Preventing ESD discharges in PRT SEM

Abstract

The present invention relates, inter alia, to a method for influencing the charge state of a sample, which comprises directing a charged particle beam onto the sample for analyzing and / or processing the sample, wherein the particles of the particle beam are accelerated onto the sample with a first accelerating voltage and lead to a charging of the sample, and directing the charged particle beam onto the sample to influence the charging of the sample, wherein the particles of the particle beam are accelerated onto the sample with a second, modified accelerating voltage, which is at least 15% of the first accelerating voltage.

Description

1. Technical area

[0001] The present invention relates to methods, a computer program and a device for influencing a charge state of a sample. 2. Technical background

[0002] Analyzing and / or processing a lithographic mask (herein also referred to as a mask) with a particle beam has been known for some time. For example, the particle beam can comprise an electron beam, ion beam, and / or a photon beam, which is provided on the mask in a defined manner for analyzing and / or processing the mask. By providing the particles of the particle beam on the mask, various interactions can be generated, which can enable various analysis and / or processing processes of the mask. Thus, particle beam-based analysis and / or processing of a mask can comprise a wide variety of methods.

[0003] For example, particle beam-based processing can comprise particle beam-induced etching and / or deposition, in which material from a mask is locally removed or created. This can, for example, comprise electron beam-induced etching and / or deposition. Furthermore, defined photon irradiation of the mask can also be necessary, for example, for processing the mask (e.g., in a laser-induced reaction). Examining a mask with a particle beam can, for example, comprise recording an image of the mask using the particles of the particle beam (e.g., as is done in a scanning electron microscope (SEM) using an electron beam).

[0004] Particle beam-based analysis and / or processing of a mask with a particle beam is now used in industry for various applications. In other applications, it may also be necessary to remove foreign matter from the surface of a mask, at least partially based on the use of a scanning probe microscope tip.

[0005] For example, in the semiconductor industry, increasingly smaller structures are being produced on a wafer in order to ensure higher integration density. Lithographic processes, among others, are used to produce the structures and image them on the wafer. The lithographic processes can include, for example, photolithography, ultraviolet (UV) lithography, DUV lithography (i.e. lithography in the deep ultraviolet spectral range), EUV lithography (i.e. lithography in the extreme ultraviolet spectral range), X-ray lithography, nanoimprint lithography, etc. Masks are usually used as objects for lithography (e.g. photomasks, exposure masks, reticles, stamps in nanoimprint lithography, etc.), which contain a pattern to image the desired structures, for example on a wafer.

[0006] As integration density increases, so do the demands on mask manufacturing (e.g., due to the associated reduction in feature sizes on the mask or the higher material requirements of lithography). The mask manufacturing processes are thus becoming increasingly complex, time-consuming, and costly. Mask defects (e.g., defects) cannot always be avoided. Therefore, mask defects are typically repaired using particle beam-based processing, since, due to their small dimensions, they can only be repaired using particle beam-based processing.

[0007] Furthermore, in the semiconductor industry, for example, it may be necessary to examine masks with a particle beam. For example, to repair mask defects, it may be necessary to use a particle beam to capture images of the mask defects or the repair site (e.g., for a high-resolution SEM image).

[0008] It may also be necessary for other industrial purposes to analyze and / or process a sample with a particle beam. For example, this can be done for the analysis (e.g., failure analysis) of a sample, which may include a microchip, a wafer, a biological sample, etc. In some cases, sample analysis may also include AFM imaging of the sample. Processing of the sample may, for example, involve removing a particle (e.g., a foreign particle) from the sample (e.g., as part of a so-called particle picking process).

[0009] However, the masks to be analyzed and / or processed with the particle beam may have an (unwanted) electrostatic charge.

[0010] The (unwanted) electrostatic charge can cause adverse effects. For example, the (unwanted) electrostatic charge can cause the particle beam to be deflected from the intended point of impact on the mask. Furthermore, the electrostatic charge can also, for example, prevent a particle beam-based reaction from achieving the desired effect. The (unwanted) electrostatic charge can therefore undesirably impair the defined analysis and / or processing of the mask.

[0011] Therefore, for a defined analysis and / or processing of the mask with a particle beam, the effects caused by the electrostatic charging of the mask must usually be technically handled.

[0012] Some solutions to this problem are already known from the state of the art.

[0013] In some cases, mask charging can be eliminated by placing an electrical contact in the area of ​​conductive structures on a mask that are surrounded by electrical insulation. However, this carries the risk of damaging the mask (scratching), contaminating it (generating foreign particles), and can limit the workable area of ​​the mask (build space limitation due to the contact). In the case of multiple unconnected structures on the mask (e.g., separated from each other by insulation), these cannot be grounded together with a single electrical contact on the mask. Instead, multiple electrical contacts on the mask may be required, for example, to enable grounding of the affected areas.

[0014] In other cases, charging can be influenced by at least local gassing of the mask. If a suitable gas is brought close to a particle beam (e.g. an electron beam of a scanning electron microscope, SEM), the gas can neutralize charges on a surface of the mask. However, the supplied gas, in interaction with the particle beam of the SEM, can undesirably change the surface of the mask (e.g. at least local cleaning, oxidation, activation of the surface). The supplied gas can also affect any repair processes carried out on the mask (e.g. etching steps, fixation of foreign particles to an AFM tip). Furthermore, the necessary pumping out of the supplied (neutralization) gas can reduce the throughput of a device implementing the neutralization process. In some cases, it can also happen that the gas orwhose ingredients can contribute to undesirable contamination of the mask.

[0015] Another way to counteract the charging of a mask can be provided, for example, by a flood gun. A flood gun irradiates the mask with an electron beam whose beam voltage and beam current are selected so that it compensates for the charging by an SEM. The disadvantage, however, is that the secondary electrons generated by a flood gun can also be detected by an SEM detector and thus create an offset that can complicate automated SEM image analysis. Furthermore, it may be necessary to align the flood gun to the SEM spot on the mask, since otherwise, depending on the mask position and structure, the charging by the SEM cannot be compensated. This alignment can often not be achieved satisfactorily due to installation space restrictions caused by the devices used.A subsequent discharge step, in which the mask position analyzed in the SEM is moved to the floodgun, can significantly reduce the throughput of such a device.

[0016] In some cases, a charge present on the mask can also be at least partially dissipated by a plasma discharge. However, such discharges from a mask (e.g., as described in US Pat. No. 9,995,764 B2) can significantly reduce the throughput of a device processing the mask. In addition, the associated need to switch valves (e.g., when using an SEM) and the associated introduction of gases can contaminate the mask.

[0017] In some cases, a charge on the mask can also be compensated by a bias voltage applied to the AFM tip of a scanning probe microscope. Using AFM techniques such as scanning Kelvin microscopy (KPFM), for example, the potential of the AFM tip can be adjusted to match the potential of the mask, typically using voltages in the range of + / - 10 V. However, an AFM tip, as well as the associated electronic and mechanical setup, is not designed for higher voltages, e.g., on the order of several kV (which can correspond to a charge on the mask), so a corresponding bias voltage cannot be applied.

[0018] The already known solutions for influencing a charge state of a mask have a number of disadvantages and only allow influencing a charge state of a mask in an unsatisfactory manner.

[0019] There is therefore a need to improve the analysis and / or examination of masks with a particle beam and to provide options for improved influencing of a mask's charge state. In particular, there is a need to provide an improved concept for influencing a mask's charge state that takes into account the multitude of possible applications (e.g., in SEM and / or AFM microscopy) in which undesired charging of a mask leads to disadvantageous analysis and / or examination of a mask. 3. Summary of the invention

[0020] The above object is at least partially achieved by the various aspects of the present invention as described below.

[0021] A first aspect of the present invention relates to a method for influencing a charge state of a sample. The method may comprise directing a charged particle beam at the sample for analyzing and / or processing the sample, wherein the particles of the particle beam are accelerated toward the sample at a first acceleration voltage and can lead to a charging of the sample. Furthermore, the method may comprise directing the charged particle beam at the sample to influence the charging of the sample, wherein the particles of the particle beam are accelerated toward the sample at a second, modified acceleration voltage that is at least 15% of the first acceleration voltage.

[0022] By selecting the second acceleration voltage such that it is at least 15% of the first acceleration voltage, the charge contained on the sample can be efficiently influenced. The applicant has recognized that lowering the first acceleration voltage to a second acceleration voltage that is small compared to the first acceleration voltage, which second acceleration voltage is significantly less than at least 15% of the first acceleration voltage, can, for example, lead to repulsion of incident particles of the particle beam if the charging of the sample leads to a repulsive opposing field for the particles of the particle beam. This can be explained by the fact that the kinetic energy of the particles of the particle beam can be reduced by interaction with the repulsive opposing field, so that they can no longer reach the sample.The applicant has recognized that this disadvantageous effect can be at least partially overcome by selecting a second acceleration voltage that is not immediately small compared to the first acceleration voltage, but rather that corresponds to at least 15% of the first acceleration voltage. In this way, it can be achieved that the particles of the particle beam accelerated by the second acceleration voltage still have sufficient kinetic energy as they approach the charged sample to overcome an electrostatic potential that, for example, has a repulsive effect on the incident particle beam and can reduce the landing energy of the incident particles.Furthermore, by selecting the second acceleration voltage, it can be achieved that particles of the particle beam accelerated by the second acceleration voltage impact the sample with lower landing energy (compared to particles of the particle beam accelerated by the first acceleration voltage). The resulting reduced landing energy of the particles can lead to an increase in secondary electron yield and thus contribute to influencing the charge present on the sample. In this way, an efficient and rapid influencing of the charge present on a sample can be provided.

[0023] The particle beam can be provided by a scanning electron microscope.

[0024] In some applications, the sample can be provided as a lithographic mask, for example.

[0025] In some cases, the second, modified acceleration voltage may be smaller than the first acceleration voltage. The second, modified acceleration voltage may, for example, be smaller in magnitude than the first acceleration voltage.

[0026] The analyzing may include recording X-rays generated by the particle beam in the sample.

[0027] By implementing the particle beam as an electron beam, a (continuous) bremsspectrum (and thus X-rays) can be generated in the sample. The obtained (initially continuous) bremsspectrum can additionally contain element-specific peaks (characteristic of the elements contained in the sample and / or of, for example, particles (foreign particles) on the sample). These element-specific peaks can be initiated, for example, by the excitation of electron transitions in the elements contained in the sample and / or of, for example, particles (foreign particles) on the sample. This excitation can occur, for example, by lifting (e.g. by means of a (resonant) component of the bremsstrahlung) electrons from an electron shell close to an atomic nucleus (of the element) to an electron shell further away from the atomic nucleus.This can be followed by a de-excitation of the atom, with the elevated electron transferring to an electron shell closer to the nucleus. This can be accompanied by the emission of element-specific radiation, which can manifest as element-specific peaks (as described above). This can enable, for example, energy-dispersive X-ray spectroscopy (EDX).

[0028] The sampling allows for elemental analysis of the elements present in the sample. This can be beneficial in analyzing possible foreign matter on the sample and, if applicable, their origin.

[0029] The first acceleration voltage may be at least 1 kV, more preferably at least 3 kV, and most preferably at least 4 kV.

[0030] In some cases, the first accelerating voltage may also have higher voltage values, such as at least 5 kV, 10 kV, 15 kV, 20 kV, 30 kV, 40 kV, 50 kV or an even higher voltage value.

[0031] In some (exemplary) cases, for example, an EDX image can be taken with an initial acceleration voltage of 4 kV. In some (exemplary) cases, for example, imaging using a scanning electron microscope (SEM) can be performed with an initial acceleration voltage of 2-3 kV.

[0032] In some cases, the sample can charge up to a potential corresponding to the first accelerating voltage.

[0033] By specifically adjusting the first accelerating voltage, the maximum frequency (according to the Duane-Hunt law) of the generated bremsspectrum can be adjusted for a specific application. By setting the first accelerating voltage to a higher value, the maximum frequency of the generated bremsspectrum can be shifted toward higher frequencies of the bremsspectrum. This can also enable targeted excitation of particles contained in the sample and / or particles (e.g., foreign particles) on the sample. This, in turn, can lead to the formation of corresponding (higher-energy) element-specific peaks in addition to the (continuous) bremsspectrum (as described above).

[0034] The second acceleration voltage may be at least 30%, preferably at least 40%, more preferably at least 50% and most preferably at least 60% of the first acceleration voltage.

[0035] In this way, a slow and controlled reduction of the second accelerating voltage can be achieved. This can ensure that particles of the particle beam can reach the (charged) sample and are not repelled by the repulsive potential of the charged sample, which may still be present, and thus cannot potentially influence the charge state of the sample.

[0036] The particle beam for analysis may have a particle current of at least 5 pA, preferably at least 1 nA and most preferably at least 150 nA.

[0037] In some alternative cases, it may be possible for the particle current to be less than 5 pA (e.g., 1 pA to 4 pA or any intermediate value) or even more than at least 150 nA, at least 200 nA, or at least 500 nA. Particularly preferably, the particle current may be selected, for example, to be in the range of 10 pA to 100 nA.

[0038] By selecting the particle current, for example, if the particles of the particle stream are provided as electrons, the number of X-ray photons generated when the particles of the particle stream impact the sample can be controlled. If, for example, a higher particle current is selected (e.g., 1000 pA instead of 10 pA), this can contribute to a higher number of X-ray photons generated and thus increase the counting rate during X-ray spectroscopy, which can reduce the time required for X-ray spectroscopy to obtain the desired counting statistics.

[0039] The particle current during analysis and / or processing of the sample may be substantially equal to the particle current during influencing the charge of the sample.

[0040] The term “essentially” in this context can be understood to mean that the particle flow can be constant except for (negligible) statistical fluctuations during the analysis and / or processing of the sample.

[0041] This can contribute to a simplified control of the influencing of the charging, since no readjustment of the particle flow is required when transitioning from analyzing and / or processing the sample to influencing the charging of the sample.

[0042] Alternatively, in some cases, a particle current can be selected to influence the charge of the sample that exceeds the particle current for analyzing and / or processing the sample. In some cases, this can contribute to a faster and more efficient influencing of the charge of the sample. Alternatively, it can also be provided that a particle current during the analysis of the sample differs from a particle current for influencing the sample. In such a case, the particle current for influencing the charge of the sample can be selected such that it lies between the particle current for analyzing the sample and the particle current for processing the sample. This can enable continuous and more precise adjustment of operating parameters for an SEM image.

[0043] The method may further comprise directing the charged particle beam onto the sample N times to influence the charging of the sample, wherein the particles are accelerated onto the sample with an Nth acceleration voltage each time, where N is greater than or equal to two.

[0044] Directing the charged particle beam can be understood as such a control (e.g. by means of appropriately selected at least one operating parameter) of the charged particle beam, which makes it possible to direct the charged particle beam with (predefined) properties onto the sample (or a region of the sample).

[0045] In some cases, the N-fold directing of the charged particle beam can be configured such that the charged particle beam is turned off and / or blocked between two consecutive iterations of directing.

[0046] This can help ensure that particles of the particle beam impinging on the sample ideally contribute to influencing the charge state of the sample and are not repelled by a possibly existing repulsive opposing field and cannot reach the sample.

[0047] In some cases, the Nth acceleration voltage may be at least 15% of the (N-1)th acceleration voltage. In some cases, the Nth acceleration voltage may be at least 30%, preferably at least 40%, more preferably at least 50%, most preferably at least 60%, and most preferably at least 70% of the (N-1)th acceleration voltage.

[0048] This can contribute to influencing the charge state of the sample as efficiently as possible.

[0049] The Nth acceleration voltage may be at least 250 V lower than the (N-1)th acceleration voltage and / or the Nth acceleration voltage may be at most 4 kV lower than the (N-1)th acceleration voltage.

[0050] However, reducing the Nth acceleration voltage compared to the (N-1)th acceleration voltage is not limited to these values. In some cases, it is also possible for the Nth acceleration voltage to be at least 200 V or at least 100 V lower than the (N-1)th acceleration voltage. In particular, the Nth acceleration voltage can be 250 V to 3 kV, more preferably 0.5 kV to 2 kV lower than the (N-1)th acceleration voltage, especially when the first acceleration voltage is 10 kV. In some cases, the Nth acceleration voltage can also be 1 kV or 1.5 kV lower than the (N-1)th acceleration voltage.

[0051] This can also contribute to influencing the charge state of the sample as efficiently as possible.

[0052] The N-fold straightening can be carried out consecutively, whereby the acceleration voltage can be reduced at least twice.

[0053] In some cases, the accelerating voltage can be reduced by at least three, four, five, or even ten times. This can contribute to a fine-grained influence on the charge state of the sample.

[0054] The reduction can be made at least twice by the same amount each time.

[0055] This can contribute to a simplified influencing of the charge state of the sample, since no change in the amount (e.g. in the sense of a redetermination of the amount) by which the accelerating voltage is reduced is required.

[0056] The reduction, at least twice, can be carried out in such a way that the reduction amounts follow a logarithmic progression.

[0057] The reduction amounts can be arranged so that they increase logarithmically with the number of reductions performed (progressive progression). In this case, the respective reduction amounts would become increasingly larger with the increasing number of reductions performed. Alternatively, the reduction contributions can also be arranged to decrease logarithmically with the number of reductions performed (degressive progression). In this case, the respective reduction contributions would become increasingly smaller with the increasing number of reductions performed.

[0058] By providing the reduction contributions so that they follow a logarithmic course, it is possible, for example, in the case of a progressive course, to initially influence the charge state of the sample only slightly (e.g. in order to initially influence the charge state only slightly and to avoid repulsion reactions of the particles in the particle beam), which is then replaced by larger reduction amounts of the acceleration voltage (e.g. when a critical area for repulsion reactions has been left), in order to achieve a faster influence on the charge state of the sample.

[0059] Alternatively, it is also possible that the reduction, at least twice, is carried out in such a way that the reduction amounts (with each of the at least two reduction steps) are chosen to decrease exponentially.

[0060] Alternatively, the at least two reductions of the acceleration voltage can also follow a continuous course (e.g., the reduction contributions can be made by the same amount if there are more than two reductions of the acceleration voltage).

[0061] The particle beam can be directed onto the sample without interruption between at least two accelerating voltages.

[0062] This means that the particle beam can be continuously directed at the sample between at least two accelerating voltages. In some cases, the particle beam can also be directed at the sample N times, so that the particle beam is continuously directed at the sample. However, by adjusting an accelerating voltage N times, the particle beam can experience a new particle beam configuration in each of the N iterations.

[0063] This can contribute to a more time-efficient influencing of the charge state of the sample, since the particle beam can be operated continuously and no time is required for switching the particle beam on and off (and possibly ramping its operating parameters).

[0064] The manipulation may include reducing the charge of the sample.

[0065] In some cases, the sample may have at least one area not connected to ground potential (such as chrome on glass blanks) which may experience charging.

[0066] Thus, the process steps described above can at least partially reduce the charging of a sample and prevent any repulsive interactions that may occur between particles of the particle stream and the charged sample.

[0067] The method may further comprise detecting at least one process parameter associated with a current charge state of the sample.

[0068] The at least one process parameter may be associated with the particles of the particle beam and / or secondary particles generated by an interaction between the particles of the particle beam and the sample. Additionally or alternatively, the at least one process parameter may be associated with X-rays generated in the sample.

[0069] Detecting the at least one process parameter may enable determining a current charge state of the sample.

[0070] The second acceleration voltage may be based at least in part on the at least one process parameter.

[0071] This allows the second acceleration voltage to be applied based at least partially on the sample's current charge state. For example, in cases where the sample is highly charged, the second acceleration voltage can be reduced by a smaller percentage relative to the first acceleration voltage than in cases where the sample is more weakly charged. This allows for a targeted and situationally tailored adjustment of the second acceleration voltage to the sample's current charge state.

[0072] The detecting may further comprise modulating the acceleration voltage and demodulating the at least one process parameter.

[0073] The combination of modulating the acceleration voltage and demodulating the at least one process parameter can provide a lock-in detection method. The modulation of the acceleration voltage can, for example, be performed periodically (e.g., by modulating a sine wave with a predetermined frequency over time). The demodulation of the at least one process parameter can, for example, be performed at the frequency with which the acceleration voltage was modulated.

[0074] In this way, efficient suppression of noise that may be present in a time profile of the at least one process parameter can be enabled. This can contribute to an increased signal-to-noise ratio (SNR) of the detected at least one process parameter.

[0075] The method may further comprise directing the particle beam onto the sample with an accelerating voltage based at least in part on a closed feedback loop including the at least one process parameter as an input.

[0076] In this way, it is possible to track the acceleration voltage so that it can react efficiently to changes (e.g., to a temporal drift) of at least one process parameter as an input variable (compared to a possibly necessary manual adjustment of the acceleration voltage).

[0077] The at least one process parameter can be kept essentially constant over time.

[0078] "Substantially" in this context can be understood to mean that the at least one process parameter is constant over a specific time interval, and any fluctuation in the at least one process parameter is merely due to statistical fluctuations (e.g., due to noise). Noise in this case can refer to both electronic noise and effects caused by statistical fluctuations in process parameters associated with the particle beam (e.g., fluctuating luminosity of the particle beam, fluctuating acceleration voltage, etc.).

[0079] In this way, it can be ensured that the method can be operated in such a way that an optimized influence on the charge state of the sample can be ensured over time.

[0080] The at least one process parameter may be associated with a secondary electron yield, SEY. In some cases, the at least one process parameter may be derived from a current value based on detectable secondary electrons.

[0081] In this way, it can be achieved that, through the above-mentioned feedback loop, an SEY (if the particles of the particle beam are provided as electrons) can be kept substantially constant over time. Preferably, the SEY can be kept substantially constant over time such that it has a value greater than 1. Preferably, the SEY can be selected such that a maximum value of the SEY is kept substantially constant.

[0082] This can allow more than one electron to leave the charged sample per incident electron of the particle beam on average over time. This can thus efficiently contribute to an optimized manipulation of the sample (e.g., reducing the sample's charge).

[0083] The process can be preceded and / or followed by taking an SEM image.

[0084] In some cases, the acquisition of an SEM image, the procedure described herein, and the subsequent acquisition of an SEM image can be performed cyclically. This can contribute to a streamlined workflow.

[0085] If the SEM image is taken after the process, the process can influence the charge state of the sample, thus suppressing unwanted effects caused by the sample's charge state. For example, if the sample is negatively charged and the particles of the particle beam are provided as electrons, unwanted deflection of the electrons of the particle beam (caused by a repulsive interaction of the charge present on the sample) can be suppressed.

[0086] The method may further comprise providing an electrically conductive element. Furthermore, the method may comprise at least partially directing the charged particle beam onto the electrically conductive element in order to release secondary particles from the electrically conductive element.

[0087] In some cases, the electrically conductive element may be made entirely of an electrically conductive material. In some cases, the electrically conductive element may be at least partially coated with an electrically conductive material. The electrically conductive material may, for example, comprise a doped semiconductor and / or a metal.

[0088] In some exemplary applications, the electrically conductive element can also be provided as a shielding element (e.g. as a net) which can be stretched above a sample, as is known, for example, from EP 1587 128 (as a shielding element).

[0089] In some cases, the electrically conductive material may comprise a scanning probe microscope (SPM) tip and / or a cantilever of an SPM. In some cases, the particle beam may be directed both at the sample and at the electrically conductive element (e.g., simultaneously). The electrically conductive element may be connected to a ground potential. The electrically conductive element may be provided such that it is located, for example, 0.5 mm - 2 mm, preferably approximately 1 mm, from a surface of the sample. In some cases, however, the distance of the electrically conductive element from the surface of the sample may be (significantly) less than 0.5 mm.

[0090] This can contribute to an improved influencing of the charge state of a sample. If, for example, a sample is discharged (e.g. to discharge a negative charge in the sample), it can happen in some cases that the negatively charged sample acquires a positive charge as a result of the discharge process and thus leads to a new, now opposite (e.g. positive) charge in the sample. This can be prevented at least in part by directing the particle beam not only at the sample itself, but also at least partially at an SPM tip and / or an SPM cantilever connected (to a ground potential). Secondary electrons can then be released from the SPM tip and / or the SPM cantilever, for example, which can be accelerated towards the positively charged sample and there can advantageously contribute to neutralising the charge.

[0091] A second aspect of the present invention relates to a method for influencing a charge state of a sample. The method may comprise providing a scanning probe microscope (SPM) tip and establishing an electrically conductive connection between the sample and the SPM tip for influencing the charge state.

[0092] In this way, an SPM tip used, for example, to remove foreign particles from the sample can also be used to influence the charge state of the sample, thereby eliminating the need for additional, separate devices to influence the charge state of the sample. This can contribute to cost-effective influencing of the sample. Furthermore, to influence the charge state of the sample, it is not necessary to switch between multiple devices (which could be provided for influencing the sample), but rather only the SPM tip already used for removing foreign particles needs to be used. This can contribute to more time-efficient influencing of the charge state of the sample.

[0093] In some cases, the SPM tip can be provided as a tip of an atomic force microscope (AFM).

[0094] The method may include directing a particle beam at the sample to analyze and / or process the sample. Establishing the electrically conductive connection may be based at least in part on a measured and / or expected charge state of the sample.

[0095] Analysis and / or processing of the sample can be provided as described above.

[0096] Measuring the charge state of the sample can be enabled, for example, by detecting at least one process parameter (as described herein). An expected transition can, for example, be based at least in part on at least one predetermined calibration function (e.g., comprising an assignment of a (first) acceleration voltage and a duration of analyzing and / or processing the sample to a resulting charge state of the sample). The calibration function can, for example, be provided as a look-up table that assigns, for example, a (first) acceleration voltage, a duration of analyzing and / or processing the sample to a resulting expected (or pre-measured) charge state of the sample.

[0097] In this way, a targeted establishment of the electrically conductive connection between the AFM tip and the sample can be initiated when a charge state of the sample is expected that could adversely affect subsequent analysis and / or processing of the sample. Thus, a proactive buildup of charge in the sample can be suppressed.

[0098] The process can be carried out in a combined scanning probe microscope-scanning electron microscope device.

[0099] In some cases, the procedure can be carried out without having to eject the sample contained in the device.

[0100] This can also enable efficient imaging of the sample (using a scanning electron microscope), e.g. to locate potentially foreign particles present on the sample, which can be further determined, for example, by an X-ray examination (as described herein). Should it subsequently become apparent that removal of the foreign particle is necessary, this can be achieved using the combined scanning probe microscope-scanning electron microscope device. This can, on the one hand, enable optimized handling of any foreign particles present on the sample and, on the other hand, by using the AFM tip of the scanning probe microscope, unwanted charging of the sample can be suppressed or, if already present, can be dissipated in order to suppress, for example, adverse effects on the scanning electron microscope image caused by a charge state of the sample.

[0101] The electrically conductive connection can be established by approaching the SPM tip to a surface of the sample.

[0102] The production can thus refer to an approach of the SPM tip to a surface of the sample in such a way that before the approach there is no electrically conductive connection between the SPM tip and the surface of the sample and only when the approach is terminated is an electrically conductive connection created between the SPM tip and the surface of the sample.

[0103] In this way, if the sample is already charged, each approach step of the SPM tip towards the sample allows for a more accurate detection of the current charge state of the sample.

[0104] The approach can be done gradually.

[0105] The approach can be achieved, for example, by moving the AFM tip using a stepper motor and / or a piezo-based actuator. The step size can be, for example, 10 µm, 20 µm, 30 µm, 40 µm, 50 µm, 60 µm, 70 µm, 80 µm, 90 µm, or 100 µm. Alternatively, the step size can be more than 100 µm or less than 10 µm. It is also possible to select the step size so that it lies between the values ​​mentioned above.

[0106] In some cases, the charge state of the sample can be determined after each step of the AFM tip towards the sample.

[0107] A stepwise approach can prevent unwanted discharge of the sample, which can lead to damage to the AFM tip and / or the sample.

[0108] The approach can be continuous.

[0109] A continuous approach can differ from a stepwise approach in that the approach does not have an explicitly designated dwell point (e.g., for a predetermined time interval) on individual steps. Any dwell that may be present in a continuous approach can be attributed to characteristics of the drive (e.g., a stepper motor used).

[0110] In some cases, the electrically conductive connection can be established by contacting the sample with the AFM tip.

[0111] Continuously approaching the AFM tip toward the sample can contribute to a faster influencing of the sample's charge state. This can be achieved by simultaneously measuring the sample's charge state and, if necessary, simultaneously directing a charged particle beam onto the sample during the approach. Alternating approach and directing may be unnecessary. In this way, parallel approach and directing can contribute to a faster influencing of the sample's charge state.

[0112] The approach may be based at least in part on detecting at least one process parameter.

[0113] The at least one process parameter can be associated with an interaction between the AFM tip and the sample. The at least one process parameter can be associated, for example, with a (measured) force (attractive or repulsive) between the AFM tip and the sample, with a deflection (e.g., bending) of a cantilever of a scanning probe microscope, and / or parameters derived therefrom.

[0114] The interaction can be based, for example, on an attractive interaction between the AFM tip and the sample. In some cases, the AFM tip may be uncharged (neutral) at the beginning of the process. By approaching the AFM tip toward the sample, if the sample already has a charge, a charge state can be induced in the AFM tip that is opposite to the charge state of the sample. This can contribute to an attractive interaction between the AFM tip and the sample.

[0115] In some cases, the approach can be initiated by detecting an actual interaction (e.g., an attractive or repulsive interaction) between the AFM tip and the sample. The detection of the interaction can be interpreted as an indicator of at least partial charging of the sample, which can be stopped and influenced (e.g., dissipated) by approaching the AFM tip toward the sample and subsequently establishing an electrically conductive connection. Thus, unwanted discharges in the sample can be prevented at an early stage.

[0116] In some cases, further approach of the AFM tip toward the sample can be aborted if the detected interaction indicates that the sample already has a charge state (e.g., a comparatively high charge) that would favor an undesired discharge (e.g., through arcing) of the sample via the AFM tip. Thus, the risk of damage to the sample and / or the AFM tip can be suppressed.

[0117] A third aspect of the present invention relates to a method for monitoring a charge state of a sample. The method may comprise detecting a process parameter associated with the charge state of the sample, wherein the process parameter was acquired by one of a scanning electron microscope (SEM), a scanning probe microscope (SPM), and / or an X-ray detector. The method may further comprise determining the charge state of the sample based at least in part on the process parameter.

[0118] The monitoring may be implemented to detect the charge state of the sample continuously, i.e., without significant temporal interruptions, based at least in part on the process parameter.

[0119] In this way, a rapid response to the charge state can be initiated, if necessary, and further charging can be prevented if undesired. Additionally or alternatively, if the charge state of the sample exceeds a predetermined threshold, measures can be initiated to influence (e.g., reduce) the charge. In this way, potentially adverse effects caused by the charge state can be prevented early on, and the throughput of a device implementing the method can be increased.

[0120] The determination can be based at least partly on a previously known relationship between the process parameter and the charge state of the sample.

[0121] The previously known relationship may be based at least in part on a calibration function and / or a look-up table, as described above.

[0122] The determination may be based at least in part on detecting an interaction between a tip of the SPM and the sample.

[0123] The detection of the interaction can be implemented as described above.

[0124] The method may further comprise initiating a method (as described herein) for influencing the charge state of the sample if a predetermined charge threshold of the sample is exceeded.

[0125] In this way, the charge state of the sample can be influenced early, before, for example, there is a risk of discharge from the sample due to a flashover from the sample to an AFM tip. This can prevent potential damage to the sample and / or the AFM tip.

[0126] The functions described above may be implemented in hardware, software executed by a processor (e.g., as a computer program), firmware, or any combination thereof. When implemented in software executed by a processor, the functions may be stored on or transmitted over a computer-readable medium as one or more instructions or code. For example, the functions described herein may be implemented using software executed by a processor, hardware, firmware, hardwiring, or combinations thereof. Features that implement functions may also be physically arranged in different locations, including being distributed such that portions of the functions are implemented in different physical locations.

[0127] A fourth aspect of the present invention relates to a device for influencing a charge state of a sample. The device may comprise an electrically conductive element, such as a scanning probe microscope, SPM, tip (and / or another electrically conductive element described herein) and / or a particle beam of a scanning electron microscope, SEM (e.g., a corresponding source), and / or an X-ray detector. The device may further comprise means for automatically executing one of the above-mentioned methods.

[0128] In this way, in addition to influencing the charge state of the sample, imaging of the sample (e.g. using the SEM) and / or processing of the sample (e.g. by removing a foreign particle from the sample using the AFM tip) can be enabled.

[0129] The device may further comprise means for controlling a distance of the SPM tip from the sample and / or an accelerating voltage of the particle beam.

[0130] The control means may comprise, for example, an (electric) motor, preferably a stepper motor. Additionally or alternatively, the control means may comprise a piezo actuator and / or a piezo-based stepping drive (e.g., for step sizes > 10 µm).

[0131] The device may further comprise means for executing the aforementioned computer program.

[0132] The means may comprise computer-readable media and / or at least one processor. Computer-readable media includes both computer storage media and communications media, including any media that facilitates the transfer of a computer program from one location to another. A processor may be responsible for managing the bus and general processing, including executing software modules stored on the machine-readable storage medium. A computer-readable storage medium may be coupled to a processor so that the processor can read and write information to the storage medium. Alternatively, the storage medium may be integrated with the processor.For example, the machine-readable medium may include a transmission line, a data-modulated carrier wave, and / or a computer-readable storage medium with instructions stored thereon separate from the wireless node, all of which can be accessed by the processor via the bus interface. Alternatively or additionally, the machine-readable storage medium, or a portion thereof, may be integrated with the processor, as may be the case with cache and / or general purpose register files. Examples of machine-readable storage media include, for example, RAM (Random Access Memory), flash memory, ROM (Read Only Memory), PROM (Programmable Read-Only Memory), EPROM (Erasable Programmable Read-Only Memory), EEPROM (Electrically Erasable Programmable Read-Only Memory), registers, magnetic disks, optical disks, hard disks, or any other suitable storage medium or combination thereof.The machine-readable medium may be embodied in a computer program product.

[0133] A fifth aspect of the present invention relates to a method for influencing a charge state of a sample. The method may comprise directing a charged particle beam at the sample for analyzing and / or processing the sample, wherein the particles of the particle beam are accelerated toward the sample with a first acceleration voltage and can lead to a charging of the sample. Furthermore, the method may comprise directing the charged particle beam at the sample to influencing the charging of the sample, wherein the particles of the particle beam are accelerated toward the sample with a second acceleration voltage, wherein the second acceleration voltage is determined such that a secondary particle yield caused by the second acceleration voltage is maximized.

[0134] By selecting the second accelerating voltage to maximize secondary electron yield, the effect of influencing the charge state of the sample can be maximized.

[0135] In some preferred cases, the particles may be provided as electrons.

[0136] The second acceleration voltage may be determined based at least in part on a modulation of the first acceleration voltage and a demodulation of a process parameter associated with the charge state of the sample.

[0137] This may include a lock-in procedure as described above.

[0138] At least a third acceleration voltage can be selected (e.g. by a feedback loop) such that the at least one process parameter is kept substantially constant over time. 4. Short description of the characters

[0139] In the following detailed description, possible embodiments of the invention are described with reference to the following figures: Fig. Figure 1 shows an exemplary curve of a secondary electron yield vs. a landing energy of electrons on a sample; Fig. 2 shows an exemplary time course of influencing a charge state of a sample according to one aspect of the present invention; Fig. Figure 3 shows an exemplary SEY curve where a landing energy of electrons undergoes a modulation; Fig. 4 shows an exemplary flowchart according to one aspect of the present invention; Fig. 5 shows an exemplary flowchart according to one aspect of the present invention; Fig. 6 shows an exemplary flowchart according to one aspect of the present invention; Fig. 7 shows an exemplary flowchart according to one aspect of the present invention; Fig. Figure 8 illustrates an exemplary implementation of a charge monitor. 5. Detailed description of possible embodiments

[0140] Embodiments of the inventive methods and devices are described in detail below. However, it should be noted that the use of the inventive devices and methods is not limited to the examples discussed below. Rather, they can be used generally to influence the charge state of a sample.

[0141] It is further noted that only individual embodiments of the invention can be described in detail below. However, those skilled in the art will understand that the features and possible modifications described in connection with these embodiments can also be further modified and / or combined with one another in other combinations or sub-combinations without this departing from the scope of the present invention. Individual features or sub-features can also be omitted if they are unnecessary to achieve the intended result. To avoid unnecessary repetition, reference is made to the statements and explanations in the preceding sections, which also remain valid for the detailed description that follows.

[0142] Fig. 1 schematically shows a diagram 100 showing a qualitative curve of the secondary electron yield (SEY) versus the electron landing energy on a sample, as already known from the prior art.

[0143] The secondary electron yield indicates the ratio of the number of electrons released as secondary electrons from the sample relative to the number of electrons impinging on the sample (e.g. by a particle beam of electrons directed onto the sample), whereby the particle beam is at least partly responsible for the release of the secondary electrons.

[0144] Under an electron landing energy E L In this context, the energy with which incident electrons hit the sample is understood (e.g. in keV). The electron landing energy E Lcan be defined by the accelerating voltage (e.g. in kV) of the electrons, decreased (or increased) by a possible counter-potential (e.g. in V or kV) of the sample, which can be caused by a charging of the sample, and repulsive (thereby braking, which reduces the electron landing energy E L can reduce) or attractive (thus accelerating, which increases the electron landing energy E L can increase) on incoming electrons.

[0145] The secondary electron yield can be dependent on the landing energy E L The course of the secondary electron yield can be divided into three areas: In a first area 110, which has a landing energy range of 0 keV ≤ E L ≤ E 1 comprises a region 120 which has a landing energy range of E 1 < E L ≤ E 2 (wherein the area 120 has a landing energy E maxfor which the secondary electron yield assumes a maximum value which is greater than 1) and a region 130 in which the landing energy E L a value E L > E 2 has.

[0146] It should be noted that according to the textbook RF Egerton: “Physical Principles of Electron Microscopy”, Springer 2005 for the lower energy threshold E 1 Landing energies of the electrons Numerical values ​​in the range of a few hundred electron volts and for the upper energy threshold E 2 Numerical values ​​in the range of approximately 1 keV to 10 keV can be specified.

[0147] In the area 110, which has a landing energy E L < E 1associated with the secondary electron yield is less than one, so that on average less than one electron is removed from the sample per incident electron. This can lead to the sample becoming slightly negatively charged, since in this region 110 more electrons are incident on the sample than are leaving it.

[0148] If the landing energy E L of the electrons is further increased (e.g. by increasing the accelerating voltage of the electrons), with increasing landing energy E L more electrons are released from the sample and the SEY can be measured at E 1 assume a value of 1 (depending on the mask material and the mask structure). At this value of the landing energy E 1 , the sample shows no change in the charge state.

[0149] A further increase in the acceleration voltage of the electrons can lead to a further increase in the landing energy E Lof electrons, so that the secondary electron yield in the range 120 can assume a value greater than one. This can mean that more electrons leave the sample than hit the sample through a particle beam of electrons directed at the sample. Since more electrons can now leave the sample than hit it, this can lead to a positive charge of the sample.

[0150] The positive charge of the sample in the 120 range can lead to the creation of an attractive potential on the sample for further electrons impinging on the sample. Incident electrons can therefore experience acceleration towards the sample due to the positive charge of the sample. In this regime, the landing energy of the electrons is not determined solely by the acceleration voltage of the electrons, but by the sum of the acceleration voltage and the positive potential of the sample. The landing energy E LThe number of electrons can therefore increase with increasing positive charge of the sample at unchanged acceleration voltage. In this regime, the secondary electron yield initially increases steadily with the landing energy E L to.

[0151] However, the positive charge of the sample is limited at a certain point by the fact that fewer and fewer electrons can be released from the sample per incident electron. This can be explained by the fact that electrons of the particle beam can penetrate deeper into the sample with increasing landing energy and can thereby release electrons from deeper layers of the sample. However, these electrons are often no longer able to leave the sample. This leads to the secondary electron yield at a landing energy E max reaches a maximum of 125 and then gradually (with increasing landing energy E L ) falls again.

[0152] The secondary electron yield can be between 120 and 130, with a landing energy E 2 , again assume a value of one. In this range, the sample does not charge. This point is also referred to as the (material-specific) balance point (BP).

[0153] A further increase in landing energy E L can cause the secondary electron yield to assume a value less than one. Consequently, more electrons impact the sample than are released from it as secondary electrons. This can lead to a negative charge on the sample.

[0154] However, it should be noted that the negative charge of the sample in the range 130 for increasing landing energy E Lof electrons exhibits saturation behavior. This can be explained by the release of electrons from deeper layers of the sample, as described above, which, however, can no longer reach the surface of the sample and therefore cannot leave the sample as secondary electrons.

[0155] Due to the negative charge of the sample in the range 130, the sample can form a repulsive counterpotential for incoming electrons, so that for an unchanged acceleration voltage of the electrons the effective landing energy E L reduced and therefore towards the balance point BP (landing energy E 2 ) aims at a secondary electron yield of 1. This can prevent further depletion of the negative charge of the sample.

[0156] In other words, if the accelerating voltage is, for example, 10 kV and the balance point BP is, for example, 2 keV, the sample potential can rise to a maximum value of -8 kV. When the mask potential has risen from 0 to -8 kV, the electron landing energy E L = 2 keV. Since this electron landing energy E L exactly the electron landing energy E associated with the balance point BP Lcorresponds, the secondary electron yield is equal to 1 and no further charging or change in the mask potential takes place. Furthermore, it should be mentioned that the secondary electron yield of a sample can depend on the orientation of the sample relative to the incident charged particle beam (e.g. electron beam). For example, by arranging the sample relative to the incident electron beam in such a way that the electron beam does not hit a surface of the sample perpendicularly, an increase in the secondary electron yield can be observed with otherwise identical operating parameters. Additionally or alternatively, by directing the electron beam onto a structure (in particular onto an edge of the structure) on the surface of the sample, an increase in the secondary electron yield can be observed. A structure of the sample can, for example, be a layer that absorbs light transmitted through the sample.

[0157] In some exemplary cases, structures contained on the sample can also lead to shielding or rebinding of released secondary electrons to atoms of the sample and / or structural material. This can occur, for example, when an electron beam is directed onto a depression (e.g., a groove, a hole, etc.) in the sample and / or structure.

[0158] Fig. 2 schematically shows a comparison of diagrams 200 showing a time course of characteristic operating parameters of a scanning electron microscope (SEM) and a process parameter (mask potential) according to one aspect of the present invention. The comparison of diagrams 200 depicts an exemplary application of SEM imaging followed by EDX analysis of the sample, as explained in more detail below.

[0159] Diagram 210 shows an example of the course of an SEM acceleration voltage over time.

[0160] Diagram 220 shows an example of the course of an SEM particle current over time.

[0161] Diagram 230 shows an example of the course of a sample potential over time.

[0162] As an example, assume that in a time interval (1) an SEM image is first acquired. In this time interval, the SEM acceleration voltage (e.g., a first acceleration voltage as shown in diagram 210) is comparatively high, while the SEM particle current (diagram 220) is comparatively low. Due to the selected high SEM acceleration voltage, the landing energy of the electrons in the range 130 (as described with reference to Fig. 1) so that this leads to a slow negative charging of the sample over time (as shown in diagram 230).

[0163] Furthermore, it is assumed that a foreign particle was localized on the sample by SEM imaging. In order to be able to determine the elemental composition of the detected foreign particle more precisely, an X-ray spectroscopy analysis (e.g., an EDX analysis) is carried out in time interval (2). This X-ray spectroscopy analysis requires the generation of X-rays, which can be generated by the electrons of the SEM. For this purpose, a high acceleration voltage of the electrons is selected (diagram 210) as well as a high SEM particle current (diagram 220). The high selected SEM particle current is associated with a large number of electrons, which can impinge on the sample due to the high SEM acceleration voltage (area 130 as in relation to Fig. 1) and generate X-rays there. However, this can also lead to a rapid negative charge of the sample over time, as shown in Diagram 230 for time interval (2).

[0164] It should be noted that the sample potential develops a saturation behavior over time (as shown in diagram 230). This can be explained by the fact that the secondary electron yield changes over time, the balance point BP as with reference to Fig. 1, since the charged sample develops an increasingly repulsive counterpotential for further electrons striking the sample, thereby reducing the effective landing energy of the electrons over time. This also means that per incident electron, only one electron is released from the sample over time, and the sample charges at a slower rate over time.

[0165] However, the negative charge now prevailing on the sample would cause the electrons required for subsequent SEM imaging to be repelled from the sample. This can result in inadequate SEM imaging. Therefore, it is necessary to influence the charge state of the sample before subsequent SEM imaging, e.g., by discharging the sample.

[0166] However, directly lowering the SEM acceleration voltage (e.g., to a value close to zero) is not effective, as the negative charge of the sample would repel electrons with a low acceleration voltage. In this case, the negatively charged sample would act as a mirror for incoming electrons, and SEM imaging would also be unsatisfactory.

[0167] In this regard, the applicant has recognized that, for example, a stepwise lowering of the SEM acceleration voltage (e.g. with the SEM particle current unchanged relative to the X-ray spectroscopy) can contribute efficiently to a discharge of the sample, as qualitatively shown in time period (3).

[0168] By reducing the SEM acceleration voltage (e.g., to a second acceleration voltage), the secondary electron yield can be increased. Preferably, the reduction contribution should be chosen so that it is slightly less than the energy associated with the balance point BP (can be determined experimentally and / or taken from the literature). This means that a deflection of the secondary electron yield from the balance point BP towards the region 120 (as described with reference to Fig. 1), which is associated with a positive charge on the sample or a reduction of a negative charge on the sample. In particular, this also means that the secondary electron yield now assumes a value greater than one. Thus, more than one electron leaves the sample for each incident electron, so that the sample's charge decreases over time.

[0169] In some cases, it may also be planned to reduce the accelerating voltage in such a way that the landing energy of the electrons E L after reduction a value E 1 < E L < E max In this way, it is possible to ensure that the secondary electron yield (in time) can assume a value greater than one for as long as possible, which enables a particularly efficient discharge of the sample.

[0170] Due to the decrease in charge on the sample, the sample potential decreases over time and thus also the repulsive counterpotential opposite to the incident electrons, as shown, for example, in diagram 230 for time interval (3).

[0171] This means that the landing energy of the electrons for the selected SEM acceleration voltage increases again over time. With reference to Fig. 1, this means in particular that the secondary electron yield drifts from the region 120 back to the balance point BP and decreases until it finally reaches a value of one again at the balance point BP.

[0172] By lowering the acceleration voltage again (e.g., to a third, fourth, ..., Nth acceleration voltage), the previously described process can be repeated, further reducing the charge or potential of the sample (step by step). Reducing the acceleration voltage can thus occur, for example, in one step, two steps, three steps, four steps, five steps, ten steps, 15 steps, or any other number of steps.

[0173] As shown in time interval (4), an initially negative charge on the sample can be reduced to a value of 0 V and subsequently assumes a slight positive charge. In this regime, it may be possible to perform SEM imaging without the adverse effects caused by sample charging described above.

[0174] For such an SEM image acquisition, the SEM acceleration voltage can be increased again to a comparatively high value (e.g., to the first acceleration voltage, as shown in diagram 210) and the SEM particle current can be reset to a low value (e.g., to the same value that was chosen for the SEM image acquisition in time interval (1)) (as shown in diagram 220).

[0175] During the SEM image acquisition performed in time interval (4), a slow negative charging of the sample can occur again, as already described with reference to time interval (1).

[0176] It should be noted that the procedure described above can be carried out periodically in order to always provide optimized conditions for SEM imaging and / or X-ray spectroscopy.

[0177] Fig. 3 shows a further advantageous aspect 300 of the present invention, in which the secondary electron yield is kept constant in a range that can lead to the fastest possible influence on a charge state (e.g., a discharge) of a sample.

[0178] Fig. 3 shows schematically the course of the secondary electron yield versus the landing energy of the electrons as already described with reference to Fig. 1. It should be noted at this point that the explanations given below are given with reference to electrons to simplify the understanding of the invention, but can also be applied, mutatis mutandis, to other suitable particle types and are therefore not limited to electrons.

[0179] As also in relation to Fig. 1, the secondary electron yield for a given landing energy assumes a maximum value of 310. At this maximum value, the secondary electron yield is greater than one, which can be advantageously used to promote an efficient and rapid influence on the charge state of the sample (in particular, a discharge of the sample).

[0180] As also described above, the secondary electron yield and the landing energy (or the acceleration voltage of the electrons) are interdependent. This means that a reduction of the acceleration voltage (e.g. an SEM acceleration voltage as related to Fig. 2) may initially lead to an increase in the secondary electron yield, although the secondary electron yield may decrease again over time (e.g. due to the SEY drifting back to the balance point BP). It may therefore be considered desirable to keep the secondary electron yield essentially constant at a certain value. It may be particularly preferable to keep the secondary electron yield constant at its maximum value 310, since at this point the largest number of electrons can be released from the sample for an incident electron, which may lead to the discharge of the sample over time.

[0181] This can be achieved, for example, by implementing a (closed) feedback loop that uses the secondary electron yield as at least one process parameter associated with a current charge state of the sample as an input to the feedback loop and using the acceleration voltage of the electrons as an operation parameter (or control parameter) of the feedback loop. In this way, for example, when the secondary electron yield decreases towards the balance point BP (as related to Fig. 1), the electron acceleration voltage can be adjusted such that ultimately no change in the secondary electron yield occurs. In this way, the secondary electron yield can be kept essentially constant at its maximum value of 310 (except for control variations caused by the feedback loop). This can support the most time-efficient manipulation of the sample's charge state (e.g., discharging the sample).

[0182] Specifically, this may mean that when the secondary electron yield drifts from its maximum value 310 towards the balance point BP (as described, for example, by the region 330), the acceleration voltage is reduced in order to return the secondary electron yield towards its maximum value 310.

[0183] Alternatively, it may be possible for the secondary electron yield to drift from its maximum value 310 toward a secondary electron yield associated with a lower landing energy than the maximum value 310 (indicated by a region 320). In this case, the feedback loop would adjust the electron acceleration voltage to increase it, thus returning the secondary electron yield to its maximum value 310.

[0184] In some cases, the secondary electron yield may be subject to statistical fluctuations (e.g., caused by noise and / or other interfering signals present in the environment of the analysis or sample processing being performed). This could, in some cases, lead to the noise associated with the secondary electron yield being transferred through the feedback loop into noise in the accelerating voltage. This can lead to an undesirable and unstable feedback loop.

[0185] It can therefore be considered advantageous to provide means to suppress noise in the secondary electron yield as much as possible. In this context, the applicant has recognized that, for example, lock-in techniques can be used to provide a feedback loop that keeps at least one process parameter (e.g., the secondary electron yield) essentially constant over time, e.g., maximizes it.

[0186] For this purpose, it can be provided to modulate the acceleration voltage (as already described above) and to demodulate the signal of the at least one process parameter (e.g. the secondary electron yield) (preferably with the modulation frequency of the acceleration voltage). In this case, it can be the case that the demodulated signal does not contain any information about an absolute value of the at least one process parameter, but is a measure of its gradient as a function of the acceleration voltage (e.g. the gradient of the secondary electron yield). The amplitude of the demodulated signal can, for example, be larger if the modulation occurs around a point on the acceleration voltage at which the process parameter has a steep gradient. In the example of the secondary electron yield, the amplitude can therefore be used as a measure of how far away its maximum is.The phase, in turn, can indicate whether the landing energy is currently to the left or right of the maximum. The acceleration voltage can be adjusted via feedback according to the demodulated signal. This allows for stable control, which can be used, for example, to adjust the acceleration voltage to maximize the secondary electron signal.

[0187] Specifically, based on the demodulated signal of at least one process parameter, it can be determined whether the secondary electron yield (e.g., with a negative sign of the amplitude) is currently assuming a value to the left of its maximum value of 310 (i.e., in the range of 320) or whether the secondary electron yield (e.g., with a positive sign of the amplitude) is currently assuming a value to the right of its maximum value of 310 (i.e., in the range of 330). However, if the secondary electron yield assumes its maximum value of 310, the amplitude can have a value of (near) zero.

[0188] In an alternative exemplary case, it may also be provided that the acceleration voltage is not subjected to a targeted modulation. In such a case, no (intentional) modulation of at least one process parameter occurs.

[0189] In such a case, the at least one process parameter can be kept at a substantially constant value by providing a feedback loop which uses the at least one process parameter as an input parameter and, based on the input parameter, determines a value for at least the acceleration voltage which results in the at least one input parameter being kept substantially constant.

[0190] One advantage of this type of control can be seen in its simple implementation. However, it can be seen as a disadvantage that in some cases, when controlling the at least one process parameter to a value that is comparatively close to the maximum value of the at least one process parameter, this type of control can lead to an undesired skip of the control from a range that is greater than the maximum value of the at least one process parameter (e.g. range 330) to a range that is smaller than the maximum value of the at least one process parameter (e.g. range 320). In this case, it may happen that the feedback loop cannot be maintained closed (e.g. at least partially based on a reversal of the sign of the slope of the curve of the at least one process parameter vs. acceleration voltage).Controlling at least one process parameter to its maximum value can therefore be made more difficult.

[0191] Furthermore, when a sample is discharged, the shape of the curve, for example of the secondary electron yield (as in Fig. 1) changes during the discharge process (e.g., the maximum value of the secondary electron yield may change, e.g., become smaller). This may complicate control of the secondary electron efficiency according to the described method without modulation, since, for example, a current maximum value of the secondary electron yield may fall below a selected control value of the secondary electron yield.

[0192] In each of the above cases, the feedback loop may be based, at least in part, on a two-point control, a proportional-integral-derivative (PID) control, or another suitable control.

[0193] The secondary electron yield can be determined, for example, by detecting the secondary electrons (e.g., with an in-lens detector) and then relating the detected number of secondary electrons to the number of electrons incident on the sample (e.g., derived from a selected particle current). It should be noted in this context, however, that the detection efficiency of the secondary electrons using an in-lens detector may depend on the electron acceleration voltage. This may require a corresponding adjustment of the determined secondary electron yield signal.

[0194] Alternatively, the secondary electron yield can also be determined using an independent chamber detector.

[0195] Fig. Figure 4 shows an exemplary flow diagram of a method 400 for influencing a charge state of a sample according to one aspect of the present invention. The method 400 is preferably performed in an apparatus that includes both a scanning electron microscope (SEM) and a scanning probe microscope (e.g., AFM).

[0196] In the following, it is assumed that the sample is provided as a mask (e.g., a lithographic mask), but is not limited to masks.

[0197] The method 400 may, for example, begin with loading 410 the mask into a device implementing the method 400.

[0198] At this time 420, the SEM beam is preferentially turned off and an AFM tip of the AFM is retracted from the mask (i.e., the AFM tip is not in contact with the mask).

[0199] Subsequently, the AFM tip and the SEM beam can be navigated 430 to a particle on the sample (e.g., a foreign particle) which, for example, is to be analyzed by the SEM beam and / or processed (e.g., removed) by the AFM tip.

[0200] Once the AFM tip has reached the location of the particle, the AFM tip can be lowered 440 toward a surface of the mask. Preferably, the AFM tip can thus establish an electrically conductive connection between the sample and the AFM tip. The AFM tip can be provided in such a way that it has sufficient conductivity to prevent and / or dissipate charging of the mask. The AFM tip can, in particular, be connected to a ground potential. The force between the AFM tip and the mask can be kept constant (and / or below a maximum force that could lead to damage to the mask and / or the AFM tip) via a control system in order to avoid damage to the AFM tip and / or the mask due to electrically conductive contact.

[0201] After establishing the electrically conductive connection, the SEM beam can be configured 450 so that it can perform imaging.

[0202] Subsequently, an SEM image can be captured 460. According to a preferred embodiment of the invention, the SEM beam can only be switched on when an electrically conductive connection is simultaneously established between the AFM tip and the mask. In some cases, it can be provided that raising the AFM tip immediately leads to the SEM beam being switched off (blanked). This can increase the reliability and speed of the method 400.

[0203] Based on the image acquisition, a decision can be made as to whether X-ray spectroscopy (analysis) of the area of ​​the mask captured by the SEM image is required, or whether a different area of ​​the mask should be analyzed. If it is decided that a different area of ​​the mask should be analyzed, steps 420-460, as previously described, can be repeated on a different area of ​​the mask. It should be noted that if a different area of ​​the mask is to be analyzed, the AFM tip must first be retracted from the mask by a few micrometers to prevent damage to the mask and / or the mask. In principle, lowering and / or raising the AFM tip only requires a few seconds and thus has only a minimal impact on the throughput of a device implementing method 400.

[0204] If, however, it is decided that the area of ​​the mask captured by the SEM image should be analyzed in more detail, the SEM beam can be configured 470 so that the SEM beam can be provided with operating parameters for further analysis of the mask. These operating parameters can include, for example, increasing the particle current and / or increasing the accelerating voltage so that the SEM beam, when it strikes the sample, can generate X-rays in the mask.

[0205] X-ray spectroscopy (e.g. EDX analysis) 480 can then be carried out.

[0206] Subsequently, a decision can be made as to whether another area of ​​the mask should be analyzed according to the previously described steps 420-480 or whether the mask should be ejected 490. It may be provided that the SEM beam is turned off and the AFM tip is retracted from the surface of the mask before ejecting the mask 490.

[0207] Fig. Figure 5 shows an exemplary flowchart of a method 500 for influencing a charge state of a sample according to another aspect of the present invention. The method 500 is preferably performed in a device that includes both a scanning electron microscope (SEM) and a scanning probe microscope (AFM).

[0208] The method 500 may begin with loading 510 the sample (e.g., a mask).

[0209] Subsequently, the SEM beam can be configured 520 so that it is configured with at least one operating parameter that can be used for imaging (analogous to step 470 as described above). The SEM beam can already be switched on or still be switched off at this point in time.

[0210] Subsequently, navigation 530 to a particle to be examined (e.g., a foreign particle) may be provided. Navigation may involve aligning the SEM beam to a region of the sample (but without switching on the SEM beam itself) and / or moving an AFM tip toward the relevant region. In parallel, the sample does not charge or at least charges slowly (depending on the selected at least one operating parameter).

[0211] Subsequently, an SEM image can be captured 540. Based at least in part on the captured SEM image, a decision can be made as to whether another area of ​​the mask should be examined or whether the particle encompassed by the SEM image should be analyzed more closely.

[0212] If it is decided that a different area of ​​the mask is to be analyzed, steps 520 - 540 can be executed again on a different area of ​​the mask, as previously described.

[0213] If, however, it is decided that further analysis of the particle is necessary, the AFM tip can be lowered 550 in the area of ​​the SEM image. The AFM tip can preferably be lowered in such a way that an electrically conductive connection is established between the AFM tip and the mask (e.g., by contacting). It can be provided that the AFM tip is lowered 550 only if at least one operating parameter is used for the SEM beam that could be expected to lead to charging of the mask (e.g., in cases where X-ray spectroscopy is required). In some cases, lowering of the AFM tip can be omitted if operating parameters are used for the SEM beam that allow a secondary electron yield of one to be expected (i.e., essentially no charging of the mask is to be expected).In this way, in some cases, step 550 may be skipped, thus advantageously increasing the throughput of a device implementing method 500.

[0214] Subsequently, the SEM beam can be configured 560 so that it can be used to analyze the area of ​​the mask captured by the SEM image (e.g., comprising the particle) (analogous to step 470 as described above).

[0215] Subsequently, an X-ray spectroscopy (e.g., an EDX analysis) can be carried out, at least in part based on the configured SEM beam.

[0216] After completing the X-ray spectroscopy, the SEM beam can be switched off and the AFM tip can be lifted from the mask.

[0217] Subsequently, a decision can be made as to whether a further region of the mask should be analyzed according to steps 530-580 or whether the mask should be ejected 590 from the device implementing the method.

[0218] In some cases, the SEM beam can be used again to acquire an SEM image. In these cases, the SEM beam can be operated with the parameters configured in step 520. In these cases (i.e., if it is not to be used to perform X-ray spectroscopy according to step 570), re-establishing an electrically conductive connection between the AFM tip and the mask can be omitted.

[0219] Fig. 6 shows an exemplary flowchart of a method 600 for influencing a charge state of a sample according to another aspect of the present invention. The method 600 is preferably performed in a device that includes both a scanning electron microscope (SEM) and a scanning probe microscope (AFM).

[0220] The method 600 may include loading 610 a mask. If the mask is successfully loaded, the loading of the mask may be communicated to a charge monitor 660.

[0221] Subsequently, an SEM-based analysis 620 of the mask can be performed to determine whether, for example, a particle (e.g., a foreign particle) is depicted in the SEM image. Before the actual analysis 620 is performed, the current charge state of the mask can first be queried from the charge monitor 660. If the current charge state of the mask reported by the charge monitor 660 falls below a (predefined) threshold value, the analysis 620 of the mask can begin immediately. This can be communicated to the charge monitor 660.

[0222] If, however, it is determined that the current charge state of the mask reported by the charge monitor 660 exceeds a (predefined) threshold value, a discharge strategy 1 is first executed. The discharge strategy 1 again requests the current charge state of the mask from the charge monitor 660. Based on the reported charge state, a suitable discharge strategy 1 can be selected, which can efficiently enable rapid discharge of the mask so that analysis 620 by SEM can begin promptly, without adverse effects for the SEM imaging and / or without potentially occurring undesired discharges from the mask to an AFM tip.

[0223] After discharge strategy 1 has been successfully executed, analysis 620 can begin. Once analysis 620 has begun, this can be communicated to the charge monitor 660.

[0224] If, after analysis 620, it is decided that X-ray spectroscopy (e.g., EDX analysis) should be performed, the current charge state of the mask can first be requested again from charge monitor 660. If the current charge state of the mask thus obtained falls below a (predefined) threshold value (up to which X-ray spectroscopy can be successfully performed), analysis 630 based on X-ray spectroscopy can begin immediately. This can be communicated to charge monitor 660.

[0225] If, however, it is determined that the current charge state of the mask reported by the charge monitor 660 exceeds a (predefined) threshold value, a discharge strategy 2 can be implemented first. Discharge strategy 2 can also request the current charge state of the mask from the charge monitor 660. Discharge strategy 2 can be selected to enable the fastest possible discharge of the mask and, based on the resulting discharge state, to ensure successful execution of the analysis 630 by means of X-ray spectroscopy. In this case, too, the execution of the analysis 630 can be communicated to the charge monitor 660.

[0226] If, for example, it is determined, at least partially based on analysis 630, that a particle (e.g., a foreign particle) on the mask is to be removed, the current charge state of the mask can first be requested again from charge monitor 660. If the current charge state of the mask reported in this way falls below a (predefined) threshold value, the gripping or removal 640 of the particle can begin immediately. This can be communicated to charge monitor 660. If, however, it is determined that the reported current charge state of the mask exceeds a (predefined) threshold value, a discharge strategy 3 can first be implemented. Discharge strategy 3 can request the current charge state of the mask from charge monitor 660.Based on the current charge state of the sample thus reported and the maximum tolerable charge of the mask for particle removal 640, a suitable discharge strategy 3 can be selected. After this has been successfully performed, particle removal 640 can begin. This can be communicated to the charge monitor 660.

[0227] The mask can then be ejected 650. However, before this step is carried out, a current charge state of the mask can be requested again from the charge monitor 660. If the reported current charge state of the mask falls below a (predefined) threshold, the ejection 650 of the mask can begin immediately. This can be communicated to the charge monitor 660. If, however, the reported current charge state of the mask exceeds the (predefined) threshold, discharge strategy 4 can be executed first. Discharge strategy 4 can request the current charge state of the mask from the charge monitor 660. Based on the current charge state of the mask thus obtained, a suitable discharge strategy 4 can be selected so that the mask can be discharged quickly and a maximum charge of the mask that is tolerable for ejection 650 can be achieved.

[0228] Discharge strategies 1-4 can be based on the same discharge strategy or can differ from each other at least with respect to two discharge strategies. Preferably, the discharge strategy is selected such that its impact on the throughput of a device implementing method 600 is minimized.

[0229] For each of the aforementioned steps 610, 620, 630, 640 and 650, an identical maximum tolerable charging threshold can be determined, based on which a decision is made about a possibly necessary discharge strategy 1-4.

[0230] Alternatively, it is possible that for each of the steps 610, 620, 630, 640 and 650 at least two different threshold values ​​are determined.

[0231] The charge monitor 660 can be configured to (continuously) monitor a current charge state of the mask.

[0232] It should also be noted that each notification of a successful execution of one of the aforementioned method steps may also include notification of the current charge state of the mask (e.g. after completion of the respective method step).

[0233] Fig. 7 shows an exemplary method 700 for monitoring a charge state of a sample (such as a mask) by a charge monitor according to one aspect of the present invention.

[0234] The monitoring can begin, for example, with the recording 710 of an SEM image.

[0235] Based at least in part on the acquired SEM image, an approach of an AFM tip towards a sample can be initiated in order to, for example, pick up a particle (e.g., a foreign particle) on the sample and, if necessary, remove it from it.

[0236] For this purpose, it may be necessary to approach an AFM tip to the sample, by means of which the particle can be removed. Before initiating the approach 720 of the AFM tip to the sample, a current charge state of the sample can first be requested from a charge monitor 750. If the current charge state falls below a (predefined) threshold value, the approach 720 of the AFM tip to the sample can be started immediately. This can be communicated to the charge monitor 750.

[0237] If the current charge state exceeds a (predefined) threshold, a discharge strategy 1 can be initiated. Discharge strategy 1 can request the current charge state of the sample from the charge monitor 750. Based on the current charge state of the sample and a maximum tolerable charge state for the approach 720, a suitable discharge strategy 1 (e.g., a plasma discharge) can be selected and executed. Subsequently, the approach 720 of the AFM tip can be started. This process can be communicated to the charge monitor 750.

[0238] The start of the approach 720 can be followed by an incremental, step-by-step approach 730. Before an incremental approach takes place, the charge monitor 750 can again query the current charge state of the sample. If this falls below a (predefined) threshold, the incremental approach 730 can begin immediately. This can be communicated to the charge monitor 750. If, however, the reported current charge state of the sample exceeds a (predefined) threshold, a discharge strategy 2 can be executed. Discharge strategy 2 can request the current charge state of the sample from the charge monitor 750. A suitable discharge strategy 2 can be determined and executed based at least in part on the requested current charge state of the sample and a maximum tolerable charge state for the incremental approach step 730.Subsequently, the incremental approach step 730 can be executed. This can again be communicated to the load monitor 750.

[0239] The described sequence of incremental approach 730 can be performed repeatedly (e.g., in a loop). In particular, during each of the incremental approach steps, the AFM tip can act as a probe that can detect an interaction between the AFM tip and a possibly charged sample. The interaction can, for example, comprise a repulsion of the AFM tip from the sample or an attraction of the AFM tip towards the sample. Thus, with each approach step of the AFM tip towards the sample, an analysis of the current charge state of the sample can be performed. The smaller the distance between the AFM tip and the sample, the better the actual charge state of the sample can be resolved.

[0240] By gradually approaching the AFM tip toward the sample, unwanted arcing from the potentially charged sample to the AFM tip, which could lead to damage to the AFM tip and / or the sample, can be effectively prevented, and detailed information about the current charge state of the sample can be obtained. For example, if it is determined that the sample already has an increased charge, a discharge of the sample can be initiated before the AFM tip is moved closer to the sample in a subsequent incremental approach step.

[0241] Finally, the approach of the AFM tip to the sample may be completed 740. Completing the approach may include establishing an electrically conductive connection between the AFM tip and the sample (e.g., by contacting) as described herein.

[0242] It should also be noted that each notification of a successful execution of one of the aforementioned method steps may also include notification of the current charge state of the sample (e.g. after completion of the respective method step).

[0243] In some cases, the incremental, step-by-step approach 730 can be at least partially replaced by a continuous approach of the AFM tip to the sample. It may be possible for information regarding a current charge state of the sample to be acquired even while the AFM tip is approaching the sample. In some cases, provision may be made to influence the charge state of the sample (e.g., discharging) in parallel with the approach. Preferably, for example, while the AFM tip is approaching the sample, an SEM beam with an acceleration voltage of, for example, 1 kV can be directed onto the sample, thereby contributing, for example, to a discharge of the sample. After establishing an electrically conductive connection between the AFM tip and the sample, the SEM beam can be configured to record an SEM image.

[0244] In some cases, the approach can be based on a combination of stepwise and continuous approach. For example, it may be possible to first continuously approach the AFM tip to a sample surface to within approximately 10 µm using a piezo. If the AFM tip has not yet touched the sample surface, the AFM tip can be retracted by 10 µm. The AFM tip can then be approached to within approximately 5-8 µm of the sample surface using a coarse drive, without touching the surface. The tip can then be approached to the sample surface again using a piezo, starting from the position of the AFM tip after approach using the coarse drive. This alternation of continuous and stepwise approach is continued until the AFM tip contacts the sample surface.

[0245] The discharge strategies, as with reference to Fig. 7, can be at least partially assigned to the discharge strategies 1-4, as described with reference to Fig. 6. In particular, a discharge strategy can also be based, at least in part, on a suitable choice of SEM parameters.

[0246] Fig. Figure 8 shows an exemplary illustration of a model 800 for monitoring a charge state of a sample according to one aspect of the present invention. In addition or alternatively to monitoring a charge state of the sample based on at least one measured process parameter (described herein), it is possible to provide monitoring based at least in part on a model of the charging process. The model may be based on a known characteristic of the influence of the at least one process parameter on a charge state of the sample.

[0247] In order to determine a charge state of the sample, for example, at least one process parameter can be selected which is at least partially based on an environment of the sample. This at least one process parameter can, for example, comprise information associated with the type and nature of the electrical contacting (possibly isolated areas present on the sample, grounding, etc.). Additionally or alternatively, it is also possible for the at least one process parameter to be associated with an environment of the sample (e.g. temperature, humidity, etc.), a gas atmosphere (in which the sample is located), or vacuum conditions to which the sample is exposed. In some cases, the at least one process parameter can be based at least partially on properties of the sample (e.g. a mask). For example, the at least one process parameter can be based on a material mix of the sample and / or a structure of the sample (e.g. the number of edges present on the sample).

[0248] Additionally or alternatively, it is possible for the model to be based, at least in part, on at least one process parameter associated with a sample charging method. This may include, for example, SEM settings (such as an SEM acceleration voltage (electron high tension (EHT)) and / or an SEM particle current.

[0249] Additionally or alternatively, it is possible for the model to be based, at least in part, on at least one parameter associated with a sample discharge method. Thus, the at least one process parameter may be associated with a plasma discharge, an SEM discharge (e.g., particle stream), and / or flood gun operation.

[0250] Additionally or alternatively, it is possible that the at least one process parameter is associated with at least one monitoring method. This can include, for example, an energy shift of secondary electrons, an SEM grayscale value, an SEM image shift and / or an SEM image drift, an AFM force-sensitive signal (e.g., an attractive force between the AFM tip and the sample), and / or an energy shift of the trailing edge of a bremsspectrum according to the Duan Hunt limit in EDX applications. The latter can, for example, allow for the current charge state of the sample to be deduced by determining the energy of the trailing edge of a bremsspectrum. This can be made possible by the energy value of the trailing edge of the bremsspectrum being equal to the accelerating voltage of the incident electrons in the absence of a charge on the sample. Any deviation from this theoretical correlation can, for example,can be explained by a charge on the sample. For example, if the sample is positively charged, incoming electrons can be accelerated towards the sample. This can lead to the effective landing energy of the electrons being higher than their acceleration voltage. This can shift the energy of the break-off edge towards a higher energy than would be expected from the acceleration energy of the electrons. If, on the other hand, the sample is negatively charged, incoming electrons can be decelerated by the counterpotential of the sample, which can lead to a correspondingly reduced landing energy of the electrons on the sample. This, in turn, can lead to a shift in the energy of the break-off edge of the deceleration spectrum towards lower energies than would be theoretically expected based on the acceleration voltage of the electrons.

[0251] The respective at least one process parameter can be fed to a charge monitor, which can (continuously) monitor a charge state of the sample based on the provided information. From this, the charge monitor can provide information regarding a current sample potential (e.g., mask potential) and / or a current sample charge (e.g., mask charge). QUOTES CONTAINED IN THE DESCRIPTION

[0000] This list of documents submitted by the applicant was generated automatically and is included solely for the convenience of the reader. This list is not part of the German patent or utility model application. The DPMA assumes no liability for any errors or omissions. Cited patent literature

[0000] US 9,995,764 B2

[0016] EP 1587 128

[0088]

Claims

[1] A method for influencing a charge state of a sample, comprising: Directing a charged particle beam onto the sample for analyzing and / or processing the sample, wherein the particles of the particle beam are accelerated onto the sample with a first accelerating voltage and lead to a charging of the sample; Directing the charged particle beam onto the sample to influence the charging of the sample, wherein the particles of the particle beam are accelerated onto the sample with a second, modified acceleration voltage which is at least 15% of the first acceleration voltage. [2] The method of claim 1, wherein the second, changed acceleration voltage is smaller than the first acceleration voltage. [3] A method according to any one of claims 1 or 2, wherein analyzing comprises receiving X-rays generated by the particle beam in the sample. [4] A method according to any one of the preceding claims, wherein the first acceleration voltage is at least 1 kV, more preferably at least 3 kV and most preferably at least 4 kV. [5] Method according to one of the preceding claims, wherein the second acceleration voltage is at least 30%, preferably at least 40%, particularly preferably at least 50% and most preferably at least 60% of the first acceleration voltage. [6] Method according to one of the preceding claims, wherein the particle beam for analyzing has a particle current of at least 5 pA, preferably at least 1 nA and most preferably at least 150 nA. [7] Method according to one of the preceding claims, wherein the particle flow during the analysis and / or processing of the sample is substantially equal to the particle flow during the influencing of the charging of the sample. [8] Method according to one of the preceding claims, comprising: Directing the charged particle beam N times at the sample to influence the charge of the sample, whereby the particles are accelerated towards the sample with an Nth acceleration voltage each time, where N is greater than or equal to two. [9] The method according to claim 8, wherein the N-th acceleration voltage is at least 30%, preferably at least 40%, more preferably at least 50%, most preferably at least 60%, and most preferably 70% of the (N-1)-th acceleration voltage. [10] Method according to one of claims 8 or 9, wherein the N-th acceleration voltage is at least 250 V lower than the (N-1)-th acceleration voltage and / or wherein the N-th acceleration voltage is at most 4 kV lower than the (N-1)-th acceleration voltage. [11] Method according to one of claims 8-10, wherein the N-fold straightening is carried out successively and the acceleration voltage is reduced at least twice. [12] Method according to claim 11, wherein the at least two reductions are carried out by the same amount each time. [13] Method according to claim 11, wherein the at least two-fold reduction is carried out in such a way that the reduction amounts follow a logarithmic curve. [14] Method according to one of the preceding claims, wherein the particle beam is directed onto the sample without interruption between at least two accelerating voltages. [15] A method according to any one of the preceding claims, wherein said influencing comprises reducing the charge of the sample. [16] A method according to any one of the preceding claims, further comprising: Detecting at least one process parameter associated with a current charge state of the sample. [17] The method of claim 16, wherein the second acceleration voltage is based at least in part on the at least one process parameter. [18] A method according to any one of claims 16 or 17, wherein the detecting further comprises: Modulating the accelerating voltage; and Demodulating at least one process parameter. [19] A method according to any one of claims 16-18, further comprising: Directing the particle beam onto the sample with an accelerating voltage based at least in part on a closed feedback loop including the at least one process parameter as an input. [20] Method according to claim 18 or 19, wherein the at least one process parameter is kept substantially constant over time. [21] The method of any of claims 16-20, wherein the at least one process parameter is associated with a secondary electron yield, SEY. [22] Method according to one of the preceding claims, wherein the method is preceded and / or followed by taking a scanning electron microscope (SEM) image. [23] A method according to any one of the preceding claims, further comprising: Providing an electrically conductive element; At least partially directing the charged particle beam onto the electrically conductive element in order to release secondary particles from the electrically conductive element. [24] A method (400; 500; 800) for influencing a charge state of a sample, comprising: Providing a scanning probe microscope, SPM, tip (420; 550; 820); Establishing (440; 550) an electrically conductive connection between the sample and the SPM tip to influence the charge state. [25] The method of claim 24, further comprising: Directing (460, 470; 540, 560) a particle beam onto the sample for analyzing and / or processing the sample; and wherein establishing (440; 550) the electrically conductive connection is based at least in part on a measured and / or expected charge state of the sample. [26] A method according to claim 24 or 25, wherein the method is carried out in a combined scanning probe microscope-scanning electron microscope device. [27] The method of claim 26, wherein the electrically conductive connection is established by approaching (440; 550; 830, 840) the SPM tip to a surface of the sample. [28] The method of claim 27, wherein the approximation is based at least in part on detecting at least one process parameter. [29] A method for monitoring a charge state of a sample, comprising: Detecting a process parameter associated with the charge state of the sample, wherein the process parameter was recorded with a scanning electron microscope, SEM, a scanning probe microscope, SPM, and / or an X-ray detector; Determining the charge state of the sample based at least in part on the process parameter. [30] The method of claim 29, wherein the determination is based at least in part on a previously known relationship between the process parameter and the charge state of the sample. [31] A method according to any one of claims 29 or 30, wherein the determining is based at least in part on detecting an interaction between a tip of the SPM and the sample. [32] A method according to any one of claims 29-31, further comprising: Initiating a process for influencing the charge state of the sample if a predetermined charge threshold of the sample is exceeded. [33] A computer program comprising code for carrying out a method according to any one of claims 1-32. [34] Device for influencing a charge state of a sample, comprising: an electrically conductive element and / or a particle beam of a scanning electron microscope, SEM and / or an X-ray detector; Means for automatically executing the method according to any one of claims 1-30. [35] The apparatus of claim 34, further comprising: Means for controlling a distance of the electrically conductive element from the sample and / or an accelerating voltage of the particle beam. [36] Apparatus according to any one of claims 34 or 35, further comprising: Means for executing the computer program according to claim 33.

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