Mask topology-based charge state control

Abstract

One aspect concerns a method for influencing the charge state of a lithographic mask. This method involves selecting a region of the mask based on the material distribution within that region. The method further includes directing a particle beam onto that region of the mask to influence its charge state.

Description

Field of invention

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

[0002] With increasing integration density, the demands on mask manufacturing also increase (e.g., due to the associated reduction in feature sizes on the mask or the higher material requirements of lithography). The manufacturing processes for such masks are therefore becoming increasingly complex, time-consuming, and expensive. Mask defects cannot always be avoided. Typically, these defects are repaired using particle beam processing, as their small dimensions often make them suitable for particle beam repair.

[0003] Furthermore, in the semiconductor industry, for example, it may be necessary to examine masks with a particle beam. For instance, to repair mask defects, it may be necessary to use a particle beam to take images of the mask defects or the repair area (e.g., for a high-resolution SEM image).

[0004] However, the masks to be analyzed and / or processed with the particle beam may exhibit an (undesired) electrostatic charge. This (undesired) electrostatic charge can cause adverse effects. For example, it can deflect the particle beam from its intended point of impact on the mask. Furthermore, it can also prevent a particle beam-based reaction from achieving the desired effect. Therefore, the (undesired) electrostatic charge can unintentionally interfere with the defined analysis and / or processing of the mask.

[0005] Therefore, in order to analyze and / or process the mask with a particle beam, the effects caused by the electrostatic charging of the mask usually have to be technically circumvented.

[0006] In some cases, a static charge on the mask can be eliminated by placing an electrical contact in the area of ​​conductive structures on the mask that are surrounded by electrical insulation. However, this carries the risk of damaging (scratching) or contaminating the mask (generating foreign particles) and can lead to a restriction of the workable area of ​​the mask (space limitation due to the contact). If there are several unconnected structures on the mask (e.g., separated by insulation), they cannot all be grounded together with a single electrical contact on the mask. Instead, multiple electrical contacts on the mask may be necessary to ground the relevant areas.

[0007] Another way to counteract mask charging can be provided, for example, by a floodgun. A floodgun irradiates the mask with an electron beam whose voltage and current are selected to compensate for the charging caused by a SEM. However, a disadvantage is that the secondary electrons generated by the floodgun can also be detected by the SEM detector, creating an offset that can complicate automated SEM image analysis. Furthermore, it may be necessary to align the floodgun with the SEM spot on the mask, as otherwise, depending on the mask's position and structure, the charging cannot be compensated for. This alignment is often difficult to achieve satisfactorily due to space limitations imposed by the equipment used.A subsequent discharge step, in which the mask position analyzed in the SEM is moved to the floodgun, can greatly reduce the throughput of such a device.

[0008] Therefore, the solutions already known for influencing the charge state of a mask are not always optimal.

[0009] In light of this technical background, there is therefore a need for improved methods to influence the loading state of a lithographic mask. Summary of the invention

[0010] This need is at least partially met by the aspects described herein.

[0011] One aspect concerns a method for influencing the charge state of a lithographic mask. This method involves selecting a region of the mask based on the material distribution within that region. The method further includes directing a particle beam onto that region of the mask to influence its charge state.

[0012] Selecting a mask area can involve choosing one area from a multitude of mask areas. For example, the mask area can be selected from the multitude of mask areas based on a material distribution within the mask area. In general, the mask can be associated with a material distribution. Specifically, the material distribution of the mask area can be based on the mask's material distribution within that area. In other words, the material distribution of the area can effectively match the mask's material distribution within that area. For example, a first mask area can be associated with a first material distribution. Additionally or alternatively, a second mask area can be associated with a second material distribution. The first and second areas can be disjoint.Alternatively or additionally, the first area can overlap at least partially with the second area.

[0013] In some embodiments, selecting the area based on its material distribution may involve comparing the material distributions of several or a multitude of areas within the mask. Specifically, the material distributions of the multitude of areas may be compared against a target material distribution. In particular, selecting the area from the multitude of areas may be based on minimizing the difference between the material distribution of the selected area and the target material distribution. For example, the first material distribution of the first area may be compared with the second material distribution of the second area. Specifically, this comparison may involve calculating an initial difference between the first material distribution and the target material distribution.Additionally, the comparison can include calculating a second difference between the second material distribution and the target material distribution. For example, the first range can be selected if the first difference is smaller than the second difference. Alternatively or additionally, the second range can be selected if the second difference is smaller than the first difference.

[0014] The material distribution of the mask can be one-dimensional. Alternatively or additionally, the material distribution of the mask can be two-dimensional. Alternatively or additionally, the material distribution of the mask can be three-dimensional. A two-dimensional material distribution of the mask can be based on a planar top view of the mask. In other words, a two-dimensional material distribution of the mask can be based on a material distribution of the mask with respect to a plane that is parallel to the plane in which the mask lies. For example, the plane can be located above a multilayer of the mask.

[0015] Directing the particle beam onto the mask area can involve scanning the beam across the area. For example, the particle beam can be directed onto the mask area in such a way that the energy of the particle beam is applied essentially homogeneously to the area. The particle beam can be a (focused) electron beam. In particular, the particle beam can be provided by a scanning electron microscope (SEM). Other particle beams are also possible in other examples.

[0016] By selecting the mask area based on its material distribution and directing the particle beam onto this selected area, the influence on the mask's charge state can be optimized. For example, the difference between the actual and intended influence on the mask's charge state can be minimized. In particular, the inventors recognized that the actual influence on the mask's charge state can depend on the local material distribution of the area toward which the particle beam is directed. Depending on this local material distribution, the area can exhibit different properties, such as those related to secondary electron emission. Therefore, selecting the area based on its material distribution allows for area-specific control of the mask's charge state.For example, an area of ​​the mask can be selected with a material distribution that results in a particularly high secondary electron emission, so that, for example, the area can be strongly positively charged.

[0017] In general, the procedure can, as an alternative or in addition to selecting a region, include selecting at least one parameter of the particle beam based on the material distribution of a region of the mask. For example, the selection of at least one parameter can be based on the material distribution of the selected region of the mask (as described above). However, it is not necessary that the region has already been selected based on the material distribution. The region can, for example, also be a predefined region (e.g., a region to be repaired and / or imaged).

[0018] At least one parameter of the particle beam can include an accelerating voltage. Alternatively or additionally, at least one parameter can include a landing energy of the particle beam. Alternatively or additionally, at least one parameter can include a beam flux of the particle beam. In particular, the landing energy and / or the accelerating voltage of the particle beam can be selected based on the material distribution of the mask area. For example, for a first area with a first material distribution, a first accelerating voltage can be selected based on the first material distribution. Alternatively or additionally, for a second area with a second material distribution, a second accelerating voltage can be selected. This is because, depending on the material distribution, for example, different accelerating voltages can be obtained.Different dependencies of secondary electron emission arise as a function of the landing energy of the particles in the particle beam. Therefore, considering the material distribution can help to achieve a desired state of charge as quickly as possible and / or with the lowest possible dose of the particle beam.

[0019] It is emphasized that the term "material distribution" used herein does not necessarily require (precise) knowledge of the mask's materials. Rather, it can also be considered "based on a material distribution" if, for example, a distribution of a characteristic parameter is used (e.g., a measure of secondary electron yield) that is related to the material distribution.

[0020] Additionally, directing the particle beam onto the area of ​​the mask can include adjusting at least one selected parameter.

[0021] By selecting at least one parameter of the particle beam based on the material distribution of the area, the particle beam, in particular its landing energy, can be adapted to the properties characteristic of the selected area, such as the specific material distribution. This allows for improved and more targeted control of the mask's charge state.

[0022] In particular, the selection of the area can be carried out in such a way that the material distribution of the area includes at least one spatial variation, especially of an edge.

[0023] The spatial variation of the material distribution can include a change in the material distribution itself. For example, the spatial variation can include a transition from a region containing (absorbing and / or phase-shifting) material to a region without (absorbing and / or phase-shifting) material. In particular, the spatial variation can include a transition from a region with a material structure to a region without the material structure. Specifically, the transition from one region to the other can include an edge. In some embodiments, the spatial variation of the material distribution can be a transition from an absorber of the mask to a clear region, e.g., a region without an absorber, of the mask.When a particle beam encounters an edge or similar variation in the material distribution, there is usually - ceteris paribus - a comparatively high secondary electron yield (compared to areas without variation in the material distribution).

[0024] For example, at least one spatial variation in the material distribution of the area can be designed in such a way that it is suitable for drift correction of the mask. Thus, in some examples, the loading state can be well controlled when rasterizing the area for drift correction.

[0025] In general, the selection of the area can also be based on the current loading state of the lithographic mask. Additionally or alternatively, the selection of the area can also be based on a target loading state of the lithographic mask.

[0026] In general, the actual charge state of the mask can encompass its current charge level. For example, the actual charge state can be negative and / or positive. Additionally, or alternatively, the target charge state can encompass the desired charge level of the mask after the particle beam is directed onto the mask's area. For example, the area can be selected based on the sign of the mask's actual charge level and / or the target charge level. Alternatively, or additionally, the area can be selected based on the difference between the mask's actual charge level and the target charge level. In particular, the area can be selected based on the absolute value of this difference.In some embodiments, directing the particle beam onto a first region with a first material distribution can lead to a first influence on the current charge state of the mask. Alternatively or additionally, directing the particle beam onto a second region with a second material distribution can lead to a second influence on the current charge state of the mask. If the current charge state of the mask includes a negative charge, e.g., the mask is negatively charged, the first region can be selected to at least partially discharge the mask. If the current charge state of the mask includes a positive charge, e.g., the mask is positively charged, the second region can be selected to at least partially discharge the mask. In some embodiments, the first region of the mask comprises a higher material distribution, e.g., a larger quantity of material, than the second region.

[0027] For example, if a positive charge of the mask is necessary to bring it into the desired state (e.g., a discharged state), an area can be selected that is associated with a high secondary electron yield when irradiated with the particle beam. The appropriate selection can be made based on the material distribution. In some examples, an area predominantly containing absorber material can be selected, as such an area generally exhibits a higher secondary electron yield than an area predominantly without absorber material. In some examples, an area with a high proportion of edges can also be preferred, as a particularly high secondary electron yield is generally expected there.

[0028] In general, at least one parameter of the particle beam can be selected based on the current state of charge of the mask. Alternatively or additionally, at least one parameter of the particle beam can be selected based on the target state of charge of the mask. For example, the accelerating voltage of the particle beam can be selected based on the current state of charge of the mask.

[0029] By selecting the area based on the mask's current state of charge, the actual or current charge level of the mask can be taken into account. Specifically, the area can be selected based on the material distribution within the area, considering the mask's current charge level. Thus, selecting the mask area based on the current charge level optimizes the manipulation of the mask's charge level. In particular, the area can be selected based on the current charge level of the mask in such a way as to minimize the difference between the mask's charge level after the particle beam is directed onto the selected area and the target charge level of the mask.

[0030] Furthermore, the method can include determining the current state of charge of the mask. In particular, determining the current state of charge of the mask can be based, at least partially, on an AFM tip approaching the mask. In some examples, determining the current state of charge of the mask can be based, at least partially, on an AFM tip approaching the mask.

[0031] Determining the current state of charge of the mask can involve determining the sign of the mask's charge. Alternatively or additionally, determining the current state of charge of the mask can involve at least partially quantifying the mask's charge. Determining the current state of charge of the mask can be based on an interaction of the AFM tip with at least a part of the mask. For example, the AFM tip can act as a probe capable of detecting an interaction between the AFM tip and a potentially charged mask. The interaction can, for example, involve a repulsion of the AFM tip from at least a part of the mask. Alternatively or additionally, the interaction can, for example, involve an attraction of the AFM tip to at least a part of the mask. In some cases, the AFM tip may be uncharged (neutral) at the beginning of the approach. By approaching the AFM tip towards the mask, if the mask is already, for example, charged, the AFM tip can be charged.The AFM tip exhibits a charge that induces a charge state opposite to that of the mask. This can contribute to an attractive interaction between the AFM tip and the mask.

[0032] Specifically, the approach of the AFM tip to the mask can be performed incrementally. This 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 greater than 100 µm or less than 10 µm. It is also possible to choose a step size between the values ​​mentioned above.

[0033] Alternatively or additionally, the approach of the AFM tip to the mask can be continuous. Continuous approach differs from stepwise approach in that the approach does not have explicitly defined dwell points (e.g., for a predetermined time interval) at individual steps. Any dwell time that may occur during continuous approach can be attributed to characteristics of the drive (e.g., a stepper motor).

[0034] In general, further approach of the AFM tip to the mask can be aborted if the detected interaction indicates that the mask already has a charge state (e.g., a comparatively high charge) that would promote an unwanted discharge (e.g., by arcing) of the mask via the AFM tip. This prevents damage to the mask and / or the AFM tip.

[0035] The determined current state of charge of the mask can be considered as a parameter when selecting the mask area and / or when selecting at least one parameter of the particle beam. Thus, determining the current state of charge of the mask contributes to optimizing the manipulation of the mask's charge state, e.g., minimizing the difference between the mask's charge state after directing the particle beam onto the (selected) area and the target charge state.

[0036] The method according to the invention can first comprise obtaining an actual state of charge of at least a part of the mask. For example, obtaining the actual state of charge can include determining the actual state of charge based on the method described above. Additionally, a target state of charge of the at least part of the mask can be obtained. For example, the target state of charge can be a neutral state of charge. Based on the actual state of charge and / or the target state of charge of the at least part of the mask, it can be determined whether the at least part of the mask needs to be charged or discharged. Specifically, determining whether the at least part of the mask needs to be charged or discharged can be based on a difference between the actual state of charge of the mask and the target state of charge of the mask. For example, it can be determined that the mask is positively charged.In some embodiments, the state of charge can be influenced by converting the positively charged mask to a neutral state. Converting the positively charged mask to a neutral state can involve applying negative charges, e.g., electrons, to the mask. Alternatively, the mask can be determined to be negatively charged. In some embodiments, the state of charge can be influenced by converting the negatively charged mask to a neutral state. Converting the negatively charged mask to a neutral state can involve removing negative charges, e.g., electrons, from the mask.

[0037] Based on the mask's state of charge, e.g., whether the mask is positively and / or negatively charged, the area of ​​the mask can be selected, e.g., the area of ​​the mask onto which the particle beam should be directed. In particular, the area of ​​the mask can be selected in such a way that the discharging and / or charging of the mask occurs optimally, e.g., at maximum speed.

[0038] For example, if the mask is negatively charged and is to be brought to a neutral charge state and / or the negative charge of the mask is to be reduced, the region of the mask can be selected such that the secondary electron yield associated with that region is maximized. A maximum secondary electron yield can be achieved by ensuring that more electrons leave at least part of the mask than are deposited by the particle beam directed at the mask. In particular, the secondary electron yield associated with the region can be σ > 1. For example, the region can be selected from a plurality of regions of the mask such that the secondary electron yield associated with the selected region is greater than (equal to) the secondary electron yields associated with the (other) regions of the plurality.Specifically, the selected area can include an edge of an absorber structure of the mask.

[0039] In general, the region can be selected from a multitude of regions with respect to predefined particle beam parameters. In other words, the secondary electron yields of the multitude of regions can be determined with respect to the predefined particle beam parameters. Specifically, the secondary electron yield can be a value for a region of the mask and predefined particle beam parameters. For example, the predefined particle beam parameters can include an accelerating voltage and / or a landing energy of the particle beam. For example, a first region of the mask for predefined particle beam parameters, e.g., a predefined accelerating voltage, can be associated with a first secondary electron yield. Furthermore, a second region of the mask for predefined particle beam parameters, e.g.,The predefined accelerating voltage can be associated with a second secondary electron yield. In particular, the first secondary electron yield can be greater than the second secondary electron yield. For example, the first region can then be selected, i.e., the region with the higher secondary electron yield.

[0040] Alternatively or additionally, a region can be associated with a multitude of secondary electron yields. For example, the region can be associated with a multitude of secondary electron yields for a multitude of values ​​for the at least one parameter of the particle beam. For example, the region can be associated with a first secondary electron yield for a first value for the at least one parameter of the particle beam. Furthermore, the region can be associated with a second secondary electron yield for a second value for the at least one parameter of the particle beam. In particular, the at least one parameter of the particle beam can include an accelerating voltage and / or a landing energy. For example, the first value can include a first accelerating voltage and / or a first landing energy. Additionally, the second value can include a second accelerating voltage and / or a second landing energy.

[0041] In some embodiments, the secondary electron yield associated with the region comprises a function and / or an assignment rule that assigns a secondary electron yield associated with the region to an accelerating voltage and / or a landing energy of the particle beam. For example, the first region may be associated with a first function and / or a first assignment rule. Furthermore, the second region may be associated with a second function and / or a second assignment rule.

[0042] In general, for a negatively charged mask, the region can be selected from the multitude of regions such that a maximum of the secondary electron yield associated with that region is greater than or equal to the maxima of the secondary electron yields associated with the other regions of the multitude. For example, a first region can be associated with a first secondary electron yield function and / or a first secondary electron yield allocation rule. In particular, the first secondary electron yield function and / or the first secondary electron yield allocation rule can include a first maximum. The first maximum can be assumed for a first accelerating voltage value and / or a first landing energy value of the particle beam. Furthermore, a second region can be associated with a second secondary electron yield function and / or a second secondary electron yield allocation rule.In particular, the second secondary electron yield function and / or second secondary electron yield assignment rule can include a second maximum. This second maximum can be assumed for a second accelerating voltage value and / or a second landing energy value of the particle beam. Generally, the region can be selected whose maximum associated secondary electron yield is greater than (equal to) the maxima of the associated secondary electron yields of the remaining regions of the plurality of regions.

[0043] In the case of a positively charged mask, the procedure described above can be applied analogously, taking into account that the crucial factor is now the smallest possible secondary electron yield (in any case less than 1), i.e., fewer electrons leaving the mask than are deposited by the particle beam. In other words, the region can be selected such that the secondary electron yield associated with that region is less than or equal to the secondary electron yields of the other regions among the multitude of regions.

[0044] In general, the procedure can also include determining the material distribution of the area. Additionally, or alternatively, the procedure can also include determining the material distribution of the lithographic mask.

[0045] Determining the material distribution can involve assigning a material value to a point in space. Specifically, the point in space can be associated with a region of its environment. For example, assigning the material value to the point in space can include assigning the material value to the environment of the point in space. Alternatively, or additionally, a material distribution based on the material value of the point in space can be assigned to the environment of the point in space, e.g., a material distribution as a function of the material value of the point in space.

[0046] In general, the material value can include a quantification of a material quantity and / or a material type. Alternatively or additionally, the material value can include an indicator of the presence of a material at a point in space. Alternatively or additionally, the material value can include an indicator of the absence of a material at a point in space. Alternatively or additionally, the material value can include an indicator of the presence of an edge at a point in space.

[0047] Determining the material distribution can involve determining a one-dimensional material distribution of the area and / or the mask. This can also include determining a material distribution along a one-dimensional path with respect to the area and / or the mask. For example, at least one point on the path can be assigned a material value.

[0048] Alternatively or additionally, determining the material distribution of the area and / or mask can include determining a two-dimensional material distribution of the area and / or mask. Determining a two-dimensional material distribution of the area and / or mask can involve determining a material distribution along a two-dimensional plane with respect to the area and / or mask. For example, the two-dimensional plane can correspond to a front face of the mask. In other words, the two-dimensional plane can be a plane parallel to a surface of the mask's multilayer, such as a plane spaced from the surface of the mask's multilayer.

[0049] Alternatively or additionally, determining the material distribution of the area and / or mask can include determining a three-dimensional material distribution of the area and / or mask. Determining the three-dimensional material distribution of the area and / or mask can include determining a material distribution within a volume. The volume can at least partially encompass the area and / or mask. For example, at least one point within the volume can be assigned a material value.

[0050] Determining the material distribution of the area and / or mask allows the area to be selected based on the actual and / or individual material distribution of the area and / or mask. This ensures that the area is selected based on the actual properties and conditions of the mask. This contributes to optimal control of the mask's charge level.

[0051] In particular, determining the material distribution of the area and / or mask can be based on a design file associated with the lithographic mask. Additionally, or alternatively, determining the material distribution of the area and / or the lithographic mask can be based on a SEM image.

[0052] For example, the mask design file can include a material distribution for the area and / or the mask. Specifically, the mask design file can include a material distribution for an ideal area and / or an ideal mask. The material distribution of the ideal area and / or the ideal mask can include a target material distribution, e.g., a (theoretically) intended material distribution for the area and / or the mask.

[0053] Alternatively or additionally, determining the material distribution of the area and / or mask can be based on a SEM image associated with the area and / or mask. For example, a SEM image can be simulated based on the mask's design file. Alternatively, or additionally, a SEM image of the area and / or mask can be acquired. For example, the SEM image of the area and / or mask can be acquired in such a way that it is suitable for determining the material distribution of the area and / or mask. In particular, the secondary electron yield of the area and / or mask can be derived from the SEM image. For example, an intensity in the SEM image can be associated with a secondary electron yield. Specifically, the secondary electron yield of the area and / or mask can be derived from an intensity distribution.

[0054] Determining the material distribution of the area and / or mask based on a mask design file and / or a SEM image, preferably an SEM image associated with the area and / or mask, enables an accurate and efficient determination of the material distribution. In particular, if the material distribution determination is based on the mask design file and / or the SEM image of a reference mask—for example, if a new (individual) SEM image does not need to be acquired for each mask—the process for influencing the mask's charge state can be significantly accelerated. Thus, determining the material distribution of the area and / or mask based on a mask design file and / or a SEM image contributes to the efficiency and / or cost-effectiveness of the process.

[0055] In general, the material distribution of the area and / or the lithographic mask can include a material distribution of an absorber structure of the area and / or the lithographic mask.

[0056] For example, the material distribution of the area and / or mask can include an indicator of the presence of an absorber structure at a point in space. Alternatively or additionally, the material distribution of the area and / or mask can include an indicator of the absence of an absorber structure at a point in space. Alternatively or additionally, the material distribution of the area and / or mask can include an indicator of an edge of the absorber structure. Alternatively or additionally, the material distribution of the area and / or mask can include the height of the mask's absorber structure.

[0057] If the material distribution of the area and / or the mask includes a material distribution of the absorber structure, the area can be selected based on the material distribution or a topology of the absorber structure. In particular, a material distribution of the area and / or the mask that includes a material distribution of the absorber structure allows the area to be selected based on the presence and / or absence of absorber material of the mask in the area and / or the presence of an edge of the absorber material in the area.

[0058] In general, the area of ​​the mask can be associated with a local secondary electron yield.

[0059] The local secondary electron yield can be specific to the selected region. In other words, the local secondary electron yield of the region can be specific or characteristic to that region, and may differ from a global secondary electron yield of the mask, such as a secondary electron yield averaged over a multitude of regions. Generally, the selection of the mask region can be based on the secondary electron yield associated with that region. Specifically, the secondary electron yield can be associated with the particle beam landing energy. For example, the secondary electron yield can be a function of the landing energy. Additionally, or alternatively, the local secondary electron yield can be based on the current state of charge of the mask.In general, a first region of the mask can be associated with a first secondary electron yield. Specifically, the first secondary electron yield can be based on a material distribution of the first region, e.g., on a material distribution of an absorber structure within the first region. Alternatively or additionally, a second region of the mask can be associated with a second secondary electron yield. Specifically, the second secondary electron yield can be based on a material distribution of the second region, e.g., on a material distribution of an absorber structure within the second region. In some embodiments, the first region can be associated with a material distribution that at least partially comprises an absorber structure. Alternatively or additionally, the second region can be associated with a material distribution that comprises a clear region of the mask, e.g., a region of the mask without an absorber structure.Specifically, the first secondary electron yield can be greater than the second secondary electron yield. For example, the first secondary electron yield can be greater than the second secondary electron yield if a first maximum associated with the first secondary electron yield is greater than a maximum associated with the second secondary electron yield. Additionally, or alternatively, a third region of the mask can be associated with a third secondary electron yield. Specifically, the third secondary electron yield can be based on a material distribution of the third region. For example, the material distribution of the third region can include an edge, such as an edge of an absorber structure of the mask. In particular, the secondary electron yield of the third region can be greater than a secondary electron yield of the second and / or the first region.

[0060] Associating a region with a local secondary electron yield allows the region to be selected based on that yield. Specifically, the selection can be based on the region's local secondary electron yield and the current and / or target state of charge of the mask. Selecting the region based on its associated secondary electron yield enables more accurate and precise control of the mask's state of charge.

[0061] For example, the selection of at least one parameter of the particle beam can be based on the local secondary electron yield. Additionally, or alternatively, the selection of at least one parameter of the particle beam can be based on the actual state of charge of the mask and / or the target state of charge of the mask.

[0062] For example, the selection of the accelerating voltage and / or the landing energy of the particle beam can be based on the local secondary electron yield of the (selected) region. Specifically, for a first region of the mask, which is associated with a first local secondary electron yield, a first parameter of the particle beam, e.g., a first accelerating voltage and / or a first landing energy, can be selected. Additionally, or alternatively, for a second region of the mask, which is associated with a second local secondary electron yield, a second parameter of the particle beam, e.g., a second accelerating voltage and / or a second landing energy, can be selected.

[0063] In general, the procedure can further include determining the secondary electron yield of the region. In particular, the determination of the secondary electron yield can be based on a mask potential measurement.

[0064] Determining the secondary electron yield of a region can involve determining the secondary electron yield for a specific landing energy and / or accelerating voltage of the particle beam. Alternatively or additionally, determining the secondary electron yield can involve determining the secondary electron yield for a variety of landing energies and / or accelerating voltages of the particle beam. Specifically, determining the secondary electron yield can involve determining a function based on this variety of landing energies and / or accelerating voltages. For example, a secondary electron yield function can be assigned to a landing energy and / or accelerating voltage. In particular, the function can be based on an interpolation of the variety of landing energies and / or accelerating voltages.In some embodiments, the interpolation may include polynomial interpolation, e.g., Lagrange and / or Newton interpolation. Additionally, or alternatively, the interpolation may include trigonometric interpolation, spline interpolation, and / or wavelet interpolation. Generally, the secondary electron yield may be based on the current state of charge of the mask. In particular, the particle beam landing energy may be based on the current state of charge of the mask. For example, for a specific accelerating voltage of the particle beam, the landing energy may be based on the current state of charge of the mask. In other examples, determining the secondary electron yield of the region may involve determining a landing energy that results in a maximum secondary electron yield and / or at which a transition from >1 to <1 of the secondary electron yield occurs (upon increasing the landing energy).

[0065] In general, determining the secondary electron yield can be based on determining the electrical capacitance of at least part of the mask. Specifically, determining the electrical capacitance of at least part of the mask can be based on the geometry of that part. For example, determining the electrical capacitance of at least part of the mask can involve approximating its geometry. This approximation can involve approximating the geometry of the at least part by a parallel-plate capacitor.

[0066] Alternatively or additionally, determining the secondary electron yield can include measuring and / or determining a mask potential. Measuring and / or determining the mask potential can involve positioning a probe over the mask. For example, the probe can comprise at least a portion of an AFM. Specifically, the probe can comprise at least a portion of the tip of an AFM and / or at least a portion of the cantilever of the AFM. In some embodiments, measuring and / or determining the mask potential can involve approximating a geometry of at least a portion of the AFM tip and / or the cantilever. For example, approximating a geometry of at least a portion of the AFM tip can involve a spherical approximation of the AFM tip. In particular, determining the capacitance of the mask can involve determining a capacitance based on a spherical-plate capacitor.In some embodiments, the determination of the capacitance may be based on different and / or more complex capacitor models. For example, a more complex capacitor model may include a model of a capacitor in which at least one capacitor surface has a more complex geometry. Generally, positioning the probe over the mask may involve positioning the probe at a distance of 0.001 µm to 1000 µm from the mask, i.e., the probe may be close to the mask. For example, the distance between the probe and the mask may be between 50 µm and 150 µm. In some embodiments, a minimum distance of 0.01 µm and / or 0.1 µm and / or 1 µm and / or 10 µm may also be provided.

[0067] Alternatively or additionally, measuring and / or determining the mask potential can involve applying a first and a second DC voltage offset, each to a first range. In particular, the first range can encompass a voltage range between -100 V and 100 V. For example, the range can encompass a voltage range between -50 V and 50 V, e.g., a range between -10 V and 10 V.

[0068] Additionally, or alternatively, measuring and / or determining the mask potential may involve applying an alternating voltage to the probe, e.g., the AFM tip and / or boom, to induce mechanical vibration of the probe. In particular, the application of the alternating voltage may involve applying an alternating voltage where the voltage frequency is based on a resonant frequency of the probe. For example, the voltage frequency may essentially correspond to the probe's resonant frequency. Alternatively or additionally, the voltage frequency may essentially correspond to a multiple of the probe's resonant frequency. A multiple of the probe's resonant frequency may be a rational multiple of the probe's resonant frequency. For example, the multiple of the probe's resonant frequency may be chosen such that a higher-order eigenmode of the probe is met.

[0069] Additionally, or alternatively, measuring and / or determining the mask potential may include determining a first induced probe deflection for the first DC offset. Specifically, the probe deflection may include an amplitude and / or a phase of the mechanical oscillation.

[0070] Additionally, measuring and / or determining the mask potential may include determining a second induced probe deflection for the second DC offset. For example, the first and / or second deflection may include an in-phase component and / or a quadrature component.

[0071] Additionally, or alternatively, measuring and / or determining the mask potential may involve determining a potential outside an interval spanned by the first and second DC offsets, at least partially based on the first and second displacements. In general, a plurality of displacements may be measured. For example, at least 10, preferably at least 30, and most preferably at least 50 displacements may be measured. In some embodiments, at least 60 displacements, preferably at least 80, and most preferably at least 100 displacements may be measured. In some examples, at most 100 displacements are measured. In general, determining the mask potential may involve interpolation and / or extrapolation. For example, the interpolation and / or extrapolation may be based on the plurality of displacements.

[0072] Furthermore, measuring and / or determining the mask potential can be based on a physical relationship between an acting electric force and a potential difference between two spaced-apart objects. For example, an electric force can act between two objects spaced apart in the z-direction with a finite potential difference ΔV according to Fel=−12∂C∂z(ΔV)2.

[0073] In particular, C ∝ z can be -1 to include an electrical capacitance. A corresponding force gradient can, for example, be expressed as follows: Fel'=∂Fel∂z include. Is a DC voltage offset V now included? CD When applied such that the potential difference ΔV disappears, no electric force F acts. el If a DC voltage offset V DC as well as a time-varying alternating voltage V AcWhen sin(ωt) is applied, the resulting force is generally variable over time. Fel(t)=−12∂C∂z(VDC+VAC sin(ωt)−VCPD)2, where V CPD The contact potential or sample potential is represented, i.e., the potential difference that corresponds to the work function difference ΔΦ between the two objects mentioned, divided by the elementary charge e: V CPD = ΔΦ / e.

[0074] In general, the force acting on the probe can be approximated by a harmonic function. In particular, the force, as a function of the voltage (the DC offset and the AC voltage) between at least part of the mask and probe, e.g., the AFM tip and / or the boom, can follow a parabola. It can be seen that applying a DC offset such that V DC - V CPD = 0, which corresponds to the vertex of the parabola. In particular, the constant V CPDthe contact potential or potential of the sample to be determined and V DC This corresponds to the applied DC voltage offset. At the vertex, the parabola can have a slope of approximately zero, so that an applied AC voltage with a frequency f mod It cannot induce a (strong) force between the probe and at least part of the mask. On the contrary, this force can approach zero. Furthermore, due to the zero crossing (and the associated sign change) in the applied voltage, the frequency of the induced force (with an amplitude approaching zero) would be 2f. mod Since this frequency is far from the probe's resonant frequency, the probe cannot be excited to oscillate there (or only with great difficulty), which further contributes to the force and oscillation amplitude approaching zero.

[0075] With a different, e.g. higher, DC offset, such that (V DC - V CPD ) 2 If the slope is greater than zero, an applied alternating voltage (e.g., with the same or different amplitude and / or frequency) leads to a relatively larger displacement or amplitude of the induced oscillation. This is evident from the fact that the parabola has a non-zero slope at all points except its vertex.

[0076] Specifically, based on a change in the mask potential and the capacitance of at least part of the mask, a change in the charge or state of charge of the mask can be determined. Alternatively or additionally, this can include determining the beam current of the particle beam. Specifically, the determination of the secondary electron yield can be based on the charge change and the beam current. For example, a secondary electron yield of 1 can be determined if, for a known beam current, the mask potential remains essentially unchanged.

[0077] In general, the area can comprise at least two non-contiguous sub-areas. For example, a difference based on the material distribution of the at least two non-contiguous sub-areas can be smaller than a target difference.

[0078] For example, the at least two non-contiguous sub-areas can be spatially separated, e.g., they can be two spaced-apart sub-areas. Specifically, the at least two non-contiguous sub-areas can have essentially the same geometry and / or size. Alternatively or additionally, the material distribution of the at least two non-contiguous sub-areas can be essentially the same. For example, a first sub-area can be associated with a first material distribution and a second sub-area can be associated with a second material distribution. In particular, the first and second material distributions can be designed such that the difference between the first and second material distributions is less than a target difference. In some embodiments, the target difference can be essentially zero, e.g.,The first material distribution can be essentially the same as the second. However, different sub-areas can also be used, which may differ, for example, in their geometries and / or sizes.

[0079] Another aspect of the present invention relates to a computer program comprising code for executing the method described above.

[0080] Another aspect of the present invention relates to a device for influencing the charge state of a lithographic mask. The device comprises means for selecting a region of the mask based on a material distribution within that region. The device further comprises means for directing a particle beam onto the region of the mask.

[0081] In general, the device may be suitable for automatically executing the computer program described above.

[0082] Furthermore, various aspects described in relation to one or more specific methods may also be applicable to other methods. Essentially, the computer program and the apparatus may exhibit the advantages described herein in relation to the methods, and vice versa.

[0083] In some embodiments, the devices may include appropriate means. Each means may perform at least one step of the procedures described herein. The means may, for example, include a data processor and / or a storage device. In some implementations, the device may include one or more computers or computer systems containing one or more data processors, which may be configured to execute one or more programs containing a variety of instructions according to the principles described above. Each data processor may contain one or more processor cores, and each processor core may contain logic circuits for processing data. A data processor may, for example, contain an arithmetic and logical unit (ALU), a control unit, and various registers. Each data processor may contain a cache memory.Each data processor can contain a system-on-a-chip (SoC), which includes multiple processor cores, random-access memory, graphics processing units, one or more controllers, and one or more communication modules. Each data processor can contain millions or billions of transistors.

[0084] The data processing described herein, such as that required to carry out the procedures, can be performed using one or more computers, which may include one or more data processors for processing data, one or more storage devices for storing data, and / or one or more computer programs containing instructions that, when executed by the one or more computers, cause them to perform the processes. The one or more computers may include one or more input devices, such as a keyboard, mouse, touchpad, and / or speech input module, and one or more output devices, such as a display and / or a speaker. In some embodiments, the one or more computing devices may include digital electronic circuits, computer hardware, firmware, software, or any combination of the elements mentioned above.The features relating to data processing can be implemented in a computer program product tangibly embodied in an information carrier, such as a machine-readable storage device, for execution by a programmable processor; and process steps can be executed by a programmable processor that executes a program containing instructions for performing functions of the described implementations. Alternatively or additionally, the program instructions can be encoded on a propagated signal, which is an artificially generated signal, such as a machine-generated electrical, optical, or electromagnetic signal, produced to encode information for transmission to a suitable receiving device for execution by a programmable processor.

[0085] The computer(s) can be configured, for example, to run a computer program and may include general-purpose and specialized microprocessors and one or more processors of any type of digital computer. Generally, a processor receives instructions and data from a read-only memory area, a random-access memory area, or both. The elements of a computer system include one or more processors for executing instructions and one or more memory areas for storing instructions and data. Generally, a computer system also includes, or is operationally coupled to, one or more machine-readable storage media, such as hard disks, magnetic disks, solid-state drives, magneto-optical disks, or optical disks, to receive data from or to them, or both.Machine-readable storage media suitable for embodying computer program instructions and data include various forms of non-volatile memory, including, for example, semiconductor storage devices such as EPROM, EEPROM, flash memory devices and solid-state drives; magnetic disks such as internal hard disks or removable media; magneto-optical disks; and CD-ROM, DVD-ROM and / or Blu-ray discs.

[0086] In some implementations, the procedures described above can be implemented using software for execution on one or more mobile computing devices, one or more local computing devices, and / or one or more remote computing devices (which may be, for example, cloud computing devices). For instance, the software forms procedures in one or more computer programs that are executed on one or more programmed or programmable computer systems, either in the mobile computing devices, local computing devices, or remote computing systems (which may have different architectures, such as...).distributed, client / server, grid or cloud systems), each comprising at least one processor, at least one data storage system (including volatile and non-volatile memory and / or storage elements), at least one wired or wireless input device or a wired or wireless port, and at least one wired or wireless output device or a wireless port.

[0087] In some embodiments, the software can be provided on a medium such as CD-ROM, DVD-ROM, Blu-ray Disc, a solid-state drive, or a hard disk, which can be read by a general-purpose or specialized programmable computer or delivered over a network to the computer on which it is executed (encoded in a transmitted signal). The functions can be executed on a specialized computer or using specialized hardware, such as coprocessors. The software can be implemented in a distributed manner, with different parts of the computations specified by the software being performed by different computers. Each such computer program is preferably stored on or downloaded to a storage medium or device (e.g., solid-state storage or media, or magnetic or optical media) that...which can be read by a programmable computer for general or special purposes to configure and operate the computer when the storage medium or device is read by the computer system to perform the procedures described herein. The system according to the invention can also be considered a computer-readable storage medium configured with a computer program, wherein the storage medium so configured causes a computer system to operate in a specific and predefined manner to perform the functions described herein.

[0088] The aspects described here are primarily related to masks. However, they can also be applied to other industrial purposes, such as analyzing and / or processing a sample with a particle beam. For example, this can be used 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. Sample processing may include, for example, the removal of a particle (e.g., a foreign particle) from the sample (e.g., within a so-called particle pick process). The aspects described here can also be applied to influencing the charge state of such samples. Brief description of the drawings

[0089] Exemplary embodiments of the invention are described below with reference to the figures. The figures show: Fig. : Exemplary illustration of a selected area of ​​a lithographic mask, wherein the selected area includes a clear area and an edge of the mask; Fig. : Exemplary illustration of a selected area of ​​a lithographic mask, wherein the selected area comprises two disjoint sub-areas; Fig. : Exemplary illustration of the lithographic mask with a graph of the secondary electron yield along a one-dimensional cross-section of the lithographic mask; Fig. : Schematic representation of two secondary electron yields as a function of the landing energy for two different areas of the mask; Fig. : Schematic representation of two secondary electron yields as a function of the landing energy for two different areas of the mask and a resulting averaged secondary electron yield as a function of the landing energy; Fig. : Schematic illustration of a method for influencing the charging state of a lithographic mask according to the present invention. Detailed description of preferred embodiments

[0090] Only a few possible embodiments of the invention are described in detail below. These exemplary embodiments can be modified and combined in various ways, provided they are compatible, and certain features can be omitted where unnecessary.

[0091] Fig. is a schematic illustration of a section 100 of a lithographic mask. Fig. Figure 100 shows section 100 of the lithographic mask in a top view, e.g., a view of section 100 of the lithographic mask from a direction perpendicular to a horizontal plane of the mask. A horizontal plane of the mask can include a plane that is substantially parallel to a base surface of the mask. Specifically, the horizontal plane can be substantially parallel to a capping layer of the mask. Section 100 of the mask can, for example, include a SEM image of the mask. Section 100 can include a material distribution (120a, 120b, 120c) of the mask. The material distribution (120a, 120b, 120c) can be associated with a secondary electron yield. That is, different materials and / or material heights and / or transitions between different materials and / or material heights can lead to different secondary electron yields.Since the secondary electron yield is a measure of the brightness in a SEM image, the SEM image can thus represent the secondary electron yield and / or material distribution.

[0092] For example, the material distribution associated with section 120a may be a clear region of the mask. A clear region 120a of the mask may comprise a region without an absorber structure of the mask (in the present application, the term absorber structure also encompasses a structure of a phase-shifting mask). In other words, region 120a essentially shows an upper layer of a multilayer and / or capping layer of the mask in section 100. Furthermore, the material distribution associated with section 120c may be an absorber structure of the lithographic mask. For example, the absorber structure of the lithographic mask may be a structure superimposed on the clear region. Region 120b of the mask may be an edge associated with the absorber structure of the mask. For example, at least part of the absorber structure may terminate in region 120b.The edge in region 120b can essentially be an absorber wall running perpendicular to the multilayer of the mask. In general, a first secondary electron yield can be associated with the first region 120a, e.g., with the material distribution of the first region 120b.

[0093] Furthermore, a second secondary electron yield can be associated with the second region 120b, e.g., with the material distribution of the second region 120b. Additionally, a third secondary electron yield can be associated with the third region 120b, e.g., with the material distribution of the third region 120c. In other words, the secondary electron yield of a clear region can differ from the secondary electron yield of an absorber. Furthermore, the secondary electron yield of an edge of the absorber can differ from both the secondary electron yield of the clear region and of the absorber itself (see also Fig. ).

[0094] The method for influencing the charge state of the mask and / or the cutout 100 of the mask may include selecting a region 110 of the cutout 100 (or the entire mask). The region 110 may be selected based on the material distribution of the region 110. For example, it may be advantageous for influencing the charge state of the mask and / or the cutout 100 to select the region 110 such that it essentially comprises a clear region 120a. In other words, it may be advantageous for influencing the charge state of the mask and / or the cutout 100 to direct the particle beam onto a region without an absorber structure 120c and / or without an edge 120b. The region 110 may then be selected such that it essentially comprises no absorber structure 120c and / or no edge 120c, e.g.Area 110 essentially comprises at least a portion of the clear area 120a of the mask and / or the cutout 100. Furthermore, area 110 can be selected such that it includes a variation 115. For example, the variation can include at least a portion of the edge 120b and / or at least a portion of the absorber structure 120b. Variation 115 comprises a change in the material distribution associated with area 110. Since area 110 essentially comprises at least a portion of the clear area 120a of the mask and / or the cutout 100, e.g., an area without an absorber structure, variation 115 in area 110 comprises a change in the material distribution such that variation 115 includes at least a portion of the edge (absorber) and / or at least a portion of the absorber (120c).

[0095] Fig. Figure 1 shows a schematic illustration of a section 200 of a lithographic mask, which comprises a clear area 220a, an absorber structure 220c, and an edge 220b of the absorber structure 220c. In general, the mask and / or section 100 can correspond to the structure of the section 100 of the mask. The section 200 further comprises a selected area 210, wherein the selected area 210 comprises two non-contiguous sub-areas, e.g., a first sub-area 210a and a second sub-area 210b. In general, the geometry and / or size of the first selected sub-area 210a can substantially correspond to the geometry and / or size of the second selected sub-area 210b. However, substantially different geometries and / or sizes can also be used.In particular, the first 210a and the second 21ob sub-area can be selected such that the difference between the material distribution of the first sub-area 210a and the material distribution of the second sub-area 210b is minimized. Additionally, or alternatively, the first 210 and the second 210b sub-area can be selected such that the difference between the secondary electron yield of the first sub-area 210a and the secondary electron yield of the second sub-area 210b is minimized. For example, the first selected sub-area 210a can comprise at least a portion of an edge 220b of the mask and / or the cutout 200. The first selected sub-area 210a can furthermore comprise at least a portion of the absorber structure 220c of the mask and / or the cutout 200.In general, the selected first sub-area 210a can comprise at least a part of the clear area 220a and / or at least a part of an edge 220b and / or at least a part of an absorber structure 220c. Additionally, or alternatively, the second selected area 210b can comprise at least a part of an edge 220b of the mask and / or the cutout 200. The second selected sub-area 210b can further comprise at least a part of the absorber structure 220c of the mask and / or the cutout 200. In general, the selected second sub-area 210b can comprise at least a part of the clear area 220a and / or at least a part of an edge 220b and / or at least a part of an absorber structure 220c.

[0096] Fig. illustrates a section 300 of the mask, which for example corresponds to section 100 or 200 from the Fig. can correspond. Fig. For example, an SEM image of the section could be included. The brightness distribution of section 300 alone can then be used to infer a relative difference in the secondary electron yield of areas 320a, 320b and 320c to each other, or to determine the material distribution of section 300.

[0097] Additionally, in Fig. A relationship between a secondary electron yield 330 along a cross-section (illustrated by the arrow 310) of the lithographic mask 300 is illustrated, which can occur, for example, when irradiated with a focused electron beam, e.g., during the acquisition of a SEM image. The lithographic mask and / or the section 300 of the lithographic mask comprises a clear region 320a, an absorber structure 320c, and an edge 320b of the absorber structure 320c. The cross-section 310 of the lithographic mask comprises a one-dimensional cross-section of the mask. For example, the cross-section 310 can comprise at least a portion of the clear region 320a of the mask. Alternatively, or additionally, the cross-section can comprise at least a portion of an edge 320b of the mask. Alternatively, or additionally, the cross-section can comprise at least a portion of an absorber structure 320c of the mask.Specifically, a material distribution of the mask can be associated with the one-dimensional cross-section 310. For example, a first part of the cross-section 310 (from left to right) can be associated with the clear area 320a of the mask. Furthermore, a second part of the cross-section 310 can be associated with an edge 320b of the mask. Finally, a third part of the cross-section 310 can be associated with an absorber structure 320c. The secondary electron yield 330 is contained in a coordinate system in which a position on the mask with respect to the cross-section 310 is plotted on the x-axis 332a. In other words, for each value on the x-axis 332a of the coordinate system, there exists a corresponding position on the lithographic mask with respect to the cross-section 310. A value of the secondary electron yield 335 associated with the position on the cross-section 310 is plotted on the y-axis 332b of the coordinate system.In particular, the plotted value of the secondary electron yield 335 can represent a secondary electron yield for a fixed acceleration voltage and / or a fixed landing energy of the particle beam. As can be seen from the plotted secondary electron yield 335, a first secondary electron yield 335a is associated with the clear region 320a of the mask (more precisely, with the clear region 320a contained in the cross-section 310). Additionally, a second secondary electron yield 335c is associated with the absorber region 320c of the mask (more precisely, with the absorber 320c contained in the cross-section 310). Furthermore, a third secondary electron yield 335b is associated with the edge 320b of the mask (more precisely, with the edge 320b contained in the cross-section 310).In particular, the third secondary electron yield 335b is greater than the second secondary electron yield 335c, and the second secondary electron yield 335c is greater than the first secondary electron yield 335a. Consequently, for a fixed accelerating voltage of the particle beam and / or a fixed landing energy of the particle beam, different secondary electron yields 335a, 335b, 335c can occur depending on the position of the particle beam on the mask, e.g., depending on the material distribution of the mask at that position. These position-dependent secondary electron yields 335a, 335b, 335c can be used to influence the charge state of the mask. For example, if the mask is negatively charged and influencing the charge state of the mask involves discharging the mask, the particle beam can be directed to an area with a high and / or maximum secondary electron yield, e.g.,on an area which includes at least part of an edge 320b.

[0098] Fig. Figure 410a and 410b illustrate two secondary electron yields with respect to two regions of the mask for different landing energies 402a. The two secondary electron yields 410a and 410b are represented as curves in a coordinate system 400. In the coordinate system 400, the x-axis 402a represents the landing energy of a particle beam, e.g., a focused electron beam. Furthermore, the y-axis 402b represents a secondary electron yield σ. For example, the first secondary electron yield 410a can be associated with a first region. In particular, the first region can comprise at least part of an absorber structure of the mask. Additionally, or alternatively, the second region can comprise at least part of a clear region of the mask. For a first range of landing energies, the secondary electron yield 410a, 410c can be associated with a value greater than one, e.g. with σ > 1.A secondary electron yield with σ > 1 can mean that more electrons leave the mask and / or are removed from the mask than are deposited by the particle beam. In other words, more electrons leave the mask than are deposited by the particle beam; for example, the charge of the mask becomes more positive. A secondary electron yield with σ = 1 can mean that the amount of electrons leaving the mask and / or being removed from the mask is essentially equal to the amount of electrons deposited by the particle beam. In other words, the particle beam deposits as many electrons as leave the mask through internal (collision) processes; for example, the charge state of the mask is essentially constant.A secondary electron yield of σ < 1 can mean that more electrons are deposited onto the mask by the particle beam than electrons leave the mask. In other words, the charge state of the mask becomes more negative. The secondary electron yield 410c includes a local maximum 415c. For example, if the mask is (originally) negatively charged, the accelerating voltage of the particle beam can be adjusted to discharge the (negatively charged) mask such that the corresponding landing energy of the particles corresponds to the maximum 415c of the secondary electron yield 410c. Thus, the mask can be discharged at a maximum and / or optimal rate.If, however, further charging during imaging, processing, and / or analysis of the mask is to be minimized and / or prevented, the accelerating voltage of the particle beam can be adjusted such that the corresponding landing energy of the particles lies in the vicinity of the value σ = 1 (characterized by the line b). For example, if the mask is (originally) positively charged, the accelerating voltage of the particle beam can be adjusted to discharge the (positively charged) mask such that the corresponding landing energy of the particles corresponds to the secondary electron yield 415a. In particular, the particle beam can be directed at the first region associated with the first secondary electron yield 410a, e.g., at a region of the mask that includes at least part of a clear region of the mask.

[0099] In general, the curves 410a, 410b of the secondary electron yields can be based on measuring and / or determining a secondary electron yield of the respective region (first or second region) for a variety of beam currents and / or mask potentials, e.g. an iterative application of the above described procedure for measuring and / or determining the secondary electron yield.

[0100] Fig. Figure 5 shows an illustration of two secondary electron yields 510a and 510c, where the first secondary electron yield 510a is associated with a first region and the second secondary electron yield 510c with a second region. For example, the first region can include at least part of an absorber structure and / or an edge of the mask. Additionally, or alternatively, the second region can include at least part of a clear region of the mask. The two secondary electron yields 510a and 510c are plotted in a coordinate system 500. The x-axis 502a represents the landing energy of the particle beam. Furthermore, the y-axis 502b represents a corresponding secondary electron yield. The coordinate system 500 also shows an average 520 of the secondary electron yields 510a and 510c.For example, the averaging 520 can be based on an arithmetic mean and / or a weighted mean (corresponding to the proportion of the regions) and / or a geometric mean and / or a general function of the secondary electron yields 510a and 510c. The averaging 520 can include a secondary electron yield 525 with σ = 1. For example, the secondary electron yield 525 of the averaging 520 can be assumed for a certain (intersection of the x-axis 502a with the line d) landing energy of the particle beam. If, for example, the particle beam is directed at both the first and the second region, e.g., scanned over the first and the second region, then an effective secondary electron yield can be based on the averaging 520.In particular, a separate aspect of the present disclosure is that the particle beam landing energy during mask processing and / or analysis can be selected such that the resulting effective secondary electron yield corresponds to the averaging 520 in point 525. In other words, if the mask processing and / or analysis involves directing the particle beam at both the first and second regions of the mask, e.g., scanning for repair and / or image acquisition, the particle beam landing energy can be adjusted (landing energy at point d) such that the mask effectively does not (further) charge, e.g., a secondary electron yield corresponding to the averaging 520 in point 525 is achieved. In other examples, the landing energy can be selected such that the resulting effective secondary electron yield leads to a predetermined desired charging or discharging.

[0101] In one example, curves corresponding to curves 510a and 510b can be at least partially determined for areas within an imaging or repair window of the mask. For instance, a curve for a clear area, an absorber area, and / or an edge area can be at least partially determined. At least partial determination can, for example, include determining the accelerating voltage at which the secondary electron yield transitions from >1 to <1. For example, by averaging and / or weighting the at least partially determined curves, an averaged and / or weighted curve can be at least partially determined. From this, for example, the value of the transition of the averaged and / or weighted curve from >1 to <1 (e.g., at point 525) can be determined. For example, the accelerating voltages determined for the areas can be averaged and / or weighted.

[0102] Fig.A process 600 for influencing the charge state of a lithographic mask, preferably a photolithographic mask, is illustrated in a flowchart. The process 600 comprises selecting a region 610 of the mask based on a material distribution of the region. Specifically, the selection 610 can include selecting at least two non-contiguous sub-regions. For example, the selection 610 of the region of the mask can be based on an actual charge state of the mask and / or a target charge state of the mask. Alternatively, or additionally, the selection 610 of the region of the mask can be based on an accelerating voltage and / or a landing energy of the particle beam. Alternatively, or additionally, the selection 610 of the region can be based on a secondary electron yield associated with the region.

[0103] The procedure 600 may further include determining 605 the actual state of charge of the mask. For example, determining 605 the actual state of charge of the mask may be performed before selecting 610 the area. In particular, the selection 610 may be based on the determined actual state of charge of the mask. Specifically, determining 605 the actual state of charge may be based, at least in part, on bringing an AFM tip close to the mask. In general, determining the actual state of charge may further include determining a charge difference relative to a target state. For example, based on the charge difference, it may be determined that influencing 600 the state of charge of the mask involves charging and / or discharging the mask. In particular, charging the mask may involve adding electrons to the mask. Additionally, or alternatively, discharging the mask may involve removing electrons from the mask.In some embodiments, charging the mask may involve the removal of electrons from the mask, e.g., effectively applying positive charges to the mask. Alternatively, or additionally, discharging the mask may involve the application of electrons to the mask, e.g., effectively removing positive charges from the mask.

[0104] Alternatively, or additionally, the procedure 600 can include determining 614 a secondary electron yield of the region. Determining 614 the secondary electron yield of the region can be based on the material distribution of the region and / or the actual charge state of the mask and / or the accelerating voltage of the particle beam and / or the landing energy of the particle beam. Determining 614 the secondary electron yield can take place before selecting 610 the region. For example, a secondary electron yield can be determined for a plurality of regions of the mask. Selecting 610 the region can include comparing the secondary electron yields of the plurality of regions. In particular, selecting 610 can include selecting one region from the plurality of regions based on the secondary electron yields of the plurality of regions.Alternatively, the determination of the secondary electron yield can take place after selecting the area.

[0105] Alternatively, or additionally, the method 600 can include selecting 618 at least one parameter of the particle beam. The selection 618 of the at least one parameter of the particle beam can be based on the material distribution of the (selected) region. Alternatively, or additionally, the selection 618 of the at least one parameter of the particle beam can be based on a secondary electron yield of the (selected) region. In general, the at least one parameter of the particle beam can be selected such that the influencing of the charge state of the mask occurs at a maximum and / or optimal rate. For example, the at least one parameter of the particle beam can be selected such that the secondary electron yield associated with the at least one parameter of the particle beam is maximal and / or minimal.In particular, the accelerating voltage of the particle beam can be chosen such that the secondary electron yield of the selected region is optimal at a land energy associated with the accelerating voltage. Alternatively, the selection of the region can be based on at least one parameter of the particle beam; for example, at least one parameter of the particle beam can be fixed.

[0106] Method 600 further comprises directing 620 a particle beam onto the (selected) area of ​​the mask. For example, directing 620 the particle beam can include adjusting at least one parameter of the particle beam. Specifically, the particle beam can be directed onto the (selected) area of ​​the mask in such a way that the charge state of the mask is influenced. For example, the particle beam can be directed onto the (selected) area of ​​the mask in such a way that the charge state of the mask is influenced and / or changed from an actual charge state of the mask to a target charge state of the mask.

Claims

[1] Method (600) for influencing a charge state of a lithographic mask (100), comprising: Selecting (610) an area (110) of the mask (100) based on a material distribution (120a, 120b, 120c) of the area (110) of the mask (100); and Directing (620) a particle beam onto the area (110) of the mask (100). [2] Method (600) for influencing the state of charge according to claim 1, further comprising: Selecting (618) at least one parameter of the particle beam based on the material distribution (120a, 120b, 120c) of the area (110) of the mask (100). [3] Method (600) for influencing the state of charge according to claim 1 or 2, wherein the selection (610) of the area (110) is carried out such that the material distribution (120a, 120b, 120c) of the area (110) comprises at least one spatial variation (115), in particular an edge (120b). [4] Method (600) for influencing the state of charge according to claim 3, wherein the at least one spatial variation (115) of the material distribution (120a, 120b, 120c) of the area (110) is designed such that it is suitable for drift correction of the mask. [5] Method (600) for influencing the state of charge according to one of claims 1 to 4, wherein the selection (610) of the area is further based on an actual state of charge of the lithographic mask and / or a target state of charge of the lithographic mask. [6] Method (600) for influencing the state of charge according to any one of claims 1 to 5, further comprising: Determining (605) an actual charge state of the mask (100), wherein determining (605) the actual charge state of the mask (100) is based at least partially on an approach of an AFM peak towards the mask (100). [7] Method (600) for influencing the state of charge according to any one of claims 1 to 6, further comprising: Determining the material distribution (120a, 120b, 120c) of the area (110) and / or the lithographic mask (100). [8] Method (600) for influencing the state of charge according to claim 7, wherein: Determining the material distribution of the area (110) and / or the mask (100) is based on a design file associated with the lithographic mask (100); and / or the determination of the material distribution of the area (110) and / or the lithographic mask (100) is based on a SEM image. [9] Method (600) for influencing the state of charge according to any one of claims 1 to 8, wherein the material distribution (120a, 120b, 120c) of the region (110) and / or the lithographic mask (100) comprises a material distribution (120a, 120b, 120c) of an absorber structure of the region (110) and / or the lithographic mask (100). [10] Method (600) for influencing the state of charge according to one of claims 1 to 9, wherein the area (110) of the mask (100) is associated with a local secondary electron yield (330). [11] Method (600) for influencing the state of charge according to claim 10, wherein the selection (618) of the area and / or the at least one parameter of the particle beam is based on the local secondary electron yield (330). [12] Method (600) for influencing the state of charge according to any one of claims 1 to 11, further comprising: Determining (614) a secondary electron yield (330) of the region (110), wherein the determination (614) of the secondary electron yield is based on a mask potential measurement. [13] Method (600) for influencing the state of charge according to one of claims 1 to 12, wherein the area (110) comprises at least two non-contiguous sub-areas (210a, 210b), preferably wherein a difference based on the material distribution (120a, 120b, 120c) of the at least two non-contiguous sub-areas (210a, 210b) is smaller than a target difference. [14] Computer program comprising code for executing a method (600) according to any one of claims 1 to 13. [15] Device for influencing a charge state of a lithographic mask, comprising: Means of selecting an area of ​​the mask based on a material distribution of the area of ​​the mask; and Means for directing a particle beam onto the area of ​​the mask. [16] Device for influencing the charge state according to claim 15, wherein the device is configured to automatically execute the computer program according to claim 14.

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