WO2021040609A1

WO2021040609A1 - Electrostatic lens for controlling beam of electrons

Info

Publication number: WO2021040609A1
Application number: PCT/SE2020/050824
Authority: WO
Inventors: Mikael OLOFSSON
Original assignee: Scienta Omicron Ab
Priority date: 2019-08-30
Filing date: 2020-08-27
Publication date: 2021-03-04
Also published as: EP4022669A1; EP4022669A4; CN114303229A

Abstract

An arrangement (100) is described which comprises an electrostatic lens (7) comprising an optical axis (6), a first electrostatic lens element (1), a second electrostatic lens element (2), and a deflector arrangement comprising a deflector package (5) with a plurality of electrodes (15) being arranged circumferentially around the optical axis (6) between the first end (26) of the first electrostatic lens element (1) and the second end (29) of the second electrostatic lens element (2), and arranged to deflect the beam of electrons, in at least a first coordinate direction (x, y) perpendicular to the optical axis (6). The deflector package (5) is arranged such that, during operation of the electrostatic lens (7), an electron, travelling from the first electrostatic lens (1) element to the second electrostatic lens element (2), first passes through the electric field between the first electrostatic lens element (1) and the deflector package (5), and subsequently passes through the electric field between the deflector package (5) and the second electrostatic lens element (2).

Description

ELECTROSTATIC LENS FOR CONTROLLING BEAM OF

ELECTRONS

TECHNICAL FIELD

The present invention relates to an arrangement comprising an electrostatic lens for controlling a beam of electrons. In particular the present invention relates to an arrangement comprising an electrostatic lens for use in a photo-electron spectrometer of hemispherical deflector type.

BACKGROUND ART

WO 2013/133739 describes an analyser arrangement for an electron spectrometer. The analyser arrangement is arranged to form an electron beam of electrons emitted from an electron emitting sample and transporting the electrons between said electron emitting sample and an entrance slit of a measurement region by means of a lens system having a substantially straight optical axis. The lens system is arranged to deflect the electron beam in at least a first coordinate direction at least a first time and a second time. By deflecting the electron beam at least two times it is possible to operate the lens system in an angle-resolved mode, such that it deflects the electron beam such that a predetermined part of the angular distribution of the electrons passes the entrance slit of the measurement region in a direction being substantially parallel to the optical axis of the lens system. The main embodiment described in WO 2013/133739 comprises a first deflector package and a second deflector package. A rudimentary explanation of the function of said lens system is as follows. The first deflector package is controlled to deflect the desired predetermined angular distribution of the electrons towards the optical axis of the lens system. The second deflector package is controlled to deflect the desired angular distribution of the electrons at the optical axis to give the electrons a direction along the optical axis of the lens system.

An advantage of the lens system described in WO 2013/133739 is that a specific angular distribution of the electrons emitted from the electron emitting sample may be controlled to enter the entrance slit of the measurement region in a direction being substantially parallel to the optical axis of the lens system without the need for tilting the electron emitting sample. SUMMARY OF THE INVENTION

An objective of the present invention is to provide an arrangement comprising an electrostatic lens for controlling a beam of electrons for entrance into an electron spectrometer, which arrangement is an alternative to the lens system described in the prior art.

Another objective of the present invention is to provide an arrangement comprising an electrostatic lens for controlling a beam of electrons, which arrangement has only one deflector arrangement with a deflector package comprising a plurality of electrodes, while still allowing electrons entering through the first opening with the same direction in relation to the optical axis to be focused to the same point at the position of the second opening along the optical axis.

Another objective of the present invention is to provide an arrangement comprising an electrostatic lens for controlling a beam of electrons, which arrangement with as few optical elements as possible enables control of electrons such that a specific angular distribution of electrons emitted from an electron emitting sample leaves the arrangement in a controllable angle and such that the electron beam from the arrangement is suitable for entering into an electron spectrometer.

At least one of these objectives is fulfilled with an aperture device, an analyser arrangement, or a method according to the independent claims.

Further advantages are achieved by means of the features of the dependent claims.

An arrangement according to the invention is configured to be used with an electron spectrometer and comprises an electrostatic lens having an interior volume, a first opening for entrance of electrons into the interior volume, a second opening for exit of electrons from the interior volume, and a substantially straight optical axis, extending from the first opening to the second openingthrough the interiorvolume. The electrostatic lens is configured to form a beam of electrons entering through the first opening and to transport the beam of electrons to the second opening. The electrostatic lens also comprises a first electrostatic lens element with a first end facing the first opening and a second end facing away from the first opening, a second electrostatic lens element with a first end facing the first electrostatic lens element and a second end facing the second opening, and a deflector arrangement comprising a deflector package with a plurality of electrodes being arranged circumferentially around the optical axis between the first end of the first electrostatic lens element and the second end of the second electrostatic lens element, and arranged to deflect the beam of electrons, in at least a first coordinate direction perpendicular to the optical axis. The arrangement is characterised in that the deflector package is arranged such that, during operation of the electrostatic lens, an electron, travelling from the first electrostatic lens element to the second electrostatic lens element, first passes through the electric field between the first electrostatic lens element and the deflector package, and subsequently passes through the electric field between the deflector package and the second electrostatic lens element, and wherein the electrodes are electrically separated from each other and from the first and second electrostatic lens elements. The arrangement is controllable such that the beam of electrons that exit through the second opening is directed along the optical axis of the electrostatic lens.

During operation of the electrostatic lens, voltages are applied to the lens elements and to the electrodes of the deflector package. The arrangement is controllable by controlling the voltages to the different lens elements and the voltages to the different electrodes of the deflector package.

When the beam of electrons is directed along the optical axis of the electrostatic lens it is suitable for entering into the electron spectrometer. Thus, when it is possible to control the electrostatic lens in such a way, no direction changes are necessary after the second opening. In other words, all direction changes necessary for making the electron beam suitable for entering the electron spectrometer are made before the second opening.

According to this application an electrode is considered to be a separate electrode only if it is electrically separated from the other electrodes. Thus if two electrodes are electrically connected and thus always on the same potential they are considered to be part of the same electrode.

With electrically separated is meant that the electrodes/lens elements may be set at different voltages independently of each other. By the electrodes being electrically separated from each other and from the first and second electrostatic lens elements it is possible to apply different voltages to the first and second electrostatic lens elements and to the different electrodes. The different voltages applied to the electrodes results in a centre voltage. Electrons that pass through the first electrostatic lens element, the deflector package and the second electrostatic lens element will thus experience firstly an electric field between the first electrostatic lens element and the deflector package, and secondly and subsequently an electric field between the deflector package and the second electrostatic lens element. These two different electric fields together with the different applied voltages applied on the electrodes results in effectively two deflections of the electrons. Thus, the arrangement according to the invention provides operational degrees of freedom with regard to the deflection of the electrons and enables tuneable control of efficiently two deflections in the coordinate direction perpendicular to the optical axis.

An arrangement according to the invention may be controlled such that a specific angular distribution of the electrons emitted from the electron emitting sample may be controlled to exit through the second opening in a controllable angle.

The angle of the electrons that exit through the second opening is preferably controlled to be parallel to the optical axis in one of the coordinate directions perpendicular to the optical axis. This means that the electrons which exit through the second opening may be controlled to enter the entrance slit of a measurement region in a direction being substantially parallel to the optical axis of the lens system.

The arrangement is controlled with voltages being applied to the electrostatic lens elements and the electrodes.

The first electrostatic lens element may be arranged adjacent to the second electrostatic lens element with a gap between the first electrostatic lens element and the second electrostatic lens element. The deflector package may span at least part of the gap between the first electrostatic lens element and the second electrostatic lens element. In principle, there is always a gap between the first electrostatic lens element and the second electrostatic lens element. However, if the gap is sufficiently large there is a risk that exterior electric field penetrate the gap and effects the electrons. In order for electrons passing through the electrostatic lens not to be effected by such electric fields the deflector package spans at least a part of the gap.

The deflector package may comprise at least 2 electrodes, preferably at least 4 electrodes and most preferred at least 8 electrodes, arranged around the optical axis, wherein n is an integer. Thus, the minimum number of electrodes is 2. This allows the electrons to be deflected two times.

The deflector package may comprises at least 4 electrodes arranged in a formation of essentially rotational symmetry, wherein the electrodes of the deflector package serves as deflectors in at least two coordinate directions. By having at least 4 electrodes it is possible to negate spherical deformation.

The electrodes in the deflector package may be arranged at a minimum electrode separation distance from the optical axis. Preferably, all electrodes are arranged at the same distance from the optical axis. If the electrodes are not arranged at the same distance from the optical axis the electrode being closest defines the minimum electrode separation distance.

The length of the deflector package may be at least 50 %, preferably at least 100 % and most preferred at least 150 % of the minimum electrode separation distance from the optical axis in the deflector package. This is favourable to enable two deflections with reasonable voltages on the electrodes and the first and second electrostatic lens elements.

The distance parallel to the optical axis between the deflector package and any of the first and second electrostatic lens element may be less than 10 %, preferably less than 5 %, and most preferred less than 2 % of the minimum electrode separation distance from the optical axis. This limitation is relevant when the deflector package only extends over a part of the gap between the first electrostatic lens element and the second electrostatic lens elements.

The deflector arrangement may comprises a metal tube, wherein the deflector package is arranged in the metal tube and wherein the metal tube is arranged electrically separated from the deflector package, the first electrostatic lens element and the second electrostatic lens element. Such a metal tube may be advantageous for mechanical reasons for easy attachment of the electrodes. The second opening may be elongated in a plane perpendicular to the optical axis, wherein the ratio of the width to the height of the second opening is at least 10:1 and preferably at least 30:1. An elongated opening is advantageous in that it cuts off electrons in a suitable way for the electron spectrometer.

The first opening may be arranged in the first lens element and the second opening may be arranged in the second lens element. An arrangement comprising only two lens elements is the simplest embodiment.

The arrangement may comprise also a third electrostatic lens element arranged such that the first electrostatic lens element is arranged between the third electrostatic lens element and the second electrostatic lens element, and a fourth electrostatic lens element arranged such that the second electrostatic lens is arranged between the fourth electrostatic lens element and the first electrostatic lens element. By having the additional third lens element and fourth lens element it is possible to control the electrons, with lower voltage differences between the lens elements. Lower voltage differences are preferable. With a third and a fourth lens element it is also easier to get the same focus properties for different energies of the electrons that are analysed. Additionally, with a third electrostatic lens element and a fourth electrostatic lens element it is possible to maintain the electrons close to the optical axis when they are deflected on their path from the first opening to the second opening, which leads to smaller aberrations.

The electrostatic lens may be arranged to be operated in an angle-resolved mode, such that electrons entering through the first opening with the same direction in relation to the optical axis are focused to the same point at the position of the second opening along the optical axis, and such that electrons which exits through the second opening exits at a controllable angle to the optical axis in at least one coordinate direction perpendicular to the optical axis. This is preferable when using the arrangement together with, e.g., a photo-electron spectrometer in order to analyse photo-electrons.

The electrostatic lens may be arranged to be operated also in an imaging mode, such that electrons entering through the first opening from the same point on the electron emitting sample are focused to the same point at the position of the second opening along the optical axis, and such that electrons which exits through the second opening exits at a controllable angle to the optical axis in at least one coordinate direction. The angle of the electrons which exits through the second opening is preferably controlled to be essentially zero in one of the coordinate directions perpendicular to the optical axis. In case the second opening is elongated along a first coordinate direction the angle of the electrons which exits through the second opening is preferably controlled to be essentially zero in a second coordinate direction.

The arrangement may be configured to be used in an analyser arrangement, for determining at least one parameter related to electrons emitted from an electron emitting sample, wherein the arrangement is to be arranged with the first opening facing the electron emitting sample and with the second opening adjacent to an entrance slit of a measurement region of the analyser, for transporting electrons from the electron emitting surface to the entrance slit of the measurement region. This is a favourable implementation of the arrangement.

The arrangement may also comprise a control unit configured to apply individual voltages to each one of the electrodes of the deflector arrangement. The application of individual voltages enables a good control of the electrons. The control unit may also be configured to apply individual voltages to each one of the electrostatic lens elements. This makes it possible to use only one control unit to be able to provide different voltages to the electrostatic lens elements.

BRIEF DESCRIPTION OF THE DRAWINGS In the following preferred embodiments of the invention will be described with reference to the appended drawings in which:

Fig. 1 shows an analyser arrangement in which an arrangement comprising an electrostatic lens is arranged to control electrons emitted from an electron emitting sample.

Fig. 2 shows in a perspective sectional view an arrangement comprising an electrostatic lens according to a first embodiment of the present invention.

Fig. 3 shows in a cross sectional side view the arrangement shown in Fig. 2. Fig. 4 shows in a perspective sectional view an arrangement comprising an electrostatic lens according to a second embodiment of the present invention.

Fig. 5 shows in a perspective sectional view an arrangement comprising an electrostatic lens according to a third embodiment of the present invention. Fig. 6 shows in a cross sectional side view an arrangement comprising an electrostatic lens according to a fourth embodiment of the present invention.

Fig. 7 shows in a cross sectional view along the optical axis towards the second opening, an arrangement according to the embodiments in Figs. 2-6.

Fig. 8 shows in a cross sectional view along the optical axis towards the second opening, an arrangement according to an alternative embodiment.

DETAILED DESCRIPTION

In the following description of preferred embodiments the same reference numeral will be used for similar features in the different drawings. The drawings are not drawn to scale. Fig. 1 shows a photo-electron spectrometer 200 of hemispherical deflector type according to prior art. An arrangement comprising an electrostatic lens 7 is arranged in the photo-electron spectrometer 200. In a photo-electron spectrometer 200 of hemispherical deflector type, a central component is the measurement region 8 in which the energies of the electrons are analysed. The measurement region 8 is formed by two concentric hemispheres 9, mounted on a base plate 10, and with an electrostatic field applied between them. The electrons enter the measurement region 8 through the second opening 21 and continues through an entrance slit 11 and electrons entering the region between the hemispheres 9 with a direction close to perpendicular to the base plate 10 are deflected by the electrostatic field, and those electrons having a kinetic energy within a certain range defined by the deflecting field will reach a detector arrangement 12 after having travelled through a half circle. In a typical instrument, the electrons are transported from their source (typically a sample 13 that emits electrons after excitation with photons, electrons or other particles) to the entrance slit 11 of the hemispheres 9 by an electrostatic lens 7 comprising a plurality of lens elements 1-4 having a common and substantially straight optical axis 6 and a deflector package 5. The electrostatic lens 7 comprises a first opening 20, which faces the sample 13 in the embodiment shown in Fig. 1, and a second opening 21 at the opposite end of the electrostatic lens 7. The deflector package comprises a plurality of electrodes 15. In contrast to electrostatic lenses according to the prior art the electrostatic lens comprises a first electrostatic lens element 1 and a second electrostatic lens element 2, in relation to which the deflector package 5 is arranged such that it overlaps both the first electrostatic lens element 1 and the second electrostatic lens 2. The arrangement comprising the electrostatic lens 7 will be described in more detail below with reference to Figs.

2 and 3. The electrostatic lens 7 is configured to form a beam of electrons entering through the first opening 20 and to transport the beam of electrons to the second opening 21 and further on to the entrance slit 11. The electrons which enters through the first opening 20 originates from the sample 13. The third electrostatic lens element 3 and the fourth electrostatic lens element 4 are optional. In the embodiment shown in Fig. 1 the third electrostatic lens element

3 could form a part of the first electrostatic lens element 1 and the fourth electrostatic lens element 4 could form a part of the second electrostatic lens element 2. It is, however, advantageous to have the third electrostatic lens element 3 and the fourth electrostatic lens element 4 electrically separated from the first electrostatic lens element 1 and the second electrostatic lens element 2, as will be described below.

The detector arrangement 12 typically comprises a multichannel electron-multiplying plate (MCP) 14 which is arranged in the same plane as the entrance slit 11 of the hemispheres 9 and which generates a measurable electrical signal at the position of an incoming electron, which can then be registered either optically by a phosphorous screen and a video camera 17 or as an electrical pulse e. g. on a delay line or a resistive anode detector. Alternatively, some of the energy-selected electrons may be analysed further, in particular with respect to their spin, after leaving the hemisphere region through an exit aperture 16 leading to a spin detector 18. The detector arrangement 12 may of course be arranged in other ways. The MCP 14 and the entrance slit 11 may for example be arranged in different planes.

Fig. 2 shows an arrangement 100 comprising an electrostatic lens 7 having an interior volume 19, a first opening 20 for entrance of electrons into the interior volume 19, a second opening 21 for exit of electrons from the interior volume 19, and a substantially straight optical axis 6, extending from the first opening 20 to the second opening 21 through the interior volume 19. The electrostatic lens 7 is configured to form a beam of electrons entering through the first opening 20 and to transport the beam of electrons to the second opening 21. The electrostatic lens 7 comprises a first electrostatic lens element 1 in which the first opening 20 is arranged, and a second electrostatic lens 2 element in which the second opening 21 is arranged. The electrostatic lens also comprises a deflector arrangement comprising a deflector package 5 with a plurality of electrodes 15, which is arranged overlapping the first electrostatic lens element 1 and the second electrostatic lens element 2. The deflector package 5 is arranged to deflect the beam of electrons, in at least a first coordinate direction (x, y) perpendicular to the optical axis 6. The electrostatic lens elements 1, 2, are electrically separated from each other and from the deflector package 5, such that different voltages may be applied to each one of the electrostatic lens elements 1, 2, and to each one of the deflector elements 15 in the deflector package to the deflector package 5. This is achieved by having a gap B between the first electrostatic lens elements 1 and the second electrostatic lens element 2, to prevent electrical contact between the first electrostatic lens element 1 and the second electrostatic lens element 2. The gap B between the first electrostatic lens elements 1 and the second electrostatic lens element 2 may be filled with an insulating material (not shown in Fig. 2). In that way the electrostatic lens elements 1, 2, are mechanically connected. The electrostatic lens elements 1, 2, and the deflector arrangement may be arranged within a magnetic shield (not shown in Fig. 2). The arrangement 100 also comprises a control unit 22 which is arranged to apply voltages to the electrostatic lens elements 1-4 and to each one of the electrodes of the deflector package 5. The deflector package 5 is arranged such that, during operation of the electrostatic lens, an electron, travelling from the first electrostatic lens element 1 to the second electrostatic lens element 2, first passes through the electric field between the first electrostatic lens element 1 and the deflector package 5, and subsequently passes through the electric field between the deflector package 5 and the second electrostatic lens element 2. This may be achieved in different ways. In the embodiment of Fig. 2 the deflector package extends, in the direction of the optical axis 6, over the gap B between the first electrostatic lens element 1 and the second electrostatic lens element 2.

The deflector package 5 comprises electrodes arranged around the optical axis 6. A separate voltage is applied to each one of the electrodes of the deflector package 5 to achieve deflection in a respective coordinate direction. The electrodes are arranged at a minimum electrode separation distance D from the optical axis. The minimum number of electrodes is 2, to enable deflection such that electrons entering the first opening 20 in a specific angle in the x and y directions in relation to the optical axis enters the second opening 21. The minimum number of electrodes is 4, to enable electrons entering the first opening in the same angle in relation to the optical axis 6 in the x-direction to enter the second opening essentially irrespective of their angles in the y-direction when they enter the first opening. This will be described in more detail below.

In operation the control unit applies different voltages to the electrostatic lens elements 1, 2, and to the deflector package 5. A centre voltage is applied to the deflector package 5. To each one of the electrodes 15 is also a separate deflection voltage applied. The deflection voltages are added to the centre voltage. The deflection voltages are applied on the electrodes in order to choose which electrons entering the first opening that are to hit the second opening, with a positive deflection voltage on one of the electrodes 15 in the pair and a negative deflection voltage on the opposite electrode 15 in the pair. A first voltage is applied on the first lens element 1. The first voltage is the same as the voltage on the sample 13, when the arrangement is used in a photo-electron spectrometer 200 (Fig. 1). A different voltage is applied on the second electrostatic lens element 2. The voltage differences between the first voltage and the second voltage together with the voltage difference between the centre voltage and the first voltage control the focussing of the electrons entering the interior volume 19 through the first opening 20. By controlling said voltages it is possible to control where the electrons are focussed. Thus, the arrang

Fig. 3 illustrates in a cross sectional side view electrons 25 entering through the first opening 20 with an angle a to the optical axis 6 in the x-direction, i.e., perpendicular to the direction of the largest extension of the second opening. By applying appropriate voltages on the first electrostatic lens element 1 the second electrostatic lens element 2 and the deflector package 5 said electrons will hit the second opening 21 parallel to the optical axis 6. The deflection voltages control the deflection of the electrons. The deflection voltages together with the difference between the centre voltage and the first voltage, determines which angular distribution of the electrons, entering through the first opening 20, that are to hit the slit constituting the second opening 21. The mentioned factors affect the path of the electrons. A first deflection of the electrons is effected by the difference between the first voltage and the centre voltage and the difference between the deflection voltages. A second deflection of the electrons is effected primarily by the difference between the centre voltage and the second voltage. By adjusting the different voltages the first deflection and the second deflection might be adjusted to the desired angular distribution of the electrons so that the electrons in the desired angular distribution travel can pass the second opening 21 parallel to the optical axis.

It is desirable that the length L of the deflector package 5 is at least 50 %, preferably at least 100 % and most preferred at least 150 % of the minimum electrode separation distance D in the deflector package 5 to achieve a good control of the electrons.

The electrostatic lens may, thus, be operated in an angle-resolved mode, such that electrons entering through the first opening with the same direction in relation to the optical axis are focused to the same point at the position of the second opening along the optical axis. Electrons that enter the interior volume 19 of the electrostatic 7 lens through the first opening with the same angle in a first plane x, but in different angles in a second plane y perpendicular to the first plane form a line when traveling parallel with the optical axis. Such electrons may be controlled to exit through an elongated slit forming the second opening 21.

Fig. 4 shows an arrangement 100 comprising an electrostatic lens 7 having an interior volume 19, a first opening 20 for entrance of electrons into the interior volume 19, a second opening 21 for exit of electrons from the interior volume 19, and a substantially straight optical axis 6, extending from the first opening 20 to the second opening 21 through the interior volume 19. The electrostatic lens 7 is configured to form a beam of electrons entering through the first opening 20 and to transport the beam of electrons to the second opening 21. The electrostatic lens 7 of Fig. 4 is similar to the electrostatic lens of Figs. 2 and 3 but comprises in addition to the first electrostatic lens element l and the second electrostatic lens element 2 a third electrostatic lens element 3 in which the first opening 20 is arranged. The electrostatic lens 7 also comprises a fourth electrostatic lens element 4 in which the second opening 21 is arranged. The electrostatic lens also comprises a deflector arrangement comprising a deflector package 5 with a plurality of electrodes 15 being arranged between the first electrostatic lens element 1 and the second electrostatic lens element 2. The deflector package 5 is arranged to deflect the beam of electrons, in at least a first coordinate direction x, y perpendicular to the optical axis 6, which extends in the z-direction. The electrostatic lens 7 also comprises a fourth electrostatic lens element 4 arranged between the third electrostatic lens element 3 and the second electrostatic lens element 2. In Fig. 5 the second opening 21 is arranged in a sub-electrode 4' to the fourth electrode. The sub-electrode 4' is electrically connected to the fourth electrode 4 by the electrical connection 30. Thus, the fourth electrode and the sub-electrode, within the meaning of this application, effectively constitutes parts of the same electrode. The sub-electrode 4' is, apart from the electrical connection 30, physically separated from the fourth electrode. A sub opening 21' is arranged in the fourth electrode 4. The sub-opening 21' is essentially circular. The arrangement with a sub-opening 21' and a sub-electrode 4 is advantageous for constructional reasons. The electrostatic lens elements 1-4 are electrically separated from each other and from the deflector package 5, such that different voltages may be applied to each one of the electrostatic lens elements 1-4 and to the deflector package 5. This is illustrated in Fig. 4 by gaps between the electrostatic lens elements 1-4. The electrostatic lens elements 1-4 are, however, preferably mechanically connected with non-conducting connection means (not shown in Fig. 4). The arrangement 100 also comprises a control unit 22, which is arranged to apply voltages to the electrostatic lens elements 1-4 and to each one of the electrodes of the deflector package 5. The deflector package 5 is arranged such that, during operation of the electrostatic lens 7, an electron, travelling from the first electrostatic lens element 1 to the second electrostatic lens element 2, first passes through the electric field between the first electrostatic lens element 1 and the deflector package 5, and subsequently passes through the electric field between the deflector package 5 and the second electrostatic lens element 2. This may be achieved in different ways. Fig. 5 shows in a cross sectional side view an arrangement according to another embodiment. In the embodiment of Fig. 5 the deflector package 5 extends, in the direction of the optical axis 6, along the third electrostatic lens element 3, essentially over the entire gap B between the first electrostatic lens element 1 and the second electrostatic lens element 2. This is essentially the only difference between the embodiments of Fig. 4 and Fig. 5.

The deflector package 5 comprises electrodes arranged in a formation of essentially rotational symmetry with respect to the optical axis 6. The electrodes of the deflector package 5 serves as deflectors in a respective coordinate direction. The electrodes are arranged at a minimum electrode separation distance D from the optical axis 6.

In Fig. 6 an arrangement according to another embodiment is shown in a cross sectional side view. The only difference between the embodiment of Fig. 5 and the embodiment of Fig. 6 is that the deflector package 5 is surrounded by a tube 23. Electrostatically, the tube 23 has no function as it is shielded from the interior 19 of the lens.

Fig. 6 illustrates in a cross sectional side view electrons 25 entering through the first opening 20 with an angle a to the optical axis 6. By applying appropriate voltages on the first electrostatic lens element 1 the second electrostatic lens element 2 and the deflector package 5 said electrons will hit the second opening 21 parallel to the optical axis 6. In operation the control unit 22 applies different voltages to the electrostatic lens elements 1-4 and to the deflector package 5. A centre voltage is applied to the deflector package 5. To each one of the electrodes 15 is also a separate deflection voltage applied. The deflection voltages are added to the centre voltage. Different voltages are applied on the first electrostatic lens element 1, second electrostatic lens element 2, the third electrostatic 3, and the fourth electrostatic voltage 4, respectively. The voltage differences between the third voltage applied on the third electrostatic lens element 3 and the first voltage together with the voltage difference between the first voltage and the centre voltage control the focussing of the electrons entering the interior volume 19 through the first opening 20. By controlling said voltages it is possible to control where the electrons are focussed. The deflection voltages control the deflection of the electrons. The deflection voltages together with the differences between the centre voltage, the first voltage, and the second voltage determines which angular distribution of the electrons, entering through the first opening 20, that are to hit the slit constituting the second opening 21. The mentioned factors affect the path of the electrons. A first deflection of the electrons is effected by the difference between the third voltage and the centre voltage and the difference between the deflection voltages. A second deflection of the electrons is effected primarily by the difference between the centre voltage and the fourth voltage. By adjusting the third voltage, the centre voltage and the deflection voltages, the first deflection might be adjusted to the desired angular distribution of the electrons. The fourth voltage might then be adjusted to bend the electrons in the desired angular distribution so that they travel parallel to the optical axis and can pass the second opening.

It is desirable that the length L of the deflector package 5 is at least 50 %, preferably at least 100 % and most preferred at least 150 % of the minimum electrode separation distance D in the deflector package 5 to achieve a good control of the electrons. The electrostatic lens may, thus, be operated in an angle-resolved mode, such that electrons entering through the first opening of the first electrostatic lens element 1 with the same direction in relation to the optical axis are focused to the same point at the position of the second opening along the optical axis. Electrons that enter the interior volume 19 of the electrostatic lens 7 through the first opening with the same angle in a first plane x, but in different angles in a second plane y perpendicular to the first plane form a line when traveling parallel with the optical axis. Such electrons may be controlled to exit through an elongated slit forming the second opening 21. This will be described in more detail below with reference to Fig. 7. By controlling the voltages on the electrostatic lens elements 1-4 and the electrodes 15 differently from how the voltages are controlled in the angle-resolved mode, it is possible to operate the electrostatic lens 7 in an imaging mode. In the imaging mode the electron emitting surface is imaged on the plane of the second opening. Only a part of the image of the electron emitting sample hits the second opening 21. This part corresponds to a specific part of the electron emitting sample. It is possible to control the voltages on the electrostatic lens elements 1-4 and the electrodes 15 so that a different part of the image hits the second opening 21. It is also possible to control the angle to the optical axis, in at least one coordinate direction, of the electrons which exits through the second opening exits at a controllable angle.

In Fig. 6 the first electrostatic lens element 1 and the second electrostatic lens element 2 are arranged with a gap B between the first electrostatic lens element land the second electrostatic lens element 2. The deflector package 5 spans a part of the gap between the first electrostatic lens element 1 and the second electrostatic lens element 2. The distance G parallel to the optical axis 6 between the deflector package arrangement and any of the first and second electrostatic lens element 2 is less than 10 %, preferably less than 5 %, and most preferred less than 2 % of the minimum electrode separation distance D from the optical axis 6.

The deflector arrangement comprises a metal tube 23, wherein the deflector package 5 is arranged in the metal tube 23 and wherein the metal tube 23 is arranged electrically separated from deflector package 5, the first electrostatic lens element 1 and the second electrostatic lens element 2. Fig. 7 shows the arrangement according to Figs. 2-6 in a view along the length axis towards the second opening 21 and as indicated in Figs. 3 and 4. The arrangement comprises a deflector package 5 comprising eight electrodes 15a-15h. The dots 24 illustrate five different beams of electrons entering through the first opening 20 at an angle a in relation to the optical axis in the x direction but with five different angles in relation to the optical axis 6 in the y direction. The main function of electrodes 15a and 15e is to select the elevation angle that goes through the second opening 21. The main function of electrodes 15c and 15g is to focus the beams 24 of electrons in the y direction. The main function of electrodes 15b, 15d, 15f and 15h is to negate spherical deformation so that beams 24 having the same elevation angle go through the slit independently of their angle to the optical axis 6 in the y direction. The electrostatic lens 7 is preferably controlled such that electrons exit through the second opening essentially parallel to the optical axis in the x-direction. The second opening has a width W and a height H. The ratio of the width W to the height H is more than 10.

Fig. 8 shows an alternative to the arrangement shown in Fig. 7. The arrangement comprises a deflector package 5 comprising two electrodes 15a, 15b. The dots 24 illustrate five different beams of electrons entering through the first opening 20 at an angle a in relation to the optical axis in the x direction but with five different angles in relation to the optical axis 6 in the y direction. With only two electrodes in the deflector package it is not possible to avoid spherical deformation. This is reflected in Fig. 8 by that the side beams 24a, 24e are too high for entering the second opening 21, and the centre beam 24c is too low to enter the second opening 21.

The above described embodiments may be amended in many ways without departing from the scope of the invention, which is limited only by the appended claims.

Claims

1. Arrangement (100) for an electron spectrometer, the arrangement (100) comprising an electrostatic lens (7) having an interior volume (19), a first opening (20) for entrance of electrons into the interior volume (19), a second opening (21) for exit of electrons from the interior volume (19), and a substantially straight optical axis (6), extending from the first opening (20) to the second opening (21) through the interior volume (19), wherein the electrostatic lens (7) is configured to form a beam of electrons entering through the first opening (20) and to transport the beam of electrons to the second opening (21), wherein the electrostatic lens (7) also comprises

- a first electrostatic lens element (1) with a first end (26) facing the first opening (20) and a second end (27) facing away from the first opening (20),

- a second electrostatic lens element (2) with a first end (28) facing the first electrostatic lens element (1) and a second end (29) facing the second opening (21), and

-a deflector arrangement comprising a deflector package (5) with a plurality of electrodes (15) being arranged circumferentially around the optical axis (6) between the first end (26) of the first electrostatic lens element (1) and the second end (29) of the second electrostatic lens element (2), and arranged to deflect the beam of electrons, in at least a first coordinate direction (x, y) perpendicular to the optical axis (6), characterised in that the deflector package (5) is arranged such that, during operation of the electrostatic lens (7), an electron, travelling from the first electrostatic lens (1) element to the second electrostatic lens element (2), first passes through the electric field between the first electrostatic lens element (1) and the deflector package (5), and subsequently passes through the electric field between the deflector package (5) and the second electrostatic lens element (2), and wherein the electrodes are electrically separated from each other and from the first and second electrostatic lens elements, wherein the arrangement is controllable such that the beam of electrons that exit through the second opening is directed along the optical axis of the electrostatic lens (7).

2. The arrangement (100) according to claim 1, wherein the first electrostatic lens element (1) is arranged adjacent to the second electrostatic lens element (2) with a gap (B) between the first electrostatic lens element (1) and the second electrostatic lens element (2), and wherein the deflector package (5) spans at least part of the gap (B) between the first electrostatic lens element (1) and the second electrostatic lens element (2).

3. The arrangement (100) according to claim 1 or 2, wherein the deflector package comprises at least 2 electrodes (15), preferably at least 4 electrodes (15) and most preferred at least 8 electrodes (15) arranged around the optical axis (6).

4. The arrangement (100) according to claim 3, wherein the deflector package (5) comprises at least 4 electrodes (15) arranged in a formation of essentially rotational symmetry, wherein the electrodes (15) of the deflector package (5) serves as deflectors in at least two coordinate directions (X, Y).

5. The arrangement (100) according to any one of the preceding claims, wherein the electrodes (15) in the deflector package (5) are arranged at a minimum electrode separation distance (D) from the optical axis (6).

6. The arrangement (100) according to claim 5, wherein the length (L) of the deflector package (5) is at least 50 %, preferably at least 100 % and most preferred at least 150 % of the minimum electrode separation distance (D) from the optical axis (6) in the deflector package.

7. The arrangement (100) according to claim 5 or 6, wherein the distance (G) parallel to the optical axis (6) between the deflector package and any of the first and second electrostatic lens element is less than 10 %, preferably less than 5 %, and most preferred less than 2 % of the minimum electrode separation distance (D) from the optical axis (6).

8. The arrangement (100) according to any one of the preceding claims, wherein the deflector arrangement comprises a metal tube (23), wherein the deflector package (5) is arranged in the metal tube (23) and wherein the metal tube (23) is arranged electrically separated from deflector package (5), the first electrostatic lens element (1) and the second electrostatic lens element (2).

9. The arrangement (100) according to any one of the preceding claims, wherein the second opening is elongated in a plane perpendicular to the optical axis, wherein the ratio of the width to the height of the second opening is at least 10:1 and preferably at least 30:1.

10. The arrangement (100) according to any one of the preceding claims, wherein the first opening is arranged in the first lens element and the second opening is arranged in the second lens element.

11. The arrangement (100) according to any one of claims 1-9, also comprising

- a third electrostatic lens element (3) arranged such that the first electrostatic lens element (1) is arranged between the third electrostatic lens element (3) and the second electrostatic lens element (2), and

- a fourth electrostatic lens element (4) arranged such that the second electrostatic lens element (2) is arranged between the fourth electrostatic lens element (4) and the first electrostatic lens element (1).

12. The arrangement (100) according to claim 11, wherein the first opening (20) is arranged in the third lens element (3) and the second opening (21) is arranged in the fourth lens element (4).

13. The arrangement (100) according to any one of the preceding claims, wherein the electrostatic lens (7) is arranged to be operated in an angle-resolved mode, such that electrons entering through the first opening (20) with the same direction in relation to the optical axis (6) are focused to the same point at the position of the second opening (21) along the optical axis (6), and such that electrons which exits through the second opening exits at a controllable angle to the optical axis.

14. The arrangement (100) according to any one of the preceding claims, configured to be used in an analyser arrangement, for determining at least one parameter related to electrons emitted from an electron emitting sample (13), wherein the arrangement is to be arranged with the first opening (20) facing the electron emitting sample (13) and with the second opening (21) adjacent to an entrance slit (11) of a measurement region (8) of the analyser, for transporting electrons from the electron emitting surface to the entrance slit (11) of the measurement region (8).

15. The arrangement (100) according to any one of the preceding claims, also comprising a control unit (22) configured to apply individual voltages to each one of the electrodes (1- 4) of the deflector package (5).

16. The arrangement (100) according to any one of the preceding claims, wherein the control unit (22) is also configured to apply individual voltages to each one of the electrostatic lens elements (1-4).