PARTICLE BEAM SYSTEM

A particle beam system comprises a particle beam column, a detection system and a controller. The particle beam column is configured to generate a particle beam and to direct it onto a sample, as a result of which charged particles are emitted by the sample. The detection system detects charged particles and comprises: an electrode, which can accelerate the charged particles; a potential source, which applies an adjustable electrical potential to the electrode; a scintillator; and a light detector, which outputs a detection signal. The controller controls the potential source and is configured to change the potential on the basis of the detection signal such that the scintillator operates outside its saturation and such that the light detector operates outside its saturation.

CROSS-REFERENCE TO RELATED APPLICATION

This application claims benefit under 35 U.S.C. § 119 to German Application No. 10 2021 125 639.9, filed Oct. 4, 2021. The contents of this application is hereby incorporated by reference in its entirety.

FIELD

The present disclosure relates to a particle beam system comprising a detection system for detecting charged particles which are emitted by a sample as a result of interaction of a particle beam with the sample. As an example, the disclosure relates to an electron beam system comprising a detection system for detecting electrons which are emitted by a sample as a result of interaction of an electron beam with the sample.

BACKGROUND

EP 2 487 703 A1 discloses what could be considered a conventional detection system which is used in a particle beam microscope. The detection system comprises a scintillator, a light guide connected to the scintillator, and a light detector connected to the light guide. The scintillator emits light on account of charged particles (in particular electrons) impinging on the scintillator, the light being fed to the light detector by the light guide. The light detector detects the light and outputs a detection signal representing the detected light. The light detector amplifies the light with an adjustable gain factor. The gain factor is adjusted such that the light detector operates below its saturation limit.

Such a conventional detection system is able to specify a current intensity of an electric current formed from the charged particles to be detected, by way of the detection signal. The range of the current intensity of the electric current in which the detection system operates outside its saturation is referred to as the input dynamic range of the detection system. The gain factor brings about an increased input dynamic range since, in the case of an increased current intensity of the current of charged particles to be detected, the gain factor can be reduced in order to keep the detection signal below the saturation limit.

However, the configuration of such a conventional detection system is not able to sufficiently accurately detect very high current intensities of the current of the charged particles to be detected, even if the gain factor is reduced. Accordingly, the imaging dynamic range is generally restricted at very high current intensities of the current of the charged particles to be detected in a particle beam microscope. This can lead, inter alia, to reduced image contrasts, non-linearities in the imaging characteristic, but can also lead to temporal signal blur and thus, in the image, blurred controls and ghost images.

SUMMARY

The present disclosure proposes a particle beam system which is able to reduce the disadvantages mentioned above.

The particle beam system according to the disclosure comprises: a particle beam column configured to generate a particle beam and to direct it onto a sample, as a result of which charged particles are emitted by the sample; a detection system for detecting the charged particles, wherein the detection system comprises an electrode, a potential source, a scintillator and a light detector, wherein the potential source is configured to apply an adjustable electrical potential to the electrode, as a result of which the charged particles can be accelerated to the scintillator, wherein the scintillator is configured to emit light as a result of interaction of the charged particles with the scintillator, and wherein the light detector is configured to detect the light emitted by the scintillator and to output a detection signal corresponding to the detected light; and a controller, which controls the potential source and is configured to change the potential such that the scintillator operates outside its saturation and such that the light detector operates outside its saturation.

The electrode can bring about an adjustable acceleration for charged particles as a result of the adjustable electrical potential applied to the electrode. As a result, the current intensity—fed to the scintillator—of an electric current composed of charged particles to be detected can be adjustable, as a result of which a large input dynamic range can be realized. This process can function in detail as follows.

The electrode accelerates the charged particles to the electrode in a variably adjustable manner, as a result of which the kinetic energy of the charged particles impinging on the scintillator is variably adjustable. The kinetic energy of a charged particle impinging on the scintillator crucially determines the number of photons which are generated from the particle by the scintillator and are emitted by the scintillator. That is to say that the kinetic energy of the charged particles impinging on the scintillator crucially determines the number of photons generated from the particles and emitted by the scintillator. This conversion ratio of generated photons for each charged particle is adjustable on account of the adjustable electrical potential.

The electrode steers the charged particles to the electrode, i.e. a change in the trajectory of the charged particles, which brings about an increase in the charged particles impinging on the scintillator. The increase is adjustable, however, on account of the adjustable potential.

In a first operating mode, the sample is in a high vacuum. The high vacuum is generated in a vacuum chamber in which the sample is arranged. A high vacuum mechanism, for example, that a pressure of at most 0.1 pascal is present in the vacuum chamber. In the first operating mode, particles emanating from the sample and generated as a result of interaction with the particle beam and the sample collide with gas particles in the vacuum chamber to a non-significant extent on their way to the scintillator on account of the high vacuum. Charged particles or radiation generated as a result of collisions of the particles emanating from the sample with the gas in the vacuum chamber as a result of interaction on their way to the scintillator therefore contribute(s) to the detection signal to a negligible degree.

In a second operating mode, the sample is not in a high vacuum, but rather in a gas environment. A gas environment mechanism, for example, that a pressure of at least 1 pascal is present in the vacuum chamber in which the sample is arranged. In the second operating mode, particles emanating from the sample and generated as a result of interaction with the particle beam and the sample collide with gas particles in the vacuum chamber to a significant extent on their way to the scintillator on account of the gas environment.

Charged particles generated as a result (impact ionization) are in turn accelerated by the electrode of the detection system and can for their part collide again with gas particles in the vacuum chamber, as a result of which a cascade of impact ionizations can be triggered. The number of charged particles impinging on the scintillator can be greatly increased as a result. The increase is adjustable, however, an account of the adjustable potential.

Besides charged particles, radiation in the form of light can also be generated during such impact processes. If it reaches the light detector, it is detected by the light detector and increases the detection signal in this way. The increase is adjustable, however, on account of the adjustable potential.

The gas in the vacuum chamber can be air or a specially supplied gas (for example nitrogen, water vapour or the like). The pressure in the vacuum chamber can be adjusted by a vacuum pump and/or a gas supply system, for example. The vacuum pump and the gas supply system can be controlled by the controller.

The light detector can be for example a light detector in accordance with one of the following types: photomultiplier (PMT), silicon photomultiplier (SiPM), low gain avalanche photodetector (LGAD), avalanche photodiode (APD), photodiode (PN), PIN photodiode, microchannel plate (MCP) and the like.

The controller adjusts the electrical potential applied to the electrode such that neither the scintillator nor the light detector operates in saturation. Saturation is defined as follows, for example: A device which generates an output signal (for example emitted light, detection signal, etc.) depending on an input signal (for example charged particles, light, etc.) has an operating range, in which a change in the input signal leads to a change in the output signal, and a saturation range, in which a change in the input signal no longer leads to a change in the output signal or leads only to a significantly smaller change compared with the change in the operating range. The operating range defines the input dynamic range. In the saturation range, the output signal no longer uniquely maps the input signal. The device operates outside its saturation when it operates in the operating range, and operates in saturation when it operates in the saturation range.

What is achieved in accordance with an aspect of the present disclosure is that neither the scintillator nor the light detector operates in saturation by virtue of the detection signal being used to adjust and/or to change the electrical potential applied to the electrode. By way of example, on the basis of the detection signal, the controller checks whether or not a predefined criterion is satisfied, the result of the check indicating whether or not the detection system is operating outside its saturation or is operating close to its saturation. The controller then changes the electrical potential applied to the electrode if the result of the check indicates that the detection system is operating in saturation or close to its saturation.

What is achieved in accordance with an aspect of the present disclosure is that neither the scintillator nor the light detector operates in saturation by virtue of the fact that the potential is adjusted and/or changed on the basis of application data, the application data being stored in a data storage unit and specifying information about the sample and/or information about an adjustment of at least one operating parameter of the particle beam column. By way of example, on the basis of the application data, the controller determines an expected value specifying an expected current of the charged particles, and adjusts the potential such that the expected value satisfies a predefined condition according to which neither the scintillator nor the light detector operates in saturation.

Embodiments of the disclosure are explained in greater detail below with reference to figures.

DETAILED DESCRIPTION

FIG.1shows an exemplary particle beam system1suitable for carrying out the methods and processes described herein, in particular for analysing and/or processing a sample3.

The particle beam system1comprises a particle beam column10. The particle beam column10comprises a particle source11configured to generate a particle beam2composed of charged particles. The particle beam2is formed from electrons or ions, for example.

The particle beam column10furthermore comprises an acceleration electrode13, to which an electrical potential can be applied in order to accelerate the particles of the particle beam2to a predetermined kinetic energy.

The particle beam column10furthermore comprises a beam tube15arranged downstream of the acceleration electrode13. The particles of the particle beam2accelerated by the acceleration electrode13pass in the beam tube15and emerge from the beam tube15and the particle beam column10at an opening17. An electrical potential can be applied to the beam tube15.

The particle beam column10furthermore comprises a particle-optical lens19(objective lens) suitable for focusing the particle beam2onto the sample3. The particle-optical lens19is designed as a magnetic lens, for example. The particle-optical lens19is one example of a component for manipulating the particle beam2.

The particle beam column10furthermore comprises a deflection system21suitable for deflecting the particle beam2, such that the particle beam2can be directed onto different locations of the surface of the sample3. The deflection system21can be suitable for deflecting the particle beam2along two directions oriented perpendicularly to one another, which are each in turn oriented perpendicularly to a central axis23of the particle-optical lens19. The deflection system21is one example of a component for manipulating the particle beam2.

The particle beam system1furthermore comprises a vacuum chamber25. The vacuum chamber25has a chamber wall27spatially delimiting the vacuum chamber25. A vacuum can be generated in the vacuum chamber25. The vacuum chamber25is connected to the particle beam column10at the opening17, through which the particle beam2can enter the vacuum chamber25.

A sample stage4is arranged in the vacuum chamber25. The sample stage4serves for carrying, spatially positioning and orienting the sample3.

The particle beam system1furthermore comprises a controller30that is configured to control the components of the particle beam system1. In particular, the controller30is configured to control the particle beam column10. In particular, the controller30is configured to control the particle source11, the electrical potential applied to the acceleration electrode13, the electrical potential applied to the beam tube15, the particle-optical lens19and the deflection system21. The sample stage4can be controlled by the controller30, such that the controller30can spatially position and orient the sample3.

The particle beam system1furthermore comprises a data storage unit31configured to store data. The controller30can read data from the data storage unit31and write data to the data storage unit31. The data storage unit31stores application data, for example.

Application data comprise data which are used by the controller30for controlling the components of the particle beam system1, and can comprise further information. By way of example, the application data comprise information about the sample3, such as, for example, information about the structure of the sample, information about the chemical composition of the sample, and the like By way of example, the application data comprise information about a (present) adjustment of the operating parameters of the particle beam system1, in particular of the particle beam column10. The operating parameters of the particle beam system1denote parameters of the particle beam system1which have to be defined by the controller for operation of the particle beam system1. The operating parameters include in particular the (present) current intensity of the particle beam2, the electrical potential applied to the acceleration electrode13, the electrical potential applied to the beam tube15, the excitation of the particle-optical lens19and the excitation of the deflection system21. The operating parameters include in practice numerous further parameters that are not explicitly represented by an assigned structure inFIG.1, such as, for example, the pressure within the beam tube15, the pressure within the vacuum chamber25, the positioning of the sample3, the adjustment of the sample stage4and the like.

The particle beam system1furthermore comprises a plurality of detection systems40A,40B suitable in each case for detecting charged particles41generated as a result of interaction of the particle beam2with the sample3. The charged particles41can be, in particular, backscattered electrons, secondary electrons, backscattered ions or secondary ions. The detection systems described herein are also referred to as detection system40if a particular differentiation of the detection systems is not required.

The detection system40is suitable for outputting a detection signal representing the quantity and/or the energy of the detected particles41. By way of example, the detection signal represents a current intensity of an electric current formed by the charged particles41. The controller30can receive the detection signal from the detection system40and process it and display it on a display device, for example.

Some more detailed configurations of the detection system40will be explained later with reference toFIGS.6to8.

The configuration of the detection system40will firstly be explained with reference toFIG.2. The detection system40comprises an electrode E, a potential source42, a scintillator43and a light detector44.

In the example shown inFIG.2, the electrode E is provided by a metal grid45arranged on the scintillator43. The electrode E is arranged at the front side of the scintillator43, i.e. at the side at which the charged particles41impinge on the scintillator43. Alternatively, the electrode E can be arranged at the rear side of the scintillator43, i.e. at the side opposite the front side of the scintillator43. As a further alternative, the electrode E can be provided by the scintillator43itself.

The potential source42is configured to apply an adjustable electrical potential to the electrode E As a result, the charged particles41can be accelerated, as a result of which the current intensity of the current which is formed from the charged particles41and which impinges on the electrode E and the scintillator43can also be changed. By virtue of the adjustable electrical potential, the quantity of charged particles generated as a result of impact ionization and the amount of light generated as a result, which contribute to the detection signal, are additionally adjustable. By way of example, it holds true that: The greater the adjusted potential, the greater the current intensity.

The scintillator43is configured to emit light46as a result of interaction of the charged particles41with the scintillator43. In the example shown inFIG.2, the light46emitted by the scintillator43is guided to the light detector44by a light guide47. The light guide47can be an optical fibre, an imaging optical unit or the like.

The light detector44is configured to detect the light46emitted by the scintillator43and to output a detection signal corresponding to the detected light46. The detection signal is for example an electrical signal which is received by the controller30and can be processed by the latter.

In the example shown inFIG.1, the particle beam system1comprises the detection systems40A and40B. One portion of the components of the detection system40A, namely the electrode EA, the scintillator43A and one portion of the light guide47A, is arranged within the vacuum chamber25. Another portion of the components of the detection system40A, namely the other portion of the light guide47A, the light detector44A and the potential source42(not illustrated), is arranged outside the vacuum chamber25. The light guide47A penetrates through the chamber wall47. By contrast, in the case of the detection system40B, all components apart from the potential source42(not illustrated) are arranged in the vacuum of the particle beam column10. The electrode EB provided by the beam tube15, the scintillator43B and the light detector44B of the detection system40B are arranged within the particle beam column10. Further configurations will be described later with reference toFIG.8.

The detection system40shown inFIG.2furthermore comprises a collector electrode48, to which an electrical potential is likewise applied. In this case, the collector electrode48assists the electrode E in guiding the charged particles41to the scintillator43. However, the collector electrode48can also be used as an energy filter by virtue of the electrical potential applied to the collector electrode48being adjusted such that charged particles can pass the collector electrode48only if the kinetic energy of the charged particles is greater than a value defined by the potential. In this case, the electrode E has the effect, for example, that the charged particles that have passed the collector electrode48are accelerated to the scintillator43and, if appropriate, trigger a cascade of impact ionizations.

The controller30controls the potential source42, i.e. the controller30can instruct the potential source42to adjust and to change the potential to a value defined by the instruction. The controller30is configured to adjust and/or to change the potential such that the scintillator43operates outside its saturation and such that the light detector44operates outside its saturation. As a result, the detection system40has a high input dynamic range and ensures that the detection signal provides a correct mapping of the current intensity of the current of the charged particles41or of the light46impinging on the light detector44.

The controller30can be configured to adjust and/or to change the potential on the basis of the detection signal and/or on the basis of the application data. Examples of a controller based on the detection signal will be described with reference toFIGS.3and4. An example of a controller based on the application data will be described with reference toFIG.5.

The potential can be varied in the range of 50 V to 12 kV relative to earth, for example. That is to say that the potential can also be adjusted to values which are significantly different from the customary application range of approximately 8 kV to 10 kV relative to earth.

As is shown by way of example inFIG.2, the light detector44is configured to amplify a signal of the detected light46with a gain which is adjustable up to a maximum gain, and to output the amplified signal as the detection signal. The controller can adjust the potential applied to the electrode E on the basis of the detection signal and/or the application data such that the light detector44would operate outside its saturation even if the light detector44were adjusted to its maximum gain. By way of example, information specifying the present gain of the light detector44and information specifying the maximum gain of the light detector44are stored in the data storage unit31. By dividing the detection signal by the value of the present gain and multiplying that by the maximum gain, it is possible to calculate for example an estimated value that approximately specifies the detection signal with the use of maximum gain. The controller30can change the potential applied to the electrode E on the basis of the estimated value such that the scintillator43and the light detector44would operate outside their saturation even if the light detector44were adjusted to its maximum gain.

The potential can be changed continuously. That is to say that the potential is constantly adjusted anew. The potential can be adjusted repeatedly, for example at periodic intervals. The adjustment of the potential can be triggered by an event, for example by an instruction from the controller30that is triggered by the result of a check of a predetermined criterion, or by an instruction from a user.

A description is given below, with reference toFIGS.3A to3C,4and5, of exemplary processes carried out by the controller30in order to change the potential on the basis of the detection signal.

FIGS.3A to3Cshow a first process P1for changing the potential applied to the electrode E.

In step S101, the controller30obtains the detection signal from the light detector44. By way of example, the controller30stores in the data storage unit31a value indicating a digitized value of the detection signal.

In step S102, the controller30determines whether the detection signal obtained in step S101is greater than a first limit value. The first limit value is stored in the data storage unit31, for example, and specifies as of what value of the detection signal the presence of saturation is checked and ascertained. The first limit value can be adjusted by a user and can be determined empirically, for example.

If it is determined in step S102that the detection signal is greater than the first limit value, the section P1A shown inFIG.3Bis carried out. If it is determined in step S102that the detection signal is not greater than the first limit value, the controller30carries out step S103.

In step S103, the controller30determines whether the detection signal obtained in step S101is less than a second limit value. The second limit value is stored in the data storage unit31, for example, and specifies as of what value of the detection signal the presence of a potential adjusted to be too low is checked and ascertained. The second limit value can be adjusted by a user and can be determined empirically, for example.

If it is determined in step S103that the detection signal is less than the second limit value, the section P1B shown inFIG.3Cis carried out. If it is determined in step S103that the detection signal is not less than the second limit value, the controller30carries out step S104.

In step S104, the controller30waits for a predetermined time. The value of the predetermined time is stored in the data storage unit31, for example, and specifies at what intervals the first process P1is intended to be repeated. After step S104has been carried out, the controller30repeats the process P1beginning with step S101.

In the section P1A, the controller30checks whether a permanent saturation is present. Firstly, in step S105, the controller30stores the present time T1in the data storage unit31.

In step S106, the controller30waits for a predetermined time (measurement interval). The value of the measurement interval is stored in the data storage unit31, for example, and specifies at what intervals a check is intended to be made to establish whether the saturation already ascertained is still present.

In step S107, the controller30stores the present time T2in the data storage unit31.

In step S108, the controller30obtains the detection signal from the light detector44.

In step S109, the controller30determines whether the detection signal obtained in step S108is greater than the first limit value. That is to say that the controller30checks whether or not the saturation is still present.

If it is determined in step S109that the detection signal is greater than the first limit value (i.e. the saturation is still present), the controller30carries out step S103. If it is determined in step S109that the detection signal is not greater than the first limit value (i.e. the saturation is no longer present), the controller30carries out step S104.

In step S110, the controller30determines whether or not the difference between the stored time T2and the stored time T1is greater than a first limit time duration. The first limit time duration is stored in the data storage unit31, for example, and specifies for how long a saturation is present until it is ascertained that a permanent saturation is present. The first limit time duration can be adjusted by a user.

If it is determined in step S110that the difference between the stored time T2and the stored time T1is not greater than the first limit time duration (i.e. the saturation has not yet been present for long enough to ascertain a permanent saturation), the controller30carries out the section P1A once again starting from step S105. If it is determined in step S110that the difference between the stored time T2and the stored time T1is greater than the first limit time duration (i.e. the saturation has been present for long enough to ascertain a permanent saturation), the controller30reduces the potential applied to the electrode E in step S111. As a result, fewer charged particles41are guided to the scintillator43, as a result of which the scintillator43and the light detector44no longer operate in saturation.

In the section P1B, the controller30checks whether the potential applied to the electrode E is permanently adjusted to an excessively low value. Firstly, in step S112, the controller30stores the present time T1in the data storage unit31.

In step S113, the controller30waits for a predetermined time (measurement interval). The value of the measurement interval is stored in the data storage unit31, for example, and specifies at what intervals a check is intended to be made to establish whether the adjustment of the potential already ascertained as excessively low is still present.

In step S114, the controller30stores the present time T2in the data storage unit31.

In step S115, the controller30obtains the detection signal from the light detector44.

In step S116, the controller30determines whether the detection signal obtained in step S115is less than the second limit value. That is to say that the controller30checks whether or not the adjustment of the potential ascertained as excessively low is still present.

If it is determined in step S116that the detection signal is less than the second limit value (i.e. the adjustment of the potential ascertained as excessively low is still present), the controller30carries out step S117. If it is determined in step S116that the detection signal is not less than the second limit value (i.e. the adjustment of the potential ascertained as excessively low is no longer present), the controller30carries out step S104.

In step S117, the controller30determines whether or not the difference between the stored time T2and the stored time T1is greater than a second limit time duration. The second limit time duration is stored in the data storage unit31, for example, and specifies for how long an adjustment of the potential ascertained as excessively low is present until it is ascertained that the adjustment of the potential already ascertained as excessively low is permanent. The second limit time duration can be adjusted by a user.

If it is determined in step S117that the difference between the stored time T2and the stored time T1is not greater than the second limit time duration (i.e. the adjustment of the potential ascertained as excessively low has not yet been present for long enough to ascertain that the adjustment of the potential ascertained as excessively low is permanent), the controller30carries out the section P1B once again starting from step S112. If it is determined in step S117that the difference between the stored time T2and the stored time T1is greater than the second limit time duration (i.e. the adjustment of the potential ascertained as excessively low has been present for long enough to ascertain that the adjustment of the potential ascertained as excessively low is permanent), the controller30increases the potential applied to the electrode E in step S118. As a result, more charged particles41are guided to the scintillator43, as a result of which the scintillator43and the light detector44output a higher detection signal.

By way of the first process P1, the electrical potential applied to the electrode E is changed depending on the detection signal.

FIG.4shows an exemplary second process P2for changing the electrical potential applied to the electrode E. In step S201, the controller30instigates the recording of an image of the sample3with use and control of the components of the particle beam system1. The image is obtained for example by scanning the particle beam2over the sample3and simultaneously recording the detection signal. On the basis of the detection signal, the controller30generates image data representing the image and stores the image data in the data storage unit31.

In step S202, the controller30applies an analysis procedure to the image recorded in step S201, an image analysis result thereby being obtained. The analysis procedure can be for example a predefined procedure stored in the data storage unit31. The analysis procedure is for example such that the image analysis result represents a maximum value of the intensity values represented by the image. The analysis procedure is for example such that the image analysis result represents a mean value of the intensity values represented by the image. The analysis procedure is for example such that the image analysis result represents a median value of the intensity values represented by the image. Other analysis procedures that characterize the intensities in the image can be used.

In step S203, the controller30determines whether or not the image analysis result determined in step S202corresponds to a predefined criterion. The criterion is stored in the data storage unit31, for example, and can be configured by a user. By way of example, the criterion can comprise a check against a limit value, as is the case for example in steps S102and S103of the process P1. More complex checks are possible.

If it is determined in step S203that the image analysis result corresponds to the predefined criterion (i.e. that the potential ought to be changed), the controller30carries out step S204. If it is determined in step S203that the image analysis result does not correspond to the predefined criterion, the controller30repeats the process starting from step S201.

In step S204, the controller30changes the potential applied to the electrode E. In particular, the controller30changes the potential applied to the electrode E on the basis of the image analysis result.

By way of the second process P2, the electrical potential applied to the electrode E is changed depending on the detection signal.

The processes P1and P2described above are two examples of a process by which the controller30changes the electrical potential applied to the electrode E using the detection signal. Other processes are possible.

In addition or as an alternative to the detection signal, other information can also be used by the controller30in order to ascertain the desirability of changing the electrical potential applied to the electrode E and to change the potential.FIG.5shows an exemplary process P3for changing the electrical potential applied to the electrode E on the basis of application data.

FIG.5shows an exemplary third process P3for changing the electrical potential applied to the electrode.

In step S301, the controller30obtains application data from the data storage unit31. The application data specify for example a chemical composition of the sample3, a current intensity of the particle beam2and the like.

In step S302, the controller30determines an expected value specifying an expected current composed of the charged particles41. The expected value is determined using a forecast model, for example, into which the application data are input and which outputs the expected value. The forecast model can for example be implemented by an artificial neural network or the like and be trained by experiments.

In step S303, on the basis of the expected value determined in step S302, the controller30determines whether or not the potential applied to the electrode E ought to be changed and changes the potential if appropriate. By way of example, the controller30can be configured to reduce the potential if the expected value determined is greater than a third limit value. The third limit value is stored in the data storage unit31, for example, and specifies as of what value of the expected value the presence of saturation is expected. The third limit value can be adjusted by a user and can be determined empirically, for example. By way of example, the controller30can be configured to increase the potential if the expected value determined is less than a fourth limit value. The fourth limit value is stored in the data storage unit31, for example, and specifies as of what value of the expected value the presence of a potential adjusted to be too low is expected. The fourth limit value can be adjusted by a user and can be determined empirically, for example.

In accordance with a further exemplary process for changing the electrical potential applied to the electrode E, the electrical potential applied to the electrode E is increased and the gain of the light detector44is reduced in order to increase (i.e. improve) the signal-to-noise ratio of the detection signal In general, the signal-to-noise ratio of the detection signal is better if the gain of the light detector44is chosen to be lower and the potential is adjusted to a higher value in order to compensate for the low gain.

FIG.6shows a further exemplary configuration of a detection system40A. The detection system40A differs from the detection system40described with reference toFIG.2only in that the electrode E is provided by the collector electrode48arranged at a distance from the scintillator43, and in that the metal grid45is not provided. The detection system40A can be developed further by an adjustable electrical potential also being applied to the scintillator43.

FIG.7shows a further exemplary configuration of a detection system40B. The detection system40B differs from the detection system40described with reference toFIG.2only in that the electrode E is provided by a grid electrode49arranged between the scintillator43and the added collector electrode48at a distance from the scintillator43and the collector electrode48, and in that the metal grid45is not provided. The detection system40B can be developed further by an adjustable electrical potential also being applied in each case to the scintillator43and to the collector electrode48.

As is shown inFIG.1, the electrode E and the scintillator43of the detection system40can be arranged in the interior of the vacuum chamber25. As is likewise shown inFIG.1, however, the electrode E and the scintillator43of the detection system40can also be arranged in the interior of the particle beam column10. In the example inFIG.1, the electrodes E and the scintillators43of two detection systems40are arranged in the interior of the beam tube15of the particle beam column10. These are arranged between the acceleration electrode13and the particle-optical lens19, as viewed along the central axis23. It is not necessary for the light detector44of these detection systems40likewise to be arranged in the interior of the particle beam column10or in the interior of the beam tube15. Instead, the light guide47can guide the light46generated by the scintillator43in the interior of the particle beam column10through a housing of the particle beam column10and the light46is then detected by a light detector44arranged outside the housing of the particle beam column10. Alternatively, the electrode E can be provided by the beam tube15of the particle beam column10.

The electrical potential applied to the electrode E generates an electric field between itself and other parts of the particle beam system1and the sample3if these have a different electrical potential. Therefore, the electrical potential applied to the electrode E can generate an electric field which lies in the region in which the particle beam2passes. This can adversely influence the particle beam2since the particle beam2can be deformed, displaced and deflected. Some possibilities which reduce the adverse influence are presented below.

By way of example, the particle beam column10comprises a component for manipulating the particle beam2, the component being controlled by the controller30such that the influence of the electrode E and of the electrical potential applied to the electrode E on the particle beam2is reduced. Examples of the component for manipulating the particle beam2are the particle-optical lens19and the deflection system21. The particle beam system1can comprise further particle-optical lenses and deflection systems which are provided in a dedicated manner for compensating for the influence of the electrode E and of the electrical potential applied to the electrode E on the particle beam2. For this purpose, the controller30can be configured to control the component for manipulating the particle beam2on the basis of a signal indicating the potential.

The control algorithm to be executed by the controller30for controlling the component for manipulating the particle beam2can be stored in the data storage unit31. The control algorithm can be previously determined by simulation, for example. Alternatively or additionally, the control algorithm can be determined experimentally by experimental determination of correction values for the operating parameters which involve reduction of the measured influence (i.e. for example the deformation, displacement and deflection of the particle beam2). Furthermore, an image displacement, image rotation, image distortion, etc., caused by a change in the potential applied to the electrode E in images recorded by the particle beam system1can be determined by the controller30, and the controller30can control the component for manipulating the particle beam2on the basis thereof.

By way of example, the particle beam column10comprises a shielding element51, which electromagnetically shields the particle beam2from the electrode E. The shielding element51is designed and arranged such that the particle beam2passes outside a main effective region52of an electric field generable by the electrode E. In the example shown inFIG.1, the shielding element51is a plate which is arranged along the central axis23at a distance from the central axis23and which is arranged between the central axis23and the electrode E. The shielding element51delimits the main effective region52of the electric field generated by the electrode E to a spatial region arranged at a distance from the central axis23and the particle beam2.

FIG.8shows the particle beam system1with an alternative detection system40C and alternative detection systems40D. The electrode EC, the scintillator43C and the light detector44C are arranged in a ring-shaped manner around the central axis23in the vacuum chamber25. Only the potential source42(not illustrated) of the detection system40C is arranged outside the vacuum chamber25. Owing to the symmetry, the radial components of the electric field generated by the electrode EC (i.e. the components of the electric field which are oriented perpendicularly to the central axis23) approximately cancel one another out, as a result of which the influence on the particle beam2is reduced.

The electrodes ED of the detection systems40D are arranged around the central axis23such that the effects of the potentials applied to the electrodes ED of the detection systems40D (or of the electric field formed jointly by the electrodes ED) at least partly cancel one another out in the region of the central axis23. In the example shown inFIG.8, two detection systems40D are arranged in the interior of the beam tube15. Owing to the symmetry of the arrangement of the detection systems40D, the radial components of the electric fields generated by the electrodes ED (i.e. the components of the electric field which are oriented perpendicularly to the central axis23) approximately cancel one another out, as a result of which the influence on the particle beam2is reduced.

FIG.9shows the particle beam system1with an alternative detection system40E and an alternative detection system40F. The electrode EE of the detection system40E and the scintillator43E of the detection system40E are arranged in the particle beam column10, in particular in the beam tube15. A light guide47E guides the light generated by the scintillator43E to the light detector44E arranged outside the beam tube15, in particular outside the particle beam column10. In accordance with one modification of the detection system40E, the electrode EE is formed by the beam tube15. Apart from the potential source, the detection system40F is situated completely within the vacuum chamber25. That is to say that the electrode EF, the scintillator43F and the light detector44F of the detection system40F are arranged within the vacuum chamber25. In contrast to the detection system40C shown inFIG.8, the electrode EF and the scintillator43F of the detection system40F are not formed symmetrically about the central axis23.

FIG.10shows an exemplary configuration of the controller30. In this example, the controller30comprises a processor101, a data storage unit102, an input device103, an output device104and a communication device105. The processor101, the storage unit102, the input device103, the output device104and the communication device105can exchange data with one another via one or more buses106.

The processor101executes programs stored in the data storage unit102. Algorithms, in particular control algorithms, are executed as a result.

The data storage unit31is implemented by the data storage unit102, for example. The data storage unit102can comprise a recording medium on which one or more computer-readable programs are recorded, and can store all kinds of data.

The input device103is configured to receive inputs by a user and to store the data associated therewith in the data storage unit102. The input device103comprises a keyboard and a mouse, for example.

The output device104is configured to present data to a user. The output device104comprises a display screen, for example.

The communication device105is configured to transmit and receive data to and from other components of other systems.

The processor101can comprise one or more CPUs, DSPs (digital signal processors) and the like. Examples of the storage unit102are a non-volatile or volatile semiconductor memory and the like. Examples of the non-volatile or volatile semiconductor memory are a random access memory (RAM), a read-only memory (ROM), a flash memory, an erasable programmable read-only memory (EPROM) and the like.