EP1760760A2 - x-ray or XUV generation unit - Google Patents

Abstract

A particle source (10) directs a particle jet (12) of electrically charged particles towards a target (16). A deflecting system (26) diverts the central axis of the particle jet to a deflection point (20). Another deflecting system (32) diverts the central axis of the particle jet to another deflection point (22). The deflecting systems are arranged such that the deflection points are provided before the point of impact (24) on the target.

Description

The invention relates to a device referred to in the preamble of claim 1 for generating X-ray or XUV radiation.

Such devices are for generating x-rays, for example in the form of x-ray tubes US 3,793,549 and GB 1 057 284 and for generating XUV radiation, for example by WO 2004/023512 A1 . US 3,138,729 . EP 0 887 639 A1 and US 4,523,327 known. By XUV (extreme ultraviolet) radiation is understood here radiation in a wavelength range between about 0.25 and about 20 nm. The known devices are used in particular in imaging processes, for example in the investigation of electronic components, in particular printed circuit boards, as well as for the control and adjustment of optical components.

The known devices comprise means for directing a particle beam of electrically charged particles onto a target, wherein the material of the target is selected according to the desired wavelength of the emitted radiation.

A disadvantage of the known devices is that a deviation of the impingement point of the particle beam on the target from a predetermined impact point to a deterioration of the image quality the images generated by irradiation of components and in measurement and adjustment functions and adjustment tasks leads to measurement errors.

The invention has for its object to provide a device referred to in the preamble of claim 1, are reduced in the deviations of the impact point of the particle beam on the target of a given impingement point, the positional stability of the particle beam is thus improved with respect to its impact on the target.

This object is achieved by the teaching defined in claim 1.

The basic idea of the teaching according to the invention is to provide deflection means for deflecting the particle beam, by which the particle beam is deflected such that its central axis passes through a first and a second deflection point, wherein the first and the second deflection point in axis with a predetermined or predeterminable impact point of the particle beam are on the target and wherein the particle beam is deflectable by the deflection means with respect to a deflection point independent of a deflection with respect to the other deflection point.

Characterized in that according to the invention the particle beam always passes through the first and the second deflection point and these deflection points are in axis with the desired point of impingement of the particle beam on the target, a high local stability is achieved with respect to the impact point of the particle beam on the target. Essential to the invention here is that the particle beam under the action of the deflection means extends through at least two deflection points, which lie in axis with the desired point of impingement of the particle beam on the target. In other words, through the Independent deflection or deflectability of the particle beam with respect to two deflected in the beam direction spaced deflection points, which are in axis with the desired impact point of the particle beam on the target, ensures that the central axis of the particle beam is coincident with an imaginary line on which the first and the second deflection point as well as the desired impact point lie on the target.

The central axis of the particle beam may be, for example and in particular, coincident with a central axis of the device according to the invention, for example an X-ray tube.

According to the invention, it is basically sufficient if the deflection means are designed for an independent deflection of the particle beam with respect to the first deflection point and the second deflection point spaced apart in the beam direction from the first deflection point. In order to avoid undesirable deflection of the particle beam after passing through the second deflection point, it is also possible according to the invention to deflect the particle beam through the deflection means such that it is arranged not only by the first and second deflection point but in the beam direction behind the second deflection point Deflection points runs, with all the deflection points are then in axis with the desired point of impingement of the particle beam on the target.

This is particularly advantageous if there is a greater distance between the second deflection point and the target. For example, and in particular, the deflection of the particle beam with respect to the first and the second deflection point by a first and a second deflection unit, it is according to the invention possible to provide in addition to these deflection units further deflection units, which are then arranged downstream in the beam direction of the second deflection unit.

In this case, the central axis of the particle beam is understood to mean an axis passing through the geometric center of the beam cross section of the particle beam.

In principle, it is sufficient according to the invention for the deflection means to have a single deflection unit, provided that an independent deflection of the particle beam with respect to the first deflection point and the second deflection point spaced apart in the beam direction from the first deflection point is made possible. An advantageous development of the teaching according to the invention provides that the deflection means comprises a first deflection unit for deflecting the particle beam such that its central axis passes through the first deflection point, and a second deflection unit spaced from the first deflection unit in the beam direction of the particle beam for deflecting the particle beam its central axis passes through the second deflection point. Since the deflection units can be constructed essentially identical, the structural complexity of a device according to the invention is kept low in this way.

For controlling the deflection means or the deflection units control means are expediently provided.

Another development of the embodiment with the deflection units provides that the first deflection unit and the second deflection unit can be controlled by the control means independently of each other for mutually independent deflection of the particle beam with respect to the first deflection point and the second deflection point. In this way, the particle beam can be deflected with particularly high precision.

In the embodiments with the deflection units, each of the deflection units expediently has at least one deflection element. Depending on the respective requirements, more than one deflection element can also be provided per deflection unit.

Shape, size, number and design of the deflector can be selected within wide limits. An advantageous development provides insofar as the deflection element has at least one coil or coil arrangement, in particular a quadrupole. Such coils are available as simple and inexpensive standard components available and allow by selecting a corresponding Ablenkstromes a precise deflection of the particle beam.

Another development of the teaching according to the invention provides that the deflection element has at least one electrostatic deflection plate.

Another advantageous development of the teaching according to the invention provides that the deflection means are designed to deflect the particle beam in the direction of two mutually perpendicular axes. If the central axis of the particle beam runs, for example, in the Z direction, then, in this embodiment, the deflection means are designed, for example, for deflecting the particle beam along the X and Y directions.

Another advantageous development of the teaching according to the invention provides that at least one of the deflection units is associated with a diaphragm which is arranged in the beam direction behind the deflection of the deflection unit. The aperture can be used here, for example, and in particular to one from the Measuring the particle beam incident on the diaphragm electric current and to control the deflection of the particle beam in response to the measured current, as will be explained in more detail below.

A development of the aforementioned embodiment provides that the first deflection unit is assigned a first diaphragm and that the first diaphragm is assigned in the beam direction in the region of a plane of action of a deflection element of the second deflection unit. In this way, with regard to the deflection of the particle beam in the beam direction in the region of the second deflection point particularly favorable conditions.

Another embodiment of the embodiments with the diaphragm provides that the second deflection unit is associated with a second diaphragm. The second diaphragm assigned to the second deflection unit can correspond in function to the first diaphragm assigned to the first deflection unit.

An extraordinarily advantageous development of the teaching according to the invention provides that at least one diaphragm is at least partially made of an electrically conductive material and that the diaphragm is associated with a measuring unit for measuring an electric current resulting from an impingement of the particle beam on the diaphragm. In this embodiment, an electric current is measured by means of the measuring unit, which flows when the particle beam impinges on the diaphragm or an electrically conductive part of the diaphragm. If the particle beam traverses the aperture of the diaphragm without electrically charged particles hitting the diaphragm, then ideally no current flows, while in the case of the complete diaphragm Impact of the particle beam on the aperture a relatively high current flows. The measured current is thus a measure of the deviation of the central axis of the particle beam from the desired position. If, for example, it is ascertained from the measuring unit that the particle beam impinges completely on the diaphragm, then the deflection unit assigned to the diaphragm can be controlled such that the particle beam no longer impinges on the diaphragm, but instead passes through the diaphragm aperture of the diaphragm. At small deflection angles of the particle beam, there is a proportionality between the deflection current and the deflection path of the particle beam.

In this sense, an advantageous development of the teaching according to the invention provides that the measuring unit is in communication with the control means for controlling the deflection means, such that the deflection of the particle beam is effected in dependence on a current measured by the measuring means.

Another advantageous development of the teaching of the invention provides that a counter to the target is associated with a measuring unit which measures in a first mode of operation an electric current, which results from the impact of the particle beam on the surface facing away from the target of the diaphragm, and in In a second mode of operation, measuring an electric current resulting from backscattered electrically charged particles from the target. In this embodiment, the output signal of the measuring unit in its first operating mode can be used, for example, to determine a deflection current for driving the associated deflection unit in order to deflect the particle beam so that it passes through the desired Deflection point runs. In the second mode of operation, on the other hand, the current measured by the measuring unit can be used to control or regulate the target current of the target of the device by driving a particle beam generating particle source.

For this purpose, an advantageous development of the aforementioned embodiment provides that the measuring unit is connected to control and / or regulating means which control the target current by controlling a particle source for generating the particle beam in response to a measured by the measuring unit in the second operating mode current or regulate.

In order to achieve a desired focus diameter of the focus of the particle beam on the target, another advantageous development of the teaching according to the invention provides focusing means for focusing the particle beam onto the target.

In the aforementioned embodiment, the focusing means are expediently arranged downstream of the deflection means in the jet direction. In this embodiment, the particle beam is first deflected to the desired position, in which its central axis passes through the first and second deflection points and impinges on the target at the desired point of impact. Subsequently, the electron beam is focused by means of the focusing means to achieve a desired focus diameter on the target.

The invention will be explained in more detail with reference to the attached highly schematic drawing, in which an embodiment of a device according to the invention is shown. All the features described or illustrated in the drawing alone or in any combination form the subject matter of the invention, regardless of their summary in the claims or their dependency and regardless of their formulation or representation in the description or in the drawing.

Fig. 1

eine stark schematisierte Schnittansicht eines ersten Ausführungsbeispieles einer erfindungsgemäßen Vorrichtung,

Fig. 2

in gleicher Darstellung wie Fig. 1 eine ähnliche Ansicht der Vorrichtung gemäß Fig. 1 zur Verdeutlichung der Funktionsweise und

Fig. 3

eine schematisierte Ansicht einer in der Vorrichtung gemäß Fig. 1 verwendeten Blende.

It shows:

Fig. 1

a highly schematic sectional view of a first embodiment of a device according to the invention,

Fig. 2

in the same representation as Fig. 1 is a similar view of the apparatus of FIG. 1 to illustrate the operation and

Fig. 3

a schematic view of a shutter used in the apparatus of FIG. 1.

In Fig. 1, an embodiment of a device 2 according to the invention is shown, which serves in this embodiment for the generation of XUV radiation. The device 2 is constructed in the manner of an X-ray tube and has a housing 4, whose interior 6 is formed as a vacuum chamber and can be evacuated via an opening 8 by means of a vacuum pump, not shown.

In the interior of the vacuum chamber 6, a particle source 10 for generating a particle beam of electrically charged particles is arranged, wherein the electrically charged particles are formed in this embodiment by electrons emerging from a cathode. The electrons are accelerated to form a particle beam 12 by means of a ring anode 14 in the direction of a target 16 formed as a layer target in this exemplary embodiment. When hitting the target 16, the electrons forming the particle beam 12 are decelerated, resulting in bremsstrahlung whose spectrum depends on the energy of the particles and the chemical nature (atomic number) of the material of the target 16. In the embodiment shown in Fig. 1, the material of the target 16 is selected so that radiation is generated which contains a usable proportion in the XUV spectral range.

The apparatus 2 according to the invention comprises means for deflecting the particle beam 12 such that the symbolized in Fig. 1 by a dashed line 18 central axis of the particle beam 12 through a first deflection point 20 and in the beam direction behind the first deflection point 20 and spaced therefrom arranged second Deflection point 22 extends, wherein the first deflection point 20 and the second deflection point 22 are in axis with a predetermined impingement point 24 of the particle beam 12 on the target 16 and wherein the particle beam 12 by the deflection means in the beam direction with respect to the first deflection point 20 regardless of a deflection of the particle beam 12 with respect to the second deflection point 22 is deflected.

The deflection means in this embodiment comprise a first deflection unit 26 which has a deflection element 28, which in this embodiment is formed by a coil arrangement in the form of a quadrupole. In this exemplary embodiment, the first deflecting unit 26 is assigned a first aperture 30, which is spaced apart in the direction of the beam from the deflecting element 28 and arranged behind it. The first diaphragm 30 has a diaphragm opening with a circular cross-section, wherein the first deflection point 20 lies in the center of the diaphragm opening.

The deflection means further comprises a second deflection unit 32 having a deflection element 34, which in this embodiment is formed by a coil arrangement in the form of a quadrupole. In this exemplary embodiment, the second deflection unit 32 is assigned a second diaphragm 36, which is arranged behind the deflection element 34 of the second deflection unit 32 in the beam direction. The second aperture 36 has in this embodiment, a circular aperture, wherein the second. Deflection point 22 is located in the center of the aperture.

The device 2 further comprises control means 38, which in a manner explained in more detail below for driving the deflection elements 28, 34 with a deflection current and for driving a high voltage generator 40 and the particle source 10 is used. The first deflection unit 26 and the second deflection unit 32 are independently controllable by the control means 38 for mutually independent deflection of the particle beam 12 with respect to the first deflection point 20 and the second deflection point 22.

The deflection units 26, 32 are formed in this embodiment for deflecting the particle beam 12 transversely to its central axis 18 along mutually perpendicular axes, namely for deflecting the propagating in the Z direction particle beam 12 in the X and Y directions.

As can be seen from FIG. 1, in this embodiment the first diaphragm 30 is arranged in the beam direction approximately at the level of the deflection element 34 of the second deflection unit 32. The first diaphragm 30, which in this embodiment consists of an electrically conductive material, is associated with a first measuring unit 42 for measuring an electric current, which originates from an impingement of the particle beam 12 on the first diaphragm 30. The output of the first measuring unit 42 is connected to the control means 38.

In this way, the second diaphragm 36, which is opposite to the target 16, also made of an electrically conductive material, wherein it is associated with a second measuring unit 44. In a first operating mode, the second measuring unit 44 measures an electrical current which originates from the impingement of the particle beam 12 on the surface of the diaphragm 36 facing away from the target 16. In a second mode of operation, the second measuring unit 44 measures an electrical current resulting from backscattered electrically charged particles from the target 16. The backscattering of electrically charged particles from the target 16 is indicated in FIG. 1 by arrows 46.

For focusing the particle beam 12, the device 2 has focusing means, which are formed in this embodiment by an electromagnetic lens 48, which is arranged downstream in the beam direction of the second deflection unit 32 in this embodiment.

XUV radiation generated by the impact of the electrically charged particles on the target 16 exits the housing 4 through an exit window 49 formed laterally in the housing 4, as indicated at reference numeral 50. For spectral filtering of the XUV radiation, a filter 52 can be arranged in the exit window 4.

In order to prevent backscattered electrons from the target 16 impinging on the exit window 48 and this statically charging, the exit window 49 is surrounded by a trap ring 54 which on a positive potential and captures the flying in the direction of the exit window 40 backscattered electrons. The trapping ring 54 is for this reason connected to the positive pole of a voltage source 56 whose negative pole is connected to the housing 4 and to ground.

The operation of the device according to the invention is as follows.

During operation of the device 2, electrons exit from the particle source 10 and are accelerated via the ring anode 14 in the direction of the target 16, the central axis 18 of the particle beam 12 passing through the first deflection point 20 and the second deflection point 22. Since the deflection points 20, 22 lie in axis with the predetermined impingement point 24 of the particle beam 12 on the target 16, the electrons impinge on the target 16 at this point of incidence 24, whereby XUV radiation is generated, which is emitted through the exit window 49 from the device 2 exit.

FIG. 2 illustrates an operating state of the device 2 in which a disturbance has occurred with respect to the direction of the particle beam 12. Such interference may be, for example, that a filament tip of the particle source 10 is inclined, an external magnetic field acts or a thermal expansion is effective. In this case, the particle beam 12 passes obliquely through the anode hole of the annular anode 14. In this context, it should be mentioned that, for example, when using a Wehnelt cylinder surrounding the filament tip, the electrons undergo a first bundling (first crossover) in the beam direction approximately in the plane of the annular anode 14, as indicated at 58 in FIG. After the first crossover, the electrons diverge due to different Mechanisms of action, for example, due to the Boersch effect, which describes the repulsive forces of the same name charged electrons apart. Since the high voltage applied to the ring anode 14 is no longer effective after the electrons have left the plane of the ring anode 14, the electrons then continue to fly in the direction they left after leaving the crossover.

The electrons would therefore, as shown hatched in Fig. 2 at the reference numeral 60, impinge on the first aperture 30 and thus not reach the target 16.

Due to the impact of the electrons on the first diaphragm 30, the first measuring unit 42 measures a current and supplies the control means 38 with a corresponding signal.

The control means 38 then control the deflection element 28 of the first deflection unit 20 with a deflection current. The plane of action of the first deflection unit 26 is symbolized in FIG. 2 by a dashed line 62. The control means 38 in this case select the deflection current so that the particle beam 12 is deflected so that its central axis 18 passes through the first deflection point 20. The resulting direction of the particle steel 12 is indicated in Fig. 2 at reference numeral 62.

The determination of the deflection current for the deflection element 26, which is required to deflect the particle beam 12 through the first deflection point 20, will be explained in more detail below with reference to FIG. 3.

The deflection element 26 is formed in this embodiment by a quadrupole, which consists of four arranged in the square electromagnetic coils and through which the electron beam in X- as well as in Y direction is deflectable. When the electron beam passes through the aperture hole of the first aperture 30 and passes through the first deflection point 20, the current measured by the first measuring unit 42 is zero. A current is measured by the measuring unit 42 only when the particle beam 12 impinges on the diaphragm. In this case, the control means 38 control the deflector 28 so that the particle beam 12 is sequentially moved to the positions indicated by reference numerals 64, 66, 68, 70 in FIG. For example only, these positions 64, 66, 68, 70 are selected so that approximately half the cross-sectional area of the particle beam 12 impinges on the first aperture 30, so that the current measured by the first measuring unit 42 corresponds to about half of the maximum current, then is measured when the particle beam 12 completely impinges on the first diaphragm 30.

$${\mathrm{I}}_{\mathrm{Xm}}\mathrm{=}\left({\mathrm{I}}_2\mathrm{+}{\mathrm{I}}_4\right)\mathrm{/}\mathrm{2}$$

With the resulting small deflection angles of the central axis 18 of the particle beam 12, there is a proportionality between the deflection currents and the deflection path of the particle beam 12. Because of this proportionality, the deflection currents in the X and Y directions, which are required to deflect the particle beam 12 so in that its central axis 18 passes through the center of the first diaphragm 30 and thus through the first deflection point 20, as follows: $${\mathrm{I}}_{\mathrm{Ym}}\mathrm{=}\left({\mathrm{I}}_{\mathrm{1}}\mathrm{+}{\mathrm{I}}_3\right)\mathrm{/}\mathrm{2}$$

$${\mathrm{I}}_{\mathrm{xm}}\mathrm{=}\left({\mathrm{I}}_2\mathrm{+}{\mathrm{I}}_4\right)\mathrm{/}\mathrm{2}$$

• I₁: Ablenkstrom in Position 64 des Teilchenstrahles 12
• I₂: Ablenkstrom in Position 66 des Teilchenstrahles 12
• I₃: Ablenkstrom in Position 68 des Teilchenstrahles 12
• I₄: Ablenkstrom in Position 70 des Teilchenstrahles 12
• I_Ym: Ablenkstrom für die Positionierung des Teilchenstrahles 12 im Zentrum des Blendenloches in Y-Richtung
• I_Xm: Ablenkstrom für die Positionierung des Teilchenstrahles 12 im Zentrum des Blendenloches in X-Richtung

Here are:

• I ₁ : deflection current in position 64 of the particle beam 12
• I ₂ : deflection current in position 66 of the particle beam 12
• I ₃ : deflection current in position 68 of the particle beam 12
• I ₄ : deflection current in position 70 of the particle beam 12
• I _Ym : deflection current for the positioning of the particle beam 12 in the center of the aperture hole in the Y direction
• I _Xm : deflection current for the positioning of the particle beam 12 in the center of the aperture hole in the X direction

If the required deflection currents are determined in this way, the control means 38 control the coils of the deflection element 28 with these deflection currents, so that the central axis 18 of the electron beam 12 then passes through the center of the aperture stop of the first aperture 30 and thus through the first deflection point 20 , In this case, the particle beam 12 remains divergent, since the first deflection unit 26 has no focusing effect, but causes only a lateral deflection of the particle beam 12.

After the deflection thus effected, the particle beam would propagate in accordance with the profile 74 shown hatched in FIG. 2 and hit, for example, the second diaphragm 36 and a lateral wall of the vacuum chamber 6, so that it would not reach the target 16.

In order to divert the particle beam 12 so that its central axis passes through the center of the second aperture 36 and thus through the second deflection point 22, the current is first measured by the second measuring unit 44, the current when the particle beam 12 on the second panel 36 is formed. Thereafter, in the manner described above with respect to deflection by the first deflector 26, the control means 38 detects the currents required to deflect the particle beam 12 in the x and y directions and drives the deflector 34 of the second deflector 32 with these currents. Due to this, the particle beam 12 is deflected to pass through the second deflection point 22. The plane of action of the second deflection unit 32 is designated in FIG. 2 by reference numeral 72.

Since, after the deflections thus carried out, the central axis 18 of the particle beam 12 extends through both the first deflection point 20 and the second deflection point 22 and the deflection points 20, 22 are in axis with the predetermined point of incidence 24 on the target 16, the particle beam 12 hits the desired manner at the point of impact 24 on the target 16. Before impinging on the target 16, the particle beam 12 is focused by the focusing means 48, which in this embodiment comprise an electromagnetic lens.

During the determination of the deflection currents, the second measuring unit 44 is in a first operating mode in which it measures an electric current resulting from the impact of the particle beam 12 on the surface of the second diaphragm 36 facing away from the target 16. After completion of the above-described processes, the particle beam 12 is no longer incident on the second aperture 36, so that no corresponding current is measured more.

In a second mode of operation, the second measuring unit 44 then measures an electrical current resulting from electrons backscattered from the target 16. Since this current is a measure of the target current of the target 16, it can be used to control or regulate the target current. For this purpose, the control means 38 control the particle source 10 so that it generates a particle beam 12 which leads to the respective desired target current. In this way, a precise control of the target current is possible, which is a direct measure of the photon flux at constant high voltage between the particle source 10 and ring anode 14.

The device 2 according to the invention enables with simple means a highly precise deflection of the particle beam 12 and likewise a high-precision control of the target flow. It is therefore excellently suitable, for example, and in particular for use in imaging processes and in inspection and measurement in the XUV range.

Claims (16)

Device for generating X-ray or XUV radiation,
with means for directing a particle beam of electrically charged particles onto a target and with deflection means for deflecting the particle beam such that the central axis of the particle beam passes through a first deflection point and a second deflection point spaced from the first deflection point in the beam direction, the deflection means comprising a first deflection unit Deflecting the particle beam such that its central axis passes through the first deflection point, and a second deflection unit spaced from the first deflection unit in the beam direction of the particle beam for deflecting the particle beam so that its central axis extends through the second deflection point, the particle beam passing through the deflection units is deflectable with respect to a deflection point independent of a deflection with respect to the other deflection point,
characterized,
that each of the deflection units (26, 32) for a deflection of the particle beam along two mutually perpendicular axes (X-axis and Y-axis) are formed, such that the first and the second deflection point (20, 22) lie in axis with a predetermined or predeterminable point of incidence (24) of the particle beam (12) on the target. Apparatus according to claim 1, characterized by control means (38) for controlling the deflection means. Apparatus according to claims 1 and 2, characterized in that the first deflecting unit (26) and the second deflecting unit (32) are independently controllable by the control means (38), such that the particle beam (12) is movable with respect to a deflecting point (20) , 22) is deflectable independently of a deflection with respect to the other deflection point (22, 20). Device according to one of the preceding claims, characterized in that each of the deflection units (26, 32) has at least one deflection element (28, 34). Apparatus according to claim 4, characterized in that the deflecting element (28, 34) has at least one coil or coil arrangement, in particular a quadrupole. Apparatus according to claim 4 or 5, characterized in that the deflecting element comprises at least one electrostatic deflection plate. Device according to one of the preceding claims, characterized in that the deflection means for deflecting the particle beam (12) along two mutually vertical axes are formed. Device according to one of the preceding claims, characterized in that at least one of the deflection units (26, 32) is associated with a diaphragm (30, 36) which is arranged in the beam direction behind the deflection element (28, 34) of the deflection unit (26, 32) , Apparatus according to claim 8, characterized in that the first deflecting unit (26) is associated with a first diaphragm (30) and the first diaphragm (30) is arranged in the beam direction in the region of a plane of action of a deflecting element (34) of the second deflecting unit (32). Apparatus according to claim 9, characterized in that the second deflecting unit (32) is associated with a second diaphragm (36). Device according to one of Claims 8 to 10, characterized in that at least one diaphragm (30, 36) consists at least partially of an electrically conductive material and in that the diaphragm (30, 36) has a measuring unit (42, 44) for measuring an electric current is assigned, which results from an impingement of the particle beam (12) on the diaphragm (30, 36). Apparatus according to claim 11, characterized in that the measuring unit (42, 44) is in communication with the control means (38) for controlling the deflection means, such that the deflection of the particle beam (12) in response to a measurement by the measuring unit (42, 44) measured current takes place. Device according to one of Claims 8 to 12, characterized in that a diaphragm (36) which is opposite to the target (16) is associated with a measuring unit (44) which, in a first operating mode, measures an electrical current which depends on the impact of the particle beam (12 ) is due to the area of the diaphragm facing away from the target (16) and, in a second mode of operation, measures an electric current resulting from electrically charged particles backscattered from the target (16). Device according to Claim 13, characterized in that the measuring unit (44) is connected to control and / or regulating means (38) which, as a function of a current measured by the measuring unit (44) in the second operating mode, control the target current by driving a particle source (10) for generating the particle beam (12) control or regulate. Device according to one of the preceding claims, characterized by focusing means (48) for focusing the particle beam (12) on the target (16). Apparatus according to claim 15, characterized in that the focusing means (48) are arranged downstream of the deflection means in the beam direction.

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