SE543641C2 - Electrostatic lens for controlling beam of electrons - Google Patents

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

1 Electrostatic lens for controlling beam of electrons TECHNICAL FIELD The present invention relates to an arrangement comprising an electrostatic lens forcontrolling a beam of electrons. ln particular the present invention relates to an arrangementcomprising 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. Theanalyser arrangement is arranged to form an electron beam of electrons emitted from anelectron emitting sample and transporting the electrons between said electron emitting sampleand an entrance slit of a measurement region by means of a lens system having a substantiallystraight optical axis. The lens system is arranged to deflect the electron beam in at least a firstcoordinate direction at least a first time and a second time. By deflecting the electron beam atleast two times it is possible to operate the lens system in an angle-resolved mode, such that itdeflects the electron beam such that a predetermined part of the angular distribution of theelectrons passes the entrance slit of the measurement region in a direction being substantiallyparallel to the optical axis of the lens system. The main embodiment described in WO2013/133739 comprises a first deflector package and a second deflector package. Arudimentary explanation of the function of said lens system is as follows. The first deflectorpackage is controlled to deflect the desired predetermined angular distribution of the electronstowards the optical axis of the lens system. The second deflector package is controlled to deflectthe 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 angulardistribution of the electrons emitted from the electron emitting sample may be controlled toenter the entrance slit of the measurement region in a direction being substantially parallel to the optical axis ofthe lens system without the need for tilting the electron emitting sample.

SUMMARY OF THE INVENTION An objective ofthe present invention is to provide an arrangement comprising an electrostaticlens 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 ofthe present invention is to provide an arrangement comprising anelectrostatic lens for controlling a beam of electrons, which arrangement has only onedeflector arrangement with a deflector package comprising a plurality of electrodes, while stillallowing electrons entering through the first opening with the same direction in relation to theoptical 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 anelectrostatic lens for controlling a beam of electrons, which arrangement with as few opticalelements as possible enables control of electrons such that a specific angular distribution ofelectrons emitted from an electron emitting sample leaves the arrangement in a controllableangle and such that the electron beam from the arrangement is suitable for entering into an eleCtfOfi SpeCtfOmetef.

At least one ofthese 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 electronspectrometer and comprises an electrostatic lens having an interior volume, a first opening forentrance of electrons into the interior volume, a second opening for exit of electrons from theinterior volume, and a substantially straight optical axis, extending from the first opening to thesecond opening through the interior volume. The electrostatic lens is configured to form a beamof electrons entering through the first opening and to transport the beam of electrons to thesecond opening. The electrostatic lens also comprises a first electrostatic lens element with afirst 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 3end facing the second opening, and a deflector arrangement comprising a deflector packagewith a plurality of electrodes being arranged circumferentially around the optical axis betweenthe first end of the first electrostatic lens element and the second end of the secondelectrostatic lens element, and arranged to deflect the beam of electrons, in at least a firstcoordinate direction perpendicular to the optical axis. The arrangement is characterised in thatthe deflector package is arranged such that, during operation of the electrostatic lens, anelectron, travelling from the first electrostatic lens element to the second electrostatic lenselement, first passes through the electric field between the first electrostatic lens element andthe deflector package, and subsequently passes through the electric field between the deflectorpackage and the second electrostatic lens element, and wherein the electrodes are electricallyseparated from each other and from the first and second electrostatic lens elements. Thearrangement 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 ofthe electrostatic lens, voltages are applied to the lens elements and to theelectrodes of the deflector package. The arrangement is controllable by controlling the voltagesto 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 issuitable for entering into the electron spectrometer. Thus, when it is possible to control theelectrostatic lens in such a way, no direction changes are necessary after the second opening.ln 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 iselectrically separated from the other electrodes. Thus if two electrodes are electricallyconnected 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. 4By the electrodes being electrically separated from each other and from the first and secondelectrostatic lens elements it is possible to apply different voltages to the first and secondelectrostatic lens elements and to the different electrodes. The different voltages applied to theelectrodes results in a centre voltage. Electrons that pass through the first electrostatic lenselement, the deflector package and the second electrostatic lens element will thus experiencefirstly 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 secondelectrostatic lens element. These two different electric fields together with the different appliedvoltages applied on the electrodes results in effectively two deflections ofthe electrons. Thus,the arrangement according to the invention provides operational degrees of freedom withregard 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 angulardistribution 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 beparallel 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 enterthe 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 lenselement with a gap between the first electrostatic lens element and the second electrostaticlens element. The deflector package may span at least part of the gap between the firstelectrostatic lens element and the second electrostatic lens element. ln principle, there isalways a gap between the first electrostatic lens element and the second electrostatic lenselement. However, if the gap is sufficiently large there is a risk that exterior electric field penetrate the gap and effects the electrons. ln order for electrons passing through the 5electrostatic lens not to be effected by such electric fields the deflector package spa ns at least a part ofthe gap.

The deflector package may comprise at least 2 electrodes, preferably at least 4 electrodes andmost 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 com prises at least 4 electrodes arra nged in a formation of essentiallyrotational symmetry, wherein the electrodes of the deflector package serves as deflectors in atleast 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 separationdistance from the optical axis. Preferably, all electrodes are arranged at the same distance fromthe optical axis. |fthe 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 mostpreferred at least 150 % of the minimum electrode separation distance from the optical axis inthe 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 andsecond electrostatic lens element may be less than 10 %, preferably less than 5 %, and mostpreferred less than 2 % ofthe minimum electrode separation distance from the optical axis. Thislimitation 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 isarranged in the metal tube and wherein the metal tube is arranged electrically separated fromthe deflector package, the first electrostatic lens element and the second electrostatic lenselement. Such a metal tube may be advantageous for mechanical reasons for easy attachment of the electrodes. 6The second opening may be elongated in a plane perpendicular to the optical axis, wherein theratio of the width to the height of the second opening is at least 1011 and preferably at least3011. An elongated opening is advantageous in that it cuts off electrons in a suitable way for the eleCtfOfi SpeCtFOmeteF.

The first opening may be arranged in the first lens element and the second opening may bearranged 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 thefirst electrostatic lens element is arranged between the third electrostatic lens element and thesecond electrostatic lens element, and a fourth electrostatic lens element arranged such thatthe second electrostatic lens is arranged between the fourth electrostatic lens element and thefirst electrostatic lens element. By having the additional third lens element and fourth lenselement it is possible to control the electrons, with lower voltage differences between the lenselements. Lower voltage differences are preferable. With a third and a fourth lens element it isalso easier to get the same focus properties for different energies of the electrons that areanalysed. Additionally, with a third electrostatic lens element and a fourth electrostatic lenselement 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 thatelectrons entering through the first opening with the same direction in relation to the opticalaxis 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 tothe optical axis in at least one coordinate direction perpendicular to the optical axis. This ispreferable 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 thatelectrons entering through the first opening from the same point on the electron emittingsample are focused to the same point at the position of the second opening along the opticalaxis, 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. 7The angle of the electrons which exits through the second opening is preferably controlled tobe essentially zero in one of the coordinate directions perpendicular to the optical axis. ln casethe second opening is elongated along a first coordinate direction the angle of the electronswhich 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 atleast one parameter related to electrons emitted from an electron emitting sample, whereinthe arrangement is to be arranged with the first opening facing the electron emitting sampleand with the second opening adjacent to an entrance slit of a measurement region of theanalyser, 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 toeach one ofthe electrodes ofthe 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 theelectrostatic 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 ln 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 ofthe present invention.

Fig. 3 shows in a cross sectional side view the arrangement shown in Fig. 2. 8Fig. 4 shows in a perspective sectional view an arrangement comprising an electrostatic lens according to a second embodiment ofthe present invention.

Fig. 5 shows in a perspective sectional view an arrangement comprising an electrostatic lens according to a third embodiment ofthe 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 ln 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 toprior art. An arrangement comprising an electrostatic lens 7 is arranged in the photo-electronspectrometer 200. ln a photo-electron spectrometer 200 of hemispherical deflector type, acentral component is the measurement region 8 in which the energies of the electrons areanalysed. The measurement region 8 is formed by two concentric hemispheres 9, mounted ona base plate 10, and with an electrostatic field applied between them. The electrons enter themeasurement region 8 through the second opening 21 and continues through an entrance slit11 and electrons entering the region between the hemispheres 9 with a direction close toperpendicular to the base plate 10 are deflected by the electrostatic field, and those electronshaving a kinetic energy within a certain range defined by the deflecting field will reach a detectorarrangement 12 after having travelled through a half circle. ln a typical instrument, the electronsare transported from their source (typically a sample 13 that emits electrons after excitationwith 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 9substantially straight optical axis 6 and a deflector package 5. The electrostatic lens 7 comprisesa first opening 20, which faces the sample 13 in the embodiment shown in Fig. 1, and a secondopening 21 at the opposite end of the electrostatic lens 7. The deflector package comprises aplurality of electrodes 15. ln contrast to electrostatic lenses according to the prior art theelectrostatic lens comprises a first electrostatic lens element 1 and a second electrostatic lenselement 2, in relation to which the deflector package 5 is arranged such that it overlaps boththe first electrostatic lens element 1 and the second electrostatic lens 2. The arrangementcomprising 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 thefirst opening 20 and to transport the beam of electrons to the second opening 21 and furtheron to the entrance slit 11. The electrons which enters through the first opening 20 originatesfrom the sample 13. The third electrostatic lens element 3 and the fourth electrostatic lenselement 4 are optional. ln the embodiment shown in Fig. 1 the third electrostatic lens element3 could form a part of the first electrostatic lens element 1 and the fourth electrostatic lenselement 4 could form a part of the second electrostatic lens element 2. lt is, however,advantageous to have the third electrostatic lens element 3 and the fourth electrostatic lenselement 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(I\/ICP) 14 which is arranged in the same plane as the entrance slit 11 of the hemispheres 9 andwhich generates a measurable electrical signal at the position of an incoming electron, whichcan then be registered either optically by a phosphorous screen and a video camera 17 or as anelectrical pulse e. g. on a delay line or a resistive anode detector. Alternatively, some of theenergy-selected electrons may be analysed further, in particular with respect to their spin, afterleaving the hemisphere region through an exit aperture 16 leading to a spin detector 18. Thedetector arrangement 12 may of course be arranged in other ways. The I\/ICP 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 volume19, a first opening 20 for entrance of electrons into the interior volume 19, a second opening 21for 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 firstopening 20 and to transport the beam of electrons to the second opening 21. The electrostaticlens 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. Theelectrostatic lens also comprises a deflector arra ngement comprising a deflector package 5 witha plurality of electrodes 15, which is arranged overlapping the first electrostatic lens element 1and the second electrostatic lens element 2. The deflector package 5 is arranged to deflect thebeam of electrons, in at least a first coordinate direction (x, y) perpendicular to the optical axis6. The electrostatic lens elements 1, 2, are electrically separated from each other and from thedeflector package 5, such that different voltages may be applied to each one ofthe electrostaticlens elements 1, 2, and to each one of the deflector elements 15 in the deflector package to thedeflector package 5. This is achieved by having a gap B between the first electrostatic lenselements 1 and the second electrostatic lens element 2, to prevent electrical contact betweenthe first electrostatic lens element 1 and the second electrostatic lens element 2. The gap Bbetween the first electrostatic lens elements 1 and the second electrostatic lens element 2 maybe filled with an insulating material (not shown in Fig. 2). ln that way the electrostatic lenselements 1, 2, are mechanically connected. The electrostatic lens elements 1, 2, and thedeflector arrangement may be arranged within a magnetic shield (not shown in Fig. 2). Thearrangement 100 also comprises a control unit 22 which is arranged to apply voltages to theelectrostatic 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, anelectron, travelling from the first electrostatic lens element 1 to the second electrostatic lenselement 2, first passes through the electric field between the first electrostatic lens element 1and the deflector package 5, and subsequently passes through the electric field between thedeflector package 5 and the second electrostatic lens element 2. This may be achieved indifferent ways. ln the embodiment of Fig. 2 the deflector package extends, in the direction ofthe 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 separatevoltage 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 11separation distance D from the optical axis. The minimum number of electrodes is 2, to enabledeflection such that electrons entering the first opening 20 in a specific angle in the x and ydirections in relation to the optical axis enters the second opening 21. The minimum number ofelectrodes is 4, to enable electrons entering the first opening in the same angle in relation tothe optical axis 6 in the x-direction to enter the second opening essentially irrespective oftheirangles in the y-direction when they enter the first opening. This will be described in more detail below. ln 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 eachone of the electrodes 15 is also a separate deflection voltage applied. The deflection voltagesare added to the centre voltage. The deflection voltages are applied on the electrodes in orderto choose which electrons entering the first opening that are to hit the second opening, with apositive deflection voltage on one of the electrodes 15 in the pair and a negative deflectionvoltage on the opposite electrode 15 in the pair. A first voltage is applied on the first lenselement 1. The first voltage is the same as the voltage on the sample 13, when the arrangementis used in a photo-electron spectrometer 200 (Fig. 1). A different voltage is applied on thesecond electrostatic lens element 2. The voltage differences between the first voltage and thesecond voltage together with the voltage difference between the centre voltage and the firstvoltage control the focussing of the electrons entering the interior volume 19 through the firstopening 20. By controlling said voltages it is possible to control where the electrons are focussed. Th us, the arra ng Fig. 3 illustrates in a cross sectional side view electrons 25 entering through the first opening 20with an angle oL to the optical axis 6 in the x-direction, i.e., perpendicular to the direction of thelargest extension of the second opening. By applying appropriate voltages on the firstelectrostatic lens element 1 the second electrostatic lens element 2 and the deflector package5 said electrons will hit the second opening 21 parallel to the optical axis 6. The deflectionvoltages control the deflection of the electrons. The deflection voltages together with thedifference between the centre voltage and the first voltage, determines which angulardistribution of the electrons, entering through the first opening 20, that are to hit the slitconstituting 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 12centre voltage and the difference between the deflection voltages. A second deflection of theelectrons is effected primarily by the difference between the centre voltage and the secondvoltage. By adjusting the different voltages the first deflection and the second deflection mightbe 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. lt 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 electronsentering through the first opening with the same direction in relation to the optical axis arefocused to the same point at the position ofthe second opening along the optical axis. Electronsthat enter the interior volume 19 of the electrostatic 7 lens through the first opening with thesame angle in a first plane x, but in different angles in a second plane y perpendicular to the firstplane 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 volume19, a first opening 20 for entrance of electrons into the interior volume 19, a second opening 21for 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 firstopening 20 and to transport the beam of electrons to the second opening 21. The electrostaticlens 7 of Fig. 4 is similar to the electrostatic lens of Figs. 2 and 3 but comprises in addition to thefirst electrostatic lens element 1 and the second electrostatic lens element 2 a third electrostaticlens element 3 in which the first opening 20 is arranged. The electrostatic lens 7 also comprisesa fourth electrostatic lens element 4 in which the second opening 21 is arranged. Theelectrostatic lens also comprises a deflector arrangement comprising a deflector package 5 witha plurality of electrodes 15 being arranged between the first electrostatic lens element 1 andthe second electrostatic lens element 2. The deflector package 5 is arranged to deflect the beamof 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 13element 4 arranged between the third electrostatic lens element 3 and the second electrostaticlens element 2. ln Fig. 5 the second opening 21 is arranged in a sub-electrode 4' to the fourthelectrode. The sub-electrode 4' is electrically connected to the fourth electrode 4 by theelectrical connection 30. Thus, the fourth electrode and the sub-electrode, within the meaningof 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. Thearrangement with a sub-opening 21' and a sub-electrode 4 is advantageous for constructionalreasons. The electrostatic lens elements 1-4 are electrically separated from each other and fromthe deflector package 5, such that different voltages may be applied to each one of theelectrostatic lens elements 1-4 and to the deflector package 5. This is illustrated in Fig. 4 by gapsbetween 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 voltagesto the electrostatic lens elements 1-4 and to each one of the electrodes of the deflector package5. The deflector package 5 is arranged such that, during operation of the electrostatic lens 7, anelectron, travelling from the first electrostatic lens element 1 to the second electrostatic lenselement 2, first passes through the electric field between the first electrostatic lens element 1and the deflector package 5, and subsequently passes through the electric field between thedeflector package 5 and the second electrostatic lens element 2. This may be achieved indifferent ways. Fig. 5 shows in a cross sectional side view an arrangement according to anotherembodiment. ln the embodiment of Fig. 5 the deflector package 5 extends, in the direction ofthe optical axis 6, along the third electrostatic lens element 3, essentially over the entire gap Bbetween 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 rotationalsymmetry with respect to the optical axis 6. The electrodes of the deflector package 5 serves asdeflectors in a respective coordinate direction. The electrodes are arranged at a minimum electrode separation distance D from the optical axis 6. ln 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 14that 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 ofthe lens.

Fig. 6 illustrates in a cross sectiona| side view electrons 25 entering through the first opening 20with an angle oL to the optical axis 6. By applying appropriate voltages on the first electrostaticlens element 1 the second electrostatic lens element 2 and the deflector package 5 saidelectrons will hit the second opening 21 parallel to the optical axis 6. ln operation the controlunit 22 applies different voltages to the electrostatic lens elements 1-4 and to the deflectorpackage 5. A centre voltage is applied to the deflector package 5. To each one of the electrodes15 is also a separate deflection voltage applied. The deflection voltages are added to the centrevoltage. Different voltages are applied on the first electrostatic lens element 1, secondelectrostatic lens element 2, the third electrostatic 3, and the fourth electrostatic voltage 4,respectively. The voltage differences between the third voltage applied on the thirdelectrostatic lens element 3 and the first voltage together with the voltage difference betweenthe first voltage and the centre voltage control the focussing of the electrons entering theinterior volume 19 through the first opening 20. By controlling said voltages it is possible tocontrol where the electrons are focussed. The deflection voltages control the deflection of theelectrons. The deflection voltages together with the differences between the centre voltage,the first voltage, and the second voltage determines which angular distribution ofthe 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 iseffected by the difference between the third voltage and the centre voltage and the differencebetween the deflection voltages. A second deflection of the electrons is effected primarily bythe 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 thedesired angular distribution ofthe electrons. The fourth voltage might then be adjusted to bendthe electrons in the desired angular distribution so that they travel parallel to the optical axis and can pass the second opening. lt 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 electronsentering through the first opening of the first electrostatic lens element 1 with the samedirection in relation to the optical axis are focused to the same point at the position of thesecond opening along the optical axis. Electrons that enter the interior volume 19 of theelectrostatic lens 7 through the first opening with the same angle in a first plane x, but indifferent angles in a second plane y perpendicular to the first plane form a line when travelingparallel with the optical axis. Such electrons may be controlled to exit through an elongated slitforming 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 15differently from how the voltages are controlled in the angle-resolved mode, it is possible tooperate the electrostatic lens 7 in an imaging mode. ln the imaging mode the electron emittingsurface is imaged on the plane of the second opening. Only a part of the image of the electronemitting sample hits the second opening 21. This part corresponds to a specific part of theelectron emitting sample. lt is possible to control the voltages on the electrostatic lens elements1-4 and the electrodes 15 so that a different part of the image hits the second opening 21. lt isalso 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. ln Fig. 6 the first electrostatic lens element 1 and the second electrostatic lens element 2 arearranged with a gap B between the first electrostatic lens element 1 and the second electrostaticlens element 2. The deflector package 5 spans a part of the gap between the first electrostaticlens element 1 and the second electrostatic lens element 2. The distance G parallel to the opticalaxis 6 between the deflector package arrangement and any of the first and second electrostaticlens 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 isarranged in the metal tube 23 and wherein the metal tube 23 is arranged electrically separatedfrom deflector package 5, the first electrostatic lens element 1 and the second electrostatic lens element 2. 16 Fig. 7 shows the arrangement according to Figs. 2-6 in a view along the length axis towards thesecond opening 21 and as indicated in Figs. 3 and 4. The arrangement comprises a deflectorpackage 5 comprising eight electrodes 15a-15h. The dots 24 illustrate five different beams ofelectrons entering through the first opening 20 at an angle oL in relation to the optical axis inthe 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 throughthe second opening 21. The main function of electrodes 15c and 15g is to focus the beams 24of electrons in the y direction. The main function of electrodes 15b, 15d, 15f and 15h is tonegate spherical deformation so that beams 24 having the same elevation angle go throughthe slit independently of their angle to the optical axis 6 in the y direction. The electrostaticlens 7 is preferably controlled such that electrons exit through the second opening essentiallyparallel to the optical axis in the x-direction. The second opening has a width W and a height H. The ratio ofthe 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 adeflector package 5 comprising two electrodes 15a, 15b. The dots 24 illustrate five differentbeams of electrons entering through the first opening 20 at an angle oL in relation to theoptical axis in the x direction but with five different angles in relation to the optical axis 6 inthe y direction. With only two electrodes in the deflector package it is not possible to avoidspherical deformation. This is reflected in Fig. 8 by that the side beams 24a, 24e are too highfor 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 ofthe invention, which is limited only by the appended claims.

Claims (6)

1. 7 CLAll\/IS Arrangement (100) for an electron spectrometer, the arrangement (100) comprising anelectrostatic lens (7) having an interior volume (19), a first opening (20) for entrance ofelectrons into the interior volume (19), a second opening (21) for exit of electrons fromthe interior volume (19), and a substantially straight optical axis (6), extending from thefirst opening (20) to the second opening (21) through the interior volume (19), whereinthe electrostatic lens (7) is configured to form a beam of electrons entering through thefirst 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) anda second end (27) facing away from the first opening (20), - a second electrostatic lens element (2) with a first end (28) facing the first electrostaticlens element (1) and a second end (29) facing the second opening (21), and - a deflector arrangement comprising a deflector package (5) with a plurality ofelectrodes(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 secondelectrostatic lens element (2), and arranged to deflect the beam of electrons, in at least afirst coordinate direction (x, y) perpendicular to the optical axis (6), characterised in thatthe 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 secondelectrostatic lens element (2), first passes through the electric field between the firstelectrostatic lens element (1) and the deflector package (5), and subsequently passesthrough the electric field between the deflector package (5) and the second electrostaticlens element (2), and wherein the electrodes are electrically separated from each otherand from the first and second electrostatic lens elements, wherein the arrangement iscontrollable such that the beam of electrons that exit through the second opening is directed along the optical axis of the electrostatic lens (7). 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 18(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). The arrangement (100) according to claim 1 or 2, wherein the deflector package comprisesat least 2 electrodes (15), preferably at least 4 electrodes (15) and most preferred at least 8 electrodes (15) arranged around the optical axis (6). The arrangement (100) according to claim 3, wherein the deflector package (5) comprisesat 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). The arrangement (100) according to any one of the preceding claims, wherein theelectrodes (15) in the deflector package (5) are arranged at a minimum electrode separation distance (D) from the optical axis (6). The arrangement (100) according to claim 5, wherein the length (L) of the deflectorpackage (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. The arrangement (100) according to claim 5 or 6, wherein the distance (G) parallel to theoptical axis (6) between the deflector package and any of the first and second electrostaticlens element is less than 10 %, preferably less than 5 %, and most preferred less than 2 % ofthe minimum electrode separation distance (D) from the optical axis (6). The arrangement (100) according to any one of the preceding claims, wherein thedeflector arrangement comprises a metal tube (23), wherein the deflector package (5) isarranged in the metal tube (23) and wherein the metal tube (23) is arranged electricallyseparated from deflector package (5), the first electrostatic lens element (1) and the second electrostatic lens element (2). The arrangement (100) according to any one of the preceding claims, wherein the secondopening is elongated in a plane perpendicular to the optical axis, wherein the ratio of the width to the height ofthe second opening is at least 1011 and preferably at least 3011. 10. 11. 1

2. 1

3. 1

4. 1

5. 19The arrangement (100) according to any one of the preceding claims, wherein the firstopening is arranged in the first lens element and the second opening is arranged in the second lens element. 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 lenselement (1) is arranged between the third electrostatic lens element (3) and the secondelectrostatic lens element (2), and - a fourth electrostatic lens element (4) arranged such that the second electrostatic lenselement (2) is arranged between the fourth electrostatic lens element (4) and the first electrostatic lens element (1). The arrangement (100) according to claim 11, wherein the first opening (20) is arrangedin the third lens element (3) and the second opening (21) is arranged in the fourth lens element (4). The arrangement (100) according to any one of the preceding claims, wherein theelectrostatic lens (7) is arranged to be operated in an angle-resolved mode, such thatelectrons entering through the first opening (20) with the same direction in relation to theoptical 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. The arrangement (100) according to any one of the preceding claims, configured to beused in an analyser arrangement, for determining at least one parameter related toelectrons emitted from an electron emitting sample (13), wherein the arrangement is tobe arranged with the first opening (20) facing the electron emitting sample (13) and withthe second opening (21) adjacent to an entrance slit (11) of a measurement region (8) ofthe analyser, for transporting electrons from the electron emitting surface to the entrance slit (11) ofthe measurement region (8). The arrangement (100) according to any one of the preceding claims, also comprising acontrol unit (22) configured to apply individual voltages to each one ofthe electrodes (1- 4) of the deflector package (5). 1

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