Lens configuration in electron microscope system

Abstract

A charged particle beam system includes a charged particle source and a charged particle beam column to focus charged particles into a charged particle beam having a landing energy. A magnetic lens is formed in the charged particle beam column along the axis based on magnetic lens excitation in the coil. The magnetic lens focuses the charged particle beam at a first intersection on the axis. An electrostatic lens is formed in the charged particle beam along the axis based on a voltage applied to the enhancement tube. The electrostatic lens focuses the charged particle beam at a first intersection on the axis. The first intersection point is excited based on a magnetic lens. An additional cross point is introduced, so that the limitation on the maximum working distance under the conditions of very small landing energy and the maximum field of view is overcome.

Description

TECHNICAL FIELD

[0001] The present disclosure relates to charged particle microscope system components, systems, and methods. More specifically, the present disclosure describes lens configurations in electron microscope systems. BACKGROUND

[0002] Charged particle beam systems are used for a variety of applications, including manufacturing, repairing, and inspecting micro devices, such as integrated circuits, magnetic recording heads, and photolithography masks. One type of charged particle beam system can include an electron microscope. Electron microscopes are used as a tool to image by focusing a beam of electrons of sufficient size from an electron emitter onto a sample and subsequently detecting deflected electrons to generate a high resolution image of the sample. New charged particle beam systems are needed that optimize the detection of these deflected electrons. SUMMARY

[0003] According to one embodiment, a charged particle beam system includes a charged particle source and a charged particle beam column to focus charged particles into a charged particle beam having a landing energy. The charged particle beam column includes a booster tube, a set of scanning deflectors, a set of magnetic materials, and a set of magnetic lens excitation coils at least partially surrounding the booster tube and the set of scanning deflectors. A magnetic lens is formed in the charged particle beam column along an axis based on the magnetic lens excitation in the coils. The magnetic lens focuses the charged particle beam at a first crossover point on the axis. An electrostatic lens is formed in the charged particle beam column along the axis. Collectively, the magnetic lens and the electrostatic lens constitute a compound final lens of the charged particle beam column. The electrostatic lens is formed based on a potential gradient applied to the booster tube and other portions of the final lens. The electrostatic lens focuses the charged particle beam at the first crossover point on the axis. The first crossover point is between the magnetic lens and the electrostatic lens and is based on the magnetic lens excitation of the magnetic lens.

[0004] The charged particle beam system can include various optional embodiments. The landing energy can be greater than or equal to 1 eV and less than or equal to 500 eV. A working distance of the charged particle beam column is greater than or equal to 1 mm. The working distance can be based on the magnetic lens excitation. A booster tube voltage can be constant during imaging of a sample at the working distance. A current applied to the magnetic lens excitation coils can be sufficient to generate a magnetic flux greater than or equal to 200 ampere-turns and less than or equal to 1000 ampere-turns. The first crossover point can be proximate an end of the booster tube that is between the magnetic lens and the electrostatic lens.

[0005] According to another embodiment, a method for target imaging includes directing a charged particle beam along an axis of a charged particle beam column having a landing energy. The charged particle beam column includes an enhancer tube, a set of scanning deflectors, and a set of magnetic material at least partially surrounding the enhancer tube and the set of scanning deflectors. The method includes applying a voltage to the enhancer tube, thereby forming an electrostatic lens in the charged particle beam along the axis; applying a magnetic lens excitation to the set of scanning deflectors, thereby forming a magnetic lens in the charged particle beam along the axis; and controlling the magnetic lens excitation, thereby the magnetic lens focuses the charged particle beam at a first intersection point on the axis. The first intersection point is between the magnetic lens and the electrostatic lens. The electrostatic lens focuses the charged particle beam at the first intersection point on the axis.

[0006] The method can include various optional embodiments. The method can include receiving an image including image distortion and correcting the image distortion by post processing of the image or by changing a dynamic excitation of the set of scanning deflectors, where correcting the image distortion includes applying a transformation to the image using a virtual (e.g., a physical intelligence or an artificial intelligence (AI), etc.) model. The method can also include imaging a known target using at least a first setting of a scanning electron microscope including the charged particle beam column, determining an image transformation based on the imaging of the known target, generating an image of the known target based on the charged particle beam at a working distance, and updating the image based on the image transformation. The method can also include controlling the magnetic lens excitation, thereby a working distance of the charged particle beam column is equal to or greater than 1 mm. The method can also include generating a plurality of images of the known target, each image corresponding to a different one of a plurality of settings of the scanning electron microscope, where the image transformation is based on the plurality of images. Imaging the known target can include generating the image of the known target by varying at least one or more of the first intersection point, the second intersection point, a position of the known target, or a beam property, where the image transformation is based on the image. The landing energy can be greater than or equal to 1 eV and less than or equal to 500 eV. The method can also include controlling the magnetic lens excitation, thereby the first intersection point is proximate to an end of the enhancer tube.

[0007] According to yet another embodiment, one or more non-transitory computer- readable storage media store instructions that, when executed by a set of processors, cause operations including directing a charged particle beam along an axis of a charged particle beam column having a landing energy. The charged particle beam column includes an enhancer tube, a set of scanning deflectors, and a set of magnetic material at least partially surrounding the enhancer tube and the set of scanning deflectors. The operations include applying a voltage to the enhancer tube, thereby forming an electrostatic lens in the charged particle beam along the axis; applying a magnetic lens excitation, thereby forming a magnetic lens in the charged particle beam along the axis; and controlling the magnetic lens excitation, thereby the magnetic lens focuses the charged particle beam at a first intersection point on the axis. The first intersection point is between the magnetic lens and the electrostatic lens. The electrostatic lens focuses the charged particle beam at the first intersection point on the axis.

[0008] The operations can include various optional implementations. The landing energy can be greater than or equal to 1 eV and less than or equal to 500 eV. The operations can further include imaging a known target using at least a first setting of a scanning electron microscope including a charged particle beam column, determining an image transform based on the imaging of the known target, generating an image of the known target based on the charged particle beam at a working distance, and updating the image based on the image transform. The operations can further include generating a plurality of images of the known target, each image corresponding to a different one of a plurality of settings of the scanning electron microscope, wherein the image transform is based on the images. The operations can further include controlling the magnetic lens excitation such that the working distance of the charged particle beam column is equal to or greater than 1 mm. The operations can further include controlling the magnetic lens excitation such that the first crossover point is proximate to an end of the enhancement tube. BRIEF DESCRIPTION OF DRAWINGS

[0009] A further understanding of the nature and advantages of various implementations can be realized by reference to the following drawings. In the drawings, like reference numerals can designate similar structures or features. Also, various components of the same type can be distinguished by following the designation of the first component by the accompanying second designation in a hyphenated form. If only the first designation is used, the description is applicable to any of the like components having the same first designation.

[0010] Figure 1 A simplified cross-sectional view of an exemplary charged particle system is depicted.

[0011] Figure 2 A simplified cross-sectional view of an exemplary charged particle system according to implementations of the present disclosure is depicted.

[0012] Figure 3A A simplified cross-sectional view of an exemplary charged particle system with a navigation mode according to implementations of the present disclosure is depicted.

[0013] Figure 3B A simplified cross-sectional view of an exemplary charged particle system according to implementations of the present disclosure is depicted, the system having a navigation mode that scans a relatively large field of view. Figure 3A

[0014] Figure 4 A flowchart of a method for target imaging according to implementations of the present disclosure is depicted.

[0015] Figure 5 Image distortion and correction according to implementations of the present disclosure is shown.

[0016] Figure 6A and Figure 6B A flowchart of a method for correcting image distortion according to implementations of the present disclosure is included.

[0017] Figure 7 ​is a table representing image distortion according to embodiments of the present disclosure.

[0018] Figure 8 is a table representing exemplary working distances according to embodiments of the present disclosure.

[0019] Figure 9 is a block diagram of a controller for a charged particle microscope system according to embodiments of the present disclosure. DETAILED DESCRIPTION

[0020] While example embodiments have been illustrated and described, it will be understood that various changes can be made without departing from the spirit and scope of the present disclosure.

[0021] Charged particle microscopes are used in various industries, including the semiconductor industry, to analyze microscale and nanoscale structures. For example, semiconductor devices can include nanoscale transistors densely packed within a silicon wafer. Images obtained with charged particle microscopy can be used to improve process control, assess the quality of manufactured devices, and improve yield. In the case of semiconductor devices, objects such as field effect transistors (FETs) can be formed within a larger silicon wafer and adjacent to several other structures, including other FETs, vias, diode junctions, etc. Because the elements are extremely small and densely packed, imaging of these elements can be improved by careful preparation of the sample.

[0022] Imaging a sample with a charged particle microscope can include the use of a transmission electron microscope (TEM), a scanning electron microscope (SEM), a scanning TEM (STEM), or related technologies. To image some samples using these technologies, a lamella is formed and removed from a larger substrate (e.g., a silicon wafer). The lamella can include structures that form a device (e.g., an FET). The lamella can be formed and removed using a dual-beam charged particle microscope system, which generally includes a focused ion beam (FIB) and a scanning electron microscope (SEM). During lamella formation, the FIB is used to remove material from the substrate, leaving the lamella as part of the remaining material, while the SEM is used for imaging to guide the FIB process. This process has become conventional in many industries, not just the semiconductor industry, and is used to image and analyze almost any type of microscale or nanoscale structure embedded in a surrounding substrate.

[0023] SEM is a versatile instrument that can image samples of different length scales. The standard workflow involves finding a region of interest in the sample and then zooming in to the desired detail in sequence. For simple goniometric reasons, the maximum field of view can be achieved by increasing the working distance. However, if the SEM is equipped with a booster tube (also known as an acceleration tube), the maximum working distance decreases as the landing energy decreases. The booster tube is used for imaging stability at low energies (e.g., between 50 eV and 500 eV, inclusive), but it limits the maximum working distance. For example, a booster tube can have a maximum working distance of 2.8 mm at 80 eV. In addition, the booster tube limits the maximum field of view, for example, to 1.2 mm at a working distance of 2.3 mm and 200 eV.

[0024] In one example use case, for electrical failure analysis (EFA), it is desirable to lower the landing energy to tens of electron volts. Only very low beam energies (e.g., 200 eV or preferably even smaller) can be used. Otherwise, the sample degrades. In this case, the field of view needed to navigate along the sample is not large enough. At very small landing energies, the working distance is in the millimeter range. Various embodiments of the present disclosure describe a navigation mode for microscopes with booster tubes that achieve increased working distance at lower landing energies.

[0025] Charged particle microscopes such as TEM and SEM can use a range of detection techniques to acquire information about a sample. SEM and TEM techniques can be used to image various types of specimens, including the surface / interior of cells, the structure of protein molecules, the organization of molecules in viruses and cytoskeletal filaments, etc. TEM, in particular, can use various techniques depending on the type of specimen to be imaged. Due to inherent natural laws, electrons within the electron beam scatter after interacting with the specimen. As a result, many electrons experience energy loss and, thus, a focal shift of the imaging plane related to chromatic aberration, which requires adjustment of the lens optics to collect high-resolution images, as well as varying degrees of geometric aberrations, which can affect image quality due to the introduction of astigmatism and blurring. Thus, imaging resolution can be adversely affected by various aberrations, and a solution to achieve high-resolution imaging using various TEM and SEM devices can be needed.

[0026] Various embodiments of the present disclosure provide a lens configuration that increases the maximum working distance for low landing energies, particularly in SEM or TEM systems with booster tubes. At least some embodiments provide a new use of a combined static-magnetic and electrostatic final lens of a charged particle beam column. The lens configuration described herein is capable of achieving relatively large field of view navigation compared to conventional systems. In at least some embodiments, the lens configuration provides an additional crossover point in the final lens of the configuration, thereby providing a system navigation mode with a substantial increase in maximum working distance and field of view.

[0027] According to at least some embodiments, some distortion can occur during imaging using the navigation mode described herein. Compound magnetic and electrostatic lenses refract the electron beam. The longer distance that the rays travel in the electrostatic lens can cause some image distortion. Various embodiments describe a distortion model and implement a de- distortion procedure using digital post-processing.

[0028] Figure 1 is a schematic diagram of an exemplary charged particle microscope 100 according to certain embodiments of the present disclosure. The exemplary charged particle microscope 100 includes a plurality of sections, including an electron source 102, a beam column 105, and a sample chamber 110. The electron source 102 includes a high voltage power supply assembly (not shown), a vacuum system assembly, and an electron emitter (not shown) configured to generate an electron beam that is accelerated into the beam column 105. The beam column 105, in turn, can include electromagnetic lens elements and / or diaphragm blades 106 configured to shape the electron beam from the electron source 102 and to shape it into a substantially circular beam having a generally uniform profile transverse to the beam axis A, and to condition the beam for focusing onto a sample 125 by an objective lens 115.

[0029] The electron beam is generally characterized by a beam current and an acceleration voltage applied to generate the beam, as well as other standards. The range of beam currents and the range of acceleration voltages can vary between instruments, and are generally selected based on the material properties of the sample or the type of analysis being performed. However, generally, the electron beam is characterized by an energy of a few electron volts to tens of kiloelectron volts and a beam current from picoamperes to microamperes.

[0030] The sample chamber 110 and / or the beam column 105 can include a plurality of detectors for various signals, including but not limited to secondary electrons, X-ray photons (e.g., detectors for energy dispersive X-ray analysis or EDAX), other photons (e.g., visible light cameras and / or IR cameras), and / or molecular species (e.g., time-of-flight secondary ion mass spectrometry or TOF-SIMS systems) generated by the electron beam and sample interaction. The sample chamber 110 can also include a sample holder 120 that can be operably coupled with a multi-axis translation / rotation control system 104, such that the sample 125 can be repositioned relative to the beam axis A as a method of investigation and / or imaging of the sample 125. Further, the sample holder 120 can include a window that allows transmission of electrons or other charged particles through the sample and sample stage.

[0031] Various embodiments of the present disclosure redefine the lenses of a SEM system. The SEM system can include two lenses in a sequential layout, including a magnetic lens and an electrostatic lens, as will be described in further detail below. The embodiments described herein provide two crossover points in front of the electrostatic lens, such that the electrostatic lens has a constant refractive power. The actual focus correction is generated by the magnetic lens, and the shift of the first crossover point is converted to focus on the sample by the electrostatic lens. Thus, the embodiments of the present disclosure enable a significant increase in the maximum working distance and field of view range that were previously unattainable with conventional SEM systems.

[0032] While the remainder of this specification will routinely refer to SEMs, the skilled artisan will readily understand that the technology is not so limited. The present design can be used in other types of charged particle microscopes, such as transmission electron microscopes (TEMs), scanning transmission electron microscopes (STEMs), dual beam systems including ion beam sources and electron beam sources, reflection electron microscopes (REMs), circuit editing microscopes, and the like. Thus, the present disclosure and claims should not be considered limited to any particular exemplary microscope under discussion, but rather can be used broadly in any number of electron microscopes that can exhibit some or all of the electrical or chemical features of the exemplary under discussion.

[0033] While the remainder of this specification will routinely refer to SEMs, the skilled artisan will readily understand that the technology is not so limited. The present design can be used in other types of charged particle microscopes, such as transmission electron microscopes (TEMs), scanning transmission electron microscopes (STEMs), dual beam systems including ion beam sources and electron beam sources, reflection electron microscopes (REMs), circuit editing microscopes, and the like. Thus, the present disclosure and claims should not be considered limited to any particular exemplary microscope under discussion, but rather can be used broadly in any number of electron microscopes that can exhibit some or all of the electrical or chemical features of the exemplary under discussion.

[0034] Figure 2 A simplified cross-sectional view of an exemplary charged particle system is depicted. In particular, a charged particle system 200 as shown in FIG. 1 can be implemented in the systems described in detail above. Figure 2 Figure 1 Figure 2 ​​The illustrated charged particle system 200 can similarly be implemented in a SEM system having multiple optics, etc. The charged particle system 200 includes a charged particle (e.g., electron) source 202 as detailed above. A charged particle beam column 204 can be configured to focus the charged particles into a charged particle beam 206 having a landing energy. The charged particle beam column 204 can include a booster tube 208 and a set of magnetic materials 212. The set of magnetic materials 212 can at least partially surround the booster tube 208, as Figure 2 illustrated in FIG. 2.

[0035] According to various embodiments, the tube of the booster tube 208 can be made of a variety of materials, such as titanium alloy and some suitable insulating material, which electrically insulate components inside the booster tube 208 from ground potential. The booster tube 208 does not necessarily have to consist of a physical tube. It can also refer to a system that includes a mid-section of the charged particle beam column 204, which can be set to a higher voltage level.

[0036] According to various embodiments, a magnetic lens 214 is formed in the charged particle beam column 204 along an axis 216. The magnetic lens 214 can be based on a magnetic lens excitation current applied to the set of coils 210. Further, the charged particle system 200 can include an electrostatic lens 218 formed in the charged particle beam column 204 along the axis 216. The electrostatic lens 218 can be at least partially based on a voltage applied to the booster tube 208. For example, the electrostatic lens 218 can be formed by a voltage difference between a voltage applied to the booster tube 208 (e.g., 8 kV) and a voltage applied to the magnetic materials 212 (e.g., 0 V). The magnetic lens 214 and the electrostatic lens 218 can form a beam crossover 220 at or on a sample 224 for imaging the sample, etc. A working distance (WD) refers to a distance between an exit 222 of the charged particle beam column 204 and a top of the sample 224, etc.

[0037] In various conventional SEM systems, the maximum working distance is too short at low landing energies and, as a result, the field of view cannot be extended to the scale that would otherwise enable navigation throughout the sample. For example, such systems can only provide one maximum magnification at a certain working distance and / or do not include the possibility to zoom out to a different working distance.

[0038] Figure 3AA simplified cross-sectional view of an exemplary charged particle system having a navigation mode is depicted. Unless otherwise noted herein, various components of the charged particle system 200 can be related to the charged particle system 300, and like components are similarly numbered and have similar form and function. The charged particle system 300 includes a charged particle source 302, as detailed above. A charged particle beam column 304 can be configured to focus charged particles into a charged particle beam 306 having a landing energy. The charged particle beam column 304 can include an enhancer tube 308, a set of scan deflectors 311, and a set of magnetic materials 312. The set of magnetic materials 312 can at least partially surround the enhancer tube 308 and the set of scan deflectors 311, as shown in Figure 3A

[0039] According to various embodiments, a magnetic lens 314 is formed in the charged particle beam column 304 along an axis 316. The magnetic lens 314 can be based on a magnetic lens excitation in the set of coils 310. For example, as will be appreciated by one of ordinary skill in the art, a current can be applied to the set of coils 310 forming the magnetic lens 314. Further, the charged particle system 300 can include an electrostatic lens 318 formed in the charged particle beam column 304 along the axis 316. The electrostatic lens 318 can be at least partially based on a voltage applied to the enhancer tube 308. According to embodiments of the present disclosure, the magnetic lens 314 focuses the charged particle beam 306 at a first crossover 325 on the axis 316. The first crossover 325 is between the magnetic lens 314 and the electrostatic lens 318. In various embodiments, the first crossover 325 is based on the magnetic lens excitation forming the magnetic lens 314. According to at least some embodiments, the first crossover 325 is proximate to an end of the enhancer tube 308, with the end being between the magnetic lens 314 and the electrostatic lens 318, as shown in Figure 3A Further, embodiments of the present disclosure provide that the electrostatic lens 318 focuses the charged particle beam 306 at a second crossover 327 on the axis 316.

[0040] The magnetic lens excitation can affect the position of the first crossover 325. In some embodiments, the magnetic lens excitation is non-linear. However, in at least some other embodiments, the magnetic lens excitation can be proportional. In various embodiments, the magnetic lens excitation is between 200 ampere-turns and 1000 ampere-turns, inclusive, in terms of the magnetic flux potential provided by the magnetic lens.

[0041] Figure 3A ​The path of the axial rays of the charged particle beam 306 during their passage through the final lens (e.g., electrostatic lens 318) is shown as a dashed line, where the width of the beam 306 is magnified at the final lens by applying the method of the present disclosure. According to this exemplary embodiment, there is no scanning, and the charged particle beam 306 has two crossover points (e.g., first crossover point 325 and second crossover point 327) at the sample 324. In at least some embodiments, the cross-section of the charged particle beam 306 is relatively small (e.g., between about 40 microns and 100 microns, inclusive).

[0042] The working distance (WD) refers to the distance between the exit 322 of the charged particle beam column 304 and a surface, such as the sample 324. According to various embodiments of the present disclosure, the first crossover point 325 and the second crossover point 327 increase the maximum working distance for low landing energies on a SEM with the booster tube 308 and enable navigation in large fields of view. For example, the working distance of the charged particle beam column 304 is greater than or equal to 1 mm. In at least some embodiments, the working distance of the charged particle beam column 304 is greater than the maximum working distance of a conventional system without the embodiments described herein. Also, if the maximum working distance is too short at low landing energies, the field of view cannot be expanded to the scale that would otherwise enable navigation. In the present disclosure, the sample 324 is focused onto the resulting image by influencing the longitudinal position of the additional crossover point (e.g., second crossover point 327). The lens equation supports the finding that the image side of the SEM can be positioned at a relatively far distance from the charged particle beam column 304.

[0043] Various embodiments of the present disclosure create a second crossover point (e.g., second crossover point 327) in front of the electrostatic lens 318 (i.e., inside the spatial region opposite the electrostatic lens side facing the booster tube 308), such that the electrostatic lens 318 uses its refractive power to divert the second crossover point to the beam spot at the sample (e.g., along the sample 324). For example, embodiments of the present disclosure use the strong refraction of the electrostatic lens 318 to create an additional transfer stage with an additional crossover point (e.g., second crossover point 327). Thus, embodiments of the present disclosure advantageously overcome the low landing energies (e.g., greater than or equal to 1 eV and less than or equal to 500 eV) that result from the use of a booster tube. The electrostatic lens 318 can have a constant refractive power (e.g., due to a constant voltage applied thereto).

[0044] Figure 3B A simplified cross-sectional view of an exemplary charged particle system with a navigation mode that scans a relatively large field of view is depicted. Figure 3A The actual focus correction is generated by the magnetic lens 314. Figure 3BThe charged particle beam 306 is shown now to be approximately a single line (e.g., along the center of the beam) deflected due to the presence of the scan deflector 311. The two intersections of the charged particle beam 306 with the optical axis due to scanning (e.g., the first pivot point 326 and the second pivot point 328) enable a large field of view to be available in a navigation mode. Thus, the electrons, which have a relatively small landing energy, are focused at least twice (e.g., with the magnetic lens 314 and with the electrostatic lens 318). Thus, an advantage of at least some embodiments of the present disclosure is to add navigation to a SEM system with an augmentation tube, thereby enabling imaging of a relatively far field of view on the order of tens of millimeters.

[0045] Figure 4 is a flowchart of a method for imaging a target. Imaging the target according to the method 400 can include any of the embodiments described herein. For example, the target can be imaged by the charged particle system 300 described with respect to Figure 3A and Figure 3B The various steps of the method 400 can be implemented by one or more controllers described herein. For example, one or more steps of the method 400 can be implemented by the controller 130 described in detail above with respect to Figure 1 In another example, one or more steps of the method 400 can be implemented by the controller 901 described below with respect to Figure 9 to be described in further detail below.

[0046] The method 400 includes a step 402. The step 402 includes directing a charged particle beam along an axis of a charged particle beam column having a landing energy. The charged particle beam column includes an augmentation tube, a set of scan deflectors, and a set of magnetic material at least partially surrounding the augmentation tube and the set of scan deflectors, as described in detail above.

[0047] The method 400 also includes a step 404 of applying a voltage to the augmentation tube, whereby an electrostatic lens is formed in the charged particle beam along the axis. The potential applied to the augmentation tube can vary between 6000 V to 10000 V, inclusive. According to various embodiments, the voltage applied to the augmentation tube is constant during imaging of the sample, and the imaging is based on the landing energy, as will be appreciated by one of ordinary skill in the art upon reading the present disclosure. In various embodiments, a voltage can be further applied to the magnetic material to create a voltage difference between the magnetic material and the augmentation tube. In at least some embodiments, the voltage applied to the magnetic material is set to zero, for example, during standard cases where the magnetic circuit yoke is set to ground potential (i.e., zero volts). In other embodiments, a positive or negative potential in the range of -3000 volts to +3000 volts, inclusive, can be applied to a portion of the magnetic circuit yoke.

[0048] Method 400 further includes step 406, which includes applying an electrical excitation to a magnetic lens coil, thereby forming a magnetic lens along an axis in a beam of charged particles. According to various embodiments, applying the electrical excitation includes applying a current to the magnetic lens coil. The magnetic lens excitation may be between 200 ampere-turns and 1000 ampere-turns (inclusive) in terms of the magnetomotive force provided by the magnetic lens.

[0049] Method 400 includes step 408. Step 408 includes controlling an electrical excitation such that a magnetic lens focuses a charged particle beam at a first on-axis intersection. Step 408 may also include controlling the magnetic lens excitation such that the working distance of the charged particle beam column is equal to or greater than 1 mm. The first intersection may be located between the magnetic lens and the electrostatic lens. The electrostatic lens may also focus the charged particle beam at a second on-axis intersection. The magnetic lens excitation (e.g., current) applied to the magnetic lens coil can be adjusted as needed to modify the working distance and / or field of view. Therefore, embodiments of the method 400 described herein provide a navigation mode for SEM systems with intensifier tubes.

[0050] According to some implementations, the system can be preset with a range of available electrical excitations (e.g., voltage and / or current). Through prior calibration / testing, the system can map the range values ​​to cross-point distances and / or operating distances. This mapping can be stored in a table, database, etc., in the controller's memory, or in any other manner known in the art. Therefore, step 408 may include receiving input indicating the cross-point distance or operating distance, and the controller can use the stored input to look up the table and determine the current and / or voltage values ​​to be applied and control the magnetic lens excitation accordingly.

[0051] Figure 5 Image distortion and correction are illustrated. Images acquired according to the various embodiments described above may have some degree of distortion. For example, image distortion may be caused by spherical aberration of electrostatic lenses. Some distortion may occur during imaging using the navigation mode described herein. Compound magnetic lenses and electrostatic lenses refract the electron beam. A greater distance between the rays and the optical axis in an electrostatic lens can lead to some image distortion. Various embodiments describe distortion models and distortion correction procedures implemented using digital post-processing.

[0052] like Figure 5 As shown, image 502 is an exemplary image with image distortion and generated by imaging according to the method 400 detailed above. For example, image 502 includes an extended portion in the middle of the image and a compressed portion toward the image edges. Image 502 may be distorted due to pincushion distortion, barrel distortion, etc., in the imaging. According to the various methods described herein, post-processing can transform image 502 into image 504, where image 504 is a corrected image and contains less distortion and may be distortion-free. The methods described herein, particularly with respect to... Figure 6A andFigure 6B The described embodiments show post-processing according to Figure 4 a method of generating images.

[0053] Figure 6A and Figure 6B includes a flowchart of a method for correcting image distortion. The images to be corrected can be imaged according to the method 400, including any of the embodiments described herein. For example, the images can be imaged by a scanning electron microscope relative to Figure 3A and Figure 3B The charged particle system 300 described is used to image a target. The various steps of the method 600 and the method 620 can be implemented by one or more controllers described herein. For example, one or more steps can be implemented by the controller 130 described in detail above with respect to Figure 1 In another example, one or more steps can be implemented by the controller 901 described in detail below with respect to Figure 9 to be described in further detail.

[0054] Figure 6A The method 600 is shown. The method 600 includes a step 602 including imaging a known target using one or more settings of a scanning electron microscope including a charged particle beam column described herein. In various embodiments, the images contain image distortion. The known target can include a chessboard, a stripe, a known pattern, a shape, a series of shapes, etc. According to some embodiments, the step 602 includes generating a plurality of images of the known target, where each image corresponds to a different one of a plurality of settings of the scanning electron microscope. According to some embodiments, the step 602 further includes generating a plurality of images of a plurality of known targets. In some embodiments, the images of the known target can be generated and correspond to one or more of: a particular value of a first cross-over, a particular value of a second cross-over, a position of the known target, a beam characteristic, etc. These generated images can be referred to herein as distorted images.

[0055] Step 604 can also include determining an image transform based on the distorted image. According to some embodiments, the image transform can also be based on real images of the known target. These real images can be known images that are not distorted (or not significantly distorted). According to some embodiments, the transform can be output by a virtual model, where the virtual model is trained using the distorted images and the real images. The virtual model can receive a distorted image and output a corrected image. Any differences between the corresponding real image and the output image can be used to update the virtual model. This process can be repeated for multiple distorted images to iteratively update the virtual model. In various embodiments, the virtual model can include a non-machine learning model. For example, the virtual model can be a data fitting model that iteratively estimates parameters of a transformation process such that the transformed image removes the image distortion. There can be different types of data fitting models, such as those based on implementing a Levenberg-Marquardt non-linear least squares algorithm, a chi-squared test algorithm, a curve fitting algorithm, a weighted least squares fitting algorithm, a polynomial regression algorithm, a Gauss-Newton algorithm, a shift-and-cut algorithm, a gradient algorithm, a Nelder-Mead (simplex) search algorithm, or other types of fitting algorithms. Additionally or alternatively, the virtual model can include a machine learning model, such as a regression model or a convolutional neural network, that can be trained using a plurality of known virtual models and corresponding display components to output transformation parameters. The training can include inputting distorted images to the machine learning model and using corresponding real images as ground truth values. The machine learning model can output a corrected image from a distorted image. The corrected image can be compared to the corresponding real image. Differences between the corrected image and the real image can be used in a feedback loop to update parameters of the machine learning model. In embodiments where the virtual model is a machine learning model, the virtual model can not output an image transform. Instead, the parameters of the virtual model can correspond to learned knowledge that the image transform can act on. The machine learning model can be trained across all microscope settings.

[0056] According to some embodiments where the virtual model is a non-machine learning model, the image transform can be output by the virtual model and can correspond to a particular microscope setting. In such embodiments, the image transform can be stored (e.g., in a table or database) in step 606 in association with the microscope setting. For a particular setting, the corresponding image transform can be retrieved from the storage. According to some embodiments where the virtual model is a machine learning model, the virtual model itself can be stored in step 606. According to various embodiments described herein, one or more steps of method 600 can be performed offline or on a separate system (e.g., a system other than the charged particle system 300 of FIG. 1). Figure 3A and Figure 3B In addition to the charged particle system 300 of FIG. 1, the image transform or machine learning model can be pre-stored and used to correct images having image distortion, as further described in method 620.

[0057] Method 620 includes step 622. Step 622 includes receiving an image generated by a charged particle system (e.g., charged particle system 300) of Figure 3A and Figure 3B The image can include image distortion. Step 624 can include determining an image transform to be applied to the image. The image transform can be one of the image transforms generated and stored as part of method 600 described above and derived from different related settings of the microscope (e.g., by imaging a known target or from physical simulations). The image transform can be looked up based on the microscope settings. Alternatively, a machine learning model can be invoked (e.g., through an application programming interface), where the invocation can include the image, and optionally the microscope settings. Step 626 further includes correcting the image by applying the image transform to the image. The image transform can be applied as a function per se, or can be applied inherently by the machine learning model.

[0058] Step 628 can further include outputting the corrected image. According to some embodiments, the image distortion can be corrected based on applying the image transform to the image.

[0059] Figure 7 is a graph representing the image distortion. Specifically, Figure 7 is a graph of the image distortion to be compensated. As described above, various images can be taken for various settings. For example, for each setting of the system, the beam characteristics and / or the distance of the sample to the output of the enhancement tube are varied to derive a distortion curve, as shown in Figure 7 distortion curve. As will be appreciated by one of ordinary skill in the art upon reading the present disclosure, from this distortion curve, the coefficients of the image transform can be derived for this particular setting. The distortion can be understood as a deviation in the actual and nominal intersection position of the electron beam and the sample.

[0060] Figure 8 is a table representing exemplary working distances. Figure 8 include the working distance limitations of the navigation mode and the regular system as described herein. The navigation mode described herein can be used for landing energies up to 500 eV, and there will be no limitation on the maximum working distance.

[0061] Figure 9 is a block diagram of a controller of a charged particle microscope system. An example of an electron microscope system can include a charged particle system as described above with respect to Figure 3A and Figure 3BThe described charged particle system 300. As shown, controller 901 includes a processor 902 communicatively coupled to memory 904. Processor 902 may include one or more processing devices. Non-limiting examples of processor 902 include field-programmable gate arrays (FPGAs), application-specific integrated circuits (ASICs), microprocessors, or any combination thereof. Processor 902 can execute instructions 910 stored in memory 904 to perform operations, such as those from... Figure 9 The operation of process 900. In some examples, instruction 910 may include processor-specific instructions generated by an editor or interpreter from code written in any suitable computer programming language (such as C, C++, C#, Python, or Java).

[0062] Memory 904 may include one or more storage devices. Memory 904 may be non-volatile and may include any type of storage device that retains stored information when power is lost. Non-limiting examples of memory 904 include electrically erasable and programmable read-only memory (EEPROM), flash memory, or any other type of non-volatile memory. At least some portions of memory 904 may include a non-volatile computer-readable medium from which processor 902 can read instructions 910 via bus 906. Bus 906 may be a communication and / or power bus that enables processor 902 to communicate with memory 904. The non-volatile computer-readable medium may include an electronic storage device, optical storage device, magnetic storage device, or other storage device capable of providing instructions 910 or other program code to processor 902. Non-limiting examples of non-volatile computer-readable media include a magnetic disk, a memory chip, RAM, an ASIC, or any other medium from which a computer processor can read instructions 910.

[0063] The memory 904 may also include an optical lens control module 914 for controlling various embodiments according to the present disclosure (at least including...). Figure 3A and Figure 3B Charged particle system 300 and Figure 4 Method 400) voltage and / or current. The memory 904 may also include an imaging module 916 for generating, storing, processing, etc., by... Figure 3A and Figure 3B Charged particle system 300 and Figure 4 The image generated by method 400. Memory 904 may also include an image correction module 918 for implementing various embodiments of the method 600 for post-processing images detailed above, the image being at least generated by... Figure 3A and Figure 3B Charged particle system 300 and Figure 4 Method 400 is generated.

[0064] While example embodiments have been illustrated and described, it will be understood that various changes can be made without departing from the spirit and scope of the disclosure.

[0065] The systems, devices, and methods described herein are not to be interpreted in a limiting sense. Rather, the present disclosure is directed to all novel and nonobvious features and aspects of the various disclosed embodiments, alone and in various combinations and subcombinations with one another. The disclosed systems, methods, and apparatus are not limited to any specific aspect or feature or combination of aspects and features, nor do the disclosed systems, methods, and apparatus require that any one or more specific advantages be present or problems be solved.

[0066] Although the operations of some of the disclosed methods are described in a particular, sequential order for convenience, it should be understood that this manner of description encompasses rearrangement, unless a particular ordering is required by specific language set forth below. For example, operations described sequentially can in some cases be rearranged or performed concurrently. Moreover, for the sake of simplicity, the various systems, methods, and apparatuses disclosed herein can not be depicted in full detail, as some aspects of the systems, methods, and apparatuses are known to one of ordinary skill in the art. Further, the description sometimes uses terms like “produce” and “provide” to describe the disclosed methods. These terms are high-level abstractions based on the actual operations that are performed. The actual operations that correspond to these terms will vary depending on the particular implementation and are readily discernible by one of ordinary skill in the art.

[0067] In some examples, a value, program, or device is referred to as “lowest,” “best,” “smallest,” etc. It will be understood that such descriptions are intended to indicate that a selection can be made among many used functional alternatives, and that such selection need not be better, smaller, or otherwise preferred over other selections. 1. A charged particle beam system, comprising: a charged particle source; and a charged particle beam column configured to focus the charged particles into a charged particle beam having a landing energy, wherein: the charged particle beam column comprises an enhancer tube, a set of scanning deflectors, and a set of magnetic material at least partially surrounding the enhancer tube and the set of scanning deflectors, a magnetic lens is formed in the charged particle beam column along the axis based on a magnetic lens excitation in the coil, the magnetic lens being configured to focus the charged particle beam at a first intersection point on the axis, an electrostatic lens is formed in the charged particle beam column along the axis based on a voltage applied to the enhancer tube, the electrostatic lens being configured to focus the charged particle beam at a second intersection point on the axis; and A first crossover point is between the magnetic lens and the electrostatic lens and is based on the magnetic lens excitation. 2. The system of claim 1, wherein the landing energy is greater than or equal to 1 eV and less than or equal to 500 eV. 3. The system of claim 1, wherein a working distance of the charged particle beam column is greater than or equal to 1 mm. 4. The system of claim 3, wherein the working distance is based on the magnetic lens excitation. 5. The system of claim 3, wherein the voltage is constant during imaging of the sample at the working distance, wherein the imaging is based on the landing energy. 6. The system of claim 1, wherein the first crossover point is proximate an end of the booster tube, wherein the end is between the magnetic lens and the electrostatic lens. 7. A method for target imaging, the method comprising: directing a charged particle beam having a landing energy along an axis of a charged particle beam column, the charged particle beam column comprising a booster tube, a set of scanning deflectors, and a set of magnetic material at least partially surrounding the booster tube and the set of scanning deflectors; applying a voltage to the booster tube, whereby an electrostatic lens is formed in the charged particle beam along the axis; applying a magnetic lens excitation, whereby a magnetic lens is formed in the charged particle beam along the axis; and controlling the magnetic lens excitation, whereby the magnetic lens focuses the charged particle beam at a first crossover point on the axis, wherein the first crossover point is between the magnetic lens and the electrostatic lens, wherein the electrostatic lens focuses the charged particle beam at a second crossover point on the axis. 8. The method of claim 7, further comprising: receiving an image containing image distortions; and correcting the image distortions by image post-processing or by changing the excitation of the set of scanning deflectors, wherein correcting the image distortions comprises applying a transformation to the image using a virtual model. 9. The method of claim 7, further comprising: imaging a known target using at least a first setting of a scanning electron microscope comprising the charged particle beam column; determining an image transformation based on the imaging of the known target; generating an image of the known target based on the charged particle beam at a working distance; and updating the image based on the image transformation. 10. The method of claim 8, further comprising: controlling the magnetic lens excitation, whereby a working distance of the charged particle beam column is equal to or greater than 1 mm. 11. The method of claim 9, further comprising: generating multiple images of the known target, each image corresponding to a different one of a plurality of settings of the scanning electron microscope, wherein the image transformation is based on the multiple images. 12. The method of claim 9, wherein imaging the known target comprises: generating an image of the known target by varying at least one or more of the first crossover point, the second crossover point, a position of the known target, or a beam characteristic, wherein the image transformation is based on the image. 13. The method of claim 7, wherein the landing energy is greater than or equal to 1 eV and less than or equal to 500 eV. 14. The method of claim 7, further comprising: controlling the magnetic lens excitation such that the first crossover point is proximate an end of the booster tube. 15. One or more non-transitory computer-readable storage media storing instructions that, when executed by a set of processors, cause performance of operations comprising: directing a charged particle beam having a landing energy along an axis of a charged particle beam column, the charged particle beam column comprising a booster tube, a set of scanning deflectors, and a set of magnetic material at least partially surrounding the booster tube and the set of scanning deflectors; applying a voltage to the booster tube such that an electrostatic lens is formed in the charged particle beam along the axis; applying a magnetic lens excitation to the set of scanning deflectors such that a magnetic lens is formed in the charged particle beam along the axis; and controlling the magnetic lens excitation such that the magnetic lens focuses the charged particle beam at a first crossover point on the axis, wherein the first crossover point is between the magnetic lens and the electrostatic lens, wherein the electrostatic lens focuses the charged particle beam at a second crossover point on the axis. 16. The one or more non-transitory computer-readable storage media of claim 15, wherein the landing energy is greater than or equal to 1 eV and less than or equal to 500 eV. 17. The one or more non-transitory computer-readable storage media of claim 15, the operations further comprising: imaging a known target using at least a first setting of a scanning electron microscope comprising the charged particle beam column; determining an image transformation based on the imaging of the known target; generating an image of the known target based on the charged particle beam at a working distance; and updating the image based on the image transformation. 18. The one or more non-transitory computer-readable storage media of claim 17, the operations further comprising: generating multiple images of the known target, each image corresponding to a different one of a plurality of settings of the scanning electron microscope, wherein the image transformation is based on the multiple images. 19. The one or more non-transitory computer-readable storage media of claim 17, the operations further comprising: controlling the magnetic lens excitation such that a working distance of the charged particle beam column is equal to or greater than 1 mm. 20. The one or more non-transitory computer-readable storage media of claim 17, the operations further comprising: controlling the magnetic lens excitation such that the first intersection is proximate to an end of the booster tube.

Claims

1. A charged particle beam system, comprising: a charged particle source; and a charged particle beam column configured to focus the charged particle beam into a charged particle beam having a landing energy, wherein: the charged particle beam column comprises an enhancer tube, a set of scanning deflectors, and a set of magnetic material at least partially surrounding the enhancer tube and the set of scanning deflectors, a magnetic lens is formed in the charged particle beam column along an axis based on a magnetic lens excitation in a coil, the magnetic lens configured to focus the charged particle beam at a first intersection point on the axis, an electrostatic lens is formed in the charged particle beam column along the axis based on a voltage applied to the enhancer tube, the electrostatic lens configured to focus the charged particle beam at a second intersection point on the axis; and the first intersection point is between the magnetic lens and the electrostatic lens and based on the magnetic lens excitation.

2. The system of claim 1, wherein the landing energy is greater than or equal to 1 eV and less than or equal to 500 eV.

3. The system of claim 1, wherein a working distance of the charged particle beam column is greater than or equal to 1 mm.

4. The system of claim 3, wherein the working distance is based on the magnetic lens excitation.

5. The system of claim 3, wherein the voltage is constant during imaging of a sample by the working distance, wherein the imaging is based on the landing energy.

6. The system of claim 1, wherein the first intersection point is proximate to an end of the enhancer tube, wherein the end is between the magnetic lens and the electrostatic lens.

7. A method for target imaging, the method comprising: directing a charged particle beam having a landing energy along an axis of a charged particle beam column, the charged particle beam column comprising an enhancer tube, a set of scanning deflectors, and a set of magnetic material at least partially surrounding the enhancer tube and the set of scanning deflectors; applying a voltage to the enhancer tube, whereby an electrostatic lens is formed in the charged particle beam along the axis; applying a magnetic lens excitation, whereby a magnetic lens is formed in the charged particle beam along the axis; and controlling the magnetic lens excitation, whereby the magnetic lens focuses the charged particle beam at a first intersection point on the axis, wherein the first intersection point is between the magnetic lens and the electrostatic lens, wherein the electrostatic lens focuses the charged particle beam at a second intersection point on the axis.

8. The method of claim 7, further comprising: receiving an image containing image distortion; and correcting the image distortion by image post-processing or by changing an excitation of the set of scanning deflectors, wherein correcting the image distortion comprises applying a transformation to the image using a virtual model.

9. The method of claim 7, further comprising: imaging a known target using at least a first setting of a scanning electron microscope comprising the charged particle beam column; determining an image transformation based on the imaging of the known target; generating an image of the known target based on the charged particle beam at a working distance; and updating the image based on the image transformation.

10. The method of claim 8, further comprising: controlling the magnetic lens excitation, whereby a working distance of the charged particle beam column is equal to or greater than 1 mm.

11. The method of claim 9, further comprising: generating a plurality of images of the known target, each image corresponding to a different one of a plurality of settings of the scanning electron microscope, wherein the image transformation is based on the plurality of images.

12. The method of claim 9, wherein imaging the known target comprises: generating an image of the known target by varying at least one or more of the first crossover point, the second crossover point, a position of the known target, or a beam characteristic, wherein the image transformation is based on the image.

13. The method of claim 7, wherein the landing energy is greater than or equal to 1 eV and less than or equal to 500 eV.

14. The method of claim 7, further comprising: controlling the magnetic lens excitation such that the first crossover point is proximate an end of the booster tube.

15. One or more non-transitory computer-readable storage media storing instructions that, when executed by a set of processors, cause performance of operations comprising: directing a charged particle beam having a landing energy along an axis of a charged particle beam column, the charged particle beam column comprising a booster tube, a set of scanning deflectors, and a set of magnetic material at least partially surrounding the booster tube and the set of scanning deflectors; applying a voltage to the booster tube such that an electrostatic lens is formed in the charged particle beam along the axis; applying a magnetic lens excitation to the set of scanning deflectors such that a magnetic lens is formed in the charged particle beam along the axis; and controlling the magnetic lens excitation such that the magnetic lens focuses the charged particle beam at a first crossover point on the axis, wherein the first crossover point is between the magnetic lens and the electrostatic lens, wherein the electrostatic lens focuses the charged particle beam at a second crossover point on the axis.

16. The one or more non-transitory computer-readable storage media of claim 15, wherein the landing energy is greater than or equal to 1 eV and less than or equal to 500 eV.

17. The one or more non-transitory computer-readable storage media of claim 15, the operations further comprising: imaging the known target using at least a first setting of a scanning electron microscope comprising the charged particle beam column; determining an image transformation based on the imaging of the known target; generating an image of the known target based on the charged particle beam at a working distance; and updating the image based on the image transformation.

18. The one or more non-transitory computer-readable storage media of claim 17, the operations further comprising: generating a plurality of images of the known target, each image corresponding to a different one of a plurality of settings of the scanning electron microscope, wherein the image transformation is based on the images.

19. The one or more non-transitory computer-readable storage media of claim 17, the operations further comprising: controlling the magnetic lens excitation such that the working distance of the charged particle beam column is equal to or greater than 1 mm.

20. The one or more non-transitory computer-readable storage media of claim 17, the operations further comprising: controlling the magnetic lens excitation such that the first crossover point is proximate an end of the booster tube.

Images