WO2009015615A1

WO2009015615A1 - A device providing a live three-dimensional image of a speciment

Info

Publication number: WO2009015615A1
Application number: PCT/CZ2008/000050
Authority: WO
Inventors: Martin Zadrazil; Josef Rysávka; Tomás Smíd; Vojtech Filip
Original assignee: Tescan, S.R.O.
Priority date: 2007-07-30
Filing date: 2008-04-28
Publication date: 2009-02-05
Also published as: GB0922723D0; DE202008018179U1; WO2009015615A8; CZ298798B6; GB2464010A; CZ2007510A3; DE112008002044T5

Abstract

The beam of particles from the primary source is led to the secondary source (1) and a tilting and simultaneously scanning unit (2) placed above the objective (3) is inserted to the path of the output beam of particles with an axis (5). The tilting and scanning unit (2), seen in the direction from the viewed specimen (4) upwards, consists of a bottom stage (2.2) and a top stage (2.1). The top stage (2.1) and the bottom stage (2.2) consist of at least two tilting and scanning elements (6, 7) arranged to create fields orthogonal to each other in the area where the beam of particles with the axis (5) passes through them. Both the output of the first adjustable source (6.1) of a direct tilting signal and the first adjustable source (6.2) of an alternating scanning signal are connected to the first tilting and scanning element (6). Both the output of the second adjustable source (7.1) of a direct tilting signal and the second adjustable source (7.2) of an alternating scanning signal are connected to the second tilting and scanning element (7).

Description

A device providing a live three-dimensional image of a specimen

Field of the Invention

The presented invention deals with a device providing a live three- dimensional, i.e. 3D, image, suitable in particular, when manipulating small objects.

Description of the Related Art

In order to create a three-dimensional image, a pair of images must be obtained, using different viewing angles. One image is used for the right eye and the other for the left eye. Various methods were designed to obtain such pairs of images for microscopes with particle beams. Less common methods include the tilting of the whole microscope column against the plane of the specimen, which is difficult to implement, or the placing of several detectors, with off-set angles, above the specimen, which increases the costs and limits the space in the specimen chamber. More commonly used, is the simple tilting of the specimen holder, which is relatively slow and, in addition, brings along difficulties with mechanical inaccuracies, or the tilting of the axis of the beam of particles, which appears to be the most convenient solution for scanning microscopes.

In the latter option, the specimen is at first scanned by a beam with its axis tilted to one side from the axis of orthogonal fall onto the specimen and then by a beam with the axis tilted to the opposite side, thus allowing it to obtain the two necessary images. The beam axis may be tilted electrostatically (e.g. US 6,930,308) or - more commonly - electromagnetically (e.g. US 6,963,067). The standard configuration of a microscope is usually complemented with a set of tilting coils for electromagnetic tilting. The right and left images are subsequently viewed, using special devices, creating a three-dimensional image of a specimen. These may include, for instance, stereoscopic glasses for the viewing of the right and left images, while each is projected on one half of the screen (US 3,986,027), or LCD glasses synchronized with a television screen, etc. Some of the common imaging methods, however, do not allow for viewing by more persons simultaneously.

The obtaining of two initial images of the specimen corresponding to the two beams scanning the specimen under two different angles is nevertheless connected with multiple issues, especially when high magnification and/or resolution are applied. Such issues are related to the shifted incidence point when scanned with a right and left tilt, with depth of focus, lenses aberrations, insufficient accuracy of setting the tilt of a beam, etc. Existing methods of 3D viewing are only able to solve such issues at the cost of time-demanding procedures.

The mentioned time intensity makes the implementation of the so-far known methods of 3D viewing impossible for certain applications, for example, the manipulation of small objects where one needs to obtain the image of the specimen being manipulated and the image of manipulating device live in real time, which means at the moment when the manipulation takes place.

Summary of the Invention

The invention described herein aims to remove the disadvantages mentioned above and to allow a live 3D viewing and manipulation with a specimen.

In order to reach the above-mentioned aim, a device containing a basic instrument was designed, which may be e.g. an electron or field-ion microscope, emitting a beam of particles from the primary source. This beam passes through the microscope column equipped with a particle optics assembly and impinges on the viewed specimen. The principle of this device is that the beam of particles from the primary source is directed to the secondary source and that the beam of particles coming out from the secondary source must pass through a tilting and simultaneously scanning unit placed above the objective in the lower part of the column. This tilting and scanning unit, seen in the direction from the viewed specimen upwards, consists of a bottom and a top stage, and each of these stages consists of at least two tilting and scanning elements, arranged to create fields orthogonal to each other. The output from the first adjustable source of a direct tilting signal and the output from the first variable source of an alternating scanning signal are connected to the first tilting and scanning element. The output from the second adjustable source of a direct tilting signal and the output from the second adjustable source of an alternating scanning signal are connected to the second tilting and scanning element.

In one possible embodiment, the tilting elements are formed by scanning coils. The outputs from the first adjustable source of a direct tilting signal and the first adjustable source of an alternating scanning signal are connected to the first coil, while both these sources are connected in parallel. The outputs from the second adjustable source of a direct tilting signal and the second adjustable source of an alternating scanning signal are connected to the input of the second coil, while both these sources are connected in parallel. All sources mentioned above are current sources.

In another possible embodiment, the tilting elements are formed by scanning electrodes. Each stage contains two pairs of scanning electrodes. The first pair of scanning electrodes is connected in parallel to the serial connection of the first adjustable source of a direct tilting signal and the first adjustable source of an alternating scanning signal. Analogically, the second pair of scanning electrodes is connected in parallel to the serial connection of the second adjustable source of a direct tilting signal and the second adjustable source of an alternating scanning signal. In this case, all these sources are voltage sources. In another advantageous embodiment, it is possible to place an additional intermediate lens with an adjustable focal distance between the top stage of the tilting and scanning unit and the last condenser lens of the particle optics assembly, to correct the spherical aberration of the objective and to increase the depth of focus.

A secondary source of particles may be created in various ways. One of the options is that a real source is used. Such real source is mostly the closest crossover point created by an optical system of the basic instrument above the top stage of the tilting and scanning unit where the output from such crossover point is a beam of particles divergent in the direction towards the specimen. Another option is that the source of particles is a virtual source formed by a crossover point created by the intermediate lens below the bottom stage of the tilting and scanning unit. The output from such a crossover point is a beam of particles convergent in the direction towards the specimen. Yet another option is that the source of particles is a source placed at infinity, which is formed by the intermediate lens and the output of which is a parallel beam of particles.

In all embodiments of the invention, the whole specimen is at first scanned by a beam with the axis tilted to the orthogonal axis of incidence at the angle of +Φ. By using a suitable device for the detection of secondary particles emitted from the specimen, the image of the specimen "from the left" is obtained. In the next step, the same repeats with a beam with the axis tilted in the opposite direction, mostly - but not necessarily - symmetrically with an angle of -Φ. Thus an image of the specimen "from the right" is obtained.

Devices for the detection of secondary particles may include, for instance, detectors of SE₁ BSE, X-ray radiation, cathodoluminescence, etc.

Multiple methods may be selected for processing and viewing the two obtained images, which are fully compatible with the presented invention. These methods may include various combinations of common or special monitors and special glasses. For example, one may mention using special monitors in combination with LCD glasses with synchronized shutter, anaglyph viewed by glasses with chromatic filters, etc.

The device is suitable for three-dimensional viewing and three- dimensional measuring of surfaces and for use when manipulating small objects, while the resulting image is viewed live as an anaglyph. The device allows one to obtain at least four 3D images per second, which is fully satisfactory for applications such as nanomanipulation. The selected viewing method, in addition, enables multiple persons to observe the results simultaneously without additional costs.

Brief Description of the Drawings

The device, according to the presented invention, will further be described by means of drawings. Fig. 1 schematically shows the basic embodiment of the device; variable sources of tilting and scanning signals are not shown. Fig. 2 schematically shows the shape of non-tilted and tilted beams of particles. The specific connection of sources for individual tilting and scanning elements is shown in Fig. 3 and 4. Fig. 5 shows the embodiment with scanning coils as tilting and scanning elements in a horizontal section. Fig. 6 schematically shows the shape of non-tilted and tilted beams of particles when the intermediate lens is used.

Detailed Description of the Preferred Embodiments

The presented solution may be applied in connection with any instrument with a corpuscular beam. To maintain better orientation, the text below will describe a device based on a scanning electron microscope. Components not directly related to the principle of the presented invention, i.e. parts such as cathode, anode, condenser lenses, apertures, detectors, etc., are not shown in the drawings to maintain better transparency.

Fig. 1 schematically shows a basic model device in a vertical section. The primary source of the beam of particles is not shown in the drawing to maintain better transparency, only the secondary source 1 is shown, to which the beam of particles from the primary source is directed and comes out of it as the output beam of particles with axis 5. Tilting and simultaneously scanning unit 2 is inserted to the path of this output beam of particles with axis 5 and located above the objective 3. Tilting and scanning unit 2, seen in the direction from the viewed specimen 4 upwards, consists of bottom stage 2,2 and top stage 2J..

Top stage 2Λ_ and bottom stage 22 in general consist of at least two tilting and scanning elements, marked 6 and 7 in the next drawings of the specific invention embodiments, arranged to create fields orthogonal to each other. Possible connections and the horizontal section of one model embodiment of these tilting and scanning elements will be shown in Fig. 3, 4 and 5.

Tilting and scanning elements 6 and 7 may be formed by scanning coils or scanning electrodes. The appropriate connection of sources will also be applied, depending on which of these are used, see also Fig. 3 and 4 below. Also, the secondary source of particles 1 may be created in various ways. In the example shown in Fig. 1 secondary source 1 is represented by a crossover point placed below the last condenser lens, not shown, and simultaneously above the top stage 2J_. and the bottom stage Z2 of the tilting and scanning unit 2 and above the objective 3.

Fig. 1 simultaneously, in addition, shows the principle of tilting the axis 5 of the beam of particles to the directions +Φ and -Φ from the orthogonal incidence, which ensures that the tilted beams impinge on the same point 8 on specimen 4 as the non-tilted beam. To maintain better orientation, the drawing shows only axis 5 of the non-tilted beam of particles, orthogonal to the surface of the specimen 4, and axes 5J_. and 52 of the first and second tilted beams of particles. A solid line shows a situation when no offset is applied on the tilting and scanning elements. In this case the orthogonally impinging beam with axis 5 coming out from the secondary source 1 is focused by the objective 3 to point 8 on specimen 4. By setting a suitable offset on the tilting and scanning elements in the first stage 2J_. and in the second stage 2.2, the axis 5 of the beam of particles may successively be tilted to the directions represented here by the first and second axis 5J. and 52 of the first and the second tilted beams of particles, dash-and-dot line. The directions of the first and second axis 5J. and 52. of the first and the second tilted beams of particles are drawn as mirror symmetric to the plane passing through the optical axis of the device, which however, is not necessary for the invention function. After being focused by the objective 3, the first and the second tilted beams of particles with axes 5J_. and 5,2 respectively in this case impinge on the surface of specimen 4 with the angles of -Φ and +Φ respectively_! in an orthogonal line to the surface of specimen 4. Incidence point 8 on the surface of specimen 4 is identical to the orthogonal incidence and remains the same for the first and second beams of particles with axes 5.1 and 5.2 respectively.

Fig. 2, for better transparency, shows the general shape of non-tilted as well as tilted beams of the particles in one model embodiment of the presented invention. To keep the drawing clear, only the tilt to the direction +Φ is shown. Solid lines again describe the non-tilted beam of particles with axis 5; dash-and- dot lines describe the second tilted beam of particles with axis 5_2, which hits specimen 4 under an angle of +Φ. It is apparent that after tilting, the beam has the same shape as if it came out of the secondary source 1, its axis, however, having passed the objective 3, is no longer orthogonal to specimen 4.

In one model embodiment of the presented invention, tilting the and simultaneously scanning elements 6 and 7 are created using coils in both stages 2.1 and 2.2 of the tilting and scanning unit 2. Fig. 3 shows how sources are connected to these coils. The outputs of two sources mutually connected in parallel (i.e. the outputs of the first adjustable source 6J. of a direct tilting signal and of the first adjustable source 6^ of an alternating scanning signal) are connected to the input of the first coil forming first tilting and scanning element 6. The outputs of two other sources mutually connected in parallel (i.e. the second adjustable source 7J_. of a direct tilting signal and the second adjustable source 72. of an alternating scanning signal) are connected to the input of the second coil forming second tilting and scanning element 7, while all mentioned sources are current sources.

In another model embodiment of the presented invention, the tilting and simultaneously scanning elements 6 and 7 are created using electrodes, in both stages 2J_. and Z2 of the tilting and scanning unit 2. Fig. 4 shows how the sources are connected to these electrodes. According to the given example, each stage 2J. and Z2 contains two pairs of scanning electrodes, the first pair of scanning electrodes 6Λ and 6J3, and the second pair 7\A and 7J3. The first pair of scanning electrodes 6Λ, 6J3 is connected in parallel to the serial connection of the first adjustable source 6J. of a direct tilting signal and the first adjustable source 62. of an alternating scanning signal, and the second pair of scanning electrodes 7Λ, 7^ is connected in parallel to the serial connection of the second adjustable source 7Λ_ of a direct tilting signal and the second adjustable source 7^2 of an alternating scanning signal, while all these sources are voltage sources.

Tilting and scanning elements 6 and 7 located above the objective 3 in the bottom part of the column are therefore designed in such a way that, simultaneously with dynamic scanning, they also allow the static tilting of the beam of particles with axis 5 to the right and left direction. This tilt to the right or left is ideally - but not necessarily - mirror symmetric to the plane passing through the optical axis of the device. The static excitation of tilting and scanning elements 6 and 7 is calibrated and it therefore allows one to select the tilt angle. The specimen 4 is at first scanned by a beam with the axis tilted to one side and then by a beam tilted to the other side. By using a suitable device for the detection of secondary particles emitted from the specimen 4^ the left and right images of specimen 4 are obtained. Within the frame of the presented invention, various methods for the processing and viewing of the two obtained images may be selected. In one model embodiment of the presented invention, the processed signal from the detection device is connected to a viewing device, such as a television screen. The viewing device captures transitorily shifted signals corresponding to the left and right beam. These are mutually visually separated. This model embodiment of the presented invention involves chromatic separation: one image is red, the other is blue-green, so-called anaglyph. The operator watches the screen via special glasses with red filter on one eye and blue-green filter on the other eye.

In the event when tilting and scanning elements 6 and 7 are formed by coils, one specific example of the embodiment of such coils in the horizontal section is schematically shown in Fig. 5. It shows the horizontal section through the top stage 2J., while the bottom stage 22 is arranged similarly. The only difference is the number of windings in the scanning coils. Each stage contains two coils forming first tilting and scanning element 6 and second tilting and scanning element 7, both having their windings divided into four segments 61.62.63.64 and 71.72.73.74. which create magnetic fields orthogonal to each other, which is ensured by different directions of winding of individual segments and their location. In the given example, the angles between the pairs of segments with the respective order of the first and the second scanning coils are 30° and the angles between pairs of segments belonging to the same coil are 60° or 120° respectively, see Fig. 5. Segments 6_1, 62 are wound in the opposite direction than segments 63 and 64, and likewise segments 71, 74 are wound in the opposite direction than segments 72 and 73. In the top stage Zl₁ each of the segments has 8 windings, in the bottom stage TJλ_± each of the segments has 15 windings. In both cases the coils are made of copper wire 0.4 mm in diameter, wound on common ferrite core. The height of the ferrite core is 10 mm, the inner diameter of the circle formed by the core is 16 mm, the outer diameter of the circle formed by the core is 24.8 mm. The centers of the tilting and scanning coils in the top stage 2J. are distanced approximately 52 mm from the centers of the tilting and scanning coils in the bottom stage 22, the center of the bottom coils is approximately 35 mm above the objective 3. In both cases, the ferrite core is rotationally symmetric around the optical axis. The crossover point created by the last condenser lens above the tilting and scanning unit 2 is, in this model embodiment, placed approximately 180 mm above the objective 3. Naturally, this is only one of many possible examples of the embodiment of the presented invention.

As shown in Fig. 1 and Fig. 2, the proper function of the invention with specific configuration of the device requires determining the ratio of tilting signals offsets in the top stage 2J_. and in the bottom stage 22, which will ensure that the image will not shift when the beam is tilted. The most accurate results are achieved by the following experimental procedure: The beam of particles with axis 5, which enters the tilting and scanning unit 2, is tilted in the top stage 2Λ_ with the relative offset value of -1. In the bottom stage 2Jl_x the offset changes with a reverse sign until the image is restored to the original place, and the relative offset value, required to return the image to the original place, is read out. In this way, the tilting of original axis 5 of the beam of particles, e.g. to direction 5,2 is achieved, but the point S_x onto which the beam is focused on specimen 4, will remain the same compared to the situation when the offset was zero. The offset ratio ascertained using the described procedure, is subsequently input in the software and the user should no longer modify it. This offset ratio value ensures that the tilted beam has an identical shape as if it came out from the secondary source 1, but its axis, after passing through the objective 3, is no longer orthogonal to the surface of specimen 4. The tilted beam is nonetheless focused onto the same point where a non-tilted beam would be focused, see Fig. 1 and 2. The user has the option to change the absolute offset value continuously, which is in proportion to the tilt angle. This manner therefore also allows one to alter the tilt angle continuously.

In order to allow selecting the beam tilt angles directly, the tilting offset is calibrated. The calibration was made by using a specimen with a stepped rectangular profile. Experimental findings reveal that the ratio of the tilting current offset on the scanning coils at the top stage 2J. to the tilting current offset on the scanning coils at the bottom stage Z2 must be approximately (-1):(0.4) for the configuration of the tilting and scanning unit 2, which uses coils and is shown in Fig. 5 and described in closer detail in the text related to this Figure.

Fig. 6 shows the shape of the non-tilted and tilted beams of particles when an intermediate lens 9 is used above the tilting and scanning unit 2 in one model embodiment of the invention. The intermediate lens 9 is specifically placed between the top stage Zi of the tilting and scanning unit 2 and the last condenser lens of the particle optics assembly. In the situation shown in Fig. 6, the intermediate lens 9 creates a parallel beam of particles directed to the specimen 4. It means that in this case the secondary source of particles 1 is placed at an infinite distance. The non-tilted beam of particles with axis 5 is shown by solid lines, the tilted beam of particles with axis 5J3 is shown by dash- and-dot lines. In this case the shape of the tilted beam is different from the previous examples, therefore, a new index number was assigned to its axis. For better orientation, only a tilt to one side is shown. The tilted beam with axis fx3 hits the specimen 4 under an angle of Φ1. The using of the intermediate lens is advantageous for applications that require a greater depth of focus. Such intermediate lens 9 is used to correct the spherical aberration of the objective 3. The parallel beam, which enters the objective 3,. after it has passed through the intermediate lens 9^ is in fact much thinner than the divergent beam, which would enter the objective 3 without this intermediate lens 9. The dynamic change of excitation of the objective 3^ when the intermediate lens 9 is used, therefore allows one to achieve even for tilted beams, a sharp image.

The correction of the excitation current of the objective 3 for tilted beams, for instance a beam with axis 5,3, is governed by the following formula: 1/l²=1/l o²+C_s Φ² N²/KV, where I is a current through the objective 3 when the beam of particles with axis 5 is tilted by an angle of Φ, I₀ is a current through the objective 3 when the beam of particles is not tilted, with Φ=0, C₈ is a spherical aberration factor (m), Φ is the tilt angle of the beam (rad), N is the number of windings of coil in objective 3, V is the energy of the beam (eV) and K is a dimensionless constant characterizing given objective.

In another embodiment of the presented invention, the intermediate lens

9 may also create a beam of particles convergent in the direction to the specimen 4. The crossover point formed by the intermediate lens 9 is in this case located below the tilting and scanning unit 2 and creates a virtual, secondary source of particles 1

In all embodiments of the presented invention, the user shall at first select the beam tilt angle Φ. Subsequently, the whole of specimen 4 is dynamically scanned by the beam with the axis tilted from the orthogonal axis by an angle of +Φ. In the next step, the same repeats with a beam with the axis tilted in the opposite direction, typically with an angle of -Φ. Good results of three-dimensional imaging may already be obtained from the tilt angles close to 0.5°, spherical aberration may successfully be corrected up to the tilt angle of approximately 15°.

Industrial Applicability

The invention may be applied in the sphere of scanning electron microscopes and field-ion microscopes for live, three-dimensional viewing. Inter alia, it also allows for so-called nanomanipulation, i.e. live manipulation of small objects under the microscope. The invention may also be exploited for various three-dimensional measurements of the viewed surfaces.

Claims

W h a t i s c l a i m e d i s :

1. The device providing a three-dimensional, live image of a specimen consisting of a basic instrument creating the primary source of a beam of particles, which passes through the microscope column equipped with a particle optics assembly and the objective and impinges on the viewed specimen, characterized by the fact that the beam of particles from the primary source is led to secondary source (1) and that to the path of the output beam of particles with axis (5), a tilting and simultaneously scanning unit (2) placed above the objective (3) is inserted, which, seen in the direction from the viewed specimen (4) upwards, consists of a bottom stage (2.2) and a top stage (2.1), while the top stage (2.1) and the bottom stage (2.2) consist of at least two tilting and scanning elements (6, 7) arranged to create fields orthogonal to each other in the area where the beam of particles with axis (5) passes through them, and where both the output of the first variable source (6.1 ) of a direct tilting signal and the output of the first variable source (6.2) of an alternating scanning signal are connected to the first tilting and scanning element

(6), and both the output of the second variable source (7.1 ) of a direct tilting signal and the output of the second variable source (7.2) of an alternating scanning signal are connected to the second tilting and scanning element (7). 2. The device, according to claim 1 , characterized by the fact that the tilting and scanning elements (6, 7) are created using scanning coils, where the outputs of the first adjustable source (6.1 ) of a direct tilting signal and of the first adjustable source (6.2) of an alternating scanning signal are connected to the input of the first coil, the sources (6.1) and (6.2) being connected in parallel, and where the outputs of the second adjustable source (7.1 ) of a direct tilting signal and of the second adjustable source (7.2) of an alternating scanning signal are connected to the input of the second coil, the sources (7.1) and (7.2) being connected in parallel, while all these sources (6.1 , 6.2, 7.1 , 7.

2) are current sources.

3. The device, according to claim 1 characterized by the fact that the tilting and scanning elements (6, 7) are created using scanning electrodes, where each of the stages (2.1 , 2.2) contains two pairs of scanning electrodes (6.A₁ 6.B) and (7.A, 7.B), where the first pair of scanning electrodes (6.A, 6.B) is connected in parallel to the serial connection of the first adjustable source (6.1 ) of a direct tilting signal and of the first adjustable source (6.2) of an alternating scanning signal, and the second pair of scanning electrodes (7.A, 7.B) is connected in parallel to the serial connection of the second adjustable source (7.1 ) of a direct tilting signal and of the second adjustable source (7.2) of an alternating scanning signal, while all these sources are voltage sources.

4. The device, according to any of claims 1 to 3 characterized by the fact that the secondary source (1 ) is the closest crossover point created by the optical system of the basic instrument above the top stage (2.1) of the tilting and scanning unit (2), where the output of such a crossover point is a beam of particles (5) divergent in the direction towards the specimen (4).

5. The device, according to any of claims 1 to 3 characterized by the fact that between the top stage (2.1 ) of the tilting and scanning unit (2) and the last condenser lens of particle optics assembly, an intermediate lens (9) with an adjustable focal distance is located, designed to correct the spherical aberration of the objective (3) and to increase the depth of focus.

6. The device, according to claim 5 characterized by the fact that the secondary source of particles (1) is a source placed at infinity, which is formed by the intermediate lens (9) and the output of which is a parallel beam of particles with axis (5).

7. The device, according to claim 5, wherein the secondary source of particles (1 ) is a virtual source placed below the bottom stage (2.2), which is created by a crossover point formed by an intermediate lens (9) of the tilting and scanning unit (2), where the output of such a crossover point is a beam of particles with the axis (5), convergent in the direction towards the specimen (4).

8. The device, according to any of claims 1 to 7, which is suitable for three- dimensional imaging and three-dimensional measuring of surfaces and for using when manipulating small objects, while the resulting image is viewed live as an anaglyph.