Axial alignment assembly and charged particle microscope equipped with such an alignment assembly - Patents.com

Abstract

To provide an axial alignment assembly that can achieve required tolerances.SOLUTION: An axial alignment assembly 100 comprises: a first body 1101 comprising a cylindrical outer jacket and having a first alignment axis; and a second body 201 comprising a cylindrical inner jacket and having a second alignment axis, where the second body is positioned relative to the first body such that the inner jacket faces the outer jacket and such that an annular recess is formed between the inner jacket and the outer jacket. The axial alignment assembly further comprises a plurality of resilient elements 301 that are positioned within the annular recess, where each resilient element is in contact with the outer jacket of the first body and with the inner jacket of the second body and exerts a force on the outer jacket and on the inner jacket for aligning the first alignment axis and the second alignment axis.SELECTED DRAWING: Figure 6

Description

[Technical field]

[0001] overview 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, the axial alignment assembly being arranged to substantially align the first and second axial alignment axes with one another.

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

[0003] Charged particle microscopy is well known and has gained importance as a technique for imaging microscopic objects, especially in the form of electron microscopy. Historically, the basic type of electron microscope has evolved into several well-known instrument types, such as the Transmission Electron Microscope (TEM), the Scanning Electron Microscope (SEM), the Scanning Transmission Electron Microscope (STEM), and various subtypes, such as the so-called "dual beam" instruments (e.g., FIB-SEM) that employ a further "machining" Focused Ion Beam (FIB), allowing support, for example, of ion beam milling or Ion-Beam-Induced Deposition (IBID). Those skilled in the art will be familiar with the various types of charged particle microscopes. Those skilled in the art will be familiar with the different types of charged particle microscopy.

[0004] In an SEM, a scanning electron beam is directed at a sample, causing the sample to emit "auxiliary" radiation 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, a beam of electrons is passed through a sample to form an image from the interaction of the electrons with the sample as the beam passes through the sample. This image is magnified and focused onto an imaging device, such as a fluorescent screen, a layer of photographic film, or a sensor such as a scintillator attached to a charge-coupled device (CCD). The scintillator converts the primary electrons in the microscope into photons so that the CCD can detect them.

[0006] Charged particle microscopes comprise several modules that must be precisely aligned with respect to a common axial alignment axis. This common axial alignment axis is often the electron-optical axis. Modules that require precise alignment include optical modules such as electromagnetic lenses, and in particular the magnetic pole pieces of these electromagnetic lenses. For example, the tolerances required to align the top and bottom pole pieces can be on the order of 1 μm. These tight tolerances may also be required for other mechanical systems.

[0007] It is an object of the present disclosure to provide an axial alignment assembly that provides these required tolerances or at least improves upon existing axial alignment assemblies, and in particular to provide an improved charged particle microscope by incorporating such an axial alignment assembly.

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

[0009] As defined herein, an axial alignment assembly comprises a first body with a substantially cylindrical outer jacket. The first body comprises a first alignment axis. The first alignment axis generally corresponds to a longitudinal axis of a cylinder defined by said cylindrical outer jacket. The first body may be, for example, 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 centrally located with respect to the first alignment axis. Other embodiments of the first body are of course also contemplated.

[0010] As defined herein, an axial alignment assembly comprises a second body with a substantially cylindrical inner jacket. The second body comprises a second alignment axis. The second alignment axis corresponds generally to a 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 positioned at least partially in a 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 micrometers.

[0011] The axial alignment assembly as defined herein also comprises a plurality of elastic elements positioned in said annular recess. These elastic elements may in principle be of any shape, provided that at least one dimension of these elastic elements exceeds the nominal size of the annular recess. In a practical embodiment, the elastic elements are substantially spherical, the diameter of the spherical elastic element exceeding the nominal size of the annular recess, i.e. the distance between the inner jacket and the outer jacket. Each of the plurality of elastic elements as defined herein is in contact with the outer jacket of the first body and with the inner jacket of the second body. The elastic elements exert a force on the outer jacket and on the inner jacket, which aligns the first alignment axis with the second alignment axis, thus aligning the first body with the second body.

[0012] The use of an elastic element in the annular recess formed by the outer and inner cylindrical jackets ensures good centering, i.e. axial alignment, of the two bodies despite large dimensional and shape deviations that may occur in the two bodies and the elastic element.

[0013] It can be seen that an axial assembly using plastic balls is known from NL10257037C in the name of the applicant. In this disclosure, the two bodies that need to be aligned are provided with corresponding V-shaped annular grooves. The two bodies are oriented relative to each other such that the two V-shaped annular grooves from the substantially rectangular annular groove have four abutment surfaces. By providing plastic balls in the grooves and pressing the two bodies towards each other, for example using a clamping force, the spherical balls come into contact with each of the four abutment surfaces of the annular grooves and the axial alignment of the two bodies is ensured.

[0014] One drawback of this known axial alignment assembly is that the V-groove design requires the two bodies to be "pulled together." The alignment assembly can function by clamping the two bodies together and forcing the plastic balls against the four abutment surfaces. The clamping force to deform the balls is substantial. One option to reduce the clamping force is to use "softer" balls, i.e., balls that can be compressed more easily, but this has the negative side effect of reducing the force used to align the two bodies.

[0015] The axial alignment assembly defined herein utilizes an outer jacket and an inner jacket to form an annular recess in which an elastic element is provided. This is advantageous over the alignment assembly described in NL10257037C, since the axial alignment assembly according to the invention does not require the presence of four abutment surfaces and does not require the use of an axial clamping force. This provides an improved axial alignment assembly that can provide an additional tolerance of about 1 μm. This achieves the object of the present invention.

[0016] Advantageous embodiments will be further described below.

[0017] In an embodiment, the elastic element comprises a substantially spherical element. The use of a spherical element reduces the need to orient the elastic element in the right way, particularly if the spherical elastic element has a substantially isotropic elasticity. The spherical element can be produced with good dimensional tolerances. Furthermore, the use of a spherical element allows the elastic element to roll within the annular recess, leading to minimal (even zero) tangential residual forces on the elastic element that aid in axial alignment properties.

[0018] In an embodiment, the size and number of the elastic elements are adapted to the size of the outer jacket of the first body. It is preferable to have as many elastic elements as possible, but the size of the elastic elements should not be too small, as this would increase the necessary tolerances for all components (first body, second body and elastic elements). The size of the elastic elements may be in the range of 1% to 10%, preferably 5%, of the radius of the first body. This ratio ensures that about 125 elastic elements fit securely into the outer cylindrical jacket of the first body. As an example, the first body may comprise a total of 120 spherical elastic elements with a radius of about 100 mm and a radius of about 4 mm. In this case, the ratio is 4% (=4 / 100).

[0019] In some embodiments, a coil spring has turns that make up the resilient element, which can result in a simplified method of assembly for the axial alignment assembly as fewer parts need to be attached.

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

[0021] In an embodiment, the first body has a first abutment surface and the second body has a second abutment surface connected to the first abutment surface when connected to the axial alignment assembly. The first abutment surface has a normal that may be oriented substantially parallel to the first alignment axis. The second abutment surface has a normal that may be oriented substantially parallel to the second alignment axis. The normal of the first body and the normal of the second body are oriented in opposite directions.

[0022] In an embodiment, at least one of the first and second abutment surfaces comprises a surface normal that has a component parallel to the first and / or second alignment axes. 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 cylindrical inner jacket. Thus, at least one of the first and second abutment surfaces is positioned orthogonal to the outer and / or inner jacket.

[0023] In an embodiment, the axial alignment assembly comprises a holder for holding a plurality of elastic elements. The holder may be provided in a recess formed between the outer cylindrical jacket and the inner cylindrical jacket. The holder allows for a virtual manufacturing of the axial assembly, since it allows for prefabrication of the holder with the plurality of elastic elements. The holder with the elastic elements may then be inserted between the first body and the second body. Alternatively, the holder may be positioned next to the inner cylindrical jacket of the second body and the first body may be positioned in place.

[0024] In one embodiment, the holder is specifically aligned with respect to the alignment axis. parallel The elastic element includes a cage for containing the elastic element in a desired orientation.

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

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

[0027] According to one aspect, there is provided a method of axially aligning a first body and a second body, the method comprising: - providing a first body with a substantially cylindrical outer jacket and having a first alignment axis; - providing a second body with a substantially cylindrical inner jacket and having a second alignment axis; - providing a plurality of elastic elements,

[0028] - positioning the second body relative to the first body such that the inner jacket faces the outer jacket and such that a substantially annular recess is formed between the inner jacket and the outer jacket; - 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 exerts a force on the outer jacket and on the inner jacket to align the first alignment axis and the second alignment axis.

[0029] It is understood that the methods defined herein may be permuted in various ways. The steps above do not necessarily have to be performed in the order stated. The positioning of the first body, the second body, and the elastic element may be performed in any order, including the order of the first body, the second body, and the elastic element. - positioning first the first body, then the second body and finally the elastic element; - positioning first the first body, then the elastic element and finally the second body; - positioning first the second body, then the first body and finally the elastic element; positioning first the second body, then the elastic element, and finally the first body; - positioning first the elastic element, then the first body and finally the second body; - positioning first the elastic element, then the second body and finally the first body.

[0030] In an embodiment, the method includes 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 defined, the step of providing a holder can be performed in several ways. For example, the plurality of elastic elements are positioned in the holder before the combination of the holder and the elastic elements is brought into contact with either one of the first body or the second body.

[0031] In one embodiment, the plurality of elastic elements are brought into contact with one of the outer jacket and the inner jacket and then brought into contact with another of the outer jacket and the inner jacket.

[0032] In an embodiment, the method may include moving the first body relative to the second body in a direction primarily parallel to the first and second alignment axes.

[0033] The invention will now be elucidated in detail on the basis of exemplary embodiments and the accompanying schematic drawings. [Brief description of the drawings]

[0034] [Figure 1] 1 shows a longitudinal section of a charged particle microscope according to a first embodiment of the invention; [Diagram 2] 2 shows a longitudinal section of a charged particle microscope according to a second embodiment of the invention; [Diagram 3] 1 shows a longitudinal section through a first body and a second body of an axial assembly as defined herein; [Figure 4a] 1 shows a longitudinal section through an axial assembly as defined herein; [Figure 4b] 4b shows a close-up view of the axial assembly of FIG. 4a. [Diagram 5]1 illustrates an embodiment of an axial assembly as defined herein; [Figure 6] 1 illustrates a further embodiment of an axial assembly as defined herein, particularly for use with a charged particle microscope;

[0035] FIG. 1 (not to scale) is a highly schematic illustration of an embodiment of a charged particle microscope M according to an embodiment of the present invention. More specifically, the illustration shows an embodiment of a transmission microscope M, in this case a TEM / STEM (although in the context of the present invention it could just as well be, for example, a SEM (see FIG. 2) or an ion-based microscope). In FIG. 1, within a vacuum enclosure 2, an electron source 4 produces an electron beam B, which propagates along an electron optical axis B', crosses an electron optical emitter 6 and serves to direct / focus the electrons onto a selected portion of a sample S (which may for example be (locally) thinned / flattened). A deflector 8 is also illustrated, which can be used to (among other things) effect a scanning movement of the beam B.

[0036] The sample S is held in a sample holder H, which can be positioned in multiple degrees of freedom by a positioning device / stage A that moves a cradle in which the holder H is (removably) mounted; for example, the sample holder H can be equipped with fingers that can be moved in the XY plane (among other things) (see Cartesian coordinate system in the depiction, usually movements parallel to Z and tilts about X / Y are also possible). Such movements allow different parts of the sample S to be illuminated / imaged / inspected by an electron beam B moving (in Z direction) along an axis B' (and / or a scanning movement can be performed as an alternative to electron beam scanning). If desired, an optional cooling device (not depicted) can be brought in intimate thermal contact with the sample holder H, thereby maintaining the sample holder H (and the sample S thereon) at, for example, cryogenic temperatures.

[0037] The electron beam B interacts with the sample S in such a way as to cause it to emit various types of "stimulated" radiation, including (for example) secondary electrons, backscattered electrons, X-rays, and light radiation (cathodoluminescence). If desired, one or more of these types of radiation can be detected with the aid of an analysis device 22, which can be, for example, a combination of a scintillator / photomultiplier tube or an EDX or EDS (energy dispersive X-ray spectroscopy) module, and in such a case an image can be constructed using essentially the same principles as in an SEM. However, alternatively or supplementarily, the electrons that traverse (pass) the sample S, emerge / emit from the sample S, and continue to propagate (substantially, but generally, deflected / scattered to some extent) along the axis B' can be studied. Such a transmitted electron bundle enters an imaging system (projection lens) 24, which typically comprises various electrostatic / magnetic lenses, deflectors, collectors (stigmators, etc.), etc. In standard (non-scattering) TEM mode, this imaging system 24 can focus the electron flux onto a phosphor screen 26, which can be retracted / withdrawn, if desired, to bring it out of the path of axis B' (as indicated diagrammatically by arrow 26'). On the screen 26, an image (or diffractogram) of (a part of) the sample S is formed by the imaging system 24, which can be seen through a viewing port 28 located in a suitable part of the wall of the housing 2. The retraction mechanism for the screen 26 can be, for example, mechanical and / or electrical in nature and is not depicted here.

[0038] As an alternative to viewing an image on screen 26, one can instead take advantage of the fact that the focal depth of the electron flux leaving imaging system 24 is typically quite deep (e.g., about one meter). As a result, various other types of analytical devices (such as those listed below) can be used downstream of screen 26. -TEM camera 30. At the position of camera 30 the electron flux can form a still image (or diffractogram) which can be processed by controller / processor 20 and displayed on a display device 14, such as a flat panel display. When not required, camera 30 can be retracted / retracted (as shown diagrammatically by arrow 30') to move the camera off axis B'. - STEM camera 32. The output from camera 32 can be recorded as a function of the (X,Y) scanning position of beam B on sample 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 can include a single pixel, e.g., having a diameter of 20 mm, as opposed to the matrix of pixels typically present in camera 30. Furthermore, camera 32 can generally be a 10 mm wide STEM camera, e.g. 2 Much higher acquisition rates (e.g., 10 images / sec) 6 points / sec). Again, if not required, camera 32 may be retracted / pulled out (as indicated diagrammatically by arrow 32') out of the way of axis B' (such retraction may not be necessary, for example, in the case of a donut-shaped annular dark field camera 32, where a central hole may allow for bundle passage when the camera is not in use). As an alternative to imaging using the cameras 30 or 32, a spectroscopic device 34 can also be invoked, which can be, for example, an EELS module.

[0039] It should be noted that the order / position of components 30, 32, and 34 is not strict and many possible variations are possible. For example, spectroscopic device 34 could be integrated with imaging system 24.

[0040] In the illustrated embodiment, the microscope M further comprises a retractable X-ray Computed Tomography (CT) module, generally designated by the reference numeral 40. Computed tomography (also called tomographic imaging) uses electron sources and (diametrically opposed) detectors to interrogate a sample along different lines of sight to obtain an insightful view of the sample from different perspectives.

[0041] It should be noted that a controller (computer processor) 20 is connected to the various components shown via control lines (bus) 20'. This controller 20 may provide various functions such as synchronizing actions, providing set points, processing signals, performing calculations, and displaying messages / information on a display device (not shown). Of course, the controller 20 (schematically depicted) may be inside or outside the housing 2, and may be of unitary or composite construction, as desired.

[0042] Those skilled in the art will understand that the interior of the housing 2 does not have to be kept in strict vacuum conditions. For example, in so-called "environmental TEM / STEM", a background atmosphere of a given gas is deliberately introduced / maintained inside the housing 2. Those skilled in the art will also understand that in practice, it may be advantageous, if possible, to restrict the volume of the housing 2 so as to essentially embrace the axis B', taking the form of a small tube (e.g. of dimensions of the order of 1 cm), transparent to the employed electron beam, but extending outwards to accommodate structures such as the electron source 4, the sample holder H, the screen 26, the cameras 30, 32, the spectrometer 34, etc.

[0043] Referring now to Figure 2, another embodiment of the device according to the invention is shown. Figure 2 (not to scale) is a very schematic representation of a charged particle microscope M according to the invention, more specifically showing an embodiment of a non-transmission microscope M, in this case an SEM (although in the context of the invention, for example, an ion-based microscope may be equally useful). In the figure, parts corresponding to items in Figure 1 are indicated using the same reference numbers and are not described separately here. The following parts (among others) are added to Figure 1: -2a: vacuum port, which can be opened to introduce / remove items (components, samples) into / from the interior of the vacuum chamber 2 or in addition thereto, for example, auxiliary devices / modules can be attached. The microscope M can be equipped with multiple such ports 2a if desired. - 10a, 10b: Schematically depicted lenses / optical elements in the light emitter 6 -12: Optionally, a voltage source that allows the sample holder H or at least the sample S to be biased (floated) to a certain potential with respect to ground. -14: Display such as FPD or CRT. - 22a, 22b: (Segmented electron detector 22a, with a number of independent detection segments (e.g. quadrants) arranged around a central aperture 22b (allowing the passage of the beam B). Such a detector can be used, for example, to study the (angular dependence of) the flux of output (secondary or backscattered) electrons emerging from the sample S.

[0044] Several components of the charged particle microscope shown in Figures 1 and 2 need to be axially aligned. However, it may be typical to require that two or more components be axially aligned. For this reason, the present disclosure provides an axial alignment assembly.

[0045] Turning now to FIG. 3, there is shown 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. It will be appreciated that the first body 101 and the second body 201 are not necessarily cylindrical. As defined herein, the first body 101 comprises a substantially cylindrical outer jacket 103 and has a first alignment axis A1. The first body 101 may have a central bore 104, as shown in FIG. 3, although in the light of the present disclosure a substantially solid first body is also contemplated. The second body 201 as defined herein comprises a substantially cylindrical inner jacket 203 and has a second alignment axis A2. The second body 201 has an annular projection 202 extending towards the second alignment axis A2 in the illustrated embodiment. More specifically with respect to Fig. 4b, this annular projection 202 allows the first body 101 to seat on the projection of the second body 201. With further reference to Fig. 3, it can be seen that the second body 201 is positioned relative to the first body 101 such that the inner jacket 203 faces the outer jacket 103. A substantially annular recess 401 is formed between the inner jacket 103 and the outer jacket 203. It can be seen in Fig. 3 that the first axis A1 is not correctly aligned with the second axis A2. The dimensions of the annular recess are smaller on the right side of Fig. 3 and slightly wider on the left side of Fig. 3. The alignment of these two bodies poses a challenge.

[0046] Turning now to Figure 4a, it can be seen that the first body 101 and the second body 201 may be aligned with respect to their alignment axes A1, A2 by providing a plurality of elastic elements 301, 302 positioned within the annular recess 401. Each of the plurality of elastic elements 301, 302 contacts 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 exerts a force on the outer jacket 103 and on the inner jacket 203 so as to align the first alignment axis A1 and the second alignment axis A2.

[0047] In the misaligned state as shown in FIG. 3, it can be seen that the annular recess 401 is smaller on the right side of the figure. The annular recess 401 is larger on the left side of the figure. By providing multiple elastic elements 301, 302 in the annular recess 401, where the elastic elements 301, 302 have substantially the same nominal dimensions, the elastic elements 302 located in the narrower portion of the recess 401 are compressed to a greater extent than the elastic elements 301 located in the wider portion of the recess 401. The greater compression causes the elastic elements 302 in the narrower portion of the recess 401 to exert a greater force on the cylindrical jacket 103, 203 compared to 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 towards the wider portion. This causes the narrower portion of the recess to become wider and the wider portion to become narrower. This balance of forces continues 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 to form a single aligned axis A (as shown in FIG. 4a).

[0048] FIG. 4b shows a detail of the axial alignment assembly 100 as shown in FIG. 4a. 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 mainly parallel to each other. The first abutment surface 105 and the second abutment surface 205 are mainly perpendicular to the corresponding inner / outer jackets 103, 203 of the first and second bodies 101, 201. In FIG. 4b, it can be seen that the axial alignment assembly as defined herein does not require an axial compression force to be exerted on the first body 101 and the second body 201. The axial alignment force is established by the dimensioning of the outer jacket 103, the inner jacket 203 and the elastic element 301.

[0049] It is understood that the axial alignment assembly 100 as defined herein is described with respect to a cylindrical body and an annular recess. It is understood that instead of a cylindrical body, other rotationally symmetric orders may be applied to the axial alignment assembly as defined herein. For example, triangles, squares, polygons, and other shapes are considered within the scope of this disclosure and equivalent to the cylindrical body described above. In these examples, spherical elastic elements may be used. Applicant reserves the right to file one or more divisional applications in these respects.

[0050] It is further noted that the embodiments disclose the use of spherical elastic elements. These are advantageous because the elements do not need to be aligned in a particular way to work, although other shapes are contemplated.

[0051] In FIG. 4b it can be seen that the abutment surfaces 105, 205 can be in direct contact. Alternatively, a sealing element (not shown) can be provided 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 the other second side of the sealing element. The sealing element can be relatively thin and can ensure a pressure seal between the inner part of the assembly (located near the central axis A) and the part located radially outward of the first body. In an 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 inner part of the axial alignment assembly (i.e. the space located near the central axis A) has a very low pressure, such as (almost) a vacuum. This allows the metallic sealing element to provide a vacuum seal for the axial alignment assembly as defined herein. This is advantageously used for charged particle microscopes, as explained below.

[0052] Turning now to FIG. 5, an alternative embodiment of the axial alignment assembly 100 is shown. It can be seen that corresponding elements are identified using corresponding reference numerals. The main difference with respect to the axial alignment assembly as shown in FIG. 4a is the use of a holder 311 to hold the elastic elements 301, 302 in place. The holder 311 is prepared prior to the assembly of the two bodies 101, 201 by adding the elastic elements 301, 302 to the holder 311. The holder 311 can be a cargo for holding the spherical elastic elements 301, 302. Other embodiments of the holder 311 are also contemplated.

[0053] Figure 6 shows an embodiment of a part of a charged particle microscope using an assembly as defined herein to align all three bodies 1101, 1102, 201. Here, it is considered that the most important alignment is that of the upper body 1101 with the lower body 1102, which in the embodiment shown in Figure 6 are the upper and lower pole pieces 1102, respectively, of a lens for a charged particle microscope, such as the charged particle microscope as shown in Figure 1 or Figure 2. The axial alignment assembly 100 as defined herein provides an excellent way of aligning the upper and lower objective poles 1101, 1102 of a TEM.

[0054] The required alignment of the upper and lower objective poles is of the order of magnitude of 1 μm and can be achieved with an axial assembly as shown in Fig. 6. Here, the upper body 1101 is axially aligned to the outer body 201 by using a spherical elastic element 301 in the upper annular recess and the lower body 1102 is axially aligned to the outer body 201 by using a spherical elastic element 401 in the lower annular recess. This also results in the upper body 1101 being axially aligned to the lower body 1102. The elastic elements 301, 401 can be provided in respective holders 311, 411 such as cages as shown in Fig. 6.

[0055] Measurements on the axial alignment assembly defined herein can yield concentricity of a few microns relatively easily.

[0056] As mentioned before, the axial alignment assembly as defined herein can be used to provide an Ultra High Vacuum (UHV) sample chamber. It is generally accepted that metal seals and baking feasibility are necessary to achieve UHV. In the axial alignment assembly as known from the prior art, two bodies are required to exert a force on each other so that axial alignment is achieved. It is believed that the use of a metal seal would significantly increase the axial compression force required to obtain the desired axial alignment. In contrast, the axial alignment assembly as defined herein does not require the use of an axial force to obtain axial alignment, thereby allowing the use of a metal seal. For example, in the case of a ball array in a cylindrical gap, the use of the axial alignment assembly as defined herein would allow for unhindered compression of the metal seal between, for example, the pole pieces 1101, 1102 and the "inner object block" 201. In this case, a UHV sample chamber in a charged particle microscope can be obtained.

[0057] The above describes embodiments of the present invention. The desired protection is defined by the appended claims.

Claims

1. An axial alignment assembly (100), comprising: a first body (101) provided with a cylindrical outer jacket (103) and having a first alignment axis (A1); a second body (201) with a cylindrical inner jacket (203) and having a second alignment axis (A2), said inner jacket (203) facing said outer jacket (103) and positioned relative to said first body (101) such that an annular annular recess (401) is formed between said inner jacket and said outer jacket; a plurality of elastic elements (301, 302) positioned in said annular recess (401), each elastic element (301, 302) contacting said outer jacket (103) of said first body (101) and said inner jacket (203) of said second body (201) and exerting a force on said outer jacket (103) and said inner jacket (203) to align said first alignment axis (A1) and said second alignment axis (A2), the axial alignment assembly (100) comprises a holder (311, 411) for holding the plurality of elastic elements (301, 302); The holder (311) comprises a cage for containing the elastic elements (301, 302) in a direction parallel to the first alignment axis (A1) and the second alignment axis (A2) by restricting the movement of the elastic elements (301, 302) only in a direction parallel to the first alignment axis (A1) and the second alignment axis (A2), in an axial alignment assembly (100).

2. The axial alignment assembly (100) of claim 1, wherein the elastic elements (301, 302) have a nominal dimension 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 elements (301, 302) comprise spherical elements (301, 302).

4. The axial alignment assembly (100) according to any one of claims 1 to 3, wherein said elastic elements (301, 302) are made of a plastic material.

5. The axial alignment assembly (100) of any one of claims 1 to 4, wherein the first body has a first abutment surface (105) and the second body has a second abutment surface (205) connected to the first abutment surface.

6. 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 normal that has a component parallel to the first alignment axis (A1) and / or the second alignment axis (A2).

7. 7. The axial alignment assembly (100) of claim 5 or 6, wherein at least one of the first abutment surface (105) and the second abutment surface (205) is positioned orthogonally to the outer jacket (103) and / or the inner jacket (203).

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

9. The charged particle microscope of claim 8, wherein the first body is a magnetic pole piece (1101, 1102).

10. 1. A method of axially aligning a first body and a second body, comprising: - providing a first body (101) with a cylindrical outer jacket (103) and having a first alignment axis (A1); - providing a second body (201) with a cylindrical inner jacket (203) and having a second alignment axis (A2); - providing a plurality of elastic elements (301, 302), - positioning said second body (201) relative to said first body (201) in such a way that said inner jacket (203) faces said outer jacket (103) and an annular recess (401) is formed between said inner jacket (203) and said outer jacket (103); - positioning said plurality of elastic elements (301, 302) in said annular recess (401) such that each elastic element (301, 302) contacts said outer jacket (103) of said first body (101) and said inner jacket (203) of said second body (201) and exerts a force on said outer jacket (103) and said inner jacket (203) to align said first alignment axis (A1) and said second alignment axis (A2); providing a holder (311, 411) for holding the plurality of elastic elements (301, 302), the holder (311) comprising a cage for containing the elastic elements (301, 302) in a direction parallel to the first alignment axis (A1) and the second alignment axis (A2) by restricting movement of the elastic elements (301, 302) only in a direction parallel to the first alignment axis (A1) and the second alignment axis (A2).

11. The method of claim 10, comprising the steps of: providing a holder (311) for holding said plurality of elastic elements (301, 302); and positioning said plurality of elastic elements (301, 302) in said holder (311).

12. 12. The method according to claim 10 or 11, wherein the plurality of elastic elements (301, 302) are first brought into contact with one of the outer jacket (103) and the inner jacket (203) and thereafter into contact with another of the outer jacket (103) and the inner jacket (203).

13. 13. The method of claim 12, comprising moving the first body (101) relative to the second body (201) in a direction primarily parallel to the first alignment axis (A1) and the second alignment axis (A2).

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