Axial alignment assembly and charged particle microscope comprising such an alignment assembly

Abstract

The present invention relates to an axial alignment assembly (100), comprising: a first body and a second body. The first body has a substantially cylindrical outer sheath and a first alignment axis. The second body comprises a substantially cylindrical inner sheath and has a second alignment axis. The second body is positioned relative to the first body so that the inner sheath faces the outer sheath and a substantially annular recess is formed between the inner sheath and the outer sheath. The axial alignment assembly further comprises a plurality of elastic elements located within the annular recess, wherein each elastic element is in contact with the outer sheath of the first body and the inner sheath of the second body. Each elastic element applies a force to the outer sheath and the inner sheath to align the first alignment axis and the second alignment axis.

Description

Technical Field

[0001] The present invention relates to an axial alignment assembly comprising a first body having a first axial alignment axis and a second body having a second axial alignment axis, and wherein the axial alignment assembly is arranged for substantially aligning the first and second axial alignment axes with each other.

[0002] The invention also relates to a charged particle microscope comprising such an axial alignment assembly. Background Art

[0003] Charged particle microscopy, particularly in the form of electron microscopy, is a well-known and increasingly important technique for imaging microscopic objects. Historically, the basic class of electron microscopes has evolved into many well-known device types, such as the transmission electron microscope (TEM), scanning electron microscope (SEM), and scanning transmission electron microscope (STEM), and has also evolved into various sub-species, such as the so-called "dual-beam" device (e.g., FIB-SEM), which additionally employs a "machining" focused ion beam (FIB), allowing for support activities such as, for example, ion beam milling or ion beam induced deposition (IBID). The skilled person will be familiar with the different types of charged particle microscopy.

[0004] In an SEM, irradiation of a sample with a scanning electron beam promotes the emission of "secondary" radiation from the sample in the form of secondary electrons, backscattered electrons, X-rays, and cathodoluminescence (infrared, visible, and / or ultraviolet photons). One or more components of this emitted radiation can be detected and used for sample analysis.

[0005] In a TEM, an electron beam is transmitted through a sample to form an image through the interaction of the electrons with the sample as the beam passes through it. The image is then magnified and focused onto an imaging device, such as a fluorescent screen, a photographic film layer, or a sensor, such as a scintillator connected to a charge-coupled device (CCD). The scintillator converts primary electrons in the microscope into photons, allowing the CCD to detect them.

[0006] Charged particle microscopes contain multiple modules that need to be precisely aligned with respect to a common axial alignment axis. This common axial alignment axis is usually the electron optical axis. Modules that require precise alignment include optical modules, such as electromagnetic lenses, and in particular the pole pieces of these electromagnetic lenses. The tolerances required for aligning the upper and lower pole pieces can be, for example, of the order of 1 μm. These tight tolerances are sometimes also required in other mechanical systems. Summary of the Invention

[0007] It is an object of the present disclosure to provide an axial alignment assembly which provides these required tolerances, or at least to improve existing axial alignment assemblies. In particular, it is an object of the present invention to provide an improved charged particle microscope by incorporating such an axial alignment assembly.

[0008] To this end, an axial alignment assembly as defined in claim 1 is provided.

[0009] The axial alignment assembly, as defined herein, comprises a first body comprising a substantially cylindrical outer jacket. The first body comprises a first alignment axis. The first alignment axis generally corresponds to the longitudinal axis of the cylinder defined by the cylindrical outer jacket. The first body may, for example, be an optical module of a charged particle microscope, such as a pole piece of an electromagnetic lens. The first body may comprise a hollow bore centered relative to the first alignment axis. Other embodiments of the first body are of course contemplated.

[0010] As defined herein, the axial alignment assembly includes a second body comprising a substantially cylindrical inner jacket. The second body comprises a second alignment axis. The second alignment axis generally corresponds to the longitudinal axis of a (virtual) cylinder defined by the cylindrical inner jacket. The second body is positioned relative to the first body such that the inner jacket of the first body faces the outer jacket of the second body. In other words, the first body is at least partially located within the cylindrical gap defined by the virtual cylinder. The size and dimensions of the first body and the size and dimensions of the cylindrical gap are such that an annular recess is formed between the inner jacket and the outer jacket. Thus, a substantially annular recess is formed between the inner jacket and the outer jacket. The recess may have a nominal width of at least tens of millimeters, or even tens of microns.

[0011] The axial alignment assembly as defined herein further comprises a plurality of elastic elements located within the annular recess. These elastic elements can, in principle, have any geometric shape, as long as at least one dimension of these elastic elements exceeds the nominal size of the annular recess. In a practical embodiment, the elastic elements are essentially spherical, wherein the diameter of the spherical elastic elements exceeds the nominal size of the annular recess, i.e. the distance between the inner and outer sheaths. As defined herein, each of the plurality of elastic elements is in contact with the outer sheath of the first body and the inner sheath of the second body. The elastic elements apply a force to the outer and inner sheaths, and due to this force, the first alignment axis and the second alignment axis are aligned, thereby aligning the first body with the second body.

[0012] The use of a spring element in the annular recess formed by the outer and inner cylindrical jackets ensures good centering, ie axial alignment, of the two bodies despite possible large dimensional and geometrical deviations in the two bodies and the spring element.

[0013] Note that an axial alignment assembly using plastic balls is known from the applicant's NL10257037C. In this disclosure, the two bodies to be aligned are provided with corresponding V-shaped annular grooves. The two bodies are positioned relative to one another so that the V-shaped annular grooves of the two bodies form a substantially rectangular annular groove with four abutment surfaces. By placing the plastic balls in the grooves and pressing the two bodies toward one another using, for example, a clamping force, the spherical balls come into contact with each of the four abutment surfaces of the annular grooves, ensuring axial alignment of the two bodies.

[0014] One of the drawbacks of this known axial alignment assembly is that the V-groove design requires the two bodies to be "pulled together." The two bodies need to be fixed to each other, and the plastic ball needs to be pressed onto the four abutting surfaces in order for the alignment assembly to work. The clamping force required to deform the ball is quite high. One option to reduce the clamping force is to use a "softer" ball, i.e., one that can be compressed more easily, but this has the negative side effect of also reducing the force used to align the two bodies.

[0015] In the axial alignment assembly defined herein, an outer sheath and an inner sheath are used to form an annular recess in which the elastic element is disposed. This offers advantages over the alignment assembly described in NL10257037C, as the axial alignment assembly according to the present invention does not require the presence of four abutment surfaces and does not require the use of an axial clamping force. Thus, an improved axial alignment assembly is provided that is further capable of providing a tolerance of approximately 1 μm. The objectives of the present invention are thus achieved.

[0016] Further advantageous embodiments will be described below.

[0017] In an embodiment, the elastic element comprises a substantially spherical element. The use of a spherical element alleviates the need to properly orient the elastic element, particularly given the substantially isotropic elastic properties of the spherical elastic element. Spherical elements can be produced with good dimensional tolerances. Furthermore, the use of a spherical element allows the elastic element to roll within the annular recess, resulting in minimal (low to zero) tangential residual forces on the elastic element, which aids in axial alignment.

[0018] In an embodiment, the size and number of the elastic elements are adapted to the diameter of the outer sheath of the first body. Preferably, the number of elastic elements is as high as possible, but the size of the elastic elements should not be too small, as this increases the tolerances required for all components (first body, second body, and elastic elements). The size of the elastic elements can be in the range of 1% to 10% of the radius of the first body, and preferably approximately 5%. This ratio ensures that approximately 125 elastic elements can fit around the outer cylindrical sheath of the first body. As an example, the first body can have a radius of approximately 100 mm, and a total of 120 spherical elastic elements have a diameter of approximately 4 mm. In this case, the ratio is (4 / 100 =) 4%.

[0019] In an embodiment, a helical spring is provided with windings constituting the elastic element.The helical spring may provide an easier way to assemble the axial alignment assembly as fewer parts need to be installed.

[0020] In an embodiment, the elastic element is made of a plastic material, such as polyoxymethylene. Alternatively, a rubber element can also be used.

[0021] In an embodiment, the first body has a first abutment surface, and the second body has a second abutment surface, which is connected to the first abutment surface in a connected state of the axial alignment assembly. The first abutment surface includes a normal that can be oriented substantially parallel to the first alignment axis. The second abutment surface includes a normal that can be oriented substantially parallel to the second alignment axis. The normal of the first body and the normal of the second body point in opposite directions.

[0022] In an embodiment, at least one of the first abutment surface and the second abutment surface comprises a surface orthogonal to a component parallel to the first alignment axis and / or the second alignment axis. The first abutment surface may be substantially orthogonal to the outer cylindrical jacket of the first body. The second abutment surface may be substantially orthogonal to the inner cylindrical jacket. Thus, at least one of the first abutment surface and the second abutment surface is positioned orthogonally to the outer jacket and / or the inner jacket.

[0023] In one embodiment, the axial alignment assembly includes a retainer for retaining a plurality of elastic elements. The retainer can be positioned in a recess formed between an outer cylindrical sheath and an inner cylindrical sheath. The retainer enables efficient manufacturing of the axial assembly because it allows the retainer to be prefabricated with the plurality of elastic elements. The retainer with the elastic elements can then be inserted between the first and second bodies. Alternatively, the retainer can be placed adjacent to the inner cylindrical sheath of the second body, and the first body can be positioned appropriately.

[0024] In an embodiment, the holder comprises a cage for surrounding the elastic element, in particular in a direction parallel to the alignment axis.

[0025] According to an aspect, there is provided a charged particle microscope comprising an axial alignment assembly as defined herein.

[0026] In an embodiment, the first body is a pole piece of a lens.

[0027] According to an aspect, a method of axially aligning a first body and a second body is provided, wherein the method comprises the following steps:

[0028] - providing a first body comprising a substantially cylindrical outer sheath and having a first alignment axis;

[0029] - providing a second body comprising a substantially cylindrical inner sheath and having a second alignment axis; and

[0030] - providing a plurality of elastic elements;

[0031] The method further comprises the following steps:

[0032] - positioning the second body relative to the first body such that the inner sheath faces the outer sheath and a substantially annular recess is formed between the inner and outer sheaths; and

[0033] - positioning the plurality of elastic elements in the annular recess such that each elastic element contacts the outer jacket of the first body and the inner jacket of the second body and applies a force to the outer jacket and the inner jacket to align the first alignment axis and the second alignment axis.

[0034] Note that the method steps as defined herein may be permuted in various ways. The above steps do not have to be performed in the order described. Positioning the first body, the second body, and the elastic element may include:

[0035] - first positioning the first body, then the second body, and finally the elastic element;

[0036] - first positioning the first body, then positioning the elastic element, and finally positioning the second body;

[0037] - first positioning the second body, then the first body, and finally the elastic element;

[0038] - first positioning the second body, then positioning the elastic element, and finally positioning the first body;

[0039] - first positioning the elastic element, then positioning the first body, and finally positioning the second body;

[0040] - first positioning the elastic element, then positioning the second body, and finally positioning the first body;

[0041] In an embodiment, the method comprises the steps of providing a holder for holding the plurality of elastic elements, and positioning the plurality of elastic elements in the holder. As previously mentioned, the step of providing the holder can be performed in a variety of ways. For example, the plurality of elastic elements may be positioned in the holder before the combination of the holder and the elastic elements contacts either the first body or the second body.

[0042] In an embodiment, the plurality of elastic elements first contacts one of the outer sheath and the inner sheath, and subsequently contacts the other of the outer sheath and the inner sheath.

[0043] In an embodiment, the method may comprise the step of moving the first body relative to the second body in a direction substantially parallel to the first alignment axis and the second alignment axis. BRIEF DESCRIPTION OF THE DRAWINGS

[0044] The invention will now be explained in more detail based on exemplary embodiments and the accompanying schematic drawings, in which:

[0045] Figure 1 - a longitudinal sectional view showing a charged particle microscope according to a first embodiment of the present invention;

[0046] Figure 2 - a longitudinal sectional view showing a charged particle microscope according to a second embodiment of the present invention;

[0047] Figure 3 is a longitudinal cross-sectional view through the first and second bodies of an axial assembly as defined herein;

[0048] Figure 4a - a longitudinal section through an axial assembly as defined herein;

[0049] Figure 4b-Figure 4a Close-up of the axial component;

[0050] Figure 5 - an embodiment of the axial assembly as defined herein;

[0051] Figure 6 - Another embodiment of an axial assembly as defined herein, in particular for use in a charged particle microscope. DETAILED DESCRIPTION

[0052] Figure 1(not to scale) is a highly schematic depiction of an embodiment of a charged particle microscope M according to an embodiment of the present invention. More specifically, it shows one embodiment of a transmission type microscope M, which in this case is a TEM / STEM (although, in the context of the present invention, it may effectively just be a SEM (see Figure 2 ), or for example ion-based microscopy). In Figure 1 In FIG, within a vacuum housing 2, an electron source 4 generates an electron beam B that propagates along an electron-optical axis B' and passes through an electron-optical illuminator 6 for directing / focusing the electrons onto a selected portion of a specimen S (which can, for example, be (locally) thinned / planarized). A deflector 8 is also depicted, which can be used (among other things) to achieve a scanning motion of the beam B.

[0053] The sample S is held on a sample holder H, which can be positioned with multiple degrees of freedom by a positioning device / stage A that moves a carrier A' to which the holder H is (removably) attached. For example, the sample holder H may include fingers that are movable (especially) in the XY plane (see the depicted Cartesian coordinate system; generally, movement parallel to Z and tilting about X / Y are also possible). This type of movement allows different parts of the sample S to be illuminated / imaged / inspected by an electron beam B traveling along an axis B' (in the Z direction) (and / or allows a scanning motion to be performed as an alternative to beam scanning). If desired, an optional cooling device (not depicted) can be brought into close thermal contact with the sample holder H, for example, to maintain it (and the sample S thereon) at a low temperature.

[0054] The electron beam B interacts with the sample S in such a way that various types of "stimulated" radiation are emitted from the sample S, including, for example, secondary electrons, backscattered electrons, X-rays, and optical radiation (cathodoluminescence). If desired, one or more of these radiation types can be detected by means of an analysis device 22, such as a combined scintillator / photomultiplier tube or an EDX or EDS (energy dispersive X-ray spectrometer) module; in this case, an image can be constructed using essentially the same principles as in an SEM. Alternatively or additionally, however, electrons that pass through the sample S, exit / emit therefrom, and continue to propagate along the axis B' (essentially, though typically with some deflection / scattering) can be studied. This transmitted electron flux enters an imaging system (projection lens) 24, which typically includes various electrostatic / magnetic lenses, deflectors, correctors (such as an anastigmator), etc. In normal (non-scanning) TEM mode, this imaging system 24 can focus the transmitted electron flux onto a phosphor screen 26, which can be retracted / withdrawn if necessary (as schematically indicated by arrow 26') so as to be away from axis B'. An image (or diffraction pattern) of (a portion of) sample S will be formed by imaging system 24 on screen 26, and this can be viewed through a viewing port 28 located in a suitable portion of the wall of housing 2. The mechanism for retracting screen 26 can, for example, be mechanical and / or electrical in nature and is not depicted here.

[0055] Instead of observing the image on the screen 26, one can instead take advantage of the fact that the depth of focus of the electron flux leaving the imaging system 24 is typically large (e.g., about 1 meter). Therefore, various other types of analysis devices can be used downstream of the screen 26, such as:

[0056] - TEM camera 30. At camera 30, the electron flux can form a static image (or diffraction pattern), which can be processed by controller / processor 20 and displayed on display device 14, such as a flat panel display. When not needed, camera 30 can be retracted / withdrawn (as schematically indicated by arrow 30') to move it away from axis B'.

[0057] - STEM camera 32. The output from camera 32 can be recorded as a function of the (X,Y) scan position of beam B on specimen S, and an image can be constructed that is a "map" of the output from camera 32 as a function of X,Y. Camera 32 may contain a single pixel of, for example, 20 mm in diameter, as opposed to the matrix of pixels characteristically present in camera 30. In addition, the acquisition rate of camera 32 (e.g., 10 pixels per second) may be greater than 10 pixels per second. 6 points) is usually faster than a camera 30 (e.g. 10 per second 2Again, when not needed, the camera 32 can be retracted / withdrawn (as schematically indicated by arrow 32') to move it away from the axis B' (although such retraction is not necessary in the case of, for example, a donut-shaped annular dark field camera 32; in such cameras, the central aperture will allow flux to pass when the camera is not in use).

[0058] As an alternative to imaging using cameras 30 or 32 , a spectroscopic device 34 can also be called upon, which can be, for example, an EELS module.

[0059] It should be noted that the order / position of the items 30 , 32 and 34 is not critical and many possible variations are conceivable. For example, the spectroscopic device 34 can also be integrated into the imaging system 24 .

[0060] In the illustrated embodiment, microscope M also includes a retractable X-ray computed tomography (CT) module, generally indicated by the reference numeral 40. In computed tomography (also known as tomographic imaging), a source and (diametrically opposed) detectors are used to observe a sample along different lines of sight in order to obtain penetrating views of the sample from a variety of angles.

[0061] Note that a controller (computer processor) 20 is connected to the various illustrated components via control lines (bus) 20'. This controller 20 can provide a variety of functions, such as synchronizing actions, providing set points, processing signals, performing calculations, and displaying messages / information on a display device (not depicted). It goes without saying that the (schematically depicted) controller 20 can be (partially) located inside or outside of the housing 2 and can have a unitary or composite structure as desired.

[0062] Those skilled in the art will appreciate that the interior of the housing 2 need not be maintained under a strict vacuum; for example, in so-called "ambient TEM / STEMs," a background atmosphere of a given gas is intentionally introduced / maintained within the housing 2. The skilled person will also appreciate that, in practice, it may be advantageous to limit the volume of the housing 2 so that it substantially surrounds the axis B', if possible, in the form of a small tube (e.g., of the order of 1 cm in diameter) through which the electron beam used passes, but widened to accommodate structures such as the source 4, sample holder H, screen 26, camera 30, camera 32, spectroscopic equipment 34, etc.

[0063] Now refer to Figure 2 , shows another embodiment of the device according to the present invention. Figure 2 (not to scale) is a highly schematic depiction of a charged particle microscope M according to the invention; more precisely, it shows an embodiment of a non-transmission type microscope M, which in this case is a SEM (although, in the context of the present invention, it may just be effectively an ion-based microscope, for example). Figure 1 Corresponding parts of the items in the are indicated by the same reference numerals and are not discussed separately here. Figure 1 Among them are (especially) the following components:

[0064] - 2a vacuum port, which can be opened to introduce / remove objects (components, specimens) into / from the interior of the vacuum chamber 2, or to which, for example, auxiliary equipment / modules can be mounted. If necessary, the microscope M can include a plurality of such ports 2a;

[0065] - 10a, 10b: schematic representations of lenses / optical elements in the illuminator 6;

[0066] - 12: voltage source, allowing, if necessary, the sample holder H or at least the sample S to be biased (floated) to a potential relative to ground;

[0067] - 14: Display, such as FPD or CRT;

[0068] 22a, 22b: Segmented electron detector 22a, comprising a plurality of independent detection segments (e.g., quadrants) arranged around a central aperture 22b (which allows beam B to pass). This type of detector can be used, for example, to study (the angular dependence of) the output (secondary or backscattered) flux of electrons emitted from the sample S.

[0069] Figure 1 and Figure 2 Several components of the charged particle microscope shown require axial alignment. However, in general, two or more components may require axial alignment. To this end, the present disclosure provides an axial alignment assembly.

[0070] Now turn Figure 3 , shows an assembly 100 of a first substantially cylindrical body 101 having a first axial alignment axis A1 and a second substantially cylindrical body 201 having a second axial alignment axis A2. Note that the first body 101 and the second body 201 do not necessarily have to be cylindrical. As defined herein, the first body 101 includes a substantially cylindrical outer sheath 103 and has a first alignment axis A1. As Figure 3 As shown, the first body 101 can have a central hole 104, although a substantially solid first body is also contemplated in accordance with the present disclosure. The second body 201, as defined herein, comprises a substantially cylindrical inner sheath 203 and has a second alignment axis A2. In the embodiment shown, the second body 201 has an annular protrusion 202 extending toward the second alignment axis A2. This annular protrusion 202 allows the first body 101 to rest on a protrusion of the second body 201, as will be described with respect to Figure 4b More detailed explanation. Figure 3It can be seen that the second body 201 is positioned relative to the first body 101 so that the inner sheath 203 faces the outer sheath 103. A substantially annular recess 401 is formed between the inner sheath 103 and the outer sheath 203. Figure 3 It can be seen that the first axis A1 is misaligned with respect to the second axis A2. The size of the annular recess is Figure 3 The right-hand side is smaller; and Figure 3 The left-hand side is slightly wider. The alignment of these two subjects posed a challenge.

[0071] Now turn Figure 4a As can be seen, by providing a plurality of elastic elements 301, 302 located within the annular recess 401, the first body 101 and the second body 201 can be aligned with respect to their alignment axes A1, A2. Each of the plurality of elastic elements 301, 302 is in contact with the outer jacket 103 of the first body 101 and the inner jacket 203 of the second body 201. The elastic elements 301, 302 and the first body 101 and the second body 201 are shaped such that each of the elastic elements 301, 302 applies a force to the outer jacket 103 and the inner jacket 203 for aligning the first alignment axis A1 and the second alignment axis A2.

[0072] It can be seen that in Figure 3 In the misaligned state shown, the annular recess 401 is smaller on the right-hand side of the figure. It is larger on the left-hand side of the figure. By arranging multiple elastic elements 301, 302 within the annular recess 401, wherein the elastic elements 301, 302 have substantially the same nominal dimensions, the elastic elements 302 located in the narrow portion of the recess 401 will be compressed to a greater extent than the elastic elements 301 located in the wider portion of the recess 401. Due to the greater compression, the elastic elements 302 in the narrow portion of the recess 401 exert a greater force on the cylindrical sheaths 103, 203 than the elastic elements 301 in the wider portion of the recess 401. The resulting force pushes the first body 101 away from the second body 201 in the direction toward the wider portion. Consequently, the narrow portion of the recess becomes wider, and the wider portion becomes narrower. This force balance will continue until the alignment axis A1 of the first body 101 is substantially aligned with the alignment axis A2 of the second body 201 and the alignment axes coincide with a single alignment axis A (e.g., Figure 4a shown).

[0073] Figure 4b Shown as Figure 4aDetail of the axial alignment assembly 100 shown in FIG. Here it can be seen that the first body 101 has a first abutment surface 105 and the second body 201 has a second abutment surface 205. The first abutment surface 105 and the second abutment surface 205 are generally parallel to each other. The first abutment surface 105 and the second abutment surface 205 are generally orthogonal with respect to the corresponding inner jacket 103 / outer jacket 203 of the first body 101 and the second body 201. Figure 4b As can be seen in FIG, the axial alignment assembly as defined herein does not require an axial compressive force to be applied on the first body 101 and the second body 201. The axial alignment force is determined by the dimensions of the outer sheath 103, the inner sheath 203 and the elastic element 301.

[0074] It should be noted that the axial alignment assembly 100 as defined herein is described with respect to a cylindrical body and an annular recess. It should be noted that other rotationally symmetric stages may be employed in place of a cylindrical body in the axial alignment assembly as defined herein. For example, triangles, squares, polygons, and other shapes are within the scope of the present disclosure and are considered equivalent to the cylindrical body described above. In such cases, a spherical elastic element may be used. Applicant reserves the right to file one or more divisional applications in relation to these aspects.

[0075] It is also noted that the embodiments disclose the use of spherical elastic elements. These are advantageous because they do not need to be aligned in a specific way for the elements to work. However, other shapes are also conceivable.

[0076] exist Figure 4b Note that the abutment surfaces 105 and 205 can be in direct contact. Alternatively, a sealing element (not shown) can be positioned between the first body 101 and the second body 201 such that the abutment surface 105 of the first body 101 contacts a first side of the sealing element, and the abutment surface 205 of the second body 201 contacts a second side of the sealing element. The sealing element can be relatively thin and can ensure a pressure-tight seal between the interior portion of the assembly (located closer to the central axis A) and the portion radially outward of the first body. In one embodiment, the sealing element can be made of rubber. In another embodiment, the sealing element can be made of metal. This is advantageous when it is desired that the interior portion of the axial alignment assembly (i.e., the space located closer to the central axis A) has a very low pressure (e.g., a (near) vacuum). Thus, a metal sealing element can provide a vacuum seal in an axial alignment assembly as defined herein. This is advantageous when used in a charged particle microscope, as will be explained later.

[0077] Now go to Figure 5 , an alternative embodiment of the axial alignment assembly 100 is shown. Note that corresponding reference numerals are used to identify corresponding elements. Figure 4aThe main difference of the axial alignment assembly shown is the use of a retainer 311 to hold the elastic elements 301, 302 in place. The retainer 311 can be prepared by adding the elastic elements 301, 302 to the retainer 311 before assembling the two bodies 101, 201. The retainer 311 can be a cage for holding the spherical elastic elements 301, 302. Other embodiments of the retainer 311 are also conceivable.

[0078] Figure 6 An embodiment of a portion of a charged particle microscope is shown which uses an assembly as defined herein to align a total of three bodies 1101, 1102, 201. Here, the most important alignment is considered to be that of the upper body 1101 and the lower body 1102. Figure 6 In the embodiment shown, the upper body 1101 and the lower body 1102 are respectively used for a charged particle microscope (e.g. Figure 1 or Figure 2 The axial alignment assembly 100 as defined herein provides an excellent way of aligning the upper objective pole 1101 and the lower objective pole 1102 of a TEM.

[0079] The required alignment of the upper and lower objective pole pieces is of the order of 1 μm, which can be achieved by Figure 6 Here, the upper body 1101 is axially aligned relative to the outer body 201 by using the spherical elastic element 301 in the upper annular recess; and the lower body 1102 is axially aligned relative to the outer body 201 by using the spherical elastic element 401 in the lower annular recess. This results in the upper body 1101 also being axially aligned with the lower body 1102. The elastic elements 301, 401 can be arranged in corresponding retainers 311, 411, such as retainers, as shown. Figure 6 shown.

[0080] Measurements performed on an axial alignment assembly as defined herein have shown that concentricity of a few microns can be achieved in a relatively easy manner.

[0081] As previously mentioned, an axial alignment assembly as defined herein can be used to provide an ultra-high vacuum (UHV) sample chamber. To achieve UHV, it is generally believed that metal seals are required and may require baking. Axial alignment assemblies known from the prior art require that two bodies be forced towards each other in order to be able to be axially aligned. The use of metal seals would significantly increase the axial compression force required to achieve the required axial alignment. In contrast, an axial alignment assembly as defined herein does not require the use of axial forces to achieve axial alignment and therefore allows the use of metal seals. Using an axial alignment assembly as defined herein, for example an axial alignment assembly having an array of balls in a cylindrical gap, will not hinder the compression of the metal seal between, for example, the pole pieces 1101, 1102 and the "inner objective block" 201. As a result, a UHV sample chamber for a charged particle microscope can be achieved.

[0082] Embodiments of the present invention have been described above. The protection desired is defined by the following claims.

Claims

1. An axial alignment assembly (100), comprising: - a first body (101) comprising a substantially cylindrical outer jacket (103) and having a first alignment axis (A1); a second body (201) comprising a substantially cylindrical inner jacket (203) and having a second alignment axis (A2), wherein the second body (201) is positioned relative to the first body (101) such that the inner jacket (203) faces the outer jacket (103) and a substantially annular recess (401) is formed between the inner and outer jackets; and - a plurality of elastic elements (301, 302) located in the annular recess (401), wherein each elastic element (301, 302) is in contact with the outer sheath (103) of the first body (101) and the inner sheath (203) of the second body (201), and applies a force to the outer sheath (103) and the inner sheath (203) to align the first alignment axis (A1) and the second alignment axis (A2).

2. The axial alignment assembly (100) of claim 1, wherein the elastic element (301, 302) has a nominal size that exceeds a nominal distance between the outer jacket (103) and the inner jacket (203).

3. The axial alignment assembly (100) of claim 1 or 2, wherein the elastic element (301, 302) comprises a substantially spherical element (301, 302).

4. The axial alignment assembly (100) according to claim 1 or 2, wherein the elastic element (301, 302) is composed of a plastic material.

5. The axial alignment assembly (100) of claim 1 or 2, wherein the first body has a first abutment surface (105), and wherein the second body has a second abutment surface (205) connected to the first abutment surface.

6. The axial alignment assembly (100) of claim 5, wherein at least one of the first abutment surface (105) and the second abutment surface (205) has a surface orthogonal to a component parallel to the first alignment axis (A1) and / or the second alignment axis (A2).

7. The axial alignment assembly (100) of claim 5, wherein at least one of the first abutment surface (105) and the second abutment surface (205) is positioned orthogonally relative to the outer jacket (103) and / or the inner jacket (203).

8. The axial alignment assembly (100) according to any one of claims 1-2 and 6-7, wherein the axial alignment assembly (100) comprises a holder (311) for holding the plurality of elastic elements (301, 302).

9. The axial alignment assembly (100) according to claim 8, wherein the holder (311) comprises a cage for surrounding the elastic element (301, 302), in particular in a direction parallel to the alignment axis (A, A1, A2).

10. A charged particle microscope comprising an axial alignment assembly (100) according to any one of the preceding claims.

11. The charged particle microscope according to claim 10, wherein the first body is a pole piece (1101, 1102).

12. A method of axially aligning a first body and a second body, wherein the method comprises the following steps: - providing a first body (101) comprising a substantially cylindrical outer jacket (103) and having a first alignment axis (A1); - providing a second body (201) comprising a substantially cylindrical inner jacket (203) and having a second alignment axis (A2); and - providing a plurality of elastic elements (301, 302); The method further comprises the following steps: - positioning the second body (201) relative to the first body (201) such that the inner sheath (203) faces the outer sheath (103) and a substantially annular recess (401) is formed between the inner sheath (203) and the outer sheath (103); and - positioning the plurality of elastic elements (301, 302) in the annular recess (401) such that each elastic element (301, 302) is in contact with the outer sheath (103) of the first body (101) and with the inner sheath (203) of the second body (201), and applies a force to the outer sheath (103) and the inner sheath (203) to align the first alignment axis (A1) and the second alignment axis (A2).

13. The method according to claim 12, comprising the steps of providing a holder (311) for holding the plurality of elastic elements (301, 302), and positioning the plurality of elastic elements (301, 302) in the holder (311).

14. The method according to claim 12 or 13, wherein the plurality of elastic elements (301, 302) first contact one of the outer jacket (103) and the inner jacket (203), and then contact the other of the outer jacket (103) and the inner jacket (203).

15. The method according to claim 14, comprising the step of moving the first body (101) relative to the second body (201) in a direction substantially parallel to the first alignment axis (A1) and the second alignment axis (A2).

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