Electron optical module for providing an off-axis electron beam with tunable coma

Abstract

An electron optical module for providing an off-axis electron beam with tunable coma. An electron optical module for providing an off-axis electron beam with tunable coma according to the present disclosure includes: a structure positioned downstream of an electron source; and an electron lens assembly positioned between the structure and the electron source. The structure generates a decelerating electric field and is positioned to prevent electrons from passing along the optical axis of the electron lens assembly. The electron optical module further includes a microlens that is not positioned on the optical axis of the electron lens assembly and is configured to apply a lens effect to the off-axis electron beam. The combination of aberrations applied to the off-axis electron beam by the microlens and the electron lens assembly is such that the coma of the off-axis beam has an expected value in a downstream plane.

Description

Background Art

[0001] In order for scientists and engineers to continue to explore and develop technologies at increasingly smaller scales, it is necessary to continuously increase the magnification and resolution of microscopes. To achieve this, microscope components are continuously improved to enhance microscope performance (i.e., improve resolution, increase magnification, reduce aberrations, etc.). Two fundamental aberrations that need to be corrected within charged particle systems are spherical aberration (C S ), and coma. According to Scherzer's theorem, electromagnetic lenses used to focus electron beams in electron microscopes always have a positive spherical aberration coefficient. This means that charged particle systems employing such electromagnetic lenses are considered to have inevitable imaging errors, or require additional correctors, which may be difficult to fabricate, require dynamic adjustment / maintenance, and significantly increase the total cost of SEM / STEM systems. Summary of the Invention

[0002] An electro - optical module for providing an off - axis electron beam with tunable coma according to the present disclosure includes: a structure that, when used in a charged particle system, is positioned downstream of an electron source; an electron lens assembly that, when used in a charged particle system, is positioned between the structure and the electron source; and a microlens that is not positioned on the optical axis of the electron lens assembly and applies a lens effect to an off - axis electron beam that does not travel along the optical axis of the electron lens assembly. The structure can be configured to apply a voltage potential to the structure when using the electron lens and is positioned such that the structure prevents electrons from passing along the optical axis of the electron lens assembly. A first aberration applied to the off - axis electron beam by the microlens is combined with a second aberration applied by the electron lens assembly such that the off - axis beam has an expected value of off - axis aberration, specifically an expected value of coma, in a plane downstream of the electron lens. In some embodiments, by adjusting a process for one or more of the size, design, positioning, and voltage applied to individual electron lens assembly components, the electron lens can be tuned to adjust the contribution of one or more of spherical aberration, coma, field curvature, and / or astigmatism to the off - axis electron beam such that there is an expected amount of spherical aberration, coma, field curvature, and / or astigmatism at one or more downstream planes. Brief Description of the Drawings

[0003] The detailed description is described with reference to the accompanying drawings. In the drawings, the left - most digit of the reference numeral identifies the drawing in which the reference numeral first appears. The same reference numerals in different drawings represent similar or identical items.

[0004] Figure 1 An example electro - optical module for providing an off - axis electron beam with tunable coma is shown.

[0005] Figure 2 It is a diagram showing an exemplary environment for providing an off-axis electron beam with tunable coma for sample research.

[0006] Figure 3 An exemplary monochromator for providing an off-axis electron beam in a desired energy range without coma is shown.

[0007] Figure 4 It is a diagram of an exemplary environment for sample research, the exemplary environment including a monochromator for providing an off-axis electron beam in a desired energy range without coma.

[0008] Figure 5 It is a diagram of a simulated electron optical module for providing an off-axis electron beam with tunable coma.

[0009] Figure 6 It is a diagram of a simulation of the electromagnetic effect of a lens assembly in an electron optical module according to the present disclosure.

[0010] Figure 7 It is a diagram of the simulation results of a simulated electron optical module through which two groups of electrons with different energies pass Figure 5 through.

[0011] Throughout several views of the drawings, like reference numerals refer to corresponding parts. Generally, in the drawings, elements that may be included in a given instance are shown in solid lines, while elements that are optional for a given instance are shown in dashed lines. However, the elements shown in solid lines are not required for all instances of the present disclosure, and the elements shown in solid lines may be omitted from a particular instance without departing from the scope of the present disclosure. Detailed Description

[0012] The present disclosure relates to a system comprising an electron optical module for providing an off-axis electron beam with tunable coma. More specifically, a system according to the present disclosure comprises: a structure (e.g., a foil, an aperture stop, etc.) that is positioned downstream of an electron source when used in a charged particle system; an electron lens assembly that is positioned between the structure and the electron source when used in a charged particle system; and a microlens that is not positioned on the optical axis of the electron lens assembly and applies a lens effect to an off-axis electron beam that does not travel along the optical axis of the electron lens assembly. The structure is configured to have a voltage potential applied thereto when the electron optical module is used, and is positioned such that the structure prevents electrons from passing along the optical axis of the electron lens assembly. Applying a voltage to the structure, in combination with the voltage on the electron lens assembly, creates an electric field that decelerates electrons towards the structure. According to Scherzer's theorem, the total spherical aberration from the source to the sample must be positive, but due to the decelerating field, the spherical aberration contributed by the region from the source to the structure can be negative. This negative contribution to spherical aberration can be used to effectively compensate for off-axis aberrations: according to the present invention, a first aberration applied to the off-axis electron beam by the microlens is combined with a second aberration applied by the electron lens assembly such that the coma aberration of the off-axis beam has a desired value in a plane downstream of the electron lens. In various embodiments, the dimensions, layout, and voltages of the components of the electron optical module can be further configured such that the first and second aberrations also correct for spherical aberration (C S ), and / or field curvature and / or astigmatism. Additionally, in some embodiments of the present disclosure, the electron optical module of the present disclosure can be a component part of a coma correction system and / or a monochromator.

[0013] Figure 1FIG. 0 is an illustration of an exemplary electron optical module 100 for providing an off-axis electron beam with tunable coma. The optical module 100 is shown to include an electron lens assembly 102, a structure 104, and an off-axis microlens 106. The structure 104 is shown positioned downstream of the lens assembly 102 when used in a charged particle system. In some embodiments, the structure blocks the path of electrons traveling along the optical axis 108 of the lens assembly. When the electron optical module 100 is used, a voltage potential is applied at least to the upper surface of the structure 104. In some embodiments, the structure 104 holds a charge such that a charge 110 exists at the optical axis 108. The microlens 106 is positioned off the optical axis 108 of the lens assembly 102 and is configured to apply a lens effect to the off-axis electron beam 112. The off-axis electron beam 112 corresponds to a portion of the electrons 122 that do not travel along the optical axis 108 of the electron lens assembly 102. Additionally, in some embodiments of the present invention, the off-axis electron beam 112 passes through the microlens 106 along a path different from the optical axis 107 of the microlens 106. In this manner, the off-axis electron beam 112 receives contributions from the aberrations of the electron lens assembly 102 and the microlens 106. It is known to those skilled in the art that the optical axis of an electron lens is an imaginary straight line passing through the center of the lens and / or the center of the electric field generated by the lens. Those skilled in the art will understand that a portion of an electron beam whose optical axis does not pass through an electron lens will have one or more off-axis aberrations (e.g., coma, field curvature, astigmatism, etc.) applied to it by the electron lens.

[0014] In an embodiment of the present invention, when the combined contribution of the electron lens assembly 102 to the coma of the off-axis beam 112 and the contribution of the microlens 106 to the coma of the off-axis beam 112 are used in a charged particle system, the off-axis electron beam 112 has a desired coma in a plane 114 downstream of the electron lens. Alternatively, the combined contribution of the lens assembly 102 and the microlens 106 to coma can be further combined with the aberrations of other optical elements in the charged particle system such that the net coma of the off-axis electron beam 112 is zero (or near zero) in a plane (e.g., the sample plane) downstream of the electron optical module 100. Additionally, in some embodiments of the present invention, the lens assembly 102 can be configured to apply negative spherical aberration (Cs) to the off-axis electron beam 112, and the microlens 106 can be configured to apply positive spherical aberration to the off-axis electron beam 112.

[0015] Additionally, in some embodiments, the contribution of the electron lens assembly 102 to the off-axis aberrations can compensate for and / or cancel other aberrations (or the cumulative aberrations from other elements in the system) in the microlens 106, including astigmatism, field curvature, etc. For example, the negative spherical aberration of the electron lens assembly 102 may contribute to compensating for the astigmatism effect of the astigmatism effect of the microlens 106 such that the off-axis electron beam 112 does not have astigmatism in a plane downstream of the electron optical module 100.

[0016] According to the present invention, by adjusting the dimensions, layout, positioning, and voltage of the components of the electro - optical module 100, the contribution of the lens assembly 102 and / or the microlens 106 to a single one of coma, astigmatism, and field curvature can be changed to a desired value. In this way, the electro - optical module 100 can be tuned such that these contributions combine to cause the off - axis electron beam 112 to have desired values of coma, astigmatism, and field curvature in one or more planes downstream of the electro - optical module 100. That is, by adjusting the dimensions, layout, positioning, and voltage of the components of the electro - optical module 100, the compensation of the electro - optical module 100 for coma, astigmatism, and field curvature can be tuned such that the contributions of coma, astigmatism, and field curvature (or combinations thereof) are compensated for and / or eliminated.

[0017] For example, in an embodiment of the novel electro - optical module 100, the contribution of the lens assembly 102 to the spread of the source image can be represented by the following relationship:

[0018]

[0019] where d S , d 彗差 , d FC , d AS represent the spreads caused by spherical aberration, coma, field curvature, and astigmatism, respectively. The angle of the microlens with respect to the optical axis is represented by the complex number ω C = α x + i α y , where α x and α y represent the angles in the xz - plane and yz - plane, respectively, where the z - axis is the optical axis of the electron lens assembly. The complex number γ ap represents the optical elevation angle of the microlens with respect to the electron lens assembly in a similar manner. The overline above ω and γ represents the complex conjugate. The contribution of the electron lens assembly to spherical aberration is represented by C s . As in most electro - optical lenses, approximately, the off - axis aberration of the lens assembly is dominated by the off - axis effect of spherical aberration, and thus, in this instance, the off - axis aberration is approximated by the off - axis effect of spherical aberration (that is, by C s γ ap and C s γ ap 2 ). By writing these relationships in this form, it is emphasized that the coma, field curvature, and astigmatism of the off - axis beam can be simply tuned by tuning the contribution of the electron lens assembly to spherical aberration C s . It is emphasized that due to the deceleration field in front of the microlens, not only can this C S be tuned to a positive value, but it can also be tuned to a negative value.

[0020] In addition, in certain embodiments of the present invention, the contributions of the off-axis microlenses 106 in the electro-optical module 100 to spherical aberration, coma, field curvature, and astigmatism in the off-axis electron beam 112 can be expressed by the following relationships:

[0021]

[0022] where C S(ML) , γ ap ·F a(ML) , γ ap 2 ·D a(ML) , γ ap 2 ·C a(ML) are the spherical aberration coefficient, coma coefficient, field curvature aberration coefficient, and astigmatism aberration coefficient of the microlens, respectively. Thus, those skilled in the art will understand that in some embodiments of the present invention, the cumulative contribution of the electro-optical module 100 to the off-axis beam 112 can be expressed as:

[0023]

[0024] It can be understood from the exemplary relationships (1) to (12) how the dimensions, layout, and voltage of the components of the electro-optical module 100 can be adjusted such that when combined with the optical effects of one or more other optical elements of the charged particle microscope system, the net contribution to one or more of spherical aberration, coma, astigmatism, and field curvature in the off-axis beam 112 can be an expected value, zero, close to zero, and / or can be close to zero in a specific plane. In addition, those skilled in the art will understand that the mathematical relationships described above are merely exemplary and are used to help understand how the components of the electro-optical module 100 can be combined to form the electro-optical module 100 for providing an off-axis electron beam without spherical aberration or coma. The mathematical relationships represent embodiments of the present invention, but those skilled in the art will understand that many variations of the electro-optical module 100 are also included within the present disclosure based on the component and functional descriptions within the present disclosure.

[0025] The lens assembly 102 can be rotationally symmetric about the optical axis 108 and can produce a virtual image. In some embodiments, the lens assembly 102 includes extraction electrodes 116, a first set of one or more electrodes 118, and a second set of one or more electrodes 120. The lens assembly 102 is configured to apply one or more lens effects to the electron stream 122 emitted from an optional electron emitter 124 located upstream of the electron optical module 100 in a charged particle system. The lens assembly 102 can separate the electrons 122 passing through the lens assembly based on the energy of the electrons. For example, the lens assembly can provide chromatic aberration that separates the electrons 122 based on their corresponding energies, see for example EP1566826B1 of one of the present inventors. In this way, in some embodiments, this separation can cause the off-axis beam 144 to include multiple different components of different electron energies, where the different components have different trajectories when leaving the microlens 106 based on the electron energies associated with the components. In addition to this separation, the positioning of the microlens 106 off the optical axis 108 also creates an additional chromatic effect, causing the off-axis electron beam 112 to have additional dispersion. As an example, Figure 1 the off-axis electron beam 112 is shown as including a first component beam 126 composed of electrons having a first energy / energy range and a second component beam 128 composed of electrons having a second energy / energy range.

[0026] Figure 1 A structure 104 is shown that blocks the electrons 122 from passing along the optical axis 108 of the electron lens assembly 102. However, in other embodiments, the structure 104 can allow the electrons 122 to pass along the optical axis 108. In various embodiments, the structure 104 can be one or more apertures with one or several diaphragms, foils, thin films, graphene or silicone barriers, or a combination of these or other types of physical structures that can prevent the electrons 122 from passing through the physical structure but through the microlens and can receive an applied voltage such that the physical structure can hold a charge 110 at a point along the optical axis. In some embodiments, the charge 110 can be a negative charge accumulated by the electrons 122 impinging on the structure 104. A voltage potential can be applied to the structure 104 by an optional voltage source 130 electrically connected to the structure 104.

[0027] The microlens 106 is an optical lens assembly positioned off the optical axis 108. The microlens 106 can be rotationally symmetric about the optical axis 107. The aperture stop can be (partially) tilted such that the optical axis 107 is aligned with the off-axis beam 112. Such (partial) tilting can be obtained by the bending structure 104 or by adding small electrodes or a structure that effectively tilts the electric field at the microlens 106. The structure 104 can be the aperture stop and the microlens 106 can be a microaperture defined by the aperture stop, and the lens effect of the microaperture is generated by the penetration of the electrostatic field between the lens assembly 102 and the microlens 106. Alternatively or additionally, the structure 104 and the microlens 106 can be component parts of a MEMS system, and both the structure and the microlens block electrons 122 from passing along the optical axis 108 while also generating the electron lens 106. In other embodiments, the microlens 108 can correspond to and / or include a rotationally symmetric aperture with multipoles around the aperture, an electrostatic microlens, a magnetic stop, or a combination thereof. For example, the microlens 108 can include a combination of an electrostatic microlens and a magnetic microlens such that the microlens applies both an electrostatic effect and a magnetic effect simultaneously.

[0028] In some embodiments, the electron optical module 100 can include one or more additional apertures and / or lenses configured to allow a portion of the electrons 122 to pass through the structure 104. For example, Figure 1 The electron optical module 100 is shown as including an optional additional microlens / aperture 132 that is close to but off the optical axis 108. In some embodiments, such an optional lens / aperture 132 can allow a portion of the electrons 122 to pass through the structure 104 to prevent radiation damage and / or excessive charge accumulation caused by the electrons 122 incident on the structure 104. Alternatively or additionally, one or more optional additional microlens / apertures 132 can allow a portion of the electrons 122 to pass through the structure 104 such that a corresponding additional off-axis electron beam is generated that is free of spherical aberration, coma, field curvature, and / or astigmatism. In some embodiments, the electron optical module 100 can optionally include additional microlenses, where individual microlenses have different sizes such that a user can change the characteristics of the off-axis beam by selecting the particular microlens through which the off-axis beam 112 passes.

[0029] In some embodiments, the electron optical module 100 is a component part of a charged particle system. Additionally, the electron optical module 100 can be a component part of an optical component within (or constructed to be included within) a charged particle system, such as a monochromator, a coma corrector, a spherical aberration corrector, etc.

[0030] Figure 2 is an illustration of an exemplary environment 200 for providing an off-axis electron beam with tunable coma for the study of a sample 202. Specifically, Figure 2The example environment 200 is shown as including an example charged particle system 204 for the study and / or analysis of a sample 202. The example charged particle system 204 can be or include one or more different types of optical and / or charged particle microscopes, such as but not limited to a scanning electron microscope (SEM), a scanning transmission electron microscope (STEM), a transmission electron microscope (TEM), a charged particle microscope (CPM), a cryo-compatible microscope, a focused ion beam microscope (FIB), a dual beam microscope system, or a combination thereof. Figure 2 An example charged particle microscope system 204 is shown as a transmission electron microscope (TEM) 206.

[0031] The example charged particle microscope system 204 includes a charged particle source 208 (e.g., a thermionic source, a Schottky-emission source, a field emission source, etc.), which emits an electron beam 210 along an emission axis 212 and towards an electron optical module 100 for providing an off-axis electron beam 214 that is free of spherical aberration or coma. The electron optical module 100 includes an electron lens assembly 102, a structure 104, and an off-axis microlens 106. The structure 104 is shown positioned downstream of the lens assembly 102 such that the structure blocks the path of the electron beam 210 from traveling along the optical axis of the lens assembly. A voltage potential is applied to the structure 104 such that when the electron optical module 100 is used, the structure can hold a charge 110 at a point along the optical axis of the lens assembly 102. The microlens 106 is positioned off the optical axis of the lens assembly 102 and is configured to apply a lens effect to the off-axis electron beam 214.

[0032] According to the present invention, the lens assembly 102 and the microlens 106 are configured such that their individual contributions to coma are combined such that the off-axis beam 214 has a desired coma value in one or more planes downstream of the electron optical module 100. In an embodiment of the present invention, the combined contribution of the coma of the electron lens assembly 102 and the coma of the microlens 106 results in the off-axis electron beam 214 being free of coma downstream of the electron optical module 100. Alternatively, the combined contribution of the lens assembly 102 and the microlens 106 to coma can be further combined with the aberrations of other optical elements (e.g., components of the focusing column 218, the objective lens, the transfer lens, the accelerator lens, etc. or a combination thereof) in the example charged particle microscope system 204 such that the net coma of the off-axis electron beam 214 is a desired value, zero (or near zero), in a plane (e.g., the sample plane) downstream of the electron optical module 100.

[0033] Additionally, in some embodiments, the negative spherical aberration compensation of the lens assembly 102 and / or the elimination of other off-axis aberrations in the microlens 106 (or the cumulative off-axis aberrations from other elements in the system), including spherical aberration, coma, astigmatism, field curvature, etc. For example, the aberration of the lens assembly 102 may contribute to compensating for the negative spherical aberration effect of the positive spherical aberration effect of the microlens 106, such that the off-axis electron beam 214 does not have spherical aberration in the downstream plane. Similarly, by adjusting the dimensions, layout, and voltages of the components of the electron optical module 100, the contribution of the lens assembly 102 to one or more of spherical aberration, coma, astigmatism, and field curvature can compensate for and / or eliminate the contribution of the microlens 106 to the spherical aberration, coma, astigmatism, and field curvature of the off-axis electron beam 214 (or a combination thereof).

[0034] The emission axis 212 extends along the length of the exemplary charged particle microscope system 204 from the charged particle source 208 and passes through the central axis of the sample 202. In some embodiments, an accelerator lens may be positioned between the charged particle source 208 and the electron optical module 100. Such an accelerator lens accelerates / decelerates, focuses, and / or directs the electron beam 210 towards the electron optical module 100 (when positioned above the electron optical module) or towards the focusing column 218 (when positioned below the electron optical module 100).

[0035] Figure 2 The charged particle system 204 is shown to include at least a first deflector 220 configured to deflect the off-axis electron beam 214 towards the emission axis 212. The illustrated charged particle system 204 further shows at least a second deflector 222 configured to apply an additional deflection to the off-axis electron beam 214 such that the off-axis electron beam becomes an on-axis beam (i.e., travels along the optical axis of the emission axis 212 and / or the focusing column 218). In some embodiments, the second deflector 222 may optionally be positioned with or in the vicinity of a lens 224, a slit, or another optical component.

[0036] The focusing column 218 focuses the off-axis electron beam 214 such that the off-axis electron beam impinges on at least a portion of the sample 202. In some embodiments, the focusing column 218 may include one or more of an aperture, scanning coils, and an upper condenser lens. The focusing column focuses the electrons from the electron source into a small spot on the sample. The direction of the electron beam can be adjusted by the scanning coils to scan different positions of the sample 202. Additionally, the focusing column 218 can correct and / or tune the aberrations (e.g., geometric aberrations, chromatic aberrations) of the off-axis electron beam 214.

[0037] During TEM imaging, the off-axis electron beam 214 is directed such that the off-axis electron beam irradiates and / or passes through the region of interest on the sample 202. A portion of the electrons 226 passing through the sample 202 and / or the emissions 226 generated by the off-axis electron beam 214 impinge on the microscope detector system 230. In this way, the electrons and / or emissions generated during irradiation of the sample 202 are captured by the detector system 230, which then generates detector data that can be used to generate a reconstruction of the region of interest of the sample 202. In Figure 2 FIG. 2, the microscope detector system 230 is shown as including a disk-shaped bright-field detector and a dark-field detector. In some embodiments, the microscope detector system 230 may include one or more other detectors. Alternatively or additionally, the microscope detector system 230 may include a scanning electron microscope detector system, a focused ion beam detector system, a scanning electron microscope secondary electron detector system, a focused ion beam secondary electron detector system, and an optical microscope detector system.

[0038] Figure 2 The exemplary charged particle microscope system 204 is further shown as further including a sample holder 228 and a computing device 232. The sample holder 228 is configured to hold the sample 202 and is capable of translating, rotating, and / or tilting the sample 202 relative to the exemplary charged particle microscope system 204. While the sample 202 is depicted as a thin sheet attached to the sample holder, the sample holder being capable of manipulating the thin sheet within a vacuum chamber, in other embodiments, the sample holder may be a structure that includes one or more sample supports (e.g., a mesh, foil, grid, etc.), the one or more sample holders being configured to accommodate the sample and being configured to be inserted into the charged particle microscope system 204 and attached to / connected to the sample stage, the sample stage being capable of translating, rotating, and / or tilting the sample holder 202 relative to the exemplary charged particle microscope system 204. For example, the sample holder 202 may include a sample support such as a conductive foil that defines an aperture in which the sample 202 can be held for TEM studies. In cryo-TEM, the sample 202 may correspond to a biological or other substance (e.g., a protein) suspended in amorphous ice that is located within the aperture defined by the conductive sample holder foil.

[0039] Figure 2Further includes a schematic diagram showing an example computing architecture 250 of computing device 232. Example computing architecture 250 shows additional details of the hardware and software components that can be used to implement the techniques described in this disclosure. Those skilled in the art will understand that computing architecture 250 can be implemented in a single computing device 232 or can be implemented across multiple computing devices. For example, the individual modules and / or data constructs depicted in computing architecture 250 can be executed by different computing devices 232 and / or stored on the different computing devices. In this way, different process steps of the inventive method according to this disclosure can be executed and / or implemented by separate computing devices 232.

[0040] In example computing architecture 250, the computing device includes one or more processors 252 and a memory 254 communicatively coupled to the one or more processors 252. Example computing architecture 250 can include a control module 256 stored in memory 254. As used herein, the term "module" is intended to represent an example partitioning of executable instructions for discussion purposes and is not intended to represent any type of requirement or required method, manner, or organization. Thus, while various "modules" are described, their functionality and / or similar functionality can be arranged differently (e.g., combined into a smaller number of modules, broken down into a large number of modules, etc.). Additionally, while specific functions and modules are described herein as being implemented by software and / or firmware executable on a processor, in other examples, any one or all of the modules can be implemented in whole or in part by hardware (e.g., a dedicated processing unit, etc.) to perform the described functions. As discussed above in various embodiments, the modules described herein in connection with example computing architecture 250 can be executed across multiple computing devices 232.

[0041] Control module 256 can be executed by processor 252 to cause computing device 232 and / or example charged particle microscope system 204 to take one or more actions. For example, control module 256 can cause example charged particle microscope system 204 to translate, tilt, rotate, or a combination thereof, the sample holder 228. Additionally, control module 256 can cause charged particle emitter 208 to emit electron beam 210.

[0042] In some embodiments, the control module 256 may further be configured to cause the computing device 232 to adjust one or more optical characteristics (e.g., positioning, orientation, operating mode, applied voltage, etc.) of an optical element in the exemplary charged particle microscope system 204 or its components. For example, the control module 256 may cause a voltage to be applied to the lens assembly 102 and / or its component elements such that the lens assembly contributes to one or more of spherical aberration, coma, astigmatism, and field curvature of the electron beam 210, such that the spherical aberration, coma, astigmatism, and / or field curvature of the off-axis beam 214 is zero, near zero, and / or equal to a desired non-zero value in a particular plane. For example, the voltage applied to the component electrodes of the lens assembly 102 may be adjusted such that the off-axis beam 214 has a coma coefficient that, when combined with the coma contribution of the downstream optical elements of the electron optical module 100, results in an image generated by the emission 226 not having a coma effect at a particular plane.

[0043] Alternatively or additionally, the control module 256 may adjust the optical characteristics or other components of the exemplary charged particle microscope system 204 (e.g., components of the focusing column 218, objective lens, transfer lens, accelerator lens, etc. or combinations thereof) such that the combined spherical aberration, coma, astigmatism, and / or field curvature in the off-axis beam 214 at the sample 202 is zero, near zero, or equal to a desired non-zero value. The selection of such optical characteristics may be based on a predetermined mathematical relationship of the system, based on sensor inputs from the charged particle microscope system 204, based on image data, or combinations thereof. For example, based on the control module 256 detecting a coma effect in the image generated by the emission 226, the control module 256 determines adjustments to other components of the electron optical module 100, other optical components of the exemplary charged particle microscope system 204, and / or the optical characteristics of its components that will correct the detected coma effect, and then adjusts the optical characteristics such that subsequent images generated by the emission 226 do not have the detected coma effect.

[0044] As discussed above, the computing device 226 includes one or more processors 252 that are configured to execute instructions, applications, or programs stored in a memory 254 accessible by the one or more processors. In some instances, the one or more processors 252 may include hardware processors that include, but are not limited to, a hardware central processing unit (CPU), a graphics processing unit (GPU), etc. Although in many cases the techniques are described herein as being performed by one or more processors 252, in some cases the techniques may be implemented by one or more hardware logic components, such as a field programmable gate array (FPGA), a complex programmable logic device (CPLD), an application specific integrated circuit (ASIC), a system on a chip (SoC), or combinations thereof.

[0045] The memory 254 accessible by one or more processors 252 is an example of a computer-readable medium. A computer-readable medium can include two types of computer-readable media, namely computer storage media and communication media. Computer storage media can include volatile and non-volatile media and removable and non-removable media that implement for storing information such as computer-readable instructions, data structures, program modules, or other data in any method or technology. Computer storage media includes, but is not limited to, random access memory (RAM), read-only memory (ROM), erasable programmable read-only memory (EEPROM), flash memory or other memory technologies, compact disc read-only memory (CD-ROM), digital versatile discs (DVD) or other optical storage devices, magnetic tape cartridges, tapes, magnetic disk storage devices or other magnetic storage devices, or any other non-transmission medium that can be used to store the required information and can be accessed by a computing device. Generally speaking, computer storage media can include computer-executable instructions that, when executed by one or more processing units, cause the execution of various functions and / or operations described herein. In contrast, communication media embodies computer-readable instructions, data structures, program modules, or other data in a modulated data signal such as a carrier wave, or other transmission mechanism. As defined herein, computer storage media does not include communication media.

[0046] Those skilled in the art will also understand that, for purposes of memory management and data integrity, items or portions thereof can be transferred between the memory 254 and other storage devices. Alternatively, in other embodiments, some or all of the software components can be executed in the memory of another device and communicate with the computing device 226. Some or all of the system components or data structures can also be stored (e.g., as instructions or structured data) on a non-transitory computer-accessible medium or portable article for reading by an appropriate drive, various examples of which are described above. In some embodiments, instructions stored on a computer-accessible medium separate from the computing device 226 can be transmitted to the computing device 226 via a transmission medium or signal (such as an electronic, electromagnetic, or digital signal communicated through a communication medium such as a wireless link). Various embodiments can further include receiving, sending, or storing instructions and / or data implemented on a computer-accessible medium according to the above description.

[0047] Figure 3FIG. 0 is an illustration of an example monochromator 300 for providing an off-axis electron beam having a desired energy range with tunable coma. The monochromator 300 is configured to produce an off-axis electron beam 302 having a desired energy and / or energy range. Additionally, since the monochromator 300 includes an electron optical module 100, the off-axis electron beam 302 may also have zero, near-zero, or desired non-zero coefficients of one or more of spherical aberration, coma, astigmatism, field curvature contributions (or combinations thereof). By tuning one or more of these aberrations to zero or near-zero, the energy resolution of the monochromator can be improved or optimized.

[0048] The optical module 100 is shown as including an electron lens assembly 102, a structure 104, and an off-axis microlens 106. The structure 104 is shown as being positioned downstream of the lens assembly 102 when used in a charged particle system. In some embodiments, the structure may be positioned to block the path of electrons traveling along the optical axis of the lens assembly. When the electron optical module 100 is used, a voltage potential is applied to the structure 104 such that the structure can hold a charge 110 at a position along the optical axis 108. The microlens 106 is positioned outside the optical axis 108 of the lens assembly 102 and is configured to apply a lens effect to the off-axis electron beams 302 and 304.

[0049] According to the present invention, when the combined contribution of the coma of the electron lens assembly 102 and the coma contribution of the microlens 106 are used in a charged particle system, the off-axis electron beams 302 and 304 do not have coma in a plane 306 downstream of the electron lens. Alternatively, the combined contribution of the lens assembly 102 and the microlens 106 to coma can be further combined with the coma of other optical elements in the charged particle system such that the net coma of the off-axis electron beams 302 and 304 is zero (or near-zero) in a plane (e.g., the sample plane) downstream of the electron optical module 100.

[0050] Additionally, in some embodiments, the contribution of the lens assembly 102 to aberrations can compensate for and / or cancel other off-axis aberrations in the microlens 106 (or cumulative off-axis aberrations from other elements in the system), including spherical aberration, coma, astigmatism, field curvature, etc. For example, the negative spherical aberration of the lens assembly 102 may contribute to compensating for the astigmatic effect of the astigmatic effect of the microlens 106 such that the off-axis electron beams 302 and 304 do not have astigmatism in the downstream plane. Similarly, by adjusting the dimensions, layout, and voltages of the components of the electron optical module 100, the aberration contribution of the lens assembly 102 can compensate for and / or cancel the spherical aberration, coma, astigmatism, field curvature contributions (or combinations thereof) of the microlens 106 to the off-axis electron beams 302 and 304.

[0051] Such compensation or elimination can be used to improve or optimize, for example, the energy resolution of a downstream monochromatic module: The lens assembly 102 is configured to apply one or more lens effects to the electron beam 308 emitted from an optional electron emitter 310 upstream of the electron optical module 100 positioned in a charged particle system. The lens assembly 102 can produce chromatic aberrations that separate the electrons based on their corresponding energies. In this way, in some embodiments, this separation can cause the off-axis beams 302 and 304 to include multiple different components of different electron energies, where the different components have different trajectories when leaving the microlens 106 based on the electron energies associated with the microlens. For example, Figure 3 shows two off-axis beams leaving the microlens 106, a first off-axis beam 302 having a first energy / energy range and a second off-axis beam 304 having a different second energy / energy range. Those skilled in the art will understand that the chromatic aberrations applied by the lens assembly 102 will produce multiple off-axis beams corresponding to the spectrum of energies / wavelengths present in the electron beam 308. As Figure 3 shown, each of these off-axis beams will leave the microlens 106 with a slightly different trajectory based on the corresponding energy of the off-axis beam.

[0052] Figure 3 The monochromator 300 is shown as including a beam blocker 312 having an aperture 314. The beam blocker 312 includes a body that blocks one or more of the off-axis beams leaving the microlens 106 (e.g., the off-axis beam 304) from passing through, while allowing one or more off-axis beams to pass through the aperture (e.g., 302). In this way, the beam blocker 312 is configured to allow only a subset of the off-axis beams having a specific energy to pass through. For example, the aperture 314 can be a slit configured to allow only off-axis beams having a desired energy / energy range to pass through. In some embodiments, the beam blocker 312 can be translated so that off-axis beams of different energy ranges are allowed to pass through the aperture 314. Alternatively or additionally, a deflector or electron lens can be used to change the off-axis beam passing through the aperture 314 (i.e., deflect the beam so that the beam passes through the aperture 314, change the focus of the off-axis beam so that more or fewer off-axis beams pass through the aperture, etc.).

[0053] In some embodiments, the monochromator 300 may include an optional electron lens 316 or an optional electrode 316. For example, the optional electron lens 316 may adjust the focus of the off-axis electron beams 302 and / or 304 such that a desired beam path is achieved. In another example, the monochromator 300 may include an optional deflector 318 that applies a deflection to the off-axis beam 302 such that the off-axis beam is deflected toward the optical axis 320 of the charged particle system that uses the off-axis beam. The monochromator 300 may also optionally include an additional deflector 322 configured to apply an additional deflection to the off-axis beam 302 such that the off-axis beam becomes an on-axis electron beam 324. In this way, the monochromator 300 may produce an on-axis electron beam having a desired energy range, the on-axis electron beam of the desired energy range having zero, near-zero, or a desired non-zero coefficient of one or more of spherical aberration, coma, astigmatism, field curvature contributions (or combinations thereof).

[0054] Figure 4 is an illustration of an exemplary environment 400 for the study of a sample 402, the exemplary environment including a monochromator 300 for providing an off-axis electron beam of a desired energy range with tunable coma. Specifically, Figure 4 The exemplary environment 400 is shown as including an exemplary charged particle system 404 for the study and / or analysis of the sample 402. Figure 4 An exemplary charged particle microscope system 204 is shown as a transmission electron microscope (TEM) 406. However, those skilled in the art will understand from the present disclosure how the monochromator 300 may be incorporated into other types of charged particle systems 204 for the study of the sample 402.

[0055] The exemplary charged particle microscope system 404 includes a charged particle source 408 that emits an electron beam 410 along an emission axis 412 and toward the monochromator 300 for providing an off-axis electron beam 414 of a desired energy range that does not have spherical aberration or coma.

[0056] The monochromator 300 according to the present disclosure includes an electron optical module 100 that causes the off-axis electron beam 414 produced by the monochromator 300 to have zero, near-zero, or a desired non-zero coefficient of one or more of spherical aberration, coma, astigmatism, field curvature contributions (or combinations thereof). The optical module 100 includes an electron lens assembly 102, an off-axis microlens 106, and a structure 104 that, when used in a charged particle system, is positioned downstream of the lens assembly 102 such that the structure blocks the path of electrons traveling along the optical axis of the lens assembly. When the electron optical module 100 is used, the structure 104 may hold a charge 110 on the optical axis of the lens assembly 102. The microlens 106 is positioned outside the optical axis 108 of the lens assembly 102 and is configured to apply a lens effect to the off-axis electron beam 414.

[0057] In an embodiment of the present invention, when the combined contribution of the coma of the electron lens assembly 102 and the contribution of the coma of the microlens 106 are used in a charged particle system, the off-axis electron beam 414 does not have coma in a plane downstream of the electron lens. Alternatively, the combined contribution of the lens assembly 102 and the microlens 106 to coma can be further combined with the spherical aberration of other optical elements (e.g., components or combinations thereof such as the focusing column 218, objective lens, transfer lens, accelerator lens, etc.) in the charged particle system 303, such that the net coma of the off-axis electron beam 414 is zero (or near zero) in a plane downstream of the monochromator 300 (e.g., sample plane, slit plane, etc.).

[0058] Additionally, in some embodiments, the aberration contribution of the lens assembly 102 compensates for and / or cancels other off-axis aberrations in the microlens 106 (or cumulative off-axis aberrations from other elements in the system), including coma, astigmatism, field curvature, etc. For example, the contribution of the field curvature of the lens assembly 102 can compensate for the field curvature effect imposed by the microlens 106, such that the off-axis electron beam 414 does not have field curvature in the downstream plane. Similarly, by adjusting the dimensions, layout, and voltages of the components of the electron optical module 100, the aberrations of the lens assembly 102 can compensate for and / or cancel the coma, astigmatism, field curvature contributions (or combinations thereof) of the microlens 106 to the off-axis electron beam 414.

[0059] The lens assembly 102 is further configured to impose one or more lens effects on the electron beam 410. For example, the lens assembly 102 can produce chromatic aberration that separates the electrons based on their corresponding energies. In this way, in some embodiments, this separation can cause the off-axis beam 414 to include multiple different components of different electron energies, where the different components have different trajectories based on the electron energies associated with the microlens when leaving the microlens 106. For example, Figure 4 It is illustrated that three off-axis beams 414 leaving the microlens 106 have different energies / energy ranges. Those skilled in the art will understand that the chromatic aberration imposed by the lens assembly 102 will produce multiple off-axis beams corresponding to the spectrum of energies / wavelengths present in the electron beam 410 stream. As Figure 4 shown, each of these off-axis beams will leave the microlens 106 with a slightly different trajectory based on the energy corresponding to the off-axis beam. However, due to the aberration contribution of the lens assembly 102, each of these off-axis beams can have a zero, near-zero, or desired non-zero coefficient of one or more of spherical aberration, coma, astigmatism, field curvature contributions (or combinations thereof).

[0060] Figure 4The monochromator 300 is shown as further including a beam blocker 312 having an aperture 314. The beam blocker 312 includes a body that blocks one or more of the off-axis beams exiting the microlens 106 from passing through, while allowing one or more off-axis beams to pass through the aperture. In this way, the beam blocker 312 is configured to allow only a subset of the off-axis beams having a specific energy to pass through. In some embodiments, the beam blocker 312 can be translated such that off-axis beams within different energy ranges are allowed to pass through the aperture 314. Alternatively or additionally, a deflector or an electron lens can be used to change the off-axis beam passing through the aperture 314.

[0061] In some embodiments, an optional electron lens 316 or an optional electrode 316 can be included in the monochromator 300. For example, the optional electron lens 316 can adjust the focus of the off-axis electron beams 302 and / or 304 such that a desired beam path is achieved. In another example, the monochromator 300 can include an optional deflector 318 that applies a deflection to the off-axis beam 302 such that the off-axis beam is deflected towards the emission axis 412.

[0062] In some embodiments, the charged particle system 404 or the monochromator 300 itself can also optionally include an additional deflector 416 that is configured to apply an additional deflection to the off-axis beam such that the off-axis beam becomes an on-axis electron beam. In this way, the additional deflector 416 can cause the off-axis beam to become an on-axis electron beam. Figure 4 The charged particle system 404 is shown as including at least an additional deflector 416 that is configured to apply an additional deflection to the off-axis electron beam 414 such that the off-axis electron beam becomes an on-axis beam (i.e., travels along the emission axis 412 and / or the optical axis of the focusing column 418). In some embodiments, the additional deflector 416 can optionally be positioned with or near a lens, a slit, or another optical component.

[0063] The emission axis 412 is a central axis that extends along the length of the exemplary charged particle microscope system 404 from the charged particle source 408 and passes through the center of the sample 402. In some embodiments, an accelerator lens can be positioned between the charged particle source 408 and the monochromator 300. Such an accelerator lens accelerates / decelerates, focuses, and / or directs the electron beam 410 towards the monochromator 300 (when positioned above the monochromator) or towards the focusing column 418 (when positioned below the electron optical module 100).

[0064] The focusing column 418 focuses the off-axis electron beam 414 such that the off-axis electron beam is incident on at least a portion of the sample 402. In some embodiments, the focusing column 418 may include one or more of an aperture, scanning coils, and an upper condenser lens. The focusing column focuses electrons from the electron source into a small spot on the sample. The direction of the electron beam can be adjusted by the scanning coils to scan different positions of the sample 402. Additionally, the focusing column 418 may correct and / or tune aberrations (e.g., geometric aberrations, chromatic aberrations) of the off-axis electron beam 414.

[0065] During TEM imaging, the off-axis electron beam 414 is directed such that the off-axis electron beam irradiates and / or passes through the region of interest on the sample 402. A portion of the electrons 426 that pass through the sample 402 and / or emissions 426 generated by the off-axis electron beam 414 impinge on the microscope detector system 430. In this way, the electrons and / or emissions generated during irradiation of the sample 402 are captured by the detector system 430, which then generates detector data that can be used to generate a reconstruction of the region of interest of the sample 402. Figure 4 The exemplary charged particle microscope system 204 is further shown as further including a sample holder 428 and a computing device 432. The sample holder 428 is configured to hold the sample 402 and is capable of translating, rotating, and / or tilting the sample 402 relative to the exemplary charged particle microscope system 404.

[0066] Figure 4 Further included is a schematic diagram of an exemplary computing architecture 450 showing the computing device 432. The exemplary computing architecture 450 shows additional details of the hardware and software components that can be used to implement the techniques described in the present disclosure. Those skilled in the art will understand that the computing architecture 450 can be implemented in a single computing device 432 or can be implemented across multiple computing devices. For example, the separate modules and / or data constructs depicted in the computing architecture 450 can be executed and / or stored on different computing devices 432. In this way, different process steps of the inventive method according to the present disclosure can be executed and / or implemented by separate computing devices 432.

[0067] In the exemplary computing architecture 450, the computing device includes one or more processors 252 and a memory 254 communicatively coupled to the one or more processors 252. The exemplary computing architecture 450 may include a control module 456 stored in the memory 254. As discussed above in various embodiments, the modules described herein in connection with the exemplary computing architecture 450 can be executed across multiple computing devices 432.

[0068] The control module 256 can be executed by the processor 252 to cause the computing device 432 and / or the exemplary charged particle microscope system 404 to take one or more actions. For example, the control module 456 can cause the exemplary charged particle microscope system 404 to translate, tilt, rotate, or a combination thereof, the sample holder 428. Additionally, the control module 256 can cause the charged particle emitter 408 to emit an electron beam 410.

[0069] In some embodiments, the control module 456 can further be configured to cause the computing device 432 to adjust one or more optical characteristics (e.g., position, orientation, operating mode, applied voltage, etc.) of the optical elements in the exemplary charged particle microscope system 404 or its components. For example, the control module 456 can cause a voltage to be applied to the lens assembly 402 and / or its component elements such that the contributions of the lens assembly to one or more of spherical aberration, coma, astigmatism, and field curvature of the electron beam 410 result in the spherical aberration, coma, astigmatism, and / or field curvature of the off-axis beam 414 being zero, near zero, and / or equal to a desired non-zero value. For example, the voltage applied to the component electrodes of the lens assembly 102 can be adjusted such that the off-axis beam 414 has a coma coefficient that, when combined with the coma contribution of the optical elements downstream of the monochromator 300, results in an image produced by the emission 426 that does not have a coma effect.

[0070] Alternatively or additionally, the control module 456 can adjust the optical characteristics or other components of the exemplary charged particle microscope system 404 (e.g., components of the focusing column 418, objective lens, transfer lens, accelerator lens, etc., or a combination thereof) such that the combined spherical aberration, coma, astigmatism, and / or field curvature in the off-axis beam 414 at the sample 402 is zero, near zero, or equal to a desired non-zero value. The selection of such optical characteristics can be based on a predetermined mathematical relationship of the system, based on sensor input from the charged particle microscope system 404, based on image data, or a combination thereof. For example, based on the control module 456 detecting a coma effect in the image produced by the emission 426, the control module 456 determines adjustments to the other components of the monochromator 300, other optical components of the exemplary charged particle microscope system 404, and / or the optical characteristics of its components that will correct the detected coma effect, and then adjusts the optical characteristics such that subsequent images produced by the emission 426 do not have the detected coma effect.

[0071] The control module 256 can further perform operations to adjust a subset of the off-axis beam 414 passing through the aperture 314. For example, the control module 256 can apply deflections to the off-axis beam 414 such that the trajectory of the beam is changed and / or the beam blocker 312 can be translated such that different subsets of the off-axis beam 414 are blocked. In this way, the control module 256 can change the energy / energy range of the electron beam allowed to propagate out of the monochromator 300. In some embodiments, such adjustments can be applied such that the sample 402 is irradiated with an electron beam having a desired energy / energy range. Alternatively or additionally, such adjustments can be applied such that the sample 402 is irradiated with an electron beam having a desired intensity.

[0072] Figure 5 is an analog electron optical module 500 for providing an off-axis electron beam with tunable coma. That is, Figure 5 shows a simulation of an embodiment of the electron optical module 100 that has been specifically configured to provide an off-axis electron beam with a desired coma value in the downstream plane using the techniques described herein. The simulations discussed herein were performed using 3D and 3D field calculations as well as ray tracing software.

[0073] The simulation lens 500 is shown as including a lens assembly 102, a structure 104, and a microlens 106. Figure 5 Further shown is an electron stream 502 emitted downward from a point source above the lens assembly 102, and an off-axis electron beam 504 exiting the microlens 106. In the simulation 500, the structure 104 is an aperture stop, and the microlens 106 is a 100 μm aperture lens. Figure 5 Also shown is a virtual source 506 of the electron stream 502 generated by the lens assembly 102.

[0074] Figure 5 Also included is a beam blocker 508 positioned in a slit plane 510 downstream of the lens, the beam blocker being configured to block a subset of the off-axis electron beam 504 having a specific energy / energy range. The beam blocker 508 is shown as defining a slit 512 that allows a subset of the off-axis electron beam 504 having a specific energy / energy range to pass through the beam blocker 508. The analog high electron lens 500 is configured with tuned optical parameters of its components (i.e., adjusted sizes, designs, applied voltages, etc.) such that one or more of the spherical aberration, coma, field curvature, and astigmatism of the lens assembly are negative values of the spherical aberration, coma, field curvature, and astigmatism of the microlens. This particular configuration of the optical parameters of the electron optical module 100 results in the lens assembly 102 having a spherical aberration coefficient of -70 mm and a coma coefficient of -85 mm.

[0075] Figure 6It is an image 600 of a simulation of the electromagnetic effect of the lens assembly in the electro - optical module 100 according to the present disclosure. Figure 6 The lens assembly 102 is shown as including an extractor 602, a first electrode 604, and a second electrode 606. Figure 6 A virtual source 608 of the emitted electrons 610 generated by the lens assembly 120 is also shown.

[0076] Figure 7 It is a depiction of the simulation result 700 of the simulated electro - optical module 100 through which two groups of electron beams with different energies pass. Specifically, Figure 5 It corresponds to the 3D simulation results of two different - energy electrons of the simulated electro - optical module 100 traversing Figure 7 and Figure 5 The clusters 702 and 704 show the positioning of the simulated electrons of two different energies in the slit plane. Cluster 702 shows the ray - tracing result of electrons with a charge of 4500.1 eV, while cluster 704 shows the ray - tracing result of electrons with a charge of 4500 eV. As can be seen from the simulation result 700, each of the clusters in the cluster is cylindrical and clearly separated. This indicates that the simulated electron lens 500 is capable of generating two off - axis electron beams that do not have coma or any other off - axis aberrations. In other words, the lens assembly of the simulated electron lens 500 has a negative spherical aberration coefficient and a coma coefficient, which, when combined with the contributions of the other optical elements of the simulated electron lens 500, result in each of the simulated off - axis electron beams in the simulated off - axis electron beams not having spherical aberration or coma. However, those skilled in the art will understand that the optical parameters used for the simulated electron lens 500 are not restrictive. Instead, the optical parameters merely represent an exemplary embodiment of the electron lens 100 according to the present invention. Those skilled in the art will understand how to use the relationships and functional descriptions included in the present disclosure to adjust the optical parameters of the components of the electro - optical module 100 to produce many different embodiments within the present disclosure, the many different embodiments providing one or more off - axis electron beams that do not have spherical aberration or coma.

[0077] Examples of the inventive subject matter according to the present disclosure are described in the paragraphs listed below.

[0078] A1. An electron optical module for providing an off-axis electron beam with tunable coma, the electron optical module comprising: an electron lens assembly positioned downstream of an electron source when used in a charged particle system, the electron lens assembly being configured to produce a tunable lens effect; a structure positioned downstream of the electron lens assembly when used in a charged particle system, the structure being configured to produce an accelerating or decelerating electric field between the electron lens assembly and the structure; and a microlens not positioned on the optical axis of the electron lens assembly and configured to apply a lens effect to an off-axis electron beam that does not travel along the optical axis of the electron lens assembly, wherein a first aberration applied by the microlens to the off-axis electron beam is combined with a second aberration applied by the electron lens assembly such that the coma of the off-axis beam has an expected value in a plane downstream of the electron module.

[0079] A1.01. The electron optical module according to paragraph A1, wherein the electric field generated by the structure is a decelerating electric field.

[0080] A1.02. The electron optical module according to paragraph A1, wherein the electric field generated by the structure is an accelerating electric field.

[0081] A1.03. The electron optical module according to any one of paragraphs A1 to A1.02, wherein the electron lens assembly comprises at least two electrodes.

[0082] A1.04. The electron optical module according to any one of paragraphs A1 to A1.03, wherein the electron lens assembly comprises a combination of rotationally symmetric electrodes or segmented electrodes and / or multipoles.

[0083] A1.05. The electron optical module according to any one of paragraphs A1 to A1.04, wherein the electron lens assembly comprises a combination of an electrostatic lens and a magnetic lens.

[0084] A1.1. The electron optical module according to any one of paragraphs A1 to A1.05, wherein the microlens has positive spherical aberration (Cs) and the electron lens assembly has negative spherical aberration.

[0085] A1.1.1. The electron optical module according to paragraph A1.1, wherein the combination contribution of the spherical aberration of the electron lens assembly and the off-axis aberration of the microlens causes the off-axis electron beam not to have spherical aberration and / or not to have off-axis aberration in a plane downstream of the electron lens when used in a charged particle system.

[0086] A1.2. The electro-optical module according to any one of paragraphs A1 to A1.1.1, wherein the electron lens assembly further has negative coma.

[0087] A1.2.1. The electro-optical module according to paragraph A1.2, wherein the combined contribution of the coma of the electron lens assembly and the coma of the microlens results in the off-axis electron beam having no coma in the plane downstream of the electron lens when used in a charged particle system.

[0088] A1.3. The electro-optical module according to any one of paragraphs A1 to A1.2.1, wherein the electron lens assembly further has tunable astigmatism.

[0089] A1.3.1. The electro-optical module according to paragraph A1.3, wherein the combined contribution of the astigmatism of the electron lens assembly and the astigmatism of the microlens results in the off-axis electron beam having no astigmatism in the plane downstream of the electron lens when used in a charged particle system.

[0090] A1.4. The electro-optical module according to any one of paragraphs A1 to A1.3.1, wherein the electron lens assembly further has negative field curvature.

[0091] A1.4.1. The electro-optical module according to paragraph A1.4, wherein the combined contribution of the field curvature of the electron lens assembly and the field curvature of the microlens results in the off-axis electron beam having no field curvature in the plane downstream of the electron lens when used in a charged particle system.

[0092] A1.5. The electro-optical module according to any one of paragraphs A1 to A1.4.1, wherein the electron lens separates the electrons passing through the electron lens assembly according to energy.

[0093] A1.5.1. The electro-optical module according to paragraph A1.5, wherein the electron lens separates the electrons passing through the electron lens assembly based on the chromatic aberration of the electron lens.

[0094] A1.6. The electro-optical module according to any one of paragraphs A1 to A1.5, wherein the spherical aberration coefficient (Cs) and / or the chromatic aberration coefficient (Cc) of the lens can be tuned to be positive, negative, or zero.

[0095] A1.7. The electro-optical module according to any one of paragraphs A1 to A1.6, wherein the electron lens assembly produces a virtual image.

[0096] An electro - optical module according to any one of paragraphs A1 to A1.7, wherein the electron lens assembly does not produce a real image.

[0097] An electro - optical module according to any one of paragraphs A1 to A1.8, wherein the structure can impede electrons from passing along the optical axis of the electron lens assembly.

[0098] An electro - optical module according to paragraph A2, wherein the structure is a diaphragm.

[0099] An electro - optical module according to paragraph A2.1, wherein the microlens is an aperture defined by the diaphragm.

[0100] An electro - optical module according to any one of paragraphs A2.1 to A2.1.1, wherein the microlens includes a multipole aperture.

[0101] An electro - optical module according to paragraph A2.1.2, wherein the microlens includes a single lens.

[0102] An electro - optical module according to any one of paragraphs A2.1 to A2.1.2.1, wherein the microlens includes a stack of small MEMS and / or non - MEMS multipoles.

[0103] An electro - optical module according to any one of paragraphs A2 to A2.1.3, wherein the physical structure can impede electrons from passing along the optical axis of the electron lens.

[0104] An electro - optical module according to paragraph A2.2, wherein the structure is conductive.

[0105] An electro - optical module according to any one of paragraphs A2 to A2.2.1, wherein the structure includes a thin film.

[0106] An electro - optical module according to paragraph A2.3, wherein the structure is a foil.

[0107] An electro - optical module according to paragraph A2.3, wherein the structure includes a silicone film.

[0108] An electro - optical module according to any one of paragraphs A2 to A2.3.2, wherein the charge retained when using the monochromator is located on the optical axis of the electron lens assembly.

[0109] A2.4.1. The electro - optical module according to paragraph A2.4, wherein the charge is a negative charge.

[0110] A2.4.2. The electro - optical module according to any one of paragraphs A2.4 to A2.4.1, wherein the charge held on the optical axis of the electron lens assembly is the charge accumulated by electron impact on the structure.

[0111] A2.5. The electro - optical module according to any one of paragraphs A1 to A2.4.2, wherein the structure configured to hold the charge includes charges present on the surface of the structure along the optical axis of the lens assembly.

[0112] A3. The electro - optical module according to any one of paragraphs A1 to A2.5, wherein the microlens is a micro - aperture in the structure.

[0113] A3.1. The electro - optical module according to paragraph A3, wherein the micro - aperture provides a lens effect using MEMS technology.

[0114] A3.2. The electro - optical module according to any one of paragraphs A3 to A3.1, wherein the micro - aperture is a first aperture, and the structure further defines a second aperture positioned closer to the central axis of the lens assembly than the first aperture.

[0115] A3.2.1. The electro - optical module according to paragraph A3.2, wherein the second aperture allows a second electron beam to pass through the structure.

[0116] A3.2.1.1. The electro - optical module according to paragraph A3.2.1, wherein the second aperture reduces the charge accumulated on the structure at the optical axis of the lens assembly.

[0117] A3.3. The electro - optical module according to any one of paragraphs A3 to A3.2.1.1, wherein the microlens is one of a plurality of micro - apertures in the structure, and each micro - aperture is configured to allow a small beam of electrons to pass through the structure.

[0118] A3.3.1. The electro - optical module according to paragraph A3.3, wherein individual micro - apertures among the plurality of micro - apertures in the structure have different sizes.

[0119] A3.3.1.1. The electro - optical module according to paragraph A3.3.1, wherein the user can select different dispersion rates by selecting an individual micro - aperture of a desired size.

[0120] A4. The electro - optical module according to any one of paragraphs A1 to A3.3.1.1, wherein the lens assembly is rotationally symmetric.

[0121] A4.1. The electro - optical module according to paragraph A4, wherein the lens assembly includes an extraction electrode; a first electrode; and a second electrode.

[0122] A4.2. The electro - optical module according to any one of paragraphs A4 to A4.1, wherein the lens assembly produces a virtual image in front of the electron emitter when used in a charged - particle system.

[0123] A4.3. The electro - optical module according to any one of paragraphs A4 to A4.2, wherein the optical parameters of the lens assembly are tuned to compensate for the contribution of the microlenses to an off - axis electron beam in two or more of the following aspects: spherical aberration; coma; field curvature; and astigmatism.

[0124] A4.3.1. The electro - optical module according to paragraph A4.3, wherein tuning the optical parameters of the lens assembly corresponds to adjusting one or more of the size, design, and voltage applied to individual lens - assembly components such that one or more of the spherical aberration, coma, field curvature, and astigmatism of the lens assembly are negative values of the spherical aberration, coma, field curvature, and astigmatism of the microlenses.

[0125] A5. The electro - optical module according to any one of paragraphs A1 to A4.3.1, further comprising an electron source positioned downstream of the lens assembly when the electron lens is used in a charged - particle system.

[0126] A6. The electro - optical module according to any one of paragraphs A1 to A5, wherein the electro - optical module is a component element of a monochromator.

[0127] A6.1. The electro - optical module according to paragraph A6, wherein the monochromator includes: the electro - optical module; and an additional optical component positioned downstream of the electro - optical module when used in a charged - particle system.

[0128] A6.1.1. The electro - optical module according to paragraph A6.1, wherein the off - axis electron beam has no spherical aberration at all in the plane of the optical component.

[0129] A6.1.2. The electro - optical module according to any one of paragraphs A6.1 to 6.1.1, wherein the off - axis electron beam has no coma at all in the plane of the optical component.

[0130] An electron optical module according to any one of paragraphs A6.1 to 6.1.2, wherein the off-axis electron beam has no field curvature in the plane of the optical component.

[0131] An electron optical module according to any one of paragraphs A6.1 to 6.1.3, wherein the off-axis electron beam has no aberration in the plane of the optical component.

[0132] An electron optical module according to any one of paragraphs A6.1 to 6.1.4, wherein the optical component includes a lens.

[0133] An electron optical module according to any one of paragraphs A6.1 to 6.2, wherein the optical component includes a slit.

[0134] An electron optical module according to paragraph A6.3, wherein the slit allows a portion of the off-axis electron beam having a desired energy range and blocks a portion of the off-axis electron beam having an energy outside the desired energy range.

[0135] An electron optical module according to any one of paragraphs A6.3 to A6.3.1, wherein the is configured to selectively allow a portion of the off-axis electron beam having a selected energy range.

[0136] An electron optical module according to any one of paragraphs A6.1 to 6.3.2, wherein the optical component includes a deflector.

[0137] An electron optical module according to paragraph A6.4, wherein the deflector deflects the off-axis beam such that the off-axis beam becomes an on-axis beam downstream of the deflector.

[0138] An electron optical module according to any one of paragraphs A6.1 to 6.4, wherein the off-axis electron beam is focused in the plane of the optical component.

[0139] An electron optical module according to any one of paragraphs A6.1 to 6.5, wherein the plane of the optical component is perpendicular to the optical axis of the lens assembly.

[0140] An electron optical module according to any one of paragraphs A1 to A6.6, wherein the electron lens is a component element of an aberration corrector.

[0141] An electron optical module according to paragraph A7, wherein the aberration corrector corrects the coma in the electron beam of the charged particle system.

[0142] B1. The charged particle device comprises: an electron source configured to emit electrons towards an electron optical module; the electron optical module for providing an off-axis electron beam having an adjustable coma according to any one of paragraphs A1 to A7.1; an optical column configured to focus the off-axis electron beam to be incident on a sample; a sample holder configured to hold the sample; and a charged particle detector system configured to detect emissions and / or electrons generated by the off-axis electron beam incident on the sample.

[0143] C1. Use of the electron optical module for providing an off-axis electron beam that does not have spherical aberration according to any one of paragraphs A1 to A7.1.

[0144] D1. Use of the charged particle device of paragraph B1.

[0145] The systems, devices, and methods described herein should not be construed in any way as limiting. In fact, the present disclosure is directed to all novel and non-obvious features and aspects of the various disclosed embodiments, whether individually or in various combinations and sub-combinations formed with each other. The disclosed systems, methods, and devices are not limited to any specific aspect or feature or combination thereof, and the disclosed systems, methods, and devices do not require the presence of any one or more specific advantages or the solution of any one or more specific problems. Any theory of operation is for ease of explanation, but the disclosed systems, methods, and devices are not limited to such theory of operation.

[0146] Although the operations of some of the disclosed methods are described in a particular sequential order for ease of presentation, it should be understood that this description covers rearrangements unless the specific language set forth below requires a particular ordering. For example, in some cases, the operations described in sequence may be rearranged or performed simultaneously. In addition, for simplicity, the drawings may not show the various ways in which the disclosed systems, methods, and devices may be used in conjunction with other systems, methods, and devices. Further, the description sometimes uses terms such as "determine," "identify," "generate," and "provide" to describe the disclosed methods. These terms are high-level abstractions of the actual operations performed. The actual operations corresponding to these terms will vary depending on the particular implementation and are readily discernible by those skilled in the art.

Claims

1. An electron optical module for providing an off-axis electron beam with tunable coma, the electron optical module comprising: an electron lens assembly positioned downstream of an electron source when used in a charged particle system, the electron lens assembly being configured to produce a tunable lens effect; a structure positioned downstream of the electron lens assembly when used in a charged particle system, the structure being configured to produce a decelerating electric field between the electron lens assembly and the structure; and A microlens that is not positioned on the optical axis of the electron lens assembly and is configured to apply a lens effect to an off-axis electron beam that does not travel along the optical axis of the electron lens assembly, wherein a first aberration applied by the microlens to the off-axis electron beam is combined with a second aberration applied by the electron lens assembly such that the coma of the off-axis electron beam has an expected value in a plane downstream of the electron optical module, and wherein the electron lens assembly further has a negative contribution to the spherical aberration C of the off-axis electron beam s has a negative contribution.

2. The electron optical module according to claim 1, wherein: the first aberration is at least partially produced by the electron beam traveling through the microlens; and the second aberration is at least partially produced by the electron beam not traveling along the optical axis of the electron lens assembly.

3. The electron optical module according to claim 1, wherein when the electron lens is used in the charged particle system, the first aberration applied to the off-axis electron beam by the microlens is combined with the second aberration applied by the electron lens assembly and the third aberration applied by one or more other microscope elements, such that the coma of the off-axis electron beam is zero in the plane downstream of the electron lens.

4. The electron optical module according to claim 1, wherein the structure is configured to apply a voltage potential to the structure when the electron optical module is used, and wherein applying the voltage potential to the structure causes a charge to be maintained on the surface of the structure at a point along the optical axis of the electron lens assembly.

5. The electron optical module according to claim 1, wherein the structure is positioned such that the body of the structure prevents electrons from passing along the optical axis of the electron lens assembly.

6. The electron optical module according to claim 1, wherein the structure is a diaphragm, and wherein the microlens is an aperture defined by the diaphragm.

7. The electron optical module according to claim 6, wherein the microaperture is a first aperture that allows a second electron beam to pass through the structure, and the structure further defines a second aperture positioned closer to the central axis of the lens assembly than the first aperture.

8. The electron optical module according to claim 6, wherein the microlens is one of a plurality of microapertures in the structure, each microaperture being configured to allow a small beam of electrons to pass through the structure.

9. The electron optical module according to claim 6, wherein the structure is configured to apply a voltage potential to the structure when the electron optical module is used, and wherein the voltage applied to the structure produces a decelerating electric field that applies a lens effect to the electrons passing through the aperture.

10. The electron optical module according to claim 1, wherein the optical parameters of the lens assembly are tuned to compensate for the contribution of the microlens to the off-axis electron beam in two or more of the following aspects: spherical aberration; coma; curvature of field; and astigmatism.

11. The electro - optical module according to claim 10, wherein tuning the optical parameters of the lens assembly corresponds to adjusting one or more of the size, design, and voltage applied to individual lens assembly components, such that the contribution of the electron lens assembly to one or more of spherical aberration, coma, field curvature, and astigmatism is combined with the contribution of the microlens to one or more of the spherical aberration, coma, field curvature, and astigmatism of the microlens, such that the off - axis electron beam has one or more of the expected values of spherical aberration, coma, field curvature, and astigmatism in one or more planes downstream of the electron lens.

12. The electro - optical module according to claim 1, wherein when used in a charged - particle system, the combined contribution of the astigmatism of the electron lens assembly and the astigmatism of the microlens results in the off - axis electron beam having no astigmatism in the plane downstream of the electron lens.

13. The electro - optical module according to claim 1, wherein when used in a charged - particle system, the combined contribution of the field curvature of the electron lens assembly and the field curvature of the microlens results in the off - axis electron beam having no field curvature in the plane downstream of the electron lens.

14. The electro - optical module according to claim 1, wherein the electron lens assembly separates electrons passing through the electron lens assembly based on the chromatic aberration of the electron lens.

15. The electro - optical module according to claim 1, wherein the electron lens assembly is a component element of a monochromator, the monochromator including the electron lens assembly and additional optical components, the additional optical components being positioned downstream of the electron lens assembly when used in a charged - particle system, the additional optical components comprising: a body that blocks a first portion of the off - axis electron beam having an energy outside a desired energy range; and a slit or aperture that allows a portion of the off - axis electron beam having the desired energy range to pass through the additional optical components.

16. The electro - optical module according to claim 15, wherein the optical component includes a deflector configured to deflect the off - axis electron beam such that the off - axis electron beam becomes an on - axis beam downstream of the deflector.

17. The electro - optical module according to claim 15, wherein the off - axis electron beam is focused in the plane of the additional optical components.

18. The electro - optical module according to claim 1, wherein the electro - optical module is a component element of a coma corrector, and wherein the coma corrector corrects coma in the electron beam of a charged - particle system.

19. A charged - particle device, which comprises: an electron source configured to emit electrons towards an electro - optical module; the electro - optical module including: an electron lens assembly positioned downstream of the electron source, the electron lens assembly including at least two electrodes configured to produce a tunable lens effect; a structure positioned downstream of the electron lens, the structure being configured to generate a decelerating electric field between the electron lens assembly and the structure; and A microlens that is not positioned on the optical axis of the electron lens assembly and is configured to apply a lens effect to off-axis electron beams that do not travel along the optical axis of the electron lens assembly, wherein a first aberration applied by the microlens to the off-axis electron beams combines with a second aberration applied by the electron lens assembly such that the coma of the off-axis electron beams has an expected value in a plane downstream of the electron optical module, and wherein the electron lens assembly further has a negative contribution to the spherical aberration C of the off-axis electron beams s has a negative contribution; an optical column configured to focus the off-axis electron beam to be incident on the sample; a sample holder configured to hold the sample; and a charged particle detector system configured to detect emissions and / or electrons generated by the off-axis electron beam incident on the sample.

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