Multi-beam generating unit with increased focusing capability

Abstract

A multi-beam generating unit for a multi-beam system is provided that has greater individual focusing capabilities for each of a plurality of primary charged particle beamlets. The multi-beam generating unit includes an active terminal multi-aperture plate, which can be used for a larger focusing range for individual aberration-free focal spot adjustment of each beamlet of a plurality of primary charged particle beamlets.

Description

[Technical Field]

[0001] The present disclosure relates to multi-beam laser units, such as multi-beam generating units and multi-beam deflection units of multi-beam charged particle microscopes. [Background technology]

[0002] WO 2005 / 024881 discloses an electron microscope system that operates using multiple electron beamlets to scan an object to be inspected in parallel with the bundle of electron beamlets. The bundle of electron beamlets is generated by directing a primary electron beam onto a first multi-aperture plate having multiple apertures. One portion of the electrons of the electron beam enters the multi-aperture plate and is absorbed there, while another portion of the beam transmits through the apertures of the multi-aperture plate, thereby forming electron beamlets whose cross sections are defined by the cross sections of the apertures in the beam path downstream of each aperture. Furthermore, a suitably selected electric field provided in the beam path upstream and / or downstream of the multi-aperture plate causes each aperture in the multi-aperture plate to act as a lens for the electron beamlets passing through the aperture, resulting in each electron beamlet being focused within a surface located a certain distance from the multi-aperture plate. The surface where the electron beamlets are focused is imaged by downstream optics onto the surface of the object or sample to be inspected. The primary electron beamlets trigger secondary or backscattered electrons to emerge from the object as secondary electron beamlets, which are collected and imaged onto a detector. Each secondary beamlet impinges on a separate detector element, and the secondary electron intensity detected thereby provides information related to the sample at the location where the corresponding primary beamlet impinges on the sample. The bundle of primary beamlets is systematically scanned across the surface of the sample, and an electron microscope image of the sample is generated, as is typical for scanning electron microscopes. The resolution of a scanning acoustic microscope is limited by the focal diameter of the primary beamlets incident on the object. As a result, in a multi-beam electron microscope, all beamlets form the same small focal spot on the object.

[0003] The systems and methods illustrated in WO2005 / 024881 in great detail with the example of electrons are generally very applicable to charged particles. Therefore, the present invention aims to propose a charged particle beam system that operates with multiple charged particle beams and can be used to achieve higher imaging performance, such as better resolution and a narrower range of resolution for each beamlet of the multiple beamlets. The multiple beamlets of a multi-beam charged particle microscope (MCPM) are generated in a multi-beam generating unit. Multi-beam charged particle microscopes (MCPMs) typically use both micro-optical (MO) elements and macroscopic elements in their charged particle projection systems.

[0004] The multi-beam generating unit comprises elements for splitting, partially absorbing and influencing the beam of charged particles, resulting in the generation of multiple beamlets of charged particles in a predetermined raster configuration. The multi-beam generating unit comprises micro-optical elements such as a first multi-aperture plate, a further multi-aperture plate and micro-optical deflection elements, as well as macroscopic elements such as lenses in a dedicated element design and special arrangement.

[0005] The multi-beam generating unit can be formed in an assembly of two or more parallel flat substrates or wafers, for example, fabricated by silicon microstructuring. During use, a plurality of electrostatic optical elements are formed by aligned apertures in at least two of such flat substrates or wafers. Some of the apertures may comprise one or more vertical electrodes arranged axially symmetrically with respect to the apertures, for example, to create an electrostatic lens array. The optical aberrations of such electrostatic lens arrays are known to be very sensitive to manufacturing inaccuracies of the apertures.

[0006] For the production of a predetermined electrostatic optical element, it is important to precisely control the electrodes, for example, their geometry and lateral alignment with each of the plurality of charged particle beamlets, as well as the distance between the electrodes in the direction of the transmitted plurality of charged particle beams, etc. Deviations in the fabrication process of the planar substrate, the electrodes, and the planar substrate assembly create aberrations in the electrostatic optical element, causing aberrations such as aberrations of individual beamlets or deviations from a predetermined raster configuration of the beamlets.

[0007] A multi-beam microscope for wafer inspection forms multiple focal spots of multiple primary charged particle beamlets on the wafer surface. The imaging lens generates field curvature, which causes the multiple primary foci to deviate from the flat wafer surface. Recently, it has been discovered that a multi-beam microscope with a beam splitter also exhibits image plane tilt. Even after field curvature correction, the image plane on which the multiple primary foci are generated is tilted with respect to the wafer surface. The orientation of the image plane tilt depends on the Larmor rotation of the multiple primary charged particle beamlets induced by the magneto-optical lens. The field tilt and field curvature increase the large deviation of the focus positions from the wafer surface. Prior art multi-beam generating units do not provide sufficient stroke to individually change the focus position of each primary charged particle beamlet with the high accuracy required for wafer inspection tasks.

[0008] Multi-aperture plates with electrodes are typically formed by layer deposition and etching techniques, resulting in a stack of multiple different layers. For larger strokes, higher voltages need to be provided to the electrostatic lenses. Non-uniformity in the layer deposition and leakage of the electric field result in non-uniform electro-optical properties of the electrostatic elements across the multi-aperture plate. Conventional arrangements of electrodes within the multi-aperture elements can generate stray fields, which uncontrollably affect the performance of the electro-optical elements. In prior art multi-aperture stacks, optical performance is generally limited.

[0009] The multi-aperture plate comprises a thin film fabricated, for example, from a wafer by a thinning process. Deformations of the membrane, either generated during fabrication or induced, for example, by thermal expansion, cause differences in the distances between some of the multi-aperture plates and thus differences in the electrostatic elements formed during use between at least two of the multi-aperture plates. Changes in the deformation of the membrane can further introduce deviations in the field curvature of the beamlet foci or deviations in the telecentricity characteristics of the beamlets.

[0010] The prior art has considered means for improving the theoretical performance of multi-aperture arrays. For example, U.S. Patent Application Publication No. 2003 / 0209673 discloses a means for reducing crosstalk between multiple primary charged particle beamlets. U.S. Patent Application Publication No. 2003 / 0209673 discloses an electrostatic Einzel lens array for multiple electron beamlets with reduced crosstalk. The electrostatic Einzel lens array is arranged in the electron beam path downstream of the aperture array and includes upper, central, and lower electrodes of the Einzel lens, with each pair of electrodes spaced apart by a large distance of 100 μm. Shielding electrodes provided between the upper and central electrodes and between the central and lower electrodes reduce crosstalk. In another example, a means for reducing design aberrations is considered. DE102014008083, filed May 30, 2014, or corresponding U.S. Patent No. 9,552,957(B2), shows an example of a multi-aperture plate with an array of lenses that reduces spherical aberration. The reduced design aberration is achieved by having the lens apertures larger than the beam diameter. DE102014008083 suggests a distance between the multi-aperture plates in the range of 0.1 to 10 times the aperture diameter to avoid charging effects on the electrodes, but it has been found that this large range alone is not sufficient to prevent undesirable charging effects on the electrodes from scattered charged particles. Summary of the Invention

[0011] Therefore, the problem is to provide a multi-beam generating unit with a large stroke for individually changing the focal position of each primary charged particle beamlet. A further problem is to provide a multi-aperture plate that can adjust the focal position of each primary beamlet with greater precision and minimal aberrations. The problem is to provide a multi-beam generating unit that can form well-defined beamlets with small focal diameters, which have greater focusing power, high focusing accuracy, and minimal residual aberrations. A novel arrangement and optimized layout of the multi-beam generating or multi-beam rastering unit allows multiple focal points of the beamlets to be generated in a predetermined raster configuration and with large axial variations, thereby compensating for the large field curvature of the multi-beam inspection system. Similarly, a multi-beam deflection unit is provided that can deflect beamlets with high precision without introducing or increasing beamlet aberrations.

[0012] Therefore, the challenge is to provide a design for a multi-beam raster unit, such as a multi-beam generating or deflecting unit, that has a large individual optical power, is less sensitive to deviations, does not significantly introduce or increase aberrations, and generates fewer undesirable leakage fields during operation.A further challenge is to provide a multi-beam raster unit that provides more precise focus position control during use.

[0013] Therefore, the problem is to provide a multi-beam raster unit comprising at least three multi-aperture plates, including providing a manufacturing process for the multi-aperture plates that is less sensitive to deviations, produces low aberrations and fewer scattered particles, and allows for the manufacturing of multi-beam generating or multi-beam deflection units with high stability and reproducibility. The novel arrangement of the multi-aperture plates in the multi-beam raster unit allows for a large range of focusing capabilities for individually influencing the focal spot positions of multiple charged particle beamlets generated by the multi-beam raster unit.

[0014] The problem of the present invention is solved by the independent claims. The dependent claims are directed to advantageous embodiments.

[0015] According to a first embodiment, a multibeam generating unit (305) for a multibeam system (1) comprises a filter plate (304) having a plurality of first apertures (85.1) for generating a plurality of primary charged particle beamlets (3) from an incident parallel primary charged particle beam (309), the filter plate (304) being connected to ground level during use. The primary charged particle beamlets are formed by transmission through the plurality of first apertures (85.1), while a majority of the charged particles of the incident primary charged particle beam (309) are absorbed by a conductive shielding layer on the beam entrance side of the filter plate (304). The multibeam generating unit (305) further comprises a terminal multi-aperture plate (310). The terminating multi-aperture plate (310) is arranged downstream of the filter plate (304) in order of the propagation direction of the incident primary charged particle beam (309) and includes a plurality of terminating apertures (94). At each of the terminating apertures (94), a primary charged particle beamlet (3) exits the multi-beam generating unit (305). Each terminating aperture (94) includes a first plurality of individually addressable electrodes (79.2, 81.2) arranged around each of the plurality of terminating apertures (94). Downstream of the terminating multi-aperture plate (310), the multi-beam generating unit (305) includes or is connected to a condenser lens (307) having condenser electrodes (82, 84) with a single aperture configured to transmit the plurality of primary charged particle beamlets (3) during use. The capacitor electrodes (82, 84) are configured, in use, to generate a plurality of electrostatic micro-lens fields (92) penetrating each of a plurality of termination apertures (94).The multi-beam generating unit (305) further includes a control unit (830). The control unit (830) is configured to individually control the capacitor electrodes (82, 84) and each of the first plurality of individually addressable electrodes (79.2, 81.2) to affect the penetration depth and / or shape of each of the plurality of electrostatic microlens fields (92), thereby independently adjusting the lateral and axial focal positions of each of the plurality of primary charged particle beamlets (3). Accordingly, during use, the plurality of primary charged particle beamlets (3) form multiple focal points (311) within an intermediate curved image plane (321). The intermediate curved image plane (321) is curved and has a tilt component (323) for pre-compensating for field curvature and field tilt of the multi-beam system (1).

[0016] In one example, the first plurality of individually addressable electrodes (79.2, 81.2) are formed as a first plurality of electrostatic cylindrical or ring electrodes (79.2), each cylindrical or ring electrode (79.2) arranged around one of the end apertures (94) and configured to generate a suction field (88) or a depression field (90) during use. Thus, the penetration depth of each of the electrostatic microlens fields (92) can be reduced or increased within the corresponding end aperture (94), adjusting the focal length within a wide range. Thus, the axial position of the focal point (311) of each primary charged particle beamlet can be varied within a wide range.

[0017] In another example, the first plurality of individually addressable electrodes (79.2, 81.2) are formed as a first plurality of electrostatic multipole electrodes (81.2), each multipole electrode (81.2) arranged around one of the plurality of end apertures (94) and configured to generate an attraction field (88), a push field (90), and / or a deflection field and / or an aberration correction field during use. This not only reduces or increases the penetration depth of each of the electrostatic microlens fields (92), but also changes the lateral position and shape of each of the plurality of electrostatic microlens fields (92) within the corresponding end aperture (94). This allows, for example, aberrations such as astigmatism to be corrected, and the lateral position of the focal point (311) of each primary charged particle beamlet to be changed by the deflection means.

[0018] The termination multi-aperture plate (310) can comprise a first termination electrode layer (129.1, 306.3a) comprising a first plurality of individually addressable electrodes (79.2, 81.2) and a second electrode layer (306.3b) insulated from the first plurality of individually addressable electrodes (79.2, 81.2) and disposed upstream of the first termination electrode layer (129.1 306.3a). The second electrode layer (306.3b) is connected to ground level during use to form a ground electrode layer. In another embodiment, the termination multi-aperture plate (310) is fabricated from a single electrode layer (129.1).

[0019] The multi-beam generating unit (305) may further include at least a second multi-aperture plate or ground electrode plate (306.2) having a plurality of second apertures (85.2). The second multi-aperture plate forms a first ground electrode during use. The second multi-aperture plate (306.2) is disposed between the filter plate (304) and the terminating multi-aperture plate (310). The multi-beam generating unit (305) may include a third multi-aperture plate or first multi-stigmator plate (306.4, 306.41) having a plurality of fourth apertures (85.4, 85.41), each of which includes a second plurality of individually addressable multi-pole electrodes (81, 81.1) for forming electrostatic multi-pole elements disposed around the plurality of fourth apertures (85.4, 85.41). Each of the second individually addressable multipole electrodes (81, 81.1) is additionally connected to a control unit (830) configured to individually deflect, focus or correct aberrations of each of the plurality of primary charged particle beamlets (3), thereby achieving an even larger range of focusing changes and adjusting the direction of the primary charged particle beamlets (3) as they enter their corresponding end apertures (94).

[0020] The multibeam generating unit (305) may comprise a fourth multi-aperture plate or second multi-stigmator plate (306.43) having a plurality of fourth apertures (85.42), each of which comprises a plurality of individually addressable multipole electrodes (81.3) for forming electrostatic multipole elements arranged around the plurality of fourth apertures (85.42), each of which is connected to a control unit (830) configured to individually deflect, focus or correct aberrations of each of the plurality of primary charged particle beamlets (3), thereby achieving an even larger range of focusing changes.

[0021] The multi-beam generating unit (305) may further comprise a multi-aperture plate formed as an electrostatic lens array (306.3, 306.9) having a plurality of apertures (85.3, 85.9) with a plurality of second cylindrical electrodes (79), each individually connected to a control unit (830) configured to form a plurality of electrostatic lens fields during use. This allows for an even greater range of focusing variation to be achieved. The electrostatic lens array (306.3, 306.9) may be formed as a lens electrode plate (306.9) made from a single electrode layer. In another embodiment, the electrostatic lens array (306.3, 306.9) is a two-layer lens-let electrode plate (306.3) having a lens electrode layer (306.3a) and a ground electrode layer (306.3b).

[0022] In one example, the capacitor electrodes (82, 84) are formed as a segmented electrode 84 comprising a plurality of at least four electrode segments (84.1-84.4), and the control unit (830) is configured to, in use, provide an asymmetric voltage distribution to the plurality of at least four electrode segments (84.1-84.4), such that focusing of the plurality of primary charged particle beamlets (3) is facilitated in the curved intermediate image surface (321) by the tilt component (323).

[0023] In one example, the capacitor electrodes (82, 84) and the terminal multi-aperture plate (310) are disposed at an angle Φ relative to one another, such that focusing of the multiple primary charged particle beamlets (3) is facilitated within the curved intermediate image plane (321) by the tilt component (323). To adjust the angle Φ, either or both of the capacitor electrodes (82, 84) or the stack of multi-aperture plates (315) comprising the terminal multi-aperture plate (310) can be mounted on a manipulator (340) configured to tilt or rotate either or both of the capacitor electrodes (82, 84) or the stack of multi-aperture plates (315).

[0024] The multi-beam generating unit (305) can comprise second or further ground electrode plates (306.8), each arranged between a pair of multi-aperture plates, each multi-aperture plate comprising an electrode layer (129.1) and a plurality of individually addressable electrodes (79, 81), such that the individually addressable ring or multipole electrodes (79, 81) are separated in the propagation direction of the primary charged particle beamlets and are shielded from each other.

[0025] The control unit (830) is configured, in use, to provide a plurality of individual voltages to each of the plurality of electrodes (79, 81) of the terminal multi-aperture plate (3.10), the first multi-stigmator plate (306.4, 306.41) and the optional second multi-stigmator plate (306.43) and / or the electrostatic lens array (306.3, 306.9). The terminal multi-aperture plate (3.10), the first multi-stigmator plate (306.4, 306.41) and the optional second multi-stigmator plate (306.43) and / or the electrostatic lens array (306.3, 306.9) together form an array of individually addressable multi-stage microlenses (316) having an individually variable focal range variation DF, with DF > 1 mm for each individually addressable multi-stage microlens (316), preferably at least DF > 3 mm, and even more preferably DF > 5 mm.

[0026] The multi-beam generating unit (305) further comprises a plurality of spacers (83.1-83.5) or support zones (179) for holding the plurality of multi-aperture plates (304, 306.2-306.9, 310) at a predetermined distance relative to each other.

[0027] In the second embodiment, the multi-aperture plate is formed as an inverted multi-aperture plate, which has electrical wiring connections (175) for a plurality of individually addressable electrodes (79, 79.1, 79.2, 81, 81.1, 81.2, 81.3) on a first side of the inverted multi-aperture plate opposite the beam entrance side. In one example of the multi-beam generating unit (305) according to the first embodiment, at least one of the multi-aperture plates (306.4-306.9, 310) is configured as an inverted multi-aperture plate. At least one inverted multi-aperture plate further comprises a plurality of through connections (149, 149.1, 149.2) for electrically connecting to a plurality of individually addressable electrodes (79, 79.1, 79.2, 81, 81.1, 81.2, 81.3) via electrical wiring connections (175) on the lower or bottom side of the inverted multi-aperture plate, with contact pins (147, 147.1, 147.2) located on the upper or beam entrance side of the inverted multi-aperture plate. The inverted arrangement generally allows for improved electrical insulation and shielding of the electrical wiring connections (175) from, for example, X-rays generated by primary charged particles, scattered charged particles, secondary charged particles, or any type of charged particle. Thus, the individually addressable electrodes (79, 81) can be operated with high precision. The wiring connections downstream of the electrode layer (129.1) of the aperture plate (306, 310) reduce the effects of electric field leakage from the wiring connections and allow for greater voltages to be provided to each corresponding individually addressable electrode, thereby further increasing the focusing capability.

[0028] In one example, the end multi-aperture plate (310) of the multi-beam generation unit (305) further includes a conductive shielding layer (177.2) having a plurality of apertures (94). The conductive shielding layer (177.2) is electrically insulated from the first plurality of individually addressable electrodes (79.2, 81.2), and the conductive shielding layer (177.2) is disposed on the bottom side (76) of the end multi-aperture plate (310) between the individually addressable electrodes (79.2, 81.2) and the condenser lens (307). Thus, the intrusion or disturbance of the plurality of electrostatic microlens fields (92) is effectively reduced.

[0029] In a practical example, the first aperture (85.1) of the filter plate (304) has a minimum first diameter D1, and the end aperture (94) has a larger end diameter DT. The end diameter DT is typically in the range of 1.6×D1≦DT≦2.4×D1. The second aperture (85.2) of the ground electrode plate (306.2) has a second diameter D2. Typically, D2 is selected between D1 and DT, and D1<D2<DT, for example, 1.4×D1≦D2≦0.75×DT. The third or further apertures (85.3, 85.4, 85.9) of the first or second multi-stigmator plate (306.4, 306.41, 306.43) or the electrostatic lens array (306.3, 306.9) have a diameter D3. Typically, D3 is selected between D2 and DT, and as a result, D1<D2<D3<DT, for example, 1.4×D1≦D2≦0.9×D3≦0.8×DT.

[0030] According to a second embodiment of the present invention, a multi-aperture plate (306) with improved performance is provided. The improved multi-aperture plate (306) comprises a plurality of apertures (85.3, 85.4, 85.9, 94) with a plurality of insulated individually addressable electrodes (79, 81) in an insulated electrode layer (129.1). Each of the plurality of electrodes (79, 81) is disposed around one of the apertures (85.3, 85.4, 85.9, 94). The improved multi-aperture plate (306) further comprises a first conductive shielding layer (177.1) on a first side of the multi-aperture plate (306) having a first thickness T1 of about T1≦1 μm, and a layer of a plurality of electrical wiring connections (175) having a third thickness T3≦1 μm. A first planarizing insulating layer (179.5) having a second thickness T2 is disposed between the first conductive shielding layer (177.1) and the layer of electrical wiring connections (175). A third planarizing insulating layer (179.3) is formed between the layer of electrical wiring connections (175) and the insulating electrode layer (129.1). The third planarizing insulating layer (179.3) has a fourth thickness T4. The third planarizing insulating layer (179.3) is provided with wiring contacts (193) formed between each of the wiring connections (175) and the electrodes (79, 81). The first and third planarizing insulating layers (179.5, 179.3) are made of silicon dioxide and are each leveled to a second thickness T2 and a fourth thickness T4 of less than 3 μm, e.g., T2≦T4≦2.5 μm. Preferably, each of the second thickness T2 and the fourth thickness T4 is 2 μm or less. In one example, each of the wiring contacts (193) is disposed at an outer edge of each individually addressable electrode (79, 81) a distance h to the inner wall (87) of the opening (85, 94). The distance h is greater than h>6 μm, preferably h>8 μm, e.g., h≧10 μm.

[0031] The multi-aperture plate (306) further includes a second conductive shielding layer (177.2) on the second side of the multi-aperture plate (306) and having a sixth thickness T6≦1 μm, and a third planarizing insulating layer (129.2) formed between the second conductive shielding layer (177.2) and the electrode layer (129.1) and having a fifth thickness T5≦2.5 μm. The reduced thickness of the planarizing insulating layer (179) reduces disturbances of the electric field around the multi-aperture plate, allowing for more accurate photolithography processing. Thus, for example, wiring contacts can be formed with greater precision. The large distance h of the wiring contacts (193) further reduces leakage of the electric field generated from the wiring contacts (193) or the electrical wiring connections (175). Shielding layers (177.1, 177.2) are provided on both sides and connected to ground level, thereby effectively reducing penetration of electric fields into or from the multi-aperture plate. In one example, at least one of the first or second conductive shielding layers (177.1, 177.2) has multiple plunging extensions (189) into each of the multiple apertures (85, 94), forming a gap with a width g to the electrodes (79, 81), where g<4 μm, preferably g≦2 μm. This small gap further effectively reduces penetration of electric fields into or from the multi-aperture plate. In one example, the multi-aperture plate (306) further includes a shielding electrode (183) between the multiple individually addressable electrodes (79, 81). The shielding electrode (183) is connected to ground level (0 V). Thus, the individually addressable electrodes (79, 81) are effectively shielded from each other.

[0032] The improved multi-aperture plate (306) of this embodiment is one of at least two multi-aperture plates (306, 306.3, 306.4, 310) of a multi-beam generating unit (305) configured to generate and focus a plurality of primary charged particle beamlets (3) during use. In a first example, the improved multi-aperture plate (306) is a terminal multi-aperture plate (310) having a plurality of terminal apertures (94) of the multi-beam generating unit (305), and each of the plurality of primary charged particle beamlets (3) exits the multi-beam generating unit (305) at one of the terminal apertures (94). A condenser lens (307) is disposed behind the improved multi-aperture plate (306), which is the terminal multi-aperture plate (310) of the multi-beam generating unit (305). The condenser lens (307) is configured to, in use, generate a plurality of electrostatic microlens fields (92) penetrating a plurality of end apertures (94).

[0033] In one example, the improved multi-aperture plate (306, 310) is arranged in an inverted configuration with a plurality of wiring connections (175) on a first side of the multi-aperture plate (306) and a plurality of contact pins (147) on a second side of the multi-aperture plate (306) opposite the first side, and further includes a plurality of through connections (149) for connecting the plurality of wiring connections (175) on the first side with the contact pins (147) on the second side.

[0034] In a third embodiment of the present invention, a further improvement to the termination multi-aperture plate (310) is provided. The termination multi-aperture plate (310) comprises a plurality of termination apertures (94) configured, during use, to form a plurality of electrostatic microlens fields (92, 92.1, 92.2) penetrating the plurality of termination apertures (94). A plurality of individually addressable electrodes (79.2, 81.2) are disposed around the termination apertures (94). The plurality of individually addressable electrodes (79.2, 81.2) are configured to be individually connected to a control unit (830) and, during use, are configured to individually affect the penetration depth and / or shape of each of the plurality of electrostatic microlens fields (92, 92.1, 92.2). The terminal multi-aperture plate (310) further comprises a first conductive shielding layer (177.2) connected to ground (0V) at the terminal or beam exit side (76) of the terminal multi-aperture plate (310). This shields the electrostatic microlens fields (92) and prevents them from penetrating the terminal multi-aperture plate (310), penetrating only through the terminal apertures (94). The terminal multi-aperture plate (310) further comprises a shielding electrode (183) connected to ground (0V) between the individually addressable electrodes (79.2, 81.2) for shielding the individually addressable electrodes (79.2, 81.2) from each other. The terminal multi-aperture plate (310) further comprises a plurality of insulated wiring connections (175) for providing a plurality of individual voltages to the individually addressable electrodes (79.2, 81.2). A plurality of wire connections (175) are connected to a control unit (830).

[0035] In one example, the plurality of wiring connections (175) are disposed on a first side of the termination multi-aperture plate (310) and are insulated from the conductive shielding layers (177, 177.2), and the termination multi-aperture plate (310) further comprises a plurality of feedthrough connections (149) connected to the plurality of wiring connections (175). The plurality of feedthrough connections (149) are connected to the control unit (830).

[0036] The terminating multi-aperture plate (310) further comprises a second conductive shielding layer (177.1) on an upper side of the terminating multi-aperture plate (310), the upper side being the side where the plurality of charged particle beamlets (3) enter the terminating multi-aperture plate (310). The terminating multi-aperture plate (310) further comprises a plurality of planarizing insulating layers (129.2, 179, 179.1, 179.3, 179.5), a layer of a plurality of electrical wiring connections (175) between the planarizing insulating layers (129.2, 179, 179.1, 179.3, 179.5), and an electrode layer (129.1) comprising a plurality of individually addressable electrodes (79.2, 81.2). Each of the electrode layer (129.1), the layer of electrical wiring connections (175), and the first or second conductive shielding layer (177.2, 177.2) is insulated from adjacent layers by one of the planarizing insulating layers (129.2, 179, 179.1, 179.3, 179.5). Each of the planarizing insulating layers (129.2, 179, 179.1, 179.3, 179.5) is made of silicon dioxide and is leveled to a thickness T of less than T<3 μm, preferably less than T≦2.5 μm, and even more preferably less than T≦2 μm. In comparison, the electrode layer (129.1) typically has a thickness of 50 μm to 100 μm.

[0037] In a fourth embodiment of the present invention, an inverted multi-aperture plate (306) is provided. The inverted multi-aperture plate (306) comprises a plurality of apertures (85, 94) having a plurality of insulated individually addressable electrodes (79, 81) in an insulated electrode layer (129.1). Each of the plurality of electrodes (79, 81) is arranged around one of the apertures (85, 94). The inverted multi-aperture plate (306) further comprises a first conductive shielding layer (177.1) on a first side of the multi-aperture plate (306) having a first thickness T1≦1 μm, a first planarizing insulating layer (179.5) having a second thickness T2≦2.5 μm, at least a plurality of layers of electrical wiring connections (175) having a third thickness T3≦1 μm, and a second planarizing insulating layer (179.3) between the electrode layer (129.1) and at least a first layer of the electrical wiring connections (175), the second planarizing insulating layer (179.3) having a fourth thickness T4≦2.5 μm. The second planarizing insulating layer (179.3) is configured by photolithography to form through-wire contacts (193) between each of the wiring connections (175) and the electrodes (79, 81).

[0038] The inverted multi-aperture plate (306) further comprises a plurality of feedthroughs (149) and contact pins (147) for contacting the control unit (830) on a second, opposite side of the electrode layer (129.1). A plurality of electrical wiring connections (175) are disposed on a first side of the first insulated electrode layer (129.1), the feedthroughs (149) enabling electrical contact from the first side through the first insulated electrode layer (129.1) to the second side. In one example, each of the wiring contacts (193) is disposed on the outer edge of each individually addressable electrode (79, 81) at a distance h to the inner wall of the aperture (85, 94), where h is preferably greater than 6 μm, and even more preferably greater than 10 μm, e.g., h=12 μm. The inverted multi-aperture plate (306) further comprises a second conductive shielding layer (177.2) on a second side of the multi-aperture plate (306) having a sixth thickness T6≦1 μm, and a third planarizing insulating layer (129.2) formed between the second conductive shielding layer (177.2) and the opposite electrode layer (129.1) of the second planarizing insulating layer (179.3). The third planarizing insulating layer (129.2) has a fifth thickness T5≦2.5 μm. The second conductive shielding layer (177.2) comprises openings (148) for insulating the contact pins (147) from the second conductive shielding layer (177.2). In one example, at least one of the first or second conductive shielding layers (177.1, 177.2) has a plurality of protruding extensions (189) into each of the plurality of apertures (85, 94), forming a gap of width g to the electrodes (79, 81), where g<4 μm, preferably g≦2 μm. The inverted multi-aperture plate (306) further includes a shielding electrode (183) between the plurality of individually addressable electrodes (79, 81) and connected to ground level (0 V) for shielding the plurality of individually addressable electrodes (79, 81) from each other.

[0039] In a fifth embodiment, a method for individually varying the focal length of each of a plurality of primary charged particle beam spots (311) over a large range is provided. The method includes providing a plurality of individually addressable end electrodes (79.2, 81.2) at each of a plurality of end apertures (94) of a terminal multi-aperture plate (310). In a next step, the method includes providing condenser lens electrodes (82, 84) adjacent to the terminal multi-aperture plate (310) and downstream in the propagation direction of the plurality of primary charged particle beamlets (3). In a next step, the method includes providing, by a control unit (830), at least a first voltage to the condenser lens electrodes (82, 84) to generate a plurality of electrostatic microlens fields (92) penetrating the plurality of end apertures (94). In a next step of the method, a plurality of individual voltages are provided to each of the plurality of individually addressable electrodes (79.2, 81.2). The individual voltages on the individually addressable end electrodes (79.2, 81.2) are further controlled to affect the penetration depth of each of the electrostatic microlens fields (92), thereby independently adjusting the axial focus position of each of the primary charged particle beamlets (3) on the curved intermediate image plane (321) over a large range, e.g., DF > 1 mm, preferably DF > 3 mm, and even more preferably DF > 5 mm. In one example, the individually addressable electrodes (79.2, 81.2) are formed as multiple multipole electrodes (81.2), and the method further includes individually controlling the individual voltages on each of the multiple multipole electrodes (81.2) to affect the shape and / or lateral position of each of the electrostatic microlens fields (92). Thus, the lateral focus position and shape of each of the primary charged particle beamlets (3) are independently and individually adjusted on the curved intermediate image plane (321). The step of individually controlling the plurality of individual voltages can be configured to adjust the focal position of each of the plurality of primary charged particle beamlets (3) on the curved intermediate image plane (321) by the tilt component (232).

[0040] The method may further include providing a first multistigmator plate (306.4, 306.41) having a plurality of apertures (85.4) and a plurality of individually addressable multipole electrodes (81.1), and providing a plurality of individual voltages to each of the plurality of individually addressable multipole electrodes (81.1) by a control unit (830). The method according to this example further includes individually controlling the plurality of individual voltages of the multipole electrodes (81.1), thereby affecting the shape and / or lateral position of each of the plurality of primary charged particle beamlets (3) before passing through the plurality of terminal apertures (94) of the terminal multiaperture plate (310).

[0041] The method may further include providing a second multistigmator plate (306.4, 306.41) having a plurality of apertures (85.4) and a plurality of individually addressable multipole electrodes (81.3), and providing a plurality of individual voltages to each of the plurality of individually addressable multipole electrodes (81.3) by the control unit (830). The method according to this example further includes individually controlling the plurality of individual voltages of the multipole electrodes (81.3), thereby affecting the shape and / or lateral position and / or direction of each of the plurality of primary charged particle beamlets (3) before passing through the plurality of terminal apertures (94) of the terminal multiaperture plate (310).

[0042] The method may further include providing a lens array (306.3, 306.9) having a plurality of apertures (85.3, 85.9) and a plurality of individually addressable ring electrodes (79), and providing a plurality of individual voltages to each of the plurality of individually addressable ring electrodes (79) by a control unit (830). By individually controlling the plurality of individual voltages of the ring electrodes (79), the focal position of each of the plurality of primary charged particle beamlets (3) is influenced before passing through the plurality of terminal apertures (94) of the terminal multi-aperture plate (310). Thus, focusing is facilitated by the lens array (306.3, 306.9), and a focusing adjustment over a larger range (DF) of DF > 1 mm, preferably DF > 3 mm, e.g., DF > 5 mm, is achieved.

[0043] According to a further example, the method further comprises individually controlling a plurality of individual voltages on any of the multipole electrodes (81.1, 81.3) and / or on the individually addressable end electrodes (79.2, 81.2) of the ring electrode (79), such that the axial and lateral focal position, shape, and propagation direction of each of the plurality of primary charged particle beamlets (3) are both affected.

[0044] According to a further example, the method further comprises controlling the tilt or rotation angle of either or both of the condenser lens electrodes (82, 84) or the stack of multi-aperture plates (315) of the primary multi-beamlet forming unit 305. According to the method, the axial positions of each of the multiple primary charged particle beamlets (3) are influenced together to contribute to the tilt component (323) of the intermediate image plane (321).

[0045] According to a sixth embodiment of the present invention, a multibeam generating unit (305) having at least one inverted multi-aperture plate is provided. The multibeam generating unit (305) according to this embodiment includes a filter plate (304) having a plurality of first apertures (85.1) for generating a plurality of primary charged particle beamlets (3) from an incident parallel primary charged particle beam (309). The filter plate (304) is connected to ground during use. The multibeam generating unit (305) further includes a plurality of at least two multi-aperture plates (306, 306.3, 306.4, 306.9, 310), each of which includes an electrode layer (129.1) and a plurality of contact pins (147) arranged on a first side of the electrode layer (129.1). The plurality of at least two multi-aperture plates (306, 306.3, 306.4, 306.9, 310) includes a terminal multi-aperture plate (310). Each multi-aperture plate (306, 306.3, 306.4, 306.9) further includes at least one layer of a plurality of electrical wiring connections (175). At least one of the multi-aperture plates (306, 306.3, 306.4, 306.9) is configured as an inverted multi-aperture plate (306, 306.3, 306.4, 306.9) in which the layer of the plurality of electrical wiring connections (175) is disposed on a second side of the electrode layer (129.1) of the inverted multi-aperture plate (306, 306.3, 306.4, 306.9). The second side is opposite the first side on which the contact pins are disposed. Thus, each multi-aperture plate of the multi-beam generating unit (305) can be electrically contacted on the same first side, regardless of the layer position of the plurality of electrical wiring connections (175) of the inverted multi-aperture plate (306, 306.3, 306.4, 306.9). The inverted multi-aperture plates (306, 306.3, 306.4, 306.9) further comprise a plurality of feedthrough connections (149) for electrically connecting the plurality of contact pins (147) with the plurality of electrical wiring connections (175).The terminating multi-aperture plate (310) comprises an electrode layer (129.1) having a plurality of individually addressable electrodes (79.2, 81.2), a layer of electrical wiring connections (175), and a plurality of contact pins (147) disposed on a first side of the electrode layer (129.1). In one example, the layer of electrical wiring connections (175) of the terminating multi-aperture plate (310) is disposed on a second side of the electrode layer (129.1) of the terminating multi-aperture plate (310). The first side is the top or beam entrance side, and the second side is the bottom or lower side from which the primary beamlets (3) exit the multi-aperture plate (310).

[0046] The multi-beam generating unit (305) further comprises a control unit (830) configured to provide a plurality of individual voltages to each of the plurality of contact pins (147) of each of the multi-aperture plates (306, 306.3, 306.4, 306.9) and / or the terminating multi-aperture plate (310) from the same first side.

[0047] The multi-beam generating unit (305) according to the sixth embodiment further comprises a condenser lens (307) having capacitor electrodes (82, 84) with a single aperture configured to transmit a plurality of primary charged particle beamlets (3) during use. The capacitor electrodes (82, 84) are configured to generate an electrostatic microlens field (92) penetrating each of a plurality of terminal apertures (94) during use. The control unit (830) is configured to individually control the capacitor electrodes (82, 84) and each of a plurality of individually addressable electrodes (79.2, 81.2) of the terminal multi-aperture plate (310). This affects the penetration depth and / or shape of each of the plurality of electrostatic microlens fields (92) and facilitates the lateral and axial focal positions of each of the plurality of primary charged particle beamlets (3) on the curved intermediate image plane (321).

[0048] In a seventh embodiment of the present invention, a method for fabricating a multi-aperture plate (306, 310) is provided. The method includes forming a plurality of electrodes (79, 81) in an electrode layer (129.1). The method further includes forming a first insulating layer (179.1) on a first side of the electrode layer (129.1), the first insulating layer (179.1) being formed from an insulating material such as silicon dioxide (SiO2). The method further includes polishing the first insulating layer (179.1) to form a first leveling insulating layer (179.3) having a thickness of less than 2.5 μm. The method further includes forming and lithographically processing a layer of electrical wiring connections (175) on the first leveling insulating layer (179.3). The method further includes forming a second insulating layer (179.4) on the layer of electrical wiring connections (175), the second insulating layer (179.4) being formed from an insulating material such as silicon dioxide (SiO2). The method further includes polishing the second insulating layer (179.4) to form a second leveling insulating layer (179.5) having a thickness of less than 2.5 μm. The method further includes forming a first conductive shielding layer (177.1) on the second leveling insulating layer (179.5).

[0049] In one example, the method further includes forming a plurality of through-connections (149) through the electrode layer (129.1), forming a first insulating layer (179.1) on a second side of the electrode layer (129.1), the second side being opposite the first side, and polishing the first insulating layer (179.1) on the second side to form a first leveling insulating layer (179.3) having a thickness less than 2.5 μm. The method further includes forming a second conductive shielding layer (177.2) on the second side on the first leveling insulating layer (179.3), and connecting each of the through-connections on the first side to one of the electrical wiring connections (175) and each of the through-connections on the second side to a contact pin (147).

[0050] In one example, the method further includes forming a stress reduction layer (187) on the first side on the second leveling insulating layer (179.5), the stress reduction layer (187) being formed from silicon nitride (SiOx). The method further includes forming a further insulating layer (179) on the stress reduction layer (187) and polishing the further leveling insulating layer (179) to level it to a thickness of less than 2.5 μm. Thereafter, a first conductive shielding layer (177.1) according to this example is formed on the further leveling insulating layer (179).

[0051] In one embodiment, a plurality of transmitted beamlets propagate through a plurality of apertures of a plurality of multi-aperture plates in a first direction, a high voltage supply wiring connection is provided to a first electrode in at least one of the multi-aperture 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 multi-aperture plates from a third direction perpendicular to the first and second directions.

[0052] An embodiment of the present invention provides a multi-beam generating unit (305) with a wide range of focusing capabilities. The multi-beam generating unit (305) according to this embodiment comprises a filter plate (304) having a plurality of first apertures (85.1) for generating a plurality of primary charged particle beamlets (3) from an incident parallel primary charged particle beam (309). The multi-beam generating unit (305) further comprises at least a first multi-aperture plate (306.3, 306.4, 306.9) having an electrode layer (129.1) and a terminal multi-aperture plate (310) having a plurality of terminal apertures (94). The multi-beam generating unit (305) further comprises a condenser lens (307) having capacitor electrodes (82, 84), and a control unit (830) configured to provide a plurality of individual voltages to at least the first multi-aperture plate (306.3, 306.4, 306.9), the end multi-aperture plate (310), and the capacitor electrodes (82, 84). In one example, the control unit (830) is further configured to adjust the angle between the end multi-aperture plate (310) and the condenser lens (307) having the capacitor electrodes (82, 84). The multi-beam generating unit (305) according to this embodiment is configured to individually adjust each of the axial focal positions of each of the plurality of primary charged particle beamlets (3) with a focusing range DF greater than DF>1 mm, preferably DF>3 mm, even more preferably DF>5 mm, for example DF≧6 mm. In one example, the multi-beam generating unit (305) is further configured to focus each of the plurality of primary charged particle beamlets (3) onto a curved intermediate surface (321), the curved intermediate surface (321) having an inclined component (323). According to the improved multi-aperture plate according to some of the present embodiments, the multi-beam generating unit (305) is further configured to individually adjust each of the lateral focal positions of each of the plurality of primary charged particle beamlets (3) on the curved surface (321) with an accuracy of less than 20 nm, preferably less than 15 nm, and even more preferably less than 10 nm.Thus, the multi-beam generating unit (305) is configured to individually adjust the shape or aberration of each of the multiple primary charged particle beamlets (3) to form multiple aberration-free focal points (311, 311.1, 311.2, 311.3, 311.4) on the curved intermediate plane (321) with high accuracy. Due to the improvements to the multi-aperture plate provided by some of the present embodiments, higher beamlet quality is achieved, and the focal points (311) in the intermediate image plane (321) are formed with lower aberrations. Thus, the multiple focal points (5) are formed with higher accuracy and less deviation from the image plane (101) of the multi-beam charged particle system (1). Therefore, the present invention enables wafer inspection with higher accuracy, particularly with better compensation for field curvature errors of the multi-beam charged particle system (1), and consequently with lower variations in focal spot size of the focal spots (5) on the wafer surface (25) located in the image plane (101). By increasing the focusing range of the individually addressable electrostatic lens field of the multi-beam generating unit (305), the tilt component of the field curvature error of the multi-beam charged particle system (1) can be adapted to the raster rotation of the primary charged particle beamlets (3) by the objective lens (102) of the multi-beam charged particle system (1). Even if the imaging settings of the multi-beam charged particle system (1) are changed, for example, by changing the voltage supplied to the wafer (7) by the specimen voltage supply (503), changing the raster rotation of the primary charged particle beamlets (3), or changing the amount of field curvature error, the change in field curvature error can be easily compensated by the multi-beam generating unit (305) using a large individual focus change capability (DF) of more than 1 μm or 3 μm, or the DF can be made even larger by using a combination of a multi-aperture plate, a multi-aperture plate with better shielding and more precise fabrication of the wiring connections, or a combination of both, as described above in this embodiment.

[0053] It should be understood that the present invention is not limited to the present embodiments and examples, but also includes combinations and variations of the present embodiments and examples.

[0054] The embodiments of the present disclosure will now be described in more detail with reference to the drawings. [Brief explanation of the drawings]

[0055] [Figure 1] 1 is a schematic cross-sectional view of a multi-beam charged particle system for wafer inspection. [Figure 2] 3A and 3B illustrate some aspects of a multi-beam raster unit 305. [Figure 3] FIG. 2 is a diagram illustrating a first example of a multi-beam generating unit 305. [Figure 4] FIG. 3 shows some details of the two layer lenslet plate 306.3. [Figure 5] FIG. 3 shows a second example of a multi-beam generating unit 305 with an inverted two-layer lenslet plate 306.3. [Figure 6] FIG. 10 shows a third example of a multi-beam generating unit 305 in which the order of the elements is changed. [Figure 7] FIG. 3 shows a fourth example of a multi-beam generating unit 305 having a terminal multi-aperture plate 310 formed as a lenslet plate. [Figure 8a] FIG. 10 illustrates the function of the terminal multi-aperture plate 310. [Figure 8b] FIG. 10 illustrates the function of the terminal multi-aperture plate 310. [Figure 9] FIG. 10 is a diagram illustrating a fifth example of the multi-beam generating unit 305. [Figure 10] FIG. 10 shows a sixth further simplified example of a multi-beam generating unit 305. [Figure 11] FIG. 10 is a diagram illustrating a seventh example of a multi-beam generating unit 305 with increased correction capabilities. [Figure 12] FIG. 10 is a diagram illustrating an eighth example of a multi-beam generating unit 305 with increased correction capabilities. [Figure 13] FIG. 10 is a diagram illustrating a ninth example of a multi-beam generating unit 305 with increased correction capabilities. [Figure 14] FIG. 16 is a diagram showing a tenth example of a multi-beam generating unit 305 having a condenser lens 307 with ring-shaped multi-pole electrode segments. [Figure 15a] FIG. 3 is a front view of the multistigmator plate 306.4. [Figure 15b] 10 is a diagram showing ring-shaped multipolar electrode segments 84.1 to 84.8 of a condenser lens 307. FIG. [Figure 16a] 1A-1C illustrate fabrication steps for producing a lens electrode layer with improved performance. [Figure 16b] 1A-1C illustrate fabrication steps for producing a lens electrode layer with improved performance. [Figure 17] 10A-10C illustrate fabrication steps for fabricating a lens electrode layer with through-connects 149 and through-holes 151. [Figure 18] FIG. 3 shows an example of a stack of multiple multi-aperture plates including inverted multi-aperture plates 306.3 and 306.4 and wiring connections from the top or upper side (in the negative z direction). [Figure 19] FIG. 1 illustrates a multi-beam raster unit according to one embodiment with signal and voltage supply wiring lines from orthogonal directions. [Figure 20] FIG. 10 illustrates a multi-beam raster unit according to an embodiment with a constant tilt angle between the end multi-aperture plate and the condenser lens electrode. DETAILED DESCRIPTION OF THE INVENTION

[0056] In the exemplary embodiments of the present invention described below, functionally and structurally similar components are designated, whenever possible, by similar or identical reference numerals. The multi-beam raster unit in this example is depicted in an illumination beam path in which charged particles propagate in the positive z-direction, with the z-direction pointing downward. However, the multi-beam raster unit can also be applied in an imaging beam path in which secondary charged particle beamlets propagate in the negative z-direction in the coordinate system of FIG. 1 . Still, a series of multi-aperture plates are arranged sequentially in the propagation direction of the transmitted 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 transmitted charged particle beam or beamlet, and the bottom side or beam exit side is understood to be the last surface or side of the element in the direction of the transmitted charged particle beam or beamlet.

[0057] Several array elements, e.g., multiple primary charged particle beamlets, are identified by reference symbols. Depending on the context, the same reference symbol may also identify a single element or an array element. Each primary charged particle beamlet (3.1, 3.2, 3.3, 3.4) is one of multiple primary charged particle beamlets (3). Whether a single element of an element array is intended will be clear from the context.

[0058] The schematic representation of FIG. 1 illustrates basic features and functionality of a multi-beam charged particle microscope system 1 according to an embodiment of the present invention. Note that the symbols used in the drawing have been selected to symbolize their respective functionality. The type of system shown is a multi-beam scanning electron microscope (MSEM or Multi-SEM) type that uses multiple primary electron beamlets 3 to generate multiple primary charged particle beam spots 5 on a surface 25 of an object 7, such as a wafer, whose upper surface 25 is located within the object plane 101 of an objective lens 102. For simplicity, only five primary charged particle beamlets 3 and five primary charged particle beam spots 5 are shown. The features and functionality of the multi-beamlet charged particle microscope system 1 can be implemented using electrons or other types of primary charged particles, such as ions, and in particular helium ions. Further details of the microscope system 1 are provided in International Patent Application PCT / EP2021 / 066255, filed June 16, 2021, which is incorporated herein by reference in its entirety.

[0059] The microscope system 1 comprises an object illumination unit 100, a detection unit 200 and a beam splitter unit 400 for separating a secondary charged particle beam path 11 from a primary charged particle beam path 13. The object illumination unit 100 comprises a charged particle multi-beam generator 300 for generating a plurality of primary charged particle beamlets 3 and is adapted to focus the plurality of primary charged particle beamlets 3 in an object plane 101 where a surface 25 of a wafer 7 is positioned by a sample stage 500.

[0060] The primary beam generator 300 generates multiple primary charged particle beamlet spots 311 in an intermediate image plane 321, which is typically a spherically curved surface. According to an embodiment of the present invention, the intermediate image plane 321 is further tilted to compensate for tilt induced by the off-axis symmetry of the object illumination unit 100. The positions of multiple focal points (311) of the multiple primary charged particle beamlets (3) are adjusted in the intermediate image plane (321) by the multibeam generating unit (305) to pre-compensate for the field curvature and field tilt of the optical elements of the object illumination unit (100) downstream of the multibeam generating unit 305. The orientation and amount of field curvature of the field tilt 321 are adjusted according to the driving parameters of the object illumination unit 100, for example, depending on the focusing ability of the objective lens 102 or the electrostatic field generated between the objective lens 102 and the wafer surface 25 by the voltage supplied by the specimen voltage supply source (503), both of which are the main causes of the field curvature and rotation of the tilted image plane. Further details regarding the curvature and tilt of the intermediate image plane are given in German patent DE102021200799B3, which is incorporated herein by reference.

[0061] The primary beamlet generator 300 includes a source 301 of primary charged particles, such as electrons. The primary charged particle source 301 emits a diverging primary charged particle beam, which is collimated by at least one collimating lens 303 to form a collimated or parallel primary charged particle beam 309. The collimating lens 303 typically consists of one or more electrostatic or magnetic lenses, or a combination of electrostatic and magnetic lenses. The primary beamlet generator 300 further includes a deflector 302 for adjusting the angle of the collimated or parallel primary charged particle beam 309. The collimated primary charged particle beam 309 enters a primary multi-beam forming unit 305. The multi-beam forming unit 305 essentially includes a first multi-aperture plate or filter plate 304, which is illuminated by the collimated primary charged particle beam 309. The first multi-aperture or filter plate 304 comprises a plurality of apertures in a raster configuration for generating a plurality of primary charged particle beamlets 3, which are generated by transmitting a collimated primary charged particle beam 309 through the apertures. The multi-beamlet forming unit 305 comprises at least two further multi-aperture plates 306.3-306.4 located downstream of the first multi-aperture or filter plate 304 with respect to the direction of electron movement in the beam 309. For example, the second multi-aperture plate 306.3 functions as a microlens array with a plurality of ring electrodes, each of which is set to an individually defined potential so that the focal positions of the plurality of primary beamlets 3 can be independently adjusted within the intermediate image plane 321. The third multi-aperture plate 306.4 comprises, for example, four or eight electrostatic elements for each of the plurality of apertures, for example, to individually deflect each of the plurality of beamlets. The multi-beamlet forming unit 305 according to some embodiments is configured with a terminal multi-aperture plate (3.10). The multi-beamlet forming unit 305 is further configured with an adjacent electrostatic field lens 307, which in some instances is combined within the multi-beamlet forming unit 305.Further details of the multi-beamlet forming unit 305 are described below. Together with an optional second field lens 308, the multiple primary charged particle beamlets 3 are focused into or close to an intermediate image plane 321.

[0062] A beam steering multi-aperture plate 390 having multiple apertures with electrostatic electrodes, e.g., deflectors, can be arranged in or close to the intermediate image plane 321 to individually steer the propagation direction of each of the multiple charged particle beamlets 3. The apertures of the beam steering multi-aperture plate 390 are configured with larger diameters to allow multiple primary charged particle beamlets 3 to pass through even when their focal spots 311 are located on the curved intermediate image plane 321. The primary charged particle source 301, each of the active multi-aperture plates 306.3...306.4, and the beam steering multi-aperture plate 390 are controlled by a primary beamlet control module 830, which is connected to the control unit 800.

[0063] Multiple focal points of the primary charged particle beamlets 3 passing through the intermediate image plane 321 are imaged by a field lens group 103 and an objective lens 102 into an image plane 101, where the surface 25 of the wafer 7 is located. A retarding electrostatic field is generated between the objective lens 102 and the wafer surface by applying a voltage to the wafer by a specimen voltage supply (503). The object illumination system 100 further comprises a focusing multi-beam raster scanner 110 adjacent to a first beam crossover 108, which can deflect the multiple charged particle beamlets 3 in a direction perpendicular to the propagation direction of the charged particle beamlets. The propagation direction of the primary beamlets throughout this example is in the positive z-direction. The objective lens 102 and the focusing multi-beam raster scanner 110 are centered on an optical axis 105 of the multi-beam charged particle system 1, which is perpendicular to the wafer surface 25. A plurality of primary charged particle beamlets 3, forming a plurality of beam spots 5 arranged in a raster configuration, are synchronously scanned across the wafer surface 25. In one example, the raster configuration of the plurality of N primary charged particle 3 focal spots 5 is a hexagonal raster of about 100 or more primary charged particle beamlets 3, such as N=91, N=100, or N=about 300 or more beamlets. The primary beam spots 5 have a distance of about 6 μm to 15 μm and a diameter of less than 5 nm, such as 3 nm, 2 nm, or even less. In one example, the beam spot size is about 1.5 nm, and the distance between two adjacent beam spots is 8 μm. At each scanning position of each of the plurality of primary beam spots 5, a plurality of secondary electrons are generated, forming a plurality of secondary electron beamlets 9 in the same raster configuration as the primary beam spots 5. The intensity of the secondary charged particle beamlets 9 generated at each beam spot 5 depends on the intensity of the impinging primary charged particle beamlets 3 illuminating the corresponding spot 5, the material composition and topology of the object 7 below the beam spot 5, and the charging condition of the sample at the beam spot 5. The secondary charged particle beamlets 9 are accelerated by an electrostatic field generated by the sample charging unit 503 between the sample 7 and the objective lens 102.The multiple secondary charged particle beamlets 9 are accelerated by an electrostatic field between the objective lens 102 and the wafer surface 25, collected by the objective lens 102, and pass through the first focusing multi-beam raster scanner 110 in the opposite direction to the primary beamlets 3. The multiple secondary beamlets 9 are scan-deflected by the first focusing multi-beam raster scanner 110. The multiple secondary charged particle beamlets 9 are then guided by the beam splitter unit 400 to follow the secondary beam path 11 of the detection unit 200. The multiple secondary electron beamlets 9 travel in the opposite direction to the primary charged particle beamlets 3, and the beam splitter unit 400 is configured to separate the secondary beam path 11 from the primary beam path 13, typically by a magnetic field or a combination of a magnetic field and an electrostatic field. Optionally, an additional magnetic correction element 420 is present in the primary or secondary beam path.

[0064] The detection unit 200 images the secondary electron beamlets 9 onto an image sensor 207, forming multiple secondary charged particle image spots 15 there. The detector or image sensor 207 includes multiple detection pixels or individual detectors. The intensity of each of the multiple secondary charged particle beam spots 15 is detected separately, and the material composition of the wafer surface 25 is detected with high resolution for large image patches of the wafer with high throughput. For example, a raster of 10 × 10 beamlets with an 8 μm pitch generates an image patch of approximately 88 μm × 88 μm with an image resolution of, for example, 2 nm or less in a single image scan by the focused multi-beam raster scanner 110. The image patch is sampled by half the beam spot size, thus having a pixel count of 8,000 pixels per image line for each beamlet. As a result, an image patch generated by 100 beamlets contains 6.4 gigapixels. Digital image data is collected by the control unit 800. Details of digital image data collection and processing, for example using parallel processing, are described in International Patent Application No. 2020151904 and U.S. Patent No. 9,536,702, which are incorporated herein by reference.

[0065] The projection system 205 further comprises at least a second focusing raster scanner 222 connected to a scanning and imaging control unit 820. The control unit 800 and the imaging control unit 820 are configured to compensate for residual errors in the positions of the multiple focal points 15 of the multiple secondary electron beamlets 9 such that the positions of the multiple secondary electron focal spots 15 are kept constant at the image sensor 207.

[0066] The projection system 205 of the detection unit 200 comprises further electrostatic or magnetic lenses 208, 209, 210 and a second crossover 212 of the plurality of secondary electron beamlets 9 at which an aperture 214 is located. In one example, the aperture 214 further comprises a detector (not shown) connected to an imaging control unit 820. The imaging control unit 820 is further connected to the at least one electrostatic lens 206 and a third deflection unit 218. The projection system 205 may further comprise at least a first multi-aperture corrector 220 having apertures and electrodes for individually influencing each of the plurality of secondary electron beamlets 9, connected to the control unit 800 or the imaging control unit 820, and optional further active elements 216.

[0067] The image sensor 207 is configured with an array of sensing areas in a pattern that matches the raster arrangement of the secondary electron beamlets 9 focused onto the image sensor 207 by the projection lens 205. This allows each individual secondary electron beamlet to be detected independently of other secondary electron beamlets incident on the image sensor 207. The image sensor 207 shown in FIG. 1 can be an electron-sensitive detector array, such as a CMOS or CCD sensor. Such an electron-sensitive detector array can include an electron-to-photon conversion unit, such as a scintillator element or an array of scintillator elements. In another embodiment, the image sensor 207 can be configured as an electron-to-photon conversion unit or scintillator plate located in the focal plane of the multiple secondary electron particle image spots 15. In this embodiment, the image sensor 207 can further include relay optics for imaging and guiding photons generated by the electron-to-photon conversion unit at the secondary charged particle image spots 15 onto dedicated photon-detecting elements, such as multiple photomultiplier tubes or avalanche photodiodes (not shown). Such an image sensor is disclosed in U.S. Patent No. 9,536,702, cited above and incorporated by reference. In one example, the relay optics further includes a beam splitter for splitting and directing the light to a first slow photodetector and a second fast photodetector. The second fast photodetector is configured, for example, by an array of photodiodes, such as avalanche photodiodes, that are fast enough to resolve the image signals of the multiple secondary electron beamlets 9 according to the scanning speed of the multiple primary charged particle beamlets 3. The first slow photodetector is preferably a CMOS or CCD sensor that monitors the focal spot 15 or the multiple secondary electron beamlets 9 and provides high-resolution sensor data signals for controlling the operation of the multi-beam charged particle microscope 1.

[0068] The stage 500 is preferably not moved while an image patch is acquired by scanning the multiple primary charged particle beamlets 3, and after acquisition of the image patch, the stage 500 is moved to the next image patch to be acquired. In an alternative embodiment, the stage 500 is moved continuously in a second direction while an image is acquired by scanning the multiple primary charged particle beamlets 3 in a first direction by the focused multi-beam raster scanner 110. The stage movement and stage position are monitored and controlled by sensors known in the art, such as a laser interferometer, a grating interferometer, a confocal microlens array, etc.

[0069] According to one embodiment of the present invention, a plurality of electrical signals are generated, converted into digital image data and processed by the control unit 800. During image scanning, the control unit 800 is configured to trigger the image sensor 207 to detect a plurality of time-resolved intensity signals from the plurality of secondary electron beamlets 9 at predetermined time intervals, and digital images of the image patches from all scanning positions of the plurality of primary charged particle beamlets 3 are accumulated and stitched together.

[0070] The multi-beam generating unit 305 is described, for example, in U.S. Patent Application Publication No. 2019 / 0259575 and U.S. Patent No. 10,741,355 (B1), both of which are incorporated herein by reference. Further details of a multi-beam generating unit that is insensitive to fabrication errors and scattering are disclosed in WO2021180365, which is incorporated herein by reference.

[0071] Some aspects of an embodiment of the present invention are illustrated in FIG. 2. FIG. 2 shows a cross section of a multibeam generating unit 305. FIG. 2 shows only a portion of the inner zone or membrane of the multibeam generating unit 305. As explained in more detail below, the multi-aperture plate further comprises a support zone for supporting the membrane zone and providing mechanical stability. The multibeam generating unit 305 comprises a first multi-aperture or filter plate 304 having a plurality of apertures 85.1, of which only one aperture 85.1 is shown. At the entrance side 74, each aperture 85.1 has a circular shape with a diameter D1. Portions of a collimated incident electron beam 309 pass through the apertures 85.1 to form a plurality of primary charged particle beamlets 3, such as beamlet 3.1. The first multi-aperture plate 304 is coated with a metal layer 99 to stop and absorb the impinging electron beam 309 around the plurality of apertures 85.1. The metal layer 99 is formed, for example, from aluminum or gold and is connected to a large capacitance, for example, ground (0 V). During use, a large proportion of incident electrons from the electron beam 309 are absorbed in the absorbing layer 99, generating a current corresponding to the number of absorbed electrons. For example, with D1 = 30 μm and a pitch P1 of the apertures of 150 μm, approximately 97% of the incident electrons from the collimated incident electron beam 309 are absorbed, generating a high electron current. Therefore, during use, the absorbing layer 99 exhibits a fluctuating voltage difference corresponding to the induced current and is therefore not suitable for forming an electrode for an electrostatic element. The upper segment 331.1, including the metal layer 99, has a thickness L1.1, where 2 μm ≦ L1.1 ≦ 5 μm, to provide sufficient stopping power for impinging electrons of the charged particle beam 309 and support the metal film 99.

[0072] The example multi-aperture plate 304 of FIG. 2 further includes a second segment 331.2 having a z-extension L1.2 of approximately 5 μm. The first multi-aperture plate 304 has a thickness L1 of approximately 7 μm to 10 μm. At the entrance surface 74, the aperture 85.1 has a diameter D1. The second segment 331.2 is configured such that its inner wall forms a concave circular cross section in the x-z plane with a continuously increasing diameter, and the tangent vector 103 in the x-z plane points outward from the primary direction of passage of the electron beam 77. Thus, the slope of the inner wall of the second segment 101.2 points outward from the passing electron beam 77 and terminates at a maximum aperture diameter D12 at the exit or bottom surface 107 of the multi-aperture plate 73.1. The maximum aperture diameter D12 at the exit surface 107 is larger than the aperture diameter D1 of the first segment 101.1.

[0073] In one example, the beam exit surface 76 is covered by a conductive layer 98 connected to a potential, such as ground (0 V). The conductive layer, having a boundary or edge with a diameter D12, forms the opposing electrode for a subsequent second multi-aperture plate or lenslet plate 306.9 adjacent to the first multi-aperture plate 304. In use, to form multiple electrostatic lens elements, the second multi-aperture plate 306.9 is configured with a ring electrode 79, such as electrode 79.1, around each aperture 85.9, having a diameter D3. Each ring electrode 79 is connected to a separate voltage supply, which provides a predetermined voltage between 0 V and 100 V to each of the ring electrodes 79, thereby adjusting the focal position of each of the multiple primary charged particle beamlets 3, such as beamlet 3.1. The second multi-aperture plate 306.9 has a length L3 of approximately 30 μm to 300 μm.

[0074] The multi-beam generating unit 305 of FIG. 2 includes a third multi-aperture plate or ground electrode 306.8 having a plurality of apertures 85.8. The multi-aperture plate 306.8 is formed of a conductive material or is coated with a conductive layer (not shown) and connected to ground. Thus, the multi-aperture plate or ground electrode 306.8 forms the third electrode of the plurality of electrostatic Einzel lenses with the central electrode 79 of the second multi-aperture plate 306.9. The thickness of the third multi-aperture plate 306.8 is between 40 μm and 100 μm, e.g., L5 = 50 μm. The distances L2 and L4 between the multi-aperture plates 304, 306.9, and 306.8 are each within the range of 10 μm to 40 μm. The distance may be non-uniform, for example, due to bending of the multi-aperture plate or thickness distribution of the multi-aperture plate, and the distance between two multi-aperture plates may also be less than 10 μm, for example, 5 μm. In the example of FIG. 2 and throughout the following, the opening of the lower multi-aperture plate, such as plate 306.9 or plate 306.8, is configured with a larger opening compared to D1, such that D3 > D1 and D4 > D1. Preferably, diameter D3 or D4 is such that D3 > 1.5 × D1 and D4 > 1.5 × D1. More examples of increasing diameters are shown below.

[0075] The multi-beam generating unit 305 of FIG. 2 allows for compensation of field curvature and field tilt only within a limited range or stroke. Without the improved design described below, the focusing ability of each individual lenslet formed by the ring electrode 79.1 is limited in range. Typically, such an Einzel lens can achieve a focusing ability of less than 1 mm within the intermediate plane 321, and the ratio of focal position change per voltage is typically less than 1 mm / 100 V, e.g., 9 μm / 1 V. For larger focusing strokes, larger voltages must be applied to the electrodes, which can result in large aberrations and crosstalk, for example, due to induced charging and leakage of the electric field. The limited focusing range is particularly problematic for multi-beam systems 1 for wafer inspection and for multi-beam systems 1 with a larger number of primary charged particle beamlets and therefore larger fields, e.g., a plurality of N>200 or N>300 primary charged particle beamlets. In such a system, the curved intermediate image plane 321 with field tilt requires separate and independent modification of the focusing power DF of each of the multiple primary charged particle beamlets (3) with a DF > 1 mm, preferably a DF > 3 mm, or even a DF > 5 mm. For example, the orientation of the field tilt and the amount of field curvature depend on the settings of the magnetic-optical field lens group (103) and the magnetic-optical objective lens (102) of the multi-beam system 1, and for each different setting of the field lens group (103) and the objective lens 102, the focusing power DF of each of the multiple primary charged particle beamlets (3) must be independently and individually modified according to the amount of field curvature and the orientation of the field tilt.

[0076] FIG. 3 illustrates a first example of the present invention. According to FIG. 3, the multibeam generating unit 305 of the first example includes a series of five multi-aperture plates 304 and 306.2-306.5 arranged in the z direction along which electrons propagate, and a global condenser lens 307. Each multi-aperture plate 304 and 306.2-306.5 includes a plurality of apertures 85.1-85.5 spaced apart by the same lateral distance P1 within each plate, and the plates are aligned to generate and shape a plurality of primary charged particle beamlets 3. The multi-aperture plates 304 and 306.2-306.5 and the global lens electrode 307 are spaced apart by spacers 83.1-83.4 and spacer 86. The multi-beam generating unit 305 is illustrated in a cross section (x,z) in which only four apertures 85.1-85.5 are shown within each multi-aperture plate, including an inner membrane zone 335 and a support zone 333. The first multi-aperture or filter plate 304 has the same function and is similar to the filter plate 304 of FIG. 2, but does not necessarily have a conductive layer 98 on the bottom side 76. The bulk material of the filter plate 304 is made of a conductive material, such as doped silicon, and is connected to ground. The second multi-aperture plate 306.2 is a ground electrode plate similar to the multi-aperture plate 306.8 of FIG. 2. The second multi-aperture or ground electrode plate 306.2 is made of a conductive material, such as doped silicon, and is connected to ground (0 V).

[0077] The third multi-aperture plate 306.3 is a two-layer lenslet plate having a first layer 306.3a with a plurality of ring electrodes 79 of a plurality of apertures, each configured to individually change the focal position of a corresponding primary charged particle beamlet, e.g., charged particle beamlets 3.1-3.4. The second layer 306.3b, downstream of the first layer 306.3a, is insulated from the first layer and made of a conductive material, such as doped silicon. The second layer 306.3b is connected to ground (0 V). The ground electrode plate 306.2, the first layer 306.3a, and the second layer 306.3b form, in use, a plurality of individually adjustable Einzel lenses for the multiple primary charged particle beamlets 3. Further details of the two-layer lenslet plate 306.3 with a larger focusing range DF are described below.

[0078] The multi-beam generating unit 305 further includes a fourth multi-aperture multi-stigmator plate 306.4, which can also function as a multi-deflector plate. The multi-stigmator plate 306.4 includes a plurality of electrodes 81, e.g., four or more electrodes, each of which has a plurality of apertures 85.4 (not labeled in FIG. 3). During use, a different voltage in the range of −20 V to +20 V can be applied to each of the electrodes, thereby individually affecting each beamlet 3.1-3.4. For example, by using an antisymmetric voltage difference, each beamlet 3.1-3.4 can be deflected by up to several microns in each direction to pre-compensate for distortion aberrations of the illumination unit 100. Typically, distortions of approximately ±10 μm in the intermediate image plane 321 or approximately ±0.5 μm in the image plane 101 can be compensated for by a voltage of up to ±10 V. For example, astigmatism of each beamlet 3.1-3.4 can be compensated for. The offset voltage allows each multipole element to additionally function as an Einzel lens, forming an offset of the round lens field together with the second layer 306.3b and the hybrid lens plate 306.5, both of which are connected to ground (0V), thereby additionally increasing the focusing range DF.

[0079] The fifth multi-aperture plate or hybrid lens plate 306.5 is made of doped silicon and forms a further electrode connected to ground level (0 V). In one example, the fifth multi-aperture plate 306.5 can also be coated with a conductive layer, for example by depositing a metal layer, such as gold (Au), or a composite layer, such as AuPd. In the example of FIG. 3, the first condenser lens 307 is connected to the multi-beam forming unit 305. The condenser lens 307 comprises a ring electrode 82 to which a high voltage, for example, between -3 kV and -20 kV, such as between -12 kV and -17 kV, can be applied. The condenser lens 307, on the other hand, forms a global electrostatic lens field for global focusing of the multiple primary charged particle beamlets 3, including beamlets 3.1 to 3.4. An electrostatic lens field penetrates the apertures of hybrid lens plate 306.5, for example into each of apertures 85.5, and an additional electrostatic lens field with focusing capabilities is generated within each aperture of hybrid lens plate 306.5. However, the electrostatic lens fields of prior art hybrid lens plate 306.5 cannot be individually adjusted and do not allow for compensation for varying field tilt and varying amounts of field curvature.

[0080] An optional further condenser lens 308 focuses each of the multiple primary charged particle beamlets 3, including beamlets 3.1 to 3.4, into a curved and tilted intermediate image plane 321 during use to form a spot that is corrected to be stigmatic.

[0081] FIG. 4 shows a segment 306.3a of a two-layer lenslet plate 306.3 with an increased focusing range DF. The two-layer lenslet plate 306.3 includes an inner zone or membrane with multiple apertures 85.3 and 85.4 (only two are shown) and ring electrodes 79.3 and 79.4 arranged around apertures 85.33 and 85.34. The apertures are aligned with multiple apertures 85.1 in the filter plate 304 to transmit charged particle beamlets 3.3 and 3.4. The ring electrodes are insulated from the bulk silicon or SOI substrate via an insulating gap 185, e.g., by silicon dioxide, an insulating material. The bulk silicon or SOI substrate serves as a shielding electrode 183, e.g., made of doped silicon, which is set to ground level. Each ring electrode 79.3, 79.4 is electrically connected to a voltage supply, a voltage support (not shown) of the control unit 830 (see FIG. 1), via an electrical wiring connection 175, such as wiring connection 175.4, and is insulated from the substrate 183 by an insulating material 179. The insulating material is, for example, silicon oxide, which is produced either by thermal oxidation of the bulk material (doped silicon) or by deposition of silicon oxide, for example, from tetraethyl orthosilicate (TEOS). The insulating material 179 extends above the wiring connections 175.4, so that the wiring 175.4 and the bulk material 183 are completely covered on the upper side. The inner walls of the round electrode 79 are not covered by the insulating material 179. A conductive shielding layer 177 is formed above the insulating material, forming the beam entrance or upper surface 173 of the two-layer lenslet plate 306.3. The conductive layer extends into the opening by a protruding extension 189, forming a small insulating gap 181 of width g between the conductive shielding layer 177 and the electrode 79.4, thereby insulating the conductive layer 177 from the electrode 79.4. The conductive layer 177 is connected to a large capacitance, for example to ground (U=0V). Thus, in use, scattered charged particles are absorbed by the conductive shielding layer 177 and conducted outward, avoiding disturbing surface charges. The connection of the conductive layer 177 to a large capacitance creates a stable electrostatic element in use.Thus, during use, surface charge is reduced to less than 10% compared to conventional multi-aperture plates. The gap distance g is less than 6 μm, e.g., less than 4 μm, and preferably less than 2 μm, e.g., 1 μm. Surface charge within the small insulating gap 181 vanishes due to the small distance g of the insulating gap 181. Furthermore, with the improved design, the wire connection 175.4 is connected to the electrode 79.4 at a large distance h to the cylindrical inner wall of the aperture 85.4, thereby minimizing leakage of the electrostatic field induced by the wire connection through the insulating gap 181. For example, the wire connection is formed close to the outer edge of the ring electrode 79.4. This arrangement allows for larger voltages, e.g., up to 200 V, preferably 0 V to 500 V, to be applied to each of the ring electrodes 79. The distance h is preferably greater than 6 μm, e.g., 10 μm or 12 μm. By providing an extension in the conductive shielding layer 177 that extends into the opening 85 in the lenslet layer 306.3a, forming a small gap 181 of width g to the electrode 79, and a larger distance h to the wiring connection 175, a larger voltage than 100V, for example 150V or 200V or even 500V, can be provided to produce an electrostatic lens element with a larger focusing range DF and lower aberrations during use.

[0082] The conductive shielding layer 177 is made of a metal, such as aluminum, having a thickness of approximately 2 μm and is connected to ground. The wiring connection 175.4 is formed, for example, of aluminum, gold, or copper, with a thickness of d=1 μm. Each of the insulating layers of insulating silicon oxide 179 has a thickness b1, b2, or b3 of 2 μm to 4 μm. To avoid stress-induced deformation, an optional additional stress compensation layer 187 can be provided. The stress compensation layer 187 can be formed, for example, of SiNx, with a thickness of 1 μm to 2 μm. The layers 177, 175, and 187, together with the insulating material 179, form a multilayer stack MLS. Preferably, each insulating layer is planarized and leveled to a thickness of less than 2.5 μm, for example, by chemical mechanical polishing (CMP). Leveling allows for more precise lithographic processing of, for example, the wiring connection 175 or the plunge extension 189. The leveling allows the stress compensation layer 187 to be omitted, thereby reducing the overall thickness of the multilayer stack MLS. The multilayer stack of the improved multi-aperture plate does not exceed 10 μm in thickness, and preferably has a thickness of about 8 μm. This allows for a flat surface of the conductive shielding layer 177 that is less likely to disturb the electrostatic lens field.

[0083] FIG. 5 illustrates a further example of the present invention. The example of FIG. 5 is similar to the example of FIG. 3, and reference is made to FIG. 3. In FIG. 5, the order of the second multi-aperture plate or ground electrode plate 306.2 and the third multi-aperture plate or two-layer lenslet plate 306.3 is reversed, so that the primary charged particle beamlets first enter the second layer or ground layer 306.3b of the two-layer lenslet plate 306.3 and then intersect with the second layer 306.3a containing the ring electrodes. Downstream of the two-layer lenslet plate 306.3, the primary charged particle beamlets (3), including beamlets 3.1-3.4, intersect with the apertures of the ground electrode plate 306.2. This arrangement allows fewer scattered particles to impinge on the shielding layer 177 of the multilayer stack MLS of the two-layer lenslet plate 306.3, thereby generating fewer disturbing charges in the MLS. During use, the voltage provided to the multiple ring apertures 79 can be controlled with greater precision and less variation. In addition, the thickness of the MLS can be further reduced. For example, the thickness of the conductive shielding layer 177 at the bottom of the two-layer lenslet plate 306.3 can be reduced to about a=1 μm, and the thickness of the MLS can be reduced to about 7 μm.

[0084] Due to the inverted arrangement of the two-layer lenslet plate 306.3, any flow of secondary or scattered electrons into the ring electrode is significantly reduced by the ground electrode layer 306.3b upstream of the electrode layer 306.3a. Furthermore, the deep aperture holes in the ground electrode layer 306.3b reduce crosstalk and more effectively filter X-rays or bremsstrahlung before they reach the electrode layer 306.3a. The shielding layer 177 downstream of the electrode layer 306.3a can be reduced or even larger voltages can be provided. Thus, a larger focusing range DF>1 mm, e.g., DF>3 mm, can be achieved with the example of FIG. 5.

[0085] Figure 6 shows a further modification of the present invention. The example of Figure 6 is similar to the example of Figure 5, and reference is made to Figures 3 and 5. In Figure 6, the position of the multistigmator plate 306.4 has been changed. The multistigmator plate 306.4 is now located upstream of the double-layered lenslet plate 306.3. This allows for precise control of the intersection position of each beamlet 3.1-3.4, and allows for pre-compensation of residual aberrations before they enter the lenses of the double-layered lenslet plate 306.3.

[0086] FIG. 7 illustrates a further example of the present invention. FIG. 7 is similar to FIG. 6 , except that the hybrid lens plate 306.5 is replaced with a terminal multi-aperture plate 310 formed as a single lenslet layer. The terminal multi-aperture plate 310 comprises a plurality of ring electrodes 79.2 disposed around each of a plurality of terminal apertures 94 of the terminal multi-aperture plate 310. Each of the ring electrodes 79.2 is individually connected to a control unit 830, which is configured to provide a plurality of individual voltages to the ring electrodes 79.2 during use to individually and independently manipulate the penetration depth of the electrostatic lenslet field 92 (see FIG. 8 below) into the terminal apertures 94. The function of the terminal multi-aperture plate 310 is illustrated in more detail in FIG. 8 . An electrostatic field 92 is generated between the terminal multi-aperture plate 310 and the ring electrode 82 by the ring electrode 82 of the electrostatic condenser lens 307. The electrostatic field 92 penetrates the end aperture 94 of the end multi-aperture plate 310, forming microlenses (92.1, 92.2) within the end aperture 94 that contribute to the overall focusing ability of the multi-beam generating unit 305. This is shown in FIG. 8a by the equipotential lines of the electrostatic lenslet field distribution 92. The end multi-aperture plate 310 allows the penetration depth of the electrostatic lenslet field distribution 92 to be individually controlled by the multiple ring electrodes 79.2, creating individually adjustable microlenses. For example, a larger voltage difference is applied to the ring electrode 79.21 relative to the voltage of the electrostatic condenser lens 307, and during use, an attraction field 88 is generated. Therefore, a more powerful microlenslet 92.1 is generated, and the charged particle beamlet 3.1 is focused to the focal point 311.1 at a shorter distance to the multi-beam generating unit 305. A smaller voltage difference is applied to the ring electrode 79.22 relative to the voltage on the condenser lens 307, and in use a suppression field 90 is generated, thus creating a microlenslet 92.2 with a smaller focusing power, which focuses the charged particle beamlet 3.2 to a second focal point 311.2 spaced downstream from the first focal position 311.1.According to the example of electrodes 79.21 and 79.22 in FIG. 8 a, multiple electrostatic microlens fields (92), such as lens fields 92.1 and 92.2, can be individually formed or adjusted to achieve a larger focusing range of the multi-beam generating unit, for example, DF>1 mm or DF>3 mm.

[0087] FIG. 8b shows some modifications of the terminal multi-aperture plate 310. The terminal multi-aperture plate 310 is covered on both sides by conductive shielding layers 177.1 and 177.2. Both conductive shielding layers 177.1 and 177.2 are connected to ground, effectively shielding the terminal multi-aperture plate 310. Thus, the electrostatic microlens field (92) is prevented from penetrating the terminal multi-aperture plate 310, except for the terminal aperture 94. The plurality of electrodes 79.2 are further shielded by a shielding aperture 183, which is connected to ground level. This reduces crosstalk. Therefore, an even larger focusing range DF of the multi-beam generating unit can be achieved, e.g., DF>3 mm.

[0088] Electrode 79.2 can be formed at the lower edge of termination aperture 94, as shown in FIG. 8a. This has the advantage that high sensitivity is achieved. Electrode 79.2 can also be formed inside termination aperture 94 at a distance m to the bottom surface of termination multi-aperture plate 310, where m is selected between 2 μm≦m≦10 μm. A preferred distance m is given, for example, by m=4 μm or m=6 μm. A smaller distance m allows for greater sensitivity to be achieved. With greater sensitivity, a lower voltage is required at electrode 79.2 to suppress or magnify microlenslet 92.1 or 92.2. However, greater sensitivity also makes termination multi-aperture plate 310 more sensitive to aberrations or disturbances; therefore, for more stable video, a larger distance m>3 μm, such as m=4 μm or m=6 μm, is preferred. The greater distance m allows the conductive shielding layer 177.2 and the insulating layer 179 between the electrodes 79.21 and 79.22 and the conductive shielding layer 177.2 to be given greater thicknesses to prevent leakage of the electrostatic field to or from the termination multi-aperture plate 310. The conductive shielding layer 177.2 also prevents arcing between the field electrode 79.2 and the capacitor electrode 82, protecting the field electrode 79.2 and the electronic elements of the control unit (830) connected to the field electrode 79.2 from damage. The conductive shielding layer 177.2 may also be provided with a protruding extension 189 (not shown in FIG. 8 ) into the termination aperture 94, as described in more detail above. By leveling the insulating layer 179 as described above (see FIG. 4 and corresponding discussion), a high-quality, flat shielding layer 177.2 may be provided at the bottom surface 76, allowing the electrostatic lenslet field distribution 92 to be formed with high precision and low turbulence or aberrations.

[0089] 7 and 8, an even larger focusing range DF and a larger variation in the focal positions of the multiple primary charged particle beamlets can be achieved, allowing for even larger field curvatures and tilts of the image plane 101 to be pre-compensated. The electrostatic lenslet field distributions 92 are modified by individual voltages applied to the electrodes 79.2, thereby achieving highly efficient individual control of the focal positions 311 of the multiple primary charged particle beamlets (3). Therefore, the variable electrostatic lenslet field distributions 92 of the actuated terminal multi-aperture plate 310 enable more effective pre-compensation of field curvature. Because the multiple lensing effect of the variable electrostatic lenslet field distributions 92 is a first-order effect, a lower voltage is required to achieve a larger effect on the change in the focusing ability of each variable electrostatic lenslet field distribution 92, e.g., lenslet field distribution 92.1 or 92.2. The change in each variable electrostatic lenslet field distribution 92.1 or 92.2 can also be in a positive or negative direction. Therefore, even with a moderate voltage of more than approximately ±20 V, a large focusing ability can already be achieved. The focusing capability is greater, particularly as with the Einzel lens described above, with voltages exceeding, for example, 50 V or 100 V. A similar voltage difference of about ±25 V or ±50 V at the end aperture 94 allows the focusing range to be adjusted over a z-range at least twice as large as with an Einzel lens. Improved fabrication methods and means for shielding electrostatic fields, such as those described below in FIGS. 4 and 16, allow the end aperture plate 310 to be fabricated with high precision, so that even larger voltage differences exceeding ±50 V, such as ±100 V or more, can be applied, achieving an even larger focusing range.

[0090] The terminal aperture 94 of the terminal multi-aperture plate (310) has a diameter of D.sub.T. In the example of FIG. 7, several examples of the diameters of apertures 85.1-85.4 are illustrated. The terminal apertures typically have a maximum aperture within the range of 1.6 x D.sub.1 ≤ D.sub.T. ≤ 2.4 x D.sub.1. Thus, the primary beamlets formed at filter aperture 85.1 have a smaller diameter than the terminal aperture. On the other hand, the diameter of the terminal aperture is constrained so that greater focusing power can be achieved by the electrostatic microlens fields (92.1, 92.2). The diameter of the second aperture, here aperture 85.4 of multi-stigmator plate 306.4, is given by D.sub.2. D.sub.2 is D.sub.1 ≤ D.sub.2 ≤ 0.75 x D.sub.T. The third aperture 85.3 in the dual-layer lenslet plate 306.3 has a diameter D3 between D2 and DT, where 1.4*D1≦D2≦0.9*D3≦0.8*DT.

[0091] FIG. 9 illustrates a further modification of FIG. 7 , and reference is also made to the descriptions of FIGS. 7 and 8 . Contrary to FIG. 7 , the single lenslet layer of the terminal multi-aperture plate 310 has been replaced with a two-layer lenslet plate forming the terminal multi-aperture plate 310. Furthermore, the position of the ground electrode plate 306.2 has been changed to a position between the filter plate 304 and the multistigmator plate 306.4. As described above with reference to FIG. 3 , a fixed voltage offset for each of the eight electrodes of the multistigmator plate 306.4 at each of the plurality of apertures 85.4 configures the multistigmator plate 306.4, in use, to form a plurality of adjustable Einzel lenses together with the ground electrode plate 306.2 and the ground layer 306.3b. The round electrodes 79 of the ring electrode layer 306.3a of the inverted two-layer lens plate forming the terminal multi-aperture plate 310 allow control of the penetration depth of the electrostatic field into the apertures 94 of the terminal multi-aperture plate 310 during use, as described in FIG. 8 . In this example, the electrostatic capacitor or field lens 307 comprises a first ring electrode 307.1 and a second ring electrode 307.2. The first ring electrode 307.1 can be connected, for example, to ground, and the second electrode 307.2 can be connected to a high voltage, for example, 25 kV or higher. The electrostatic field 92 generated by the electrostatic capacitor with the field lenses 307.1 and 307.2 is indicated by equipotential lines. The placement of the multistigmator plate 306.4 upstream of the terminal multiaperture plate 310 allows each of the primary charged particle beamlets (3), including beamlets (3.1-3.4), to be deflected or shaped before entering the corresponding terminal aperture 94. This allows, for example, pre-compensation for aberrations in the variable electrostatic lenslet field distribution 92.

[0092] The combined action of the multiple Einzel lenses, controlled by offset voltages at the multiple apertures of the multistigmator plate 306.4, and the control of the penetration depth of the electrostatic microlens field 92 into the terminal aperture 94 of the ring electrode layer 306.3a having multiple ring electrodes 79, allows the positions of the focal points 311.1-311.4 of the beamlets 3.1-3.4 to be precisely controlled to coincide with a predetermined intermediate image plane 321 having a tilt component 323. The multistigmator plate 306.4 further allows the lateral positions of the multiple focal spots 311 to be controlled and adjusted during use, and also allows pre-compensation for astigmatism. Thus, the curvature of the intermediate image plane 321 can be achieved to pre-compensate for the field curvature and tilt of the image plane 323 of the charged particle imaging system (see FIG. 1) of the multibeam generating unit 305. The curvature of the intermediate image plane 321 is convex in the propagation direction of the primary charged particle beamlets, so that the center of curvature of the curved intermediate image plane 321 is downstream of the intermediate image plane 321 .

[0093] Figure 10 shows a further modification to Figure 9, to which reference is made, in which the ground electrode plate 306.2 has been omitted. The filter plate 304 may be provided with an electrode layer 98 (not shown in Figure 10) as shown in Figure 2.

[0094] The precision of the aperture edge of the last bottom multi-aperture plate 306.3 is crucial to the precision of the penetration field, and therefore the electrostatic microlens field 92. Therefore, the aperture edge must be manufactured with high precision. Figure 11 shows the same configuration as Figure 7, and reference is made to Figures 7 and 8. The example of Figure 11 includes two multipole elements 306.4 and 310 and one ring electrode 79 for each of the multiple primary charged particle beamlets 3.1-3.4. The difference with the example of Figure 7 is that a second multi-stigmator plate, forming the terminal multi-aperture plate 310, replaces the single lenslet layer of Figure 7. The terminal multi-stigmator plate 310 allows control of the penetration depth of the electrostatic capacitor field by applying a constant voltage offset to the eight electrodes in each terminal aperture 94, similar to that described in Figure 8. In addition, the penetration field can be shifted and shaped, and astigmatism correction for each beamlet can be achieved individually. According to this example, deviations from the ideal shape of the aperture edge of the last multi-aperture plate 310 on the bottom side 76 can be electro-optically compensated for by providing each of the multi-electrode electrodes 81.2 with a predetermined compensation voltage. These voltages can be determined, for example, in a calibration step. Figure 12 shows a further variation of the example of Figure 11, where the two-layer lenslet plate 306.3 is replaced with a ground electrode plate 306.8 and a lens electrode plate 306.9, spaced apart by an additional spacer. Figure 13 shows a further variation of Figure 12, where the lens electrode plate 306.9 is replaced with an additional multistigmator plate 306.43. Here, individual lensing for each of the beamlets 3.1-3.4 can be achieved in a different way. By applying offset voltages to the sets of eight apertures of either of the multistigmator plates 306.41 and 306.43 to form the ground electrodes 306.2 and 306.8, first and second focusing capabilities are achieved during use.A third focusing capability is achieved during use by applying offset voltages to the set of eight apertures in the terminal multi-aperture plate 310 to achieve an attraction field 88 or a suppression field 90 as shown in FIG. 8 . A fourth method of generating focusing capability during use is achieved by generating a series of quadrupole fields as described in DE102020107738B3, incorporated herein by reference. Each quadrupole of each of the at least three multipole elements is rotated relative to each other to achieve aberration-free focusing. It will be appreciated that the individual voltages supplied to the multistigmator arrays 306.41, 306.43 and the terminal multi-aperture plate 310 to change or adjust the focusing capability can each be adjusted during use to achieve additional correction of lateral beam spot position and additional correction of astigmatism. It will be further appreciated that in examples having two or more multistigmator plates 306.4 or 310, the multipole elements can be at different rotation angles for each of the multistigmator plates 306.4 or 310, allowing for compensation of higher order astigmatism or trefoil aberrations as well. By combining and controlling each of the successive electrodes 79 and 81 in the multiple multi-aperture plates 306.3-306.9 and 310, including the terminal multi-aperture plate 310, of the examples of Figures 7-14, a plurality of multi-stage microlenses 316 are formed, increasing the focusing ability or focusing range DF beyond DF > 1 mm, preferably DF > 3 mm, and even more preferably DF > 5 mm, e.g., DF ≥ 6 mm.

[0095] FIG. 14 shows another variation of the example described in FIG. 9 . Contrary to the example in FIG. 9 , the round electrode 82 of the electrostatic condenser lens 307 is divided into multiple ring segments, e.g., four or eight ring segments 84.1-84.8, thus forming a quadrupole or octopole element. Therefore, the electrostatic microlens field 92 penetrating the end aperture 94 of the end multi-aperture plate 310 during use has an asymmetry or inhomogeneity, for example, generated by the ring segments 84.1-84.8 of the segmented aperture 84. These segments of the ring electrode 84 can introduce linear variations in the electrostatic microlens field 92, for example, as indicated by equipotential surfaces. This facilitates the required tilt of the intermediate image 321. An additional deflector (not shown in FIG. 14) downstream of the electrostatic condenser lens 307 can compensate for residual tilts of the multiple primary charged particle beamlets (3).

[0096] FIG. 15a shows a schematic top view of a multistigmator plate 306.4 having eight electrodes 81.11-81.18 for each aperture 85.4 (only three are marked 85.41, 85.42, and 85.43). Together, the three electrodes 81.11-81.18 form a multipole electrode 81 capable of, for example, deflecting or shaping the transmitted primary beamlets. Each of the multipole electrodes 81 is connected to a voltage supply source by a wiring connection 175. During use, low voltages ranging from -20 V to 20 V are applied to the electrodes. Each ring of electrodes 81.11-81.18 is insulated by an insulating gap 185 from the conductive bulk material forming the shielding layer 183 between the multipole electrodes 81. The shielding layer 183 is connected to ground. Thus, the multipole electrodes 81 are embodied in a bulk material, both of which may be formed, for example, from doped silicon. The multistigmator plate 306.4 is further covered by a shielding layer (not shown in FIG. 15a).

[0097] Each electrode ring 79 or 81 around the corresponding opening 85 or 94 has a width of 6 μm to 15 μm, e.g., 12 μm. The diameter D3 of the opening 85 or 95 is given, for example, by 50 μm≦D3≦70 μm. Accordingly, the diameter D3o of each electrode ring is between 65 μm≦D3≦95 μm. The minimum pitch P1 is typically limited by the diameter D3o and the remaining insulating gap formed by the shielding layer 183 between two adjacent electrode rings 79 or 81. With a minimum shielding distance of approximately 10 μm, preferably approximately 15 μm, the pitch P1 can be selected such that P1≧75 μm, e.g., P1=100 μm or P1=150 μm. Generally, a smaller width of the electrodes reduces the volume and therefore the capacitance of each electrode. A smaller capacitance is advantageous for faster changes in the electrostatic field generated by the electrodes. Larger capacitances provide greater stability with respect to fluctuating charges or charge diffusion. Therefore, the dimensions of the electrode capacitances are selected according to the time requirements for changing the electrostatic field or maintaining a constant electrostatic field. Typically, cylindrical electrodes 79 are provided with a ring width of about 15 μm, thereby providing a large capacitance with a highly stable electromagnetic lens field. Typically, multipole electrodes 81 are provided with a smaller width, e.g., 6 μm, such that each electrode 81.1-81.8 has a small capacitance and the electromagnetic multipole field changes rapidly.

[0098] FIG. 15b shows a schematic representation of segments of a ring electrode 84, including segments 84.1 to 84.8, for applying an electrostatic field with a linear gradient.

[0099] 16a and 16b show examples for fabricating a multi-aperture plate 306, such as lens electrode plate 306.9, lens electrode layer 306.3a of two-layer lenslet plate 306.3, multistigmator plate 306.4, or terminal multi-aperture plate 310. Cylindrical apertures 85, 94 are indicated by semicircles and span steps S1-S11 on the right side of the illustration. The apertures can be formed before step S1 and protected by a removable protective coating, such as photoresist, during steps S2-S11. In an alternative solution, the apertures can be formed after the formation of steps S1-S11 by lithographic processing and well-known etching techniques.

[0100] The coordinate system is selected according to the coordinate system of FIG. 1, with the positive z-axis in the propagation direction of the primary charged particle beamlet. The positive z-direction and propagation direction is "downward" in the usual sense. Regardless of whether the positive z-direction refers to "downward" in FIG. 1, FIG. 2, or FIG. 16, the "upper" plane or position refers to the plane that the primary charged particle beamlet first intersects, and the "lower" or "bottom" plane refers to the plane that the primary charged particle beamlet subsequently intersects. Thus, in the selected coordinate system, an "upper" position has a lower z-coordinate as a lower or bottom position.

[0101] In step S1, an SOI wafer is provided having two layers: a first upper layer 129.1 and a second layer 129.2. The thicknesses of these layers are typically between 30 μm and 300 μm. The second layer 129.2 is formed as a silicon oxide layer (e.g., silicon dioxide). The second layer 129.2 can have a reduced thickness by leveling the thickness of the second layer 129.2 by chemical mechanical polishing (CMP) to approximately 2 μm or less, such as 1 μm or even 0.2 μm. The upper layer 129.1 has a thickness of, for example, 50 μm.

[0102] In an alternative example, the SOI wafer comprises a third layer (129.3, not shown), e.g., 200 μm thick, to provide the ground electrode layer of the two-layer lenslet plate 306.3. The first and optional third layers (129.1, 129.3) are composed of doped silicon and have finite conductivity, so that electrodes can be formed directly in the first or third layers.

[0103] In step S2, a circular ring is formed into the device layer 129.1, forming an insulating gap 185 between the electrode 79 and the bulk material 183. For multi-polar electrodes 81, further trenches or insulating gaps for multi-polar electrode separation are created by RIE etching.

[0104] In step S3, a thick electrically insulating layer 179.1 is formed, for example by thermal oxidation, thus forming an approximately 2-3 μm thick silicon oxide film (silicon dioxide) (note: in step 3 and further steps the illustration of the second layer 129.2 is omitted).

[0105] In step S4, the remaining gaps in the electrically insulating layer 179.1 in the insulating gaps are filled and partial planarization is achieved by deposition of a silicon oxide film 179.2 (oxide from decomposition of TEOS gas, TEOS=tetraethyl orthosilicate).

[0106] In step S5, the unnecessary portions of the SiO2 layer 179.2 and, in part, the silicon oxide layer 179.1 are removed by CMP (chemical mechanical polishing), thus forming a uniform, flat insulating layer 179.3, approximately 2 μm thick or less, for example, 1 μm or even 0.5 μm thick. This avoids a thick silicon dioxide layer and reduces stress. Furthermore, the planarized silicon oxide layer allows further photolithography processing of the multi-aperture plate to be performed with greater accuracy. The reduced thickness of the SiO2 layer is also advantageous for further etching steps. During etching of apertures and other fine structures, their contours are defined by a photoresist masking layer. Planarization and thickness reduction, for example, by CMP, improves the accuracy of the edges and sidewalls of the etched structures, which is necessary for low-aberration performance of electrostatic devices.

[0107] Both thickness and non-uniform silicon dioxide layer issues contribute to unreliable and unrepeatable etch sequences and the formation of defects (under-etching, pits, rough walls). Such defects and rough sidewalls are known sources of astigmatism and higher-order aberrations. One aspect of the present invention is that these problems are avoided by the leveling of the planarized silicon dioxide or insulating layer by step S5.

[0108] In step S6, an opening for a wiring contact 193 is formed in the insulating layer 179.3 at a location remote from the inner opening sidewall 87.

[0109] In step S7, a conductive layer is formed above the planarizing insulating layer 179.3. The conductive layer can be, for example, a 1 μm thick aluminum or copper layer. It can also be formed of gold with a thickness of about 50 nm to 200 nm. The conductive layer 175 is structured by photolithography so that all electrodes 79 or 81 can be individually supplied with predetermined individual voltages by electrical wiring connections 175 (only one is shown).

[0110] In step S8, a further insulating TEOS layer 179.4 is formed to completely cover the plurality of wiring connections 175. The TEOS layer 179.4 is structured by photolithography so as to form gaps 145 with the inner walls 87 of the openings.

[0111] In step S9, the insulating TEOS layer 179.4 is ground away by CMP, leaving a residual insulating TEOS layer 179.5 having a thickness of about 0.5 μm to 2 μm above the wiring connections 175. Step S9 can also be performed before the photolithographic structuring in step S8.

[0112] In step S10, a conductive shielding layer 177.1 is formed on the residual insulating silicon oxide layer 179.5 by metal deposition, forming a plunging extension 189 into the gap 145. A metal film having a thickness of up to 2 μm, e.g., 1 μm, is formed to provide sufficient shielding of the electric field and to absorb scattered charged particles.

[0113] In two further optional steps between steps S9 and S10, a stress compensation layer formed from SiNx is deposited on the residual insulating TEOS layer 179.5, and a further silicon dioxide insulating layer is provided to cover the stress insulating layer. The insulating layer can again be planarized by chemical mechanical polishing. By PECVD (plasma enhanced chemical vapor deposition), the desired stress of SiNx, which varies from about -1 GPa (compressive) to +1 GPa (tensile), can be achieved depending on the composition x and the deposition parameters.

[0114] In a further optional step S11 (not shown separately), the bottom side 76 can be further coated with a conductive shielding layer 177.2, similar to the layer 177.1 on the upper side of the beam. Obviously, in the case of the third layer 129.3, a second conductive shielding layer 177.2 is formed on the bottom side of the third layer 129.3. The conductive layer 177.2 can be formed, for example, by a 2 μm thick aluminum layer. Both shielding layers 177.1 and 177.2 are connected to ground to prevent leakage of the electric field into the multi-aperture plate 306. The second shielding layer 177.2 is particularly important for the inverted arrangement of the multi-aperture plate 306.3, as shown in the examples of FIGS. 5, 6, 9-11, and 14. However, the inverted arrangement is not limited to the inverted arrangement of the two-layer lenslet plate 306.3; other multi-aperture plates, such as the multistigmator plate 306.4, can also be inverted, i.e., arranged so that the wire connections 175 are behind or behind the electrode layer in the direction of charged particle propagation. In such a configuration, the wire connections 175 are better covered and less susceptible to scattered charged particles; for example, induced charges are reduced or completely prevented from the electrodes 79 or 81. In an inverted arrangement, the wire connections 175 are also better protected from bremsstrahlung radiation generated on the top surface of the filter plate 304. Therefore, in some examples of an inverted arrangement, a shielding layer below or downstream of the wire connections 175 can even be omitted.

[0115] In optional step S12 (not shown), the shielding layers 177.1 and 177.2 may be further planarized by additional polishing, for example using a CMP process.

[0116] The process steps given in Figure 16 allow for providing a larger voltage over a larger focusing stroke. Additionally, thinning the silicon oxide layer by CMP introduces less stress-induced deformation, making the multi-aperture plate 306 fabricated according to process steps S1-S12 less sensitive to thermal changes.

[0117] Through process steps S1-S12, a multi-aperture array 306 having multiple electrodes with individual metal wiring connections 175 within a thin insulating layer and conductive shielding layer 177.1 is fabricated with a significantly reduced MLS thickness of less than 6 μm, preferably less than 5 μm. Several insulator layers 179.1-179.5 are required on the surface of the first electrode layer 129.1 to fill the insulating gaps 185, form an insulating layer for the metal wiring connections 175, and insulate the conductive shielding layer 177.1. The insulating layer is then polished and planarized by chemical mechanical polishing (CMP), allowing the formation of layers or structures, such as wiring connections, to be performed with greater precision. Additionally, subsequent etching processes for etching openings or forming wiring connections or other structures are significantly reduced.

[0118] CMP allows for more repeatable fabrication of the multi-aperture array 306. Planarization results in higher quality formation of the conductive shielding layer 177.1 and allows for more precise control of the electric field.

[0119] An inverted configuration of the two-layer lenslet plate 306.3 or other multi-aperture plate 306 allows electrical wiring connections 175 to be placed on both sides of the multi-aperture plate 306. Figure 17 shows how the electrical wiring connections 175 can be fabricated and routed through the layers of the multi-aperture plate 306. Through-chip wiring connections allow each multi-aperture plate 306 to be electrically contacted from the top side so that an inverted configuration is not limited.

[0120] In step C1, an electrode layer 129.1 is provided similarly to step S6 described above. The electrode layer 129.1 is fabricated from a bulk material 183, such as doped silicon, with a thickness of 50 μm to 150 μm. The electrode layer can also be formed with a greater or lesser thickness of 30 μm to 300 μm. A first insulating layer 179.1 is formed in the insulating gap and on the outer surface of the electrode layer 129.1 by thermal oxidation.

[0121] In step C2, multiple wiring connections for voltage supplies, including wiring connections 175.1, 175.2, and 175.3, are lithographically formed on the underside of electrode layer 129.1. A set of through-holes 151 is filled with a conductive material, such as metal or doped silicon, to form through-connections 149.1 and 149.2. The number N of through-connections 149 corresponds to the number N of individually addressable ring electrodes 79 (or equivalently multipolar electrodes 81). Each individually addressable ring electrode 79 is connected to one through-connection 149; for example, ring electrode 79.1 is connected to through-connection 149.1. All connections are made on the bottom or underside of electrode layer 129.1. An additional insulating layer 179.2 is provided to insulate wiring connections 175. Chemical-mechanical polishing can be applied after each deposition step to create a flat surface for subsequent photolithography and etch processing steps. Finally, a conductive shielding layer 177.1 is applied to the bottom or underside 76 of the electrode layer 129.1.

[0122] In step C3, the feedthroughs 149.1 and 149.2 on the upper side 74 are connected to connection or soldering pins 147.1 and 147.2. These pins or pads 147 are located on the periphery of the multi-aperture plate, away from the apertures and charged particle beamlets. A further insulating layer 179.3 is provided. Finally, a conductive shielding layer 177.2 is provided, insulating it from the soldering pins 147, including the soldering pins 147.1 and 147.2. As mentioned above, plunge extensions can be made for each of the conductive shielding layers 177.1, 177.2 (not shown in FIG. 17).

[0123] A plurality of aperture holes, including apertures 85.1-85.3, are etched through electrode layer 129.1, for example, after steps C2 and C3. Each aperture 85.1-85.3 has a diameter of approximately 50 μm-70 μm, and defines a plurality of insulating gaps 185 for ring electrodes 79.1-79.3. In one example, the apertures are defined by lithography and etched via deep vertical etching (DRIE) after insulating gaps 185 are formed on the electrode layer.

[0124] Additionally, through-holes 151 are etched around the periphery of the electrode layer 129.1. The through-holes 151 can be significantly smaller, e.g., less than 10 μm, or even less than 2 μm. Several through-holes 151.1 and 151.2 are created for alignment of the electrode layer 129.1 with other multi-aperture plates 306 or spacers 83. Through-connections 149 allow each of the multiple ring electrodes 79 of the single lenslet or lens electrode plate 306.9 or the two-layer lenslet plate 306.3 to be electrically connected from the opposite side, opposite the side of the wire connections 175. Similarly, each of the multiple multi-pole electrodes 81 of the multistigmator plate 306.4 can be electrically connected from the opposite side, opposite the side of the wire connections 175. By means of the through connection 149 and process steps C1 to C3, it is also possible to achieve connection to a control device such as the primary beam path control module 830 from only one side of the multi-aperture plate 306, while connecting the ring electrode 79 or multi-pole electrode 81 from both sides.

[0125] It will be appreciated that several variations of the process are possible: for example, even before step C1, the through-holes can be created first, e.g., filled with a conductive material, and the alignment holes 151.1 and 151.2 are opened by etching in step C2.

[0126] FIG. 18 illustrates the alignment and stacking of multiple multi-aperture plates, including an inverted lens electrode plate 306.9. Advanced multi-beam charged particle systems for wafer inspection require a complex multi-beam generating unit 305 or multi-beam deflection unit 390 (see FIG. 1). According to an example of the present invention, the multi-beam generating unit 305 is formed by stacking at least three multi-aperture plates 306 with spacers. The first multi-aperture plate or filter plate 304 is used to split the incident beamlet 309 and generate multiple primary charged particle beamlets 3, including beamlets 3.1-3.3. In the example of FIG. 18, three multi-aperture plates 306.3, 306.4, and 306.9 are used to individually focus each of the multiple transmitted charged particle beams 3.1-3.3 with a large focusing power or large stroke. At least one multistigmator array 306.4 is utilized to control the lateral position of each of the beamlets 3.1-3.3 to pre-compensate for any residual astigmatism. Through contacts 149 can provide wiring connections 175, such as wiring connections 175.1 and 175.2, on the bottom side of the corresponding inverted multi-aperture plates 306.3 and 306.4, thereby minimizing the desired charging of the wiring connections due to scattered charged particles and minimizing residual stray fields in the wiring connections 175. Through contacts 149 can provide solder pins 147, including solder pins 147.3, 147.4, and 147.6, on the top or side surfaces of each multi-aperture plate 306.3, 306.4, and 306.9, respectively. Via solder pins 147.3, 147.4, and 147.6, wiring connections 157 (only 157.3 is identified in FIG. 18) can be established to control unit 830 (not shown in FIG. 18) to provide individual voltages to the plurality of ring electrodes 79.1 and 79.2 and the plurality of multipolar electrodes 82. Multi-aperture plates 306 can be stacked in an optimal, predetermined orientation. Precise alignment of the stack of multi-aperture plates is achieved by at least three through-holes 151 (not shown in FIG. 18, see FIG. 17).

[0127] In addition to the through-connections 149, two multi-aperture plates 306 can be attached to each other by flip-chip bonding techniques (eutectic or thermocompression bonding), and electrical contact to the first multi-aperture plate can be established through the through-connections 149 of the second multi-aperture.

[0128] The stack of multi-aperture plates 306 can include spacers for stacking the multi-aperture plates at a predetermined distance. In the example of FIG. 18 , a support zone 197 of a predetermined thickness is provided around the periphery of the membrane zone 199 or multi-aperture plate 306. Such a membrane-in-frame configuration allows for the adjustment of the membrane zones 199 of adjacent multi-aperture plates at small gaps of about a few μm, enabling the lateral alignment and adjustment of the aperture openings with a high accuracy of less than 1 μm, preferably less than 0.5 μm. Furthermore, the stack of multi-aperture plates can be fixed to the support zone or frame 197 by applying a large force or pressure.

[0129] To enhance the performance of a multi-beam charged particle microscope during use, each of the multiple charged particle beamlets is individually controlled, for example, by individual focusing correction using multiple individually controlled ring electrodes 79 or multiple individually controlled electrodes 81 of a stigmator or deflector. Individual control of the multiple electrodes is provided by wiring, with additional wiring for the shielding and absorbing layers or sensors described above. A multi-beam raster unit for multiple beamlets, e.g., N=100, includes approximately 1,000 or more electrodes with approximately 1,000 or more individual wiring connections. The electrodes and shielding or absorbing layers require drive voltages that differ by several orders of magnitude, e.g., between 10 V and up to 1 kV. For example, multi-focus correction requires 100 high-voltage wiring for approximately 200 V, while complex astigmatism correction requires 800 low-voltage wiring for a few volts with very low noise, and the absorbing layers generate high currents. Wires with such voltage differences can easily affect each other, thereby impairing the performance of the multi-beam generating unit 305. In one embodiment, the multi-beam generating or rastering unit 305 includes design features and structures to minimize the effects of voltage differences. The multi-beam rastering 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 by an ASIC located in vacuum with a digital interface to the external controller. Routing of signal and voltage supplies is achieved through UHV flanges. Separation of wires with different voltages is achieved by supplying the voltages from different directions. For example, depending on the first direction (z direction) of the transmitted charged particle beamlet, a low voltage is supplied from a second direction (x direction) and a high voltage is supplied from a third direction. A high-current connection to the absorbing layer can be provided from a fourth direction, such as from the z direction or parallel to the third direction. All wires can be shielded individually, or low-voltage supply wires can be shielded within groups of low-voltage wires. Fewer high voltage wires can be provided at greater distances.In one embodiment, wiring connections to the ring electrodes of the electrostatic lens are provided alternately from the top and bottom of each electrode to keep the distance between the wiring as large as possible. Figure 19 shows an example embodiment. A multibeam raster unit 305, comprising five multi-aperture plates 304-306, 309, and 310, each with a parallel-arranged membrane in membrane zone 199 and a support structure in support zone 197, is mounted on a spacer 86 with the additional function of a support substrate. Through the support structure and support substrate, high-voltage wiring connections 201 are provided in the positive and negative y-directions to the ring electrodes of the electrostatic lens in at least one of the multi-aperture plates with multiple apertures 85 (only 4 × 5 are shown). The high-voltage wiring connections are shielded by a ground wire 253 connected to ground. In the peripheral region, the high-voltage wiring is shielded by a coaxial shield and insulator 255 (only four high-voltage wiring connections and coaxial shields indicated by reference numerals 251 and 255 are shown). Low-voltage wiring connections 257 and 259 for the electrostatic stigmators and deflectors are provided in both x-directions (only the positive direction is shown) from ASICs 261 and 265 mounted on support substrate 86. The low-voltage wiring is also shielded from each other by ground wiring (not shown) between the low-voltage wiring. The ASICs receive digital signals via digital signal lines 267.1 and 267.2, as well as power via low-voltage supply lines 269.1 and 269.2. Thus, the high-voltage and low-voltage signals are separated as much as possible, reducing the adverse effects of mutual induction of leakage and achieving more reliable optical performance of the multi-beam raster unit.

[0130] FIG. 20 shows another variation of the example described in FIG. 14 . Contrary to the example in FIG. 14 , the stack of multi-aperture plates 315 and the electrode 82 of the electrostatic condenser lens 307 are not parallel but form an angle Φ between them. Therefore, the electrostatic field 92 generated between the terminal multi-aperture plate 310 and the electrode 82 exhibits asymmetry. The electrostatic field 92 penetrates the terminal aperture 94 of the terminal multi-aperture plate 310 and forms microlenslets within the terminal aperture 94, which contribute to the overall focusing ability of the multi-beam generating unit 305. The electrostatic microlens field of the electrostatic field 92 has asymmetry, which contributes to a linear variation in the focusing ability of the electrostatic microlens field across the exit surface of the terminal multi-aperture plate 310. The electrostatic microlens field forms different focal lengths, including a linear component with a linear dependence of the focal length on the x-coordinate. Therefore, a tilt component 323 of the intermediate image plane 321 is generated in addition to the field curvature. Thus, the field curvature and tilt components of the angle of the image plane of the electron optical element located downstream of the charged particle multi-beamlet generator 300 are pre-compensated. This example is not limited to the terminal multi-aperture plate 310, but can also be used in combination with a hybrid lens plate 306.5 without additional electrodes 79.

[0131] According to this example, either the electrostatic condenser lens electrode 82 or the stack of multi-aperture plates 315 of the primary multi-beamlet forming unit 305 or both are inclined with respect to the average propagation axis z of the plurality of primary charged particle beamlets 3 downstream of the primary multi-beamlet forming unit 305. In the example of FIG. 20, the source 301 and the collimating lens 303 are configured such that the propagation direction of the incident beam 309 is perpendicular to the filter plate 304. In this example, the stack of multi-aperture plates 315 including the filter plate 204 and the end multi-aperture plate 310 is inclined by an angle Φ1 with respect to the x-axis, and thus the incident beam 309 is inclined by the same angle Φ1 with respect to the z-axis. The inclination angle Φ1 of the incident beam 309 can be achieved by either the mechanical inclination of the source 301 and the collimating lens 303 or the electrostatic deflector 302 disposed upstream of the filter plate 304 that can incline the propagation direction of the incident beam 309 accordingly.

[0132] In the example of FIG. 20, further, the electrode 84 of the electrostatic condenser lens 307 is inclined by an angle Φ2 with respect to the x-axis, and a total angle of Φ = Φ1 + Φ2 between the end aperture plate 310 and the electrode 84 of the electrostatic condenser lens 307 is obtained. Thus, the inclination component 323 of the intermediate image plane 321 having an angle Φ3 is achieved. The angle Φ1 can be selected such that the exit surface of the end multi-aperture plate 310 and the plane of the inclination component 323 at the angle Φ3 coincide with and intersect each other with the unit plane of the electrostatic lens field 92 including the micro lens formed within the aperture 94 of the end aperture plate 310.

[0133] According to this example, the electrostatic condenser lens electrode 82 or the stack of multi-aperture plates of the primary multi-beamlet forming unit 305, or both, can be mounted on manipulators 340.1 or 340.2 configured to individually adjust the tilt angles Φ1 and Φ2. By appropriately adjusting the angles Φ1 and Φ2 using at least one manipulator 340, the tilt component 323 of the intermediate image plane 321 can be adjusted. As mentioned above, the field curvature and tilt component 323 are affected by the imaging settings of the multi-beamlet charged particle microscope system 1. In particular, different rotations of the tilt component 323 may be required, for example, due to different focusing capabilities of the objective lenses 203. For example, the tilt component 323 can be adjusted or rotated by at least one tilt or rotation manipulator 340.2 of the electrode 84 of the condenser lens 307 to pre-compensate for different image rotations of the magnetic objective lens 102. Thus, the control unit (800) of the multi-beam charged particle microscope system (1) can be configured to control at least one of the tilt angles Φ, Φ1, Φ2 during use depending on the image plane tilt according to the image settings of the multi-beam system (1).

[0134] According to the improvements of the present invention, a larger focusing range for individually focusing multiple primary charged particle beamlets is achieved. An improved multi-beam generating unit according to one example of the present invention includes at least a terminal multi-aperture plate having multiple individually addressable electrodes, which can form ring electrodes or multipole electrodes at each of multiple terminal apertures of the terminal multi-aperture plate. This arrangement makes it possible to individually manipulate each of the penetrating microlens fields formed by the penetration of a global electrostatic field into the terminal aperture. Thus, a large focusing range is achieved by reducing the individual voltage differences applied to the multiple individually addressable electrodes.

[0135] An example improved multi-beam generating unit includes at least a second or further multi-aperture plate. The multiple multi-aperture plates can be electrically connected to the control unit, and the electrical contacts can be located on the same side of each multi-aperture plate, for example, on a first top side or a second bottom side of each multi-aperture plate. Some of the multi-aperture plates can include feedthrough connections for electrically connecting multiple wiring connections on one side with electrical contacts on the other side.

[0136] Although a general multi-beam raster unit is described in this embodiment as a multi-beam generating unit 305, the features of this embodiment are also applicable to other multi-beam raster units, such as a multi-beam deflector or a multi-beam stigmator unit. Generally, the multi-beam raster unit with increased focusing range according to examples of the present invention can also be applied to the secondary beam path 11 (see FIG. 1), for example, as a multi-aperture corrector 220.

[0137] The features of this embodiment improve the performance of multi-beam charged particle microscopes to achieve higher resolutions of less than 5 nm, preferably less than 3 nm, more preferably less than 2 nm, or even less than 1 nm. This improvement is particularly relevant to the further development of multi-beam charged particle microscopes with larger beamlet counts, 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, for example, multi-aperture plates with larger diameters and larger apertures and electrodes, including even more wiring connections. This improvement is particularly relevant to the routine application of multi-beam charged particle microscopes, for example, in semiconductor inspection and research, where high reliability and high reproducibility and low machine-to-machine variation are required.

[0138] This embodiment provides a charged particle beam system that can be used to operate with multiple charged particle beams and achieve higher imaging performance. In particular, the larger focal range DF of the primary multi-beamlet forming unit 305 of the present invention allows for a narrower range of resolution for each beamlet of the multiple beamlets. This feature enables pre-compensation for a large range of field curvature and field tilt, which is increasingly important, especially for multi-beam systems for planar wafer inspection tasks where the number of charged particle beams is increasing. The features and methods described in this embodiment, and their combinations, provide, for example, multiple beamlets with beamlet diameters ranging from 2 nm to 2.1 nm at an average resolution of 2.05 nm. The resolution range achieved by the features and methods of this embodiment is less than 0.15%, preferably less than 0.1%, and even more preferably less than 0.05% of the average resolution.

[0139] The present invention is not limited to the above-described embodiments or examples. The embodiments or examples can be combined with each other completely or partially. As can be seen from the above description, many variations and modifications are possible, and it is clear that the scope of the present application is not limited by the specific examples.

[0140] Although the improvements are described in the example of a multi-beam charged particle microscope, the improvements are also applicable to other multi-beam charged particle systems, such as multi-beam lithography systems, limited to multi-beam charged particle systems for wafer inspection.

[0141] Throughout the present embodiments, electrons shall be generally understood as charged particles. Although some embodiments are described in the example of electrons, they should not be limited to electrons and are well applicable to all kinds of charged particles, such as helium or neon ions.

[0142] The present invention and its embodiments can be described by the following paragraphs. However, the present invention is not limited to these paragraphs. It is understood that various combinations and modifications are possible.

[0143] Item 1. A multi-beam generating unit (305) for a multi-beam system (1), comprising, in order of propagation direction of an incident primary charged particle beam (309): - a filter plate (304) having a plurality of first apertures (85.1) for generating a plurality of primary charged particle beamlets (3), the filter plate (304) being connected to ground level during use; - a terminal multi-aperture plate (310) comprising a plurality of terminal apertures (94) comprising a first plurality of individually addressable electrodes (79.2, 81.2) disposed around each of the plurality of terminal apertures (94); a condenser lens (307) having a condenser electrode (82, 84) with a single aperture configured to transmit a plurality of primary charged particle beamlets (3) during use; Equipped with - the capacitor electrodes (82, 84) are configured to generate, during use, a plurality of electrostatic microlens fields (92) penetrating each of a plurality of end apertures (94), and the multi-beam generating unit (305) further comprises a control unit (830) configured to individually control the capacitor electrodes (82, 84) and each of the first plurality of individually addressable electrodes (79.2, 81.2) to affect the penetration depth and / or shape of each of the plurality of electrostatic microlens fields (92), thereby independently adjusting the lateral and / or axial focal position of each of the plurality of primary charged particle beamlets (3) on the intermediate image plane (321) to pre-compensate for field curvature and / or field tilt of the multi-beam system (1).

[0144] Item 2. A multi-beam generating unit (305) as described in Item 1, wherein the first plurality of individually addressable electrodes (79.2, 81.2) are formed as a first plurality of electrostatic cylindrical electrodes (79.2), each cylindrical electrode (79.2) being arranged around one of the plurality of end openings (94) and configured to generate an attraction field (88) or a push field (90) during use.

[0145] Item 3. The multi-beam generating unit (305) described in Item 1, wherein the first plurality of individually addressable electrodes (79.2, 81.2) are formed as a first plurality of electrostatic multi-pole electrodes (81.2), each multi-pole electrode (81.2) being arranged around one of the plurality of end openings (94) and configured to generate an attraction field (88), a push field (90) and / or a deflection field and / or an astigmatism correction field during use.

[0146] Item 4. A multi-beam generating unit (305) according to any one of items 1 to 3, wherein the terminal multi-aperture plate (310) comprises a first terminal electrode layer (306.3a) comprising a first plurality of individually addressable electrodes (79.2, 81.2), and a second electrode layer (306.3b) insulated from the first plurality of individually addressable electrodes (79.2, 81.2) and arranged upstream of the first terminal electrode layer (306.3a), the second electrode layer (306.3b) being connected to a ground level during use to form a ground electrode layer.

[0147] Item 5. The multi-beam generating unit (305) according to any one of Items 1 to 3, wherein the terminal multi-aperture plate (310) is made from a single electrode layer.

[0148] Item 6. The multi-beam generating unit (305) according to any one of items 1 to 5, further comprising a further multi-aperture plate configured as a first multi-stigmator plate (306.4, 306.41) arranged upstream of the terminal multi-aperture plate (310), the first multi-stigmator plate (306.4, 306.41) having a plurality of apertures (85.4, 85.41), each of the plurality of apertures comprising a second plurality of individually addressable multi-pole electrodes (81, 81.1) forming a plurality of electrostatic multi-pole elements arranged around the plurality of apertures (85.4, 85.41), each of the second individually addressable multi-pole electrodes (81, 81.1) being connected to a control unit (830) configured to deflect, focus or correct aberrations of each individual beamlet of the plurality of primary charged particle beamlets (3).

[0149] Item 7. The multi-beam generating unit (305) according to Item 6, further comprising a further multi-aperture plate configured as a second multi-stigmator plate (306.43) arranged upstream of the terminal multi-aperture plate (310), the second multi-stigmator plate (306.43) having a plurality of apertures (85.43), each of the plurality of apertures comprising a third plurality of individually addressable multi-pole electrodes (81.3) forming a plurality of electrostatic multi-pole elements arranged around the plurality of apertures (85.43), each of the third individually addressable electrodes (81.3) being connected to a control unit (830) configured to deflect, focus or correct aberrations of each individual beamlet of the plurality of primary charged particle beamlets (3).

[0150] Item 8. A multi-beam generating unit (305) according to any one of items 1 to 7, further comprising a further multi-aperture plate configured as an electrostatic lens array (306.3, 306.9) arranged upstream of the terminal multi-aperture plate (310), the electrostatic lens array (306.3, 306.9) having a plurality of apertures (85.3, 85.9) with a plurality of second cylindrical electrodes (79), each individually connected to a control unit (830) configured to form a plurality of electrostatic lens fields during use.

[0151] Item 9. The multi-beam generating unit (305) according to item 8, wherein the electrostatic lens arrays (306.3, 306.9) are lens electrode plates (306.9) made from a single electrode layer.

[0152] Item 10. The multi-beam generating unit (305) according to item 8, wherein the electrostatic lens array (306.3, 306.9) is a two-layer lenslet electrode plate (306.3) having a lens electrode layer 306.3a and a ground electrode layer 306.3b.

[0153] Clause 11. In one example, the capacitor electrodes (82, 84) are formed as segmented electrodes (84) comprising a plurality of at least four electrode segments (84.1 to 84.4), and the control unit (830) is configured to provide an asymmetric voltage distribution to the plurality of at least four electrode segments (84.1 to 84.4) during use to facilitate focusing of the plurality of primary charged particle beamlets (3) within a curved intermediate image plane (321) having a tilt component (323), in a multi-beam generating unit (305) described in any one of clauses 1 to 10.

[0154] Item 12. A multi-beam generating unit (305) according to any one of items 1 to 11, further comprising at least a first ground electrode plate (306.2) having a plurality of apertures (85.2), the ground electrode plate (306.2) forming a first ground electrode during use, the ground electrode plate (306.2) being positioned between the filter plate (304) and the terminating multi-aperture plate (310).

[0155] Item 13. The multi-beam generating unit (305) according to item 12, further comprising a second ground electrode plate (306.8).

[0156] Item 14. The multi-beam generating unit (305) according to any one of items 8 to 13, wherein the control unit (830) is configured to provide, during use, a plurality of individual voltages to each of the plurality of electrodes (79, 81, 79.1, 81.1, 79.2, 81.2, 81.3) of the terminal multi-aperture plate (3.10), the first multi-stigmator plate (306.4, 306.41) and / or the second multi-stigmator plate (306.43) and / or the electrostatic lens array (306.3, 306.9) to together form an array of individually addressable multi-stage microlenses (316) having an individually variable focusing range variation DF of at least 6 mm, preferably at least 8 mm, and even more preferably more than 10 mm for each individually addressable multi-stage microlens (316).

[0157] Item 15. A multi-beam generating unit (305) according to any one of items 1 to 14, further comprising a plurality of spacers (83.1 to 83.5) or support zones (179) for holding the plurality of multi-aperture plates (306.2 to 306.9, 310) at a predetermined distance from each other.

[0158] Item 16. A multi-beam generating unit (305) according to any one of items 1 to 15, wherein at least one of the plurality of multi-aperture plates (306.4 to 306.9, 310) is configured as an inverted multi-aperture plate, the inverted multi-aperture plate having electrical wiring connections (175) for a plurality of individually addressable electrodes (79, 79.1, 79.2, 81, 81.1, 81.2, 81.3) on a lower or bottom side of the inverted multi-aperture plate opposite the beam entrance side.

[0159] Clause 17. The multi-beam generating unit (305) according to clause 16, wherein at least one inverted multi-aperture plate further comprises a plurality of through-connections (149, 149.1, 149.2) for electrically contacting the plurality of individually addressable electrodes (79, 79.1, 79.2, 81, 81.1, 81.2, 81.3) via electrical wiring connections (175) on the lower or bottom side of the inverted multi-aperture plate, and contact pins (147, 147.1, 147.2) are arranged on the upper or beam entrance side of the inverted multi-aperture plate.

[0160] Item 18. A multi-beam generating unit (305) according to any one of items 1 to 17, wherein the terminal multi-aperture plate (310) further comprises a conductive shielding layer (177.2) having a plurality of apertures (94), the conductive shielding layer (177.2) being electrically insulated from the first plurality of individually addressable electrodes (79.2, 81.2), and the conductive shielding layer (177.2) being disposed on the bottom side (76) of the terminal multi-aperture plate (310) between the individually addressable electrodes (79.2, 81.2) and the condenser lens (307).

[0161] Item 19. A multi-beam generating unit (305) according to any one of items 1 to 18, wherein in the propagation direction of the incident primary charged particle beam (309), the first openings (85.1) of the filter plate (304) have a first diameter D1 and the end openings (94) each have an end diameter DT, where DT is in the range between 1.6 × D1 ≦ DT ≦ 2.4 × D1.

[0162] Item 20. In the propagation direction of the incident primary charged particle beam (309), the first aperture (85.1) of the filter plate 304 has a first diameter D1, the second apertures (85.2, 85.3, 85.4, 85.9) of the further multi-aperture plates (306.2, 306.3, 306.4, 306.9) have a second diameter D2, the terminal aperture (94) has a terminal diameter DT, D1 < D2 < DT, and preferably 1.3×D1 ≤ D2 ≤ 0.8×DT. The multi-beam generation unit (305) according to Items 6 to 19.

[0163] Item 21. In the propagation direction of the incident primary charged particle beam (309), the first aperture (85.1) of the filter plate 206.1 has a first diameter D1, the second apertures (85.2, 85.3, 85.4, 85.9) of the second multi-aperture plates (306.2, 306.3, 306.4, 306.9) have a second diameter D2, the third apertures (85.2, 85.3, 85.4, 85.9) of the third or further multi-aperture plates (306.3, 306.4, 306.41, 306.43, 306.9) have a diameter D3, the terminal aperture (94) has a terminal diameter DT, the multi-aperture plates are arranged in the propagation direction of the primary charged particles, D1 < D2 < D3 < DT, and preferably 1.4×D1 ≤ D2 ≤ 0.9×D3 ≤ 0.8×DT. The multi-beam generation unit (305) according to Items 6 to 20.

[0164] Item 22. A multi-aperture plate (306), - a plurality of apertures (85.3, 85.4, 85.9, 94) having a plurality of insulated individually addressable electrodes (79, 81) in an insulating electrode layer (129.1), the plurality of electrodes (79, 81) being arranged around the apertures (85.3, 85.4, 85.9, 94), the plurality of apertures (85.3, 85.4, 85.9, 94), and - a first conductive shielding layer (177.1) on a first side of the multi-aperture plate (306) having a first thickness T1, and - a first planarizing insulating layer (179.5) having a second thickness T2 - a layer of a plurality of electrical wiring connections (175) of a third thickness T3; a second planarization insulating layer (179.3) between the electrode layer (129.1) and the layer of electrical wiring connections (175), whereby wiring contacts (193) are formed between the wiring connections and each of the electrodes (79, 81), the second planarization insulating layer (179.3) having a fourth thickness T4; Equipped with The multi-aperture plate (306) has first and second planarizing insulating layers (179.5, 179.3) made of silicon dioxide and leveled to a second thickness T2 and a fourth thickness T4 each less than 2 μm, where T2≦T3≦2 μm.

[0165] Item 23. A multi-aperture plate (306) according to item 22, wherein each of the wiring contacts (193) is arranged at the outer edge of each individually addressable electrode (79, 81) at a distance h to the inner wall (87) of the aperture (85, 94), and h is preferably greater than h≧6 μm, preferably h>8 μm, for example h≧10 μm.

[0166] Item 24. The multi-aperture plate (306) according to item 22 or 23, further comprising: a second conductive shielding layer (177.2) on a second side of the multi-aperture plate (306) and having a sixth thickness T6; and a third planarizing insulating layer (129.2) formed between the second conductive shielding layer (177.2) and the electrode layer (129.1) and having a fifth thickness T5<2.5 μm.

[0167] Item 25. A multi-aperture plate (306) according to any one of items 22 to 24, wherein at least one of the first or second conductive shielding layers (177.1, 177.2) has a plurality of protruding extensions (189) into each of the plurality of openings (85, 94), forming a gap with a width g relative to the electrodes (79, 81), where g<4 μm, preferably g≦2 μm.

[0168] Item 26. A multi-aperture plate (306) according to any one of items 22 to 25, further comprising a shielding electrode layer (183) connected to a ground level (0 V) between the plurality of individually addressable electrodes (79, 81) for shielding the plurality of individually addressable electrodes (79, 81) from each other.

[0169] Item 27. A multi-aperture plate (306) according to items 22 to 26, wherein the multi-aperture plate (306) is one of a plurality of at least two multi-aperture plates (306, 306.3, 306.4, 306.9, 310) of a multi-beam generating unit (305) configured to focus a plurality of primary charged particle beamlets (3) during use.

[0170] Item 28. The multi-aperture plate (306) is a terminal multi-aperture plate (310) having a plurality of terminal apertures (94) in a multi-beam generating unit (305), and during use, each of a plurality of primary charged particle beamlets (3) exits the multi-beam generating unit (305) at one of the plurality of terminal apertures (94), and the plurality of electrodes (79, 81) are configured to manipulate a plurality of penetrating microlens fields (92) that are penetrating into the plurality of terminal apertures (94) during use, in accordance with items 22 to 27.

[0171] Item 29. A multi-aperture plate (306) according to item 28, wherein a condenser lens (307) is arranged behind the multi-aperture plate (306), which is a terminal multi-aperture plate (310) of the multi-beam generating unit (305), and is configured to generate, during use, a plurality of electrostatic microlens fields (92) penetrating a plurality of terminal apertures (94).

[0172] Item 30. The multi-aperture plate (306) according to any one of items 22 to 29, wherein the multi-aperture plate (306) is arranged in an inverted configuration with a plurality of wiring connections (175) on a first side of the multi-aperture plate (306) and a plurality of contact pins (147) on a second side of the multi-aperture plate (306) opposite the first side, and further comprises a plurality of through-connections (149) for connecting the plurality of wiring connections (175) on the first side with the contact pins (147) on the second side.

[0173] Item 31. A terminal multi-aperture plate (310), a plurality of end apertures (94) configured to form, in use, a plurality of electrostatic microlens fields (92, 92.1, 92.2) penetrating the plurality of end apertures (94); a plurality of individually addressable electrodes (79.2, 81.2) arranged around the periphery of the termination aperture (94), the plurality of individually addressable electrodes (79.2, 81.2) configured to be individually connected to a control unit (830) and configured, in use, to individually affect the penetration depth and / or shape of each of the plurality of electrostatic microlens fields (92, 92.1, 92.2); A terminal multi-aperture plate (310) comprising:

[0174] Item 32. The termination multi-aperture plate (310) described in Item 31, further comprising a first conductive shielding layer (177.2) on the termination or beam exit side (76) of the termination multi-aperture plate (310) connected to a ground level (0V), the first conductive shielding layer (177.2) being configured to shield the plurality of electrostatic microlens fields (92) from penetrating into the termination multi-aperture plate (310) so that, during use, the plurality of electrostatic microlens fields (92) penetrate only into the termination aperture (94).

[0175] Item 33. The termination multi-aperture plate (310) according to item 31 or 32, further comprising a shielding electrode layer (183) connected to a ground level (0V) between the plurality of individually addressable electrodes (79.2, 81.2), configured to shield the plurality of individually addressable electrodes (79.2, 81.2) from each other during use.

[0176] Item 34. A terminal multi-aperture plate (310) described in any one of items 31 to 33, further comprising a plurality of wiring connections (175) for providing a plurality of individual voltages to the plurality of individually addressable electrodes (79.2, 81.2), the plurality of wiring connections (175) being configured to be connected to a control unit (830).

[0177] Item 35. A termination multi-aperture plate (310) as described in Item 34, wherein the plurality of wiring connections (175) are arranged on a first side of the termination multi-aperture plate (310) and are insulated from the conductive shielding layer (177, 177.2), and the termination multi-aperture plate (310) further comprises a plurality of through-connections (149) connected to the plurality of wiring connections (175) and configured to be connected to a control unit (830).

[0178] Section 36. a second conductive shielding layer (177.1) on the upper side of the terminal multi-aperture plate (310), the upper side being the side on which the plurality of charged particle beamlets (3) enter the terminal multi-aperture plate (310); - a plurality of planarizing insulating layers (129.2, 179, 179.1, 179.3, 179.5); - a plurality of layers of electrical wiring connections (175); - an electrode layer (129.1) containing a plurality of individually addressable electrodes (79.2, 81.2); Furthermore, 36. The termination multi-aperture plate (310) according to any one of clauses 32 to 35, wherein each of the electrode layer (129.1), the layer of electrical wiring connections (175) and the first or second conductive shielding layer (177.2, 177.2) is insulated from adjacent layers by one of the planarizing insulating layers (129.2, 179, 179.1, 179.3, 179.5), each of the planarizing insulating layers (129.2, 179, 179.1, 179.3, 179.5) being made of silicon dioxide and leveled to a thickness T of less than T<3 μm, preferably less than T≦2.5 μm.

[0179] Item 37. The termination multi-aperture plate (310) according to Item 36, wherein the electrode layer (129.1) has a thickness of 50 μm to 100 μm.

[0180] Item 38. An inverted multi-aperture plate 306, - a plurality of apertures (85, 94) having a plurality of insulated individually addressable electrodes (79, 81) in an insulated electrode layer (129.1), the plurality of electrodes (79, 81) being arranged around the periphery of the apertures (85, 94); a first conductive shielding layer (177.1) on a first side of the multi-aperture plate (306), the first conductive shielding layer having a first thickness T1; - a first planarizing insulating layer (179.5) of a second thickness T2; - a layer of a plurality of electrical wiring connections (175) of a third thickness T3; a second planarization insulating layer (179.3) between the electrode layer (129.1) and the layer of electrical wiring connections (175), wherein through-wire contacts (193) are formed between each of the wiring connections and the electrodes (79, 81), the second planarization insulating layer (179.3) having a fourth thickness T4; - a plurality of feedthrough connections (149) and contact pins (147) for contacting the plurality of electrical wiring connections (175) through the first insulated electrode layer (129.1), configured to electrically connect the plurality of electrical wiring connections (175) on a first side of the first insulated electrode layer (129.1) with the contact pins (147) on a second, opposing side of the electrode layer (129.1); An inverted multi-aperture plate 306 comprising:

[0181] Item 39. A multi-aperture plate 306 according to item 38, wherein each of the wiring contacts (193) is arranged at the outer edge of each individually addressable electrode (79, 81) at a distance h to the inner wall (87) of the aperture (85, 94), where h is preferably greater than h > 6 μm, and even more preferably h > 10 μm, e.g., h = 12 μm.

[0182] Item 40. The multi-aperture plate 306 according to item 38 or 39, further comprising: a second conductive shielding layer (177.2) on a second side of the multi-aperture plate (306) and having a sixth thickness T6; and a third planarization insulating layer (129.2) having a fifth thickness T5<2.5 μm and formed between the second conductive shielding layer (177.2) and the electrode layer (129.1) opposite the second planarization insulating layer (179.3), wherein the second conductive shielding layer (177.2) comprises an opening (148) for insulating the contact pin (147) from the second conductive shielding layer (177.2).

[0183] Item 41. The multi-aperture plate 306 according to items 38 to 40, wherein at least one of the first or second conductive shielding layers (177.1, 177.2) has a plurality of protruding extensions (189) into each of the plurality of openings (85, 94), forming a gap of width g to the electrodes (79, 81), where g<4 μm, preferably g≦2 μm.

[0184] Item 42. The multi-aperture plate 306 according to items 38 to 41, further comprising a shielding electrode (183) connected to ground level (0V) between the plurality of individually addressable electrodes (79, 81) for shielding the plurality of individually addressable electrodes (79, 81) from each other.

[0185] Item 43. A method for individually changing the focal length of each of a plurality of primary charged particle beam spots (311), comprising: - providing a plurality of individually addressable termination electrodes (79.2, 81.2) in each of a plurality of termination apertures (94) of a termination multi-aperture plate (310); - providing condenser lens electrodes (82, 84) adjacent to the terminal multi-aperture plate (310) and downstream of the terminal multi-aperture plate (310) in the direction of propagation of the plurality of primary charged particle beamlets (3); - providing, by a control unit (830), at least a first voltage to the condenser lens electrodes (82, 84) to generate a plurality of electrostatic microlens fields (92) penetrating a plurality of end apertures (94); - providing, by a control unit (830), a plurality of individual voltages to each of a plurality of individually addressable electrodes (79.2, 81.2); - individually controlling a plurality of individual voltages on the individually addressable end electrodes (79.2, 81.2) to affect the penetration depth of each of the plurality of electrostatic microlens fields (92) and thereby independently adjust the axial focal position of each of the plurality of primary charged particle beamlets (3) on the curved intermediate image plane (321); A method comprising:

[0186] Clause 44. The method of clause 43, wherein the plurality of individually addressable end electrodes (79.2, 81.2) are formed as a first multipole electrode (81.2), and the method further comprises the step of individually controlling a plurality of individual voltages to the first multipole electrode (81.2) to affect the shape and / or lateral position of each of the plurality of electrostatic microlens fields (92), thereby independently adjusting the lateral focal position and shape of each of the plurality of primary charged particle beamlets (3) on the curved intermediate image plane (321).

[0187] Clause 45. The method according to clause 43 or 44, wherein the step of individually controlling the plurality of individual voltages is configured to adjust the focal position of each of the plurality of primary charged particle beamlets (3) on the curved intermediate image plane (321) by means of a tilt component (232).

[0188] Section 46. - providing a first multi-stigmator plate (306.4, 306.41) having a plurality of apertures (85.4) and a plurality of individually addressable second multipolar electrodes (81.1) upstream of the terminal multi-aperture plate (310); - providing, by a control unit (830), a plurality of individual voltages to each of a plurality of individually addressable second multipolar electrodes (81.1); - individually controlling a plurality of individual voltages of the second multipole electrode (81.1) to influence the shape and / or lateral position of each of the plurality of primary charged particle beamlets (3) before passing through the plurality of termination openings (94) of the termination multi-aperture plate (310); Item 46. The method according to any one of items 43 to 45, further comprising:

[0189] Section 47. - providing a second multistigmator plate (306.4, 306.41) having a plurality of apertures (85.4) and a plurality of individually addressable third multipolar electrodes (81.3); - providing, by a control unit (830), a plurality of individual voltages to each of a plurality of individually addressable third multipolar electrodes (81.3); - individually controlling a plurality of individual voltages of the third multi-pole electrode (81.3) to influence the shape and / or lateral position and / or direction of each of the plurality of primary charged particle beamlets (3) before passing through the plurality of termination openings (94) of the termination multi-aperture plate (310); Item 47. The method of item 46, further comprising:

[0190] Section 48. - providing a lenslet plate (306.3, 306.9) having a plurality of apertures (85.3, 85.9) and a plurality of individually addressable ring electrodes (79); - providing, by a control unit (830), a plurality of individual voltages to each of a plurality of individually addressable ring electrodes (79); - individually controlling a plurality of individual voltages of the ring electrode (79) to influence the focal position of each of the plurality of primary charged particle beamlets (3) before passing through a plurality of end apertures (94) of the end multi-aperture plate (310); Item 48. The method according to any one of items 43 to 47, further comprising:

[0191] Clause 49. The method of any one of clauses 43 to 48, further comprising individually controlling a plurality of individual voltages of any of the multipole electrodes (81.1, 81.3) and / or of the individually addressable end electrodes (79.2, 81.2) of the ring electrode (79) of the lenslet plate (306.3, 306.9) to jointly influence the axial and lateral focal position, shape, and propagation direction of each of the plurality of primary charged particle beamlets (3).

[0192] Item 50. A multi-beam generating unit (305) for a multi-beam system (1), comprising: - a filter plate (304) having a plurality of first apertures (85.1) for generating a plurality of primary charged particle beamlets (3), the filter plate (304) being connected to ground level during use; a plurality of multi-aperture plates (306, 306.3, 306.4, 306.9), each multi-aperture plate (306, 306.3, 306.4, 306.9) comprising an electrode layer (129.1) and a plurality of contact pins (147) arranged on a first side of the electrode layer (129.1); a terminal multi-aperture plate (310), wherein each multi-aperture plate (306, 306.3, 306.4, 306.9) further comprises a layer of multiple electrical wiring connections (175), and at least one of the multiple multi-aperture plates (306, 306.3, 306.4, 306.9) is configured as an inverted multi-aperture plate (306, 306.3, 306.4, 306.9), wherein the layer of multiple electrical wiring connections (175) is disposed on a second side of the electrode layer (129.1) of the inverted multi-aperture plate (306, 306.3, 306.4, 306.9); and A multi-beam generating unit (305) comprising:

[0193] Item 51. The multi-beam generating unit (305) according to Item 50, wherein the inverted multi-aperture plate (306, 306.3, 306.4, 306.9) further comprises a plurality of through-connections (149) for electrically connecting the plurality of contact pins (147) with a plurality of electrical wiring connections (175).

[0194] Clause 52. A multi-beam generating unit (305) according to clause 50 or 51, wherein the terminal multi-aperture plate (310) comprises an electrode layer (129.1) having a plurality of individually addressable electrodes (79.2, 81.2), a layer of a plurality of electrical wiring connections (175), and a plurality of contact pins (147) arranged on a first side of the electrode layer (129.1).

[0195] Item 53. A multi-beam generating unit (305) according to item 52, wherein a layer of a plurality of electrical wiring connections (175) is disposed on a second side of the electrode layer (129.1) of the terminating multi-aperture plate (310).

[0196] Item 54. A multi-beam generating unit (305) described in any one of items 50 to 53, further comprising a control unit (830) configured to provide multiple voltages to each of the multiple contact pins (147) of each multi-aperture plate (306, 306.3, 306.4, 306.9) and / or the terminal multi-aperture plate (310) from the same first side.

[0197] Section 55. - a condenser lens (307) arranged downstream of the terminal multi-aperture plate (310) and having a condenser electrode (82, 84) with a single aperture configured to transmit a plurality of primary charged particle beamlets (3) during use; - capacitor electrodes (82, 84) configured to generate, in use, a plurality of electrostatic microlens fields (92) penetrating each of a plurality of termination apertures (94); a control unit (830) configured to individually control the capacitor electrodes (82, 84) and each of the plurality of individually addressable electrodes (79.2, 81.2) of the terminating multi-aperture plate (310) to affect the penetration depth and / or shape of each of the plurality of electrostatic microlens fields (92), thereby independently adjusting the lateral and axial focal positions of each of the plurality of primary charged particle beamlets (3) on the curved intermediate image plane (321); The multi-beam generating unit (305) according to any one of items 50 to 54, further comprising:

[0198] Item 56. A multi-beam generating unit (305) for a multi-beam system (1), comprising: - a filter plate (304) having a plurality of first apertures (85.1) for generating a plurality of primary charged particle beamlets (3) from the incident primary charged particle beamlets (309); - at least a first multi-aperture plate (306.3, 306.4, 306.9) having an electrode layer (129.1); a terminal multi-aperture plate (310) having a plurality of terminal openings (94); a condenser lens (307) having capacitor electrodes (82, 84); - a control unit (830) configured to provide a plurality of individual voltages to at least the first multi-aperture plate (306.3, 306.4, 306.9), the end multi-aperture plate (310) and the capacitor electrodes (82, 84), wherein the multi-beam generating unit (305) is configured to individually adjust each of the axial focal positions of each of the plurality of primary charged particle beamlets (3) with a focusing range DF greater than DF>3 mm, preferably DF>4 mm, even more preferably DF>6 mm, for example DF≧8 mm.

[0199] Item 57. A multi-beam generating unit (305) as described in Item 56, wherein the terminal multi-aperture plate (310) comprises a plurality of individually addressable electrodes (79.2, 81.2) arranged around each of the plurality of terminal openings (94), and the control unit (830) is configured, during use, to provide a plurality of individual voltages to each of the plurality of individually addressable electrodes (79.2, 81.2).

[0200] Clause 58. A multi-beam generating unit (305) according to clause 56 or 57, wherein the multi-beam generating unit (305) is further configured to focus each of the plurality of primary charged particle beamlets (3) onto a curved intermediate surface (321).

[0201] Clause 59. The multi-beam generating unit (305) according to clause 58, wherein the curved intermediate surface (321) has an inclined component (323).

[0202] Clause 60. A multi-beam generating unit (305) according to clause 58 or 59, wherein the multi-beam generating unit (305) is further configured to individually adjust each of the lateral focal positions of each of the plurality of primary charged particle beamlets (3) on the curved surface (321) with an accuracy of less than 20 nm, preferably less than 15 nm, and even more preferably less than 10 nm.

[0203] Item 61. A multi-beam generating unit (305) according to any one of items 58 to 60, wherein the multi-beam generating unit (305) is further configured to individually adjust each of the shapes or aberrations of each of the plurality of primary charged particle beamlets (3) to form a plurality of aberration-free focal points (311, 311.1, 311.2, 311.3, 311.4) on the curved intermediate surface (321).

[0204] Clause 62. A multi-beam generating unit (305) described in any one of clauses 58 to 61, further comprising a step of providing a first multi-stigmator plate (306.4, 306.41) having a plurality of apertures (85.4) and a plurality of individually addressable multi-pole electrodes (81.1), wherein the control unit (830) is further configured to provide a plurality of individual voltages to each of the plurality of individually addressable multi-pole electrodes (81.1), and the control unit (830) individually controls the plurality of individual voltages of the multi-pole electrodes (81.1) to affect the shape and / or lateral position of each of the plurality of primary charged particle beamlets (3) before passing through the plurality of terminal apertures (94) of the terminal multi-aperture plate (310).

[0205] Item 63. A method for producing a multi-aperture plate (306, 310), comprising: - forming a plurality of electrodes (79, 81) in an electrode layer (129.1); - forming a first insulating layer (179.1) on a first side of the electrode layer (129.1), the first insulating layer (179.1) being formed from an insulating material such as silicon dioxide; - polishing the first insulating layer (179.1) to form a first leveling insulating layer (179.3) having a thickness below 2.5 μm; - forming and lithographically processing a layer of electrical wiring connections (175) on the first leveling insulating layer (179.3); - forming a second insulating layer (179.4) on the layer of electrical wiring connections (175), the second insulating layer (179.4) being formed from an insulating material such as silicon dioxide; - polishing the second insulating layer (179.4) to form a second leveling insulating layer (179.5) having a thickness below 2.5 μm; - forming a first conductive shielding layer (177.1) on the second leveling insulating layer (179.5); A method comprising:

[0206] Section 64. - forming a plurality of through-connections (149) through the electrode layer (129.1); - forming a first insulating layer (179.1) on a second side of the electrode layer (129.1), the second side being opposite to the first side; - polishing the first insulating layer (179.1) on the second side to form a first leveling insulating layer (179.3) having a thickness below 2.5 μm; - forming a second conductive shielding layer (177.2) on the first leveling insulating layer (179.3) on a second side; - connecting each of the feedthroughs on the first side with one of the electrical wiring connections (175) and each of the feedthroughs on the second side with a contact pin (147); Item 64. The method of Item 63, further comprising:

[0207] Section 65. - forming a stress reduction layer (187) on the first side of the second leveling insulating layer (179.5), the stress reduction layer (187) being formed from silicon nitride (SiNx); - forming a further insulating layer (179) on the stress reduction layer (187) and polishing the further leveling insulating layer (179) to level it to a thickness of less than 2.5 μm; - forming a first conductive shielding layer (177.1) on the further levelling insulating layer (179); Item 65. The method of item 63 or 64, further comprising:

[0208] Item 66. A multi-beam system (1), - a charged particle beam source (301) and at least one collimating lens 303 for generating a collimated charged particle beam (309); a multi-beam generating unit (305) for generating a plurality of primary charged particle beamlets (3); a beam splitter (400) for separating the plurality of primary charged particle beamlets (3) from the plurality of secondary electron beamlets (9); an objective lens (102) for focusing, in use, a plurality of primary charged particle beamlets (3) onto the surface (25) of the sample (7) and for collecting, in use, a plurality of secondary electron beamlets (9) generated at the surface (25) of the sample (7); Equipped with The multi-beam generating unit (305) - a stack of multi-aperture plates (315) comprising at least one filter plate (304) with a plurality of first apertures (85.1) for generating a plurality of primary charged particle beamlets (3), and a hybrid or end multi-aperture plate (306.5, 310) comprising a plurality of end apertures (94); a condenser lens (307) having capacitor electrodes (82, 84) with a single aperture configured to transmit a plurality of primary charged particle beamlets (3) during use, the capacitor electrodes (82, 84) configured to generate a plurality of electrostatic microlens fields (92) penetrating each of a plurality of end apertures (94); and It is equipped with The stack of multi-aperture plates (315) and the condenser electrodes (82, 84) of the condenser lens (307) form an angle Φ with respect to each other, i.e., an angle f that deviates from 0° to pre-compensate for the image plane tilt of the multi-beam system (1).

[0209] Clause 67. The system (1) described in clause 66, wherein at least one of the stack of multi-aperture plates (315) or the capacitor electrodes (82, 84) of the condenser lens (307) is mounted on a manipulator (340.1, 340.2) configured to adjust the tilt angle Φ1 of the stack of multi-aperture plates (315) or the tilt angle Φ2 of the capacitor electrodes (82, 84) of the condenser lens (307).

[0210] Clause 68. The system (1) according to clause 66 or 67, further comprising a quasi-static deflector (302) arranged in the propagation direction of the collimated charged particle beam (309) upstream of the filter plate (304), configured to adjust the propagation angle of the collimated charged particle beam (309) so that it is perpendicular to the inclined stack of multi-aperture plates (315).

[0211] Item 69. A system (1) described in any one of items 66 to 68, wherein the terminal aperture plate (310) comprises a first plurality of individually addressable electrodes (79.2, 81.2) arranged around each of the terminal openings (94).

[0212] Clause 70. A system (1) described in any one of clauses 66 to 69, wherein the multi-beam generating unit (305) further comprises a control unit (830) configured to individually control each of the capacitor electrodes (82, 84) and the first plurality of individually addressable electrodes (79.2, 81.2) to affect the penetration depth and / or shape of each of the plurality of electrostatic microlens fields (92), thereby independently adjusting the lateral and / or axial focal position of each of the plurality of primary charged particle beamlets (3) on the intermediate image plane (321) to pre-compensate for field curvature and field tilt of the multi-beam system (1).

[0213] Clause 71. The system (1) described in clause 69 or 70, wherein the first plurality of individually addressable electrodes (79.2, 81.2) are formed as a first plurality of electrostatic cylindrical electrodes (79.2), each cylindrical electrode (79.2) being arranged around one of the terminal openings (94) and configured to generate an attraction field (88) or a pressure field (90) during use.

[0214] Clause 72. The system (1) of clause 69 or 70, wherein the first plurality of individually addressable electrodes (79.2, 81.2) are formed as a first plurality of electrostatic multi-pole electrodes (81.2), each multi-pole electrode (81.2) being arranged around one of the plurality of end openings (94) and configured to generate an attraction field (88), a push field (90) and / or a deflection field and / or an astigmatism correction field during use.

[0215] Clause 73. The system (1) described in any one of clauses 66 to 72, wherein the multi-beam generating unit (305) further comprises a further multi-aperture plate configured as a first multi-stigmator plate (306.4, 306.41) arranged upstream of the terminal multi-aperture plate (310), the first multi-stigmator plate (306.4, 306.41) having a plurality of apertures (85.4, 85.41), each of the plurality of apertures comprising a second plurality of individually addressable multi-pole electrodes (81, 81.1) forming a plurality of electrostatic multi-pole elements arranged around the plurality of apertures (85.4, 85.41), each of the second individually addressable multi-pole electrodes (81, 81.1) being connected to a control unit (830) configured to deflect, focus or correct aberrations of each individual beamlet of the plurality of primary charged particle beamlets (3).

[0216] Clause 74. The system (1) described in clause 73, wherein the multi-beam generating unit (305) further comprises a further multi-aperture plate configured as a second multi-stigmator plate (306.43) arranged upstream of the terminal multi-aperture plate (310), the second multi-stigmator plate (306.43) having a plurality of apertures (85.43), each of the plurality of apertures comprising a third plurality of individually addressable multi-pole electrodes (81.3) forming a plurality of electrostatic multi-pole elements arranged around the plurality of apertures (85.43), each of the third individually addressable electrodes (81.3) being connected to a control unit (830) configured to deflect, focus or correct aberrations of each individual beamlet of the plurality of primary charged particle beamlets (3).

[0217] Item 75. A system (1) described in any one of items 69 to 74, wherein at least one of the multi-aperture plates (306, 310) is configured as an inverted multi-aperture plate, the inverted multi-aperture plate having electrical wiring connections (175) for a plurality of individually addressable electrodes (79, 81) on a lower or bottom side of the inverted multi-aperture plate opposite the beam entrance side.

[0218] Clause 76. The system (1) of clause 75, wherein at least one inverted multi-aperture plate further comprises a plurality of feedthrough connections (149, 149.1, 149.2) for electrically contacting the plurality of individually addressable electrodes (79, 79.1, 79.2, 81, 81.1, 81.2, 81.3) via electrical wiring connections (175) on the lower or bottom side of the inverted multi-aperture plate, and contact pins (147, 147.1, 147.2) are arranged on the upper or beam entrance side of the inverted multi-aperture plate.

[0219] Clause 77. The system (1) described in any one of clauses 67 to 76, further comprising a control unit (800) configured to control, during use, at least one of the tilt angles Φ, Φ1, Φ2 depending on the image plane tilt in accordance with an image setting of the multi-beam system (1), wherein the image setting includes an image rotation by the objective lens (102). [Explanation of symbols]

[0220] 1. Multi-beamlet charged particle microscope system 3 Primary charged particle beamlet or multiple primary charged particle beamlets 5 Primary charged particle beam spot 7 Object 9 Secondary electron beamlet forming multiple secondary electron beamlets 11 Secondary electron beam path 13 Primary beam path 15 Secondary charged particle image spot 25 Wafer surface 74 Beam entrance or upper side 76 Bottom side or beam exit side 79 Ring Electrode 81 Multipolar electrode 82 Ring electrode 83 Spacer 84 segmented ring electrodes 85 Aperture 86 Spacer 87 Inner wall of opening 88 Suction field 90 Suppression field 92 Electrostatic microlens field (equal potential lines) 94 End opening 98 layers of conductive material 99 Absorption and Conduction Layers 100 Object Irradiation Unit 101 Image plane 102 Objective Lens 103 Field Lens Group 105 Optical axis of multi-beamlet charged particle microscope system 108 First beam crossover 110 Condensed multi-beam raster scanner 115 wafer surface 145 Gap 147 Soldered contacts or contact pins 148 Openings insulating contact pins from the shielding layer 149 Through-connection 151 Through hole 153 Support Unit 157 Connection wire to control unit 173 Beam entrance or upper surface of second multi-aperture plate 175 Electrical Wiring Connections 177 Conductive Shielding Layer 179 Insulating Materials 181 Insulation gap 183 Bulk material forming the shielding electrode 185 Insulation gap 187 Stress compensation layer 189 Entry Extension 191 Outer edge of ring electrode 193 Openings for wiring contacts 195 Multiple Openings 197 Support Zone 199 Membrane Zone 200 detection units 205 Projection System 206 Electrostatic Lens 207 Image Sensor 208 Imaging Lens 209 Imaging Lens 210 Imaging Lens 212 Second Crossover 214 Aperture Filter 216 Active Elements 218 Third Deflection System 220 Multi-aperture corrector 222 Second Deflection System 251 High Voltage Wiring Connection 253 Ground wire 255 Coaxial Shielding and Insulation 261 ASIC 265 ASIC 267 Digital Signal Line 269 ​​Low Voltage Supply Line 300 Charged Particle Multi-Beamlet Generator 301 Charged Particle Source 302 Quasi-static deflector 303 Collimating Lens 304 Filter Plate 305 Primary Multibeamlet Formation Unit 306 Multi-aperture plate 306.2 Grounding Electrode Plate 306.3 Double-layer small lens plate 306.4 Multistigmator Plate 306.5 Hybrid Lens Plate 306.8 Grounding electrode plate 306.9 Lens electrode plate 307 First Field Lens 308 Second Field Lens 309 Primary Electron Beam 310 End Multi-Aperture Plate 311 Primary electron beamlet spot 315 Multi-aperture plate stack 316 Multi-stage microlens 321 Intermediate image plane 323 Intermediate image plane tilt component 331.1 Upper Segment 331.2 Second Segment 333 Support Zone 335 Membrane Zone 340 tilt or rotation manipulator 390 Beam Steering Multi-Aperture Plate 400 Beam Splitter Unit 420 Magnetic Elements 500 sample stage 503 Specimen voltage supply 800 Control Unit 820 Imaging Control Module 830 Primary Beam Path Control Module

Claims

1. A multi-beam generating unit (305) for a multi-beam system (1), comprising, in order of propagation direction of an incident primary charged particle beam (309): a filter plate (304) having a plurality of first apertures (85.1) for generating a plurality of primary charged particle beamlets (3), said filter plate (304) being connected to ground level in use; a terminal multi-aperture plate (310) comprising a plurality of terminal apertures (94) comprising a first plurality of individually addressable electrodes (79.2, 81.2), the electrodes (79.2, 81.2) being arranged around each of said terminal apertures (94); a condenser lens (307) having a capacitor electrode (82, 84) with a single aperture configured to transmit the plurality of primary charged particle beamlets (3) in use, the capacitor electrode (82, 84) configured to generate a plurality of electrostatic microlens fields (92) penetrating each of the plurality of end apertures (94); Equipped with The multi-beam generating unit (305) further comprises a control unit (830) configured to individually control the capacitor electrodes (82, 84) and each of the first plurality of individually addressable electrodes (79.2, 81.2) to affect the penetration depth and / or shape of each of the plurality of electrostatic microlens fields (92), thereby independently adjusting the lateral and / or axial focal position of each of the plurality of primary charged particle beamlets (3) on an intermediate image plane (321) to pre-compensate for field curvature and / or field tilt of the multi-beam generating unit (305).

2. 2. The multi-beam generating unit (305) of claim 1, wherein the first plurality of individually addressable electrodes (79.2, 81.2) are formed as a first plurality of electrostatic cylindrical electrodes (79.2), each cylindrical electrode (79.2) being arranged around one of the plurality of end openings (94) and configured to generate an attraction field (88) or a push field (90) during use.

3. 2. The multi-beam generating unit (305) of claim 1, wherein the first plurality of individually addressable electrodes (79.2, 81.2) are formed as a first plurality of electrostatic multipole electrodes (81.2), each multipole electrode (81.2) being arranged around one of the plurality of end apertures (94) and configured to generate an attraction field (88), a push field (90) and / or a deflection field and / or an astigmatism correction field during use.

4. 4. The multi-beam generating unit according to claim 1, wherein the terminating multi-aperture plate comprises a first terminating electrode layer comprising the first plurality of individually addressable electrodes and a second electrode layer insulated from the first plurality of individually addressable electrodes and arranged upstream of the first terminating electrode layer, the second electrode layer being connected to the ground level in use to form a ground electrode layer.

5. The multi-beam generating unit (305) according to any one of claims 1 to 3, wherein the terminating multi-aperture plate (310) is made from a single electrode layer.

6. 6. The multi-beam generating unit (305) according to claim 1, further comprising a further multi-aperture plate configured as a first multi-stigmator plate (306.4, 306.41) arranged upstream of the end multi-aperture plate (310), the first multi-stigmator plate (306.4, 306.41) having a plurality of apertures (85.4, 85.41), each of the plurality of apertures comprising a second plurality of individually addressable multi-pole electrodes (81, 81.1) forming a plurality of electrostatic multi-pole elements arranged around the plurality of apertures (85.4, 85.41), each of the second individually addressable multi-pole electrodes (81, 81.1) connected to the control unit (830) configured to deflect, focus or correct aberrations of each individual beamlet of the plurality of primary charged particle beamlets (3).

7. 7. The multi-beam generating unit (305) of claim 6, further comprising a further multi-aperture plate configured as a second multi-stigmator plate (306.43) arranged upstream of the terminal multi-aperture plate (310), the second multi-stigmator plate (306.43) having a plurality of apertures (85.43), each of the plurality of apertures comprising a third plurality of individually addressable multi-pole electrodes (81.3) forming a plurality of electrostatic multi-pole elements arranged around the plurality of apertures (85.43), each of the third individually addressable electrodes (81.3) connected to the control unit (830) configured to deflect, focus or correct aberrations of each individual beamlet of the plurality of primary charged particle beamlets (3).

8. 8. The multi-beam generating unit (305) according to claim 1, further comprising a further multi-aperture plate configured as an electrostatic lens array (306.3, 306.9) arranged upstream of the terminal multi-aperture plate (310), the electrostatic lens array (306.3, 306.9) having a plurality of apertures (85.3, 85.9) with a plurality of second cylindrical electrodes (79), each aperture being individually connected to the control unit (830) configured to form a plurality of electrostatic lens fields during use.

9. 9. The multi-beam generating unit (305) according to claim 8, wherein the electrostatic lens array (306.3, 306.9) is a lens electrode plate (306.9) made from a single electrode layer.

10. 9. The multi-beam generating unit (305) according to claim 8, wherein the electrostatic lens array (306.3, 306.9) is a two-layer lenslet electrode plate (306.3) having a lens electrode layer 306.3a and a ground electrode layer 306.3b.

11. 11. The multi-beam generating unit (305) according to claim 1, wherein the capacitor electrodes (82, 84) are formed as segmented electrodes (84) comprising a plurality of at least four electrode segments (84.1 to 84.4), and the control unit (830) is configured to provide, during use, an asymmetric voltage distribution to the plurality of at least four electrode segments (84.1 to 84.4) to facilitate focusing of the plurality of primary charged particle beamlets (3) in the curved intermediate image plane (321) having a tilt component (323).

12. 12. The multi-beam generating unit (305) according to any one of claims 1 to 11, further comprising at least a first ground electrode plate (306.2) having a plurality of apertures (85.2), said ground electrode plate (306.2) forming a first ground electrode in use, said ground electrode plate (306.2) being arranged between said filter plate (304) and said terminating multi-aperture plate (310).

13. The multi-beam generating unit (305) according to any one of claims 1 to 12, wherein the condenser lens (307) having the capacitor electrodes (82, 84) and the terminal multi-aperture plate (310) are arranged at an angle Φ relative to each other, the angle Φ being different from 0°.

14. 14. The multi-beam generating unit (305) according to any one of claims 8 to 13, wherein the control unit (830) is configured to provide, in use, a plurality of individual voltages to each of the plurality of electrodes (79, 81, 79.1, 81.1, 79.2, 81.2, 81.3) of the terminal multi-aperture plate (3.10), the first multistigmator plate (306.4, 306.41) and / or the second multistigmator plate (306.43) and / or the electrostatic lens array (306.3, 306.9) to together form an array of individually addressable multi-stage microlenses (316) having an individually variable focusing range variation DF of at least 6 mm, preferably at least 8 mm, even more preferably more than 10 mm for each individually addressable multi-stage microlens (316).

15. The multi-beam generating unit (305) according to any one of claims 1 to 14, further comprising a plurality of spacers (83.1 to 83.5) or support zones (179) for holding the plurality of multi-aperture plates (306.2 to 306.9, 310) at a predetermined distance relative to each other.

16. 16. The multi-beam generating unit (305) according to any one of claims 1 to 15, wherein at least one of the plurality of multi-aperture plates (306.4-306.9, 310) is configured as an inverted multi-aperture plate, the inverted multi-aperture plate having electrical wiring connections (175) for the plurality of individually addressable electrodes (79, 79.1, 79.2, 81, 81.1, 81.2, 81.3) on a lower or bottom side of the inverted multi-aperture plate opposite to a beam entrance side.

17. 17. The multi-beam generating unit (305) according to claim 16, wherein the at least one inverted multi-aperture plate further comprises a plurality of feedthrough connections (149, 149.1, 149.2) for electrically contacting the plurality of individually addressable electrodes (79, 79.1, 79.2, 81, 81.1, 81.2, 81.3) via the electrical wiring connections (175) on a lower or bottom side of the inverted multi-aperture plate, and wherein contact pins (147, 147.1, 147.2) are arranged on a top or beam entrance side of the inverted multi-aperture plate.

18. 18. The multi-beam generating unit (305) according to any one of claims 1 to 17, wherein the terminal multi-aperture plate (310) further comprises a conductive shielding layer (177.2) having the plurality of openings (94), the conductive shielding layer (177.2) being electrically insulated from the first plurality of individually addressable electrodes (79.2, 81.2), the conductive shielding layer (177.2) being disposed on the bottom side (76) of the terminal multi-aperture plate (310) between the individually addressable electrodes (79.2, 81.2) and the condenser lens (307).

19. 19. The multi-beam generating unit (305) according to claim 1, wherein in the propagation direction of the incident primary charged particle beam (309), the first opening (85.1) of the filter plate (304) has a first diameter D1 and the end opening (94) has an end diameter DT, DT being in the range between 1.6×D1≦DT≦2.4×D1.

20. 20. The multi-beam generating unit (305) according to claim 6, wherein in the propagation direction of the incident primary charged particle beam (309), the first opening (85.1) of the filter plate (304) has a first diameter D1, the second openings (85.2, 85.3, 85.4, 85.9) of further multi-aperture plates (306.2, 306.3, 306.4, 306.9) have a second diameter D2, and the terminal opening (94) has a terminal diameter DT, with D1<D2<DT, preferably 1.3*D1≦D2≦0.8*DT.

21. 14. The multi-beam generating unit (305) of claim 13, wherein at least one of the condenser lens (307) having the capacitor electrodes (82, 84) or the end aperture plate (310) is mounted on a manipulator (340, 340.1, 340.2) configured to adjust the tilt angle or rotation of at least one of the condenser lens (307) having the capacitor electrodes (82, 84) or the end aperture plate (310).

22. A terminal multi-aperture plate (310), a plurality of end apertures (94) configured, in use, to form a plurality of electrostatic microlens fields (92, 92.1, 92.2) penetrating said plurality of end apertures (94); a plurality of individually addressable electrodes (79.2, 81.2) arranged around the periphery of said termination opening (94); Equipped with A terminating multi-aperture plate (310), wherein the plurality of individually addressable electrodes (79.2, 81.2) are configured to be individually connected to a control unit (830) and, in use, configured to individually influence the penetration depth and / or shape of each of the plurality of electrostatic microlens fields (92, 92.1, 92.2).

23. 23. The termination multi-aperture plate (310) of claim 22, further comprising a first conductive shielding layer (177.2) on a termination or beam exit side (76) of the termination multi-aperture plate (310) connected to a ground level (0V), the first conductive shielding layer (177.2) being configured to shield the plurality of electrostatic microlens fields (92) from penetrating into the termination multi-aperture plate (310) so that, during use, the plurality of electrostatic microlens fields (92) penetrate only into the termination aperture (94).

24. 24. The termination multi-aperture plate (310) according to claim 22 or 23, further comprising a shielding electrode layer (183) between the plurality of individually addressable electrodes (79.2, 81.2), connected to a ground level (0V), configured, in use, to shield the plurality of individually addressable electrodes (79.2, 81.2) from each other.

25. 25. The termination multi-aperture plate (310) of any one of claims 22 to 24, further comprising a plurality of wiring connections (175) for providing a plurality of individual voltages to the plurality of individually addressable electrodes (79.2, 81.2), the plurality of wiring connections (175) being configured to be connected to the control unit (830).

26. 26. The termination multi-aperture plate (310) of claim 25, wherein the plurality of wiring connections (175) are disposed on a first side of the termination multi-aperture plate (310) and are insulated from the conductive shielding layer (177, 177.2), and the termination multi-aperture plate (310) further comprises a plurality of feedthrough connections (149) connected to the plurality of wiring connections (175) and configured to be connected to the control unit (830).

27. a second conductive shielding layer (177.1) on the upper side of the terminal multi-aperture plate (310), said upper side being the side on which the plurality of charged particle beamlets (3) enter the terminal multi-aperture plate (310); a plurality of planarizing insulating layers (129.2, 179, 179.1, 179.3, 179.5); - a plurality of layers of electrical wiring connections (175); an electrode layer (129.1) comprising said plurality of individually addressable electrodes (79.2, 81.2); Furthermore, each of the electrode layer (129.1), the layer of electrical wiring connections (175) and the first or second conductive shielding layer (177.2, 177.2) is insulated from an adjacent layer by one of the planarizing insulating layers (129.2, 179, 179.1, 179.3, 179.5); 27. The termination multi-aperture plate (310) according to any one of claims 22 to 26, wherein each of the planarization insulating layers (129.2, 179, 179.1, 179.3, 179.5) is made from silicon dioxide and is leveled to a thickness T of less than T<3 μm, preferably less than T≦2.5 μm.

28. The termination multi-aperture plate (310) according to claim 27, wherein said electrode layer (129.1) has a thickness of between 50 μm and 100 μm.

29. 1. A method for individually varying the focal length of each of a plurality of primary charged particle beam spots (311), comprising: - providing a plurality of individually addressable termination electrodes (79.2, 81.2) in each of a plurality of termination openings (94) of a termination multi-aperture plate (310); - providing condenser lens electrodes (82, 84) adjacent to said terminal multi-aperture plate (310) and downstream of said terminal multi-aperture plate (310) in the direction of propagation of the plurality of primary charged particle beamlets (3); providing, by a control unit (830), at least a first voltage to said condenser lens electrodes (82, 84) to generate a plurality of electrostatic microlens fields (92) penetrating said plurality of end apertures (94); - providing, by said control unit (830), a plurality of individual voltages to each of said plurality of individually addressable electrodes (79.2, 81.2); - individually controlling the individual voltages of the individually addressable end electrodes (79.2, 81.2) to affect the penetration depth of each of the electrostatic microlens fields (92) and thereby independently adjust the axial focal position of each of the primary charged particle beamlets (3) on a curved intermediate image plane (321); A method comprising:

30. 30. The method of claim 29, wherein the plurality of individually addressable end electrodes (79.2, 81.2) are formed as a first multipole electrode (81.2), and the method further comprises the step of individually controlling the plurality of individual voltages to the first multipole electrode (81.2) to affect the shape and / or lateral position of each of the plurality of electrostatic microlens fields (92), thereby independently adjusting the lateral focal position and shape of each of the plurality of primary charged particle beamlets (3) on the curved intermediate image plane (321).

31. 31. The method according to claim 29 or 30, wherein the step of individually controlling the plurality of individual voltages is configured to adjust a focal position of each of the plurality of primary charged particle beamlets (3) on the curved intermediate image plane (321) by a tilt component (232).

32. - providing a first multistigmator plate (306.4, 306.41) upstream of said terminal multi-aperture plate (310) having a plurality of apertures (85.4) and a plurality of second individually addressable multipolar electrodes (81.1); - providing, by said control unit (830), a plurality of individual voltages to each of said plurality of individually addressable second multipolar electrodes (81.1); - individually controlling the individual voltages of the second multipole electrode (81.1) to influence the shape and / or lateral position of each of the primary charged particle beamlets (3) before passing through the end openings (94) of the end multi-aperture plate (310); The method of any one of claims 29 to 31, further comprising:

33. - providing a second multistigmator plate (306.4, 306.41) having a plurality of apertures (85.4) and a plurality of individually addressable third multipolar electrodes (81.3); - providing, by said control unit (830), a plurality of individual voltages to each of said plurality of individually addressable third multipolar electrodes (81.3); - individually controlling the plurality of individual voltages of the third multipole electrode (81.3) to influence the shape and / or lateral position and / or direction of each of the plurality of primary charged particle beamlets (3) before passing through the plurality of end openings (94) of the end multi-aperture plate (310); 33. The method of claim 32, further comprising:

34. - providing a lenslet plate (306.3, 306.9) having a plurality of apertures (85.3, 85.9) and a plurality of individually addressable ring electrodes (79); - providing, by said control unit (830), a plurality of individual voltages to each of said plurality of individually addressable ring electrodes (79); - individually controlling the individual voltages of the ring electrode (79) to influence the focal position of each of the primary charged particle beamlets (3) before passing through the end openings (94) of the end multi-aperture plate (310); The method of any one of claims 29 to 33, further comprising:

35. 35. The method according to any one of claims 29 to 34, further comprising individually controlling the plurality of individual voltages on any of the multipole electrodes (81.1, 81.3) and / or on the individually addressable end electrodes (79.2, 81.2) of the ring electrode (79) of the lenslet plate (306.3, 306.9) to jointly influence the axial and lateral focal position, shape and propagation direction of each of the plurality of primary charged particle beamlets (3).

36. A multi-beam generating unit (305) for a multi-beam system (1), comprising: a filter plate (304) having a plurality of first apertures (85.1) for generating a plurality of primary charged particle beamlets (3), said filter plate (304) being connected to ground level in use; a plurality of multi-aperture plates (306, 306.3, 306.4, 306.9), each multi-aperture plate (306, 306.3, 306.4, 306.9) comprising an electrode layer (129.1) and a plurality of contact pins (147) arranged on a first side of said electrode layer (129.1); - a terminating multi-aperture plate (310) and Equipped with - each multi-aperture plate (306, 306.3, 306.4, 306.9) further comprises a plurality of layers of electrical wiring connections (175); a multi-beam generating unit (305) wherein at least one of the plurality of multi-aperture plates (306, 306.3, 306.4, 306.9) is configured as an inverted multi-aperture plate (306, 306.3, 306.4, 306.9), and the plurality of layers of electrical wiring connections (175) are disposed on a second side of the electrode layer (129.1) of the inverted multi-aperture plate (306, 306.3, 306.4, 306.9).

37. 37. The multi-beam generating unit (305) of claim 36, wherein the inverted multi-aperture plate (306, 306.3, 306.4, 306.9) further comprises a plurality of through-connections (149) for electrically connecting the plurality of contact pins (147) with the plurality of electrical wiring connections (175).

38. 38. The multi-beam generating unit (305) according to claim 36 or 37, wherein the terminal multi-aperture plate (310) comprises an electrode layer (129.1) having a plurality of individually addressable electrodes (79.2, 81.2), a layer of a plurality of electrical wiring connections (175), and a plurality of contact pins (147) arranged on a first side of the electrode layer (129.1).

39. 39. The multi-beam generating unit (305) of claim 38, wherein the layer of the plurality of electrical wiring connections (175) is disposed on the second side of the electrode layer (129.1) of the terminating multi-aperture plate (310).

40. 40. The multi-beam generating unit (305) of any one of claims 36 to 39, further comprising a control unit (830) configured to provide a plurality of voltages to each of a plurality of contact pins (147) of each multi-aperture plate (306, 306.3, 306.4, 306.9) and / or the terminal multi-aperture plate (310) from the same first side.

41. a condenser lens (307) arranged downstream of said terminal multi-aperture plate (310) and having a capacitor electrode (82, 84) with a single aperture configured to transmit said plurality of primary charged particle beamlets (3) in use; said capacitor electrodes (82, 84) being configured to generate, in use, a plurality of electrostatic microlens fields (92) penetrating each of said plurality of termination apertures (94); a control unit (830) configured to individually control the capacitor electrodes (82, 84) and each of the plurality of individually addressable electrodes (79.2, 81.2) of the terminating multi-aperture plate (310) to influence the penetration depth and / or shape of each of the plurality of electrostatic microlens fields (92), thereby independently adjusting the lateral and axial focal position of each of a plurality of primary charged particle beamlets (3) on a curved intermediate image plane (321); The multi-beam generating unit (305) according to any one of claims 36 to 40, further comprising:

42. A multi-beam generating unit (305) for a multi-beam system (1), comprising: a filter plate (304) with a plurality of first apertures (85.1) for generating a plurality of primary charged particle beamlets (3) from the incident primary charged particle beamlet (309); at least a first multi-aperture plate (306.3, 306.4, 306.9) with an electrode layer (129.1); a terminal multi-aperture plate (310) having a plurality of terminal openings (94); a condenser lens (307) with capacitor electrodes (82, 84); a control unit (830) configured to provide a plurality of individual voltages to said at least first multi-aperture plate (306.3, 306.4, 306.9), said terminal multi-aperture plate (310) and said capacitor electrodes (82, 84); Equipped with The multi-beam generating unit (305) is configured to individually adjust each of the axial focal positions of each of the plurality of primary charged particle beamlets (3) over a focusing range DF of greater than DF > 3 mm, preferably DF > 4 mm, even more preferably DF > 6 mm, for example DF ≥ 8 mm.

43. 43. The multi-beam generating unit (305) of claim 42, wherein the terminal multi-aperture plate (310) comprises a plurality of individually addressable electrodes (79.2, 81.2) arranged around each of the plurality of terminal openings (94), and the control unit (830) is configured, during use, to provide a plurality of individual voltages to each of the plurality of individually addressable electrodes (79.2, 81.2).

44. The multi-beam generating unit (305) of claim 42 or 43, wherein the multi-beam generating unit (305) is further configured to focus each of the plurality of primary charged particle beamlets (3) onto a curved intermediate surface (321).

45. 45. The multi-beam generating unit (305) according to claim 44, wherein the curved intermediate surface (321) has an inclined component (323).

46. The multi-beam generating unit (305) of any one of claims 42 to 45, further configured to individually adjust each of the lateral focal positions of each of the plurality of primary charged particle beamlets (3) on the curved surface (321) with an accuracy of less than 20 nm, preferably less than 15 nm, and even more preferably less than 10 nm.

47. The multi-beam generating unit (305) according to any one of claims 42 to 46, wherein the multi-beam generating unit (305) is further configured to individually adjust each of the shapes or aberrations of each of the plurality of primary charged particle beamlets (3) to form a plurality of aberration-free focal points (311, 311.1, 311.2, 311.3, 311.4) on the curved intermediate surface (321).

48. 48. The multi-beam generating unit (305) according to any one of claims 42 to 47, further comprising a first multistigmator plate (306.4, 306.41) having a plurality of apertures (85.4) and a plurality of individually addressable multipole electrodes (81.1), wherein the control unit (830) is further configured to provide a plurality of individual voltages to each of the plurality of individually addressable multipole electrodes (81.1), and wherein the control unit (830) is configured to individually control the plurality of individual voltages of the multipole electrodes (81.1) to influence a shape and / or a lateral position of each of the plurality of primary charged particle beamlets (3) before passing through the plurality of end apertures (94) of the end multi-aperture plate (310).

Images