EP0545064B1 - Device for filtering charged particles, energy filter and analyser using such an energy filter - Google Patents

Description

The present invention relates to a method for Filtering of electrically charged particles according to the The preamble of claim 1, an energy filter according to that of claim 6 and an analyzer with such an energy filter according to claim 24.

The mentioned energy filtering is particularly used in connection with plasma mass spectrometry. Using known mass spectrometry a filter system is formed, creating a beam charged molecular or atomic particles a selection regarding transmission is made in Function of the masses of the mentioned particles.

Regarding technology of mass spectrometry for plasma analysis the writing "Methods of plasma characterization "from Balzers, K. Höfler, BG 800 184 PA (8410), referenced as well as the writing same company "partial pressure measurement in vacuum technology", BG 800 169 PD (8711).

Often it is desirable to have a molecular beam Above-mentioned type fed to a mass spectrometer is going to subject this beam to energy filtering, around the mass spectrometer molecular beam particles to selectively supply certain kinetic energies, be it in a defined energy band or with energies that are not of a given measure exceed.

In a first aspect, the present invention on the technology of the mentioned energy filtering directed. Such is e.g. from EP-A-0 223 520 previously known. Basically, the one known from it works Energy filter technology based on the well-known principle of the cylinder mirror. Following this principle charged particles of a particle beam in the field space a cylindrical capacitor and are introduced through the cylinder jacket forming the outer electrode electrostatically deflected, i.e. mirrored to then exit the cylinder assembly. The energy filter effect is based on being higher energetic particles at a given electrostatic Field, a less curved trajectory pass through as deeper energetic particles with what only particles of a given energy band an intended exit opening through the mirror space to reach.

According to the mentioned EP-A becomes the beam of charged particles axially supplied to the mirror cylinder assembly occurs into a coaxial opening arrangement which is formed is by a first pair, a deflection capacitor forming electrode surfaces. These electrode surfaces define a radially outward curved Field space, in which, according to the charge polarity and the capacitor polarity, charged particles be deflected radially outwards. After leaving of the curved, entrance-side field space the charged particles in the actual mirror room of the cylinder mirror, consisting of a internal coaxial electrode core and the coaxial Mirror capacitor outer jacket. In the mirror room the charged particles are redirected and occur symmetrically with respect to a radial plane to the entrance-side, curved field space, in the formed between two further electrode surfaces Exit field space, from which they, accordingly steered back, in one axis, with the entry axis aligned, emerge from the filter arrangement.

The radially inner electrode surface of the inlet deflection arrangement, the inner electrode area of the Mirror capacitor arrangement and the inner electrode surface the exit electrode assembly formed by one and the same cylinder core. There all beam deflections due to electrostatic Fields are realized, both on the input side, curved field space as well as in the mirror space and at the equally curved exit field space, similar to centrifugal separation, filtering on the incoming, loaded Particles in each of the field spaces mentioned. Too deep energetic particles collide on the inside of the curve on electrode surfaces, energetically too high particles outside of the curve.

The known filter arrangement mentioned takes effect that between the input pair of electrodes, which defines the curved input field space, generated electrostatic field even in the coaxial Cylinder condenser mirror space, with which on the one hand the electrostatic field conditions, due to the resulting overlays in the transition area the particles from the input field space into the cylinder mirror space, are difficult to estimate, and with what decoupled setting of the electrostatic fields, because of the field penetration, is not possible.

The same conditions arise in the transition area between the cylinder mirror space and the curved outlet electrode arrangement. Those in the transition zones mentioned zones created by field overlay undefined field course can also not provided by a shield ring be kept at the same potential becomes like the cylinder core. Between this umbrella ring and the outer cylinder electrode of the mirror cylinder capacitor forms a distinct field in Direction of movement of the charged particles from which accelerating or decelerating and thus the Falsified filter properties of the arrangement.

From Soviet Inventions Illustrated, week 9004, March 7, 1990, N90-022454, Derwent Publications Ltd., GB London, and from SU-A-1492 397 an energy filter is known, which according to Principle of the cylinder mirror works. In a first axial Section is between a first pair of capacitor electrodes a room area or field space is formed, which by a Propagate opening in the inner electrode radially outwards Beam through another opening in said electrode redirects. The beam then enters an axially adjoining another field space, formed by a to the first pair of capacitor electrodes coaxial, second pair of capacitor electrodes. Between the axially adjacent inner electrodes A field-free space is formed between the two pairs of electrodes.

The outer, axially adjacent capacitor electrodes of the the two field spaces are separated by an air gap.

From US-A-3 805 057 an energy filter is known, which also works on the principle of the cylinder mirror. In a first axial section is between a first pair of capacitor electrodes a field space or room area is formed, which in turn is through an opening in the inner capacitor electrode radially outward propagating beam redirects another opening in said electrode. It the beam enters an axially adjoining one Field space or spatial area, formed by a further pair of capacitor electrodes, which is both axial and radial is offset from the first.

The inner capacitor electrode of the first extends Pair axially over a portion of the inner capacitor electrode of the second pair and, axially, also over a region of the outer capacitor electrode of the second Couple.

Finally, from "A Soft X-Ray Source for Photoelectron Spectroscopy ", A.D. McLachlan et al., Review of Scientific Instruments, Vol. 44, No. 7, July 1973, pp. 873-876, a process or an energy filter of the type mentioned above. One Electron multiplier facing the principle following the cylinder mirror, a first pair of capacitor electrodes provided between which a field space or room area is formed. Through openings in the inner capacitor electrode said couple enters the beam Field space in and, redirected, out again.

Axially, the beam then enters another field space or spatial area, formed by a second, continuously curved Pair of capacitor electrodes. The inner capacitor electrode of this second pair is, terminal, with oneself perpendicular to the beam entering the second field space extending aperture portion provided, wherein an opening is provided, through which the beam, after passing through the first field space, enters the second.

It is an object of the present invention, starting from the method or from the energy filter of the latter type, a method or to propose an energy filter which is much more compact can be realized and yet mutual field influencing problems fixes.

This is done by proceeding according to the characterizing part of claim 1 achieved or by the energy filter, built according to the license plate of claim 6.

By providing an umbrella designed in this way, it is possible to that the fields in the mentioned areas or Field spaces do not influence each other, which is also an attitude the deflection fields, each in the compactly built areas, remains decoupled from each other. So that's it further possible, depending on the space areas mentioned by the electrostatic deflection fields formed actual filter stages set independently.

When proceeding according to the wording of claim 2, an additional Separation between the room areas possible. Because the loaded Particles after passing through one of the electrode pairs mentioned and redirected in the corresponding area, straight cross the intended, essentially field-free space, it now becomes possible to find a desired beam divergence or beam focusing using the design and adjustment to realize the fields in the previously traversed area, without deflection fields in this beam section would have to be considered. This is the mastered optimization of the beam path significantly simplified.

When proceeding according to the wording of claim 3, the structure is special simply by using the screen as one of the Electrodes for the first electrostatic field is used.

In the following it is preferably carried out according to the wording of claim 4 that the beam is substantially parallel exits to the direction of entry.

This makes it possible to add one for the analysis of neutral particles Ionization source and / or the energy filter downstream mass spectrometer, preferably quadrupole mass spectrometer, to grow without kink.

Furthermore, following the wording of claim 5, are preferred and with regard to the first mentioned area two second room areas are provided, one located on the entrance side, one on the outlet side, with the jet each in one of the enters the second area and exits the other. The redirections are further increased by the now three electrostatic Fields made so that the entry and exit axis of the Beam. This makes it possible to do the above Structure from energy filter, possibly ionization source, mass spectrometer, to build along a common axis.

Preferred embodiments of the energy filter according to the invention are specified in claims 7 to 23, an analyzer with such a filter in claims 24 to 27.

While up to now on the inventive design of a Energy filter with two electrostatic deflection levels , two such are preferred, two-stage arrangements put together, with which a first beam deflection on the entry side, then a deflection and again results in a deflection such that the beam does not as in the device described so far essentially runs through an S-Bahn, but essentially a double S-Bahn.

An advantage of the filter arrangement mentioned above as known according to EP-A-0 223 520 is its coaxial structure. Coaxial to Axis of the cylinder mirror arrangement with the cylinder capacitor are also inlet and outlet deflection electrodes. The fed Ray is at a sharp, kind of singularity Tip of the cylindrical core forming an electrode surface divided and runs mirror-symmetrically to the axis through the arrangement. As is well known, such tips form high ones Field strengths.

Particles that can enter exactly on the axis of the arrangement the latter never happen. This also applies to particles, which occur immediately next to the axis. Particles the Tip just barely have, with respect to the cylinder mirror, unfavorable entry parameters.

It has now been recognized that such a beam splitter tip, also because of the high field strengths that develop there to be realized as steadily and mastered as possible Beam guidance, as mentioned, has an adverse effect.

This disadvantage is eliminated on the energy filter by the fact that according to the wording of claim 19, the beam path with respect the cylinder axis of the cylinder capacitor guided asymmetrically is.

It has been recognized that, surprisingly, by asymmetric Beam guidance through the energy filter, with which a beam splitting the energy filter transmission is omitted in symmetrical beam paths is not reduced and also the problematic No entry peak. Particles in the center of the beam are let through with a particularly high transmission rate. Furthermore, an alignment of Entry and exit axis of the beam even with asymmetrical Beam guidance can be maintained.

As for the constructive compilation of an analyzer with optionally upstream ion source and / or downstream Quadrupole mass spectrometer of primary importance is that the entry and exit axes of the beam are at the Energy filters are aligned and far less so that these axes too are placed in the axis of the cylindrical capacitor, the Following wording of claim 20, proposed entry and exit axis of the beam to the axis of the cylinder capacitor offset.

This enables further, despite asymmetrical beam guidance with respect to the cylinder capacitor axis, the cross-sectional area the cylinder arrangement for the beam guidance better use.

It becomes further, according to the wording of claim 21, the cylindrical capacitor formed by the two central pairs of electrodes, the entry and exit arrangements through the outer electrode pairs.

Preferably, following the wording of claim 22, a cross-sectional quadrant of the cylindrical capacitor as a mirror capacitor used, and there are entry and exit arrangements in the axially symmetrically opposite cross-sectional quadrant intended. The asymmetrical structure enables also not to provide any radial brackets in the mirror room.

By providing the inventive energy filter on the inventive one Analyzer becomes a selective adjustability optimally enables the energy spectrum to be supplied to the mass filter, where in the preferred variants of the Energy filter with aligned beam entry and exit axes the entire analyzer structure becomes compact.

An electron impact ionization source is preferably attached to it provided according to the wording of claim 25. It follows thanks to the axially extended accelerator tube, which means the neutral particles homogeneous, with the accelerating grid controllable, ionized by electron bombardment, a high Ionization yield. Especially in their training after Claim 26 or 27 results in an extremely homogeneous ionization distribution.

For the potential setting on the provided electrode pairs those skilled in the art apply to the energy filter according to the invention well-known considerations, and in particular can the mentioned energy filter thanks to the decoupled adjustability its "filter stages" as an extremely narrow-band energy filter be used. This is because the vote of the mentioned "Filter stages" due to their field decoupling by the provided shielding can be done optimally. On the other hand allows the energy filter ensures that the Beam propagation through the filter without becoming one Displacement of the entry and exit axis of the Lead beam.

The invention will subsequently be presented under its various Aspects, for example, based on figures explained.

Fig. 1

schematisch eine bekannte Strahlumlenkanordnung im Längsschnitt,

Fig. 2

in Darstellung analog zu Fig. 1 das Vorgehen zur Strahlumlenkung gemäss vorliegender Erfindung,

Fig. 3

in Darstellung analog zu den Fig. 1 und 2 eine Weiterausbildung des erfindungsgemässen Vorgehens nach Fig. 2,

Fig. 4

eine weitere bevorzugte Ausbildungsvariante des erfindungsgemässen Vorgehens,

Fig. 5

schematisch im Längsschnitt die bekannte Strahlumlenkanordnung, betrachtet unter einem weiteren Aspekt,

Fig. 6

in Darstellung analog zu Fig. 5 unter einem weiteren Aspekt das erfindungsgemässe Vorgehen beim Strahlumlenken,

Fig. 7

in Darstellung analog zu den Fig. 5 und 6 eine weitere bevorzugte Ausbildungsvariante des erfindungsgemässen Vorgehens,

Fig. 8

schematisch eine Querschnittsdarstellung gemäss Linie IIX-IIX von Fig. 7,

Fig. 9

schematisch eine bevorzugte Ausführungsform eines erfindungsgemässen Energiefilters im Längsschnitt mit Kombination der erfindungsgemässen Massnahmen sowie, schematisch, dem Filter vorgeschaltet, eine Crossbeam-Ionisierungsquelle,

Fig. 10

schematisch im Längsschnitt eine Ionisierungsquelle, vorzugsweise mit dem erfindungsgemässen Filter kombiniert.

Show it:

Fig. 1

schematically a known beam deflection arrangement in longitudinal section,

Fig. 2

in illustration analogous to FIG. 1, the procedure for beam deflection according to the present invention,

Fig. 3

in representation analogous to FIGS. 1 and 2, a further development of the procedure according to the invention according to FIG. 2,

Fig. 4

another preferred embodiment of the procedure according to the invention,

Fig. 5

schematically in longitudinal section the known beam deflection arrangement, viewed from a further aspect,

Fig. 6

in a representation analogous to FIG. 5 with a further aspect the procedure according to the invention for beam deflection,

Fig. 7

in the representation analogous to FIGS. 5 and 6, a further preferred embodiment of the procedure according to the invention,

Fig. 8

schematically a cross-sectional view according to line IIX-IIX of FIG. 7,

Fig. 9

schematically shows a preferred embodiment of an energy filter according to the invention in longitudinal section with a combination of the measures according to the invention and, schematically, upstream of the filter, a crossbeam ionization source,

Fig. 10

schematically in longitudinal section an ionization source, preferably combined with the filter according to the invention.

1 schematically shows a longitudinal section through a known deflection arrangement for a beam of charged particles, for example known from EP-A-0 223 520. The beam of positively charged ions 1, for example, enters a curved field space 3, formed between essentially equally curved ones Electrode surfaces 3a and 3b on electrode bodies 3a ', 3b'. As a result of the potential laying of the two electrode surfaces 3a and 3b, shown schematically with + and -, an electrostatic field E _{3 is} generated in the field space ₃ , essentially perpendicular to the dashed line of the beam S of charged ions 1. The field E ₃ shows the Ions are deflected through the curved field space 3 from their original entry direction.

Ions with greater kinetic energy experience less deflection in field E ₃ than ions with lower kinetic energy. In this way, essentially ions of a defined energy band pass through the curved field space 3, while higher-energy and lower-energy ions collide with one of the two electrode surfaces and are neutralized.

The electrode surface 3b on the outside of the curvature is continued at an acute angle after the exit region 5 from the field space 3 to the exit direction of the particle beam and forms with this extension electrode surface 7b of a further pair of electrode surfaces with 7a. A further electrostatic field E _{7 is} created between the pair of electrode surfaces 7a and 7b, essentially polarized inversely with respect to the field E ₃ , with which the ions are redirected back in the path shown schematically in dashed lines, possibly already to an outlet arrangement 4 shown in dashed lines 7 applies that the ions are deflected more or less according to their kinetic energy, so that only ions of a certain energy band hit the opening at the outlet arrangement 4 and leave the energy filter.

As shown in dashed lines at E ₃₇ , a well-known stray field is created in the field area 7 at the exit area 5 of the field space 3, whereby a superimposition of this stray field E ₃₇ and the primary field E ₇ prevailing there arises in this area with a resulting field that is both of E ₇ as well depends on E ₃ . If, as proposed in the known arrangement, a shield ring 9 is provided and, as proposed at the same time, is connected to the same potential as the electrode surfaces 3b and 7b, the result is the additional field E ₇₉ shown in FIG. 1, which depends on the field E ₇ and depending on the ion polarity exerts an accelerating or decelerating effect on the ions arriving in the field space 7 and thus falsifies their paths in the sense of poorer energy resolution or transmission.

With the subsequently described, according to the invention Arrangement according to the inventive method the field spaces correspond to 3 and 7 of FIG. 1 regarding the prevailing electrostatic Fields decoupled, with the above-mentioned interference effects to be avoided on the beam and due to the mutual Field isolation the electrostatic conditions in both field rooms independently of each other can be optimally adjusted.

Instead of the particle beam now leaving the curved field space 3, in the exit region 5, directly entering the further electrical field E ₇ applied between the further pair of electrodes, a shield 11 is provided according to the invention, which the beam S, as shown in dashed lines, on one Passes through slot 13. The potential of the screen 11 can initially be set as desired (dashed line at 6) if, by a suitable choice of the geometric arrangement of screen 11, electrodes 3a and 3b, the influence of the field between these three electrodes on the kinetic energy and deflection of the particles 1 between the exit zone 5 and passage slot 13 is minimized. This can be done, for example, by placing the potential of the screen 11 at an intermediate potential between the potential of the electrode 3a 'and that of the electrode 3b', which essentially compensates for the resulting fields between the electrodes 11 and 3a or 11 and 3b in the beam path region , as shown in E _11a , E _11b .

Preferably, and as shown in Fig. 2 at 6a, the screen 11 is placed on the potential of the outer electrode 3b '. By choosing the preferred entry angle α≈45 °, the influence of the electrostatic field E _11a between the screen 11 and the electrode body 3a 'is negligible due to the oblique passage of the space D through the beam.

The screen 11, as further shown in FIG. 2, is preferably used as an electrode of the pair 7a, 7b according to FIG. 1. As can be seen, there is no field influence between the fields E ₇ and E ₃ due to the provision of a screen 11 penetrated by the beam, even if combined with the electrode 7b for the essential structural simplification.

FIG. 3 schematically shows a first preferred embodiment of the arrangement shown in principle with reference to FIG. 2. Again, the same item numbers are used for the same structural parts. As can be seen from this, in this preferred embodiment the curvature outer electrode surface 3b or the body 3b 'defining it is continued away from the electrode surface 3a, and it surrounds - in one or more parts - this continuation 3d, in the sense of 3b' potentially identical parts, a cavity 15 which is traversed at an oblique angle by the beam between the exit region 5 and the passage slot 13. The interference field E _3a arises in accordance with the dimensions of the chamber 15 and the potential difference between the electrode surfaces 3b and 3a practically only in zones of the space 15 which are not traversed by the beam S, so that this interference field has hardly any influence on the beam deflection or the energy of its particles takes.

The cavity 15 is, in particular in its from Beam S traversed area, essentially field-free, because of walls at the same potential edged. The one opposite the exit area 5 Wall section which borders the space 15, in turn forms the electrode surface 7b of the another pair of electrode surfaces 7a, 7b, where between the beam, following the principle of reflection, is redirected becomes. Because of the field-free space, which the beam after leaving the curved field space 3 the influence of between Screen 11 and that forming the electrode surface 3a Body 3a 'minimized interference field, and in particular, by appropriate training of Electrode pair 3a ', 3b' and its field application and, if necessary, by providing more ion-optical Means, or preferably an aperture 15a, the Beam path in field-free room 15 before entry optimized in the field space 7, for example focused, become. Through the aperture 15a are outer Hidden parts of the beam. All without that further fields would have to be taken into account. Furthermore, for ion-optical reasons, the smallest diameter dimension of the slot 13 at most equal to the wall thickness d of the screen 11 selected.

4 is a preferred embodiment of the inventive Energy filter shown in the constructed essentially symmetrically to a plane E. is and in mirror image two of the with reference to FIG. 2 or 3 arrangements shown. There are again the same for the same components or sizes Position symbol used.

Based on the explanations, in particular with respect to FIG. 3, the structure and mode of operation of the preferred arrangement according to FIG. 4 are readily apparent. In turn, deflection fields E ₃ and field E ₇ for deflecting positive ions are entered. As can be seen, this arrangement allows the entry axis A _E and the exit axis A _{A to be} aligned on the filter according to the invention by corresponding arrangement of the two curved field spaces 3 on the input and output sides, which, for the time being also without rotationally symmetrical design, creates the possibility of an analyzer with a downstream mass spectrometer , in particular a quadrupole mass spectrometer and possibly an upstream ionization source, in the common entry / exit axis A _EA . As shown in dashed lines at 8 in FIG. 4, the screen sections 11 can, if appropriate, be put together or separately, each at different potentials with respect to part 3b '. Of course, this requires electrical insulation of the parts mentioned.

5, again schematically, shows a known beam deflection arrangement in accordance with EP-A-0 223 520 with the aspect of the further object to be achieved. Again, the same reference numerals are used for the same sizes or components. As can be seen, the inlet arrangement with curved field spaces 3, inner electrode surfaces 3a and outer electrode surfaces 3b and the electrode pairs 7a and 7b is cylindrical with a cylinder axis A _Z. The incoming beam S is split at a sharp tip P of an inner cylinder body 3b ', which forms the electrode surfaces 3b and 7b and is mounted on a retaining web 17 in the field space 7. The beam path S is mirror-symmetrical to the cylinder axis A _Z , in that the incoming beam S, as mentioned, is divided at the tip P - a kind of singularity - and passes through electrode pairs formed in mirror image with respect to the axis A _Z or field fields therebetween. Because of the tip P, ions entering the axis A _Z cannot pass through the arrangement. This also applies to ions that enter close to the axis A _Z. Ions that can just pass the tip P have unfavorable entry parameters with respect to the cylinder mirror in space 7.

It has now been further recognized that the singularity or peak at P on the input side, ie any beam splitting, has an extremely disadvantageous effect on the beam divergence and controllability. An advantage of this known arrangement, however, is that there are essentially aligned entry and exit axes, the entry and exit _axes lying essentially also in the cylinder axis A _Z because of the symmetrical beam guidance.

In Fig. 6, an energy filter arrangement according to the invention is again shown schematically, in which on the one hand with mirror-image formation on the input and output sides, for example to plane E, input axis A _E and exit axis A _A , as shown, in the cylinder axis A _{Z of} the cylindrical filter may lie, but a beam splitting is avoided. Again, the same reference numbers are used. According to the previous explanations, FIG. 6 readily shows the arrangement in which the outer edge of the filter, essentially given by the outer electrode surfaces 7a, is cylindrical to the axis A _Z , but not within the cylinder the beam path of the beam S. This can now be inserted axially and correspondingly axially omitted again with a symmetrical design, but only one beam path is provided, the beam is not divided. It has been shown that the behavior of the filter with only one beam path provided asymmetrically to the cylinder axis A _{Z has} no disadvantages compared to a symmetrical beam path, but the advantage of none of the singularities that perform beam splitting. Instead of supporting parts of the inlet or outlet by means of webs 17 which disrupt the beam transmission, instead of supporting parts of the inlet or outlet, as shown in FIG. 6, the support of cylinder-central parts in a cylinder part not used for the beam path, as shown at 17a , will be realized.

However, as can now be seen from FIG. 6, the cross-sectional dimension of the filter, given by the outer cylinder 7a ', is poorly used in this configuration, in which the coaxiality of the filter structure, beam feed and path guidance can be realized. This is improved in the preferred embodiment, as shown in FIG. 7. In addition, the design according to FIG. 7 is much simpler in terms of production technology. It was assumed that holding onto a beam in and out of alignment with the cylinder axis A _Z brings only minor advantages for the compilation of an analyzer system and these advantages are practically retained if the input axis A _E and the exit axis A _{A are in} alignment, the cross-sectional expansion is better utilized and significant advantages are obtained in terms of production technology.

As can now be seen from FIG. 7, in which the same parts and sizes are identified in the same way and which shows a construction variant symmetrical to the plane E in a preferred manner, the jet inlet and jet outlet are axially aligned, but offset in such a way with respect to the cylinder axis A ' _Z that if the inlet and outlet are provided in a cross-sectional quadrant Q ₁ , the field space 7, in which the beam is deflected back in a mirror-reflecting manner, is arranged in the quadrant Q ₂ opposite to the axis A ' _Z. The axis A ' _Z is shifted with respect to the axes A _E and A _A , as shown at A' _Z in FIG. 6.

FIG. 8 schematically shows a cross-sectional illustration along line IIX-IIX of FIG. 7, the two bodies defining the electrode surfaces 3a and 3b again being designated 3a ′ and 3b ′ and, in dash-dot lines, the quadrants Q ₁ , Q _{2 are} entered. Here, the insulation 9 between the parts 3a ', 3b' is visible, as is of course provided in some way in all the design variants according to FIGS. 2 to 4, 6 to 7. As can be seen from FIGS. 7 and 8, the cross-sectional dimension of the filter is better utilized.

In Fig. 9 the essential elements are preferred Energy filter according to the present invention shown in longitudinal section, an inventive Filter, which one Providing one Between the following field spaces and Utilization of the cylinder mirroring without beam splitting, taking advantage of the cross-sectional extent of the mirror cylinder, are realized according to a Combination of the arrangements according to FIGS. 4 and 7. Again, to facilitate cross-comparisons chosen the same reference numerals.

Along an entrance axis A _e of beam S in the curved field space 3 occurs, is formed between an electrode surface 3a and an electrode surface 3b, the former in a rotationally symmetrical to a cylinder axis A _Z endcap portion 3a ', the latter in a rotationally symmetrical to the axis A _Z hollow cylinder portion 3b' . The above-mentioned manufacturing advantage compared to the embodiment according to FIG. 6 can be seen: The electrode bodies 3a ', 3b' are rotating bodies. The two parts 3a 'and 3b' that define the field space 3 are, as shown at 20, electrically insulated, corresponding to 9 of FIG. 8. The exit direction for the beam S from the curved field space 3 in the exit region 5 is A _E and / or A _Z approx. 45 °. The hollow cylinder 3b 'forms the essentially field-free spaces 15 and has the passage slots 13 for the deflected beam S. With respect to the hollow cylinder 3b ', as shown at 22, electrically insulated, the mirror cylinder 7a' is provided, which forms the electrode surface 7a as a cylindrical capacitor surface with respect to the electrode surface 7b on the hollow cylinder 3b '.

The beam outlet, again with a curved field space 3, is constructed symmetrically with respect to the beam inlet, the beam exit axis A _{A is} aligned with the beam entry axis A _E , and both axes are offset with respect to the axis of rotation A _{Z of} the cylindrical arrangement. For the deflection and therefore energy filtering of positive ions, the potential differences applied are entered, for example, as shown schematically in U ₁ and U ₂ with adjustable voltage sources. For example, both parts 3a 'are connected to the same potential, which is not mandatory. In this regard, the hollow cylinder 3b 'is placed at a positive potential, which according to the invention forms shield 11, field-free space 15 and electrode of field space 7. The outer electrode 7a, corresponding to the hollow cylinder 7a ', is set to a positive potential with respect to the hollow cylinder 3b'. A mass spectrometer, preferably a quadrupole mass spectrometer 24, is preferably connected downstream of the energy filter, as shown, to form an analyzer according to the invention. If neutral particles are to be analyzed on the analyzer, an ionization source, preferably an electron impact ionization source 26, is connected upstream of the energy filter. A beam diaphragm 15 is preferably provided in a field-free space 15. In this space, the beam is preferably focused on the cylinder axis A 'Z, and the diaphragm 15a suppresses edge regions and scattered ions of the beam. At focus F there is a crossover of the ion beam, ie a crossover of the ion trajectories.

Of course, like the person skilled in the art familiar, the aggregates shown on vacuum operated, and the parts to be analyzed for example withdrawn from a plasma, charged particles electrostatic, neutral by diffusion in the Ionization source 26, for ionization.

An ionization source is shown in FIG. 10, which is preferably used with the energy filter shown. Through an aperture 30 with an opening 32, neutral particles are withdrawn from the plasma by diffusion and enter an axially extended cylinder grid 34. Radially located outside the grid 34, at least one electron emitter, preferably in the form of at least one hot cathode 36, is provided, preferably a plurality of hot cathodes 36 are arranged azimuthally around the grid 34. As shown at U ₃ , the electron emitter cathodes 36 are set to a negative potential with respect to the grating 34, which means that the grating 34 acts as an acceleration grating for the emitted electrons e ^- . The heating current at the electron emitter cathodes 36 is set at current sources I. The ions generated within the grid 34 by electron impact emerge through a further aperture 38 with a controllable potential corresponding to U ₄ . The potential of the aperture 38 is preferably chosen to be at least substantially equal to that of the grid 34. Because of the axially extended lattice arrangement and the provided, preferably several and identical electron emitters outside the lattice, neutral particles within the lattice are homogeneously ionized with a high ionization rate. The axial extension L of the electron current is preferably chosen to be L> = 1.5 Ø, preferably L> = 3 Ø, where Ø denotes the grid diameter.

As has been mentioned, the ionization source 10 preferably with the inventive energy filter according to the preceding Figures, especially Fig. 9, combined to with a mass spectrometer connected downstream of the latter, preferably quadrupole mass spectrometer, to form a neutral particle analyzer.

Claims (27)

1. Process for filtering electrically charged particles of a particle beam according to their kinetic energy in which the beam is deflected by a first electrostatic field (E₇) between a pair of first condenser electrode surfaces (7a, 7b) of a first condenser electrode pair in a first chamber area (7) and deflected in opposition in a second chamber area (3), connected before and/or after the first chamber area (7) in the direction of beam propagation, by a second electrical field (E₃) between a pair of second condenser electrode surfaces (3a, 3b) of a second condenser electrode pair (3a', 3b'), and the first chamber area (7) is screened from the second (3) against electrical fields (E) by means of screen (11) which is laid to the electrical potential of one of the first condenser electrode surfaces (7b) and which (11) has a first surface facing the first chamber area (7) and a second surface facing the second chamber area (3), characterised in that

   the one of the first condenser electrode surfaces (7b) is formed by the first surface of the screen (11) penetrated by the beam (13);

   by means of the second surface of the screen (11) and one surface of one of the condenser electrodes (3b') of the second condenser electrode pair (3a', 3b'), a further condenser electrode surface pair is formed with a third chamber area (D) through which passes the beam (S) and which connects the first (7) and the second (3) chamber areas;

   the screen (11) is laid to a given electrostatic potential (6, 6a).
2. Process according to claim 1, characterised in that the screen (11) is laid to the electrical potential of the one (3b') of the second condenser electrode pairs (3a', 3b') and hence the third chamber area (D) formed field-free.
3. Process according to any of claims 1 or 2, characterised in that the second chamber area (3) is generated between two essentially equally curved second condenser electrode surfaces (3a, 3b) and the screen (11) is formed by continuing the condenser electrode (3b') forming the outside of the curve of the condenser electrode surfaces (3b).
4. Process according to any of claims 1 to 3, characterised in that the beam (S) enters the first or second chamber area (3, 7) and emerges from the second or the first accordingly, where the deflections occur so that the inlet and outlet are essentially parallel to each other.
5. Process according to any of claims 1 to 4, characterised in that two second chamber areas (3) are provided each with a second condenser electrode pair which forms the second condenser electrode surfaces, the beam (S) enters and emerges from one of the two second chamber areas (3), where the deflections occur so that the inlet and outlet directions are essentially aligned.
6. Energy filter to filter electrically charged particles of a particle beam according to their kinetic energy with a beam inlet and an outlet arrangement and at least two condenser electrode pairs (3a, 3b; 7a, 7b) which are arranged one behind the other, extending essentially in the beam passage direction between inlet and outlet, and which each generate an electrical field (E₃, E₇) inversely polarised relative to each other and essentially vertical to the beam propagation direction, where

   a first (7a, 7b) of the condenser electrode pairs forms a pair of first condenser electrode surfaces between which is defined a first (7) chamber area;

   a second (3a', 3b') of the condenser electrode pairs forms a pair of second condenser electrode surfaces (3a, 3b) between which is defined a second chamber area (3),

   furthermore with an electrical screen (11) between the chamber areas (3, 7) which has a first surface facing the first chamber area (7) and a second surface facing the second chamber area (3), where also the screen (11) is laid to the potential of one of the first condenser electrodes (7b), characterised in that

   the one of the first condenser electrode surfaces (7b) is formed by the first surface of the screen (11) which has a passage opening (13) for the beam (S);

   the second surface of the screen (11), in the area of the passage opening (13), forms with a surface of one of the second condenser electrodes (3b') a third condenser electrode surface pair and between this a third chamber area (D) which connects the first and second chamber areas;

   the screen (11) is laid to a given potential (6, 6a).
7. Energy filter according to claim 6, characterised in that the screen (11) is laid to the potential of the one (3b') of the second condenser electrodes (3a', 3b').
8. Energy filter according to any of claims 6 or 7, characterised in that the second condenser electrode surface pair (3a, 3b) defines between its electrode surfaces a curved second chamber area (3) and the condenser electrode (3b') forming the outside curve surface (3b) with a continuation forms the screen (11).
9. Energy filter according to any of claims 6 to 8, characterised in that the third chamber area (D, 15) is essentially field-free with boundary laid to equipotential, where the boundary of the third chamber area (D, 15) is preferably formed by a continuation of the one (3b') of the second condenser electrodes (3a', 3b').
10. Energy filter according to claim 9, characterised in that provided in the third chamber area (D, 15) is at least one diaphragm (15a).
11. Energy filter according to any of claims 6 to 10, characterised in that the beam inlet and outlet are essentially parallel to each other.
12. Energy filter according to any of claims 6 to 11, characterised in that two of the first and two of the second condenser electrode pairs are provided.
13. Energy filter according to claim 12, characterised in that the middle two condenser electrode pairs are first condenser electrode pairs and preferably structurally connected (7a, 7b).
14. Energy filter according to any of claims 12 or 13, characterised in that the two outer condenser electrode pairs are second condenser electrode pairs (3a', 3b') and each define a curved second chamber area (3) curved in the same direction and each of the two condenser electrodes (3b') of the pair which are laid on the outside of the curve has a continuation forming the screen (11).
15. Energy filter according to claim 14, characterised in that the two condenser electrodes (3b') on the outside of the curve are structurally connected.
16. Energy filter according to claim 15, characterised in that the two continuations (11) are structurally connected.
17. Energy filter according to any of claims 6 to 16, characterised in that the wall thickness (d) of the screen (11) is at least equal to the smallest diameter extension of the passage opening (13).
18. Energy filter according to any of claims 14 to 17, characterised in that the two outer condenser electrode pairs (3a, 3b) define essentially parallel inlet tangents or outlet tangents for the beam and preferably these tangents are aligned.
19. Energy filter according to any of claims 6 to 18, characterised in that it is constructed on the principle of the cylinder mirror in a cylinder condenser with inlet and outlet devices for the beam to the cylinder condenser, where the inlet and outlet axes (A_E, A_A) are arranged essentially aligned and the beam inlet (S) is asymmetrical in relation to the cylinder axis (A_Z) of the cylinder condenser.
20. Energy filter according to claim 19, characterised in that the inlet and outlet axes (A_E, A_A) are offset parallel to the axis (A_Z) of the cylinder condenser.
21. Energy filter according to any of claims 19 or 20, characterised in that the cylinder condenser (7a, 7b) is formed by the two central electrode pairs, the inlet and outlet arrangements (3a, 3b) by the outer pairs according to any of claims 11 to 18.
22. Energy filter according to any of claims 19 to 21, characterised in that the cylinder condenser (7a, 7b) has an outer cylinder (7a) and acts in a cross-section quadrant as a mirror condenser, and inlet and outlet arrangements (3a, 3b) are provided in the quadrant of the cylinder condenser cross-section area lying axially symmetrically opposite the said quadrant.
23. Energy filter according to any of claims 19 to 22, characterised in that the beam is focussed on the axis of the cylinder condenser.
24. Analyser, preferably plasma analyser, with an energy filter according to at least one of claims 6 to 23 and a mass filter connected after the energy filter, preferably a quadrupole mass analyser.
25. Analyser according to claim 24, characterised in that it has an electron bombardment ionisation source connected before the energy filter with inlet opening arrangement for neutral particles and an outlet arrangement for ions, and that coaxial to the transmission axis defined between the inlet and outlet arrangement is an axially extended acceleration grid tube and radially outside at least one hot cathode.
26. Analyser according to claim 25, characterised in that radially outside the axially extended acceleration grid, preferably distributed regularly, are several hot cathodes.
27. Analyser according to any of claims 25 or 26, characterised in that the ratio of the length of the electron incident area on the grid tube to its diameter is at least 1.5, preferably 3, preferably greater than 3.

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