Charged particle beam apparatus and method for inspecting and / or imaging a sample

Abstract

Describe a charged particle beam apparatus 10 for imaging and / or inspecting a sample 140. The charged particle beam apparatus comprises: a beam emitter 150 that emits a primary charged particle beam 105, the charged particle beam apparatus being adapted to direct the primary charged particle beam along an optical axis 101 towards the sample to release signal particles; a blocking field device 100 that blocks the primary charged particle beam before it hits the sample, the blocking field device comprising an objective lens 110 and a surrogate electrode 130, wherein the surrogate electrode comprises an opening 131 that allows the primary charged particle beam and the signal particles to pass through; a first detector 120 for off-axis backscattered particles between the surrogate electrode and the objective lens; and a preamplifier 121 that amplifies the signal of the first detector, wherein the preamplifier is at least one of the following: (i) integrated with the first detector, (ii) arranged adjacent to the first detector inside the vacuum housing 102 of the charged particle beam apparatus, and (iii) fixedly mounted in the vacuum chamber of the charged particle beam apparatus. Also describe a method of imaging and / or inspecting a sample using the charged particle beam apparatus.

Description

Technical Field

[0001] The embodiments described herein relate to an apparatus for imaging and / or inspecting a sample with one or more charged particle beams, specifically an electron beam. In particular, a charged particle beam apparatus with a retarding field device is described, which is configured to decelerate the charged particle beam before it hits the sample. The embodiments particularly relate to an electron beam inspection system for inspecting a sample having a 3D structure or a structure with a high aspect ratio by detecting backscattered electrons (BSE). The embodiments further relate to a method for inspecting and / or imaging a sample using a charged particle beam apparatus. Background Art

[0002] Charged particle beam equipment has many functions in a number of industrial fields, including but not limited to critical dimension measurement during the manufacture of semiconductor devices, defect review of semiconductor devices, inspection of semiconductor devices, exposure systems for lithography, detection devices, and test systems. Therefore, there is a high demand for structuring, testing, and inspecting samples or specimens at the micron and nanometer scales.

[0003] The control, inspection, or structuring of micron and nanometer scale processes is typically accomplished using a charged particle beam such as an electron beam, which is generated and focused in a charged particle beam apparatus such as an electron microscope. Compared to, for example, a photon beam, the charged particle beam offers superior spatial resolution due to its short wavelength.

[0004] In recent years, it has become increasingly attractive to inspect and / or image image samples having a 3D structure or a structure with a large aspect ratio (such as a large ratio of depth to opening width). Devices such as 3D FinFETs and 3D NANDs have structures with a large aspect ratio, which are difficult to image in a scanning electron microscope (SEM) when using secondary electrons (SEs) (i.e., low-energy signal electrons generated when a primary electron beam hits the sample surface). SEs may be difficult to escape from structures with a high aspect ratio and may generally not be detectable with a reasonable signal-to-noise ratio. In particular, critical dimension (CD) measurement of high aspect ratio trenches and contact holes is a challenge. Image modes using backscattered electrons (BSEs) (i.e., high-energy electrons backscattered from the sample) are particularly commonly used in the semiconductor industry to improve the quality of imaging and / or inspection.

[0005] In modern charged particle beam inspection systems, it would be beneficial to simultaneously detect secondary charged particles and backscattered charged particles with high detection efficiency. This would allow accurate inspection of sample surfaces that extend substantially in the xy plane and 3D structures that have depth in the z direction with high resolution. In some systems, backscattered charged particles that leave the sample at various angles relative to the optical axis are primarily detected using a first detector that is arranged close to the sample (e.g., between an objective lens and the sample). On the other hand, secondary charged particles are primarily detected using a second detector that is arranged at a greater distance from the sample, such as between a beam source and an objective lens. However, it is difficult to effectively achieve high BSE detection without significantly reducing the detection efficiency of lower energy signal charged particles.

[0006] In view of the foregoing, it would be beneficial to provide a charged particle beam apparatus and method for inspecting and / or imaging a sample that overcomes at least some of the problems in the art. Summary of the Invention

[0007] In view of the above, a charged particle beam apparatus and a method for examining and / or imaging a sample using a charged particle beam apparatus are provided according to the independent claims. Further aspects, advantages and features are apparent from the dependent claims, the description and the drawings.

[0008] According to one aspect, a charged particle beam apparatus for imaging and / or inspecting a sample is provided. The charged particle beam apparatus comprises: a beam emitter for emitting a primary charged particle beam, the charged particle beam apparatus being adapted to direct the primary charged particle beam along an optical axis to the sample for releasing signal particles; a retarding field apparatus for retarding the primary charged particle beam before striking the sample, the retarding field apparatus comprising an objective lens and a proxy electrode, wherein the proxy electrode comprises an opening for allowing the primary charged particle beam and the signal particles to pass through; a first detector for detecting off-axis backscattered particles between the proxy electrode and the objective lens; and a preamplifier for amplifying a signal of the first detector, wherein the preamplifier is at least one of: (i) integrated with the first detector, (ii) arranged adjacent to the first detector inside a vacuum housing of the charged particle beam apparatus, and (iii) fixedly mounted in a vacuum chamber of the charged particle beam apparatus.

[0009] According to another aspect, there is provided a scanning electron microscope including a charged particle beam device as described herein. The beam emitter is an electron source configured to emit a primary electron beam, and the scanning electron microscope further includes: a sample stage for supporting the sample; and a scanning deflector for scanning the primary electrons on the surface of the sample in a predetermined scanning pattern.

[0010] According to another aspect, there is provided a method for imaging and / or inspecting a sample using a charged particle beam device. The method includes: emitting a primary charged particle beam; guiding the primary charged particle beam along an optical axis to the sample for generating signal particles; focusing and retarding the primary charged particle beam using a retarding field device including an objective lens and a surrogate electrode disposed between the objective lens and the sample; detecting off-axis backscattered particles using a first detector disposed between the surrogate electrode and the objective lens; and pre-amplifying a signal of the first detector using a pre-amplifier mounted adjacent to the first detector in a vacuum environment inside the charged particle beam device.

[0011] There is further described a charged particle beam device for imaging and / or inspecting a sample. The charged particle beam device includes: a beam emitter for emitting a primary charged particle beam, the charged particle beam device being adapted to guide the primary charged particle beam along an optical axis to the sample for releasing signal particles; a retarding field device for retarding the primary charged particle beam before impinging on the sample, the retarding field device including an objective lens and a surrogate electrode; and a first detector for off-axis backscattered particles between the surrogate electrode and the objective lens. The surrogate electrode has an opening allowing passage of the primary charged particle beam and the signal particles, wherein the opening is sized to allow charged particles backscattered from the sample to pass at an angle (α) of 0° to 20° or higher relative to the optical axis.

[0012] A charged particle beam device for imaging and / or inspecting a sample is further described. The charged particle beam device includes: a beam emitter configured to emit a primary charged particle beam, the charged particle beam device being adapted to direct the primary charged particle beam along an optical axis to the sample for releasing signal particles; a retarding field device configured to retard the primary charged particle beam before it hits the sample, the retarding field device including an objective lens and a surrogate electrode, wherein the surrogate electrode includes an opening that allows the primary charged particle beam and the signal particles to pass through; and a first detector configured to detect off-axis backscattered particles between the surrogate electrode and the objective lens, wherein the first detector is configured to act as an additional electrode for influencing the primary charged particle beam and includes at least one of a conductive inner surface directed towards the optical axis and a conductive top surface directed towards the objective lens and configured to be set at a predetermined electric potential.

[0013] A method for imaging and / or inspecting a sample using a charged particle beam device is further described. The method includes: emitting a primary charged particle beam; directing the primary charged particle beam along an optical axis to the sample for generating signal particles; focusing and retarding the primary charged particle beam using a retarding field device including an objective lens and a surrogate electrode arranged between the objective lens and the sample, wherein the surrogate electrode has an opening that allows the primary charged particle beam and the signal particles to pass through, wherein the opening is sized to allow charged particles backscattered from the sample to pass through at an angle (α) of 0° to 20° or more relative to the optical axis; and detecting off-axis backscattered particles using a first detector arranged between the surrogate electrode and the objective lens.

[0014] Embodiments also relate to an apparatus for performing the disclosed methods and include apparatus components for performing each method feature described. Method features may be performed by hardware components, a computer programmed with suitable software, by any combination of the two, or in any other manner. Additionally, embodiments also relate to a method of manufacturing the described apparatus and a method of operating the described apparatus. Embodiments include method features for performing each function of the apparatus. BRIEF DESCRIPTION OF THE DRAWINGS

[0015] For a more particular description of the above-described features of the present disclosure, reference may be made to the embodiments, which are related to the embodiments of the present disclosure and are described below:

[0016] Figure 1 is a schematic view of a charged particle beam device according to an embodiment described herein;

[0017] Figure 2 is Figure 1Magnified view of the surrogate electrode and the first detector of the charged particle beam device;

[0018] Figure 3 The surrogate electrode for a charged particle beam device according to an embodiment described herein is shown in a top view;

[0019] Figures 4a to 4b The first detector of the charged particle beam device described herein is shown in a perspective bottom view and a perspective top view;

[0020] Figure 5 is a schematic diagram of a charged particle beam device according to an embodiment described herein; and

[0021] Figure 6 shows a flowchart of a method for imaging and / or inspecting a sample using a charged particle beam device according to an embodiment described herein. Detailed Description

[0022] Reference will now be made in detail to various embodiments, one or more examples of which are shown in the accompanying drawings. In the following description, like reference numerals refer to like components. Generally, only the differences regarding each embodiment are described. Each example is provided by way of explanation and not limitation. Additionally, features shown or described as part of one embodiment can be used on or in combination with other embodiments to yield another embodiment. It is intended that the description include such modifications and variations.

[0023] Without limiting the scope of protection of the present application, hereinafter, the charged particle beam device or its components will be exemplarily referred to as an electron beam device configured to detect signal electrons. Signal electrons specifically include secondary electrons and / or backscattered electrons, specifically both secondary electrons and backscattered electrons (SE and BSE). However, it should be understood that the embodiments described herein can be applied to devices and components for detecting other small bodies (such as secondary and / or backscattered charged particles in ionic form) in order to obtain a sample image or inspection result. Therefore, in the embodiments described herein, charged particles are not limited to electrons.

[0024] As used herein, "sample", "specimen" or "wafer" includes, but is not limited to, semiconductor wafers, semiconductor workpieces, and other workpieces such as memory disks. A "specimen" may specifically be any workpiece having a structure or on which materials are deposited. The sample, specimen or wafer may include a surface to be inspected and / or imaged, e.g., a structured surface or a surface on which a layer or a pattern of material is deposited. For example, the specimen may be a substrate or a wafer on which a plurality of electronic devices to be inspected are provided. According to some embodiments, the devices and methods described herein relate to electron beam inspection (EBI), critical dimension measurement, and defect review applications, where the devices and methods described herein can advantageously be used to obtain increased throughput and improved detection accuracy. According to some embodiments, an electron beam inspection (EBI), critical dimension (CD) measurement tool, and / or defect review (DR) tool may be provided, where high resolution, large field of view, and high scan speed can be achieved.

[0025] Figure 1 FIG. shows a schematic diagram of a charged particle beam apparatus 10 for imaging and / or inspecting a specimen according to an embodiment described herein. The charged particle beam apparatus 10 includes a beam emitter 150 for emitting a primary charged particle beam (specifically, an electron beam). The charged particle beam apparatus 10 is configured to direct the primary charged particle beam 105 along an optical axis 101 towards the specimen 140 to release signal particles from the specimen. The specimen 140 may be placed on a specimen stage 50, which includes a specimen support surface extending substantially in the x-y plane.

[0026] The beam emitter 150 may be a cold field emitter (CFE), a Schottky emitter, a TFE, or a charged particle source with high current and / or high brightness, specifically an electron source. At 100 mrad or higher, a high current is considered to be 5 μA.

[0027] The charged particle beam apparatus 10 further includes a retarding field device 100 for retarding the primary charged particle beam 105 before it impinges on the specimen 140. The retarding field device 100 includes an objective lens 110 and a surrogate electrode 130. As used herein, a "surrogate electrode" may be understood as an electrode disposed near the specimen, specifically between the objective lens 110 and the specimen 140 (or the specimen stage 50). In other words, the surrogate electrode 130 is disposed downstream of the objective lens 110 in the propagation direction of the primary charged particle beam 105, and is typically the last electrode through which the primary charged particle beam passes before impinging on the specimen surface. For example, during operation, the distance D1 between the surrogate electrode 130 and the specimen 140 (see Figure 2)It can be 5 mm or smaller, specifically 3 mm or smaller, more specifically 1 mm or smaller, or even 200 μm or smaller.

[0028] According to some embodiments described herein, a charged particle beam device is adapted to direct a primary beam in a column of the charged particle beam device along an optical axis 101 to a sample for generating signal particles released from the sample, the signal particles including secondary particles generated upon impact and backscattered particles reflected from the sample. The surrogate electrode 130 includes an opening 131 that allows the primary charged particle beam 105 to pass through toward the sample and allows the signal particles to pass through the opening 131 from the sample in the opposite direction. Generally, the opening 131 is aligned with the optical axis 101. Specifically, the optical axis 101 of the charged particle beam device may intersect the opening 131 of the surrogate electrode 130 at the center.

[0029] Generally, the primary charged particle beam 105 travels through the column of the charged particle beam device before hitting the sample to be imaged and / or inspected. The interior of the column can be evacuated, i.e., the charged particle beam device generally includes a vacuum housing 102 such that the primary charged particle beam travels through an environment having a pressure lower than atmospheric pressure (e.g., a pressure of 1 mbar or smaller, specifically 1×10 -5 mbar or smaller, even 1×10 -8 mbar or smaller (ultra-high vacuum)). The beam emitter and the objective lens can be arranged inside the vacuum housing 102 of the charged particle beam device. The surrogate electrode 130 can be provided adjacent to the front end of the vacuum housing 102 and / or can protrude into a sample chamber provided with a sample stage. The sample chamber can be configured for a pressure lower than atmospheric pressure (e.g., high vacuum), while in some embodiments, the vacuum housing 102 of the charged particle beam device can be configured for ultra-high vacuum.

[0030] When the primary charged particle beam 105 hits the sample, different reactions occur on or in the sample. For example, secondary particles are released from the sample: the primary beam hitting the sample dissociates other particles in the sample particularly by the energy provided by the particles of the primary charged particle beam. These secondary particles leave the sample after being released from the sample and can be detected by a suitable detector. However, the primary charged particle beam causes further effects: the particles of the primary beam bounce back from the sample (from the surface or after entering the sample to a certain depth) and are reflected from the sample. The particles of the primary charged particle beam that bounce back from the sample and leave the sample are referred to as backscattered particles. The backscattered particles can be detected at various backscattering angles to obtain spatial information about the sample. Generally, the secondary particles and the backscattered particles are collectively referred to as signal particles or signal electrons.

[0031] The detection of backscattered electrons is particularly beneficial for the imaging and inspection of 3-D structures in the semiconductor industry. For example, devices such as 3D FinFETs and 3D NANDs have structures with large aspect ratios, which are difficult to image in charged particle beam devices using only secondary particles. A large aspect ratio can be understood as a ratio of the depth of the structure in the sample to the opening width of the structure of about 5:1 or higher, such as 10:1 or even 20:1 or higher. In a simplified example, the structure can be a substantially cylindrical hole in the sample, providing a depth into the sample and a width roughly corresponding to the diameter of the substantially cylindrical hole, as will be explained in more detail below.

[0032] Secondary particles such as secondary electrons cannot easily escape from structures with large aspect ratios and generally cannot be detected with a reasonable signal-to-noise ratio. In particular, CD measurements of high aspect ratio trenches and contact holes are a challenge. However, in the embodiments described herein, backscattered particles can be used for imaging and / or inspecting structures with large aspect ratios. Backscattered particles can leave holes and trenches because backscattered particles have sufficient energy to escape from deep structures and may not require the use of a high extraction field for extracting backscattered particles from the sample (which is different from secondary electrons). Additionally, at a suitable (moderate) landing energy of the primary beam, backscattered particles can pass through the sidewalls and can leave the sample, such that a larger amount of backscattered particles can contribute to the overall backscattered particle signal. An effective backscattered particle detector is advantageously used, which can detect backscattered particles at small angles (which are reflected from high aspect ratio features) as well as backscattered particles at large angles that have passed through the surrounding material.

[0033] In known devices, a surrogate electrode with several openings is utilized: a central opening for signal particles to leave the sample at a small angle relative to the optical axis, and at least one additional opening for signal particles (off-axis BSE) to leave the sample at a large angle relative to the optical axis. However, a surrogate electrode with multiple openings for signal particles propagating at different angles may reduce the overall detection efficiency.

[0034] In view of the above, embodiments described herein include a surrogate electrode 130 having an opening 131 sized to permit charged particles backscattered from a sample to pass through at an angle α of 0° to 20° or greater relative to the optical axis 101. In particular, the surrogate electrode may have only a single opening rather than multiple openings. Specifically, as described herein, the following particles propagate through the same opening of the surrogate electrode: (a) a primary charged particle beam; (b) “axial” signal particles, including secondary particles and backscattered particles, that leave the sample substantially along the optical axis (e.g., at an angle between 0° and 5° relative to the optical axis); and (c) “off-axis” signal particles, including large-angle backscattered electrons that propagate at an angle greater than 15° relative to the optical axis, that leave the sample at a larger angle (e.g., at an angle between 5° and 20°) relative to the optical axis. Thus, signal particles that do not substantially carry valuable information about the sample are blocked by the body of the surrogate electrode, and backscattered particles at small angles and backscattered particles at large angles can be detected downstream of the surrogate electrode in the direction of propagation of the signal particles after having passed through the same opening 131 of the surrogate electrode.

[0035] In some embodiments, which may be combined with other embodiments described herein, an opening 131 of the surrogate electrode 130 is sized to permit charged particles backscattered from a sample to pass through at an angle α of 0° to 45° or greater, or even at an angle of 0° to 65° or greater relative to the optical axis. Thus, signal particles that are backscattered from the sample only at very large angles relative to the optical axis can propagate through an opening 131 of the surrogate electrode 130 without the risk of being blocked by the body of the surrogate electrode. This effectively improves the detection of signal particles, specifically off-axis backscattered particles that carry valuable information about the structure on the sample.

[0036] In some embodiments, an opening 131 of the surrogate electrode 130 is a circular opening or a circular aperture that may intersect the optical axis 101 at the center. In some embodiments, during operation of the charged particle beam device, the surrogate electrode is arranged very close to the sample surface, e.g., at a first distance D1 of 5 mm or less, specifically 3 mm or less, more specifically 1 mm or less, or even 200 μm or less (see Figure 2) At this point. The small first distance D1 also allows backscattered electrons at large angles to propagate through an opening 131. On the other hand, the first distance D1 is typically at least 100 μm, such that signal electrons can still be extracted from the sample by providing an extraction region between the sample and the surrogate electrode. Alternatively or in addition, the diameter D4 of an opening 131 can be 1 mm or greater, specifically 3 mm or greater, or even 5 mm or greater. The large diameter D4 of an opening 131 also allows backscattered electrons at large angles to propagate through an opening 131. On the other hand, the diameter D4 of an opening can be 8 mm or less, such that a predetermined electric field can be generated in the extraction region between the sample and an opening 131 of the surrogate electrode by applying a predetermined potential U 代理 to the surrogate electrode.

[0037] The charged particle beam device further includes a first detector 120 for off-axis backscattered particles, wherein the first detector 120 is arranged between the surrogate electrode 130 and the objective lens 110. "Off-axis backscattered particles" are particles that are backscattered at an angle (e.g., at an angle of 5° or greater) with respect to the optical axis. Thus, off-axis backscattered electrons (which typically have a particle energy of several keV or several tens of keV) can be detected by the first detector 120 at a position directly downstream of the surrogate electrode 130 along the propagation direction of the backscattered electrons. This improves the detection efficiency for off-axis backscattered particles.

[0038] For example, the first detector 120 can be a backscattered electron detector, specifically a semiconductor detector, specifically a PIN diode. In particular, the first detector 120 can be a multi-channel backscattered electron detector including a plurality of detection segments, and the signals of the plurality of detection segments can be processed separately, e.g., mixed and / or combined separately. For example, the signals from the plurality of detection segments can be combined for compositional imaging and / or processed separately to improve topographical contrast.

[0039] Optionally, a second detector ( Figure 1 not shown in the figure) configured to detect additional signal particles released from the sample, specifically secondary charged particles and / or axially backscattered electrons that are substantially along the optical axis or backscattered at a small angle, can be arranged downstream of the objective lens in the traveling direction of the signal particles. The second detector can be a secondary electron detector. Thus, secondary charged particles and / or axially backscattered particles that are substantially propagating along the optical axis can be detected by the second detector at a position between the objective lens and the beam emitter.

[0040] In some embodiments, the first detector 120 can be a backscattered electron detector, specifically an in-lens detector having a detection surface 125 that can extend annularly around the optical axis 101. In some embodiments, the first detector 120 is an in-lens detector having a hole that allows a primary charged particle beam 105 to pass through and having an annular detection surface around the hole.

[0041] In some embodiments, the detection surface 125 of the first detector 120 can be sized to detect at least charged particles backscattered from the sample at an angle between 15° and 30° relative to the optical axis, specifically at an angle between 10° and 35°, more specifically between 7° and 40°, or even at a larger angle. For example, as Figure 2 exemplarily shown in, the first detector 120 can have a detection surface 125 that is sized to detect charged particles backscattered from the sample in a range between a first angle (α1) of 15° or less and a second angle (α2) of 30° or greater. Axially backscattered particles and particles backscattered at a very small angle relative to the optical axis (e.g., an angle of 5° or less) may pass through the hole of the first detector without being detected by the first detector. Axially backscattered particles can optionally be detected by a second detector downstream of the objective lens along the propagation direction of the signal particles. Charged particles backscattered at a very large angle relative to the optical axis (e.g., an angle of 35° or greater, or 45° or greater) may strike the support of the first detector outside the radial extent of the detection surface 125 of the first detector without being detected, or may have been blocked by the body of the surrogate electrode 130. In some embodiments, the size of an opening 131 of the surrogate electrode 130 can be adapted to the size of the detection surface 125 of the first detector such that charged particles backscattered at a very large angle that would strike the first detector outside the radial extent of the detection surface are blocked by the surrogate electrode.

[0042] In some embodiments that can be combined with other embodiments described herein, the retarding field device 100 includes an electrostatic magnetic objective lens (or magnetic objective lens) and a surrogate electrode 130. Generally, in a retarding field device, the electron energy in the column is reduced to a final landing energy before striking the sample. The overall performance of the retarding field device can be determined by an immersion coefficient, which is the ratio of the column energy to the landing energy. The higher the immersion coefficient, the better the performance in terms of resolution.

[0043] In some embodiments, the retardation field device 100 is adapted to generate an extraction field for secondary particles released from a sample. For example, the retardation field device 100, acting as a retardation lens for a primary charged particle beam, can act as an acceleration lens for secondary particles emitted by the sample. The retardation field device can be controlled to adjust operating parameters for the purpose of decelerating the primary charged particle beam and accelerating the secondary particles. For low landing energies, the focusing power of the retardation field device is based on the combined effect of the objective lens and the surrogate electrode that retard the primary electrons before the collision.

[0044] In the context of the embodiments described herein, a retardation field device for a charged particle beam device describes a device for acting on a charged particle beam with an initially high electron energy that is decelerated to a lower landing energy shortly before hitting the sample. The ratio between the electron energy in the column after acceleration and the landing energy before hitting the sample can be about 4 or greater, for example 8 or more. The landing energy can be 10 keV or lower, for example 5 keV or lower, such as 1 keV.

[0045] According to some embodiments, the surrogate electrode can be understood as the beam-influencing electrode closest to the sample or the sample stage. In one example, the distance between the surrogate electrode and the sample stage or the sample is less than the distance between the objective lens and the sample stage or the sample.

[0046] According to the embodiments described herein, by using a surrogate electrode with an opening 131 as an incident window for backscattered particle detection, it is achieved that the detection of large-angle backscattered particles can be performed with reduced detection losses. The surrogate electrode can also be used to decelerate the primary charged particle beam as the final component of the retardation field device. The surrogate electrode may also be capable of controlling the extraction field strength for secondary particles.

[0047] Since the retardation field device provides a significant potential difference of generally 5 keV or higher, 15 keV or even 30 keV or higher (e.g., about 35 keV) between the sample and the column of the charged particle beam device, the backscattered particles passing through an opening 131 are accelerated before reaching the first detector 120, which is advantageous for efficient detection. The first detector 120 can act as an acceleration electrode and is set at a corresponding potential. Accelerating the backscattered particles is particularly beneficial when detecting backscattered particles at a low landing energy (e.g., below 10 keV, e.g., below 3 keV or even 1 keV), or when the backscattered particles have lost a part of their energy while traveling through the sample material. In the case where the column is at ground potential, since the detector and the detector electronics can be set at ground potential, it may be feasible to perform detection using a semiconductor detector such as a pin diode.

[0048] Figure 2An enlarged cross-sectional view of the surrogate electrode 130 and the first detector 120 of a charged particle beam apparatus according to an embodiment described herein. Figure 3 The surrogate electrode 130 is shown in a schematic top view, and Figure 4a and Figure 4b the first detector 120 is shown in schematic top and bottom views.

[0049] As Figure 2 and Figure 3 shown, the surrogate electrode 130, which is the electrode closest to the sample stage, has an opening 131 that allows a primary charged particle beam 105 and signal particles to pass through. The opening 131 is sized to allow charged particles backscattered from the sample to pass through at an angle of 0° to 20° or more with respect to the optical axis 101. Specifically, the opening 131 can be a circular opening with a diameter D4 of 3 mm or more, specifically 4 mm or more, or even 6 mm or more. Thus, substantially all signal electrons carrying valuable information about the sample (including off-axis backscattered electrons and secondary electrons propagating substantially along the axis) can propagate through the same opening of the surrogate electrode. The off-axis backscattered electrons propagate towards the first detector 120 to be detected and / or the secondary electrons propagate towards an optional second detector to be detected. The first detector 120 for detecting off-axis backscattered electrons is arranged between the surrogate electrode and the objective lens.

[0050] The first detector 120 can be a lens-in detector having a detection surface 125 sized to detect off-axis backscattered electrons backscattered within an angular range between a first angle (α1) of 15° (or less) and a second angle (α2) of 30° (or more), specifically within an angular range between a first angle (α1) of 10° (or less) and a second angle (α2) of 35° (or more). The detection surface 125 can be substantially annular in shape.

[0051] In Figure 4bThe detection surface 125 is shown in more detail in FIG. 4, which shows the first detector 120 in a perspective view from below (i.e., from the sample side): the detection surface 125 can be annular and can extend around a hole 123 provided in the first detector (e.g., at the center of the detection surface 125). A primary charged particle beam and axial signal particles can propagate through the hole 123 in opposite directions. In some embodiments, the detection surface 125 can be segmented and can include a plurality of detection segments 126, specifically two or more detection segments, more specifically four or more detection segments. At least two detection segments can be provided for detecting signal particles within different angular ranges relative to the optical axis (such as a first angular range of 10° to 20° and a second angular range of 20° to 30°, where these values should be understood as examples). Specifically, as Figure 4b schematically depicted, detection segments can be provided to cover at least two different radial ranges relative to the optical axis 101. Alternatively or in addition, at least two detection segments can be provided for detecting different azimuthal ranges. For example, the first detection segment can have the shape of an annular section (e.g., a first annular section covering 180°), and the second detection segment can have the shape of another annular section (e.g., a second annular section covering the remaining 180°), as Figure 4b schematically depicted. In some embodiments, more than two annular portions can be provided, for example, segments for the top, bottom, left, and right, i.e., four annular sections each extending more than 90°. Each detector segment can detect a defined portion of the signal particles (e.g., polarity and / or azimuth) and thus generate a topographical contrast. The contrast is mainly caused by shadows on the descending side of the topographical features. By providing several detection segments covering different azimuthal ranges, the topographical contrast can be increased, and three-dimensional features can be inspected and / or imaged with improved accuracy and / or resolution. In Figure 4b the embodiment shown, four detection segments are provided for covering two different radial ranges and two different azimuthal ranges.

[0052] In some embodiments, the diameter of the aperture 123 of the first detector 120 can be 1.5 mm or greater, specifically 2 mm or greater. Alternatively or in addition, the diameter of the aperture 123 can be 10 mm or less, specifically 6 mm or less. Specifically, the diameter of the aperture 123 can be from 2 mm to 5 mm. A small diameter increases the detection efficiency of the first detector for backscattered charged particles, but may also increase the risk of instability, for example due to charging or contamination of the first detector. A large diameter reduces the detection efficiency of the backscattered particles, but also reduces the instability, for example because the primary charged particle beam can be guided through the aperture at a position at a certain distance from the edge of the aperture. Alternatively or in addition, the diameter of the detection surface 125 of the first detector 120 can be 12 mm or greater and / or 20 mm or less, specifically about 15 mm.

[0053] In some embodiments, the second distance D2 between the surrogate electrode 130 and the first detector 120 is 3 mm or greater and / or 6 mm or less, specifically 4 mm or greater and / or 5 mm or less. A small second distance D2 increases the risk of instability, such as the risk of arcing, but can provide a more compact retarding field device, thereby improving the achievable resolution. A large second distance facilitates the accommodation of the first detector and reduces the risk of instability, but may result in a compact device with reduced resolution.

[0054] In some embodiments, the third distance D3 between the sample and the first detector can be 3 mm or greater and / or 12 mm or less, specifically 4 mm or greater and 10 mm or less. The third distance D3 within the above range provides good achievable resolution and good topographical contrast.

[0055] In some embodiments that can be combined with other embodiments described herein, the first detector 120 is configured to act as an additional electrode 122 (provided in addition to the surrogate electrode 130), the additional electrode 122 being arranged between the objective lens and the surrogate electrode 130 and being configured to influence the primary charged particle beam and / or the signal particles. Specifically, the first detector 120 can be configured to be set at a predetermined potential U det thereon, so as to influence the primary charged particle beam propagating through the aperture of the first detector 120, and / or so as to influence the signal particles propagating through an opening 131. Herein, the surrogate electrode can also be referred to as the "lower electrode", and the first detector can also be referred to as the "upper electrode".

[0056] In some embodiments, the additional electrode 122 provided by the first detector 120 is configured to be set at a predetermined potential U via a corresponding voltage connection detAbove. Specifically, the additional electrode 122 may be configured to be set at a ground potential, which may correspond to the column potential of the charged particle beam device and / or may be different from the potential U of the surrogate electrode and / or different from the potential U of the sample. 代理 Different and / or from the potential U of the sample. 样品 Different.

[0057] Specifically, in some embodiments, the additional electrode 122 and / or the column may be set at a ground potential during operation of the device, and the surrogate electrode 130 and / or the sample 140 may be set at a high voltage potential, for example, between 3 keV and 35 keV. The voltage difference between the additional electrode 122 and the surrogate electrode 130 may decelerate a primary charged particle beam before it hits the sample and / or may accelerate signal particles through an opening of the surrogate electrode.

[0058] In some embodiments, the first detector 120 includes a conductive surface configured to be set at a predetermined potential U. det Above. For example, the first detector may include a housing or support (made of a conductive material) or may be at least partially coated with a conductive material such as metallization. The conductive surface may include at least one of a conductive inner surface 128 directed towards the optical axis 101 and a conductive top surface 129 directed towards the objective lens (i.e., directed in the upstream direction of the primary charged particle beam). The conductive surface of the first detector may be set at a ground potential, which may correspond to the column potential of the charged particle beam device. Thus, the first detector 120 or at least its conductive part (specifically used in combination with the surrogate electrode 130) may act as one of the electrodes of an electromagnetic electrostatic objective lens to decelerate the primary charged particle beam between the first detector 120 and the surrogate electrode and / or accelerate signal particles between the surrogate electrode and the first detector. For example, the surface, support, or housing of the first detector may be made of a conductive material or may include a conductive material, for example, via metallization, such that the first detector can be set at a predetermined potential U. det Above.

[0059] In some embodiments, a potential difference may be applied between the surrogate electrode 130 and the column of the charged particle beam device, such as to decelerate the primary charged particle beam before it hits the sample. The potential difference may be 3 keV or higher and / or 50 keV or lower, specifically 10 keV or higher and 35 keV or lower. In particular, the potential difference between the surrogate electrode 130 and the column of the charged particle beam device set at a predetermined potential U may be between 3 keV and 35 keV (see 柱 )). Figure 1 )).

[0060] When the first detector 120 serves as the additional electrode 122, the first detector 120 can be substantially set at the potential of the column. Specifically, the first detector 120 can be grounded. The potential difference between the surrogate electrode 130 and the first detector serving as the additional electrode can be 3 keV or higher and 35 keV or lower.

[0061] By using the first detector 120 as an electrode of the electromagnetic electrostatic objective lens device, another electrode can be saved and combined with the surrogate electrode to provide a more compact retarding field device. Specifically, the objective lens 110 can be a magnetic or electrostatic objective lens, and the combination of the objective lens 110 with the first detector 120 serving as the upper electrode and the surrogate electrode 130 serving as the lower electrode can provide an electromagnetic electrostatic retarding objective lens device. Specifically, since it may not be necessary to provide two electrodes in addition to the first detector in the range downstream of the objective lens 110, the objective lens can be arranged closer to the sample, thereby improving the achievable resolution. In addition, a defined deceleration path for the primary charged particle beam can be provided within the range between the first detector 120 and the surrogate electrode 130.

[0062] Combining the aspect of the surrogate electrode 130 having one opening as described herein with the aspect of the first detector 120 serving as the additional electrode as described herein is particularly beneficial. Due to the high detection efficiency and higher resolution brought by the compact retarding field device with the first detector as the electrode, three-dimensional features can be inspected with high precision and high contrast.

[0063] Even when the first detector 120 serving as the additional electrode 122 as described herein is beneficially combined with the surrogate electrode 130 having one opening 131 as described herein, the first detector 120 serving as the additional electrode 122 is described as an independent aspect herein. Specifically, the charged particle beam device described herein can include a first detector 120 for off-axis backscattered particles arranged between the surrogate electrode and the objective lens. The first detector is configured to serve as an additional electrode for influencing the primary charged particle beam and / or signal particles, and includes a conductive surface configured to be set at a predetermined potential U det thereon. The conductive surface can include at least one of a conductive inner surface directed towards the optical axis and a conductive top surface directed towards the objective lens. In some embodiments, the additional electrode 122 can be connected to the ground potential during the operation of the device. Specifically, the additional electrode 122 can be set at a predetermined potential corresponding to the column potential of the device.

[0064] In some embodiments, which can be combined with other embodiments described herein, the beam emitter 150 is adapted to emit a primary electron beam, and the charged particle beam apparatus includes electron beam optics for guiding the primary electron beam along the optical axis 101 to a sample for generating secondary electrons and backscattered electrons. The charged particle beam apparatus may further include a sample stage 50 for supporting the sample 140 to be inspected.

[0065] In particular, embodiments herein may relate to a scanning electron microscope having a charged particle beam apparatus as described herein. In such a charged particle beam apparatus, the beam emitter is an electron source configured to emit a primary electron beam, and the scanning electron microscope further includes a scanning deflector for scanning the primary electrons over the surface of the sample in a predetermined scanning pattern, the sample being supported on the sample stage.

[0066] According to yet another aspect of an independent aspect that can be applied to any of the embodiments described herein and is described herein as combinable with other features described herein, the charged particle beam apparatus includes a preamplifier 121 for amplifying the signal of the first detector 120. In some embodiments, the preamplifier 121 may be an electronic amplifier, specifically an operational amplifier. In some embodiments, the first detector 120 may be a solid-state detector or a semiconductor detector, specifically including a PIN diode. The first detector 120 may provide an electrical signal preamplified by the preamplifier. Then, the preamplified signal may be forwarded to a signal amplification module and / or a signal evaluation module, e.g., the signal amplification and evaluation module 160 schematically depicted in Figure 1 . The signal amplification module is optional and may further amplify the preamplified signal before evaluation. Alternatively or additionally, the preamplified signal may be directly evaluated.

[0067] In some embodiments, which can be combined with other embodiments described herein, an amplifier (also referred to herein as the "main amplifier 160") is provided for amplifying the preamplified signal provided by the preamplifier. The main amplifier may be arranged outside the vacuum enclosure of the charged particle beam apparatus, specifically in an atmospheric environment. Specifically, the preamplifier may be arranged in the vacuum enclosure of the charged particle beam apparatus, specifically in the column adjacent to the objective lens and / or adjacent to the first detector, and the pre-signal provided by the preamplifier is further amplified by the main amplifier arranged outside the vacuum.

[0068] If the first detector 120 is a multi-channel backscattered electron detector including a plurality of detection segments 126, the preamplifier 121 can be a multi-channel preamplifier and / or the main amplifier can be a multi-channel amplifier. For example, the first detector 120 includes four (or more) detection segments, and the preamplifier 121 includes a 4-channel (or >4-channel) amplifier for pre-amplifying the signals of the four detection segments.

[0069] In some embodiments that can be combined with other embodiments described herein, the preamplifier 120 is at least one of the following: integrated with the first detector 120, disposed adjacent to the first detector 120 in the vacuum enclosure of the charged particle beam apparatus (e.g., inside the vacuum enclosure provided by the column, such as mounted at or at the magnetic part of the objective lens), and fixedly mounted inside the vacuum enclosure of the charged particle beam apparatus (e.g., fixedly mounted inside the column, such as mounted at or at the magnetic part of the objective lens). More specifically, the first detector 120 can be connected to the preamplifier 121 inside the vacuum enclosure of the charged particle beam apparatus and can be fixedly mounted at a position that is also fixedly mounted close to the first detector. For example, the distance between the detection surface of the first detector and the preamplifier can be 3 cm or less. In some embodiments, the first detector and the preamplifier can be mounted, for example, at the objective lens, such as at the downstream end of the magnetic part of the objective lens.

[0070] In some embodiments, the first detector 120 includes a support 180, such as a plate or housing on which the preamplifier 121 is fixedly mounted. The support 180 of the first detector 180 can be disposed adjacent to the downstream end of the column of the charged particle beam apparatus, such as fixed at the objective lens 110. For example, the first detector 120 and the preamplifier 121 can be provided as an integrated detector module that includes a preamplifier integrated with the first detector on a common support 180 of the first detector 120 (as shown in FIG. 4) or even on a single chip. In some embodiments, a detector module is provided that includes a support that supports both the detector surface 125 and the preamplifier 121 at a close distance (e.g., 3 cm or less).

[0071] It is beneficial to arrange a preamplifier in the vicinity of the first detector, specifically inside the vacuum enclosure of the charged particle beam apparatus (e.g., inside the column), and / or to integrate the preamplifier with the first detector to provide an integrated detector module, because the detection speed and detection efficiency can be increased. Fixing the preamplifier at a position close to the first detector, such as mounting it on the support 180 or on the objective lens, can further increase the signal-to-noise ratio and improve the detection efficiency. For example, an increased signal strength can be achieved by arranging the preamplifier at a position close to the first detector. This can enable a very fast imaging speed at a high scan rate, such as 50 MHz or higher, or even up to 100 MHz.

[0072] The first detector 120 can provide a high collection efficiency, such as for electron energies as low as 1 keV, and / or can provide a low signal capacitance, such as as low as 3 pF. In some embodiments, the detector module including the first detector and the preamplifier can be compact, for example, the thickness in the optical axis direction can be 2 mm or less, specifically 1.5 mm or less.

[0073] As described herein, it is beneficial to combine the aspect of the surrogate electrode 130 having an opening 131 and the aspect of the preamplifier 121 integrally mounted with or arranged adjacent to the first detector 120. Combining these two aspects can increase the collection efficiency of off-axis backscattered particles because substantially all relevant signal particles can reach the first detector 121 and be directly and rapidly preamplified, thereby further increasing the collection efficiency and the signal-to-noise ratio. Additionally, the above two aspects are beneficially combined with a third aspect related to the use of the first detector 120 as another (upper) electrode in addition to the surrogate electrode 131 (lower electrode) as described herein. Using the first detector 120 as an additional electrode provides a more compact arrangement of the components downstream of the objective lens and thus further increases the collection efficiency. Therefore, combining the above three aspects provides a charged particle beam apparatus that enables the detection of low-noise signals of off-axis backscattered particles at a low range of energies and combines it with high-speed imaging. Thus, three-dimensional structures can be inspected quickly and reliably with high precision and good topographical contrast.

[0074] However, it should be noted that, as described herein, aspects of the preamplifier 121 for amplifying the signal of the first detector 120 can be applied to charged particle beam devices independently of the other two aspects. Accordingly, the embodiments described herein also relate to charged particle beam devices for imaging and / or inspecting a sample using the following features: a beam emitter 150 for emitting a primary charged particle beam; a charged particle beam device adapted to direct the primary charged particle beam along an optical axis to a sample for releasing signal particles; a blocking field device 100 for blocking the primary charged particle beam before it hits the sample, the blocking field device 100 including an objective lens 110 and a surrogate electrode 130, wherein the surrogate electrode includes an opening allowing the primary charged particle beam and signal particles to pass through; a first detector for off-axis backscattered particles between the surrogate electrode and the objective lens; and a preamplifier for amplifying the signal of the first detector.

[0075] The preamplifier 121 described herein is at least one of the following: (a) integrated with the first detector, (b) arranged adjacent to the first detector in a vacuum housing of the charged particle beam device (specifically arranged inside the column, e.g., mounted at the objective lens together with the first detector), and (c) fixedly mounted in a vacuum housing of the charged particle beam device (specifically, fixedly mounted at the objective lens together with the first detector or integrated with the objective lens, e.g., integrated with a magnetic part of the objective lens). The integration of the preamplifier with the first detector may include a support 180 of the first detector 120 on which the preamplifier is mounted (e.g., fixedly mounted). The support 180 may be a plate arranged at a downstream position of the objective lens, or the support may be mounted at a downstream end of the objective lens. The support may carry both the detection surface 125 of the first detector and the preamplifier. Alternatively, the integration may include a single chip carrying both the detection surface and the preamplification circuit.

[0076] In the arrangement of the preamplifier "adjacent to" the first detector, the distance between the detection surface and the preamplifier may be 5 cm or less, specifically 3 cm or less. Both the preamplifier and the first detector may be arranged in a vacuum housing of the charged particle beam device, e.g., arranged inside the column near its downstream end.

[0077] Fixing the preamplifier in a position close to the first detector can be understood as a substantially immovable positioning of the preamplifier in a position close to the first detector, and means a distinction from other solutions where the BSE detector can pivot or otherwise move towards and away from a detection position close to the sample in the sample chamber (i.e., outside the column).

[0078] In some embodiments, the first detector 120 is an in-lens detector having a hole that permits a primary charged particle beam to pass therethrough and having a detection surface that at least partially surrounds the hole. The first detector may include a support disposed between the objective lens and the surrogate electrode or mounted at or integrated with the objective lens, where the preamplifier may be mounted on the support, specifically fixedly mounted on the support. More specifically, the first detector may include a semiconductor detector having a detection surface, and the preamplifier may be disposed inside the vacuum enclosure of the charged particle beam apparatus at a distance of 3 cm or less from the detection surface. The first detector may include a plurality of detector segments, and the preamplifier may be a multi-channel preamplifier. Each detector segment may be associated with a respective amplification channel such that the signal of the detector segment may be amplified individually before evaluation.

[0079] As explained above, integrating the preamplifier with the first detector and / or fixedly mounting the preamplifier adjacent to the first detector at the support of the first detector significantly improves the collection efficiency and the detection speed.

[0080] Figure 5 A charged particle beam apparatus 10 is shown, such as an SEM imaging device, i.e., a wafer imaging system. The column 20 of the charged particle beam apparatus may provide a first chamber 21, a second chamber 22, and a third chamber 23. The first chamber (which may also be referred to as the gun chamber) includes a beam emitter 150 having a particle emitter 31 and a suppressor 32. The retarding field device 110 may be accommodated in the third chamber, and the surrogate electrode 130 may be provided at the front end of the column 20.

[0081] According to some embodiments described herein, the particle emitter 31 is connected to a power supply 331 for supplying a voltage to the particle emitter. In some examples described herein, the potential provided to the particle emitter is such that the primary charged particle beam is accelerated to an energy of 20 keV or higher. Thus, generally, the particle emitter is biased to a potential of -20 keV or higher negative voltage. As described above, it is a typical embodiment to make the particle emitter 31 at a negative potential, and its advantage is that the column and the beam duct may be grounded or at an intermediate potential.

[0082] A primary charged particle beam is generated by the beam emitter 150, for example, a primary electron beam. In Figure 5In the example, the beam is aligned with the beam-limiting aperture 450, and the size of the beam-limiting aperture 450 is set to shape the beam, i.e., block a portion of the beam. The beam can then pass through the beam separator 380, which separates the primary electron beam from secondary electrons (and, optionally, axially backscattered electrons). The primary electron beam is focused on the sample 140 by the objective lens. The sample can be positioned on the sample stage 50. For example, secondary or backscattered electrons are released from the sample 140 upon impact of the primary electron beam. The second detector 398 can detect secondary electrons and / or axially backscattered electrons and can be referred to herein as the second detector.

[0083] According to some embodiments that can be combined with other embodiments described herein, a condenser lens system 420 and a beam-forming or beam-limiting aperture 450 are provided. A two-stage deflection system 440 can be provided between the condenser lens system 420 and the beam-limiting aperture 450 for aligning the beam with the aperture.

[0084] As Figure 5 shown, the objective lens has a magnetic lens component having pole pieces 64 / 63 and a coil 62 that focuses the primary electron beam on the sample 140. Figure 5 The objective lens shown includes an upper pole piece 63, a lower pole piece 64, and a coil 62 that form the magnetic lens component of the objective lens. One or more electrodes can be provided for forming an electrostatic lens component of the objective lens. According to some embodiments described herein, the magnetic lens component and the electrostatic lens component substantially overlap each other to form a compound lens, also referred to herein as a "retarding field device", which further includes a surrogate electrode 130 disposed close to the sample.

[0085] In addition, a scanning deflector assembly 370 can be provided. The scanning deflector assembly 370 can be a magnetic scanning deflector assembly or an electrostatic scanning deflector assembly for high pixel rates. According to exemplary embodiments that can be combined with other embodiments described herein, the scanning deflector assembly 370 can be a single-stage assembly as Figure 5 shown. Alternatively, a two-stage or even a three-stage deflector assembly can be provided. Each stage can be disposed at a different position along the optical axis 101.

[0086] According to some embodiments, secondary and / or axial backscattered electrons are extracted from the sample and accelerated by a retarding field device. A beam separator 380 separates the primary electron beam from the signal electrons. The beam separator can be a Wien filter and / or can be at least one magnetic deflector such that the signal electrons are deflected away from the optical axis 101. The signal electrons can then be guided by a beam bender 392 (e.g., a hemispherical beam bender) and a lens system 394 to a second detector 398. Other elements such as a filter 396 can be provided. According to some embodiments, the second detector 398 can be a segmented detector for detecting signal electrons based on the starting angle at the sample.

[0087] According to the embodiments described herein, a surrogate electrode 130 is disposed in a position close to the sample. The surrogate electrode is arranged according to any one of the embodiments described herein, such that reference can be made to the above explanations and will not be repeated here.

[0088] Figure 5 The charged particle beam device shown further includes a first detector 120 for detecting off-axis backscattered particles (e.g., electrons) that have passed through an opening of the surrogate electrode 130. Depending on the intended application, the first detector 120 (e.g., a scintillator, a pin diode, or other electron-sensitive device) can have different shapes. For example, if only the total backscattered particle signal is of interest, an annular detector can be provided. According to some embodiments, for topographical contrast detection, a quadrant detector can be a possible choice. In some embodiments, different annular regions (which can be further segmented) can be used to detect specific portions of the angular backscattered particle distribution (such as angular segmentation and polarity segmentation). By detecting specific portions of the angular distribution of backscattered particles, depth information can be collected. Collecting depth information enables the collection of 3D information on the composition of the sample (particularly of structures with a high aspect ratio). By combining the detection of the angular distribution of backscattered particles with the varying landing energy of the primary charged particle beam, sample tomography can be achieved.

[0089] According to some embodiments, an adjustable energy supply can be provided for the primary charged beam. Generally, the energy of the primary charged particle beam is selected to be high enough such that backscattered particles from the interesting depth can penetrate the surrounding environment (such as the walls of the sample structure). On the other hand, the energy of the primary charged particle beam is selected such that it is not too high to avoid penetrating into deeper sample layers and reducing the signal-to-noise ratio with unwanted depth information.

[0090] The potentials of the emitter, column, and electrode can be provided in the system according to any one of the embodiments described herein. As a typical example, the beam duct (also referred to herein as the "column") can be at ground potential. Thus, electrons travel through the column at ground potential. The housing of the column can be set at ground potential. The housing at ground potential is in Figure 5is represented by reference numeral 3 in the figure.

[0091] Figure 6 FIG. 4 shows a flow chart of a method for inspecting and / or imaging a sample with a charged particle beam according to an embodiment described herein. The sample is inspected and / or imaged with a charged particle beam provided by a charged particle beam apparatus having a column, an optical axis, and a sample stage for supporting the sample during imaging and / or inspection as described herein.

[0092] The method includes, in block 510, emitting a primary charged particle beam. The beam can be emitted by a beam emitter, specifically by an electron source. The method includes, in block 520, guiding the primary charged particle beam in the column of the charged particle beam apparatus along the optical axis to the sample for generating signal particles, specifically including backscattered and secondary particles. Optical elements can be provided for guiding and / or shaping the primary charged particle beam from the beam emitter to the sample. Figure 5 FIG. 5 shows examples of optical elements, such as condenser lens systems, apertures, beam splitters, etc. Those skilled in the art will understand that the charged particle beam apparatus can include additional or alternative optical elements depending, for example, on the planned application or operating mode, the sample, the structure to be inspected and / or imaged, the energy of the primary charged particle beam, etc.

[0093] The method further includes, in block 530, focusing and retarding the primary charged particle beam with a retarding field device including an objective lens and a surrogate electrode disposed between the objective lens and the sample, wherein the surrogate electrode can include an opening that allows the primary charged particle beam and signal particles to pass through.

[0094] Retarding the primary charged particle beam can be performed within the above ranges, such as retarding the primary beam to a landing energy of about 10 keV or less (e.g., about 5 keV or less, e.g., 1 keV) on the sample. Generally, the retarding field device includes an electromagnetic electrostatic objective lens and a surrogate electrode between the electromagnetic electrostatic objective lens and the sample stage. The primary charged particle beam passes through an opening of the surrogate electrode. The opening of the surrogate electrode is sized to allow charged particles backscattered from the sample to pass through at an angle of 0° to 20° or greater relative to the optical axis.

[0095] The primary charged particle beam - after having passed through an opening of the surrogate electrode - impinges on the sample and causes signal particles (such as secondary particles and backscattered particles) to leave the sample, particularly in a direction away from the sample. The backscattered particles can include axial and small-angle backscattered particles and large-angle backscattered particles. Both axial backscattered particles and off-axis backscattered particles can propagate through an opening of the surrogate electrode, thus allowing the backscattered particles to pass through at an angle of 0° to 20° or greater relative to the optical axis.

[0096] The method further includes, at block 540, detecting off-axis backscattered particles using a first detector disposed between the surrogate electrode and the objective lens. Optionally, secondary particles released from the sample and propagating through the aperture of the first detector may be detected by a second detector. For example, the second detector may be disposed behind the objective lens in the direction of travel of the secondary particles. According to some embodiments, the first detector and / or the second detector may be the detector as described above.

[0097] In an embodiment, a preamplifier mounted adjacent to the first detector in the vacuum environment of the charged particle beam apparatus (specifically mounted in the vacuum enclosure provided by the column) may be used to preamplify the signal of the first detector. The preamplifier may be at least one of the following: (i) integrated with the first detector, for example, by being provided on a common support with the first detector, (ii) disposed inside the vacuum enclosure of the charged particle beam apparatus at a distance of 3 cm or less from the detection surface of the first detector, and (iii) fixedly mounted in the vacuum enclosure of the charged particle beam apparatus. In some embodiments, the first detector includes a support (such as a plate) extending between the objective lens and the sample or mounted at the objective lens, and the preamplifier is mounted on the support.

[0098] In some embodiments, the potential difference between the surrogate electrode and the column of the charged particle beam apparatus may be between 3 keV and 35 keV to decelerate the primary charged particle beam before it impinges on the sample. In particular, the first detector may act as an additional electrode that is substantially set at the potential of the column. In particular, both the column and the first detector may be substantially grounded. In some embodiments, the potential difference between the surrogate electrode and the additional electrode may be between 3 keV and 35 keV.

[0099] In some embodiments combinable with other embodiments described herein, a preamplifier mounted adjacent to the first detector in the vacuum environment of the charged particle beam apparatus (specifically mounted inside the column of the charged particle beam apparatus) may be used to amplify the signal of the first detector. The preamplified signal of the first detector may then be directed to a signal amplification and evaluation module, which may be disposed outside the vacuum enclosure of the charged particle beam apparatus. The signal amplification and evaluation module may evaluate the preamplified signal to obtain spatial information about the sample, specifically for inspecting and / or imaging the sample.

[0100] In some embodiments, during sample inspection, at least one or more of the following distances are provided: a first distance D1 between the sample and the surrogate electrode may be 200 μm or greater and 3 mm or less. A second distance D2 between the surrogate electrode and the first detector may be 3 mm or greater and 6 mm or less, specifically 4 mm or greater and 5 mm or less. A third distance D3 between the sample and the first detector may be 3 mm or greater and 10 mm or less, specifically 4 mm or greater and 9 mm or less.

[0101] Notwithstanding the foregoing with respect to the embodiments, other and further embodiments may be devised without departing from the basic scope, and the scope thereof is determined by the appended claims.

Claims

1. A charged particle beam device for imaging and / or inspecting a sample, comprising: a beam emitter for emitting a primary charged particle beam, the charged particle beam device being adapted to direct the primary charged particle beam along an optical axis towards the sample for releasing signal particles; a retardation field device for retarding the primary charged particle beam before it impinges on the sample, the retardation field device including an objective lens and a surrogate electrode, wherein the surrogate electrode includes an opening that allows the primary charged particle beam and the signal particles to pass through; a first detector for off-axis backscattered particles between the surrogate electrode and the objective lens; a preamplifier for amplifying the signal of the first detector, wherein the preamplifier is at least one of the following: (i) integrated with the first detector, (ii) arranged adjacent to the first detector inside the vacuum enclosure of the charged particle beam device, and (iii) fixedly mounted in the vacuum enclosure of the charged particle beam device; and an amplifier for amplifying the pre-amplified signal provided by the preamplifier, the amplifier being arranged outside the vacuum enclosure of the charged particle beam device.

2. The charged particle beam device according to claim 1, wherein the first detector is an in-lens detector having a hole that allows the primary charged particle beam to pass through and having a detection surface that at least partially surrounds the hole.

3. The charged particle beam device according to claim 1, wherein the first detector includes a support member arranged between the objective lens and the surrogate electrode or mounted at the objective lens, and the preamplifier is mounted on the support member.

4. The charged particle beam device according to any one of claims 1 to 3, wherein the first detector includes a semiconductor detector having a detection surface, and the preamplifier is arranged inside the vacuum enclosure of the charged particle beam device at a distance of 3 cm or less from the detection surface.

5. The charged particle beam device according to any one of claims 1 to 3, wherein the first detector includes a plurality of detector segments, and the preamplifier is a multi-channel preamplifier.

6. The charged particle beam device according to any one of claims 1 to 3, wherein the first detector has an annular detection surface sized to at least detect charged particles backscattered from the sample at an angle between 15° and 30° relative to the optical axis.

7. The charged particle beam device according to claim 6, wherein the annular detection surface is segmented and includes at least four detection segments.

8. The charged particle beam device according to any one of claims 1 to 3, wherein the surrogate electrode includes one opening that allows the primary charged particle beam and the signal particles to pass through, wherein the one opening is sized to allow charged particles backscattered from the sample to pass through at an angle of 0° to 20° or higher relative to the optical axis.

9. The charged particle beam device according to claim 8, wherein the one opening is sized to allow charged particles backscattered from the sample to pass through at an angle of 0° to 45° or higher with respect to the optical axis.

10. The charged particle beam device according to claim 8, wherein the one opening is a circular opening or a circular aperture that intersects the optical axis at the center and has an opening diameter of 2 mm or more and 6 mm or less.

11. The charged particle beam device according to any one of claims 1 to 3, wherein the first detector is configured to act as an additional electrode for influencing at least one of the primary charged particle beam and the signal particles, and the additional electrode is disposed between the objective lens and the surrogate electrode.

12. The charged particle beam device according to claim 11, wherein the first detector includes a conductive surface configured to be set at a predetermined electric potential.

13. The charged particle beam device according to claim 11, wherein the additional electrode provided by the first detector is configured to be set at a ground electric potential.

14. The charged particle beam device according to any one of claims 1 to 3, further comprising a second detector for secondary charged particles released from the sample, the second detector being disposed downstream of the objective lens in the traveling direction of the secondary charged particles.

15. A scanning electron microscope, comprising the charged particle beam device according to claim 1, wherein the beam emitter is an electron source configured to emit a primary electron beam, and the scanning electron microscope further comprises: a sample stage for supporting the sample; a scanning deflector for scanning the primary electron beam over the surface of the sample in a predetermined scanning pattern.

16. A method for imaging and / or inspecting a sample using a charged particle beam device, comprising: emitting a primary charged particle beam; guiding the primary charged particle beam along the optical axis to the sample for generating signal particles; focusing and retarding the primary charged particle beam using a retarding field device including an objective lens and a surrogate electrode disposed between the objective lens and the sample; detecting off-axis backscattered particles using a first detector disposed between the surrogate electrode and the objective lens; pre-amplifying the signal of the first detector using a pre-amplifier mounted in a vacuum environment adjacent to the first detector; and amplifying the pre-amplified signal from the pre-amplifier using an amplifier disposed outside the vacuum enclosure of the charged particle beam device.

17. The method according to claim 16, wherein the first detector includes a support disposed between the objective lens and the sample or mounted at the objective lens, and the pre-amplifier is mounted on the support.

18. The method according to claim 16 or 17, wherein the proxy electrode includes an opening that allows the primary charged particle beam and the signal particles to pass through, and wherein the opening is sized to allow charged particles backscattered from the sample to pass through at an angle of 0° to 20° or higher with respect to the optical axis.

19. The method according to claim 16 or 17, wherein the first detector acts as an additional electrode substantially at the potential of the column of the charged particle beam device.

Images