detect vibration modes of the stage, such as twist, tilt, rotation, and shift in the translational X or Y axis and the rotational Rx and Ry axes. In some embodiments, a first position sensor for detecting vibrations along the X axis, a second position sensor for detecting vibrations along the Y axis, a third sensor for detecting vibrations about the Rx axis, and a fourth sensor for detecting vibrations about the Ry axis. The position sensor may be in communication with a control module (e.g., control module 1570 of FIG. 15) so that the output signal of the position sensor may be analyzed and used to further adjust the beam characteristics to compensate for vibrations. The output signal may include a displacement signal.

[0231]

[0248] The position sensor may be disposed on a surface of the receiving chamber or attached to the receiving chamber. The position sensor may include a laser interferometer. The position sensor may be mechanically coupled to the receiving chamber such that vibrations of the receiving chamber cause the position sensor to vibrate. The position sensor may be configured to adjust the position of the stage or sample in one or more of the X, Y, Z, Rx, Ry, and Rz axes and to detect vibrations in one or more of the X, Y, Z, Rx, Ry, and Rz axes. The position sensor may include, for example, a homodyne laser interferometer or a heterodyne laser interferometer. A homodyne laser interferometer uses a single-frequency laser source, whereas a heterodyne laser interferometer uses a laser source with two closely spaced frequencies. The laser source may include a He-Ne gas laser emitting laser light at a wavelength of 633 nm. It is understood that other laser sources with single or multiple wavelength or frequency emissions may also be used as appropriate. The position sensor may generate a displacement or distance signal based on the frequency or type of vibration mode of the detected vibration.

[0232]

[0249] In step 1730, a vibration compensation signal may be applied to the SEM column to compensate for vibrations in the electro-optical and electromechanical components. The vibration compensation signal may be generated by a controller (e.g., signal processor 1572 of FIG. 15 ), also referred to herein as a dynamic vibration estimation controller (DVEC). The controller may be configured to receive signals related to vibration detection from the position sensors and acceleration sensors, process the received signals, and generate the vibration compensation signal based on the processed vibration signals. The DVEC may include a field programmable gate array (FPGA)-based controller and may be configured to process the vibration signals from the position sensors and acceleration sensors.

[0233]

[0250] The DVEC may be configured to predict or calculate vibration compensation signals based on signals from the position and acceleration sensors using a dynamic vibration estimation algorithm, which may include identifying vibration modes of the SEM column and stage in each of the X, Y, Z, Rx, Ry, and Rz axes based on vibration measurements from the position and acceleration sensors, estimating vibrations of the SEM column and stage based on the identified vibration modes, and predicting or calculating vibrations in six degrees of freedom applied to the SEM column.

[0234]

[0251] The algorithm may be implemented in real time and executed by the DVEC. In the vibration mode identification step, the vibration measurement signals from the position sensor and the acceleration sensor may be utilized to identify vibration modes of the stage and the SEM column, respectively. The DVEC may perform the vibration mode identification. The vibration mode identification may include adapting the signals from the position sensor and the acceleration sensor. For example, the vibration measurement signal from the acceleration sensor may include a voltage signal, whereas the vibration measurement signal from the position sensor may include a distance signal or a displacement signal. The DVEC may convert the voltage signal from the acceleration sensor into a corresponding displacement signal, so that the input signals for vibration mode identification from the stage and the SEM column are adapted.

[0235]

[0252] Identifying the vibration modes may further include forming a vibration mode identification matrix of vibration measurements from six degrees of freedom for the stage and the SEM column based on the fitted vibration measurement signals. The vibration mode identification matrix may include measurements of vibration in each direction (X, Y, Z, Rx, Ry, and Rz). In this step, the vibration modes of the SEM column may be identified relative to the stage.

[0236]

[0253] Identifying the vibration modes may further include using vibration measurements from the acceleration sensor to decouple vibrations of the position sensor from vibrations of the stage. Because the position sensor is mounted or mechanically coupled to the receiving chamber, vibrations of the receiving chamber may result in vibrations of the position sensor. The vibration measurements obtained by the position sensor may include vibrations and vibration modes of the position sensor in addition to vibrations of the stage. Thus, vibrations of the stage are decoupled and isolated from vibrations of the position sensor. Based on the vibration mode identification matrix, vibration modes of the SEM column and stage may be determined, and corresponding output signals may be generated.

[0237]

[0254] The identified vibration modes may be used to estimate the vibrations of the SEM column and stage using simulation or mathematical models. A three-dimensional finite element analysis model (3D-FEM) may be used to estimate the vibrations of the SEM column and stage along the X, Y, Z, Rx, Ry, and Rz axes. It will be understood that other simulation models may be used as appropriate.

[0238]

[0255] Vibrations of the SEM column and stage may be predicted based on estimated vibrations. One of several problems encountered with digital signal processing techniques involves computation and measurement delay, also known as "one sample delay." To mitigate the adverse effects of signal processing delays, it may be desirable to determine and apply a "predicted" vibration signal to compensate for the vibrations.

[0239]

[0256] In this context, a one-sample delay may refer to the delay between measuring vibration and applying an actuation signal or beam deflection signal. For example, a vibration measurement may be performed at a first timestamp, and a correction signal or beam deflection signal to compensate for the measured vibration may be performed at a second timestamp, with the time difference between the first and second timestamps being the amount of time required to process the measured vibration signal to generate a vibration compensation signal. Due to the time delay, the measured vibration and the applied compensation signal are asynchronous, thereby resulting in inaccurate vibration compensation. To compensate for the digital signal processing delay, vibration may be predicted or forecast based on the estimated vibration of the SEM column and stage at the second timestamp, such that the vibration measurement and the application of the compensation signal can be synchronized.

[0240]

[0257] The predicted vibration signal may be applied to an image controller (e.g., digital image controller 1576 in FIG. 15) in combination with a beam scan signal (e.g., beam scan signal 1575 in FIG. 15). The beam scan signal may be applied directly to the digital image controller or may be applied to the digital image controller via a control module. In some embodiments, the beam scan signal may be generated by a user, a host, or a beam control module (e.g., beam control module 365 in FIG. 3). The image controller may be configured to generate a compensated beam scan signal based on the beam scan signal and the predicted vibration signal from a signal processor or controller.

[0241]

[0258] An actuator (e.g., actuator 1578 in FIG. 15 ) may be configured to receive the compensated beam scanning signal from the image controller and generate a beam deflection signal (e.g., beam deflection signal 1580 in FIG. 15 ) based on the received compensated beam scanning signal. The actuator may include a digital wave generator configured to generate an electrical waveform using digital signal processing techniques. The beam deflection signal may be applied to the SEM column to adjust beam characteristics to compensate for vibrations. The beam deflection signal may be applied to the SEM column through a beam deflection controller (e.g., beam deflection controller 367 in FIG. 3 ) or a beam control module. The beam deflection signal may be configured to compensate for vibrations in the charged particle beam system, for example, by adjusting characteristics of the primary charged particle beam based on the detected vibrations. While the signal processor, digital image controller, and actuator are illustrated as components of a control module, it will be understood that one or more of these components may be used as independent elements of a charged particle beam system.

[0242]

[0259] The embodiments may be further described using the following clauses. Article 1. 1. A charged particle beam system comprising: the stage configured to hold a sample and movable in at least one of an XY and a Z axis; a position sensing system configured to determine lateral and vertical displacement of the stage; applying a first signal to deflect a primary charged particle beam incident on the sample to at least partially compensate for the lateral displacement of the stage; and Applying a second signal to adjust the focus of the deflected charged particle beam incident on the sample to at least partially compensate for the vertical displacement of the stage. With a controller configured as 1. A charged particle beam system comprising: Article 2. 2. The system of claim 1, wherein the first signal comprises an electrical signal that affects how the primary charged particle beam is deflected in at least one of the X and Y axes. Article 3. 3. The system of claim 2, wherein the electrical signal comprises a signal having a bandwidth in the range of 10 kHz to 50 kHz. Article 4. 4. The system of any one of clauses 1 to 3, wherein the lateral displacement corresponds to a difference between a current position of the stage and a target position of the stage in the at least one of an X and Y axis. Article 5. The system of any one of clauses 1 to 4, wherein the controller is further configured to dynamically adjust at least one of the first signal or the second signal during scanning of the primary charged particle beam on the sample. Article 6. The system of any one of clauses 1 to 5, wherein the second signal includes a voltage signal applied to the stage that affects how the deflected charged particle beam incident on the sample is focused in the Z axis. Article 7. 7. The system of claim 6, wherein the voltage signal comprises a signal having a bandwidth in the range of 50 kHz to 200 kHz. Article 8. 8. The system of any one of clauses 1 to 7, wherein the vertical displacement corresponds to the difference between a current position of the stage in the Z axis and a target position of the stage, and the vertical displacement varies during scanning of the primary charged particle beam over the sample to at least partially compensate for angular rotation about at least one of the X or Y axes. Article 9. 9. The system of any one of clauses 1-8, further comprising a stage motion controller, the stage motion controller comprising a plurality of motors configured to be individually controlled by a third signal. Article 10. 10. The system of claim 9, wherein each of the plurality of motors is individually controlled to adjust the leveling of the stage so that the stage is substantially perpendicular to the optical axis of the primary charged particle beam. Article 11. 11. The system of any one of clauses 9 and 10, wherein the third signal includes a plurality of control signals, each of the plurality of control signals corresponding to at least one of the plurality of motors. Article 12. 12. The system of any one of clauses 9 to 11, wherein the plurality of motors includes at least one of a piezoelectric motor, a piezoelectric actuator, or an ultrasonic piezoelectric motor. Article 13. a first component configured to form an embedded control signal based on the plurality of control signals; a second component configured to extract at least one of the plurality of control signals from the embedded control signal; 12. The system of claim 11, further comprising: Article 14. 14. The system of any one of clauses 10 to 13, wherein adjusting the leveling of the stage is based on a geometric model of the actuation output of the stage. Article 15. 15. A system according to any one of clauses 1 to 14, wherein the position sensing system uses a combination of a laser interferometer and a height sensor to determine the lateral and vertical displacement of the stage. Article 16. 16. The system of clause 15, wherein the laser interferometer is configured to determine at least the lateral displacement of the stage. Article 17. 16. The system of clause 15, wherein the height sensor is configured to determine the vertical displacement of the stage. Article 18. 1. A charged particle beam system comprising: the stage configured to hold a sample and movable in at least a Z-axis; a position sensing system configured to determine vertical displacement of the stage; a controller configured to apply a voltage signal to the stage that affects how the charged particle beam incident on the sample is focused in the Z-axis; 1. A charged particle beam system comprising: Article 19. 19. The system of claim 18, wherein the vertical displacement corresponds to a difference between a current position of the stage in the Z axis and a target position of the stage, and wherein the vertical displacement varies during a scan of the primary charged particle beam over the sample to at least partially compensate for angular rotation about at least one of the X or Y axes. Article 20. 20. The system of any one of clauses 18 and 19, wherein the controller is further configured to dynamically adjust the voltage signal during a scan of the primary charged particle beam over the sample. Article 21. 21. The system of any one of clauses 18 to 20, wherein the voltage signal comprises a signal having a bandwidth in the range of 50 kHz to 200 kHz. Article 22. 22. The system of any one of clauses 18-21, further comprising a stage motion controller, said stage motion controller comprising a plurality of motors configured to be individually controlled by control signals. Article 23. 23. The system of claim 22, wherein each of the plurality of motors is individually controlled to adjust leveling of the stage so that the stage is substantially perpendicular to the optical axis of the primary charged particle beam. Article 24. 24. The system of any one of clauses 22 and 23, wherein the control signals include a plurality of control signals, each of the plurality of control signals corresponding to at least one of the plurality of motors. Article 25. a first component configured to form an embedded control signal based on the plurality of control signals; a second component configured to extract at least one of the plurality of control signals from the embedded control signal; 25. The system of clause 24, further comprising: Article 26. 26. A system according to any one of clauses 18 to 25, wherein the positioning system includes a height sensor for determining the vertical displacement of the stage. Article 27. 1. A method for irradiating a sample disposed on a stage in a charged particle beam system, comprising: generating a primary charged particle beam from a charged particle source; determining lateral and vertical displacements of the stage, the stage being movable in at least one of an XY and a Z axis; applying a first signal to deflect the primary charged particle beam incident on the sample to at least partially compensate for the lateral displacement of the stage; applying a second signal to the stage to adjust a focus of the deflected charged particle beam incident on the sample to at least partially compensate for the vertical displacement of the stage; A method comprising: Article 28. 28. The method of clause 27, wherein the first signal comprises an electrical signal that affects how the primary charged particle beam is deflected in the at least one of the X and Y axes. Article 29. 29. The method of claim 28, wherein the electrical signal comprises a signal having a bandwidth in the range of 10 kHz to 50 kHz. Article 30. 30. The method of any one of clauses 27 to 29, wherein the lateral displacement corresponds to a difference between a current position of the stage and a target position of the stage in the at least one of an X and Y axis. Article 31. 31. The method of any one of clauses 27 to 30, wherein the vertical displacement corresponds to a difference between a current position of the stage and a target position of the stage in the Z axis, and the vertical displacement is varied during a scan of the primary charged particle beam over the sample to at least partially compensate for angular rotation about at least one of the X or Y axes. Article 32. 32. The method of any one of clauses 27 to 31, further comprising dynamically adjusting at least one of the first signal or the second signal during a scan of the primary charged particle beam over the sample. Article 33. 33. The method of any one of clauses 27 to 32, wherein the second signal comprises a voltage signal applied to the stage that affects how the deflected charged particle beam incident on the sample is focused in the Z axis. Article 34. 34. The method of claim 33, wherein the voltage signal comprises a signal having a bandwidth in the range of 50 kHz to 200 kHz. Article 35. 35. The method of any one of clauses 27 to 34, further comprising applying a third signal to a stage motion controller, the stage motion controller comprising a plurality of motors configured to be individually controlled by the third signal. Article 36. 36. The method of claim 35, wherein each of the plurality of motors is individually controlled to adjust leveling of the stage so that the stage is substantially perpendicular to an optical axis of the primary charged particle beam. Article 37. 37. The method of any one of clauses 35 and 36, wherein the third signal includes a plurality of control signals, each of the plurality of control signals corresponding to at least one of the plurality of motors. Article 38. 38. The method of any one of clauses 35 to 37, wherein applying the third signal includes embedding the plurality of control signals to form an embedded control signal, and extracting at least one of the plurality of control signals from the embedded control signal. Article 39. 39. The method of any one of clauses 36 to 38, wherein adjusting the leveling of the stage is based on a geometric model of the actuation output of the stage. Article 40. 40. The method of any one of clauses 27 to 39, wherein the lateral and vertical displacements of the stage are determined by a position sensing system. Article 41. 41. The method of clause 40, wherein the position sensing system determines the lateral and vertical displacement of the stage using a combination of a laser interferometer and a height sensor. Article 42. 42. The method of claim 41, wherein the laser interferometer is configured to determine the lateral displacement of the stage. Article 43. 42. The method of claim 41, wherein the height sensor is configured to determine the vertical displacement of the stage. Article 44. 1. A method for irradiating a sample disposed on a stage in a charged particle beam system, comprising: generating a primary charged particle beam from a charged particle source; determining a vertical displacement of the stage, the stage being movable in a Z-axis; applying a voltage signal to the stage to adjust a focus of the deflected charged particle beam incident on the sample to at least partially compensate for the vertical displacement of the stage; A method comprising: Article 45. 45. The method of claim 44, wherein the vertical displacement corresponds to a difference between a current position of the stage and a target position of the stage in the Z axis, and the vertical displacement is varied during a scan of the primary charged particle beam over the sample to at least partially compensate for angular rotation about at least one of the X or Y axes. Article 46. determining a lateral displacement of the stage, the stage being movable in at least one of an X and Y axis; applying a beam deflection signal to deflect a focused charged particle beam incident on the sample to at least partially compensate for the lateral displacement; 46. ​​The method of any one of clauses 44 and 45, further comprising: Article 47. 47. The method of any one of clauses 44 to 46, further comprising dynamically adjusting at least one of the voltage signal or the beam deflection signal during a scan of the primary charged particle beam over the sample. Article 48. 48. The method of any one of clauses 44 to 47, wherein the voltage signal comprises a signal having a bandwidth in the range of 50 kHz to 200 kHz. Article 49. 47. The method of clause 46, wherein the beam deflection signal comprises an electrical signal that affects how the focused charged particle beam is deflected in the at least one of an X and Y axis. Article 50. 50. The method of claim 49, wherein the electrical signal comprises a signal having a bandwidth in the range of 10 kHz to 50 kHz. Article 51. 51. The method of any one of clauses 46 to 50, wherein the lateral displacement corresponds to a difference between a current position of the stage and a target position of the stage in the at least one of an X and Y axis. Article 52. 52. The method of any one of clauses 44 to 51, further comprising applying control signals to a stage motion controller, the stage motion controller comprising a plurality of motors configured to be individually controlled by the control signals. Article 53. 53. The method of claim 52, wherein each of the plurality of motors is individually controlled to adjust leveling of the stage so that the stage is substantially perpendicular to an optical axis of the primary charged particle beam. Article 54. 54. The method of any one of clauses 52 and 53, wherein the control signals include a plurality of control signals, each of the plurality of control signals corresponding to at least one of the plurality of motors. Article 55. 55. The method of any one of clauses 52 to 54, wherein the plurality of motors includes at least one of a piezoelectric motor, a piezoelectric actuator, or an ultrasonic piezoelectric motor. Article 56. 56. The method of any one of clauses 52 to 55, wherein applying the control signal includes embedding the plurality of control signals to form an embedded control signal, and extracting at least one of the plurality of control signals from the embedded control signal. Article 57. 57. The method of any one of clauses 53 to 56, wherein adjusting the leveling of the stage is based on a geometric model of the actuation output of the stage. Article 58. 58. The method of any one of clauses 46 to 57, wherein the lateral and vertical displacements of the stage are determined by a position sensing system. Article 59. 59. The method of clause 58, wherein the position sensing system determines the lateral and vertical displacement of the stage using a combination of a laser interferometer and a height sensor. Article 60. 60. The method of clause 59, wherein the laser interferometer is configured to determine the lateral displacement of the stage. Article 61. 60. The method of clause 59, wherein the height sensor is configured to determine the vertical displacement of the stage. Article 62. 1. A non-transitory computer-readable medium comprising a set of instructions executable by one or more processors of an apparatus to cause said apparatus to perform a method, said apparatus including a charged particle source for generating a primary charged particle beam, said method comprising: determining a lateral displacement of a stage, the stage being movable in at least one of an X and Y axis; instructing a controller to apply a first signal to deflect the primary charged particle beam incident on the sample to at least partially compensate for the lateral displacement; 1. A non-transitory computer-readable medium comprising: Article 63. The set of instructions executable by the one or more processors of the device: determining a vertical displacement of the stage, the stage being movable in a Z-axis; applying a second signal to instruct the controller to adjust a focus of the primary charged particle beam incident on the sample to at least partially compensate for the vertical displacement; 63. The medium of claim 62, further causing the device to perform: Article 64. The set of instructions executable by the one or more processors of the device: applying a third signal to a stage motion controller configured to adjust leveling of the stage so that the stage is substantially perpendicular to an optical axis of the primary charged particle beam; 64. The medium of any one of clauses 62 and 63, further causing the device to perform: Article 65. A method for focusing a charged particle beam onto a sample, irradiating the sample disposed on a stage of a charged particle beam system with the charged particle beam; adjusting a location of a first focal point of the charged particle beam relative to the sample using a first component of the charged particle system; using a second component located downstream of a focusing component of an objective lens of the charged particle system to manipulate an electromagnetic field associated with the sample to form a second focal point by adjusting the first focal point of the charged particle beam relative to the sample; A method comprising: Article 66. 66. The method of clause 65, wherein adjusting the location of the first focal point includes adjusting a position of the stage in a Z axis. Article 67. Adjusting the position of the stage in the Z axis includes: determining a position of the sample in the Z axis using a height sensor; adjusting the position of the stage in the Z axis based on the determined position of the sample using a stage motion controller; 67. The method of claim 66, including: Article 68. 68. The method of any one of clauses 65 to 67, wherein the first component is configured to adjust a focal depth of the charged particle beam relative to the sample. Article 69. 69. A method according to any one of clauses 65 to 68, wherein the first component is located upstream of the focusing component of the objective lens of the charged particle system. Article 70. 70. The method of claim 69, wherein the first component comprises a charged particle source, an anode of the charged particle source, or a focusing lens, and the first component of the charged particle system is different from the second component of the charged particle system. Article 71. 71. The method of any one of clauses 65 to 70, wherein manipulating the electromagnetic field comprises adjusting an electrical signal applied to the second component of the charged particle system. Article 72. 72. The method of any one of clauses 65 to 71, wherein the second component of the charged particle system comprises one or more of a control electrode of the objective lens, the sample, or the stage. Article 73. 73. A method according to any one of clauses 71 to 72, wherein the landing energy of the charged particle beam on the sample is adjusted by adjusting the electrical signal applied to the second component. Article 74. Adjusting the electrical signal includes: adjusting a first component of the electrical signal applied to the control electrode of the objective lens; adjusting a second component of the electrical signal applied to the stage; and 74. The method of any one of clauses 72-73, comprising: Article 75. 75. The method of claim 74, wherein the first focus of the charged particle beam is coarsely adjusted relative to the sample by adjusting the first component of the electrical signal applied to the control electrode, and the first focus of the charged particle beam is finely adjusted relative to the sample by adjusting the second component of the electrical signal applied to the stage. Article 76. 76. The method of any one of clauses 74-75, wherein the first component of the electrical signal is determined based on an acceleration voltage and the landing energy of the charged particle beam. Article 77. 77. A method according to any one of clauses 74 to 76, wherein the first component of the electrical signal comprises a voltage signal having an absolute value in the range of 5KV to 10KV, and the second component of the electrical signal comprises a voltage signal having an absolute value in the range of 0V to 150V. Article 78. 78. The method of any one of clauses 65 to 77, wherein manipulating the electromagnetic field further comprises adjusting an electric field configured to affect a characteristic of the charged particle beam. Article 79. 79. The method of any one of clauses 65 to 78, wherein manipulating the electromagnetic field further comprises adjusting a magnetic field configured to affect a characteristic of the charged particle beam. Article 80. 80. The method of any one of clauses 78 and 79, wherein the characteristics of the charged particle beam include at least one of a path, a direction, a velocity, or an acceleration of the charged particle beam. Article 81. 81. The method of any one of clauses 73 to 80, wherein the landing energy of the charged particle beam is in the range of 500 eV to 3 keV. Article 82. 1. A method for focusing a charged particle beam onto a sample, comprising: irradiating the sample disposed on a stage of a charged particle beam system with the charged particle beam; adjusting a location of a first focal point of the charged particle beam relative to the sample using a first component of the charged particle system; manipulating an electromagnetic field associated with the sample by adjusting a first component of an electrical signal applied to a control electrode of an objective lens to adjust the first focus of the charged particle beam on the sample to form a second focus; A method comprising: Article 83. 83. The method of clause 82, wherein adjusting the location of the first focal point includes adjusting a position of the stage in a Z axis. Article 84. Adjusting the position of the stage in the Z axis includes: determining a position of the sample in the Z axis using a height sensor; adjusting the position of the stage in the Z axis based on the determined position of the sample using a stage motion controller; 84. The method of claim 83, including: Article 85. 85. The method of any one of clauses 82 to 84, wherein the first component is configured to adjust the focal depth of the charged particle beam relative to the sample. Article 86. A method according to any one of clauses 82 to 85, wherein the first component is located upstream of a focusing component of the objective lens of the charged particle system, and the first component comprises a charged particle source, an anode of the charged particle source, or a focusing lens. Article 87. 87. A method according to any one of clauses 82 to 86, wherein the control electrode comprises a second component of the charged particle system and is located downstream of a focusing component of the objective lens of the charged particle system. Article 88. 88. The method of clause 87, wherein adjusting the electrical signal applied to the second component adjusts the landing energy of the charged particle beam on the sample. Article 89. 89. The method of claim 88, wherein the landing energy of the charged particle beam is in the range of 500 eV to 3 keV. Article 90. 90. A method according to any one of clauses 87 to 89, wherein the second component of the charged particle system comprises one or more of the control electrode of the objective lens, the sample, or the stage. Article 91. 91. The method of any one of clauses 87 to 90, wherein the first component of the charged particle system is different from the second component of the charged particle system. Article 92. 92. The method of any one of clauses 82 to 91, wherein manipulating the electromagnetic field further comprises adjusting a second component of the electrical signal applied to the stage. Article 93. 93. The method of any one of clauses 88 to 92, wherein the first component of the electrical signal is determined based on an acceleration voltage and the landing energy of the charged particle beam. Article 94. 94. A method according to any one of clauses 92 and 93, wherein the first component of the electrical signal comprises a voltage signal having an absolute value in the range of 5KV to 10KV, and the second component of the electrical signal comprises a voltage signal having an absolute value in the range of 0V to 150V. Article 95. A method according to any one of clauses 92 to 94, wherein the first focus of the charged particle beam is coarsely adjusted by adjusting the first component of the electrical signal applied to the control electrode, and the first focus of the charged particle beam is finely adjusted relative to the sample by adjusting the second component of the electrical signal applied to the stage. Article 96. 96. The method of any one of clauses 82-95, wherein manipulating the electromagnetic field further comprises adjusting a magnetic field configured to affect a characteristic of the charged particle beam. Article 97. 97. The method of clause 96, wherein the properties of the charged particle beam include at least one of a path, a direction, a velocity, or an acceleration of the charged particle beam. Article 98. 1. A charged particle beam system comprising: the stage configured to hold a sample and movable along at least one of an X-axis, a Y-axis, or a Z-axis; A controller having circuitry, adjusting a location of a first focal point of the charged particle beam relative to the sample using a first component of the charged particle system; a second component, located downstream of a focusing component of an objective lens of the charged particle system, using the second component to manipulate an electromagnetic field associated with the sample to adjust the first focus of the charged particle beam relative to the sample, thereby forming a second focus. The controller configured as above 1. A charged particle beam system comprising: Article 99. 99. The system of claim 98, wherein adjusting the location of the first focal point includes adjusting a position of the stage in the Z axis. Article 100. A system described in any one of clauses 98 and 99, further comprising a position sensing system configured to determine the position of the sample in the Z axis, the position sensing system comprising a height sensor including a laser diode sensor assembly. Article 101. 101. The system of claim 100, wherein the controller is configured to adjust the position of the stage in the Z axis based on the position of the sample determined by the position sensing system. Article 102. A system described in any one of clauses 100 and 101, wherein the height sensor is configured to determine the position of the sample in the Z axis, and the controller is configured to adjust the position of the stage in the Z axis to form the first focus of the charged particle beam on the sample. Article 103. 103. The system of any one of clauses 98 to 102, wherein the first component is configured to adjust the focal depth of the charged particle beam relative to the sample. Article 104. 104. A system according to any one of clauses 98 to 103, wherein the first component is located upstream of the focusing component of the objective lens of the charged particle system. Article 105. The system of clause 104, wherein the first component comprises a charged particle source, an anode of the charged particle source, or a focusing lens, and the first component of the charged particle system is different from the second component of the charged particle system. Article 106. 106. A method according to any one of clauses 98 to 105, wherein manipulating the electromagnetic field comprises adjusting an electrical signal applied to the second component of the charged particle system. Article 107. 107. A system according to any one of clauses 98 to 106, wherein the second component of the charged particle system comprises one or more of a control electrode of the objective lens, the sample, or the stage. Article 108. 108. The system of any one of clauses 106 and 107, wherein adjusting the electrical signal applied to the second component adjusts the landing energy of the charged particle beam on the sample. Article 109. The adjustment of the electrical signal may include: adjusting a first component of the electrical signal applied to the control electrode of the objective lens; adjusting a second component of the electrical signal applied to the stage; and 109. The system of any one of clauses 107 and 108, comprising: Article 110. The system described in clause 109, wherein adjusting the first component of the electrical signal applied to the control electrode coarsely adjusts the first focus of the charged particle beam, and adjusting the second component of the electrical signal applied to the stage finely adjusts the first focus of the charged particle beam relative to the sample. Article 111. The system of any one of clauses 98 to 110, wherein the controller is further configured to manipulate the electromagnetic field by adjusting a magnetic field configured to affect the characteristics of the charged particle beam. Article 112. 112. The system of claim 111, wherein the characteristics of the charged particle beam include at least one of a path, a direction, a velocity, or an acceleration of the charged particle beam. Article 113. 13. The system of any one of clauses 110 to 112, wherein the first component of the electrical signal is determined based on an acceleration voltage and the landing energy of the charged particle beam. Article 114. A system as described in any one of clauses 110 to 113, wherein the first component of the electrical signal comprises a voltage signal having an absolute value in the range of 5KV to 10KV, and the second component of the electrical signal comprises a voltage signal having an absolute value in the range of 0V to 150V. Article 115. 115. The system of any one of clauses 109 to 114, wherein the landing energy of the charged particle beam is in the range of 500 eV to 3 keV. Article 116. 1. A non-transitory computer-readable medium comprising a set of instructions executable by one or more processors of an apparatus to cause said apparatus to perform a method, said apparatus including a charged particle source for generating a charged particle beam, said method comprising: adjusting a location of a first focal point of the charged particle beam relative to the sample using a first component of the charged particle system; using a second component located downstream of a focusing component of an objective lens of the charged particle system to manipulate an electromagnetic field associated with the sample to form a second focal point by adjusting the first focal point of the charged particle beam relative to the sample; 1. A non-transitory computer-readable medium comprising: Article 117. The set of instructions executable by one or more processors of the device: determining a position of the sample in a Z-axis using a height sensor; adjusting the position of the stage in the Z-axis based on the determined position of the sample using a stage motion controller to form the initial focus of the charged particle beam on the sample; 117. The non-transitory computer-readable medium of claim 116, further causing the device to perform the following: Article 118. The set of instructions executable by one or more processors of the device: adjusting a first component of an electrical signal to coarsely adjust the first focal point of the charged particle beam on the surface of the sample; adjusting a second component of the electrical signal to the stage to fine-tune the first focus of the charged particle beam on the surface of the sample; 118. The non-transitory computer-readable medium of any one of clauses 116 and 117, further causing the apparatus to manipulate an electromagnetic field associated with the sample by: Article 119. 1. A method for generating a 3D image of a sample in a charged particle beam device, comprising: irradiating the sample placed on a stage with a charged particle beam; manipulating an electromagnetic field associated with the sample to adjust the focus of the charged particle beam relative to the sample; forming a plurality of focal planes substantially perpendicular to a primary optical axis of the charged particle beam based on said manipulation of said electromagnetic field; generating a plurality of image frames from the plurality of focal planes of the sample, wherein one image frame of the plurality of image frames is associated with a corresponding one of the plurality of focal planes; generating a 3D image of the sample from the plurality of image frames and corresponding focal plane information; A method comprising: Article 120. 120. The method of clause 119, wherein manipulating the electromagnetic field comprises adjusting a first component of an electrical signal applied to a control electrode of an objective lens of the charged particle beam device. Article 121. 121. The method of clause 120, wherein manipulating the electromagnetic field further comprises adjusting a second component of the electrical signal applied to the stage of the charged particle beam device. Article 122. 122. The method of claim 121, wherein adjusting the second component of the electrical signal adjusts the landing energy of the charged particle beam on the sample. Article 123. A method according to any one of clauses 121 and 122, wherein the first focus of the charged particle beam is coarsely adjusted by adjusting the first component of the electrical signal applied to the control electrode, and the first focus of the charged particle beam is finely adjusted relative to the sample by adjusting the second component of the electrical signal applied to the stage. Article 124. 124. A method according to any one of clauses 121 to 123, wherein the first component of the electrical signal comprises a voltage signal having an absolute value in the range of 5KV to 10KV, and the second component of the electrical signal comprises a voltage signal having an absolute value in the range of 0V to 150V. Article 125. 125. The method of any one of clauses 122 to 124, wherein the landing energy of the charged particle beam is in the range of 500 eV to 3 keV. Article 126. 126. The method of any one of clauses 119 to 125, further comprising forming a first focal plane of the plurality of focal planes to coincide with a top surface of the sample. Article 127. 127. The method of clause 126, further comprising forming a second focal plane of the plurality of focal planes a distance below the first focal plane. Article 128. 128. The method of claim 127, wherein the distance between the first focal plane and the second focal plane is dynamically adjusted based on the feature being imaged or the material of the sample. Article 129. 129. A method according to any one of clauses 119 to 128, further comprising generating a plurality of image frames at each focal plane of said plurality of focal planes of said sample. Article 130. 130. The method of any one of clauses 119 to 129, wherein generating the 3D image comprises reconstructing the plurality of image frames using a reconstruction algorithm. Article 131. 1. A charged particle beam system comprising: the stage configured to hold a sample and movable along at least one of an X-axis, a Y-axis, or a Z-axis; manipulating an electromagnetic field associated with the sample to adjust the focus of the charged particle beam relative to the sample; forming a plurality of focal planes substantially perpendicular to a primary optical axis of the charged particle beam based on said manipulation of said electromagnetic field; generating a plurality of image frames from the plurality of focal planes, wherein one image frame of the plurality of image frames is associated with a corresponding focal plane of the plurality of focal planes; generating a 3D image of the sample from the plurality of image frames and corresponding focal plane information; a controller having a circuit configured as follows: 1. A charged particle beam system comprising: Article 132. 132. The system of claim 131, wherein manipulating the electromagnetic field comprises adjusting a first component of an electrical signal applied to a control electrode of an objective lens of the charged particle beam system. Article 133. 133. The system of claim 132, wherein manipulating the electromagnetic field further comprises adjusting a second component of the electrical signal applied to the stage of the charged particle beam system. Article 134. 134. The system of claim 133, wherein adjusting the second component of the electrical signal adjusts the landing energy of the charged particle beam on the sample. Article 135. A system as described in any one of clauses 133 and 134, wherein adjusting the first component of the electrical signal applied to the control electrode coarsely adjusts the first focus of the charged particle beam, and adjusting the second component of the electrical signal applied to the stage finely adjusts the first focus of the charged particle beam relative to the sample. Article 136. 136. A system as described in any one of clauses 133 to 135, wherein the first component of the electrical signal comprises a voltage signal having an absolute value in the range of 5KV to 10KV, and the second component of the electrical signal comprises a voltage signal having an absolute value in the range of 0V to 150V. Article 137. 137. The system of any one of clauses 134 to 136, wherein the landing energy of the charged particle beam is in the range of 500 eV to 3 keV. Article 138. 138. The system of any one of clauses 131 to 137, wherein the plurality of focal planes includes a first focal plane that coincides with a top surface of the sample. Article 139. 139. The system of claim 138, wherein the plurality of focal planes includes a second focal plane formed a distance below the first focal plane. Article 140. 139. The system of claim 139, wherein the distance between the first focal plane and the second focal plane is dynamically adjusted based on the feature being imaged or the material of the sample. Article 141. 141. The system of any one of clauses 131 to 140, wherein the controller is further configured to generate a plurality of image frames at each focal plane of the plurality of focal planes of the sample. Article 142. The system of any one of clauses 131 to 141, wherein the controller is further configured to generate the 3D image of the sample by reconstructing the plurality of image frames using a reconstruction algorithm. Article 143. 1. A non-transitory computer-readable medium comprising a set of instructions executable by one or more processors of an apparatus to cause said apparatus to perform a method, said apparatus including a charged particle source for generating a charged particle beam, said method comprising: manipulating an electromagnetic field associated with a sample to adjust the focus of the charged particle beam relative to the sample; forming a plurality of focal planes substantially perpendicular to a primary optical axis of the charged particle beam based on said manipulation of said electromagnetic field; generating a plurality of image frames from the plurality of focal planes of the sample, wherein one image frame of the plurality of image frames is associated with a corresponding one of the plurality of focal planes; generating a 3D image of the sample from the plurality of image frames and corresponding focal plane information; 1. A non-transitory computer-readable medium comprising: Article 144. The set of instructions executable by the one or more processors of the device: forming a first focal plane of the plurality of focal planes coincident with a top surface of the sample; forming a second focal plane of the plurality of focal planes spaced a predetermined distance below the first focal plane; 144. A non-transitory computer-readable medium as described in clause 143, further causing the device to perform the following: Article 145. 1. A method for determining vibrations of a charged particle beam device, comprising: Detecting a first oscillation of an electro-optical component configured to direct the charged particle beam toward the sample; detecting a second vibration of an electromechanical component configured to hold the sample; and applying a vibration compensation signal to the electro-optical component to compensate for the first vibration and the second vibration based on the determined vibration of the charged particle beam device; A method comprising: Article 146. 146. The method of claim 145, further comprising adjusting the position of the sample relative to one or more axes, wherein adjusting the position of the sample causes vibration of the electro-optical component and the electromechanical component. Article 147. A method according to any one of clauses 145 and 146, wherein detecting the first vibration includes detecting vibration of the electro-optical component around one or more axes using a first sensor. Article 148. Clause 148. The method of clause 147, wherein the first sensor includes an acceleration sensor mechanically coupled to the electro-optical component. Article 149. 149. The method of claim 148, wherein the acceleration sensor comprises a piezoelectric sensor, a capacitive accelerometer, a microelectromechanical system (MEMS)-based accelerometer, or a piezoresistive accelerometer. Article 150. 149. The method of any one of clauses 147 to 149, wherein the first sensor is configured to generate a voltage signal based on the frequency of the detected first vibration. Article 151. The method of any one of clauses 150, wherein detecting the second vibration includes detecting vibration of the electromechanical component in translational and rotational axes using a second sensor. Article 152. Clause 152. The method of clause 151, wherein the second sensor includes a plurality of position sensors configured to generate a displacement signal based on a frequency of the detected second vibration. Article 153. The method of claim 152, wherein a first position sensor of the plurality of position sensors is configured to detect vibration of the electromechanical component in a translational axis, and a second position sensor of the plurality of position sensors is configured to detect vibration of the electromechanical component in a rotational axis. Article 154. receiving, by a first controller, the voltage signal and the displacement signal; determining, using the first controller, the vibration compensation signal based on the received voltage signal and the received displacement signal; 154. The method of any one of clauses 152-153, further comprising: Article 155. Determining the vibration compensation signal comprises: identifying a plurality of vibration modes based on the information related to the first vibration and the second vibration; estimating the vibrations of the electro-optical component and the electromechanical component based on the identified vibration modes; determining the vibration in multiple axes based on the estimated vibration of the electro-optical component and the electro-mechanical component; determining the vibration compensation signal based on the determined vibration in the plurality of axes; 154. The method of claim 154, including: Article 156. 156. A method according to any one of clauses 145 to 155, wherein the vibration compensation signal is determined to compensate for the vibration based on an estimation of predicted vibration for a future time relative to a measurement time of the first vibration and the second vibration. Article 157. 157. The method of any one of clauses 155 and 156, wherein identifying the plurality of vibration modes includes converting the voltage signals into corresponding distance signals. Article 158. The method of any one of clauses 155 to 157, wherein identifying the plurality of vibration modes further comprises separating the second vibration of the electromechanical component from vibration of a housing of the electromechanical component. Article 159. 159. The method of any one of clauses 155 to 158, wherein estimating the vibrations of the electro-optical and electro-mechanical components comprises using a simulation model. Article 160. 159. The method of claim 159, wherein the simulation model comprises a three-dimensional finite element analysis model (3D-FEM), a finite difference analysis model (FDM), or a mathematical analysis model. Article 161. The method of any one of clauses 154 to 160, further comprising receiving, by a second controller, the determined vibration compensation signal. Article 162. receiving, by the second controller, a beam scanning signal; generating, by the second controller, a modified beam scanning signal based on the received beam scanning signal and the received vibration compensation signal; 162. The method of claim 161, further comprising: Article 163. 163. The method of clause 162, further comprising generating, by a signal generator, a beam deflection signal based on the modified beam scanning signal. Article 164. 164. The method of claim 163, wherein the beam deflection signal is applied to the electro-optical component and is used to adjust the characteristics of the charged particle beam incident on the sample. Article 165. 165. The method of any one of clauses 163 and 164, wherein the beam deflection signal is applied to a beam deflection controller associated with the electro-optical component. Article 166. 166. The method of any one of clauses 164 and 165, wherein the characteristics of the charged particle beam include a beam scan speed, a beam scan frequency, a beam scan duration, or a beam scan range. Article 167. A method according to any one of clauses 158 to 166, wherein the plurality of position sensors are disposed on a surface of the housing of the electromechanical component. Article 168. A method according to any one of clauses 145 to 167, wherein the electro-optical component includes a charged particle column and the electromechanical component includes a stage configured to hold the sample and movable in one or more of the X, Y or Z axes. Article 169. a first sensor configured to detect a first vibration of an electro-optical component of the charged particle beam system; a second sensor configured to detect a second vibration of an electromechanical component of the charged particle beam system; and a first controller including circuitry for generating a vibration compensation signal based on the detected first vibration and the detected second vibration applied to the electro-optical component; 1. A charged particle beam system comprising: Article 170. 169. The system of claim 169, wherein the electro-optical component includes a charged particle column and is configured to direct a charged particle beam toward the sample. Article 171. 171. The system of claim 170, wherein the electromechanical component includes a stage configured to hold the sample and movable in one or more of the X, Y, or Z axes. Article 172. A system as described in any one of clauses 170 and 171, wherein adjusting the position of the sample causes vibration of the electro-optical component and the electromechanical component. Article 173. The system of any one of clauses 169 to 172, further comprising a housing configured to accommodate the electromechanical components of the charged particle beam device. Article 174. 174. The system of claim 173, wherein the electromechanical component is mechanically coupled to the housing such that moving the stage causes vibration of the housing. Article 175. A system as described in any one of clauses 173 and 174, wherein the electro-optical component is mechanically coupled to the housing such that the vibration of the housing causes the first vibration of the electro-optical component. Article 176. A system described in any one of clauses 169 to 175, wherein the first sensor is further configured to detect the first vibration of the electro-optical component about one or more axes. Article 177. 177. The system of any one of clauses 169 to 176, wherein the first sensor includes an acceleration sensor mechanically coupled to the electro-optical component. Article 178. The system of clause 177, wherein the acceleration sensor comprises a piezoelectric sensor, a capacitive accelerometer, a microelectromechanical system (MEMS)-based accelerometer, or a piezoresistive accelerometer. Article 179. A system described in any one of clauses 169 to 178, wherein the first sensor is configured to generate a voltage signal based on the frequency of the detected first vibration. Article 180. The system of any one of clauses 179, wherein the second sensor is configured to detect the second vibration of the electromechanical component in the translational and rotational axes. Article 181. A system described in any one of clauses 179 and 180, wherein the second sensor includes a plurality of position sensors configured to generate a displacement signal based on the frequency of the detected second vibration. Article 182. The system described in clause 181, wherein a first position sensor of the plurality of position sensors is configured to detect vibration of the electromechanical component in a translational axis, and a second position sensor of the plurality of position sensors is configured to detect vibration of the electromechanical component in a rotational axis. Article 183. The system described in clause 182, wherein the first position sensor and the second position sensor are positioned on a surface of the housing of the electromechanical component. Article 184. The system of any one of clauses 181 to 183, wherein the first controller is further configured to receive the voltage signal and the displacement signal and determine the vibration compensation signal based on the voltage signal and the displacement signal. Article 185. The first controller identifying a plurality of vibration modes based on information related to the first vibration and the second vibration; estimating the vibrations of the electro-optical component and the electromechanical component based on the identified vibration modes; determining vibrations in multiple axes based on the estimated vibrations of the electro-optical component and the electro-mechanical component; determining the vibration compensation signal based on the determined vibration in the plurality of axes; The system described in any one of 169 to 184, including a circuit for: Article 186. A system described in any one of clauses 169 to 185, wherein the vibration compensation signal is determined to compensate for the vibration based on an estimate of predicted vibration for a future time relative to a measurement time of the first vibration and the second vibration. Article 187. The system of any one of clauses 185 and 186, wherein identifying the plurality of vibration modes includes converting the voltage signal into a corresponding distance signal. Article 188. The system of any one of clauses 185 to 187, wherein identifying the plurality of vibration modes further includes decoupling the second vibration of the electromechanical component from vibration of the housing of the electromechanical component. Article 189. The system of any one of clauses 184 to 188, wherein estimating the vibrations of the electro-optical component and the electro-mechanical component includes using a simulation model. Article 190. 189. The system of claim 189, wherein the simulation model comprises a three-dimensional finite element analysis model (3D-FEM), a finite difference analysis model (FDM), or a mathematical analysis model. Article 191. 191. A system as described in any one of clauses 184 to 190, further comprising a second controller including circuitry for receiving the determined vibration compensation signal. Article 192. The second controller Receives a beam scanning signal, generating a modified beam scanning signal based on the received beam scanning signal and the vibration compensation signal; 192. The system of claim 191, including circuitry for: Article 193. 193. The system of claim 192, further comprising a signal generator configured to generate a beam deflection signal based on the modified beam scanning signal. Article 194. 194. The system of claim 193, wherein the beam deflection signal is applied to the electro-optical component and configured to adjust the characteristics of the charged particle beam incident on the sample. Article 195. A system as described in any one of clauses 193 and 194, wherein the beam deflection signal is applied to a beam deflection controller associated with the electro-optical component. Article 196. 196. The system of any one of clauses 194 and 195, wherein the characteristics of the charged particle beam include a beam scanning speed, a beam scanning frequency, a beam scanning duration, or a beam scanning range. Article 197. 1. A non-transitory computer-readable medium comprising a set of instructions executable by one or more processors of a charged particle beam device to cause the device to perform a method for determining vibrations of the device, the method comprising: detecting a first oscillation of an electro-optical component configured to direct the charged particle beam toward a sample; detecting a second vibration of an electromechanical component configured to hold the sample; and applying a vibration compensation signal to the electro-optical component to compensate for the first vibration and the second vibration based on the determined vibration of the charged particle beam device; 1. A non-transitory computer-readable medium comprising: Article 198. The non-transitory computer-readable medium described in clause 197, wherein the set of instructions executable by the one or more processors of the device further causes the device to adjust the position of the sample relative to one or more axes, and adjusting the position of the sample causes vibration of the electro-optical component and the electromechanical component. Article 199. The set of instructions executable by the one or more processors of the apparatus further cause the apparatus to determine a vibration compensation signal based on the voltage signal and the displacement signal, the determining including: identifying a plurality of vibration modes based on the information related to the first vibration and the second vibration; estimating the vibrations of the electro-optical component and the electromechanical component based on the identified vibration modes; determining the vibration in multiple axes based on the estimated vibration of the electro-optical component and the electro-mechanical component; determining the vibration compensation signal based on the determined vibration in the plurality of axes; 199. The non-transitory computer-readable medium of any one of clauses 197 and 198, comprising: Article 200. The set of instructions executable by the one or more processors of the device: receiving, by a controller, a beam scanning signal; generating a modified beam scanning signal based on the received beam scanning signal and the vibration compensation signal; generating, by a signal generator, a beam deflection signal based on the modified beam scanning signal, the beam deflection signal being applied to the electro-optical component and configured to adjust a characteristic of the charged particle beam incident on the sample; applying the beam deflection signal to a beam deflection controller associated with the electro-optical component; A non-transitory computer-readable medium as described in any one of clauses 197 to 199, further causing the device to perform the following.

[0243]

[0260] Non-transitory computer-readable media may be provided that store instructions for a processor (e.g., a processor of controller 109, processor 430) to execute algorithms to perform wafer inspection, wafer imaging, stage calibration, displacement error calibration, displacement error compensation, manipulate electromagnetic fields associated with the sample, communicate with an image acquisition system, activate an acceleration sensor, activate a laser interferometer, operate a DVEC, estimate vibrations of the SEM column and stage, motion of a charged particle beam instrument or other imaging device, etc. Common forms of non-transitory media include, for example, a floppy disk, a flexible disk, a hard disk, a solid-state drive, magnetic tape, or any other magnetic data storage medium, a compact disk read-only memory (CD-ROM), any other optical data storage medium, any physical medium with a pattern of holes, random access memory (RAM), programmable read-only memory (PROM) and erasable programmable read-only memory (EPROM), flash EPROM, or any other flash memory, non-volatile random access memory (NVRAM), cache, registers, any other memory chip or cartridge, and networked versions thereof.

[0244]

[0261] The block diagrams in the figures illustrate the architecture, functionality, and operation of possible implementations of systems, methods, and computer hardware or software products according to various exemplary embodiments of the present disclosure. In this regard, each block in a flowchart or block diagram may represent a module, segment, or portion of code, including one or more executable instructions for implementing the specified logical function(s). It should be understood that in some alternative implementations, the functions depicted in the blocks may occur out of the order depicted in the figures. For example, two blocks shown in succession may be executed or performed substantially simultaneously, or in some cases, the two blocks may be executed in the reverse order, depending on the functionality involved. Some blocks may also be omitted. It should also be understood that each block of the block diagrams, and combinations of blocks, may be implemented by a dedicated hardware-based system that performs the specified functions or acts, or by a combination of dedicated hardware and computer instructions.

[0245]

[0262] It will be understood that the embodiments of the present disclosure are not limited to the exact configurations described above and illustrated in the accompanying drawings, and that various modifications and changes may be made without departing from the scope thereof.

Claims

1. a stage configured to hold the sample and movable in at least one of the XY and Z axes; a position sensing system configured to determine lateral and vertical displacement of the stage; applying a first signal to deflect a primary charged particle beam incident on the sample to at least partially compensate for the lateral displacement of the stage; Applying a second signal to adjust the focus of the deflected charged particle beam incident on the sample to at least partially compensate for the vertical displacement of the stage. With a controller configured as 1. A charged particle beam system comprising:

2. The system of claim 1 , wherein the first signal comprises an electrical signal that affects how the primary charged particle beam is deflected in the at least one of the XY axes.

3. The system of claim 2 , wherein the electrical signal comprises a signal having a bandwidth in the range of 10 kHz to 50 kHz.

4. The system of claim 1 , wherein the lateral displacement corresponds to a difference between a current position of the stage and a target position of the stage in the at least one of the X and Y axes.

5. The system of claim 1 , wherein the controller is further configured to dynamically adjust at least one of the first signal or the second signal during a scan of the primary charged particle beam over the sample.

6. 2. The system of claim 1, wherein the second signal comprises a voltage signal applied to the stage that affects how the deflected charged particle beam incident on the sample is focused in the Z-axis.

7. The system of claim 6 , wherein the voltage signal comprises a signal having a bandwidth in the range of 50 kHz to 200 kHz.

8. 2. The system of claim 1, wherein the vertical displacement corresponds to a difference between a current position of the stage and a target position of the stage in the Z-axis, and the vertical displacement varies during a scan of the primary charged particle beam over the sample to at least partially compensate for angular rotation about at least one of an X-axis or a Y-axis.

9. The system of claim 1 , further comprising a stage motion controller, the stage motion controller comprising a plurality of motors configured to be individually controlled by a third signal.

10. 10. The system of claim 9, wherein each of the plurality of motors is individually controlled to adjust the leveling of the stage so that the stage is substantially perpendicular to an optical axis of the primary charged particle beam.

11. The system of claim 9 , wherein the third signal comprises a plurality of control signals, each of the plurality of control signals corresponding to at least one of the plurality of motors.

12. The system of claim 9 , wherein the plurality of motors comprises at least one of a piezoelectric motor, a piezoelectric actuator, or an ultrasonic piezoelectric motor.

13. a first component configured to form an embedded control signal based on the plurality of control signals; a second component configured to extract at least one of the plurality of control signals from the embedded control signal; The system of claim 11 further comprising:

14. The system of claim 10 , wherein adjusting the leveling of the stage is based on a geometric model of an actuation output of the stage.

15. 1. A non-transitory computer-readable medium comprising a set of instructions executable by one or more processors of an apparatus to cause the apparatus to perform a method, the apparatus including a charged particle source for generating a primary charged particle beam, the method comprising: determining a lateral displacement of a stage, the stage being movable in at least one of an X and Y axis; instructing a controller to apply a first signal to deflect the primary charged particle beam incident on the sample to at least partially compensate for the lateral displacement; 1. A non-transitory computer-readable medium comprising:

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