Device and method for local control of charged particle beam

Abstract

In various aspects, a phase plate (210) for a charged particle inspection system is disclosed, the phase plate being configured and arranged to modify the local phase of charged particles in a beam (600) to reduce the effects of lens aberrations. The phase plate is composed of an array of apertures, wherein the voltage and / or obscuration of the apertures are controlled individually or in groups.

Description

[0001] CROSS-REFERENCE TO RELATED APPLICATIONS

[0002] This application claims priority to EP application 19183767.3 filed on July 2, 2019, the entire contents of which are incorporated herein by reference. Technical Field

[0003] The embodiments described herein relate to charged particle devices having one or more charged particle beams, such as electron microscopy equipment utilizing one or more electron beams. Background Art

[0004] Integrated circuits are manufactured by creating patterns on a wafer (also called a substrate). The wafer is supported on a wafer stage in an apparatus used to create the pattern. One part of the process of manufacturing integrated circuits involves observing or "inspecting" portions of the wafer. This can be done with a charged particle system, such as a scanning electron microscope, or SEM.

[0005] Conventional microscopes use visible light and one or more transparent lenses or mirrors to make objects as small as about 1 micrometer visible. The resolving power of such microscopes is limited by the wavelength of the light used for illumination. Charged particle systems use beams of charged particles instead of light and use electromagnetic or electrostatic lenses to focus the particles. They are able to measure position with an accuracy as small as one-tenth of a nanometer.

[0006] Charged particle systems include a column with elements similar to those of a light microscope. The light source of a light microscope is replaced by a charged particle source built into the column. Instead of glass lenses, charged particle systems have electromagnetic or electrostatic lenses. The focal length (focal length) of these lenses can be changed by changing the current through the lens coils or by changing the voltage of the electrodes. Devices that manipulate beams, such as by shaping, focusing or collimating the beam, are called optical devices, similar to light-based microscopes.

[0007] More specifically, a charged particle source can image a sample at the bottom of the column through a dual-lens optical system. For an ideal lens, the charged particles will pass through the lens and gather together at a single point in the image plane (or more generally, the image surface). However, a real lens cannot focus precisely to a single point. For example, the second lens may distort the wavefront of the charged particle beam. These deviations from the idealized lens performance are called aberrations of the lens. Aberrations cause the image formed by the lens to be blurred or distorted. It is necessary to minimize aberrations so that the image of the charged particle source on the sample is as focused as possible, so that the image of the sample is clear and focused. Summary of the invention

[0008] A simplified overview of one or more embodiments is presented below in order to provide a basic understanding of these embodiments. This overview is not an extensive review of all contemplated embodiments, and is not intended to identify key or important elements of all embodiments, nor is it intended to delineate the scope of any or all embodiments. Its sole purpose is to present some concepts of one or more embodiments in a simplified form as a prelude to a more detailed description that is presented later.

[0009] According to an aspect of the embodiments, an apparatus and method for reducing the effects of lens aberrations in a charged particle system is disclosed.

[0010] Other features and advantages of the present invention and the structure and operation of various embodiments of the present invention are described in detail below with reference to the accompanying drawings. Note that the present invention is not limited to the specific embodiments described herein. These embodiments proposed here are for illustrative purposes only. Based on the teachings contained herein, other embodiments will be apparent to those skilled in the relevant art. BRIEF DESCRIPTION OF THE DRAWINGS

[0011] The accompanying drawings, which are incorporated herein and form a part of the specification, illustrate the present invention and, together with the description, further serve to explain the principles of the invention and enable those skilled in the relevant art to make and use the invention.

[0012] Figure 1 is a block diagram of a charged particle imaging system according to an aspect of an embodiment.

[0013] Figure 2A and Figure 2B is a diagram illustrating the underlying principle of one aspect of the embodiment.

[0014] Figure 3A , Figure 3B , Figure 3C and Figure 3D is a schematic plan view of a phase plate according to aspects of the embodiments.

[0015] Figure 4A and Figure 4B is a partially schematic plan view of a phase plate according to aspects of an embodiment.

[0016] Figure 5A and Figure 5B is a partially schematic plan view of a phase plate according to aspects of an embodiment.

[0017] Figure 6 is a schematic diagram of a particle imaging system according to an aspect of an embodiment.

[0018] Figure 7 is a schematic diagram of a particle imaging system according to an aspect of an embodiment.

[0019] Figure 8is a schematic diagram of a particle imaging system according to an aspect of an embodiment.

[0020] Fig. 9 is a schematic diagram of a particle imaging system according to an aspect of an embodiment.

[0021] Fig.10 is a schematic diagram of a particle imaging system according to an aspect of an embodiment.

[0022] Fig.11 is a schematic diagram of a particle imaging system according to an aspect of an embodiment.

[0023] Fig.12 is a flow chart illustrating a method of using a charged particle imaging system according to an aspect of an embodiment.

[0024] Fig.13 is a flow chart illustrating a method of using a charged particle imaging system according to an aspect of an embodiment.

[0025] Fig.14 is a flow chart illustrating a method of using a charged particle imaging system according to an aspect of an embodiment.

[0026] Fig.15A , Fig. 15B and Fig. 15C is a schematic plan view of a phase plate according to aspects of the embodiments. DETAILED DESCRIPTION

[0027] Reference will now be made in detail to exemplary embodiments, examples of which are shown in the accompanying drawings. The following description refers to the accompanying drawings, in which the same numbers in different drawings represent the same or similar elements, unless otherwise specified. The embodiments set forth in the following description of the exemplary embodiments do not represent all embodiments consistent with the present invention. Instead, they are merely examples of systems, devices, and methods consistent with the relevant aspects of the present invention described in the appended claims. For clarity, the relative sizes of the components in the drawings may be exaggerated.

[0028] Electronic devices consist of circuits formed on a silicon chip called a substrate. Many circuits can be formed together on the same silicon chip and are called integrated circuits or ICs. The size of these circuits has been reduced significantly so that many of them can fit on a substrate. For example, an IC chip in a smartphone can be as small as a thumbnail and can also include more than 2 billion transistors, each of which is less than 1 / 1000 the size of a human hair.

[0029] Manufacturing these extremely small ICs is a complex, time-consuming and expensive process that typically involves hundreds of individual steps. An error in even one step can result in a defect in the finished IC, rendering it useless. Therefore, one goal of the manufacturing process is to avoid such defects in order to maximize the number of functional ICs manufactured in the process, i.e., to increase the overall yield of the process.

[0030] An integral part of improving yield is monitoring the chip manufacturing process to ensure that it is producing sufficient numbers of functional integrated circuits. One way to monitor the process is to inspect the chip circuit structures at various stages of their formation. Inspection can be done using a scanning electron microscope (SEM). The SEM can be used to image these extremely small structures, in effect, taking a "photograph" of the structures. The image can be used to determine if the structure was formed correctly and if it was formed in the correct location. If the structure is defective, the process can be adjusted so that the defect is less likely to recur.

[0031] As the name implies, SEM uses electron beams because such electron beams can be used to see structures that are too small to be seen by microscopes using light. However, the ability to see smaller structures is limited by the fact that the lens cannot truly focus the charged particle beam to a point on the sample. Instead, the lens will deform the beam due to lens aberrations. The full potential of increasing the resolution of the SEM needs to be realized by minimizing the effects of such lens aberrations. One of the several disclosures in the present application is a system and method in which the effects of lens aberrations are controlled by introducing one or more devices in the beam path that can adjust the beam locally (i.e., at one or more locations in the beam cross section). These adjustments can counteract the effects of lens aberrations. Of course, this is an approximate description, and the actual details are more fully and accurately set forth below.

[0032] Without limiting the scope of the present disclosure, the description and drawings of the embodiments may illustratively refer to the use of electron beams. However, these embodiments are not intended to limit the present invention to specific charged particles. For example, systems and methods for beam forming may be applicable to photons, x-rays, and ions, etc. In addition, the term "beam" may refer to a primary electron beam, a primary electron beamlet, a secondary electron beam, or a secondary electron beamlet, etc.

[0033] As used herein, unless otherwise specifically stated, the term "or" encompasses all possible combinations unless not feasible. For example, if it is stated that a component may include A or B, then unless otherwise specifically stated or not feasible, the component may include A, or B, or A and B. As a second example, if it is stated that a component may include A, B, or C, then unless otherwise specifically stated or not feasible, the component may include A, or B, or C, or A and B, or A and C, or B and C, or A and B and C.

[0034] In the specification and claims, the terms "upper", "lower", "top", "bottom", "vertical", "horizontal" and similar terms may be used. Unless otherwise indicated, these terms are intended to show only relative orientations and not any absolute orientation, such as orientation relative to gravity. Similarly, terms such as left, right, front, back, etc. are intended to give only relative orientations.

[0035] Reference now Figure 1 , which shows a charged particle system in the form of an exemplary electron beam inspection (EBI) system 10 according to an embodiment of the present disclosure. Figure 1 As shown, the EBI system 10 includes a main chamber 11, a load / lock chamber 20, an electron beam tool 100, and an equipment front end module (EFEM) 30. The electron beam tool 100 is located in the main chamber 11.

[0036] The EFEM 30 includes a first load port 30a and a second load port 30b. The EFEM 30 may include additional load ports. For example, the first load port 30a and the second load port 30b may receive a wafer front opening pod (FOUP) containing wafers (e.g., semiconductor wafers or wafers made of other materials) or samples to be inspected (wafers and samples may be collectively referred to as "wafers" hereinafter). One or more robotic arms (not shown) in the EFEM 30 may transfer the wafers to the load / lock chamber 20.

[0037] The load / lock chamber 20 is connected to a load / lock vacuum pump system (not shown), which removes gas molecules in the load / lock chamber 20 to reach a first pressure lower than the atmospheric pressure. After reaching the first pressure, one or more robotic arms (not shown) can transfer the wafer from the load / lock chamber 20 to the main chamber 11. The main chamber 11 is connected to a main chamber vacuum pump system (not shown), which removes gas molecules in the main chamber 11 to reach a second pressure lower than the first pressure. After reaching the second pressure, the wafer is inspected by the electron beam tool 100. The electron beam tool 100 can be a single beam system or a multi-beam system, or a multi-column system. The controller 19 is electrically connected to the electron beam tool 100. Although the controller 19 is Figure 1 1 as being external to the structure including the main chamber 11 , the load / lock chamber 20 , and the EFEM 30 , but it is understood that the controller 19 may be part of the structure.

[0038] Although the present disclosure provides an example of a main chamber 11 housing an electron beam inspection system, it should be noted that aspects of the present disclosure in its broadest sense are not limited to a chamber housing an electron beam inspection system. Instead, it should be understood that the principles discussed herein can also be applied to other tools operating at a second pressure.

[0039] Figure 2A Shown as Figure 1 An exemplary electron beam tool 100 as part of an EBI system of FIG. The electron beam tool 100 (also referred to herein as “device 100”) includes an electron source 110, a first lens 120, and a second lens 130. For clarity, Figure 2A Other components that are typically present, such as apertures and deflectors, are not shown. Sample 140 having sample surface 150 may be disposed on a movable stage (not shown). Electron source 110, lens 120, and lens 130 may be aligned with a primary optical axis 160 of apparatus 100.

[0040] The electron source 110 may include a cathode (not shown) and an extractor or anode (not shown), wherein during operation, the electron source 110 is configured to emit primary electrons from the cathode, and the primary electrons are extracted or accelerated by the extractor or anode to form a primary electron beam shown as a series of wavefronts, i.e., (multiple) surfaces (real or virtual) as follows: on the (multiple) surfaces, the oscillation phases are the same. It can be seen that the wavefront of the beam emitted by the light source 110 is substantially spherical. The lens 120 used as a converging lens makes the wavefront substantially planar. Ideally, the second lens used as an objective lens focuses the wavefront onto the surface 150, thereby imaging the source 110. However, the aberrations of the second lens 130 deform the shape of the wavefront and deviate from the ideal shape, resulting in a blurred image on the surface 150.

[0041] Figure 2B An apparatus or device 200 is shown in which an element is introduced into the beam path to compensate for aberrations. Specifically, a phase plate 210 is introduced between the lenses to pre-shape the wavefront so that the net effect of the pre-shaping and the aberrations is a properly focused beam. As described in more detail below, it will be understood that the placement of the phase plate 210 in the device 200 is merely an example, and the phase plate 210 may be placed at other locations in the device 200.

[0042] Moreover, in the examples described below, the phase plate is described primarily in terms of correcting aberrations produced by the lens. However, the phase plate may also or instead be used to shape a charged particle beam. For example, the phase plate may be used to make the beam cross-sectional profile annular rather than point-like on the sample. This may provide advantages in certain applications, such as for imaging the sidewalls of contact holes. As another example, the beam profile may be made less divergent at the wafer to produce a greater depth of focus. For some applications, full aberration correction using a phase plate may not be possible simultaneously with special beam shaping using a phase plate, but the phase plate may be tuned to achieve the best compromise for a given application.

[0043] Lens 110 can be a movable converging lens, which can be configured so that the position of its first principal plane is movable. The movable converging lens can be configured to be magnetic, electrostatic or electromagnetic (e.g., composite). A movable converging lens is further described in U.S. Patent No. 9,922,799 and U.S. Patent Application Publication No. 2017 / 0025243, the entire contents of which are incorporated herein. In some embodiments, the converging lens can be an anti-rotation lens that can keep the rotation angle of the off-axis beamlet constant while changing the current of the beamlet. In some embodiments, the converging lens can be a movable anti-rotation converging lens comprising an anti-rotation lens having a movable first principal plane. An anti-rotation or movable anti-rotation converging lens is further described in International Application No. PCT / EP2017 / 084429, which is incorporated herein by reference in its entirety.

[0044] Figure 3A An exemplary embodiment of a phase plate 200 is shown, such as may be used in a device 200. As shown, the phase plate 200 is configured as an array of holes 210 in a plate element 220. Figure 3A The array in is an arrangement of 35 holes 210 arranged as a central hole with concentric rings having 6, 12, and 16 holes 210. Obviously, other arrangements can be used, including square arrays, hexagonal arrays, or random arrays, or combinations of these arrays. For some implementations, it may be advantageous for the hole pattern to have at least four-fold symmetry in the azimuthal direction. For example, for a pattern including concentric circles, the number of holes per concentric circle may be at least a multiple of 4.

[0045] The hole 210 may be circular as shown or other suitable shapes, such as elliptical or rectangular. Holes 210 having shapes different from each other, such as a combination of circular holes and elliptical holes, may be arranged on the same plate element 220. The plate element 220 in the example shown may be square and planar as shown, or may be another suitable shape such as circular, and the plate element 220 need not be planar, for example, the plate element 220 may be curved to correspond to the curvature of the wavefront.

[0046] Each of the holes 210 in the phase plate 200 has an individual voltage control 230 configured to establish a voltage in the hole. Thus, the phase plate 200 is programmable because the voltage can be set differently for each hole 210 or group of holes, and the voltage can be changed as needed. The adjustment of the voltage locally changes the phase of the electron wave. If it is desired to have fewer voltage controls 230, this can be achieved by providing fewer but larger holes 210, or by connecting groups of holes 210 to a common voltage control 230. As described below, according to another aspect, the degree of opening of the holes can be controlled in a similar manner, in which case the voltage control 230 can also or instead control the degree of opening of the holes.

[0047] For some embodiments, it may be advantageous to match the size of the phase plate's holes or segments to the beam diameter with the smallest hole that can impinge on the phase plate. For an example with 3 rings of holes or segments for the phase plate and a minimum beam diameter of about 20 μm, the hole diameter or segment gap should be on the order of 1 μm or a few μm. The wiring design for the holes or segments is more challenging for small sizes, but the voltage required is smaller and the total number of wires required will be smaller when using segments instead of holes.

[0048] Figure 3B An arrangement is shown in which the holes 210 are shaped as annular segments. Figure 3B In the specific example of , each ring has one segment (i.e. one support member). Figure 3C In a specific example, each ring has two segments (i.e., two supports). The supports can be used to carry electrical connections to electrodes in the holes, which are used to establish an electric field in the holes. In certain implementations using segments instead of rings, the advantages of reducing the number of required voltage controls 230 (e.g., for axially symmetric aberrations) can be provided, and transmittance can be increased by using less support material for the phase plate opening. As shown, the segmented openings can be arranged as concentric rings around the optical axis (the center of the plate 220). These rings can be divided into 1, 2 or more segmented openings with mechanical supports between them. The ring width (range in the radial direction) can vary from ring to ring. The segmented openings in one or more rings can have the same voltage to further limit the number of required voltage controls. The phase plate 220 can be rotated during use to average the rotational asymmetric contribution (the rotational asymmetric contribution is caused, for example, by mechanical support between the segmented openings). Figure 3D An arrangement with hexagonal holes 210 in a hexagonal phase plate 220 is shown.

[0049] The mechanical stability of the phase plate is mainly determined by its geometrical design. The final mechanical design will be a combination of maximum openness (high transmittance) and adequate mechanical interconnection between the rings (for stiffness and thermal reasons, but also for wiring). For a phase plate not positioned in or close to the focal plane, the SEM system performance will not be very sensitive to mechanical vibrations of the phase plate.

[0050] During use, a focused electron beam is scanned across the surface of a sample. During scanning of the focused electron beam over a large field of view, the shape and intensity distribution of the image of the source on the sample surface, i.e., the spot profile, may change. The use of a programmable phase plate provides the ability to correct or reduce these scanning effects where it is desired to dynamically control the programmable phase plate. As described above, a programmable phase plate can be configured as a plate with holes, each hole having a separate voltage control. Using voltage control to adjust the voltage at the hole locally changes the phase of the electron wave, i.e., if a portion of the electron wave passes through the hole, the formation of an electron spot (probe) can be controlled. As a specific example, synchronizing the phase plate voltage with the scanning of the electron beam over the sample enables the formation of the probe to be dynamically controlled over the entire scanning field of view.

[0051] Scanning is performed by using a deflector that changes the direction of the beam so that the beam is sequentially directed to different parts of the sample. The deflector is controlled by a clock signal that synchronizes the scan. In one embodiment, the same clock signal used for scanning can be used to synchronize the phase plate voltage with the beam deflector of the scanning system. Dynamic control can be limited to the voltage of a subset of the apertures of the phase plate. The voltage used for dynamic control can be in addition to the bias voltage for the apertures in the phase plate, or in addition to the bias voltage for the apertures in the phase plate in the case of a system using multiple electron beams, which is called a multi-beam system.

[0052] The scan profile, i.e., the pattern in which the beam is scanned across the sample, can be any of a number of options. The scan profile can be discontinuous, such as a sawtooth, raster, or typewriter type scan, in which the beam is scanned in a series of lines across the sample. Such a scan profile can be used for dynamic phase plate voltage control. For some embodiments, it is advantageous to combine dynamic phase plate voltage control with a continuous scan profile (e.g., for a zigzag, serpentine, or other similar scan profile of the beam) to limit the rate of change of voltage on the phase plate. That is, this scan pattern reduces the need to change the voltage because the scan is essentially continuous rather than discontinuous, so fewer sudden voltage changes are required.

[0053] The synchronization of the phase plate voltage with the scanning can be limited to only one scanning direction of the beam. Moreover, as described more fully below, it is possible to control not only the voltage at the aperture, but also its degree of shielding, i.e., whether the aperture freely allows a portion of the beam to pass, or partially or completely blocks the beam from passing through a physical barrier or other device. The synchronization of the phase plate voltage can be combined with the synchronization of the open / partially open / closed profile (transmission profile) of the phase plate aperture.

[0054] Dynamic control of the phase plate voltage can also be used to control the formation of the electron probe when scanning a relatively small field of view around different positions located at a relatively large distance from the optical axis. For one position at a relatively large distance from the optical axis, the same phase plate voltage profile can be used when scanning a relatively small field of view around that position. The phase plate voltage profile can be changed only when the beam has moved to the next position for scanning a relatively small field of view. In this case, the phase plate voltage profile will change once for each small field of view.

[0055] Figure 4A and Figure 4B Examples of possible phase distributions for a programmable phase plate for two different electron beam positions are shown. Figure 4A shows the possible phase distribution at the center of the field of view, and Figure 4B A possible phase distribution at the corners of the field of view is shown, where four gray levels represent four different phases, such as 0, π / 2, π, and 3π / 2. In some implementations, this can provide the following advantages: improving the uniformity of image quality across the field of view by correcting or reducing aberrations that cause the probe size to change across the field of view, and thus increasing the maximum allowable field of view by correcting or reducing aberrations across the field of view.

[0056] As described above, for enhanced electron beam correction, in some implementations, it may be advantageous to locally control the amplitude of the electron wave in addition to or instead of controlling the phase by controlling the voltage at the aperture only. For some implementations, not all aberrations may be fully corrected with phase control in the phase plate alone. Local amplitude control changes the shape and symmetry of the beam profile. Increasing amplitude control allows for a larger field of application. It may be advantageous to add the ability to locally adjust the amplitude of the electron wave by combining and / or averaging over closed, partially closed, and open apertures. The amplitude can be programmed by changing the distribution of closed and open apertures on the phase plate, i.e., the openness or transmission distribution. This can be done independently of or in combination with local voltage control of the phase.

[0057] Various means may be used to achieve local control of beam obscuration and, conversely, local control of beam transmission. For example, a beam blanker or deflector may be added to or integrated into a phase plate to partially, fully, or not at all obscure the aperture. As another example, a mechanical shutter may be added to or integrated into a phase plate to partially, fully, or not at all obscure the aperture. As another example, an electrical mirror may be added to or integrated into a phase plate to partially, fully, or not at all obscure the aperture.

[0058] As another example, an additional plate with holes and any one of these devices or a combination of these devices can be located upstream (closer to the source) or downstream (farther away from the source) of the phase plate. The additional plate can have more holes than the phase plate in order to better tune the amplitude of a particular phase plate hole. As with the phase plate, the holes in the additional plate can be arranged in any of a variety of patterns, such as concentric circles around the optical axis, a hexagonal pattern around the optical axis, or a rectangular pattern around the optical axis. Moreover, the holes can have any shape or combination of different shapes, such as circular or elliptical. Similarly, as with the phase plate, for some implementations it may be advantageous for the hole pattern to have at least four-fold symmetry in the azimuthal direction. For example, for a pattern comprising concentric circles, the number of holes in each concentric circle can be at least a multiple of 4. Figure 5A and Figure 5B are examples of two different hole distributions that produce different electron wave variations but have the same total transmittance. Figure 5A and Figure 5B In the experiment, 8 of the 35 wells were blocked.

[0059] Therefore, instead of or in addition to controlling the phase distribution, a plate with holes can be used to attenuate the amplitude distribution of the wavefront.For simplicity, a plate with holes for attenuating the amplitude distribution of the wavefront instead of or in addition to controlling the phase distribution is also called a phase plate.

[0060] There are several options for incorporating a phase plate in a single or multi-beam SEM system. The choice of option may be informed by various technical considerations. For example, with respect to the position of the phase plate relative to the other components of the system, for some implementations it may be advantageous to position the phase plate after the beam limiting aperture of the system, as this is the portion of the beam produced by the source that will be imaged on the sample, and it is this portion that will be optimized with the phase plate so positioned. For some embodiments, it may be advantageous to position the phase plate outside the path of the secondary (or backscattered) electrons from the sample to the detector, to avoid signal loss caused by secondary electrons striking the phase plate before reaching the detector. For some embodiments, it may be advantageous in terms of ease of use of phase plate modeling and control for arranging the phase plate so that parallel beams impinge on the phase plate. If the beam portion in which the phase plate is positioned is converging or diverging, it may be advantageous to position the phase plate away from the (virtual) focal plane for practical reasons (e.g. available volume). The phase plate may, for example, be located at or near a conjugate plane of the optical system.

[0061] exist Figure 6 In the configuration of , the phase plate 210 is located between the beam limiting aperture 610 and the Wien filter 620, which deflects the secondary electrons to the detector 630. This means that the beam 600 diverges at the phase plate 210. In order to control the beam current and the opening angle, the aperture size is usually variable in SEMs. This means that if it is desired to use the phase plate 210 for the entire current range, the lateral dimensions of the phase plate 210 should be large enough to span the entire width of the beam 600 when the beam 600 leaves the beam limiting aperture 610 at the maximum selectable beam limiting aperture size. If for a particular application under consideration the phase plate 210 is to be used only under certain conditions, for example for lower beam currents, it can be made retractable or folded and deployed only under those conditions. It is also possible to use different phase plate designs for different beam sizes and make them selectable by using motorized straps, as is usually done with apertures in SEMs.

[0062] Figure 7 A second configuration of phase plate placement is shown, where the phase plate 210 additionally performs the function of a beam limiting element, which eliminates the need for a separate beam limiting aperture. In this case, the beam diameter and current can be varied by using different phase plate designs for different beam sizes or by closing the apertures or segments of the phase plate when needed (e.g., closing the apertures or segments of the outer ring if a small beam diameter is required).

[0063] exist Figure 8In the configuration shown, an additional lens is added between the beam limiting aperture 610 and the phase plate 210 to produce a parallel beam at the phase plate 210. In this case, the beam diameter at the phase plate 210 is the same as the beam diameter in the objective 130, which means that the phase plate is larger and the aperture diameter or segment gap can be larger. All or part of the function of the lens 650 can also be achieved by using a large bias voltage on the phase plate 210, which thus acts as part of an electrostatic lens. Possible additional aberrations produced by the lens 650 can be reduced again by the phase plate function.

[0064] As mentioned above, for some embodiments it may be advantageous to arrange a second plate in the system to locally control the transmittance. Fig. 9 Such an arrangement is shown in , where a second plate 650 is placed above (upstream) the phase plate 210. Thus, the plate 650 controls the local transmittance, while the phase plate 210 controls the local phase, thereby providing an additional degree of control over the beam shape and profile. Also as described above, the plate 650 can have an aperture configuration that matches or differs from the aperture configuration of the phase plate 210.

[0065] The above principles can also be applied to multi-beam systems. Due to off-axis aberrations, the resolution of beamlets in a multi-beam system deteriorates for beamlets that are further away from the optical axis. This limits the maximum number of beamlets that can be produced for a given resolution specification. A programmable phase plate can use a separate hole or group of holes for each beamlet in a multi-beam system, making it possible to individually correct or reduce the aberrations (e.g. off-axis aberrations) of each beamlet.

[0066] The holes of the phase plates for all beamlets can be distributed on mechanically separate plates, or can be distributed on one large plate. The separate plates can be located at different positions along the optical axis of the electron beam system (i.e., at different positions along the general direction of travel of the electrons).

[0067] The separate plates may be at different angles to each other. The plate for amplitude control may be a separate plate and may be located above or below the plate for phase control. The plates may, for example, be located at or near a conjugate plane of the electron beam optics.

[0068] The voltage distribution over the apertures may be different for each group of apertures assigned to a particular beamlet or each plate. The voltage distribution may be the same for certain groups of apertures or plates to limit the number of individual voltage controls required. The aperture transmittance distribution over open, closed and partially closed apertures may be different for each group of apertures assigned to a particular beamlet per plate. The aperture distributions for different beamlets may be chosen so that for all beamlets the total transmittance of their respective aperture distributions is the same, so that the beamlet current may be the same for all beamlets.

[0069] The voltage on the aperture and the open / closed aperture transmittance profile can be adjusted as a function of the landing energy of the beamlet to enable correction or reduction of aberrations at different electron beam system settings associated with different landing energies. The voltage on the aperture and the open / closed aperture profile can be adjusted as a function of the position of the beamlet on the sample. For example, the position of the beamlet can be a measure of whether the beamlet is off-axis or to what extent it is off-axis to optimize the correction or reduction of aberrations at various off-axis positions of the beamlet.

[0070] The voltage across the aperture and the transmission profile can be adjusted as a function of the beam current of the beamlet to enable correction or reduction of aberrations at different electron beam system settings associated with different beamlet currents. The voltage across the aperture and the open / closed aperture profile can be adjusted as a function of the landing angle of the beamlet at the sample to enable correction or reduction of aberrations at different electron beam system settings associated with different landing angles.

[0071] The voltage across the aperture and the open / closed aperture (amplitude) distribution can be adjusted as a function of the electric field at the sample to enable correction or reduction of aberrations at different electron beam system setups associated with different electric fields at the sample.

[0072] The voltage and amplitude distribution may also and / or alternatively be adjusted as a function of the landing energy, beam current, landing angle and electric field of the individual beams.

[0073] Using programmable phase plate control of individual beamlets allows aberration correction or reduction for each beamlet. Using phase plate phase and amplitude control allows a larger field of application than using phase control alone.

[0074] Fig.10 One possible arrangement incorporating a phase plate in a multi-beam SEM system is shown as an example. Since the aberrations may be different for different beamlets (due to off-axis aberrations), the described implementation provides an individual phase plate function for each beamlet. Fig.10 In the system of FIG. 6 , the phase plate 210 is positioned between the beam limiting aperture 610 and the combination of the microlens 660 and the microdeflector 670, which is used to generate and manipulate the beamlets of the multi-beam system. In this way, the phase plate manufacturing can be incorporated into the overall MEMS manufacturing process for the multi-beam aperture array. The advantage is also that parallel beams impinge on the phase plate 210 for different beamlets.

[0075] exist Fig.11In the system shown, the phase plate 210 is positioned below the microlens 660 and the MEMS aperture array with beam limiting apertures 670 and deflectors 670. In this way, the phase plate 210 can form a mechanically independent set of elements that can be manufactured in a separate and possibly different manner from the MEMS array that produces the beamlets. If this is not required for certain applications, the phase plate set can be retractable or foldable, or removable to enable selection between different sets with phase plate geometries on a larger plate.

[0076] All of the above descriptions of phase plates, including geometry, voltage control at the apertures, transmittance control at the apertures, grouping of apertures, and use of multiple plates, apply to the deployment of phase plates in multibeam systems.

[0077] According to another aspect of the embodiments, a method of applying local control to a portion of a cross-section of a charged particle beam using a phase plate is disclosed. Fig.12 , in a first step S10, a charged particle beam is generated. Then, in step S20, the beam passes through a first lens. Then, in step S30, a phase plate is used to perform local control of the beam phase, which essentially pre-shapes the beam. In step "clamping", that is, passing through an aperture. In step S40, the pre-shaped beam passes through a second lens. The end result of the beam being pre-shaped and passing through an objective is that the pre-shaping corrects the aberrations of the objective. In step S50, the beam is used to illuminate a sample.

[0078] Fig.13 is a flow chart describing a method of dynamically configuring a phase plate according to a sample area being scanned. In step S60, the phase plate is configured to have a first distribution of phase, transmittance, or both. In step S70, a first area of ​​the sample is scanned using a charged particle beam passing through the phase plate having the first distribution. In step S80, the phase plate is configured to have a second distribution of phase, transmittance, or both. In step S90, a second area of ​​the sample is scanned using a charged particle beam passing through the phase plate having the second distribution.

[0079] Fig.14 is a flow chart showing a method of scanning a sample using a phase plate configured for locally controlling phase and transmittance. In step S100, the phase plate is configured to have a desired aperture voltage distribution. In step S110, the phase plate is configured to have a desired aperture transmittance distribution. It is obvious to one of ordinary skill in the art that the order of these two steps can be reversed. In step S120, the sample is scanned by passing a charged particle beam through the phase plate.

[0080] The above description is in terms of a phase plate with apertures, for example in the form of a ring with circular apertures or curved segments around a central aperture, with separate voltage and / or shutter control for each aperture or segment. In the case of voltage control, an arrangement is described in which each aperture or segment is provided with a single voltage. However, depending on the requirements of a particular application, it may be advantageous to provide two or more voltages to each aperture. In this way, an electric field with a gradient can be generated across the opening of the aperture or segment, which provides the opportunity to better tune the wavefront shape locally rather than by using several discrete small apertures or segments with an electric field of a single voltage.

[0081] Therefore, if Fig.15A As shown, the aperture arrangement in the phase plate may include, for example, two curved segments 700 and 710, wherein a first voltage V1 is applied to curved segment 700 and a second voltage V2 is applied to segment 710, which may or may not be different from V1. Fig. 15B As shown, the aperture arrangement in the phase plate may include, for example, a curved segment 720, a first voltage V1 being applied to an inner electrode 730 of the curved segment 720, and a second voltage V2 different from the first voltage V1 being applied to an outer electrode 740 of the curved segment 720 to generate a radial gradient in the electric field E on the segment between the electrodes. The curved segment may be concentric with the optical axis 750 of the imaging system. Typically, there may be another ring segment 760 arranged symmetrically with respect to the optical axis 750.

[0082] Radial variations in the wavefront are often a significant contributor to aberrations in charged particle imaging systems, and by using an adjustable radial gradient, the wavefront can be better controlled with an electric field that varies smoothly in the radial direction. For some applications, this can reduce the need for multiple curved concentric segments with small radial openings that can produce discrete steps in the radial waveform. It can also reduce the complexity of the phase plate design and allow increased transmittance because less material may be required and larger openings are possible. As shown, the two voltages on the curved segment can be separated at its outer ends. For some applications, it may be advantageous to avoid charging the electrically separated portions (such as in MEMS structures for multi-beam systems).

[0083] These embodiments may be further described using the following terms:

[0084] 1. A programmable phase plate for a charged particle beam imaging system, the phase plate comprising:

[0085] plate elements;

[0086] a plurality of holes arranged in the plate-like element; and

[0087] A plurality of aperture control elements are respectively associated with each aperture of the plurality of apertures, each aperture control element being arranged to control interaction of the associated aperture with charged particles at the aperture.

[0088] 2. A programmable phase plate according to clause 1, wherein the plurality of holes comprises a plurality of arcuate holes in the plate-like element.

[0089] 3. A programmable phase plate according to clause 1, wherein the plurality of holes comprises a plurality of annular segmented holes in the plate-like element.

[0090] 4. A programmable phase plate according to clause 1, wherein the annular segment is formed by a plurality of segments separated by a mechanical support, and wherein the mechanical support comprises an electrical contact for providing a voltage to an electrode at the aperture.

[0091] 5. A programmable phase plate according to clause 1, wherein the plurality of holes comprises a plurality of circle-segment-shaped holes arranged in at least two concentric circles in the plate-like element.

[0092] 6. A programmable phase plate according to clause 1, wherein the number of holes per concentric circle is at least a multiple of 4.

[0093] 7. The programmable phase plate of clause 1, wherein the radial width of the apertures is in the range of about 10 microns to less than 1 micron.

[0094] 8. A programmable phase plate according to clause 1, wherein the radial width of the apertures varies from ring to ring.

[0095] 9. A programmable phase plate according to clause 1, wherein the means connected to at least one of the apertures for interacting with the charged particle beam comprises means electrically connected to the at least one aperture so as to alter the electric field at the aperture.

[0096] 10. A programmable phase plate as recited in clause 1, wherein a subset of the apertures have a common voltage.

[0097] 11. A programmable phase plate according to clause 1, wherein the means connected to at least one of the apertures for interacting with the charged particle beam comprises: means connected to the at least one aperture for selectively blocking the charged particle beam from passing through the aperture.

[0098] 12. A programmable phase plate according to clause 11, wherein the means for selectively blocking the aperture is controllable to completely block the aperture, partially block the aperture, or leave the aperture unblocked.

[0099] 13. A programmable phase plate according to clause 11, wherein the available degree of blocking is in the range of 0% to 100%.

[0100] 14. A programmable phase plate according to clause 11, wherein the distribution of aperture blocks comprises a distribution of closed, partially closed and open apertures.

[0101] 15. A programmable phase plate according to clause 11, wherein the amplitude of the electron wave is varied in the cross section of the beam by controlling the distribution of aperture blockages.

[0102] 16. A programmable phase plate according to clause 1, wherein the phase plate has an axis of symmetry, and further comprising: means for rotating the phase plate about the axis of symmetry.

[0103] 17. A programmable phase plate according to clause 1, wherein the aperture is circular.

[0104] 18. A programmable phase plate according to clause 1, wherein the aperture is elliptical.

[0105] 19. A programmable phase plate according to clause 1, wherein the aperture is rectangular.

[0106] 20. A programmable phase plate according to clause 1, wherein the hole shape varies across the phase plate.

[0107] 21. A programmable phase plate as claimed in clause 1 or clause 20, wherein the aperture size varies across the phase plate.

[0108] 22. A programmable phase plate as recited in clause 1, wherein the pattern of holes comprises a circular pattern.

[0109] 23. A programmable phase plate as described in clause 1, wherein the hole pattern comprises a square pattern.

[0110] 24. A programmable phase plate as recited in clause 1, wherein the pattern of holes comprises a polygonal pattern.

[0111] 25. A system for imaging a charged particle beam, comprising:

[0112] a charged particle beam source; and

[0113] A programmable phase plate is arranged to receive the beam.

[0114] 26. The system of clause 25, wherein the phase plate is located at or near a conjugate plane of the system.

[0115] 27. The system of clause 25, wherein the programmable phase plate comprises: a plurality of segmented holes arranged in concentric rings around an optical axis of the system.

[0116] 28. A system according to clause 25, wherein the holes are arranged in a hexagonal pattern around an optical axis of the system.

[0117] 29. The system of clause 25, wherein the phase plate is moveable into and out of the path of the beam.

[0118] 30. The system of clause 25, wherein the phase plate comprises a plurality of beam blankers integrated into the phase plate, the beam blankers being arranged such that each beam blanker is capable of blanking a portion of the charged particle beam at a corresponding aperture.

[0119] 31. The system of clause 25, further comprising a plurality of MEMS aperture arrays, the MEMS aperture arrays comprising: beam limiting apertures, lenses, and deflectors, wherein the phase plate is located downstream of the MEMS aperture arrays.

[0120] 32. The system of clause 25, wherein the phase plate comprises a plurality of deflectors integrated into the phase plate, the deflectors being arranged such that each deflector is capable of deflecting a portion of the charged particle beam at a respective aperture.

[0121] 33. The system of clause 25, wherein the phase plate comprises a plurality of mechanical shutters integrated into the phase plate, the shutters being arranged such that each shutter is capable of at least partially blocking a portion of the charged particle beam at a corresponding aperture.

[0122] 34. The system of clause 25, wherein the phase plate comprises a plurality of electro-mirrors integrated into the phase plate, the electro-mirrors being arranged such that each electro-mirror is capable of reflecting at least a portion of the charged particle beam at a respective aperture.

[0123] 35. The system of clause 25, further comprising at least one of an additional blanker plate, deflector plate, shutter plate or mirror plate upstream of the phase plate.

[0124] 36. The system of clause 25, further comprising at least one of an additional blanker plate, deflector plate, shutter plate, or mirror plate downstream of the phase plate.

[0125] 37. A system according to clause 25, comprising: a first phase plate and a second phase plate, wherein the first phase plate is configured to provide control of one of the cross-sectional amplitude distribution of the beam and the cross-sectional phase distribution of the beam, and the second phase plate is configured to provide control of the other of the cross-sectional amplitude distribution of the beam and the cross-sectional phase distribution of the beam.

[0126] 38. The system of clause 37, wherein the first phase plate has a different number of holes than the second phase plate.

[0127] 39. The system of clause 37, wherein the apertures on the first phase plate have a first shape and the apertures on the second phase plate have a second shape different from the first shape.

[0128] 40. The system of clause 37, wherein the apertures on the first phase plate have a first size and the apertures on the second phase plate have a second shape different from the first shape.

[0129] 41. The system of clause 37, wherein the holes on the first phase plate have a first distribution and the holes on the second phase plate have a second distribution different from the first distribution.

[0130] 42. A system for imaging a charged particle beam, comprising:

[0131] Sources of charged particle beams;

[0132] a beam limiting aperture arranged to receive and shape the charged particle beam; and

[0133] A programmable phase plate is arranged downstream of the beam limiting aperture and receives the beam after the beam has been shaped by the beam limiting aperture.

[0134] 43. A system for imaging a charged particle beam, the system comprising:

[0135] Sources of charged particle beams;

[0136] a lens for shaping the beam into a shaped beam; and

[0137] A programmable phase plate is arranged downstream of the lens for receiving the shaped beam.

[0138] 44. The system of clause 43, wherein the beam diameter at the phase plate is the same as the beam diameter at the lens.

[0139] 45. A system for imaging a charged particle beam, the system comprising:

[0140] a source of a charged particle beam; and

[0141] A phase plate is configured to act as a beam defining element and an element for controlling the relative phases of portions of the cross-section of the beam.

[0142] 46. ​​The system of clause 45, further comprising: a lens disposed between the beam limiting aperture and the phase plate to control beam divergence across the phase plate.

[0143] 47. The system of clause 45, wherein the phase plate comprises a plurality of controlled aperture elements, each aperture element comprising an aperture and a voltage control arranged to control the electric field at the aperture.

[0144] 48. A system for imaging a plurality of charged particle beamlets, the system comprising:

[0145] a source of a plurality of charged particle beamlets; and

[0146] A programmable phase plate is arranged to receive at least one of said beamlets.

[0147] 49. The system of clause 48, wherein the programmable phase plate is arranged to receive a plurality of beamlets and has a plurality of controlled aperture elements, and wherein each beamlet has an associated set of controlled aperture elements.

[0148] 50. The system of clause 48, wherein each beamlet has an associated phase plate.

[0149] 51. A system according to clause 50, wherein the associated phase plates are arranged at different positions along an optical axis of the system.

[0150] 52. A system according to clause 50, wherein the associated phase plates are arranged at different positions along a beamlet propagation direction.

[0151] 53. The system of clause 50, wherein the associated phase plates are at different angles with respect to each other.

[0152] 54. A system according to clause 50, comprising a plurality of first phase plates and a plurality of second phase plates, wherein the plurality of first phase plates are configured to provide control over the cross-sectional amplitude distribution of the sub-beams, and the plurality of second phase plates are configured to provide control over the cross-sectional phase distribution of the sub-beams.

[0153] 55. The system of clause 54, wherein the first plurality of phase plates are positioned upstream of the second plurality of phase plates.

[0154] 56. The system of clause 54, wherein the plurality of first phase plates are positioned downstream of the plurality of second phase plates.

[0155] 57. The system according to clause 48, further comprising:

[0156] at least one beam limiting aperture; and

[0157] at least one micro-deflector;

[0158] And wherein the programmable phase plate is positioned between the at least one beam limiting aperture and the at least one micro deflector.

[0159] 58. The system of clause 50, wherein the hole pattern varies from one phase plate to another.

[0160] 59. The system of clause 50, wherein the number of holes varies from one phase plate to another.

[0161] 60. The system of clause 50, wherein the voltage distribution across the apertures is different for each set of apertures assigned to a particular beamlet.

[0162] 61. The system of clause 50, wherein the voltage distribution across the aperture is different for each phase plate.

[0163] 62. The system of clause 50, wherein the voltage profile is the same for the first group of holes.

[0164] 63. The system of clause 50, wherein the voltage distribution is the same for the first group of panels.

[0165] 64. A system according to claim 50, wherein the plurality of holes includes a first group of holes having a first degree of openness and a second group of holes having a second degree of openness, the first group of holes being arranged in the path of a first sub-beam, and the second group of holes being arranged in the path of a second sub-beam.

[0166] 65. A system according to claim 50, wherein the holes of the first group are arranged in the path of the first sub-beam and the holes of the second group are arranged in the path of the second sub-beam, and wherein the first opening distribution of the holes in the first group and the second opening distribution of the holes in the second group are selected so that the magnitude of the first beam current of the first sub-beam is the same as the magnitude of the second beam current of the second sub-beam.

[0167] 66. The system of clause 52, wherein a voltage and an openness aperture distribution across the aperture are adjusted based at least in part on a landing energy of the beamlet.

[0168] 67. The system of clause 52, wherein the voltage and the openness aperture distribution are adjusted based at least in part on at least one of a distance between beamlets or a distance from a beamlet to the optical axis.

[0169] 68. The system of clause 52, wherein at least one of a voltage distribution and an openness distribution across the aperture is adjusted based at least in part on a beam current of the beamlet.

[0170] 69. The system of clause 52, wherein at least one of a voltage profile and an openness aperture profile is adjusted as a function of a landing angle of the beamlet at the sample.

[0171] 70. The system of clause 52, wherein at least one of the voltage profile and the openness pore distribution is adjusted as a function of the magnitude of the electric field at the sample.

[0172] 71. A system for imaging a charged particle beam, the system comprising:

[0173] a phase plate comprising a plurality of apertures, at least one of the apertures having a voltage control to determine an aperture voltage; and

[0174] Means for synchronizing the aperture voltage or amplitude with the scanning of at least one charged particle beam over the sample to dynamically control probe formation over the entire scan field of view.

[0175] 72. A system according to clause 71, further comprising

[0176] Clock means for generating a clock signal applied to synchronize the aperture voltage with a voltage applied to scan the beam.

[0177] 73. A system according to clause 71, wherein the beam is scanned using a discontinuous scanning profile.

[0178] 74. A system according to clause 71, wherein the beam is scanned using a continuous scan profile.

[0179] 75. The system of clause 71, wherein the aperture voltage distribution is synchronized in only one scan direction of the beam.

[0180] 76. The system of clause 71, further comprising a voltage source arranged to provide a bias voltage applied in addition to the voltage applied by the voltage control for synchronization with scanning of the beam.

[0181] 77. The system of clause 71, wherein synchronization of the phase plate voltage or amplitude is performed in conjunction with synchronization of an openness distribution of an aperture of the phase plate.

[0182] 78. A method of imaging a charged particle beam, the method comprising the steps of:

[0183] a scanning field of view around a plurality of different locations located at relatively large distances from an optical axis of the charged particle beam system; and

[0184] The voltage or amplitude of the aperture of the phase plate is dynamically controlled to control the formation of the electron probe.

[0185] 79. A method of imaging a charged particle beam, the method comprising the steps of:

[0186] Scanning a first portion of the sample at or at a first position off the optical axis of the charged particle beam system using a distribution of aperture voltage or amplitude of the phase plate; and

[0187] A second portion of the sample is scanned at a second position offset from the optical axis with a second distribution of aperture voltage or amplitude of the phase plate.

[0188] 80. The method of clause 79, wherein the voltage and openness aperture distribution across the aperture are adjusted based at least in part on a landing energy of the beamlet.

[0189] 81. The method of clause 79, wherein at least one of a voltage distribution and an openness distribution across the aperture is adjusted based at least in part on a beam current of the beamlet.

[0190] 82. The method of clause 79, wherein at least one of a voltage profile and an openness aperture profile is adjusted as a function of a landing angle of the beamlet at the sample.

[0191] 83. The method of clause 79, wherein at least one of the voltage distribution and the openness pore distribution is adjusted as a function of the magnitude of the electric field at the sample.

[0192] 84. A programmable phase plate for a charged particle beam imaging system, the phase plate comprising:

[0193] plate elements;

[0194] a structure defining a hole disposed in the plate-like element, the structure having a first conductive portion and a second conductive portion electrically isolated from the first conductive portion;

[0195] a first voltage source arranged to apply a first voltage to the first conductive portion; and

[0196] a second voltage source arranged to apply a second voltage different from the first voltage to the second conductive portion; and.

[0197] 85. A programmable phase plate according to clause 84, wherein the structure defining the aperture comprises structure defining an annular semicircle segment having an inner edge and an outer edge.

[0198] 86. A programmable phase plate according to clause 85, wherein the annular semicircle segment is concentric with the optical axis of the charged particle beam imaging system.

[0199] 87. The programmable phase plate of clause 85, wherein the first conductive portion comprises the inner edge and the second conductive portion comprises the outer edge.

[0200] The above description of specific embodiments will fully reveal the general concept of the present invention, so that others can easily modify and / or adjust such specific embodiments for various applications by applying the knowledge within the technology of the art, without too much experimentation, without departing from the general concept of the present invention. Therefore, based on the teachings and guidance given herein, such adjustments and modifications are intended to be within the meaning and scope of the equivalents of the disclosed embodiments. It should be understood that the wording or terminology herein is for the purpose of description rather than limitation, so that the terms or wording of this specification will be interpreted by the technician according to teaching and guidance.

Claims

1. A programmable phase plate for a charged particle beam imaging system, the phase plate comprising: plate elements; a plurality of holes arranged in the plate-like element; as well as a plurality of aperture control elements, respectively associated with each aperture of the plurality of apertures, each aperture control element being arranged to control the interaction of the associated aperture with charged particles at the aperture, Wherein the aperture control element is configured to provide two or more voltages to each aperture of the plurality of apertures.

2. A programmable phase plate according to claim 1, wherein the plurality of holes comprises a plurality of arcuate holes in the plate-like element.

3. The programmable phase plate of claim 1, wherein the plurality of holes comprises a plurality of annular segmented holes in the plate-like element.

4. The programmable phase plate of claim 3, wherein the annular segmented aperture is formed by a plurality of segments separated by a mechanical support, and wherein the mechanical support comprises electrical contacts for providing the voltage to electrodes at the aperture.

5. The programmable phase plate of claim 1, wherein the plurality of holes comprises a plurality of circle-segment-shaped holes in the plate-like element, the plurality of circle-segment-shaped holes being arranged in at least two concentric circles.

6. The programmable phase plate of claim 1, wherein the number of holes on each concentric circle is at least a multiple of 4.

7. The programmable phase plate of claim 1, wherein the radial width of the apertures is in the range of 1 micron to 10 microns.

8. The programmable phase plate of claim 1, wherein the radial width of the aperture varies along the ring.

9. A programmable phase plate according to claim 1, wherein the means for interacting with the charged particle beam connected to at least one of the apertures comprises: Means for varying the electric field at the aperture are electrically connected to the at least one aperture.

10. The programmable phase plate of claim 1, wherein a subset of the apertures have a common voltage.

11. A programmable phase plate according to claim 1, wherein the means for interacting with the charged particle beam connected to at least one of the apertures comprises: Means connected to the at least one aperture for selectively blocking the charged particle beam from passing through the aperture.

12. A programmable phase plate according to claim 11, wherein the means for selectively blocking is controllable to completely block the aperture, partially block the aperture, or leave the aperture unblocked.

13. A programmable phase plate as claimed in claim 11, wherein the available degree of blocking is in the range of 0% to 100%.

14. A system for imaging a charged particle beam, comprising: Sources of charged particle beams; as well as The programmable phase plate of claim 1, arranged to receive the charged particle beam.

15. A method of imaging a charged particle beam, the method comprising the steps of: scanning the field of view around a plurality of different locations located at relatively large distances from an optical axis of the charged particle beam system; as well as The voltage or amplitude in the aperture of the programmable phase plate according to claim 1 is dynamically controlled to control the formation of the electron probe.

Images