Multi-beam system with backscattered electron inspection

Abstract

A multi-beam electron system with a backscattered electron detector is provided. In an example, the backscattered electron detector includes a plurality of apertures with locally confined regions of scintillating material in the vicinity of the apertures. Thereby, backscattered electrons are converted into photons which are then guided by optical means, such as a light guide of an optical imaging lens system, to a spatially resolving photon detector.

Description

Technical Field

[0001] The present invention relates to a multi-electron beam system having a detector for detecting backscattered electrons. Background Technology

[0002] WO 2005 / 024881 A2 discloses an electron microscope system that operates using multiple electron beams to scan an object to be examined in parallel with a single electron beam. The beam of primary charged particles is generated by guiding the primary charged particle beam onto a multi-beam forming unit comprising at least one porous plate having multiple openings. A portion of the electron beam is incident on the porous plate and absorbed there, while another portion of the electron beam passes through the openings of the porous plate, thereby forming electron beams in the beam path downstream of each opening, the cross-section of which is defined by the cross-section of the corresponding opening. Multiple primary charged particle beams are focused onto the sample surface by an objective lens, triggering secondary electrons or backscattered electrons to emit secondary electron beams from the sample. These secondary electron beams are collected and imaged onto a detector. Each secondary beam is incident on a separate detector element or group of detector elements, such that the intensity of the secondary electrons thus detected provides information about the sample surface at the location where the corresponding primary beam was incident on the sample. This signal typically depends on the signal generated by secondary electrons, which in turn depends on the secondary electron (SE) yield per primary electron and the geometric collection efficiency of the electron microscope. The SE yield depends on material properties and the kinetic energy of the primary electrons.

[0003] Recently, there has been a growing demand for examining samples such as wafers using backscattered electrons (BSE) instead of secondary electrons. Typically, single-beam scanning electron microscopy uses an in-lens detector to detect BSE. For example, it is well known from single-beam systems to arrange electron-to-light conversion elements in the circumference of the backscattered electron beam. In US 8,598,525 B2, a scintillator is connected to a photon detector via a light guide element. WO 2023 / 011824 A1 illustrates this idea in the context of a multi-beam system with a single beam; however, no practical examples of how to implement such a solution are lacking. Typically, with such an in-lens detector, the individual information of each beam in a multi-beam system is lost. In another example schematically illustrated in WO 2023 / 011824 A1, the application of free-space imaging instead of a light guide element between the scintillator and the photon detector is proposed. However, the system described in WO 2023 / 011824 A1 has very low efficiency and requires improvement.

[0004] WO 2023 / 280642 A1 discloses a detector for a charged particle device used to evaluate an apparatus for detecting charged particles from a sample. The detector includes: a backscattering detector component set to a backscattering bias potential and configured to detect higher-energy charged particles; and a secondary detector component set to a secondary bias potential and configured to detect lower-energy charged particles. A potential difference exists between the backscattering bias potential and the secondary bias potential.

[0005] Therefore, there is a need for an improved multi-beam electron beam imaging system capable of detecting the backscattered electrons of each individual beam. This also necessitates an improved multi-beam electron beam imaging system with high-efficiency signal detection of the backscattered electrons. Summary of the Invention

[0006] Objective technical problems are solved through the subject matter of the independent claims. Dependent claims relate to advantageous embodiments.

[0007] This patent application claims priority to German Patent Application No. 10 2024 202 846.0, filed on March 25, 2024, the entire disclosure of which is incorporated herein by reference.

[0008] The solution to this problem provides a multi-beam system for wafer inspection using a backscattered electron detector. In one embodiment, the multi-beam system for inspection using backscattered electrons includes: a multi-beam generating device configured to generate a plurality of primary electron beams from at least one electron source; and at least one electron optical imaging lens for forming a plurality of spatially separated focal points in the image plane of the multi-beam system. The backscattered electron detector is arranged parallel to the image plane at a distance D, for example, 10 μm, wherein the backscattered electron detector includes a plurality of apertures for transmitting the plurality of primary electron beams and a plurality of electron detection elements. At each aperture, at least one electron detection element is arranged adjacent to the corresponding aperture such that backscattered electrons detected by the electron detection element are individually distributed to a specific primary electron beam passing through the corresponding aperture. The electron detection element includes a scintillation material configured to convert backscattered electrons into photons. The multi-beam system also includes at least one photon detector for spatially resolving photons generated within each of the electron detection elements. The multi-beam system also includes a wafer stage configured to arrange the surface of the wafer in the image plane. In one example, the at least one photon detector is formed by a spatially resolved image sensor, and the system further includes a photon imaging lens system for imaging photons excited within the plurality of electronic detection elements onto the at least one photon detector. In another example, the backscattering electron detector further includes a photon optical lens array disposed on the upper side of the backscattering electron detector, wherein the upper side faces the incident primary electron beam, and each aperture extends through at least one of the photon optical array lenses. In yet another example, the backscattering electron detector further includes a photon light field lens attached to the backscattering electron detector, and each aperture extends through the photon light field lens. The collection efficiency of light or photons generated within the backscattering electron detector is increased by utilizing either or a combination of array lenses and field lenses (each used for photon optical imaging). Using a photon light field lens, photons excited from the plurality of electronic detection elements are guided to a common overlap or pupil region, where imaging lenses can be arranged to collect photons. Using an array lens, the collection efficiency of isotropically excited photons is increased for each electronic detection element. Therefore, attaching at least one photonic optical lens to or near the backscattering electron detector increases the collection efficiency of photons generated by backscattering electrons, thereby increasing throughput or reducing noise.

[0009] In the example, the multi-beam system includes a beam tube segment with a conical shape, the conical shape having a decreasing diameter in the propagation direction of the multiple primary electron beams. The conical beam tube segment can be arranged within the upper pole shoe of at least one electron optical imaging lens. Therefore, the collection efficiency of the light generated within the backscattered electron detector is further improved.

[0010] In the example, the backscattering electron detector is connected to the lower pole shoe of at least one electron optical imaging lens, wherein the lower pole shoe is electrically insulated from the upper pole shoe. In the example, a voltage VE is supplied to the lower pole shoe electrically connected to the backscattering electron detector to generate a decelerating or accelerating electric field between the backscattering electron detector and the beam tube segment. Thus, a voltage for decelerating or accelerating electrons can be supplied to the backscattering electron detector. In the example, the upper and lower pole shoes form an axial gap. In the example, the backscattering electron detector comprises a nickel-steel alloy. Thus, the magnetic field can be confined to the region between the lower and upper pole shoes.

[0011] In the example, at least one of the photon detectors is connected to the corresponding electronic detection element via a light guide. The light guide may be integrated within the backscattering electron detector or formed on its top side.

[0012] In the example, at least one electron optical imaging lens is a magnetic lens with an axial gap, and wherein a backscattering electron detector is arranged between the lower pole shoe of the magnetic lens and the image plane.

[0013] Generally, a backscattered electron detector may include a thin metallic reflective coating on the back side, facing the image plane. Backscattered electrons can penetrate the thin metallic reflective coating, while the light generated within the backscattered electron detector is reflected and guided upwards in the direction of the light guide or optical imaging lens system.

[0014] Typically, a backscattered electron detector may include a conductive coating on the upper side facing the incident primary electron beam. The conductive coating is grounded. This prevents the generation of surface charges. The conductive coating may be formed as a transparent coating, such as an ITO coating, to cover at least one of a photonic optical array lens array, a photonic optical field lens, or a light guide.

[0015] In the example, at least one aperture of the backscattered electron detector is tilted by an angle relative to the normal N of the image plane. The primary electron beam is then tilted accordingly. Therefore, the largest distribution of backscattered electrons impacts the backscattered electron detector adjacent to the aperture, and backscattered electron collection is increased. In the example, the tilt angle of the aperture increases with the distance to the optical axis of at least one electron optical imaging lens. Thus, the tilt angle is adjusted, for example, to align with the Larmor rotation of the primary electron beam within the magnetic field lens. Attached Figure Description

[0016] This invention is useful for wafer inspection. However, it is not limited to wafer inspection, but can also be used to inspect other objects, such as semiconductor masks. Examples and embodiments can also be combined with each other. Embodiments of this disclosure will be explained in more detail with reference to the accompanying drawings, in which:

[0017] Figure 1 A cross-sectional view of a multi-beam electron beam system with a backscattering electron detector, according to an example, is shown.

[0018] Figure 2a , 2b Figure 2c shows an example of the arrangement of a backscattering electron detector.

[0019] Figures 3a and 3b An example of a backscattering electron detector is shown.

[0020] Figures 4a and 4b An example of a backscattering electron detector is shown.

[0021] Figure 5a , 5b Figure 5c shows an example of a backscattered electron detector with an optical imaging system.

[0022] Figure 6 An example of a backscattering electron detector with an optical imaging system is shown.

[0023] Figure 7a , 7b An example of a backscattered electron detector with increased backscattered electron efficiency is shown.

[0024] Figure 8 Another example of a backscattering electron detector with an optical imaging system is shown.

[0025] Figures 9a and 9b Another example of a backscattering electron detector used for optimized image acquisition is shown.

[0026] Figure 10 A cross-sectional view of a multi-beam electron beam system with a backscatter electron detector and a secondary electron detection system is shown. Detailed Implementation

[0027] In the exemplary embodiments of the invention described below, components with similar functions and structures are represented by similar or identical reference numerals whenever possible. Some array elements (e.g., multiple primary electron beams) are identified by reference numerals. Depending on the context, the same reference numerals may also identify individual elements within the array elements. Each primary electron beam (3.1, 3.2, 3.3) is one of multiple primary electron beams (3). It should be understood that details or features of the examples can be combined or modified without hindrance.

[0028] Figure 1 This is a schematic diagram of a multi-beam electron imaging system 1 (hereinafter referred to as multi-beam system 1) according to an embodiment. Multi-beam system 1 uses multiple electron beams to form an image of an object 7. Multi-beam system 1 generates multiple primary particle beams 3 that strike the object 7 to produce interaction products, such as backscattered electrons, which are emitted from the object 7 and subsequently detected. Multi-beam system 1 is an electron microscope that uses multiple primary electron beams 3 that are incident on the surface of the object 7 at multiple locations and generate multiple primary electron beam focal spots 5 thereon, these focal spots being spatially separated from each other. The object 7 to be inspected can be of any desired type, such as a semiconductor wafer or semiconductor mask, and may include an arrangement of miniaturized components. The surface 25 of the object 7 is arranged in the object plane 101 of the objective lens 102 of the object illumination unit 100. The object 7 can be a wafer or a semiconductor mask.

[0029] The diameter of the minimum beam spot or focal spot 5 can be shaped to be small in the object plane 101. An exemplary value for this diameter is less than 4 nanometers, for example, 3 nanometers or less. Focusing of the primary electron beam 3 used to shape the focal spot 5 is performed by the objective lens system 102. In this case, the objective lens system 102 may include a magnetically immersed lens. Other examples of focusing devices are described in German Patent DE 102020125534 B3, the entire contents of which are incorporated herein by reference.

[0030] Multiple focal spots 5 of the primary electron beam 3 form a regular grating arrangement of incident positions, which is formed in the object plane 101. The number J of the primary electron beam 3 can be five, twenty-five, or more. In practice, the number J of the beams 3, and therefore the number of incident positions or focal spots 5, can be chosen to be significantly larger, for example, J = 10 × 10, J = 2791, J = 20 × 30, or J = 100 × 100. An exemplary value for the pitch P between the incident positions is 1 micrometer, 10 micrometers, or larger, for example, 40 micrometers. For simplicity, in Figure 1Only three primary electron beams 3.1, 3.2, and 3.3 with corresponding focal points 5.1, 5.2, and 5.3 are shown. The primary electron beams 3 impacting object 7 produce interaction products, such as backscattered electrons, which are emitted from the surface of object 7. A backscattered electron detector 601 is arranged near the object plane 101. The gap distance D between surface 25 and the backscattered electron detector is, for example, D = 10 μm or greater, such as D = 15 mm or D = 20 μm (see also below for illustration). Figure 2a However, smaller distances, such as D = 8 μm or even smaller, such as D = 5 μm, can also be chosen. The backscattered electron detector 601 includes multiple apertures, allowing multiple primary electron beams 3 to pass through. The detector 601 includes multiple detection elements arranged near the multiple apertures. The detection elements can be, for example, diodes or CMOS detection elements such as PMDs, and can be provided with electron-to-light conversion elements, or can be formed as direct electron detection elements. In one example, the detector 601 includes: an electron-to-light conversion element, such as one formed of a scintillating material, through which backscattered electrons are converted into light; and multiple light detection elements. The combination of the electron-to-light conversion element and the multiple light detection elements thus forms multiple electron detection elements. The detector or image sensor 601 may also include a relay optics system for imaging and guiding photons generated by the electron-to-photon conversion unit on a dedicated photon detection element (e.g., multiple photomultiplier tubes or avalanche photodiodes (not shown)).

[0031] A primary particle beam 3 is generated in a beam generating apparatus 300, which includes at least one electron emitter 301, at least one collimating lens 303, a porous arrangement 305, and a first electron optical field lens 331 and a second electron optical field lens 333. The electron emitter 301 is connected to a voltage source for providing an emitter voltage VK to the emitter 301 and generates at least one diverging electron beam 309, which is at least substantially collimated by at least one collimating lens 303 and irradiates the porous arrangement 305. The porous arrangement 305 includes at least one first porous or filter plate having a plurality of J openings formed therein in a first grating arrangement. Particles illuminating the particle beam 309 pass through the J openings or holes of the first porous plate and form a plurality (J) of primary small beams 3. Particles impacting the first porous plate that irradiate the beam 309 are absorbed by the first porous plate and do not contribute to the formation of the primary small beams 3. The aperture arrangement 305 typically includes additional array elements, such as an array of electro-optical lenses, an array of astigmatism correctors, or an array of electro-optical deflectors. In this example, the particle beam 309 is fully collimated by the collimating lens 303. However, the aperture arrangement 305 can also be designed for divergent or converging incident particle beams 309.

[0032] The aperture arrangement 305, together with the electron optical field lens 331 and the electron optical second field lens 333, focuses each primary small beam 3 such that the focal point is formed in the intermediate image surface. The intermediate image surface can be real or virtual. The intermediate image surface can be curved to pre-compensate for the field curvature and image plane tilt of the electron imaging system arranged downstream of the intermediate image surface.

[0033] At least one electron optical field lens 103 and electron optical objective 102 provide a first imaging particle optical unit for imaging an intermediate image surface onto an object plane 101, such that a second grating configuration forms the focal spot 5 of the primary electron beams 3 thereon. Typically, the surface 25 of the object 7 is arranged in the object plane 101, and the focal spot 5 is formed accordingly on the object surface 25. A plurality of primary beams 3 form an intersection point 108, and a multipole corrector or deflector 110 is arranged near the intersection point 108. The multipole corrector deflector 110 is used to deflect the plurality of primary beams 3 jointly and synchronously, such that the plurality of focal spots 5 can move simultaneously on the surface 25 of the object 7. The multipole corrector deflector 110 is driven by a multi-electron beam control unit 860. Additionally, the multi-beam system 1 may include further static deflectors and multipole elements 112 configured to adjust the position and beam shape of the plurality of primary beams 3.

[0034] Further information relating to such multi-beam particle systems and components (e.g., particle sources, perforated plates, and lenses) used therein can be obtained from international patent applications WO 2005 / 024881, WO 2007 / 028595, WO 2007 / 028596, WO2011 / 124352, and WO 2007 / 060017, and German patent applications with publication numbers DE 10 2013 016 113 A1 and DE 10 2013 014976 A1, the entire disclosure of which is incorporated herein by reference.

[0035] The multi-beam electron imaging system 1 also includes a control unit 800 configured to control the various particle optics components of the multi-beam system and to evaluate and analyze the signals acquired by the detector 601. In this case, the control unit or controller unit 800 may be constructed from multiple separate computers or electronic components. For example, the control unit 800 includes a control operation processor 880 and a control module 830 for controlling the electron optics of the primary small-beam generation unit 300. The control unit 800 further includes a stage control module 850 for positioning the sample surface 25 or the sample 7 within the object plane 101 via the stage 500. The control unit 800 further includes a control module for adjusting the sample voltage VS, which is connected to a module 503 for supplying the sample voltage VS to the sample 7, the sample voltage VS also being referred to as the extraction voltage. Thus, during use, an extraction field is generated between the backscattered electron detector 601 and the surface 25 of the object 7. During use, the extraction field decelerates the primary electrons of the primary electron beam 3 before reaching the sample surface 25 and produces an additional focusing effect on the multiple primary electron beams 3. Meanwhile, the extraction field is used during use to accelerate backscattered electrons from the surface 25 of object 7 to the backscattered electron detector 601.

[0036] Detector 601 includes multiple sets of detection elements, one set of which is used for each primary electron beam 3. During use, each set of detection elements is configured to record the intensity signal of the assigned backscattered electrons. The multiple intensity signals of the multiple backscattered electrons are transmitted to an image data acquisition unit or imaging control module 810, where the image data is processed and stored in memory 890.

[0037] During the acquisition of image blocks via multiple primary electron beams 3, the stage 500 moves continuously at least in a first direction or the x-direction, and after acquiring an image block, the stage 500 moves to the next image block to be acquired. In one embodiment, the stage 500 moves continuously in the first direction or the x-direction while acquiring images by scanning multiple primary electron beams 3 in the first direction using a grating scanner 110. The stage movement and stage position are monitored and controlled by sensors known in the art, such as laser interferometers, grating interferometers, confocal microlens arrays, or the like.

[0038] During the image scanning operation step, the control unit 800 is configured to trigger the image sensor 601 to detect multiple timely resolved intensity signals from multiple backscattered electrons at predetermined time intervals, and to accumulate and stitch together a digital image of image blocks from all positions of multiple primary electron beams 3.

[0039] Figure 2 illustrates an example of a backscattered electron detector 601. (Used with...) Figure 1 The same reference numerals are used in the accompanying drawings, and also refer to... Figure 1 The description. In Figure 2a In this configuration, a backscattering electron detector 601 is positioned between the pole piece 165 of the magnetic objective 102 and the image plane 101, with the surface 25 of the wafer 7 placed by a wafer stage 500. Primary electron beams 3 pass through an electron beam tube 151 with a given kinetic energy. The beam tube 151 is connected to a tube potential VT, which is given, for example, by ground potential. The backscattering electron detector 601 is connected to a potential VE, which exerts a decelerating force on the primary electrons of the primary electron beams 3.1 to 3.3. The backscattering electron detector 601 includes a plurality of apertures 85.1 to 85.3, allowing the primary electron beams 3.1 to 3.3 to pass through. The backscattering electron detector 601 is positioned at a distance D above the image pane 101, with the surface (25) of the wafer 7 arranged via a stage 500 (not shown). The electron beams 3.1 to 3.3 are focused by the objective 102 through a magnetic field generated by a coil 161, to which a current I is supplied. In this example, the magnetic lens 102 with pole shoes 165 forms an axial gap lens, wherein the gap 167 between the lower and upper pole shoes for generating the magnetic field is oriented in an axial direction almost perpendicular to the image plane 101. The pole shoes may not be formed as a single piece, but can be formed from two electrically isolated portions forming the upper and lower pole shoes.

[0040] Therefore, a focusing magnetic field is generated above the backscattering electron detector 601 and the wafer surface 25. The wafer is also connected to a voltage source 503, which is configured to supply a voltage VL to the wafer 7 during use. This further decelerates the primary electrons before they reach the wafer surface 25. For example, the primary electrons are accelerated to approximately 30 keV upstream of tube 151 and propagate through tube 151 with a constant kinetic energy of 30 keV. The primary electrons are focused by the magnetic field of the magnetic lens 102 and decelerated in two steps by the voltage VE supplied to the backscattering electron detector 601 and the voltage VL supplied to the wafer, causing the primary electrons to strike the surface 25 of the wafer 7 with a landing energy, for example, less than 2 keV, less than 1 keV, or even lower (e.g., 300 eV or 200 eV). For example, the absolute value of the voltage supplied to the backscattering electron detector 601, |VE|, is less than the absolute value of the voltage supplied to the wafer, i.e., |VE| < |VL|. However, for backscattered electron detection, higher landing energies are also possible; for example, the voltage VL supplied to the wafer 7 can be adjusted for landing energies greater than 2 keV, greater than 5 keV, or even up to 50 keV. Backscattered electrons (not shown) are generated at the interaction volume produced at the focal spots 5.1 to 5.3 of the three small beams 3.1 to 3.3 shown, which are backscattered from the wafer surface 25 with kinetic energy similar to the landing energy. The backscattered electrons are then accelerated towards the backscattered electron detector 601 and partially focused into the detection region of the backscattered electron detector 601 (see below). By selecting VE, the kinetic energy of the backscattered electrons upon impacting the backscattered electron detector 601 can be adjusted.

[0041] Figure 2bAnother example is shown. A backscattering electron detector 601 is arranged between the lower pole shoes 169 of a magnetic objective lens 102. A primary electron beam 3 passes through a beam tube 151 with a given kinetic energy. The beam tube 151 is connected to a tube potential VT, which is given, for example, by ground potential. In this example, the magnetic lens 102 with pole shoes 165 forms a radially gap lens, wherein the gap 167 between the lower pole shoes 169 and the upper pole shoes for generating the magnetic field has an extension almost parallel to the image plane 101. Thus, the focusing magnetic field is generated directly above the surface 25 of the wafer 7. Such a magnetic lens 102 is sometimes also referred to as an immersion lens. Thus, the backscattering electron detector 601 is arranged within the magnetic field of the immersion lens. The backscattering electron detector 601 may be connected to a potential VE, which optionally exerts a decelerating force on the primary electrons of the primary electron beams 3.1 to 3.3 before they enter the backscattering electron detector 601. The backscattered electron detector 601 includes a plurality of apertures 85.1 to 85.3, allowing a plurality of primary electron beams 3.1 to 3.3 to pass through. The wafer is also connected to a voltage source 503, configured to supply a voltage VL to the wafer 7 during use. This decelerates the primary electrons before they reach the wafer surface 25. The primary electrons are thus focused by the magnetic immersion lens of the magnetic lens 102 and decelerated in at least one step by the voltage VL supplied to the wafer, causing them to strike the surface 25 of the wafer 7 with landing energies below 2 keV, below 1 keV, or even lower (e.g., 300 eV or 200 eV). Backscattered electrons (not shown) are generated at the interaction volume created at the focal spots 5.1 to 5.3 of the three beams 3.1 to 3.3 shown, which backscatter from the wafer surface 25 with kinetic energy similar to the landing energy. These backscattered electrons are then accelerated to the backscattered electron detector 601 and partially focused into the detection region of the backscattered electron detector 601 (see below).

[0042] In this example, the backscattering electron detector 601 comprises a paramagnetic material, such as aluminum, magnesium, or tungsten, having a permeability close to 1 μR. Other paramagnetic materials are provided by paramagnetic semiconductors. In this example, the backscattering electron detector 601 comprises a diamagnetic material, such as bismuth or copper. In this example, the backscattering electron detector 601 comprises quartz (SiO2). Thus, the magnetic field of the objective lens 102 is at least partially diverted or increased by the backscattering electron detector 601.

[0043] In the example, the backscattered electron detector 601 comprises a nickel-iron alloy, such as Permanorm, which has a high permeability of, for example, about 10,000 μR. Figure 2cAn example is illustrated where the backscattering electron detector 601 forms an extension of the lower pole shoe of the magnetic objective lens 102. Consequently, the magnetic field generated by the objective lens 102 is confined to the region between the objective lens 102 and the backscattering electron detector 601. This reduces the magnetic field between the backscattering electron detector 601 and the surface 25 of the wafer 7, and also reduces the Larmor rotation of the electron beam below the backscattering electron detector 601.

[0044] In this example, the backscattered electron detector 601 comprises a hard magnetic material, such as samarium cobalt, ferrite, or neodymium. This modifies the magnetic field from the objective lens 102. Consequently, for example, the Larmor rotation of electrons within or between the backscattered electron detector 601 and the surface 25 of the wafer 7 is reduced.

[0045] Figure 3 illustrates a first example of a backscattering electron detector 601 having multiple apertures 85.1 to 85.3 for transmitting primary electron beams 3.1 to 3.3. Figure 3a shows a cross-section through the backscattering electron detector 601, while Figure 3b shows a view on the backside 611 of the backscattering electron detector 601, pointing towards and opposite the surface 25 of the wafer 7. Figure 3a shows only three primary electron beams 3.1 to 3.3, but there can be more beams, such as 91 beams, more than 100 beams, more than 300 beams, such as 2791 beams. Figure 3b shows seven apertures 85.1 to 85.7, but there can be more apertures, for example, corresponding to the number of primary electron beams 3. Each primary electron beam 3 is controlled by an objective lens 102 (see Figure 3). Figure 1 As shown in Figure 2), the primary electron beam 3 is focused by the deceleration field generated by voltages VL and VE and transmitted through corresponding apertures 85.1 to 85.7. Each primary electron beam 3 strikes the surface 25 of the wafer 7 at a focal point 5, which includes focal points 5.1 to 5.3 in Figure 3a. At each focal point 5, some electrons are scattered back and form backscattered electrons 9, including backscattered electrons 9.1 to 9.3. The backscattered electrons 9.1 to 9.3 propagate in the direction of the backscattered electron detector 601. Using the electrostatic field generated by VL and VE, the backscattered electrons 9.1 to 9.3 are accelerated and slightly focused, and strike detection elements 607.1 to 607.7 arranged on the backside 611 of the backscattered electron detector 601. At least one detection element 607 is assigned to each aperture 85 and is arranged, for example, as a ring-shaped circular detection element 607 surrounding each corresponding aperture 85. Thus, the backscattered electrons 9 can be detected individually and separately for each primary beam 3.

[0046] Here, only one individual detection element 607.1 to 607.7 for each of the individual apertures 85.1 to 85.7 is shown. However, more than one detection element 607 may also be provided for a single aperture 85. Thus, the angular distribution of backscattered electrons can be detected.

[0047] In the example, electron detection element 607 includes a scintillating material. Within the scintillating material, photons are generated by backscattered electrons 9 within the scintillating material. An example is shown in Figure 4a. Electron detection elements 607.1 to 607.3 include scintillating material and are connected to optical guides 609.1 to 609.3 (only two are shown in the cross-section of Figure 4a). Photons excited within electron detection elements 607.1 to 607.3 are guided within optical guides 609.1 to 609.3 to photon detectors 613.1 to 613.3. Photon detectors 613.1 to 613.3 are connected to an imaging control module 810, which is configured to capture image data corresponding to the backscattered electron count received by backscattered electron detector 601. The cross-section of optical guides 609.1 to 609.3 can be very small, approximately a few micrometers, and can be formed using well-known planar fabrication techniques for integrated optics, such as through structured ion exchange within glass or as a SiO2 structure within a conductive semiconductor sample. The photoconductors 609.1 to 609.3 have the advantages of being formed of a linear dielectric material, and the photons do not interact with the electrons and electric or magnetic fields present near the aperture 85. In one example, the bulk material of the backscattered electron detector 601 includes a conductive material, such as doped silicon or Permanorm. The bulk material is connected to a voltage supply for providing voltage VE to assist in the generation of an accelerating or decelerating electric field between the backscattered electron detector 601 and the wafer surface 25. The use of a conductive material also prevents the backscattered electron detector 601 from charging during exposure to, for example, backscattered electrons. The photoconductors 609.1 to 609.3 can be embedded within the conductive material (as shown in Figure 4a). In another example, the photoconductors 609.1 to 609.3 can be covered by a conductive coating, such as ITO or aluminum, to avoid the accumulation of surface charge on the exposed surfaces of the photoconductors 609.1 to 609.3.

[0048] Another example is shown in Figure 4b. Electron detection elements 607.1 to 607.3 include a scintillation material and are directly connected to photon detectors 613.1 to 613.3. Photon detectors 613.1 to 613.3 are connected to an imaging control module 810 via embedded and isolated electrical connections 619.1 to 619.3, which is configured to capture image data corresponding to the backscattered electron count received by the backscattered electron detector 601. The embedded electrical connections 619.1 to 619.3 can be formed from localized regions of doped semiconductors embedded within, for example, an isolated SiO2 structure. Compared to the optical light guide 609, the diameter of the embedded electrical connections 609.1 to 609.3 can be smaller, for example, 1 μm or even smaller.

[0049] In the two examples illustrated in Figures 4a and 4b, the backside 411 of the backscattered electron detector 601 is covered by a reflective coating 621 (for example, including a thin aluminum coating). Aluminum has low blocking power for backscattered electrons, but it reflects photons generated in the electron detection elements 607.1 to 607.3, thus reducing light loss from the electron detection elements 607.1 to 607.3. In one example, the electron detection elements 607.1 to 607.3 are completely encapsulated by the reflective coating except for the aperture openings leading to the light guide 609 or the photon detector 613.

[0050] Figure 5 illustrates an example of a backscattered electron detector 601 having a detection element 607 including a scintillation material. The same reference numerals as in the previous figures are used, and reference is also made to the description of the previous figures. Figure 5a and Figure 5b In the diagram, the size is reduced, and the beam tube 151 is shown with the backscattered electron detector 601 below. The beam tube 151 may have a diameter of about 10 mm or greater.

[0051] Here, photons generated within detection elements 607.1 to 607.3 are imaged onto a detector camera (not shown in the light propagation direction 631) by a photonic optical imaging lens system 627. Figure 5aIn the first example shown, the backscattering electron detector 601 includes a photonic optical lens array having photonic optical array lenses 629.1 to 629.3. Each photonic optical array lens 629.1 to 629.3 is arranged on the upper side 603 of the backscattering electron detector 601, opposite at least one of the detection elements 607.1 to 607.3. Therefore, photons generated within the detection element 607 are collimated by the photonic optical array lens 629, and the collection efficiency of the photonic optical lens system 627 is increased, even when confined within the electron beam tube 151. At the electron beam crossing point 108, a photonic optical folding mirror 651 is arranged with an aperture 653 for allowing multiple electron beams, including small beams 3.1 to 3.3, to pass through. The primary electron beams 3.1 to 3.3 propagate through the aperture 653 arranged at the electron beam crossing point 108 and further through the beam tube 151. Through the electron objective 102 (not shown here, see [link to documentation]). Figure 1 Alternatively, primary electron beams 3.1 to 3.3 are focused and pass through apertures 85.1 to 85.3 of the backscattered electron detector 601 before striking surface 25 or wafer 7 (see also Figures 3 and 4). Backscattered electrons 9.1 to 9.3 are scattered back from focal points 5.1 to 5.3 or primary electron beams 3.1 to 3.3 and directed toward individual electron detection elements 607.1 to 607.3. Backscattered electrons 9.1 to 9.3 are transmitted through reflective coating 621 on the backside of the backscattered electron detector 601 and converted into photons within electron detection elements 607.1 to 607.3. Photons are collimated by photonic optical array lenses 629.1 to 629.3, which are assigned to electronic detection elements 607.1 to 607.3, and imaged by a photonic optical imaging lens system 627 onto a spatially resolved detector (not shown) along a folded optical path 631 formed by a folded mirror 651. This detector distributes the light detected in different detection regions to different individual primary electrical beams 3.1 to 3.3. The photonic optical array lenses 629.1 to 629.3 can be formed from optically transparent lens materials (e.g., silicon dioxide or fused silica) and can be formed using conventional planar fabrication techniques for photonic optical microlens arrays (e.g., for CMOS sensors). An aperture 85 is formed through each of the photonic optical array lenses 629.1 to 629.3. The lens surfaces (including the open surfaces within the apertures 85 of the photonic optical array lenses 629.1 to 629.3) can be covered with a conductive material (e.g., ITO) to prevent charge adhesion to the surface of the insulating lens material.

[0052] Figure 5bAnother example of a photonic optical imaging lens system 627 is shown, having a photonic field lens 623 disposed on the upper side 603 of a backscattering electron detector 601. The photonic field lens 623 and the photonic optical array lens 629 can also be combined. This further improves collection efficiency. The photonic field lens 623 can be formed, for example, from molten silicon and attached to the backscattering electron detector 601 by twisting or using van der Waals forces. An aperture 85 can be formed in the photonic field lens, for example, by directional RIE etching. The open surfaces of the photonic field lens 623 (including the open surfaces within the aperture 85) can be covered with a conductive coating 633 comprising a conductive material such as ITO to prevent charge adhesion to the surface of the insulating lens material.

[0053] All lens surfaces of the photonic optical imaging system 627, arranged in a vacuum, can be covered with a conductive material such as ITO to prevent electrons and other charged particles from adhering to the normally insulated lens material surfaces. The photonic optical folding mirror 651 can be a mirror with a highly reflective metallic coating (e.g., aluminum or silver coating). The folding mirror 651 and the photonic optical lenses of the imaging optics system 627 are grounded, preventing charge accumulation within the optical system.

[0054] Figure 5c This illustrates an example of increased collection efficiency for light generated within the backscattering electron detector 601. Here, the functions of the photonic optical array lens 629 and the photonic light field lens 623 for collimating the light are combined within the spatially variable photonic optical array lens 629, such that the photonic optical lens having a larger distance to axis 105.1 has a larger prism capability to refract light in the direction of axis 105.1. The folding angle 117 is here chosen to be greater than 45°, such that the reflected optical axis 105.2 points upward (or, in...). Figure 5cIn the coordinate system (in the negative z-direction). The electron optical objective 102 has an upper pole piece 163, which has a conical inner portion with an increasing diameter in the direction of light along the negative z-direction. Inside the upper pole piece 163, the conical section of the electron beam tube 151.2 is arranged to have a decreasing diameter in the direction of the primary electron 3 (here in the positive z-direction). The upper diameter L1 is given, for example, 20 mm or greater, such as 30 mm or even 40 mm. The lower diameter L2 near the end section of the upper pole piece 163 is, for example, less than 15 mm, such as 10 mm or even smaller, such as 8 mm. An axial gap 167 is formed between the end section of the upper pole piece 163 and the lower pole piece 169. The lower pole piece 169 is electrically isolated from the upper pole piece 163 by an isolator 171. The lower pole piece 169 is connected to a backscattering electron detector 601, which can be formed of the same material as the pole piece 163, such as a nickel-steel alloy. In the nickel-steel alloy, a plurality of apertures 85 are provided, and near each aperture 85, an optically transparent electron detection element 607 comprising a scintillating material is provided. The lower pole piece is set to a potential of voltage VE, such that primary electrons are slowed down, for example, before passing through the apertures 85 of the backscattering electron detector 601. The conical design of the beam tube 151.2 and the combined effect of the photonic optical array lens 629 and the additional photon-collecting light field lens 623 increase the efficiency of the electron detection element 607. Figure 5c The collection efficiency of light generated within the beam (not shown). The multi-beam charged particle system 1 also includes an upper section of beam tube 151.1, which includes branch sections for light trajectories (e.g., light trajectories 617.11 and 617.31) to pass through after reflection at metal mirror 651. Beam tubes 151.1 and 151.2 and metal mirror 651 are connected to ground, such that there is no charge accumulation, and primary electrons propagate within beam tubes 151.1 and 151.2 through a vacuum without interfering electric field.

[0055] exist Figure 5c In the example, the floating space between the lower surface of the beam tube 151.2, set to ground level, and the backscattered electron detector 601, set to voltage VE, determines the primary contribution for decelerating or accelerating electrons. However, the wafer 7 can be set to voltage VL to generate additional decelerating or accelerating electric fields between surface 25 or the back side of the wafer and the backscattered electron detector 601.

[0056] In one example, the primary electron beams 3.1 to 3.3 can be scanned across surface 25 within a limited range based on the diameters of apertures 85.1 to 85.3 using the multipole deflection element 110. For example, with a beam spacing of 10 μm, a scan range of 2 μm, 3 μm, or even larger is possible. For example, the typical aperture angle of the primary beam 3 is less than 10 mrad, such that the diameter of the beam at a distance of 100 μm from wafer surface 25 is approximately 1 μm. A scan range of, for example, 2 μm is possible using the aperture diameter of aperture 85 of the backscattered electron detector 601, for example, 4 μm. After repeatedly performing image scans to acquire multiple image blocks within an allowable scan range of, for example, 2 μm, and laterally moving wafer 7 by wafer stage 500 approximately within the allowable scan range (e.g., 2 μm), a spatially resolved backscattered electron image of a closed segment of surface 25 of wafer 7 is acquired by repeated image scans and stitching.

[0057] Figure 6 An example of a photonic optical imaging system is shown. The photonic optical imaging lens system 627 is thus formed by a first photonic field lens 623.1 arranged at a backscattering electron detector 601, an intermediate photonic optical imaging lens 625, and a second photonic field lens 623.1 arranged in front of a spatially resolved detector 635, the spatially resolved detector having multiple detection regions, including a detection region 633 for different individual primary electron beams 3.1 and backscattered electrons generated by those beams 3.1. The photonic optical imaging lens system 627 is schematically shown in an unfolded system with a photonic optical mirror plane 651, wherein the system is folded at a half-fold angle of, for example, 20°, 30°, or 45° or greater. The photonic optical folding mirror 651 is again positioned at the beam crossing point 108, allowing the primary electron beams to pass through the photonic optical mirror 651 through a small aperture 653.

[0058] In this example, the backscattering electron detector 601 may be entirely made of a dielectric material (e.g., fused silica), with doped regions forming electron detection elements 607 for converting electrons into photons. A reflective coating may be formed by stacking dielectric layers. This minimizes the influence of the magnetic field on the magnetic lens 102. The surface of the backscattering electron detector 601 is further completely covered by an ITO coating to prevent the accumulation of localized surface charges. In one example, as described above, the backscattering electron detector 601 may still include a thin aluminum coating 621 on the back side 611 facing the wafer surface 25.

[0059] In one example, the primary electron beam 3 forms a telecentric beam close to the image plane 101, meaning all electron beams 3 are parallel to each other. However, the telecentric characteristic does not require the beams to be perpendicular to the image plane 101 in which the wafer 7 is disposed. In one example, the telecentric beam of the primary electron beam 3 is tilted at an angle 17 relative to the optical axis 105, which is perpendicular to the image plane 101. In such an example, the aperture 85 can be arranged at the same angle 17 within the backscattered electron detector 601 to allow the transmission of the tilted primary electron beams 3.1 to 3.3. Figure 7a An example of this backscattered electron detector 601 is illustrated. Since backscattered electrons 9.1 to 9.3, which include ballistic scattering processes, are generated, the backscattered electron distribution includes a strong directional or angular distribution mirrored by the directional or angular distribution of the primary electrons. Therefore, the backscattered electron collection efficiency is increased by backscattering electrons at a mirror angle 17 of the incident primary electron beams 3.1 to 3.3, such that the maximum value of the backscattered electron distribution is not guided back into the aperture 85, but rather guided to the electron detection element 607, which is arranged adjacent to the aperture 85. The tilt angle 17 can be approximately 5°, 10°, or greater, such as 15°. In such an example, electron detection elements 607.1 to 607.3 can, for example, be arranged only on one side of the aperture 85 in the direction of the incident angle 17. The principle of using tilted primary electron beams is not limited to telecentric beams, but can also be applied to concentric beams of primary electron beams 3. It is understandable that, for example, within the immersion lens field, the electron beam is further tilted to the optical axis 105 perpendicular to the wafer surface 25 by Larmor rotation, increasing the tilt angle relative to the optical axis 105. Figure 7b In the example shown, the tilt angles 17.2 and 17.3 of apertures 85.2 and 85.3 are individually adjusted to compensate for this increased tilt in each corresponding electron beam due to Larmor rotation. The aperture tilt is shown here in the xz plane; however, it should be understood that Larmor rotation generally results in a tilt angle in the azimuth direction of both the primary and backscattered electron beams, i.e., in... Figure 7b In the illustration, the tilted aperture can be tilted in the y-direction perpendicular to the xz plane, with a radially increasing tilt angle of 17. It should also be understood that the lateral displacement K of the crosspoint of the ballistic backscattered electrons relative to the center of aperture 85 increases with the increase of the gap distance D, applying K = 2dtan(g), where the tilt angle is g( Figure 7b (Ref. 17 in the text). Therefore, in the case of a large tilt angle, for example up to several mrad (e.g. up to 5 mrad), within the immersion lens 102, a smaller gap distance D of D < 15 or even D < 10 μm is preferred.

[0060] Figure 8Another example of a multi-beam charged particle system 1 is shown. In this example, the backscattered electron detector 601 includes an array of apertures 85, in which electron sources 301 are arranged. Only two electron sources 301.1 and 301.2 are shown, but there can be more, for example, 469 electron sources 301 forming 469 beams. The backscattered electron detector 601 further includes multiple isolation layers 693 and an extraction electrode layer 697. By providing an appropriate voltage to the extraction electrode layer 697, electrons are accelerated from electron sources 301.1 and 303.3 and focused by an electrostatic lens field within the apertures 85 formed by the lens electrode layer 698. Electron beams 3.1 and 3.2 strike the surface 25 of the wafer 7, causing the backscattered electrons to be guided backward in the direction of the backscattered electron detector 601. The backscattered electron detector 601 includes electron detection elements 607.1 and 607.2, each arranged near the apertures 85. Electron detection elements 607.1 and 607.2 include scintillating material to convert electrons into photons. The photons emitted from electron detection elements 607.1 and 607.2 are then imaged onto a spatially resolved photon detector 635 by a photonic optical imaging lens system 627. Figure 8 The example has the following advantages: detecting backscattered electrons by converting them into photons within localized and confined electron detection elements 607.1, 607.2 requires no electrical connections. The interaction of photons within linear materials is inert, and imaging can be performed without interfering with electron optics or charged particles.

[0061] A typical photon detector is formed by a spatially resolved image sensor 635, such as a CMOS sensor. The image field of the multi-beam system 1 has a diameter of, for example, 100 μm or larger. A small spatially resolved image sensor 635 with high resolution is familiar from camera sensors in smartphones. For small sensors, a moderate magnification M (e.g., M=1, M=2, or M=5) of the imaging lens system 627 is sufficient. Therefore, the system extension of the imaging lens system 627 can be kept small.

[0062] In such Figure 8 In one example of the backscattered electron detector 601 shown, electron sources 301.1 and 303.2 are formed by photocathodes exposed by focused light. In such an example, the photonic optical system 627 also includes a photonic optical beam splitter for directing focused excitation light to a specific location at the photocathode to excite electrons at the source location within the aperture 85.

[0063] Figure 9 illustrates another example of the backscattered electron detector 601. The same reference numerals as in the previous figures are used, and reference is also made to the description of the previous figures. Here, apertures 85.1 to 85.5 are formed as elongated slits to allow for a larger scanning range of the primary electron beam (see Figure 9). Figure 8 (b) For example, primary electrons are scanned in the y-direction, while wafer 7 moves continuously in the x-direction via stage 500. Therefore, the entire surface area of ​​surface 25 of wafer 7 can be imaged by scanning multiple small beams 3 in parallel in the first direction while wafer 7 moves in the second direction.

[0064] Figure 10 This illustrates another example of a multi-beam charged particle system 1 with a backscattering electron detector 601. Figure 10 The backscattering electron detector 601 can be used for Figure 1 The backscattered electron detector 601 shown in 7 or 9 is used. In addition to the backscattered electron detector 601, the multi-beam charged particle system 1 also includes an electron optical beam splitter 400. The beam splitter 400 separates the backscattered electrons and secondary electrons 19 that pass through the aperture 85 of the backscattered electron detector 601 along the secondary electron beam path 11 into the electron optical detection system 200. Both types of electrons are further described, but not limited to, the secondary electrons 19. The electron optical detection system 200 includes electron optical lenses 206, 208, and 210 to image the secondary electrons 19 onto a spatially resolved detector 209, with focal points 15.1 to 15.3 of the secondary electrons 19 formed on the spatially resolved detector 209. Using according to... Figure 10 The multi-beam charged particle system 1 can detect backscattered electrons 9 and secondary electrons 19, which typically have lower kinetic energy, respectively, and can obtain more information about the surface 25 of the wafer 7.

[0065] Throughout the embodiments and examples, only a small number of primary electron beams, optical paths, or backscattered electrons are shown for illustrative purposes. However, it should be understood that the embodiments and examples are generally applicable to large numbers of primary electron beams, such as J=91 beams, J=300 beams, J=469 beams, or even more, such as J=2791 beams.

[0066] This disclosure is summarized by the following terms, but the invention should not be considered limited to the following terms, but also covers various combinations and modifications thereof.

[0067] Clause 1: A multi-beam system (1) for wafer inspection using backscattered electrons (9), comprising:

[0068] - A multi-beam generating device (300) is configured to generate multiple primary electron beams (3) from at least one electron source (301).

[0069] - At least one electron optical imaging lens (102, 698) is used to form a plurality of spatially separated electron focal spots (5) in the image plane (101) of the multi-beam system (1).

[0070] - A wafer stage (500) configured to arrange the surface (25) of a wafer (7) in the image plane (101),

[0071] - A backscattering electron detector (601) is arranged parallel to the image plane (101) at a distance D, wherein the backscattering electron detector (601) includes a plurality of apertures (85) for transmitting the plurality of primary electron beams (3) and a plurality of electron detection elements (607), wherein for each aperture (85), at least one electron detection element (607) is arranged adjacent to the corresponding aperture (85), wherein each of the electron detection elements (607) includes a scintillation material configured to convert backscattered electrons (9) into photons.

[0072] - At least one photon detector (613, 635) for spatially resolving the detection of photons generated within each of the electronic detection elements (607),

[0073] - A photonic imaging lens system (627) for imaging photons excited by the electronic detection element (607) onto the at least one photonic detector (635), wherein the photonic imaging lens system (627) includes at least one photonic optical lens (623, 629) attached to the backscattering electronic detector (601), and wherein each aperture (85) extends through the at least one photonic optical lens (623, 628).

[0074] Clause 2: The system as described in Clause 1, wherein the at least one photonic optical lens (623, 629) is formed as a single-photon field lens (623) disposed on the upper side (603) of the backscattered electron detector (601), wherein the upper side (603) faces the incident primary electron beam (3), and wherein each aperture (85) extends through the photonic field lens (623).

[0075] Clause 3: The system as described in Clause 1, wherein the at least one photonic optical lens (623, 629) comprises a photonic optical lens array (629) disposed on the upper side (603) of the backscattering electron detector (601), wherein the upper side (603) faces the incident primary electron beam (3), and wherein each aperture (85) extends through one of the photonic optical lenses in the photonic optical lens array (629).

[0076] Clause 4: The system as described in any one of Clauses 1 to 3, wherein the at least one photonic optical lens (623, 629) is formed as a hybrid lens, the hybrid lens being formed by a single photonic field lens integrated into an array of photonic optical lenses (629), the array of photonic optical lenses being arranged on the upper side (603) of the backscattering electron detector (601), wherein the upper side (603) faces the incident primary electron beam (3), and wherein each aperture (85) extends through the photonic optical lens (629).

[0077] Clause 5: A system according to any one of Clauses 1 to 4, wherein the at least one photon detector (613, 635) is formed by a spatially resolved image sensor (635).

[0078] Clause 6: A multi-beam system (1) for wafer inspection using backscattered electrons (9), comprising:

[0079] - A multi-beam generating device (300) is configured to generate multiple primary electron beams (3) from at least one electron source (301).

[0080] - At least one electron optical imaging lens (102, 698) is used to form a plurality of spatially separated electron focal spots (5) in the image plane (101) of the multi-beam system (1).

[0081] - A wafer stage (500) configured to arrange the surface (25) of a wafer (7) in the image plane (101),

[0082] - A backscattering electron detector (601) is arranged parallel to the image plane (101) at a distance D, wherein the backscattering electron detector (601) includes a plurality of apertures (85) for transmitting the plurality of primary electron beams (3) and a plurality of electron detection elements (607), wherein for each aperture (85), at least one electron detection element (607) is arranged adjacent to the corresponding aperture (85), wherein each of the electron detection elements (607) includes a scintillation material configured to convert backscattered electrons (9) into photons.

[0083] - At least one photon detector (613, 635) for spatially resolving the detection of photons generated within each of the electronic detection elements (607),

[0084] -The backscattering electron detector (601) includes a plurality of light guides (609) for guiding photons from the lower side of the backscattering electron detector (601) to the upper side (603), wherein the upper side (603) faces the incident primary electron beam (3).

[0085] Clause 7: The system according to Clause 6, wherein the backscattered electron detector (601) comprises a conductive material, such as a nickel-steel alloy, and wherein the plurality of photoguides (609) are embedded within the conductive material.

[0086] Clause 8: A multi-beam system (1) for wafer inspection using backscattered electrons (9), comprising:

[0087] - A multi-beam generating device (300) is configured to generate multiple primary electron beams (3) from at least one electron source (301).

[0088] - At least one electron optical imaging lens (102, 698) is used to form a plurality of spatially separated electron focal spots (5) in the image plane (101) of the multi-beam system (1).

[0089] - A wafer stage (500) configured to arrange the surface (25) of a wafer (7) in the image plane (101),

[0090] - A backscattering electron detector (601) is arranged at a distance D parallel to the image plane (101), wherein the backscattering electron detector (601) includes a plurality of apertures (85) for transmitting the plurality of primary electron beams (3) and a plurality of electron detection elements (607), wherein the backscattering electron detector (601) includes a conductive coating (633) on the upper side (603) facing the incident primary electron beams (3).

[0091] Clause 9: A multi-beam system (1) for wafer inspection using backscattered electrons (9), comprising:

[0092] - A multi-beam generating device (300) is configured to generate multiple primary electron beams (3) from at least one electron source (301).

[0093] - At least one electron optical imaging lens (102, 698) is used to form a plurality of spatially separated electron focal spots (5) in the image plane (101) of the multi-beam system (1).

[0094] - A wafer stage (500) configured to arrange the surface (25) of a wafer (7) in the image plane (101),

[0095] - A backscattering electron detector (601) is arranged parallel to the image plane (101) at a distance D, wherein the backscattering electron detector (601) includes a plurality of apertures (85) for transmitting the plurality of primary electron beams (3) and a plurality of electron detection elements (607), wherein for each aperture (85), at least one electron detection element (607) is arranged adjacent to the corresponding aperture (85), wherein each of the electron detection elements (607) includes a scintillation material configured to convert backscattered electrons (9) into photons.

[0096] - At least one photon detector (613, 635) for spatially resolving the detection of photons generated within each of the electronic detection elements (607),

[0097] - A bundle tube segment (151.2) having a conical shape, the conical shape having a reduced diameter in the propagation direction of the plurality of primary electron beams (3).

[0098] Clause 10: The system according to Clause 9, wherein the conical bundle segment (151.2) is arranged within the upper pole shoe (163) of the at least one electro-optical imaging lens (102).

[0099] Clause 11: A system as described in Clause 9 or 10, wherein the backscattering electron detector (601) is connected to the lower pole shoe (169) of the at least one electron optical imaging lens (102), and wherein the lower pole shoe (169) is electrically insulated from the upper pole shoe (163).

[0100] Clause 12: The system according to Clause 11, wherein the upper pole shoe (163) and the lower pole shoe (169) form an axial clearance (167).

[0101] Clause 13: A multi-beam system (1) for wafer inspection using backscattered electrons (9), comprising:

[0102] - A multi-beam generating device (300) is configured to generate multiple primary electron beams (3) from at least one electron source (301).

[0103] - At least one electron optical imaging lens (102, 698) is used to form a plurality of spatially separated electron focal spots (5) in the image plane (101) of the multi-beam system (1).

[0104] - A wafer stage (500) configured to arrange the surface (25) of a wafer (7) in the image plane (101),

[0105] - A backscattering electron detector (601) is arranged at a distance D parallel to the image plane (101), wherein the backscattering electron detector (601) includes a plurality of apertures (85) for transmitting the plurality of primary electron beams (3), wherein during use, a voltage VE is provided to the backscattering electron detector (601) to generate a decelerating or accelerating electric field.

[0106] Clause 14: The system according to Clause 13, wherein, during use, a voltage VL is provided to the wafer (7), and wherein |VE|<|VL|.

[0107] Clause 15: A multi-beam system (1) for wafer inspection using backscattered electrons (9), comprising:

[0108] - A multi-beam generating device (300) is configured to generate multiple primary electron beams (3) from at least one electron source (301).

[0109] - At least one electron optical imaging lens (102, 698) is used to form a plurality of spatially separated electron focal spots (5) in the image plane (101) of the multi-beam system (1).

[0110] - A wafer stage (500) configured to arrange the surface (25) of a wafer (7) in the image plane (101),

[0111] - A backscattering electron detector (601) is arranged at a distance D parallel to the image plane (101), wherein the backscattering electron detector (601) includes a plurality of apertures (85) for transmitting the plurality of primary electron beams (3), wherein the backscattering electron detector (601) comprises a conductive material, such as a nickel-steel alloy.

[0112] Clause 16: A multi-beam system (1) for wafer inspection using backscattered electrons (9), comprising:

[0113] - A multi-beam generating device (300) is configured to generate multiple primary electron beams (3) from at least one electron source (301).

[0114] - At least one electron optical imaging lens (102, 698) is used to form a plurality of spatially separated electron focal spots (5) in the image plane (101) of the multi-beam system (1).

[0115] - A wafer stage (500) configured to arrange the surface (25) of a wafer (7) in the image plane (101),

[0116] - A backscattering electron detector (601) is arranged at a distance D parallel to the image plane (101), wherein the backscattering electron detector (601) includes a plurality of apertures (85) for transmitting the plurality of primary electron beams (3), wherein the backscattering electron detector (601) includes a dielectric material, such as fused silica or glass, and wherein the backscattering electron detector (601) is coated with a conductive material such as ITO.

[0117] Clause 17: A multi-beam system (1) for wafer inspection using backscattered electrons (9), comprising:

[0118] - A multi-beam generating device (300) is configured to generate multiple primary electron beams (3) from at least one electron source (301).

[0119] - At least one electron optical imaging lens (102, 698) is used to form a plurality of spatially separated electron focal spots (5) in the image plane (101) of the multi-beam system (1).

[0120] - A wafer stage (500) configured to arrange the surface (25) of a wafer (7) in the image plane (101),

[0121] - A backscattering electron detector (601) is arranged at a distance D parallel to the image plane (101), wherein the backscattering electron detector (601) includes a plurality of apertures (85) for transmitting the plurality of primary electron beams (3), wherein the backscattering electron detector (601) includes a thin metal reflective coating on the back side (611) facing the image plane (101).

[0122] Clause 18: A multi-beam system (1) for wafer inspection using backscattered electrons (9), comprising:

[0123] - A multi-beam generating device (300) is configured to generate multiple primary electron beams (3) from at least one electron source (301).

[0124] - At least one electron optical imaging lens (102, 698) is used to form a plurality of spatially separated electron focal spots (5) in the image plane (101) of the multi-beam system (1).

[0125] - A wafer stage (500) configured to arrange the surface (25) of a wafer (7) in the image plane (101),

[0126] - Backscattering electron detector (601), the backscattering electron detector (601) is arranged parallel to the image plane (101) at a distance D, wherein the backscattering electron detector (601) includes a plurality of apertures (85) for transmitting the plurality of primary electron beams (3), wherein at least one of the apertures (85) of the backscattering electron detector (601) is tilted by an angle (17) relative to the normal N of the image plane (101).

[0127] Clause 19: The system according to Clause 18, wherein the tilt angle (17, 17.2, 17.3) increases with the increase of the distance to the optical axis (105) of the at least one electro-optical imaging lens (102).

[0128] Clause 20: A multi-beam system (1) for wafer inspection using backscattered electrons (9), comprising:

[0129] - A multi-beam generating device (300) is configured to generate multiple primary electron beams (3) from at least one electron source (301).

[0130] - At least one electron optical imaging lens (102, 698) is used to form a plurality of spatially separated electron focal spots (5) in the image plane (101) of the multi-beam system (1).

[0131] - A wafer stage (500) configured to arrange the surface (25) of a wafer (7) in the image plane (101),

[0132] - A backscattering electron detector (601) is arranged at a distance D parallel to the image plane (101), wherein the backscattering electron detector (601) includes a plurality of apertures (85) for transmitting the plurality of primary electron beams (3), wherein at least one of the apertures (85) of the backscattering electron detector (601) has an elongated shape in one direction to allow a larger scanning range in said one direction.

[0133] A multi-beam electron system with a backscattered electron detector is provided. In one example, the backscattered electron detector includes multiple apertures with locally confined regions of scintillation material near the apertures. Backscattered electrons are thus converted into photons, which are then guided by an optical device (such as a light guide in an optical imaging lens system) to a spatially resolved photon detector.

[0134] A list of reference numerals is provided:

[0135] 1. Multi-beam system

[0136] 3. Small bundles or multiple small bundles of primary charged particles

[0137] 5 Primary charged particle beam spot

[0138] 7 objects

[0139] 9 Backscattered electrons

[0140] 13 Secondary electron beam paths

[0141] 15 secondary charged particle image spots

[0142] 17. Inclination Angle

[0143] 19 secondary electrons

[0144] 25. Object surface

[0145] 85 One or more holes

[0146] 100 object illumination units

[0147] 101 Object plane

[0148] 102 Objective Lens

[0149] 103 field lens

[0150] 105 optical axes

[0151] 108 bundle intersections

[0152] 110 Multi-pole deflector element

[0153] 112 Multipole Corrector Component

[0154] 117 Folding Angle

[0155] 151 Electron Beam Tube

[0156] 161 Lens Coil

[0157] 163 Ultra Boots

[0158] 165 Extreme Boots

[0159] 167 Magnetic pole gap

[0160] 169 lower pole boots

[0161] 171 Isolation Bridge

[0162] 200 Detection System

[0163] 206 Electro-optical Lens

[0164] 208 Electro-optical Lens

[0165] 209 Electronic Detector

[0166] 210 Electro-optical lens

[0167] 300-beam generation equipment

[0168] 301 Charged Particle Source

[0169] 303 Collimating Lens

[0170] 305 multi-hole arrangement

[0171] 309 Primary Electron Beam

[0172] 331 First Field Lens

[0173] 333 Second Field Lens

[0174] 400 beam splitter

[0175] 500 sample stage

[0176] 503 Sample Voltage Source

[0177] 601 Backscattered Electron Detector

[0178] 603 upper side

[0179] 607 Electronic Detection Components

[0180] 609 Optical Guide

[0181] 611 Backside of the backscattered electron detector

[0182] 613 One or more photon detectors

[0183] 617 Light

[0184] 619 Electrical Connections

[0185] 621 Reflective Coating

[0186] 623 field lens

[0187] 625 Imaging Lens

[0188] 627 Imaging Lens System

[0189] 629 Array Lens

[0190] 631 Optical Path

[0191] 633 Conductive Coating

[0192] 635 Spatial Resolution Detector

[0193] 651 Folding Reflector

[0194] 653 holes

[0195] 693 Isolation Layer

[0196] 697 Extraction Electrode

[0197] 698 Lens Electrode Layer

[0198] 800 Control Unit

[0199] 810 Imaging Control Module

[0200] 830 Primary Beam Path Control Module

[0201] 850 control modules

[0202] 860 Scan Operation Control Unit

[0203] 880 Control Operation Processor

[0204] 890 memory

Claims

1. A multi-beam system (1) for wafer inspection using backscattered electrons (9), comprising: - A multi-beam generating device (300) configured to generate multiple primary electron beams (3) from at least one electron source (301). - At least one electron optical imaging lens (102, 698) is used to form a plurality of spatially separated electron focal spots (5) in the image plane (101) of the multi-beam system (1). - A wafer stage (500) configured to arrange the surface (25) of a wafer (7) in the image plane (101), - A backscattering electron detector (601) is arranged parallel to the image plane (101) at a distance D, wherein the backscattering electron detector (601) includes a plurality of apertures (85) for transmitting the plurality of primary electron beams (3) and a plurality of electron detection elements (607), wherein for each aperture (85), at least one electron detection element (607) is arranged adjacent to the corresponding aperture (85), wherein each of the electron detection elements (607) includes a scintillation material configured to convert backscattered electrons (9) into photons. - At least one photon detector (613, 635) for spatially resolving the detection of photons generated within each of the electronic detection elements (607), - A photonic imaging lens system (627) for imaging photons excited by the electronic detection element (607) onto the at least one photonic detector (635), wherein the photonic imaging lens system (627) includes at least one photonic optical lens (623, 629) attached to the backscattering electronic detector (601), and wherein each aperture (85) extends through the at least one photonic optical lens (623, 628).

2. The system according to claim 1, wherein, The at least one photonic optical lens (623, 629) is formed as a single-photon light field lens (623) arranged on the upper side (603) of the backscattered electron detector (601), wherein the upper side (603) faces the incident primary electron beam (3), and wherein each aperture (85) extends through the photonic light field lens (623).

3. The system according to claim 1, wherein, The at least one photonic optical lens (623, 629) is formed as an array of photonic optical lenses (629) arranged on the upper side (603) of the backscattering electron detector (601), wherein the upper side (603) faces the incident primary electron beam (3), and wherein each aperture (85) extends through one of the photonic optical lenses in the array of photonic optical lenses (629).

4. The system according to any one of claims 1 to 3, wherein, The at least one photonic optical lens (623, 629) is formed as a hybrid lens, which is formed by a single-photon light field lens integrated into an array of photonic optical lenses (629), the array of photonic optical lenses being arranged on the upper side (603) of the backscattering electron detector (601), wherein the upper side (603) faces the incident primary electron beam (3), and wherein each aperture (85) extends through the photonic optical lens (629).

5. The system according to any one of claims 1 to 4, wherein, The at least one photon detector (613, 635) is formed by a spatially resolved image sensor (635).

6. The system according to any one of claims 1 to 5, wherein, The backscattering electron detector (601) further includes a plurality of light guides (609) for guiding photons from the lower side of the backscattering electron detector (601) to the upper side (603), wherein the upper side (603) faces the incident primary electron beam (3).

7. The system according to any one of claims 1 to 6, wherein, The multi-beam charged particle system (1) includes a beam tube segment (151.2) having a conical shape, the conical shape having a decreasing diameter in the propagation direction of the plurality of primary electron beams (3).

8. The system according to claim 7, wherein, The conical beam tube segment (151.2) is arranged within the upper pole shoe (163) of the at least one electro-optical imaging lens (102).

9. The system according to claim 7 or 8, wherein, The backscattering electron detector (601) is connected to the lower pole shoe (169) of the at least one electron optical imaging lens (102), wherein the lower pole shoe (169) is electrically insulated from the upper pole shoe (163).

10. The system according to claim 9, wherein, The upper pole shoe (163) and the lower pole shoe (169) form an axial gap (167).

11. The system according to any one of claims 1 to 10, wherein, A voltage VE is provided to the backscattering electron detector (601) to generate a decelerating or accelerating electric field between the backscattering electron detector (601) and the beam tube segment (151.2).

12. The system according to claim 11, wherein, During use, a voltage VL is supplied to the wafer (7), wherein |VE|<|VL|.

13. The system according to any one of claims 1 to 12, wherein, The backscattered electron detector (601) comprises a conductive material, such as a nickel-steel alloy.

14. The system according to claim 13, wherein, At least one optical guide (609) is embedded in the conductive material.

15. The system according to any one of claims 1 to 12, wherein, The backscattering electron detector (601) includes a dielectric, such as fused silica or glass, and wherein the backscattering electron detector (601) is coated with a conductive material such as ITO.

16. The system according to any one of claims 1 to 15, wherein, The at least one electro-optical imaging lens (102) is a magnetic lens with an axial gap (167), and wherein the backscattering electron detector (601) is arranged between the lower pole shoe (169) of the magnetic lens (102) and the image plane (101).

17. The system according to any one of claims 1 to 16, wherein, The backscattering electron detector (601) includes a thin metallic reflective coating on a back side (611) facing the image plane (101).

18. The system according to any one of claims 1 to 17, wherein, The backscattering electron detector (601) includes a conductive coating (633) on the upper side (603) facing the incident primary electron beam (3), the conductive coating (633) covering at least one of the at least one photonic optical lens (623, 629) or light guide (609).

19. The system according to any one of claims 1 to 18, wherein, At least one of the apertures (85) of the backscattered electron detector (601) is tilted by an angle (17) relative to the normal N of the image plane (101).

20. The system according to claim 19, wherein, The tilt angles (17, 17.2, 17.3) increase with the increase of the distance to the optical axis (105) of the at least one electro-optical imaging lens (102).

21. A multi-beam system (1) for inspecting wafers using backscattered electrons (9), comprising: - A multi-beam generating device (300) configured to generate multiple primary electron beams (3) from at least one electron source (301). - At least one electron optical imaging lens (102, 698) is used to form a plurality of spatially separated electron focal spots (5) in the image plane (101) of the multi-beam system (1). - A wafer stage (500) configured to arrange the surface (25) of a wafer (7) in the image plane (101), - A backscattering electron detector (601) is arranged parallel to the image plane (101) at a distance D, wherein the backscattering electron detector (601) includes a plurality of apertures (85) for transmitting the plurality of primary electron beams (3) and a plurality of electron detection elements (607), wherein for each aperture (85), at least one electron detection element (607) is arranged adjacent to the corresponding aperture (85), wherein each of the electron detection elements (607) includes a scintillation material configured to convert backscattered electrons (9) into photons. - A plurality of photon detectors (613, 635), including at least one photon detector (613, 635) for detecting photons generated within each of the plurality of electronic detection elements (607). - Multiple optical guides (609).

22. The system according to claim 21, wherein, The backscattered electron detector (601) comprises a nickel-steel alloy.

23. The system according to any one of claims 21 to 22, wherein, The at least one electro-optical imaging lens (102) is a magnetic lens with an axial gap (167), and wherein the backscattering electron detector (601) is arranged between the lower pole shoe (169) of the magnetic lens (102) and the image plane (101).

24. The system according to any one of claims 21 to 23, wherein, The backscattering electron detector (601) includes a thin metallic reflective coating on a back side (611) facing the image plane (101).

25. The system according to any one of claims 21 to 24, wherein, The backscattered electron detector (601) includes a conductive coating (633) on the upper side (603) of the incident primary electron beam (3).

26. The system according to any one of claims 21 to 25, wherein, At least one of the apertures (85) of the backscattered electron detector (601) is tilted by an angle (17) relative to the normal N of the image plane (101).

27. The system according to claim 26, wherein, The tilt angles (17, 17.2, 17.3) increase with the increase of the distance to the optical axis (105) of the at least one electro-optical imaging lens (102).

28. A multi-beam system (1) for inspecting wafers using backscattered electrons (9), comprising: - A multi-beam generating device (300) configured to generate multiple primary electron beams (3) from at least one electron source (301). - At least one electron optical imaging lens (102, 698) is used to form a plurality of spatially separated electron focal spots (5) in the image plane (101) of the multi-beam system (1). - A wafer stage (500) configured to arrange the surface (25) of a wafer (7) in the image plane (101), - A backscattering electron detector (601) is arranged parallel to the image plane (101) at a distance D, wherein the backscattering electron detector (601) includes a plurality of apertures (85) for transmitting the plurality of primary electron beams (3) and a plurality of electron detection elements (607), wherein for each aperture (85), at least one electron detection element (607) is arranged adjacent to the corresponding aperture (85). The multi-beam system (1) is configured such that at least one of the primary electron beams (3) crosses the image plane (101) at an angle of inclination (17) relative to the normal N of the image plane (101), and wherein at least one of the apertures (85) of the backscattered electron detector (601) is tilted at the angle of inclination (17) relative to the normal N of the image plane (101).

29. The system according to claim 28, wherein, The tilt angle (17, 17.2, 17.3) of the aperture (85) increases with the increase of the distance to the optical axis (105) of the at least one electro-optical imaging lens (102).

30. The system according to claim 28 or 29, wherein, Each of the electronic detection elements (607) includes a scintillation material configured to convert backscattered electrons (9) into photons, and wherein the multi-beam system (1) further includes at least one photon detector (613, 635) for spatially resolving detection of photons generated within each of the electronic detection elements (607).

31. The system according to any one of claims 28 to 30, further comprising a photonic imaging lens system (627) for imaging the electronic detection element (607) onto the at least one photonic detector (635), wherein, The photonic imaging lens system (627) includes at least one photonic optical lens (623, 629) attached to the backscattered electron detector (601), and wherein each aperture (85) extends through at least one photonic optical lens (623, 629) at the tilt angle (17, 17.2, 17.3).

Images