Multibeam grating unit and multibeam charged particle microscope

Abstract

Certain improvements to multibeam grating units, such as multibeam generation units and multibeam deflection units, for multibeam charged-particle microscopes are provided. The improvements include the design, fabrication, and tuning of the multibeam grating units, including apertures of specific shapes and sizes. The improvements enable multibeam generation and deflection, or stigmation, to be performed with greater precision. These improvements are relevant to general applications of multibeam charged-particle microscopes, such as semiconductor inspection and review, where high reliability and reproducibility, as well as low machine-to-machine variation, are required.

Description

Technical Field

[0001] The present disclosure relates to a multi-beam grating unit of a multi-beam charged particle microscope, such as a multi-beam generating unit and a multi-beam deflector unit. Background Art

[0002] WO 2005 / 024881 A2 discloses an electron microscope system that uses multiple electron beamlets to operate so as to scan the object to be inspected in parallel with a beam of electron beamlets. A beam of electron beamlets is generated by directing a primary electron beam onto a first porous plate having multiple openings. A portion of the electrons in the electron beam are incident on the porous plate and absorbed there, while another portion of the beam passes through the openings of the porous plate, thereby forming an electron beamlet whose cross section is limited by the cross section of the opening in the beam path downstream of each opening. In addition, an appropriately selected electric field provided in the beam path upstream and / or downstream of the porous plate causes each opening in the porous plate to act as a lens when the electron beamlet passes through the opening, so that each electron beamlet is focused on a surface at a certain distance from the porous plate. The surface forming the focus of the electron beamlet is imaged onto the surface of the object to be inspected or the sample by downstream optical components. The primary electron beamlet triggers secondary electrons or backscattered electrons to be emitted from the object as secondary electron beamlets, which are collected and imaged onto a detector. Each secondary beamlet is incident on a separate detector element, so that the secondary electron intensity detected by it provides information about the sample at the location where the corresponding primary beamlet was incident on the sample. A primary beamlet is systematically scanned over the surface of the sample, and an electron microscopic image of the sample is generated in the usual manner of a scanning electron microscope. The resolution of a scanning electron microscope is limited by the focal diameter of the primary beamlets incident on the object. Therefore, in multibeam electron microscopy, all beamlets should form the same small focal spot on the object.

[0003] It will be appreciated that the systems and methods described in detail in WO 2005 / 024881 using electrons as an example are generally very applicable to charged particles. Correspondingly, the present invention aims to provide a charged particle beam system that operates using multiple charged particle beams and can be used to achieve higher imaging performance, such as better resolution and narrower resolution for each of the multiple beamlets. The multiple beamlets used in a multi-beam charged particle microscope (MCPM) are generated in a multi-beam generation unit. A multi-beam charged particle microscope (MCPM) generally uses both micro-optical (MO) elements and macro elements in the charged particle projection system.

[0004] The multi-beam generation unit includes elements for splitting, partially absorbing, and influencing the charged particle beam. Thus, a collection of sub-beams of charged particles in a predefined grating configuration is generated. The multi-beam generation unit includes a special element design and a special arrangement of micro-optical elements (such as a first porous plate, additional porous plates, and micro-optical deflection elements) as well as macro elements (such as lenses).

[0005] The multi-beam generating unit can be formed in an assembly of two or more parallel planar substrates or wafers, for example manufactured by silicon microstructuring. During use, a plurality of electrostatic optical elements are formed by aligned holes in at least two such planar substrates or wafers. Some of the holes can be equipped with one or more perpendicular electrodes, arranged axially symmetrically around the hole, for example to create an electrostatic lens array. It is known that the optical aberrations of such electrostatic lens arrays are highly sensitive to manufacturing inaccuracies of the multiple holes. Roughness of the profile or edge of each hole can lead to astigmatism and higher-order aberrations. The inner surface of the electrostatic lens is typically formed in silicon by perpendicular anisotropic etching, the roughness of the inner surface typically being between 100 nm and 500 nm.

[0006] To generate a predefined electrostatic optical element, it is important to precisely control the plurality of electrodes (e.g., the geometry of the electrodes and the lateral alignment relative to each of the plurality of charged particle beamlets) and the distance between the electrodes in the direction of the transmitted plurality of charged particle beamlets. Deviations in the manufacturing process of the planar substrate, the electrodes, and the planar substrate assembly generate aberrations in the electrostatic optical element and lead to aberrations (such as aberrations of individual beamlets) or deviations from the predefined grating configuration of the beamlets. Furthermore, deviations in the manufacturing process can generate scattered particles, which can degrade the image quality of the MCPM.

[0007] In current manufacturing processes, the diameter of the holes in the multi-beam generating unit can vary from hole to hole within a wafer, or from wafer to wafer. For example, non-uniformity in the isotropic etching step can increase roughness, leading to aberrations and image blur in conventional multi-hole plates. Aberrations at the upper hole edge, which is responsible for generating multiple sub-beams from an incident charged particle beam, are increased by the manufacturing process of the prior art and therefore exhibit significant non-uniformity from beam to beam. In addition, deviations in the manufacturing process can generate deviations between several individual multi-beam generating units used in several different individual MCPMs. Such differences (also known as machine-to-machine deviations) are undesirable for many applications of MCPMs.

[0008] The lateral alignment of two or more parallel planar substrates or wafers to form a multi-beam generation or multi-beam deflection unit is not sufficiently precise in current alignment processes. Electrostatic optical elements formed between at least two planar substrates during use require very precise lateral alignment of the at least two planar substrates or wafers. Improved imaging performance and reduced machine-to-machine variation require lateral alignment below 0.5 μm.

[0009] The porous plates comprise a thin film, for example, manufactured from a wafer through a thinning process. Deformations of the membrane, generated during the manufacturing process or caused, for example, by thermal expansion, result in different distances between the multiple porous plates, thereby causing differences in the electrostatic elements formed between at least two of the porous plates during use. Variations in membrane deformation can also introduce deviations in the curvature of field of the multiple focal points of the beamlets or in the telecentricity of the multiple beamlets.

[0010] In the prior art, components for improving the theoretical performance of porous arrays have been considered. For example, US 2003 / 0209673 A1 discloses a component for reducing crosstalk between multiple primary charged particle beamlets. US 2003 / 0209673 A1 discloses an electrostatic single (Einzel) lens array for multiple electron beamlets with reduced crosstalk. The electrostatic single lens array is arranged in the electron beam path downstream of the aperture array and includes an upper electrode, an intermediate electrode and a lower electrode of a single lens, wherein each pair of electrodes is separated by a large distance of 100 μm. Crosstalk is reduced by providing shielding electrodes between the upper electrode and the intermediate electrode and between the intermediate electrode and the lower electrode. In another example, components for reducing design aberrations are considered. DE 10 2014 008 083 A1 filed on May 30, 2014 or the corresponding US 9,552,957 B2 shows an example of a porous plate including a lens array with reduced spherical aberration. Design aberrations are reduced by making the lens apertures larger than the beam diameter. DE 10 2014 008 083 A1 proposes a distance between the porous plates in the range of 0.1 to 10 times the aperture diameter to avoid charging effects on the electrodes. However, this large range has proven insufficient to prevent unwanted charging effects on the electrodes by scattered charged particles.

[0011] The object is therefore to minimize aberrations in a multibeam rastering unit, such as a multibeam generating or multibeam deflecting unit. The object is to provide a multibeam generating unit that is capable of forming well-defined sub-beams with a small focal diameter and minimal residual aberrations in a predefined rastering configuration, thereby generating as few scattered particles as possible during use. The object is to provide a multibeam deflecting unit that is capable of deflecting sub-beams with high precision without introducing or increasing aberrations in the beamlets, thereby generating as few scattered particles as possible during use. Summary of the Invention

[0012] Therefore, the task is to provide a design of a multi-beam grating unit, such as a multi-beam generating or multi-beam deflecting unit, which is less sensitive to deviations and does not significantly introduce or increase aberrations and generates fewer scattered particles, and which allows the manufacture of the multi-beam generating or multi-beam deflecting unit with high repeatability.

[0013] The task is therefore to provide a multibeam grating unit comprising at least two porous plates, including providing a manufacturing process for the porous plates that is less sensitive to deviations, generates low aberrations and fewer scattered particles, and which manufacturing process allows the manufacture of a multibeam generating or multibeam deflecting unit with high repeatability.

[0014] The object of the invention is achieved by the independent claims. The dependent claims are directed to advantageous embodiments.

[0015] With respect to the cited prior art US 2003 / 0209673 A1 and DE 10 2014 008 083 A1, the present invention discloses a structural component for alleviating manufacturing errors to improve the beam quality of multiple sub-beams, such as reducing the roughness of the inner wall to reduce the scattering of transmitted electrons, or preferably selecting the diameter of the hole and the distance between the holes to reduce the influence of manufacturing errors of the electrodes of the electrostatic element.

[0016] In an embodiment of the invention, a multibeam grating unit is configured to minimize the influence of deviations of the apertures from a predefined shape. The multibeam grating unit according to this embodiment comprises a first porous plate provided with a smooth, well-defined conductive surface on the bottom side, serving as a relative electrode for forming an electrostatic element with a subsequent second porous plate. The multibeam grating unit (such as a porous unit or a multibeam deflector or a multibeam stigmator) is configured to form a plurality of electrostatic elements during use for influencing a plurality of transmission sub-beams of charged particles. The multibeam grating unit is configured to position the edges and the inner side walls of the apertures at a large distance from the transmission sub-beams of the charged particles and thus the influence of deviations of the electrode edges and the inner side walls of the apertures on the beam properties is minimized by a factor of 10 or more. The task is achieved by means of a porous plate with apertures of a special geometry and a special shape.

[0017] In an embodiment, a design and manufacturing method for a porous plate is provided that minimizes the deviation of the wells from a predefined shape so that the wells have well-defined, clear and smooth shapes (surfaces and edges) with low roughness values ​​and no local errors or deviations.

[0018] The multi-beam grating unit according to the embodiment includes a first porous plate, the first porous plate having an inner region, a beam incident side, and a beam exit side, the inner region forming a membrane having a first thickness L1 and a plurality of first holes. The membrane of the first porous plate includes at least a first section and a second section, the first section having a first section thickness L1.1, wherein a plurality of cylindrical holes have a first diameter D1 on the beam incident side, and the second section having a plurality of holes of a second diameter D2 on the beam exit side. The multi-beam grating unit also includes a second porous plate, the second porous plate having an inner region and a beam incident side, the membrane formed in the inner region having a plurality of second holes, wherein the plurality of holes have a third diameter D3 on the beam incident side, and the first porous plate and the second porous plate form a gap, the gap having a thickness L2 between the membranes of the first porous plate and the second porous plate. The multi-beam grating unit further comprises at least a first electrode and at least a plurality of second electrodes, wherein the at least first electrode is arranged near the first hole of the first porous plate on the beam exit side of the first porous plate, and the at least a plurality of second electrodes are arranged near the plurality of second holes of the second porous plate on the beam entrance side of the second porous plate, for forming a plurality of electrostatic elements between the plurality of first holes and the second holes of the first and second porous plates during use. The multi-beam grating unit is configured with a second diameter D2 that is larger than the first diameter D1, and the second diameter D2 is within the range between the second thickness L2 and twice the second thickness L2, such that L2<D2<2*L2. The first section thickness L1.1 is less than 10 μm, preferably less than 5 μm. In an example, the first porous plate is arranged in the beam path upstream of the second porous plate in the direction of the plurality of transmission sub-beams of charged particles and forms the upper or entrance porous plate of the multi-beam grating unit. In another example, at least a third multi-aperture plate is arranged in the beam path upstream of the first and second multi-aperture plates in the direction of the plurality of transmission sub-beams of charged particles.

[0019] In one embodiment, at least one section of the inner wall of the holes in the second section has a surface shape that is tilted away from the transmission beamlet of charged particles. In one embodiment, the surface shape is curved and tilted away from the transmission beamlet of charged particles. In one embodiment, the surface shape in the direction of the transmission beamlet of charged particles is a spherical shape. In one embodiment, the inner sidewall surface of at least one hole in the plurality of holes in the second section has a surface shape such that the diameter of the hole opening continuously increases with increasing z-coordinate. In one embodiment, the spherical shape is formed by isotropic etching.

[0020] In an embodiment, the first porous plate includes an absorption layer on the beam incident side, wherein the absorption layer is connected to ground during use. During use, a large portion of the incident electrons are absorbed in the absorption layer, generating a current corresponding to the number of absorbed electrons. For example, with D1 = 30 μm and a pitch of 150 μm between adjacent holes, approximately 97% of the incident electrons from the incident electron beam are absorbed, generating a high current of electrons. The absorption layer therefore exhibits a fluctuating voltage difference corresponding to the induced current during use and is therefore unsuitable for forming an electrode for an electrostatic element.

[0021] In an embodiment, the first porous plate includes a conductive layer on the beam exit side, which forms the first electrode. Preferably, the conductive layer substantially completely covers the beam exit surface of the first porous plate, with only the apertures themselves being uncovered. However, it is also possible for only a portion of the beam exit side to be covered by the conductive layer. Depending on the embodiment, this conductive layer forms the first electrode, acting as a passive or counter electrode for driving the second electrode.

[0022] In an embodiment, the beam exit side of the first porous plate comprises an annular conductive layer or electrode around or adjacent to the aperture of diameter D2, which is connected to a constant voltage potential during use, the annular conductive layer or electrode forming the first electrode. Preferably, the annular conductive layer or electrode forms the first electrode, acting as a passive or counter electrode to the second electrode.

[0023] In an embodiment, the beam exit side of the first porous plate does not comprise a shielding electrode. According to the present invention, it is not necessary to apply such a shielding electrode for reducing crosstalk.

[0024] In an embodiment, the second multiwell plate comprises a ring electrode arranged around the second well, wherein during use a driving voltage is applied to the ring electrode, the ring electrode forming the second electrode.

[0025] In an embodiment, the annular electrodes extend substantially through the second porous plate. Preferably, they all extend from the beam entrance side through the second porous plate to the beam exit side.

[0026] In an embodiment of the present invention, a porous plate of a multibeam grating unit is configured with etch stop rings around a plurality of holes (e.g., holes on the beam exit side of a first porous plate or the beam entrance side of a second porous plate). The etch stop rings achieve high precision in the shape and roughness of the hole openings in the entrance or exit surface of the porous plate. A manufacturing process for a porous plate with etch stop rings is provided.

[0027] In an embodiment, the surface roughness of the inner sidewall surface of at least one hole of the plurality of holes in a segment is less than 50 nm rms, preferably less than 25 nm rms, even more preferably less than 10 nm rms. A method for manufacturing holes having inner sidewall roughness less than 50 nm rms, preferably less than 25 nm rms, even more preferably less than 10 nm rms is provided.

[0028] The diameter D1 of the upper edge performs the function of stopping and shaping the charged particle beam in the multi-beam generation unit. In one embodiment, to achieve optimal performance of the electrostatic element, diameter D1 is within the range of 10 μm ≤ D1 ≤ 30 μm, while the average aperture diameter and diameter D2 of the lower edge or beam exit edge are greater than D1. In one example, the second diameter D2 is within the range between the first thickness L1 and twice the first thickness L1, such that L1 < D2 < 2*L1. In another example, the second diameter D2 is within the range between the first section thickness L1.1 and twice the first section thickness, such that L1.1 < D2 < 2*L1.1. In another example, the second diameter D2 is within the range between the second thickness L2 and twice the second thickness L2, such that L2 < D2 < 2*L2. In another example, the third diameter D3 is greater than the first diameter D1, for example, within the range between the first diameter D1 and the second diameter D2, such that D1 < D3 < D2.

[0029] In one embodiment, a method for manufacturing a porous plate is provided in which the electrode edges and the inner sidewalls of the holes are positioned at a large distance from the transmission beamlets. A process for microstructuring a porous plate of a multibeam grating unit having holes of a special shape, such as a curved shape, is provided. The porous plate is manufactured by double-sided processing on a homogeneous planar substrate or in a composite substrate (such as SOI-silicon on insulator) wafer. In one embodiment, a manufacturing method for double-sided processing is provided for high-precision production of critical hole openings on the entrance side and the exit side of the porous plate.

[0030] In an embodiment, a multi-beam grating unit includes a first porous plate and a second porous plate having at least two sections. In an example, the second porous plate includes a first section and a second section separated by a spacer and an etch stop layer. The first section includes a plurality of electrodes formed around a plurality of holes to form a plurality of electrostatic elements during use. The second section has a maximum thickness L7 between 100 μm and 400 μm, wherein the hole diameter D7 is equal to or greater than the hole diameter D3 in the first section. The second section provides shielding around the electrostatic field and improves the performance of the plurality of electrostatic elements.

[0031] In an embodiment, the multi-beam grating unit includes a second porous plate having a first section and a second section and a third section, each section being separated by a spacer and an etch stop layer. The first section includes a plurality of electrodes formed around a plurality of holes to form a plurality of electrostatic elements during use. The second section has a large thickness L7 between 100 μm and 400 μm, wherein the hole diameter D7 is equal to or greater than the hole diameter D3 in the first section. The second section provides shielding around the electrostatic field and improves the performance of the plurality of electrostatic elements. The third section is arranged between the first section and the second section and has holes formed in combination with the holes of the first section to minimize the effects of alignment errors caused by double-sided processing of the second porous plate. The thickness L8 of the third section is less than or equal to the thickness L3 of the first section.

[0032] In an embodiment, the beam incident side of the second porous plate is covered by a shielding layer having at least one plunging extension inserted into at least one of the holes of the second porous plate.

[0033] In an embodiment, the effect of deviation on optical performance is reduced by functional separation between the upper edge of the porous plate (which acts as a beam stop and forms the beam) and the lower edge of the porous plate (which forms an electrostatic lens with the subsequent second micro-optical grating element). In an example, the first porous plate includes two or more separate planar segments or substrates, each prepared separately by single-sided or double-sided structuring, which are assembled together to form a composite first porous plate. Therefore, the size, position and low roughness of the higher definition of the two edges are provided. The first section and the second section are separate sections attached to each other. The porous plate is achieved by aligning and fixing these sections together, for example, by bonding, gluing or fixing to special holders for mutual alignment and adjustment, which allows precise passive or active alignment and the porous plate is maintained in this aligned state. In the example of active alignment, the actuator formed by the substrate between the separate substrates is adjustable. The diameter D1 of the upper edge (whose function is to stop and shape the charged particle beam) is in the range of 10 μm ≤ D1 ≤ 30 μm, and the diameter D2 of the lower edge or beam exit edge is larger to achieve optimal performance of the electrostatic element.

[0034] In an embodiment, a method for manufacturing a multi-aperture plate for a multi-beam grating unit comprising two or more separate segments is provided. The separate segments are manufactured by double-sided processing on a homogeneous planar substrate or in a composite substrate (eg, SOI-Silicon on Insulator) wafer.

[0035] In one embodiment, a multibeam grating unit includes a holder for mutually aligning and adjusting at least first and second porous plates. In one embodiment, a porous plate is provided having a membrane region comprising first, second, and third segments. The third segment is formed of a different material or material composition and is located between the first and second segments, forming an etch stop and isolation layer. In one embodiment, a method for manufacturing a porous plate having a membrane region comprising three segments is provided. In one example, an inner sidewall of at least one of the plurality of pores in the second segment has a curved shape.

[0036] In an embodiment, the multi-beam grating unit includes a porous plate formed from an SOI wafer, having an inner region forming a membrane, the porous plate having at least three layers, in the order of silicon, silicon dioxide, and silicon. In an example, the porous plate having an inner region forming a membrane is formed from an SOI wafer, having five layers, in the order of silicon, silicon dioxide, silicon, silicon dioxide, and silicon.

[0037] In an embodiment, a structure and method for adjusting deformation of a porous plate are provided. A membrane of a porous plate includes at least a layer having a predetermined thickness, the layer causing stress-induced deformation of the membrane.

[0038] In an embodiment, the multi-beam grating unit comprises at least a first porous plate and a second porous plate, which form an inner region or a membrane region, and a support region for attaching the porous plates to each other. In an example, the first porous plate comprises an inner region with a diameter D4, and a support region. The support region of the second porous plate is attached to the inner region or the membrane region of the first porous plate, and a z distance is formed between the membrane regions of the first porous plate and the second porous plate in the direction of transmitting the plurality of charged particle sub-beams, which is lower than 50 μm, preferably lower than 30 μm or even more preferably lower than 20 μm. In a further example, the multi-beam grating unit comprises a porous plate having a thick membrane with a thickness between 100 μm and 500 μm.

[0039] In an embodiment, a structure is provided for 3D alignment of a multi-beam grating unit comprising at least two porous plates. The porous plates each further comprise a support area having a thickness >100 μm, or >50 μm, with a maximum deviation in thickness being less than 10%. The porous plate further comprises through holes having different hole diameters A1 and A2 for aligning the first porous plate and the second porous plate with each other. In the example, due to stacking of a plurality of at least three porous plates, the multi-beam grating unit has an additional thickness ZU in the direction of transmitting a plurality of charged particle sub-beams, and a z distance ZA of the through holes (so that ZA is less than ZU) to achieve mutual alignment of the porous plates. In an embodiment, at least one porous plate comprises a reduction or lowering at the first through hole to form a z distance from a corresponding through hole of an adjacent porous plate, wherein the z distance is less than 30 μm to achieve mutual alignment of the porous plates. In an example, the multi-beam grating unit includes at least two alignment axes for mutual alignment of at least two pairs of porous plates, the porous plates including at least two reductions or lowerings at a first through-hole and a second through-hole, each forming a z distance from a corresponding through-hole of an adjacent porous plate, the z distance being lower than 30 μm to achieve mutual alignment of the porous plate pairs.

[0040] In an embodiment, a plurality of transmission sub-beams propagate through a plurality of holes of a plurality of porous plates in a first direction, a high voltage supply wiring connection is provided to a first electrode in at least one of the porous plates from a second direction perpendicular to the first direction, and a low voltage supply wiring connection is provided to a second electrode in at least one of the porous plates from a third direction perpendicular to the first direction and the second direction.

[0041] In an embodiment, a multibeam charged-particle microscope comprises a multibeam grating unit according to one of the embodiments. BRIEF DESCRIPTION OF THE DRAWINGS

[0042] Embodiments of the present disclosure will be explained in more detail with reference to the accompanying drawings, in which:

[0043] Figure 1 is a schematic cross-sectional view of a multi-beam charged particle microscope according to an embodiment

[0044] Figure 2 shows the inner region or membrane portion of a multibeam grating unit according to an embodiment

[0045] Figure 3 Shows the electrostatic element formed between two porous plates during use

[0046] Figure 4 A multi-beam grating unit according to an embodiment is shown, wherein the porous plate of the unit has holes with curved inner side walls.

[0047] Figure 5A multi-beam barrier unit according to an embodiment is shown, having a porous plate comprising two separate segments

[0048] Figure 6 A multi-beam grating unit according to an embodiment is shown, wherein the porous plate of the unit has a hole having two separate sections and a curved inner side wall.

[0049] Figure 7 A multi-beam grating unit according to an embodiment with an etch stop ring is shown.

[0050] Figure 8 A multi-aperture plate of a multi-beam grating unit according to an embodiment is shown.

[0051] Figure 9 The steps of the method for manufacturing a porous plate of a multi-beam grating unit according to an embodiment are shown.

[0052] Figure 10 Additional or alternative steps of a method for manufacturing a porous plate of a multi-beam grating unit according to an embodiment are shown

[0053] Figure 11 A second porous plate comprising two sections according to an embodiment is shown.

[0054] Figure 12 A second porous plate comprising three segments according to an embodiment is shown.

[0055] Figure 13 FIG. 1 shows an assembly and alignment structure of a multi-aperture plate of a multi-beam grating unit according to an embodiment of the present invention.

[0056] Figure 14 FIG. 1 shows an assembly and alignment structure of a multi-aperture plate of a multi-beam grating unit according to an example of an embodiment

[0057] Figure 15 Showing details of the alignment structure of the multi-beam grating unit according to an embodiment

[0058] Figure 16 A multi-beam grating unit with a multi-aperture plate having a membrane with a predetermined and actively controlled deformation according to an embodiment is shown.

[0059] Figure 17 Shows a multi-hole plate with a shielding layer

[0060] Figure 18 A multi-beam grating unit according to an embodiment is shown with signal and voltage supply connections from orthogonal directions

[0061] Figure 19 An example showing voltage supply to multiple electrodes of a multi-well plate DETAILED DESCRIPTION

[0062] Figure 1 A multi-beam charged particle microscope (MCPM) of one embodiment is shown. The charged particle system 1 comprises an illumination system 3. The illumination system 3 is configured to focus a set of sub-beams 5 of charged particles in an image plane 7. In the image plane 7, a sample 9 can be placed on a sample stage with an actuator (not shown) to allow the sample 9 to be precisely positioned in the image plane 7 with five or more degrees of freedom. The set of sub-beams 5 comprises several sub-beams of charged particles in a grating configuration, for example, beamlets distributed on a circle or a hexagonal grating. The number of sub-beams can be from 10 to 10,000 or more, a typical example of a hexagonal grating configuration comprising, for example, more than 90 beamlets. Each beamlet in the set of sub-beams 5 is focused at a spot on the sample 9. The spot distance in the image plane 7 (on the object 9) is typically 5 μm–15 μm, but other distances, for example 1 μm–200 μm, are also possible. For high resolution, the illumination system 3 is configured to generate a small spot diameter, for example a diameter below 5 nm, below 3 nm or even below 1 nm. The set of sub-beams 5 of charged particles may comprise electron beamlets, but other charged particles are also possible. The charged particles interact with the sample 9 and generate secondary charged particles, including secondary electrons and backscattered charged particles. The secondary charged particles from each spot together form a set of sub-beams 15 of secondary charged particles. The imaging system 11 is configured to collect at least some of the secondary charged particles and focus the set of sub-beams 15 of secondary charged particles into the detector plane 19. The imaging system 35 of the illumination system 3 and the projection system 11 in the beam path of the secondary charged particles from the image plane 7 to the detector plane are configured so that the image plane 7 of the imaging system 35 coincides with the object plane 17 of the imaging system 11. The imaging system 35 of the illumination system 3 comprises a global deflection unit 67. The imaging systems 35 and 11 are combined by a beam splitting and combining unit 65. The objective system 37 is located in a common imaging path of both imaging systems 11 and 35. The imaging system 11 further comprises an additional imaging element 69. In the detector plane 19, a spatially resolved charged particle detector 13 is arranged. For each of the sub-beams 15 of secondary charged particles, the spatially resolved charged particle detector 13 detects the secondary charged particles of the sub-beam with at least one detector element.

[0063] The illumination system 3 includes a source unit 21 to generate a set of sub-beams 5 of charged particles. Multi-beam generating units are explained, for example, in U.S. application Ser. No. 16 / 277,572 (published as US2019 / 0259575) and U.S. application Ser. No. 16 / 266,842, filed on Feb. 4, 2019, both of which are incorporated herein by reference.

[0064] The source unit 21 comprises a charged particle emitter 22, which generates a diverging beam 23 of charged particles. A condenser system 25 collimates the beam 23 onto a multi-aperture arrangement 27. The multi-aperture arrangement 27 comprises a first multi-aperture plate having a plurality of apertures and micro-optical grating elements. The multi-aperture arrangement 27 converts the beam 23 into a set of sub-beams 5 of charged particles. The set of sub-beams 5 of charged particles is focused onto an intermediate focal surface 29, wherein a focal point 31 is formed for each of the sub-beams 5 of charged particles. Focusing is achieved by the micro-optical grating elements of the multi-aperture arrangement 27 in combination with the collimating capability of the condenser system 25 and an optional additional imaging element 33. The intermediate focal surface 29 can then be curved to compensate for the field curvature of an imaging system 35. The imaging system 35 images the intermediate focal surface 29 into an image plane 7. The imaging system 35 comprises an objective system 37 and a further imaging element 39. The illumination system 3 is configured to focus the sub-beam set 5 onto the sample 9 so that the sub-beam set 5 forms a telecentric bundle of beamlets, wherein each beamlet is tilted perpendicularly to the image surface 7 in which the sample 9 is arranged. To achieve the telecentric sub-beam set 5, a multi-beam deflector unit 41 is arranged in the intermediate image surface (intermediate focal surface 29). The deflector unit 41 includes a micro-optical grating element configured as a deflector array to individually adjust the propagation angle of each beamlet in the sub-beam set 5. A multi-beam grating unit similar to the multi-beam generating unit 27 or the multi-beam deflector unit 41 includes a plurality of porous plates or micro-optical grating elements formed in a planar substrate or wafer. Figure 2 A representative multi-beam barrier unit 71 comprising three multi-aperture plates 73.1, 73.2, 73.3 is illustrated. Figure 2 A portion of the inner region or membrane region of the porous plates 73.1, 73.2, and 73.3 is shown. For example, the first porous plate 73.1 is configured with a collection of openings or holes 75.1, 75.2, and 75.3. The collection of holes can be arranged in various raster configurations, such as a hexagonal raster, or in a circular arrangement, for example. In the example, the porous plates are configured to generate a collection of multiple electron beamlets 77.1, 77.2, and 77.3 from an incident single electron beam 70. In this configuration, the incident single electron beam 70 passes through the holes, thereby forming a plurality of electron beamlets 77.1, 77.2, and 77.3 in a raster configuration. In another example, for example in a multi-beam deflection unit, a first porous plate 73.1 is configured to transmit a pre-shaped set of electron beamlets 77.1, 77.2, 77.3 and includes apertures 75.1, 75.2, 75.3 arranged in a grating configuration for the pre-shaped set of electron beamlets. In each example, at least one of the plurality of electron beamlets 77.1, 77.2, 77.3 passes through or is transmitted by a corresponding aperture 75.1, 75.2, 75.3 of the micro-optical grating element 73.1.

[0065] The multi-beam grating unit comprises a second micro-optical grating element 73.2, 73.3 adjacent to the porous plate 73.1 upstream or downstream in the direction of the incident electron beam 70. Each second micro-optical grating element 73.2, 73.3 comprises a set of holes similar or identical in a grating configuration to the porous plate 73.1 and a set of electrostatic elements configured to individually and independently influence each sub-beam in the set of electron sub-beams. For example, the electrostatic lens element 80 is generated as an electrostatic field (not shown) by applying a drive voltage to an annular electrode 79 arranged around the holes of the micro-optical grating element 73.2, and the lower side or bottom side 107 of the first porous plate 73.1, which acts as a counter electrode. During use, the electrostatic lens element 80 focuses the sub-beams 77.1 into a focal plane (intermediate focal surface 29) (see Figure 1 Other examples of electrostatic elements are multipole elements, for example comprising four or eight electrodes 81.1, 81.2 (only two are shown) centered around a hole in the third micro-optical grating element 73.3, to individually and independently correct the shape of the sub-beams 77.3 or to act as deflectors, as stigmators for fine adjustment of the focus. Figure 2 The example in FIG illustrates the focusing capability of the lens element 80 in the example of a beamlet 77.1 and the deflection of a beamlet 77.3 by means of electrodes 81.1, 81.2. The beamlet 77.3 is deflected, for example, in the multi-beam generating unit 27 to minimize deviations from predefined positions in the grating configuration or in the multi-beam deflector unit 41 to achieve a telecentric imaging condition.

[0066] In one example, the multi-beam generating unit (multi-beam raster unit 71) comprises a planar element 84, such as an electrostatic element located downstream of the micro-raster element 73.3 in the direction of the electron beam 70. The planar element 84 is configured with at least one electrode 82 and is used to globally focus or deflect the entire set of beamlets. The electrostatic element, comprising the set of electrodes 82 arranged around the opening, is configured to affect the plurality of charged particle beamlets as a whole. In the example, a single electrode 82 is provided, forming a ring electrode. During use, a uniform electrostatic field is formed between the global ring electrode 82 and the proximal porous plate 73.3, as well as small electrostatic fields within the holes of the porous plate 73.3, which focus each of the plurality of beamlets in the same manner.

[0067] Figure 1The multibeam charged particle microscope (MCPM) further comprises an operating unit 43, which comprises supply hardware and a control unit for providing voltage and current to the optical components of the charged particle microscope and controlling the operation of the MCPM according to user instructions and control software. The operating unit 43 is connected to an image processing unit 49 for processing image data from the detector 13. The operating unit 43 is also connected to a stage control unit 51, which controls the position or movement of a stage with an actuator, such as a five-axis stage holding the sample 9. The operating unit 43 is also connected to a user interface and other devices, such as a memory or a network (not shown). The operating unit 43 is connected to a multibeam grating control unit 45, which controls at least one of the multibeam grating units, like the multibeam generation unit 27 or the multibeam deflector unit 41. Each multibeam grating unit further comprises local control units 47.1 and 47.2. During use, the multibeam grid control unit 45 and the local control units 47.1 and 47.2 provide voltages and currents to the electrodes of the multibeam grid unit for individually controlling electrostatic elements, such as electrostatic lenses, deflectors or stigmators.

[0068] Each electrostatic element is formed during use between electrodes in at least two different planar substrates of the micro-optical element, for example a plurality of electrostatic lenses 80 are formed between the first porous plate 73.1 and the second porous plate 73.2, a plurality of deflectors or correctors are formed between the porous plates 73.2 and 73.3 during use, and a global electrostatic lens is formed between the porous plate 73.3 and the planar element 84. Each of the porous plates 73.1 to 73.3 or the planar element 84 is implemented as a planar substrate or wafer. Therefore, for each electrostatic element, two planar substrates or wafers need to be adjusted with high precision. Spacers 83.1, 83.2 and 83.3 are arranged between the elements of the multi-beam generating unit (multi-beam grating unit 71) to maintain a constant and predefined distance between the elements and to isolate the elements from each other. The high-precision lateral alignment according to an embodiment of the present invention is described in more detail below.

[0069] Throughout the disclosure, it is understood that in an illumination beam path having a multi-beam generating unit or a multi-beam deflecting unit (multi-beam grating unit 71), the charged particle beam 70 and the plurality of sub-beams 77 propagate in the positive z-direction, wherein the z-direction points downwards and a sequence of planar substrates or wafers, such as multi-aperture plates 73.1, 73.2, 73.3 are arranged in sequence in the direction of transporting the charged particle beam or sub-beams in the positive z-direction. The beam entrance side or top side 74 is understood to be the first surface or side of the element in the direction of transporting the charged particle beam or sub-beam, and the bottom side or beam exit side 107 is understood to be the last surface or side of the element in the direction of transporting the charged particle beam or sub-beam. However, the present disclosure should not be limited to charged particle beams only in the positive z-direction with the z-direction pointing downwards.

[0070] Each electrostatic element is configured by a collection of one or more electrodes, symmetrically arranged in a plurality of holes of, for example, two porous plates 73.1 and 73.2, configured to form an electrostatic element, such as an electrostatic lens, a beam stigmator or a beam deflector for each of a plurality of electron beamlets 77. During use, a different voltage is applied to each electrode, and an electric field is generated in the hole and between the plurality of porous plates. In the example, an electrostatic element 80 is arranged near at least one hole 85 of the porous plate 73.1 and is configured to form, for example, an electrostatic lens during use of the electron microscope. During operation, a specific voltage is applied to each electrode 79, 81.1, 81.2 of the electrostatic element and a predefined electrostatic field is generated. Figure 3 An example is illustrated in detail in FIG. The porous plate 73.1 is formed by a conductive element having through holes or holes such as hole 85. For simplicity, Figure 3 Only one of the multiple holes is shown. The function of the first porous plate 73.1 is to split the incident beam 70 into a plurality of sub-beams, including sub-beam 77.1, which are further propagated in the electron optical projection system. During use, electrons of the incident beam 70 pass through holes such as holes 85 of the first porous plate 73.1 or are absorbed by conductive elements of the first porous plate 73.1. Therefore, the first porous plate 73.1 is configured with a stopping capability for high-energy particles on the incident side of the incident electron beam 70. In order to avoid the generation of repulsive voltage potentials and charging, the first porous plate 73.1 is covered by a conductive absorption layer 99, which is connected to a large capacity such as ground to empty or dump the absorbed charges. At hole 85, the electron beam 70 passes through the hole 85 of the porous plate 73.1 and generates electron sub-beams 77.1. The sub-beams 77.1 pass through a predefined electrostatic lens element 80 and are focused into a focal surface (intermediate focal surface 29) (see Figure 1 ).

[0071] In this example, the first porous plate 73.1 acts as an opposing electrode with at least a second planar substrate 73.2, so that an electrostatic lens 80 is formed between the first porous plate 73.1 and the second planar substrate 73.2. This is achieved by configuring the bottom side or beam exit side 107 of the first porous plate 73.1 with a layer of conductive material 108, for example. The electrostatic lens element 80 is generated by applying a drive voltage difference to the electrode 79 and the conductive layer 108, and the electrostatic field 80 extends in the free space between the electrode 79 and an additional conductive or isolating element near the electrode, such as the conductive layer 108 with holes 85. The equipotential lines of the electrostatic field of the electrostatic lens 80 are at Figure 3 In detail, the electrostatic field also passes through the holes 85 of the porous plate 73.1.

[0072] It is known that the optical aberrations of micro-optical elements such as electrostatic lens element 80 are highly sensitive to manufacturing inaccuracies of the aperture. The deviation of the aperture cross section from the predefined shape is Figure 3 1. The lower half of the diagram shows the upper or top surface 74 of the porous plate 73.1. The upper or beam entrance surface 74 is typically the first surface of the porous plate in the direction of the charged particle beam. The outer contour 89 of the aperture 85 deviates from the ideal circle shown by the dashed circle 91. Deviations in the shape of the electrodes, the shapes of the additional conductive or isolating elements, and particularly the shape of the apertures such as the apertures 85 of the porous plate 73.1, generate deviations 93 from the predefined electrostatic field 80 during use, thereby generating aberrations that degrade the electron beamlets (such as beamlet 77.1) from their predefined properties. For example, slowly varying deviations from the predefined or ideal outer contour 89 of the aperture 85 result in, for example, tilt or astigmatism, as shown by the electron beam trajectory 97, which deviates from the ideal trajectory of the beamlet 77.1 as shown by the dashed line. High-frequency deviations such as roughness (defined as the standard deviation of the minimum distance between the profile and the ideal shape) result in higher-order aberrations or are responsible for the generation of scattered particles. Typical deviations in etching processes can be up to 0.5 μm rms. Typically, aberration increases with the power of the electrostatic element or the voltage applied to the electrode. Scattered particles are generated, for example, at the upper edge of the electron beam 70 or at the hole 85 on the incident side. In the prior art, the shape of the upper edge and the inner wall deteriorates the designed shape due to statistical process variations and the residual inhomogeneity of deep etching, thereby showing significant roughness, inhomogeneity and deviation from the designed shape. The diameter of the lower profile of the exit surface diameter of the hole forming the first porous plate can vary with the difference between the hole and the wafer. The inhomogeneity of the isotropic etching step increases the roughness. These deviations lead to deviations in the electrostatic field near the hole, which can therefore lead to aberrations and image blur in the sub-beam. In addition, for example, the tilt angle of the inner wall 87 may cause the scattering of electrons passing through a cylindrical hole such as hole 85 to increase, as shown in the scattered electron trajectory 95.

[0073] The first porous plate 73.1 of the multi-beam generating unit 27 is the main cause of scattered particles, but other micro-optical grating elements may also be subject to deviations from a predefined shape due to manufacturing inaccuracies, which reduces image quality, such as resolution or contrast, of the image generated by the multi-beam electron microscope 1. In order to achieve high resolution, high contrast and high throughput, the task of the present invention is to minimize aberrations and scattered charged particles.

[0074] In the first embodiment of the present invention, the multi-beam grating unit is configured so that the edge of the electrode and the inner wall of the hole are located at a large distance from the transmission sub-beam of the charged particles, thereby minimizing the impact of the deviation between the inner wall of the hole and the edge of the electrode on the beam properties.

[0075] Figure 4 An embodiment of the present invention is illustrated. In this embodiment, the inner wall of at least one segment of the aperture opening 85 is configured to bend and tilt away from the passing charged particle beam so that the exit diameter of the forming electrode is larger than the entrance diameter of the aperture. "Tilt away" is generally understood to mean that the inner wall of the segment is configured so that the tangent of the inner wall at a point in the z-axis direction points away from the passing charged particle beam. Therefore, the diameter of the segment of the aperture increases continuously with increasing z coordinate. In this example, the lower segment or second segment has an increasing diameter in the direction of the transmission electron beam and in the intersection plane ( Figure 4 In the xz plane in the figure, a concave circular cross section is formed. Figure 4 In FIG. 8 , an example of one hole 85.1 in a porous plate 73.1 is shown. Typically, a porous plate comprises a plurality of such holes 85 in a grating configuration, Figure 4 Only one is shown in FIG. The inner wall of the aperture 85.1 is configured to rotate symmetrically around an axis of symmetry 105 of the aperture 85.1, which is parallel to the incident electron beam 70. The porous plate comprises an absorption layer 99 at the incident side 74. The absorption layer is connected to ground.

[0076] During use, most of the incident electrons from the electron beam 70 are absorbed in the absorption layer 99, and a current corresponding to the number of absorbed electrons is generated. For example, in the case of D1 = 30 μm and a pitch of 150 μm, approximately 97% of the incident electrons from the incident electron beam 70 are absorbed, generating a large current. Therefore, the absorption layer 99 exhibits a fluctuating voltage difference corresponding to the induced current during use and is therefore unsuitable for forming an electrode for the electrostatic element 80.

[0077] The porous plate 73.1 having apertures 85 includes a first section 101.1 and a second section 101.2 having z-extents L1.1 and L1.2. The incident electron beam 70 strikes parallel to the z-direction and is absorbed in the absorption layer 99 and directed away from or through the apertures 85.1. At the entrance surface 74, the apertures 85.1 have a diameter D1. The second section 101.2 is configured with inner sidewalls forming a concave circular cross-section in the xz plane, whose diameter continuously increases, with a tangent vector 103 in the xz plane pointing away from the main direction of the passing electron beam 77. The inclined surface at the inner wall of the second section 101.2 thus points away from the passing electron beam 77 and culminates in a maximum aperture diameter D2 at the exit or bottom surface 107 of the porous plate 73.1. The maximum aperture diameter D2 at the exit surface 107 is greater than the average aperture diameter D2A within the second section 101.2, which is greater than the aperture diameter D1 of the first section 101.1. The beam exit surface 107 is covered by a conductive layer 108, which is connected to an electrical potential, for example to ground potential. The conductive layer having a boundary or edge with a diameter D2 forms a counter electrode for a subsequent second porous plate 73.2 in the z direction, which is adjacent to the first porous plate 73.1. In order to form an electrostatic element during use, the second porous plate 73.2 is provided with an annular electrode 79 around the holes 85.2 with a diameter D3, so that an electrostatic lens 80 is formed between the conductive layer 108 and the annular electrode 79 during use (see also Figure 3 ). At least in section 102.1, the inner walls of the holes 85.2 of the second porous plate 73.2 may also be configured to be curved or tilted away from the passing electron beam 77. In another example, the inner wall of the electrode may be configured to be parallel to the z-axis. Figure 4 In one example, the second porous plate 73.2 embodiment includes a segment 102.1 having an electrode 79, and in another example, the second porous plate 73.2 includes an additional segment 102.2 (see below). The second porous plate including the electrode 79 has a length L3 of approximately 30 μm-300 μm. An example of a manufacturing method and design of the second porous plate 73.2 is described in US20190259575, which is incorporated herein by reference.

[0078] according to Figure 4In the example of FIG. 7 , although only one aperture 85.1, 85.2 is shown, multiple electrostatic elements in a grating configuration between a pair of apertures, such as apertures 85.1 and 85.2, are configured as multiple electrodes, such as an annular electrode 79, on the entrance side of the second porous plate 73.2, and multiple electrodes, such as a conductive layer 108, provided on the exit side of the first porous plate 73.1. The multiple electrostatic elements with the annular electrode 79 form multiple electrostatic lenses, including lens 80, in the grating configuration during use. In another embodiment, the multiple electrostatic elements are configured with multiple electrodes 81 in a grating configuration to form, together with, for example, the conductive layer 108, multiple deflectors or correctors in the grating configuration during use. At least the second or lower section of the first porous plate 73.1, forming an electrode opposite the electrodes of the second porous plate 73.2, includes an inner wall configured to bend or tilt away from the passing electron beam 77, forming an aperture diameter D2 on the beam exit side that is larger than D1. Manufacturing tolerances in the aperture openings in the exit surface 107 produce optical aberrations in the electrostatic elements. By increasing the second diameter D2 by more than 10% relative to the first diameter D1, a 5-10 times reduction in optical aberrations is achieved. The first beam entrance section 101.1 of the first porous plate 73.1 is configured as a conductive film having holes (openings), with the film area between the holes acting as an aperture stop for the incident electron beam 70 and defining the sub-beam sets 77.

[0079] In the beam entry section 101.1, the holes are cylindrical with a transverse diameter D1 and have a small extension L1.1 in the z-direction, where 2μm≤L1.1≤5μm. Therefore, the thickness of the first section with parallel sidewalls is significantly reduced compared to the thickness L1 of the first porous plate 73.1. The thickness of the beam entry section is determined as a trade-off between its ability to stop incident charged particles between the holes and controlling scattering along its sidewalls. Reducing the thickness of the parallel sidewalls of the porous plate by a factor of two reduces the scattering by 50%. In this example, the second section 101.2 with curved sidewalls reduces the thickness of the cylindrical holes to L1.1=L1 / 2, thereby reducing the scattering of the first porous plate 73.1 to 50%. An even further reduction of L1.1 to L / 3 reduces the scattering of the first porous plate 73.1 to approximately 30%.

[0080] The hole center to hole center distance P1 is typically in the range of 30 μm ≤ P1 ≤ 250 μm. The surface ratio of the hole opening surface to the total surface of the orifice plate defines the transmission rate of the orifice plate. The transmission rate tr is typically 5% ≤ tr ≤ 20%, preferably 10% ≤ tr ≤ 15%.

[0081] In one example, the following parameters were selected: D1 = 30 μm, D2 = 40 μm, D3 = 55 μm, D4 = 55-75 μm, L1.1 = 5 μm, L1.2 = 5 μm, L1 = 10 μm, L2 = 20 μm, and L3 > 400 μm. In another example, the following parameters were selected: D1 = 18 μm, D2 = 25 μm, D3 = 20 μm, L1.1 = 5 μm, L1.2 = 10 μm, L1 = 15 μm, L2 = 20 μm, and L3 > 40 μm. Preferably, L1.2 ≤ 10 μm.

[0082] In another example, the following relationship applies: within the range between the first thickness L1.1≤D2≤4*L1.1, preferably L1.1≤D2≤3*L1.1, more preferably L1.1≤D2≤2*L1.1.

[0083] Generally, the incident side hole diameter D1 of the absorption layer 99 is within the range of 10 μm ≤ D1 ≤ 50 μm, and the lateral exit surface diameter D2 of the holes in the electrode layer 108 is greater than D1, i.e., D2 > D1, and D2 can be configured within the range of 15 μm ≤ D2 ≤ 60 μm. The thickness of the first perforated plate 73.1 is preferably 3 μm ≤ L1 ≤ 15 μm. It is generally advantageous to have a thin first perforated plate 73.1, where L1 < D2, or even L1 < D2 / 2, or even better L1 < D1, or even better L1 < D1 / 2. In one example, L1 is greater than or equal to D2 / 4. It is further advantageous to have D2 within the range between L1 and 5 times L1, or L1 < D2 < 5*L1, preferably L1 < D2 < 4*L1, or even more preferably L1 < D2 < 2*L1. In each configuration, the thickness L1 is thin enough to avoid unnecessary scattering of the transmitted charged particles, and in parallel, the thickness L1 is thick enough to achieve sufficient absorption of the incident beam of charged particles between the holes. The incident diameter D3 and the exit diameter D4 of the second perforated plate 73.2 are preferably between 15 μm and 75 μm. The distance L2 between the first perforated plate and the second perforated plate 73.1 and 73.2 is preferably very small, such as 10 μm ≤ L2 ≤ 30 μm. The electrostatic crosstalk between multiple electrostatic elements is avoided by an axial distance (in the z direction) L2 that is less than the hole diameter D2 or D3. Preferably, D2 is greater than L2 but less than 3 times L2, preferably less than 2 times L2. Preferably, the thickness L3 of the first section 102.​1 of the second perforated plate 73.2 is similar to the diameter D3 or D4. In an example, the incident diameter D3 of the holes in the second perforated plate 73.2 having the electrode 79 is between D1 and D2, so D1 < D3 < D2, but in another example, D3 can also be larger than D, D3 > D2. Generally, D1 has the smallest diameter such that D1 < D2, D1 < D3, D1 < D4. Through such design and manufacturing, D2 is greater than D1 and L1, preferably 2*L2 > D2 > L2, even more preferably D3 > D2, and the influence of any deviation of the electrode edge profile in the elements 73.1 and 73.2 on the performance and properties of the electrostatic elements is reduced.

[0084] As explained in more detail below, the first porous plate may include a third section 101.3. By configuring the inner wall of at least the second or third section 101.2, 101.3 of the aperture opening to be curved and tilted away from the passing charged particle beam 77, and by forming a second or third or fourth diameter D2 to D4 of the apertures in the porous plate (which is larger than the diameter D1 of the first thin section of the aperture), scattering of the passing charged particles 77 is reduced. By configuring the inner wall of the lower section 101.2 of the porous plate 73.1 to be tilted away from the passing charged particle beam 77, so that the second section ends with a larger aperture diameter D2 at the exit surface 107 or the porous plate 73.1, the negative impact of deviations and manufacturing tolerances on the electrostatic field of the electrostatic lens 80 during the manufacturing process of the aperture plate is reduced, and as Figure 3 As shown, aberrations of the passing charged particle beam 77 are reduced. High shape precision and positional accuracy can be achieved for electrodes, such as electrode 79 in the porous plate 73.2, and the opposing electrode at the lower boundary or edge of the aperture 85, whose increased diameter D2>D1 in the exit surface 107 of the porous plate 73.1 is covered by a conductive layer 108. In the example, the conductive layer 108 also covers the sidewalls of at least the apertures of the second section 101.2 of the porous plate 73.1. Therefore, any secondary or scattered electrons that strike the sidewalls are conducted away and do not interfere with the electrostatic elements formed below. For example, a precise distance L2 is achieved by spacers, and during use, multiple electrostatic elements of a multi-beam generating unit or multi-beam deflector unit are formed with high precision. Each of the first beam entry section 101.1 and the second beam exit section 101.2 is formed in a single substrate or block by double-sided processing, as will be described in more detail below.

[0085] Figure 4 The first section 101.1 comprises parallel inner side walls, similar to a conventional aperture. In another embodiment, the first section 101.1 can also be configured with inner walls that are tilted away from the passing charged particle beam 77. In this case, the transmission of the electron beam forms a transition region, wherein the transmission gradually decreases with increasing distance from the aperture center 105.

[0086] Figure 4 Only a portion of the inner region or membrane of the porous plates 73.1 and 73.2 is shown.As will be explained in more detail below, the porous plates also include a support region to support the membrane region and provide mechanical stability.

[0087] In a second embodiment of the present invention, the multi-beam grating unit 71 is configured with at least two separate segments. The effect of deviation on optical performance is reduced by functional separation of the upper edge of the porous plate (which acts as a beam stop and forms a beam) and the lower edge of the porous plate (which forms an electrostatic element with a subsequent second micro-optical grating element). In an example, the first porous plate includes two or more separate planar separation segments or substrates, each individually prepared by single-sided or double-sided structuring. These segments are assembled to form a composite porous plate. Therefore, a more accurate definition of the size and position of the two edges and low roughness are provided by separate processing of at least two segments. In addition, since the electrode edge and the inner side wall of the hole are located at a greater distance from the transmission sub-beam of the charged particles, the effect of the deviation of the electrode edge and the inner side wall of the hole on the beam properties is further minimized.

[0088] Figure 5 The diagram shows a porous plate divided into at least two sections that perform different functions. The two sections 101.1 and 101.2 are formed as separate sections and are adjusted and connected together using known techniques. This achieves functional separation between a first beam entry section 101.1 that forms the passing charged particle beam 77 and a lower second beam exit section 101.2 that forms an electrostatic lens for an adjacent porous plate 73.2 with an electrode 79. The first section 101.1 is covered by a conductive metal film that has the ability to absorb and conduct away most of the impinging charged particles 70. The second section is formed as a silicon or SOI film with a conductive metal layer 108, forming an electrode opposite the subsequent electrode in the z-direction. The two films are aligned and fixed together, for example, by glue or by bonding or welding using fixing points 111 such as glue or welding points. Preferably, the distance L1.3 between the two separated sections 101.1 and 101.2 is made as small as possible, for example, less than the thickness L1.2 of the second section 101.2 or less than the thickness L1.1 of the first section 101.2. Figure 4As in the example described, it is advantageous to configure D2 to be greater than the total thickness L1 formed by the sum of L1.1 plus L1.2 plus L1.3, but not greater than 5 times L1, preferably 3 times L1, preferably 2 times L1. In addition, the diameter D2 of the second section 101.2 is greater than D1. Generally, the same restrictions as above are preferred for the dimensions. In another embodiment, the inner wall of the second section 101.2 can also be shaped to be inclined away from the passing charged particle sub-beam 77. The thin second section 101.2 is precisely structured and aligned with the adjacent aperture plate 73.2 having the electrode 79, thereby defining a precise and aberration-free electrostatic lens during use. In the first porous plate 73.1 comprising at least two separate sections 101.1 and 101.2, each section can be formed by single-sided processing. Each of the segments 101.1 and 101.2 can be structured by known planar processing techniques of planar substrates (such as metal films, silicon or SOI wafers) and can be formed together with the second porous plate 73.2 along the plurality of holes 85 ( Figure 5 The multiple symmetry axes 105 of the one shown in FIG are precisely aligned.

[0089] In another example, the two segments 101.1 and 101.2 are attached to each other using special supports that allow for fine passive or active alignment. For active alignment, the holder comprises a guiding element and an actuator, such as a piezoelectric actuator.

[0090] The upper aperture diameter D1 of the entrance surface 74 can be in the range of 10 μm ≤ D1 ≤ 50 μm, while the exit aperture diameter D2 can be larger, for example, 15 μm ≤ D2 ≤ 60 μm. The smaller distance L2 is preferably in the range of 10 μm ≤ L2 ≤ 30 μm and can be very precisely controlled with the required sub-μm accuracy. By configuring two separate segments 101.1 and 101.2, the first segment 101.1 is structured from the top or entrance side 74 and achieves high precision of the entrance aperture diameter D1, while the second segment 101.2 is structured from the bottom 107, thus achieving high precision of the aperture diameter D2 of the second segment 101.2 at the bottom side 107. By configuring the porous plate 73.1 comprising at least a first separate section 101.1 and a second separate section 101.2 such that the second section 101.2 ends at the exit surface 107 or the porous plate 73.1 with a hole diameter D2 that is larger than D1, the negative influence of deviations and manufacturing tolerances during the manufacture of the porous plate on the electrostatic field of the electrostatic lens 80 is reduced and aberrations of the passing charged particle beam 77 are reduced, as Figure 3As shown. As a result, the shape of the passing charged particle beam 77 is well controlled, and the electrostatic element formed between the lower side or bottom side 107 having the conductive film 108 and the electrode 79 is also well defined. Through such design and manufacturing, high shape accuracy and positional accuracy of the electrode 79, the lower boundary or edge of the aperture 85 having an increased diameter D2>D1 in the exit surface 107 of the second section 101.2 of the porous plate 73.1, and the distance L2 are achieved. During use, the multiple electrostatic elements of the multi-beam generating unit or multi-beam deflector unit are formed with high precision. The positional accuracy of the electrode 79 and the lower boundary or edge of the aperture 85 in the exit surface 107 are well defined with an accuracy of better than 0.5 μm.

[0091] In the third embodiment, structural elements for reducing aberration and scattering are combined to improve resolution and image contrast. As a result, aberration is further reduced. Figure 6 An example is shown in FIG. The first porous plate 73.1 of this embodiment comprises three sections and comprises two separate parts. The absorbing and conductive surface metal layer forms part of the first beam incident section 101.1 of the first porous plate 73.1. The second section 101.2 is as shown in FIG. Figure 4 The first section 101.1 and the second section 101.2 have the same Figure 4 . , and for example form part of a manufacturing process produced by double-sided processing. The first porous plate 73.1 further comprises a third thick beam exit section 101.3, which is formed as a separate section, for example made of silicon or SOI with through holes or holes and attached to the bottom side of the second section 101.2, for example taking the attachment point 111 as an example. Thus, a small gap of width L1.3 between 5-15 μm is maintained. In another example, the section 101.3 can be directly attached to the section 101.2 and no gap is formed. The length of the third section 101.3 is approximately 50-300 μm, and the bottom surface of the third section 101.3 forms the bottom surface or exit surface 107 of the porous plate 73.1. The holes at the exit side 107 have a maximum diameter D2>D1 and have an exit diameter in the exit surface 107. D2 can be in the range of 30 μm≤D2≤70 μm. The exit surface 107 of the third section 101.3 includes an annular conductive layer or electrode 114 around or near the hole of diameter D2, which is connected to a constant voltage potential, for example to ground level, and forms a counter electrode to the subsequent second porous plate 73.2 in the z-direction. Alternatively, the exit surface 107 of the second section 101.3 and the inner sidewalls of the plurality of holes in the third section 101.3 can also be covered by a conductive layer, such as layer 108.

[0092] The second porous plate 73.2, including the electrode 79, is configured with a distance L2 between 15 μm and 30 μm from the first porous plate 73.1 and, during use, forms an electrostatic lens with the electrode of the third segment 101.3. The third segment 101.3 is structured from the bottom side 107, thereby achieving high precision in the pore diameter D2 of the third segment 101.3. This effectively controls the shape of the passing charged particle beam 77, and defines the electrostatic element formed between the electrode 114 and the electrode 79. This design and manufacturing achieves high shape and positional accuracy of the electrode 79, the lower boundary or edge of the third segment 101.3, which is covered by the conductive layer 114 and has a diameter D2, in the exit surface 107, and the distance L2. During use, the multiple electrostatic elements of the multi-beam generating unit or multi-beam deflector unit form a highly precise grating structure. Throughout the thickness L1.3 of the third section 101.3, the minimum inner diameter D5 of each hole through the third section 101.3 is greater than D1, so that scattering of charged particles can be avoided even if the thickness L1.3 is large.

[0093] In a fourth embodiment of the present invention, the porous plate is provided with an etch stop ring around the plurality of holes. Using the etch stop ring, a high precision in the shape and roughness of the hole openings in the entrance or exit surface of the porous plate can be achieved. Figure 7 In the example of FIG. 1 , an etch stop ring 109 of length L1.22 is formed in the bottom or exit surface 107 of the porous plate 73.1 and is covered with a conductive layer 108. The etch stop ring 109 is formed with high precision by photolithography and directional etching, and has an inner diameter D2 that is greater than D1. For example, each etch stop ring is etched into a silicon or SOI wafer by directional etching to form a circular groove and refilled with, for example, SiO2 or other suitable etch stop material. With the etch stop ring 109 precisely formed around the circumference of the hole opening 85 at the exit surface 107, the hole opening can be etched by, for example, isotropic etching limited by the etch stop ring 109. The etch stop ring 109 allows for high-precision control of the diameter D2 to achieve an accuracy of 0.5 μm or 0.25 μm or 0.1 μm or even lower, and the roughness can be controlled to be well below 0.1 μm or even below 0.05 μm. Thus, the electrostatic lens in combination with the porous plate 73.2 including the electrodes 79 is formed with high precision and very low aberrations during use.

[0094] The present invention Figure 4 、 5, 6, and 7 illustrate an example of a second porous plate 73.2 including a ring electrode 79 to form an electrostatic lens element 80 between the first and second porous plates. In other examples, the second porous element 73.2 may include multiple electrodes 81 to form an electrostatic multi-stigmator, corrector, or deflector element having multiple electrodes 81 arranged around each aperture. The embodiments are explained using circular apertures as an example, but the present invention is not limited to circular apertures and can also be applied to, for example, elliptical apertures or apertures of other shapes, including correspondingly shaped etch stop rings and correspondingly shaped electrodes.

[0095] Figure 8 The diagram shows Figure 7 The porous plate 73.1 comprises an inner or central area or membrane 123 and a support area 121 arranged at the outer circumference of the porous plate 73.1. Figure 2-7 In each of the figures, for each porous plate, only a portion of the inner region, central region or membrane 123 is illustrated, for example having a thickness L1 of about 10 μm. At least the membrane 123 is covered by an absorbing and conductive metal layer and includes a plurality of holes 85 (only four are shown) with a spacing P1 for transmitting sub-beams of charged particles 77.1, 77.2, 77.3 and 77.4 from the incident charged particle beam 70. The thickness L1 of the inner or central region is <15 μm. The holes at the exit surface 107 include etch stop rings 109 (only one is indicated by the reference numeral 109). The support area 121 includes additional support structures to improve the mechanical rigidity of the porous plate 73.2, for example a first layer 117 with a thickness L0 and a second layer 119 with a thickness LS. The first layer 117 and the second layer 119 may include an insulating or conductive or semiconductor material, such as disiloxane (SiO2), a metal or silicon. Adjustment elements 115.1, 115.2 for attaching and adjusting subsequent multiwell plates are attached to the bottom surface 107. By processing the top surface 74 and the bottom surface 107 in a planar processing operation, a high precision of the well openings at the top surface 74 and the bottom surface 107 can be maintained.

[0096] According to an embodiment, each porous plate is formed in an assembly of one, two or more parallel plane substrates, for example, formed by silicon microstructuring. Other manufacturing techniques are, for example, additive manufacturing. In silicon microstructuring, a planar substrate is manufactured on a silicon or SOI wafer. The central portion of the wafer is structured as a film with a hole or through-hole having a thickness of 3-20 μm. The wafer with the hole or through-hole comprises two zones. The hole is achieved by an etching process, including, for example, an isotropic etching process such as SF 6 plasma etching, anisotropic vertical etching such as DRIE (gas cutting or low temperature) or wet etching. Local etching is controlled by a mask formed by a standard photolithography process using a precise photolithography mask. The wafer is optionally covered by a conductive layer, for example, by gold, to increase its conductivity and blocking ability to rapidly incident (30 keV) electrons.

[0097] The manufacturing process of the first porous plate 73.1 adopts a double-sided process, wherein the first process is carried out on the incident side 74 and the second process is carried out from the back side or bottom side 107. The inner sidewall forming the circular segment is produced, for example, by isotropic plasma etching of silicon or SOI with SF6 plasma. The process can also start from the processing of the second section 101.2 of the bottom side or underside 107 of the porous plate 73.1, and in a second step, the beam group defining the aperture in the first section 101.1 is produced. The second porous plate 73.2 is attached to the first porous plate 73.1, for example, by spacers in the periphery of the porous plate, and an isolating vacuum gap is formed between the two porous plates 73.1 and 73.2.

[0098] Figure 9The method for manufacturing a porous plate according to an embodiment is described in more detail. Reference will be made to the porous plate 73.1, but the steps of the manufacturing method can also be applied to the other porous plates 73.2 or 73.3. In step S1, an SOI wafer is provided with three layers, a first thick top layer 129.1, a second intermediate layer 129.2 and a third or device layer 129.3. The intermediate layer 129.2 is formed as a buried oxide layer. The third layer 129.3 is polished to a thickness equal to a film thickness of approximately 10 μm. Optionally, the bottom surface 107 is further configured, for example by wet etching, to include alignment or adjustment spacers in the periphery of the wafer. After step S1, in step S2, a circular etch stop ring 109 is formed from the bottom side 107 into the device layer 129.3. First, circular trenches are formed by directional RIE etching through a first etch mask (not shown) formed photolithographically on bottom side 107, with a depth of approximately 30-75% of the SOI thickness (e.g., 3 μm to 7.5 μm). The first etch mask (not shown) is removed and the trenches are filled by depositing SiO2, which forms the etch stop material for etch stop rings 109. After step S2, in step S3, second segments 101.2 are formed by isotropic silicon plasma etching. For plasma etching, a second etch stop mask 131 is formed by photoresist deposition and photolithographic structuring. Second etch stop mask 131 includes a plurality of small circular openings 133 concentric with the plurality of circular etch stop rings 109. After the isotropic silicon plasma etching, structures 125 in the form of spherical segments are formed in device layer 129.3. The etch shape is controlled by openings 133, etching time, and etch stop rings 109. After step S3, in step S4, through-holes 127 are formed in device layer 129.3 by directional plasma assisted etching, for example by DRIE (deep reactive ion etching) of silicon. The etching depth is limited by the intermediate layer 129.2, which acts as an etch stop layer. This forms a first section 101.1 with cylindrical sidewalls and a second section 101.2 with curved sidewalls of the porous plate 73.1. The bottom side 107 can be further protected by a protective coating (not shown). In step S5, the result of further etching the first layer 129.1 and the second layer 129.2 is shown. Support structures 117 and 119 that penetrate the first layer 129.1 and the second intermediate layer 129.2 and form the support area 121 are etched through by known processes. The second etch stop mask 131 and the optional protective coating are removed. After step S5, in step S6, an electron blocking and conductive layer 99 is formed at least at the upper side of the porous plate 73.1 by depositing, for example, gold or other dense metals. A conductive layer 114 is formed at the bottom or underside 107 to form a counter electrode for a subsequent porous element. Optionally, the porous plate 73.1 is completely covered by the conductive layer 99 or 114 from all sides.

[0099] Figure 10 A manufacturing method for manufacturing the holes of the porous plate 73.1 according to a double-sided directional etching process is described. In these process steps, the multiple holes of the porous plate 73.1 or 73.2 or 73.3 are formed in the SOI substrate by a double-sided etching process, and each etching process step is limited by the buried oxide layer of the SOI wafer. Reference will be made to the porous plate 73.1, but the steps of the manufacturing method can also be applied to the other porous plates 73.2 or 73.3. In the inner region or membrane region 123 (see Figure 8 ), after step S7, a wafer having layers 135.1, 135.2, and 135.3 is configured. In step 8, a first etching mask 137 is formed on the incident side 74, and a plurality of circular openings 141 (only one is shown) having a diameter D1 are formed. Utilizing DRIE etching (RIE 1) from the incident side, the hole openings 141 are etched through the first layer 135.1. The second layer 135.2 acts as an etch stop layer. The first etching mask 137 is removed, and in step S9, a second etching mask 139 is formed on the back side 107 opposite to the incident side 74. The second etching mask 139 includes a plurality of circular openings 143 (only one is shown) having a diameter D2 greater than D1. Each circular opening 143 in the etch stop layer 135.3 is formed with photolithographic precision so as to be concentric with one of the circular openings 141 in the first layer 135.1. The hole openings in the third layer 135.3 are then DRIE-etched from the back side or opposite side 107. In another embodiment, smaller openings are formed in the etching mask 139 and isotropic etching is applied, similar to that described in step S3. After the isotropic silicon plasma etching, a curved structure in the form of a spherical segment is formed in the device layer 135.3. The etching shape is controlled by the opening (not shown), the etching time, and the etching stop layer 135.2. This method uses a photolithography process and an etching process from both sides of the wafer, thereby very accurately defining the hole openings on the incident and exit sides of the porous plate. Thereafter, in step 10, the intermediate layer 135.2 is removed at least in the opening 141 by, for example, wet etching from the back side 107. A conductive absorption layer 99 and an electrode layer 108 are applied.

[0100] The porous plate manufactured according to any of steps S7 to S10 includes a first layer 135.1 and a second layer 135.3 in the inner region, and a third layer 135.2 of a different material (e.g., SiO2). The membrane region of the corresponding porous plate 73.1 thus includes a layer of different material between the first section 101.1 and the second section 101.2. In the example, a section of the inner sidewall of at least one of the plurality of wells has a curved shape.

[0101] Figure 9 and 10The manufacture of a porous plate according to an embodiment of a first porous plate example is shown. Steps S1 to S10 should not be understood as continuous steps that must be in order 1 to 10. Those skilled in the art understand that other sequences including steps selected in a particular order are possible, as well as variations of individual steps or combinations with other steps not described herein. For example, an electrode layer 114 is deposited on the back surface or exit surface 107 of the porous plate in step S1, and is etched through the electrode layer 114 with the same photolithography mask in step S2 to form an etching stop ring. In another example, an absorption layer 99 is formed at the incident side 74 in step S7 before the RIE etching of the hole 141. Using this process, a multilayer porous plate is etched at one time, reducing the alignment error between several photolithography processes and etching processes, further improving the performance of the porous plate. Layers of different materials are etched at one time, for example, including SiO2, SiNx, silicon and metal layers based on fluorescent plasma etching (RIE or DRIE) and wet or gas chemical etching. In addition, alignment marks or holes as described below can be structured and manufactured together with the holes using the same photolithographic mask and etching process as described above. The manufacturing method including steps S1 and S10 described in the example of the first porous plate 73.1 is generally also applicable to the porous plate used in the multi-beam grating unit according to the embodiment of the present invention.

[0102] The second porous plate according to an embodiment comprises electrodes to form electrostatic elements during use to influence the emitted plurality of charged particle beamlets. In an embodiment, the second porous plate is configured as a porous plate comprising at least first and second sections 102.1, 102.2, similar to the first porous plate described above. The second porous plate comprising at least first and second sections 102.1, 102.2 is manufactured by a manufacturing process comprising the process steps described above. Figure 11 An example of a second porous plate 73.2 comprising at least a first section and a second section is shown. The second porous plate 73.2 comprises a first section 102.1, a second section 102.2, both comprising, for example, doped silicon as bulk material, and an isolation etch stop layer 305, for example made of SiO2, located therebetween. The first section 102.1 comprises an electrode 79.3, for example a ring-shaped electrode around the holes 85.31, 85.32, which is connected to a voltage supply 47.1 or 47.2 (see FIG. 1 ) via a connection 175 (only one shown). Figure 1In other examples, the second porous plate includes multiple electrodes for use as an stigmator or deflector as described above. Electrode 79.3 is isolated from bulk material 183 by an isolation gap 309 filled with an insulating material, such as SiO2. On top of bulk material 183, such as silicon, and electrode 79.3, such as metal or silicon, is an isolation layer 311, in which, for example, wire 175 is embedded and isolated. On top of porous plate 73.2 is a shielding layer 177. The thickness L3 of first section 102.1 is in the range of 30 μm ≤ L3 ≤ 50 μm.

[0103] The thickness L7 of the second segment 102.2, separated by the isolation etch stop layer 305, is between 100 μm and 400 μm. The apertures in the second segment of the second porous plate 73.2 have an entrance diameter of D3 between the electrodes 79.3, and optionally have a larger diameter D7 in the second segment. As explained above in conjunction with manufacturing steps S7 to S10, the isolation etch stop layer 305 allows for double-sided processing of apertures 85.31 and 85.32. Consequently, the position and diameter of the apertures are controlled with very high precision, and the segments of apertures 85.31 and 85.32 are matched to within an accuracy of less than 1 μm. The thick second segment 102.2 is connected to a given potential, such as ground, and serves to limit the electrostatic field generated during use, improving the performance of multiple electrostatic components while reducing crosstalk between adjacent electrostatic components. The distance between the bottom or beam exit side 107 and the electrostatic components is increased, so that during use, the electrostatic field is shielded from negative external influences in the apertures of the second segment, having a diameter of D7.

[0104] In the double-sided treatment according to steps S7 to S10, for the structured porous plate (see Figure 10 ) Residual alignment errors between the etching masks 137 and 139 on both sides will cause residual aberrations in the electrostatic element during use. The residual aberrations caused by alignment errors can be minimized by the third segment in the second porous plate. Figure 12 An example of a second multiwell plate comprising at least a first section and a second section is shown. Figure 12Second porous plate 73.2 shows a first segment 102.1, a second segment 202.2, and a third segment 102.3 arranged between the first and second segments. The three segments 102.1, 102.2, and 102.3 are separated by isolation etch stop layers 305 and 313. Manufacturing process steps S7 through S10 are used for fabrication. The third segment is etched from above to form the inner sidewalls of third segment 102.3 in conjunction with the inner sidewalls of first segment 102.1, which have a diameter D3. The apertures of second segment 102.2 have a larger diameter D7 to minimize electron scattering. The thickness of first segment L3 is approximately 30 to 50 μm, the thickness of third segment L8 is approximately 20 to 50 μm, and the thickness of third segment L7 is approximately 50 to 300 μm. The distance between the bottom, or beam exit side 107, and the electrostatic components is increased, thereby shielding the electrostatic field from negative external influences during use within the apertures of second segment 102.2, which have a diameter D7. The configuration of third segment 102.3 adjacent to first segment 102.1 and the inner sidewalls of the aperture formed between first segment 102.1 and third segment 102.3 improve the precision of the electrostatic element during use, reducing the negative effects of the approximately 1 μm misalignment dx formed by the aperture in second segment 102.2 (formed by deep backside processing). During use, the electrostatic field extends through the aperture section of third segment 102.3, precisely aligning with the aperture section in first segment 102.1 and shielding the electrostatic field in third segment 102.3 from external influences. The aperture diameter D7 in second segment 102.2 is greater than D3, for example, greater than 10 μm, so that a misalignment dx of approximately 1 μm has no effect and reduces scattered electrons. In the above example, holes 85.31 and 85.32, 85.41 and 85.42 are etched at once through at least some of the layers and segments formed in second porous plate 73.2 using a single photolithographic mask and dry etching step to form holes in upper spacer (isolation layer 311), first doped silicon layer (bulk material 183), isolation etch stop layer 305, and third isolation layer. In the example, the diameter D7 of the hole in second segment 102.2 is the same as the diameter D3 of the hole in first segment 102.1, and holes 85.31 and 85.32, 85.41 and 85.42 are etched at once through second porous plate 73.2 using a single photolithographic mask and dry etching step.

[0105] By manufacturing the porous plate from two separate sections, critical hole openings can be manufactured on the incident and exit sides of the porous plate with high lithographic accuracy, thereby manufacturing a multi-beam grating unit with high precision and less impact of manufacturing inaccuracies on the optical performance of the electrostatic element. By manufacturing holes with curved sidewalls that are tilted away from the transmission sub-beams of the charged particles, the multi-beam grating unit can be manufactured with high precision and less impact of manufacturing inaccuracies on the optical performance of the electrostatic element. Further improvements can be achieved by improving the manufacturing method of the holes. For example, in step S4, a through hole 127 with cylindrical sidewalls is etched in silicon by a DRIE method, and the roughness of the hole edge and sidewalls is still about 100-500nm rms. Scattering reduces the small thickness L1.1 of the first section 101.1 below 10μm (preferably below 5μm). In an embodiment, a method is provided for significantly reducing the roughness of about 100nm rms by controlling the smoothing of the sidewalls by thermal oxidation of the silicon surface and removal of the formed silicon oxide layer. Oxidation removes the larger surface bumps in the sidewalls. This roughness is reduced by more than a factor of two by applying a smoothing-then-oxidation process. Consequently, after applying the smoothing-then-oxidation process, the surface roughness of approximately 100 nm is reduced to below 50 nm rms, for example, 25 nm rms. First, hole 127 is formed by DRIE etching, reducing its pore diameter, for example, by 0.5 μm-1 μm. A silicon oxide layer is formed by a heat treatment for a predetermined time, and the surface layer of the silicon substrate is oxidized. The thickness of the silicon oxide layer is controlled by the oxidation time, so a 1 μm-2 μm oxide layer can be formed, for example. The silicon oxide layer is removed by etching in HF acid, thereby increasing the pore diameter in the silicon by approximately 0.5-1 μm, thereby achieving a pore sidewall with a roughness below 50 nm rms and the desired pore diameter. In some examples, the smoothing-then-oxidation process can be repeated to achieve a surface roughness of the inner sidewall below 25 nm rms, or even below 10 nm rms. Furthermore, the doping and doping concentration of the pore sidewalls and near the sidewall surfaces are altered by oxidation. Thus, scattering in the sidewalls of the first section 101.1 of the porous plate of small thickness L1.1 is further reduced. Smoothing-then-oxidation can also be applied to at least the other holes in the section of the porous plate. In the example, the roughness of the inner sidewalls of the hole carrying the electrode is reduced by smoothing-then-oxidation, thereby reducing aberrations of the electrostatic element during use.

[0106] Advanced MCPM requires a complex multi-beam generating unit or a multi-beam deflecting unit. In an embodiment of the present invention, the multi-beam grating unit 71 (such as the multi-beam generating unit 27 or the deflector unit 41) is formed by stacking at least two porous plates and spacers, but the advanced multi-beam generating unit or the multi-beam deflecting unit comprises a larger number of porous plates, for example more than 3 or even more than 5 wafers or plates stacked on each other and having a large extension in the z direction. For the individual and precise shaping and correction of each of the multiple transmitted charged particle beams, more than two porous elements are required. An example of a multi-beam generating unit comprises a first porous plate, a second focusing porous lens array, a third aberration correcting porous stigmator, a fourth field curvature correcting porous lens array, a fifth deflecting porous deflector to correct for telecentricity. Many different orders of the porous elements are possible and the numbering should not limit the order of the porous plates. In the example of a multi-beam generating unit, a first porous plate for the multi-beam generating unit 73.1 is arranged in sequence upstream of a fourth field curvature correcting porous lens array (such as porous plate 73.2), and two third aberration correcting porous stigmators (such as porous plate 73.3), which together act as stigmators and deflectors, and finally followed by a focusing porous lens array and a global lens (such as element 84). Precise alignment between at least the first and second wafers is achieved, for example, by mechanical alignment or attachment structures provided on the first and second wafers bonded to each other, respectively. The alignment or attachment structures are manufactured with photolithographic precision and have an accuracy of less than 1 μm or even less than 0.5 μm. The alignment or attachment structures are formed to maintain a predefined gap between the wafers, such as a predefined distance L2 between the lower surface or bottom surface of the first porous plate 73.1 and the second porous plate 73.2. In an embodiment, the multi-beam generating unit or the multi-beam deflector unit comprises spacers to define, for example, the distance L2 with high precision. For example, the multi-beam generating unit comprises four spacers with a thickness of 10 μm. The separation S between a multiwell plate and a subsequent multiwell plate is thus maintained in a given range S (10 μm≤S≤30 μm) with a high accuracy below 1 μm or even below 0.5 μm.

[0107] In an embodiment, precise lateral alignment with a lateral accuracy of less than 1 μm is achieved through active 3D alignment of multiple porous plates. The z-position and z-distance of the wafers in the stack can be precisely controlled by planar fabrication of the wafers and the use of spacers. Lateral alignment relative to the transported charged particle beam is achieved through active lateral alignment and fixation in the aligned state. Active alignment can be achieved by lateral displacement of the wafers forming the porous plates, for example with the aid of 3D alignment marks extending over a large z-distance. Figure 13An embodiment in an example is illustrated. A multi-beam grating unit 71 (such as a multi-beam generating unit or a multi-beam deflecting unit) comprises four porous plates 151.1 to 151.4, which are manufactured, for example, as described according to one of the above embodiments, and a support unit 153. At least some of the porous plates 151.1 to 151.4 have an inner region (which forms a membrane 123 with a thickness of about 10 μm-50 μm), which inner region has a plurality of holes 157 (only five are shown), and a support region 121 around each inner region 123. Each support region 121 of each porous plate 151.1 to 151.4 has a z extension Z1 to Z4 in the direction of transmission of the charged particle beam, each of which is in the order of 100 μm or even higher. The porous plates 151.1 to 151.4 are attached to one another in a specific order with mechanical precision on the order of several μm in lateral position. To achieve even more precise alignment, at least each subsequent pair of porous plates 151.1 to 151.4 includes at least two alignment holes A1 to A4, or alignment marks, produced with the precision of a photolithographic process along at least two alignment axes 155.1 and 155.2. The diameters A1 to A4 are selected to be between 50 μm and 200 μm. The thickness of the membrane in the inner region and the thickness of the spacers of each porous plate are between 10 μm and approximately 100 μm. By configuring the porous plates with membranes in the inner region 157 and support areas 121 of different diameters, the porous plates 151.1 to 151.4 can be stacked with membranes spaced closely together, with the z-extension ZA between the first alignment hole A1 and the last alignment hole A4 being between 75 μm and several 100 μm. In this example, the diameter O4 of the 4th orifice plate 151.4 is configured to be little so that the 4th orifice plate 151.4 can be attached to the film of the 3rd porous plate 151.3. First, the 3rd porous plate 151.3 is attached to the second porous plate 151.2 to realize the higher mechanical stability of the film of the 3rd porous plate 151.3. After this, the 4th porous plate 151.4 is attached to the film of the 3rd porous plate 151.3 with enhanced stability. Alignment holes A1 to A4 are therefore shaped in a manner that allows the deep optical alignment of tool with high precision. The precision alignment of the order of 1 μm requires the conventional wavelength of 0.5-0.65 μm, for aligning the optical numerical aperture (NA) of 0.35, which corresponds to the large numerical aperture of the extremely low depth of focus of tool lower than several microns. Therefore, for the porous plate with large z distance, conventional high-precision alignment technology cannot be adopted. The diameters A1 to A4 and positions of the alignment holes are therefore selected to allow deep optical precision alignment of the lowest porous plate 151.4 through the upper porous plates 151.1 to 151.3, with an accuracy better than 1 μm, preferably 0.5 μm, and an optical microscope with a low NA of about 0.1 and below, and a depth of focus greater than 30 μm, for example 75 μm, where the NA is below 0.07.The aperture diameters A1 to A4 thus increase in reverse order from A4 to A1, allowing, for example, the half-aperture angle B to be limited to approximately 6°-8°. When viewed through the alignment axis in the z-direction with an optical microscope, apertures A1 to A4 are visible, enabling precise alignment despite the large distance ZA over which the alignment apertures A1 to A4 extend, even though the microscope's resolution is only on the order of a few μm, for example, 3 μm. Lateral accuracies of 1 μm or even 0.5 μm are achieved by edge detection and image processing of images of circular apertures with diameters A1 to A4, formed with photolithographic precision to an accuracy of better than 100 nm. The centers of the circular apertures A1 to A4 are thus accurately determined. Lateral alignment is performed by lateral motion via a precision actuator under optical monitoring until concentric rings formed by precisely aligned apertures A1 to A4 are achieved. Figure 13 The diagram is simplified in the lower part of .

[0108] Figure 14 Another example of an embodiment is shown. The multi-beam grating unit 71 (multi-beam generating unit or multi-beam deflecting unit) comprises five porous plates 151.1 to 151.5 and a support unit 153, which are manufactured, for example, as described according to one of the above embodiments. At least some of the porous plates 151.1 to 151.5 have an inner region 123 and a support region 121 around each inner region 123, the inner region 123 forming a membrane with a thickness of about 10 μm–50 μm, which has a plurality of holes 157 (only five are shown). Each support region of each porous plate 151.1 to 151.5 has a z extension Z1 to Z5 in the direction of the transported charged particle beam, each of which is in the order of 100 μm or even more. The multi-beam generating unit or multi-beam deflecting unit (multi-beam grating unit 71) comprises at least one porous plate with a thick membrane (such as Figure 14 The thickness of the thick film is higher than 100 μm, for example 400 μm, as for example according to the combination Figure 11 and 12 The second porous plate 73.2 of the example is explained. The thickness of the other membranes in the inner zone and the thickness of the spacers used for each porous plate is between 15 μm and about 100 μm. In order to achieve more precise alignment, each of the porous plates 151.1 to 151.5 includes at least two alignment holes A1 to A5, which are manufactured along at least two alignment axes 155.1 and 155.2 with the precision of a photolithographic process. The alignment holes A1 to A5 are shaped in a way that allows deep optical alignment with high precision. The diameter A1 to A5 and the position of the alignment holes are therefore selected to allow deep optical precision alignment. The lateral alignment is performed by lateral movement via a precision actuator under optical monitoring until concentric rings formed by the precisely aligned holes A1 to A5 are achieved. In this Figure 14Several alignment holes can be placed in parallel to achieve alignment in two transverse coordinates and individual precision alignment between selected multi-well plates. For example, two or more alignment holes or marks (e.g. comprising relative alignment structures) are provided with at least one circular hole (e.g. referring to FIG. Figure 13 and Figure 14 As described above, it is etched with photolithographic precision through at least two of the porous plates, which have increasing hole diameters in the direction of the alignment axis in at least two of the porous plates. Because precision alignment using image processing requires that the hole diameters match the image field of the microscope, the conical opening used for observation must allow an opening angle corresponding to the numerical aperture of the microscope, for example a half-opening angle greater than 6°, and the diameter of the see-through hole in the upper porous plate may be too large for aligning the upper porous plate with sufficient precision below 1 μm. If the diameters A2 and A3 of the porous plates 151.2 and 151.3 used for deep alignment of the lower porous plates 151.4 and 151.5 are too large for precision lateral alignment, a second alignment structure with smaller diameters A1 and A2 is provided for aligning the upper porous plates 151.2 and 151.3, which is parallel to the first hole used for aligning the deeper porous plates 151.4 and 151.5. In Figure 15 An example is shown in FIG. The two lower porous plates 151.2 and 151.3 are aligned with each other from above (in the positive z-direction) on an alignment axis 155.3, wherein the large holes passing through the porous plate 151.1 with the large hole diameter A1.1 and the thick second porous plate 151.2 with the large hole diameter A1.1 are reduced or lowered 160 to reduce the z distance ZA3 of the alignment marks with the diameters A2.3 and A3.2 to less than 30 μm, thereby allowing mutual optical alignment of the deep alignment edges of the porous plates 151.2 and 151.3, with a z distance of approximately 30 μm, a half-opening angle B1 of approximately 8° and a lateral accuracy of less than 1 μm. The first two upper porous plates 151.1 and 151.2 (which require a very precise lateral alignment, e.g., with a lateral accuracy of about 0.5 μm) comprise additional alignment marks of diameters A1.2 and A2.1 on the second alignment axis 155.4, which are only used to align the first and second porous plates. The first porous plate also has a first reduction or lowering 160 to reduce the z distance ZA2 of the alignment marks of diameters A1.2 and A2.1 to less than 30 μm. The larger opening angle B2 of about 10° is achieved by this reduction or lowering 160 with the larger diameter A0.2. Figure 15Optical alignment in the negative z-direction of the coordinate system indicated, using alignment marks with diameters A3.4 and A4.3, can achieve a third mutual alignment of the lower porous plates 151.3 and 151.4 from the back side. For alignment from the back side, the alignment mark diameter A3.4 of the porous plate 151.3 is selected to be smaller than the alignment mark diameter A4.3 of the porous plate 151.4, and the alignment mark diameter A4.3 of the porous plate 151.4 is selected to be smaller than the through-hole with diameter A5.4 in the lower porous plate 151.5, allowing a half-opening angle B3 of about 8° for optically aligning the porous plates 151.3 and 151.4 with an accuracy of about 1 μm in 3D. Alignment from the back side or bottom side is advantageous if, for example, the exit side of the porous plate is covered with a metal film having a higher reflectivity than silicon or SOI. In the example, the surface of the second multi-well plate (to which the first multi-well plate having an alignment hole of diameter A1 is aligned) contains alignment marks, such as circular holes or reflective (metal) structures having a diameter A2 that is smaller than diameter A1. The reflective structures (e.g., circular structures) ensure high contrast and brightness and allow alignment in deep alignment holes.

[0109] After achieving a lateral 3D alignment with an accuracy of 1 μm or less, at least a pair of multiwell plates or the entire stack of multiwell plates is fixed by a fixing technique (such as by clamping, gluing or adhesive bonding). Using a directional etching process, each well is axisymmetric (along the well axis) and parallel to the alignment axis, which is Figure 13 and 14 3D alignment structures are provided at at least two locations of the multiwell plate to allow alignment in the lateral direction as well as in rotation.

[0110] After design, manufacture and assembly according to one of the above-described embodiments, the multi-beam grating unit is manufactured with high precision and with little impact of manufacturing inaccuracies and deviations on the optical properties of the electrostatic element. However, the optical properties of the electrostatic element decrease during use (e.g. bending or deformation of the membrane during use), resulting in, for example, curvature of the focal plane of the multiple charged particle sub-beams or deviations from the telecentricity properties of the multiple sub-beams. The telecentricity property is generally the beam aiming of each of the multiple sub-beams. A perfect sub-beam group is concentric or telecentric, which means that the multiple sub-beams converge to a single coincidence point or diverge from a single coincidence point. Strictly speaking, telecentricity means that the convergence point is at infinity and the sub-beams all propagate in parallel, e.g. parallel to the z-direction. Deviations from the telecentricity property are deviations of individual sub-beams from a predefined coincidence point. The multibeam grating unit is designed for a specific shape of the field plane (intermediate focal surface 29) (e.g., a planar shape or a spherical shape), or for specific telecentricity properties (e.g., multiple completely parallel sub-beams or multiple sub-beams with a predefined coincidence point). In an embodiment, the multibeam grating unit includes a deformable membrane with passive or active deformation of the membrane to achieve the predefined shape of the field plane (intermediate focal surface 29) or the specific telecentricity properties. Using a capacitive sensor, membrane deformation caused by, for example, thermal effects or active membrane deformation as described below can be monitored.

[0111] Passive deformation is achieved, for example, by applying a coating of a specific thickness. The coating contributes compressive or expansive stress to the coated element, and the coated element is deformed into a convex or concave shape. According to an embodiment of the present invention, the deformation of the porous plate is measured after manufacturing, and the film thickness of the stress compensation film is determined to introduce a specific amount of deformation into the porous plate. The film is deposited on the porous plate and thereby compensates for undesired deformations, or achieves a predetermined deformation in the porous plate. The stress compensation layer can, for example, be a SiNx layer with a thickness between 100 nm and 1 μm. By this method of stress engineering with an additional stress compensation layer, a passive deformation between 20 μm and 30 μm in the z direction is achieved with an accuracy of less than several 1 μm, for example less than 1 μm.

[0112] In an embodiment, active deformation is achieved by electrodes on at least two porous plates or using existing electrodes and applying a voltage difference to the electrodes to deform at least one of the membranes in the inner region of a porous plate. In another embodiment, active deformation of the membrane of the porous plate is achieved by heating or cooling a membrane having different thermal expansion layers (such as a metal layer). In another example, active deformation of a membrane comprising holes or electrodes to form an electrostatic element is achieved by an actuator in the support area of ​​the membrane, which generates a bending force on the membrane in the inner region of the porous plate during use. Thus, during use, active deformation with an accuracy of less than 1 μm between 20 μm and 30 μm in the z direction is achieved.

[0113] Figure 16 The diagram illustrates an example of a deformable membrane 161 with deformation control. In a multi-beam grating unit 71, the membrane 161 of the second porous plate 73.2 is deformed in the inner region 123 according to a predetermined deformation to achieve field curvature. The designed deformation is achieved by stress engineering with a SiNx coating 163 having a predetermined thickness. A capacitive sensor 165 monitors the deformation of the membrane 161 in the inner region 123 of the second porous plate 73.2, thereby controlling the distance from the membrane 171 of the first porous plate 73.1. During use, the deformation is varied by an actuator 169 (e.g., a piezoelectric actuator), which introduces a bending force into the outer periphery of the membrane 161. The designed field curvature is thus achieved and maintained during use through passive and active deformation of the membrane 161.

[0114] During use, an incident beam of charged particles is absorbed or transmitted through multiple holes in a first porous plate and forms a plurality of sub-beams. The plurality of sub-beams pass through the multiple holes of a plurality of subsequent porous plates and each sub-beam is focused, aberration corrected or deflected in a predetermined manner by the electrostatic elements as described above. Even with the improved design and manufacture as described above, some charged particles are still scattered and absorbed at, for example, the upper surface or beam incident surface or the inner sidewalls of the holes of the second or third porous plates. Scattered charged particles can generate x-rays. During use, the absorbed charged particles or x-rays generate, for example, surface charges in the isolator, which have a negative impact on the electrostatic elements and thus introduce aberrations. In a further improvement of an embodiment of the present invention, a design and manufacturing method is provided to reduce the absorption of charged particles. According to the improvement, in addition to the conductive and absorption layer 99 on the beam incident side of the first porous plate, a conductive layer is provided on the beam incident side of the second and further subsequent porous plates of the multi-beam grating unit. In an example, the isolators of the electrostatic components (which are positioned near the edges of the plurality of holes and serve to isolate the electrodes, wiring connections, and substrate) are shielded with a conductive shielding layer. Figure 17, an example of a first section 102.1 of a second porous plate 73.2 is shown. The second porous plate 73.2 includes an inner region or membrane having a plurality of holes 85.21 and 85.22 (only two are shown) and annular electrodes 79 and 79.2 arranged around the holes 85.21 and 85.22. The holes are aligned with the plurality of holes of the first porous plate to transmit the plurality of charged particle beamlets 77.4 (only one is shown). The annular electrodes are isolated from the bulk silicon or SOI substrate (bulk material 183) via an isolation gap 185, such as by an isolation material, silicon oxide. Each annular electrode 79, 79.2 is electrically connected to a voltage supply via an electrical connection 175, 175.2 to a voltage support (not shown) and is isolated from the substrate (bulk material 183) by an isolation material 179 (e.g., silicon oxide). The connection 175, 175.2 can be from the upper or lower side of the second porous plate, or alternately from electrode to electrode from both sides. This insulating material 179 extends over the wiring 175, completely covering the wiring 175, the electrode 70, and the bulk material 183 on the upper side. The inner sidewall of the electrode 79 is not covered by the insulating material 179. A conductive shielding layer 177 is formed on the insulating material, which forms the beam entrance surface or upper surface 173 of the second porous plate. The conductive layer is inserted into the hole with an insert extension 189, and a small isolation gap 181 is formed between the conductive shielding layer 177 and the electrode 79.1, thereby isolating the conductive layer 177 from the electrode 79.1. The conductive layer 177 is connected to a large capacity, such as ground (U = 0V). During use, scattered charged particles 187 are thus absorbed by the conductive shielding layer 177 and conducted away, avoiding interference with surface charges. Using the conductive layer 177 connected to the large capacity creates a stable electrostatic element during use. Surface charges in the small isolation gap 181 dissipate due to the small distance of the isolation gap 181. Thus, the surface charge is reduced to less than 10% during use compared to a conventional second porous plate. After passing through the first porous plate, any scattered and secondary particles formed by the transmission of the charged particle beamlet 77 have lower kinetic energy, and the conductive shielding layer 177 made of metal (e.g., aluminum) has a lower thickness or density than the conductive absorption layer 99 of the first porous plate 73.1, and the scattered charged particles are absorbed and guided away. In the example, the multilayer electrodes 79 and the shielding layer 177 of the electrostatic element are realized by an "etching at once" method, which uses the same hole ( 177 ) as the hole 85.2. Figure 17The invention relates to a method for producing a plurality of electrostatic elements with a plurality of holes 73.2 and 73.2, wherein the plurality of holes 73.2 and 73.2 are formed by etching the shield layer 177 with the extension 189 inserted into the inner wall of the electrode 79. The invention also ...

[0115] In order to enhance the performance of the multi-beam charged particle microscope during use, individual focus corrections are provided, for example, by using a plurality of individually controlled annular electrodes 79, or a plurality of individually controlled electrodes of an stigmator or deflector, to individually control each of the plurality of charged particle beamlets. Individual control of the plurality of electrodes is provided by wiring, with additional wiring provided for the shielding and absorption layers described above, for the capacitive sensors and actuators described above, or for other sensors. A multi-beam grating unit for a plurality (e.g., 100) of beamlets comprises about 1000 or more electrodes, having about 1000 or more individual wiring connections. The electrodes and the shielding or absorption layers require drive voltages of varying magnitudes, for example, between 10 V and up to 1 kV. For example, multiple focus corrections require 100 high voltage wirings for about 200 V, and multiple astigmatism corrections require, for example, 800 low voltage wirings for several volts with very low noise, and the absorption layers generate high currents. Wirings with such voltage differences can easily affect each other and thereby reduce the performance of the multi-beam grating unit. In an embodiment, the multi-beam grating unit includes design features and structures to minimize the effects of voltage differences. The multi-beam grating unit includes a mixed signal architecture for different voltages and currents. The high voltage is provided by an external controller. The low voltage is provided to the external controller using a digital interface via an ASIC placed in a vacuum. The routing of the signal and voltage supply is achieved via a UHV-Flange (ultra-high voltage flange). The separation of wirings with different voltages is achieved by supplying voltages from different directions. In the first direction (z direction) of the transporting charged particle beamlet, for example, the low voltage is supplied from the second direction (x direction) and the high voltage is supplied from the third direction. A high current connection to the absorption layer can be provided from a fourth direction (for example from the z direction or parallel to the third direction). All wirings can be shielded individually, or the low voltage supply wiring can be shielded in groups of low voltage wirings. Fewer high voltage wirings can be provided at a greater distance. In an embodiment, the wire connections to the ring electrodes for the electrostatic lens are provided alternately from top to bottom and from electrode to electrode in order to keep the distance between the wires as large as possible. Figure 18The diagram illustrates an embodiment in one example. A multibeam grating unit 71 (comprising five porous plates 73.1 to 73.5, each having a membrane arranged in parallel in a membrane region 199 and a support structure in a support region 197) is mounted on a support plate 153. High-voltage wiring connections 201 are provided in the positive and negative y directions via the support structure and the support plate to the annular electrodes of the electrostatic lens in at least one of the porous plates having a plurality of holes 195 (only 4 x 5 are shown; 91, 100, 300, or more holes could be provided). This high-voltage wiring connection is shielded by a ground wire 203, which is connected to ground. In the peripheral region, the high-voltage wiring is shielded by a coaxial shield and spacer 205 (four high-voltage wiring connections and coaxial shields are shown; reference numerals 201 and 205 designate only one). Low-voltage wiring connections 207 and 209 for the electrostatic stigmator and deflector are provided in two x directions (only the positive direction is shown) from ASICS 211 and 215 mounted on the support plate 153. The low-voltage wiring is also shielded from each other by a ground connection (not shown) between the low-voltage wiring. The ASICs receive digital signals via digital signal lines 217.1 and 217.2, and receive power via low-voltage supply lines 219.1 and 219.2. This keeps high-voltage and low-voltage signals as separate as possible, reduces the negative effects of mutual leakage inductance, and achieves more reliable optical performance of the multi-beam grating unit.

[0116] Figure 19 Schematically illustrated are a plurality of low voltage wiring connections 207 of the porous plate 73.3, comprising a plurality of stigmators or deflectors, which during use are formed by eight electrodes 81.1 ... 81.8 for each of the plurality of holes 85 (reference numerals 85.1 and 85.2 designate only two) in a hexagonal grating arrangement with a pitch P1. The electrodes at 0°, 90°, 180° and 270° orientations are connected in the x-direction and on the beam entrance side of the porous plate 73.1 to the peripheral ASICS 211, 215 (see Figure 18 ), which is Figure 19 The correction electrodes at 45°, 135°, 225° and 315° orientations are connected to the peripheral ASICS 211, 215 in the x-direction and on the back side or different layers of the porous plate 73.3 (see Figure 18 ), so in Figure 19 During use, low voltages in the range of 5V-100V are applied to the electrodes in the x-direction. This low voltage is separate from a high voltage applied to, for example, the first porous plate, which is supplied in the y-direction.

[0117] The multibeam grating unit of the embodiment is described in the context of an illumination beam path with charged particles propagating in the positive z-direction, which is pointing downwards. However, the multibeam grating unit can also be applied in an imaging beam path, in which the charged particle beamlets are directed in the positive z-direction. Figure 1 The order of the porous plates is still the same as that in the propagation direction of the charged particle beam or beamlet. The beam entrance side or top side is understood to be the first surface or side of the element in the direction of the propagation of the charged particle beam or beamlet, and the bottom side or beam exit side is understood to be the final surface or side of the element in the direction of the propagation of the charged particle beam or beamlet.

[0118] Although the multibeam barrier unit according to the present invention is described in some embodiments as a multibeam generating unit, features of the embodiments may also be applied to other multibeam barrier units according to the present invention, such as a multibeam deflector or a multibeam stigmator unit.

[0119] Features of an embodiment improve the performance of a multi-beam charged particle microscope to achieve a higher resolution of less than 5 nm, preferably less than 3 nm, more preferably less than 2 nm or even less than 1 nm. The improvement is particularly relevant for the further development of multi-beam charged particle microscopes with a larger number of multiple beamlets, such as more than 100 beamlets, more than 300 beamlets, more than 1000 beamlets or even more than 10000 beamlets. Such multi-beam charged particle microscopes require multi-well plates with larger diameters and a larger number of holes and electrodes, including, for example, even more wiring connections. The improvement is particularly relevant for conventional applications of multi-beam charged particle microscopes, such as in semiconductor inspection and review, where high reliability and high reproducibility, as well as low machine-to-machine variations, are required.

[0120] Embodiments provide a charged particle beam system that operates with multiple charged particle beams and can be used to achieve higher imaging performance. Specifically, a narrower range of resolution is achieved for each of the multiple beamlets. Utilizing the features and methods described in the embodiments, and combinations thereof, each of the multiple beamlets has a beamlet diameter, for example, spanning from 2 nm to 2.1 nm, with an average resolution of 2.05 nm, and the range of resolution achieved by the features and methods of the embodiments is less than 0.15%, preferably 0.1%, and even more preferably 0.05% of the average resolution.

[0121] The present invention is not limited to the above-mentioned embodiments. The embodiments may be combined with each other in whole or in part. As can be seen from the above explanation, various changes and modifications are possible, and it is obvious that the scope of this application is not limited by the specific embodiments.

[0122] Although the improvements are described with the example of a multi-beam charged particle microscope, the improvements are not limited to multi-beam charged particle microscopes but can be applied to other multi-beam charged particle systems, such as a multi-beam photolithography system.

[0123] In all embodiments, electrons are generally understood to be charged particles. Although some embodiments are explained with the example of electrons, they should not be limited to electrons, but can be applied to various charged particles, such as helium or neon ions.

[0124] A list of reference numerals is provided:

[0125] 1 Charged particle system

[0126] 3 Lighting system

[0127] 5 Beamlet collection of charged ions

[0128] 7 Image plane

[0129] 9 samples

[0130] 11 Imaging System

[0131] 13 Spatially Resolved Charged Particle Detector

[0132] 15 Secondary charged particle beamlet collection

[0133] 17 Object Plane

[0134] 19 Detector plane

[0135] 21 Source Unit

[0136] 22 Charged Particle Emitters

[0137] 23 Scattering beams of charged particles

[0138] 25 Condenser System

[0139] 27 Multi-beam generating unit

[0140] 29 Intermediate focal surface

[0141] 31 Multiple Focuses

[0142] 33 Imaging element

[0143] 35 Imaging System

[0144] 37 Objective lens system

[0145] 39 Imaging element

[0146] 41 Multi-beam deflector unit

[0147] 43 operating units

[0148] 45 Multi-beam grating control unit

[0149] 47 Local Control Unit

[0150] 49 signal processing unit

[0151] 51 control unit

[0152] 65 beam splitting and combining units

[0153] 67 Global Deflection Unit

[0154] 69 Imaging Element

[0155] 70 Incident electron beam

[0156] 71 Multi-beam grating unit

[0157] 73.1, 73.2, 73.3, 73.5 porous plates

[0158] 74 Beam incident or upside

[0159] 75.1, 75.2, 75.3 Openings or holes

[0160] 77, 77.1, 77.2 Multi-electron beamlet

[0161] 79 Ring Electrode

[0162] 80 electrostatic lens elements

[0163] 81.1, 81.2 Electrodes

[0164] 82 electrodes

[0165] 83.1, 83.2, ...83.3 spacers

[0166] 84 Planar Components

[0167] 85 holes

[0168] 87 inner wall

[0169] 89 Outer contour of hole

[0170] 91 Ideal Circle

[0171] 93 Deviation of electrostatic field

[0172] 95 Scattered Electron Trajectory

[0173] 97 Electron beam trajectory

[0174] 99 Conductive Absorption Layer

[0175] 101.1, 101.2, 101.3 Segment of the first perforated plate

[0176] 102.1, 102.2, 102.3 Segment of the second perforated plate

[0177] 103 Tangential vector in the xz plane

[0178] 105 Axis of symmetry of hole

[0179] 107 Bottom side or beam exit side

[0180] 108 conductive material layer

[0181] 109 Etch Stop Ring

[0182] 111 Fixing or attachment points

[0183] 114 electrodes

[0184] 115.1, 115.2 Adjustment elements

[0185] 117 First layer support structure

[0186] 119 Second layer support structure

[0187] 121 support zone

[0188] 123 Inner or membrane region

[0189] 125 Structure in the form of a spherical segment

[0190] 127 through holes

[0191] Layers 129.1, 129.2, and 129.3

[0192] 131 Etch stop mask

[0193] 133 circular opening

[0194] 135.1, 135.2, 135.3 layers

[0195] 137 first etch stop layer

[0196] 139 second etch stop layer

[0197] 141 circular opening

[0198] 143 circular opening

[0199] 151.1, 151.2, ..., 151.5 porous plates

[0200] 153 support unit

[0201] 155.1, 155.2, 155.3, 155.4 align with the axis

[0202] 157 multiple holes

[0203] 160 reduce or lower

[0204] 161 Deformation membrane of the second porous plate

[0205] 163 SiN coating

[0206] 165 Capacitive Sensor

[0207] 169 Actuator

[0208] 171 Membrane of the first porous plate

[0209] 173 Beam incident or upper surface of the second porous plate

[0210] 175 Electrical wiring

[0211] 177 Conductive shielding layer

[0212] 179 Isolation Materials

[0213] 181 Isolation interval

[0214] 183 body materials

[0215] 185 Isolation Gap

[0216] 187 Scattering Particles

[0217] 189 Extension

[0218] 195+ holes

[0219] 197 Support Zone

[0220] 199 membrane area

[0221] 201 High voltage wiring connection

[0222] 203 ground wire

[0223] 205 Coaxial Shielding and Isolation

[0224] 207 Low voltage wiring connector

[0225] 209 Low voltage wiring connector

[0226] 211 ASIC

[0227] 215 ASIC

[0228] 217.1, 217.2 digital signal lines

[0229] 219.1, 219.2 Low voltage supply lines

[0230] 305 Isolation Etch Stop Layer

[0231] 309 Isolation Gap

[0232] 311 Isolation Layer

[0233] 313 Etch stop or isolation layer

Claims

1. A multi-beam grating unit configured to form, during use, a plurality of electrostatic elements for influencing a plurality of transmitted sub-beams of charged particles, the multi-beam grating unit comprising: - A first perforated plate having an inner region, a beam incident side, and a beam exit side, the inner region forming a membrane having a first thickness L1 and a plurality of first holes, - The membrane of the first perforated plate includes at least a first section and a second section, the first section having a first section thickness L1.1 and having a plurality of cylindrical holes with a first diameter D1 on the beam incident side, and the second section having a plurality of holes with a second diameter D2 on the beam exit side, - A second perforated plate having an inner region and a beam incident side, the inner region forming a membrane having a plurality of second holes, and the plurality of second holes having a third diameter D3 on the beam incident side, - A gap of thickness L2 between the membranes of the first perforated plate and the second perforated plate, - At least a first electrode configured on the beam exit side of the first perforated plate near at least one first hole of the first perforated plate, and - At least a plurality of second electrodes configured on the beam incident side of the second perforated plate near the plurality of second holes of the second perforated plate for forming, during use, the plurality of electrostatic elements between the plurality of first holes of the plurality of first perforated plates and the second holes of the second perforated plate, - Wherein the second diameter D2 is greater than the first diameter D1, and wherein the second diameter D2 is within the range between the second thickness L2 and twice the second thickness L2, so that L2 < D2 < 2*L2, and - Wherein the first section thickness L1.1 is less than 10 μm, and - Wherein the first electrode and each of the plurality of second electrodes are configured to form, during use, electrostatic elements for influencing a plurality of transmitted sub-beams of charged particles.

2. The multi-beam grating unit according to claim 1, wherein: The multi-beam grating unit is a porous unit or a multi-beam deflector or a multi-beam astigmatism corrector.

3. The multi-beam grating unit according to claim 1, wherein: The first section thickness L1.1 is less than 5 μm.

4. The multi-beam grating unit according to claim 1, wherein: The inner wall surface of at least one of the plurality of holes in the second section has a surface shape that slopes away from the transmitted sub-beam of charged particles.

5. The multi-beam grating unit according to claim 4, wherein: The surface shape is a curved surface shape in the direction of the transmitted sub-beam of charged particles.

6. The multi-beam barrier unit according to any one of claims 1 to 5, wherein: The inner wall surface of at least one of the plurality of holes in the second section has a surface shape such that the diameter of the hole opening continuously increases as the z coordinate increases.

7. The multi-beam grating unit according to claim 5, wherein: The surface shape in the direction of the transmitted sub-beam of charged particles is a spherical shape formed by isotropic etching.

8. The multi-beam grating unit according to any one of claims 1 to 5, further comprising an etch stop ring at the beam incident side of the second perforated plate or at the holes at the beam exit side of the first perforated plate.

9. The multi-beam barrier unit according to any one of claims 1 to 5, wherein: In the direction of the plurality of transmitted sub-beams of charged particles, the first perforated plate is arranged in the beam path upstream of the second perforated plate.

10. The multi-beam barrier unit according to any one of claims 1 to 5, wherein: At least a third porous plate is arranged in the beam path upstream of the first and second porous plates in the direction of the plurality of transmission sub-beams of charged particles.

11. The multi-beam barrier unit according to any one of claims 1 to 5, wherein: The surface roughness of the inner sidewall surface of at least one of the plurality of holes in the first section is less than 50 nm rms.

12. The multi-beam grating unit according to claim 11, wherein: The surface roughness is lower than 25 nm rms.

13. The multi-beam grating unit according to claim 11, wherein: The surface roughness is lower than 10 nm rms.

14. The multi-beam barrier unit according to any one of the preceding claims 1 to 5, wherein: The second diameter D2 is within a range between the first section thickness L1.1 and four times the first section thickness L1.1, so L1.1≤D2≤4*L1.

1.

15. The multibeam barrier unit according to claim 14, wherein L1.1≤D2≤3*L1.

1.

16. The multibeam barrier unit according to claim 14, wherein: L1.1≤D2≤2*L1.

1.

17. The multi-beam barrier unit according to any one of claims 1 to 5, wherein: The third diameter D3 is greater than the first diameter D1.

18. The multi-beam barrier unit according to any one of claims 1 to 5, wherein: The third diameter D3 is within a range between the first diameter D1 and the second diameter D2.

19. The multi-beam barrier unit according to any one of claims 1 to 5, wherein: The first porous plate (73.1) comprises an absorption layer (99) on the beam entrance side (74), wherein the absorption layer (99) is connected to ground during use.

20. The multi-beam barrier unit according to any one of claims 1 to 5, wherein: The first porous plate (73.1) comprises a conductive layer (108) on the beam exit side (107), the conductive layer (108) forming the first electrode.

21. The multi-beam barrier unit according to any one of claims 1 to 5, wherein: The beam exit side (107) of the first porous plate (73.1) comprises an annular conductive layer or electrode (114) around or adjacent the aperture of diameter D2, which is connected to a constant voltage potential during use, the annular conductive layer or electrode (114) forming the first electrode.

22. The multi-beam barrier unit according to any one of claims 1 to 5, wherein: The beam exit side (107) of the first porous plate (73.1) does not include a shielding electrode.

23. The multi-beam barrier unit according to any one of claims 1 to 5, wherein: The second porous plate (73.2) comprises an annular electrode (79) arranged around the second holes, wherein during use a driving voltage is applied to the annular electrode (79), the annular electrode (79) forming the second electrode.

24. The multi-beam barrier unit according to claim 23, wherein: The ring electrode extends substantially through the second porous plate (73.2).

25. The multi-beam barrier unit according to any one of claims 1 to 5, wherein: The beam incident side of the second porous plate is covered by a shielding layer, and at least one insertion extension of the shielding layer is inserted into at least one of the holes of the second porous plate.

26. The multi-beam barrier unit according to any one of claims 1 to 5, wherein: The first segment and the second segment are separate segments attached to each other.

27. The multi-beam grid unit according to claim 26, comprising a holder for aligning and adjusting the first section and the second section of the first multi-aperture plate with respect to each other.

28. The multibeam barrier unit according to any one of claims 1 to 5, comprising a holder for aligning and adjusting the at least first and second porous plates with respect to each other.

29. The multi-beam barrier unit according to any one of claims 1 to 5, wherein: At least the membrane of one porous plate comprises a layer of predetermined thickness, said layer causing stress-induced deformation of said membrane.

30. The multibeam barrier unit according to any one of claims 1 to 5, wherein: The multi-well plates each further comprise a support region with a thickness >50 μm and a maximum deviation in thickness of less than 10%.

31. The multi-beam barrier unit according to claim 30, wherein: The thickness of the support area is >100 μm.

32. The multi-beam barrier unit of claim 30, wherein: The multi-well plate further comprises through-holes having different hole diameters A1 and A2 for aligning the first multi-well plate and the second multi-well plate with each other.

33. The multi-beam barrier unit of claim 32, wherein: At least one of the multiwell plates comprises a reduction or lowering at a first through-hole to form a z distance from a corresponding through-hole of an adjacent multiwell plate, wherein the z distance is below 30 μm to achieve mutual alignment of the multiwell plates.

34. The multibeam barrier unit according to any one of claims 1 to 5, wherein: The multiple transmission sub-beams propagate through multiple holes of a multiple porous plates in a first direction, a high voltage supply wiring connection is provided to a first electrode located in at least one of the porous plates from a second direction perpendicular to the first direction, and a low voltage supply wiring connection is provided to a second electrode located in at least one of the porous plates from a third direction perpendicular to the first direction and the second direction.

35. A multi-beam charged particle microscope comprising the multi-beam grating unit according to any one of claims 1 to 34.

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