Method for creating a trench in a sample and computer program product

Abstract

Method for producing a trench with a target trench depth (DX) in a sample (3) by removing material from the sample (3) using a particle beam generated by a particle beam system (100) and focused into a working area (4) of the particle beam system (100), comprising: defining a particle beam system setting, which is a setting of the particle beam system (100) for performing one removal unit step with the particle beam; acquiring calibration data sets using the defined particle beam system setting on a calibration sample (3K); determining a regression curve (R) based on the acquired calibration data sets, wherein the regression curve is defined as a function of at least one parameter characterizing the removal unit step; determining a number of executions (X) based on the determined regression curve (R) and the target trench depth (DX);and creating a trench in the sample (3) by repeatedly performing the removal unit step with the specified particle beam system setting according to the specified number of executions (X).;

Description

The present invention relates to methods for generating a trench of defined trench depth in a sample and to a computer program product for implementing the methods on a particle beam system. The methods are carried out with a particle beam system configured to generate a particle beam which can remove material from the sample. The particle beam can be, for example, a light beam, a laser beam, a continuous laser beam, a pulsed laser beam, an electron beam or an ion beam.BackgroundNumerous applications in the field of structurizing, producing and analyzing materials and devices (sample), in particular semiconductor devices, require material to be ablated from the sample in a predefined spatially limited region. Because of relatively high removal rates, a laser beam is first used to remove material. For ablation at low ablation rates, an ion beam or an electron beam may be used. In both cases, but in particular during the removal with a laser beam, it is important to limit the removal to a predetermined depth.Application cases in which a limitation of the material removal to a specific depth is necessary are, for example: laser cutting a cross section of a semiconductor chip in a housing up to a defined desired depth, for example in such a way that a chip is cut transversely, but not an underlying carrier; removal of stacked semiconductor chips in a housing up to a defined desired depth, for example in such a way that a specific number of chips in a chip stack are removed from above. It may also be desired that a chip last exposed is only partially ablated to a desired residual thickness; thinning a semiconductor chip from the substrate side, such that the thickness of the substrate is reduced to a few μm or a few 10 μm ("backside thinning"); laser cutting an opening in semiconductor chips in a package to a defined desired depth, for example until certain electrical connection points are exposed.In addition, in sample processing, it is generally advantageous not to ablate more material than necessary in order to minimize the following effects: redeposition of already ablated material; burring at the upper edge of a cross section due to interaction of the particle beam with the redeposited material during a cutting operation; deposition of ablated material on the sample surface around a cut.The depth of the material removal depends on the physical properties of the material of the sample itself and on a multiplicity of working parameters of the particle beam system (for example power, pulse frequency in the case of pulsed beam, raster speed, focusing of the particle beam, etc.), which generates the particle beam and rasters it over the sample. It has been found that the depth achieved of a removal of material, wherein the removal is carried out by carrying out a uniform removal process a plurality of times, has a non-linear relationship to the number of executions of the uniform removal process.For the targeted setting of the depth of a removal, conventionally complicated experiments have to be carried out. To do this, material is ablated from numerous test samples having numerous different combinations of material properties and operating parameters. The depths achieved are then measured and the combination selected with which the desired desired depth was achieved most precisely. This combination is then used for processing the actual samples.This procedure is associated with numerous disadvantages: great time and labor costs due to a large number of combinations of material properties and working parameters to be measured; correspondingly great area consumption of test samples. Due to the large number of combinations of material properties and working parameters to be measured, only a part of the combinations can actually be tested in practice. Interpolation to depths that lie between experimentally determined depths and also extrapolation to depths that are greater than the experimentally determined depths are generally too inaccurate due to the non-linear relationship between the achieved depth and the number of executions of the uniform ablation process.On the other hand, extensive mathematical models exist for simulating material processing, which however require precise knowledge of some physical properties of the material of the sample, for example ablation thresholds, various optical, electrical or magnetic properties. However, these are usually not known in the case of microscopic samples.The prior art also includes the disclosures of publications WO 2021 / 180 600 A1 and WO 2020 / 099 011 A1.Technical TaskThe object of the present invention is therefore to provide a rapid method which is easy to use and by means of which material can be ablated from a microscopic sample to a predetermined desired depth.Solution of the Technical ProblemThe object is achieved by the subject matters of the independent claims. Advantageous further developments of the invention are defined in the dependent claims.First AspectA first aspect of the invention relates to a method for generating a trench having a trench setpoint depth in a sample by removing material from the sample by means of a particle beam generated by a particle beam system and focused into a working region of the particle beam system, comprising: establishing a particle beam system setting, which is a setting of the particle beam system for carrying out an removal unit step with the particle beam; acquiring calibration datasets using the established particle beam system setting on a calibration sample; determining a regression curve based on the acquired calibration datasets, wherein the regression curve is defined as a function of at least one parameter characterizing the removal unit step; determining a number of execution based on the determined regression curve and the trench setpoint depth; generating a trench in the sample by repeatedly performing the ablation unit step with the set particle beam system setting according to the determined performing number.The method according to the first aspect is based on a regression curve which determines an accurate estimate of a number of executions of an ablation unit step (i.e. the number of executions of the ablation unit step) for a desired trench nominal depth. The regression curve takes into account the physical properties of the ablation process. Parameters of the regression curve will be determined with few calibration measurements. Based on the regression curve, it is possible to accurately indicate an accurate relationship between the execution number of the ablation unit step and the trench depth even with few calibration measurements.Second AspectA second aspect of the invention relates to a method for generating a trench having a trench nominal depth in a sample by removing material from the sample by means of a particle beam generated by a particle beam system and focused into a working region of the particle beam system, comprising: providing a database having a plurality of data sets, wherein each of the data sets contains a particle beam system setting, which is a setting of the particle beam system for carrying out an removal unit step with the particle beam, a sample property, which is a property of the sample, and a regression curve, wherein the regression curve is defined as a function of at least one parameter characterizing the removal unit step; selecting a first particle beam system setting and a first sample property, which are contained in one of the data sets of the database; acquiring a first regression curve from the dataset of the database, which contains the first particle beam system setting and the first sample property; determining a performance number based on the first regression curve and the trench setpoint depth; and generating a trench in the sample by repeatedly performing the ablation unit step with the first particle beam system setting corresponding to the determined performance number.The method according to the second aspect is based on the fact that different regression curves are stored in the database, which allow an accurate estimation of a number of executions of the ablation unit step (i.e. the number of executions of the ablation unit step) for a desired trench target depth, wherein the different regression curves are associated with different combinations of a particle beam system setting (working parameter) and a sample property (material of the sample) and take into account the physical properties of the ablation process. The regression curves are each determined, for example, by means of the method according to the first aspect by a few calibration measurements and are then stored in the database.A sample can be ablated to a desired trench target depth by first acquiring the regression curve of the dataset that includes a predetermined particle beam system setting and a predetermined sample property of a calibration sample that is the same or similar to the sample property of the sample, and then determining the number of executions of the ablation unit step required to generate the trench having the trench target depth with the selected regression curve. If the database already contains a regression curve associated with this combination for a predetermined combination of a particle beam system setting and a sample property, it is therefore not necessary to determine the regression curve by new calibration measurements, but rather the regression curve can be obtained directly from the database.Third AspectA third aspect of the invention relates to a method for generating a trench having a trench setpoint depth in a sample by removing material from the sample by means of a particle beam generated by a particle beam system and focused into a working region of the particle beam system, comprising: providing a database having a plurality of data sets, each of the data sets comprising a particle beam system setting, which is a setting of the particle beam system for carrying out an removal unit step with the particle beam, a sample property, which is a property of the sample, and a plurality of calibration data sets, each of the calibration data sets containing a predetermined number of executions of the removal unit step and a depth of a trench generated by carrying out the removal unit step corresponding to the predetermined number of executions; selecting a first particle beam system setting and a first sample property, which are contained in one of the data sets; acquiring first calibration data sets from the data set containing the first particle beam system setting and the first sample property; determining a regression curve based on the acquired first calibration data sets, wherein the regression curve is defined as a function of at least one parameter characterizing the ablation unit step; determining a performance number based on the determined regression curve and the trench target depth; and generating a trench in the sample by repeatedly performing the ablation unit step with the first particle beam system setting corresponding to the determined performance number.The method according to the third aspect is based on the fact that a plurality of data sets are stored in the database, each of the data sets comprising a particle beam system setting, a sample property, and a plurality of calibration data sets, each of the calibration data sets comprising a performance number of the ablation unit step and a depth of a trench generated by performing the ablation unit step corresponding to the performance number. A regression curve is calculated from the calibration data sets of a data set, which then enables an accurate estimation of a number of executions of the removal unit step (i.e. the number of executions of the removal unit step) for a desired trench nominal depth. The data sets can be determined by means of the method according to the first aspect by a few calibration measurements and subsequently stored in the database. A new sample can be ablated to a desired trench target depth by first selecting from the database the dataset containing a predetermined particle beam system setting and a predetermined sample property, then determining a regression curve that takes into account the physical properties of the ablation process based on the calibration datasets of the selected dataset, and finally determining the number of executions of the ablation unit step required to generate the trench having the trench target depth with the determined regression curve. If the database already contains a plurality of calibration datasets associated with this combination for a predetermined combination of particle beam system setting and sample property, it is therefore not necessary to determine the regression curve by new calibration measurements, but rather the regression curve can be determined directly from the calibration datasets of one of the datasets.Fourth AspectA fourth aspect of the invention relates to a method for generating a trench having a trench nominal depth in a sample by removing material from the sample by means of a particle beam generated by a particle beam system and focused into a working region of the particle beam system, comprising: providing a database having a plurality of data sets, wherein each of the data sets comprises a particle beam system setting, which is a setting of the particle beam system for carrying out an removal unit step with the particle beam, a sample property, which is a property of the sample, and a regression curve, wherein the regression curve is defined as a function of at least one parameter characterizing the removal unit step; selecting a first sample property from one of the data sets; selecting one of the data sets including the selected first sample property and a first regression curve associating the trench target depth with a value satisfying a predetermined condition; acquiring a first particle beam system setting included in the selected data set; determining a first execution number based on the regression curve included in the selected data set and the trench target depth D x; and generating a trench in the sample by repeatedly performing the ablation unit step with the acquired first particle beam system setting corresponding to the determined first execution number.The method according to the fourth aspect relates, for example, to the case in which a performance number determined for a trench setpoint depth by means of one of the methods of the first to third aspects has a value which deviates (significantly) from an integer. Since the removal unit step can only be carried out according to an integer, it can occur that an actual trench depth deviates from the target trench depth (significantly) if the determined execution number has a value which deviates (significantly) from an integer, and the removal unit step has been carried out according to a number rounded to the nearest integer. In order to avoid such inaccuracies, according to the method according to the fourth aspect, a particle beam system setting is determined for a predetermined trench setpoint depth and a predetermined sample property, the associated regression curve of which provides a number of executions of the ablation unit step for the predetermined trench setpoint depth, which number satisfies a predetermined condition, for example is as close as possible to an integer. The method according to the fourth aspect therefore determines, at a predetermined trench setpoint depth and a predetermined sample property, a particle beam system setting and a number of executions which meet the predetermined condition. A trench can thus be produced whose actual depth comes particularly close to the desired trench setpoint depth.Fifth AspectA fifth aspect of the invention relates to a computer program product comprising a computer program with instructions which control a particle beam system such that one of the methods described herein is executed. The computer program product may be a computer program embodied in an information carrier, e.g., a machine readable storage device (a computer readable medium, a non-transitory computer readable storage medium, and the like), or in a propagated signal, for processing by or controlling processing of a data processing apparatus, e.g., a programmable processor, a computer, or multiple computers.Brief Description of the DrawingsFIG. 1 shows a flow diagram of a method for producing a trench according to a first embodiment. FIG. 2 shows a flow chart of the acquisition of calibration datasets according to step S 102 of the method shown in FIG. 1. FIG. 3 shows an example content of a database. FIG. 4 shows an exemplary representation of acquired calibration data sets and a regression curve. FIG. 5 shows a flow chart of the generation of a trench according to step S 106 of the method shown in FIG. 1. FIG. 6 shows a schematic illustration of the trench produced according to step S 106 in cross section after carrying out different numbers of ablation unit steps. FIG. 7 shows a schematic illustration of a particle beam system for carrying out the method shown in FIG. 1. FIG. 8 shows a flow diagram of a method for producing a trench according to a second embodiment. FIG. 9 shows an exemplary content of a database according to the second embodiment. FIG. 10 shows a flow diagram of a method for producing a trench according to a third embodiment. FIG. 11 shows an exemplary content of a database according to the third embodiment. FIG. 12 shows a flow diagram of a method for producing a trench according to a fourth embodiment. FIG. 13 shows an exemplary representation of a plurality of different regression curves according to the fourth embodiment.DESCRIPTION OF EMBODIMENTSEmbodiments of the invention are explained in more detail below with reference to figures.First EmbodimentA first embodiment will be described below with reference to Figs. 1 to 7. FIG. 1 shows a flow diagram of a method for producing a trench 1 in a sample 3 according to the first embodiment. The aim of the method is to produce, in a homogeneous sample 3, a trench 1 having a base which is as flat as possible and a desired depth, which is referred to as the trench nominal depth D X by removing material from the sample 3 by means of a particle beam 5. The particle beam 5 is generated by a particle beam system 100 and focused by the particle beam system 100 into a working region 4.The particle beam system 100 is, for example, a laser and accordingly the particle beam is a laser beam, i.e. a beam of photons. The laser beam may be a beam of laser pulses characterized by a pulse length (i.e., a time length of a single pulse) and a pulse repetition rate (i.e., a frequency at which the laser pulses are emitted). The laser beam may be a continuous laser beam.The particle beam system 100 is, for example, an electron beam system, and accordingly, the particle beam is an electron beam. The particle beam system 100 is, for example, an ion beam system, and accordingly, the particle beam is an ion beam.Step S 101 comprises: defining a particle beam system setting, which is a setting of the particle beam system 100 for carrying out an ablation unit step with the particle beam 5. For example, an operator of the particle beam system 100 sets the particle beam system setting by inputs input to a controller 101 through an input device 102 (see FIG. 7 ). The particle beam system setting is a setting of the particle beam system 100 for carrying out the ablation unit step with the particle beam 5. Details of the removal unit step will be described with reference to FIG. 6.The particle beam system setting comprises, for example, one or more of the following settings: a setting of a strength of the particle beam 5 (for example an intensity of a laser beam, a current strength of an electron beam, etc.); a setting of a pulse length and a pulse repetition rate of pulses of the particle beam 5; a setting of a dwell time of the particle beam at each raster location (i.e. the time duration during which the particle beam 5 is directed at a single raster location before the particle beam 5 is directed at the next raster location; or the time duration required for the particle beam 5 to sweep over a single raster location); a setting of a raster path (i.e. a spatial arrangement of raster locations and an order according to which the particle beam 5 sweeps over the raster locations); an adjustment of a raster speed (i.e. a speed of the particle beam 5 over the raster locations); an adjustment of a focus displacement distance (f 0) ( i.e. a spatial length measured along a depth direction 7 of the trench 1 between the focus of the particle beam 5 during an ablation unit step and the focus of the particle beam 5 during the subsequent ablation unit step). The focus shift distance f 0 may be zero or other than zero.Step S 102 following step S 101 comprises: acquiring calibration data sets using the particle beam system setting set (in step S 101) on a calibration sample 3K. The aim of this step is to record a plurality of calibration datasets by ablating material from the calibration sample 3K by performing the ablation unit step multiple times with the defined particle beam system setting and by measuring a resulting trench depth, wherein each of the calibration datasets consists of a performance number (i.e. the number of performances of the ablation unit step) and a measured depth of a trench generated by performing the ablation unit step corresponding to the performance number.The calibration sample 3K and the sample 3 have the same sample characteristics. Specifically, the calibration sample 3K and the sample 3 are made of the same material. The calibration sample 3K and the sample 3 are, for example, spatially separated regions of the same object or are different objects of the same material.An example implementation of step S 102 will be described with reference to FIG. 2.Step S 21 comprises: arranging a calibration sample 3K in the working region 4 of the particle beam system 100. The calibration measurements on the calibration sample 3K and the processing of the sample 3 are preferably carried out using the same particle beam system 100. In contrast, the calibration measurements on the calibration sample 3K and the processing of the sample 3 can be carried out in different particle beam systems. Step S 21 is carried out, for example, by an operator of the particle beam system 100.Step S 22 following step S 21 includes: performing the ablation unit step with the particle beam system setting set (in step S 101). As a result, material is removed from the calibration sample 3K. Step S 22 is carried out by the particle beam system 100.Step S 23 following step S 22 includes: checking whether a calibration measurement is to be performed. Step S 23 is carried out by the particle beam system 100. For example, the operator of the particle beam system 100 specifies execution numbers which each indicate a number of executions of the ablation unit step (step S 22) after which a calibration measurement is to be carried out. For example, the operator of the particle beam system 100 specifies that a calibration measurement is to be carried out after carrying out 10, 20 and 50 ablation unit steps. For example, the particle beam system 100 (controller 101) checks whether a calibration measurement is to be performed by comparing the number of ablation unit steps performed with the set execution numbers. If the check reveals that no calibration measurement is to be carried out (no in step S 23), the method continues with step S 22. If the check reveals that a calibration measurement is to be carried out (yes in step S 23), the method is continued with step S 24.Step S 24 includes: measuring a current depth of the trench generated by the previous ablation unit steps (step S 22). The measurement can be carried out fully automatically, partially automatically or manually using the particle beam system 100 or another device (for example a scanning force microscope). For this purpose, the particle beam system 100 can comprise a measuring device, for example a scanning electron microscope. The measured current trench depth and the number of previously carried out ablation unit steps are stored as a calibration dataset, for example in a data memory 105 of the particle beam system 100.Step S 25 following step S 24 comprises: checking whether a further calibration dataset is to be acquired. Step S 25 is carried out by the particle beam system 100. For example, the particle beam system 100 (controller 101) checks whether a calibration measurement has already been carried out for all the specified execution numbers by comparing the number of carried out ablation unit steps with the largest of the specified execution numbers. If the check reveals that a further calibration measurement is to be carried out (a further calibration dataset is detected) (yes in step S 25), the method is continued with step S 22. If the check reveals that no further calibration measurement is to be carried out (no further calibration data set is detected) (no in step S 25), the method is continued with step S 26.Step S 26 comprises: storing a data set comprising the particle beam system setting (determined in step S 101) and the calibration data sets (acquired in step S 24). The dataset may further comprise a sample property of the calibration sample 3K. The data record is stored, for example, in a database in the data memory 105.In this way, a predetermined number of calibration data sets are acquired and stored as a data set in association with the particle beam system setting used and the sample property of the calibration sample.FIG. 3 shows an exemplary content of a database in which a plurality of different such data sets are stored. Each dataset corresponds to a row in the database of FIG. 3. A dataset in row #1 comprises a particle beam system setting A 1, a sample property B 1 and a set K 1 of calibration datasets consisting of the calibration datasets (10; D 10); (20; D 20) and (50; D 50), wherein the first indication in the bracket indicates a performance number and the second indication in the bracket indicates the measured depth of the trench after performance of the performance number of ablation unit steps. For the method according to the first aspect, the storage of the particle beam system setting and the sample property is optional.FIG. 4 shows an exemplary representation of the calibration data sets as circles in a diagram, the horizontal axis of which indicates the number of executions and the vertical axis of which indicates the trench depth. Specifically, three calibration data sets (pass count, trench depth) are shown: (10; D 10), (20; D 20) and (50; D 50). The above-mentioned non-linear relationship between the feedthrough number and the trench depth can be seen.Step S 103 (FIG. 1 ) following step S 102 comprises: determining a regression curve R based on the calibration data sets acquired (in step S 102), wherein the regression curve is defined as a function of at least one parameter characterizing the ablation unit step. The regression curve R indicates a convergence between a number of executions of the ablation unit step and a trench depth. In other words, the regression curve R assigns a pass count to any trench depth.In order that the regression curve R can indicate the relationship between the performance number and the trench depth solide even in the case of a small number of calibration datasets obtained by calibration measurements, the regression curve R is defined as a function of at least one parameter which characterizes the ablation unit step. In other words, the regression curve R is parameterized, wherein the parameterization maps the physical process of ablation by means of a repeated ablation unit step.Examples of the parameters include: a depth of ablation d 0 of an individual ablation unit step in the case of ideal focusing (i.e. in the case of focusing of the particle beam 5 onto a surface to be ablated); a deviation F 0 of the position of the focus of the particle beam 5 in the depth direction 7 from a surface of the sample 3 to be ablated in the first execution of the ablation unit step; a focus displacement distance f 0, by which the position of the focus of the particle beam 5 in the depth direction 7 is displaced between successive ablation unit steps; a length A of a section of the particle beam 5 along the depth direction 7, in which a local strength of the particle beam 5 exceeds an ablation threshold of the sample 3.The ablation threshold of the sample 3 specifies the strength of the particle beam 5, from which material ablation (for the given material of the sample 3) by the particle beam 5 takes place. This means that material is ablated by the particle beam if the local thickness of the particle beam 5 exceeds the ablation threshold, and that no material is ablated by the particle beam 5 if the local thickness of the particle beam 5 does not exceed the ablation threshold.A concrete example of such parameterization will be described below in detail with reference to the ablation unit step described in FIG. 6. Ablation begins with the provision of the sample 30 (at n=1, left side). In the example shown, the sample 30 has a planar surface oriented perpendicularly to the depth direction 7.The particle beam 5 is then directed along the depth direction 7, which runs from top to bottom in FIG. 6, onto different raster locations (i.e. locations on the surface of the sample 30). The particle beam 5 is focused, which is illustrated in FIG. 6 in that the cross section of the particle beam 5 (i.e. the width of the particle beam 5 in the horizontal direction of FIG. 6, which is oriented perpendicularly to the depth direction 7; illustrated as dotted lines) firstly decreases along the depth direction 7, has the narrowest cross section at a location which is referred to as the focus of the particle beam 5, and increases again after the focus. The position of the focus in the n-th execution of the ablation unit step is referred to as F n. In the first execution of the ablation unit step, the particle beam 5 is focused on the surface having the position D 0 in the depth direction 7, i.e. F 1= D 0. During the scanning of the particle beam 5 over the sample 30, the focusing (i.e. the position of the focus of the particle beam 5 in the depth direction 7) remains unchanged. As a result, removal with an approximately rectangular cross section is achieved, whereby a sample 31 (at n=1, right side) having a trench 1 with an actual depth D 1 is obtained. The first execution of the removal unit step (n=1) is thus completed.In a subsequent second execution of the ablation unit step (n=2), the focus of the particle beam 5 is shifted by the focus shift distance f 0 along the depth direction 7 and thus has the position F 2= F 1+ 1 · f 0. This is intended to focus the particle beam 5 onto the bottom of the trench 1, wherein the actual depth D 1 is unknown. Then, the particle beam 5 is scanned with the focusing F 2 over the sample 31, more precisely over the trench 1 in the sample 31, whereby material is removed again from the bottom of the trench 1 and the sample 32 is obtained. Thus, the trench 1 of the sample 32 has an actual depth D 2.In a subsequent third execution of the ablation unit step (n=3), the focus of the particle beam 5 is again shifted by the focus shift distance f 0 along the depth direction 7 and thus has the position F 3= F 1+ 2 · f 0. This is intended to focus the particle beam 5 onto the bottom of the trench 1, wherein the actual depth D 2 is unknown. Then, the particle beam 5 is scanned with the focusing F 3 over the sample 32, more precisely over the trench 1 in the sample 32, whereby material is removed again from the bottom of the trench 1 and the sample 33 is obtained. Thus, the trench 1 of the sample 32 has an actual depth D 3.Subsequent executions of the removal unit step are carried out analogously.Ideally, in each ablation unit step, the focus of the particle beam 5 would be set to a position corresponding to the actual position of the bottom of the trench 1. However, this is not the case in practice. A slight defocusing, i.e. a distance between the bottom of the trench 1 and the focus of the particle beam 5, leads to less material being ablated compared to the ideal focusing. A slight defocusing is shown at n=3. As a result, defocusing increases as the number of executions of the ablation unit step increases. Defocusing contributes to the non-linear relationship between the number of feedthroughs and the trench depth shown in FIG. 4.The method described above of removing material by carrying out the removal unit step multiple times can be parameterized, for example, by formula (1): where n≥1, D 0= 0 and where: d n specifies the removal during the nth execution of the removal unit step, n specifies the nth execution of the removal unit step, d 0 specifies a depth of removal of a single removal unit step during ideal focusing, F n specifies a position of the focus of the particle beam 5 in a depth direction 7 for the nth execution of the removal unit step, F 0 indicates a deviation of the position of the focus of the particle beam 5 in the depth direction 7 from a surface of the sample 3 to be ablated during the first execution of the ablation unit step, f 0 indicates a focus displacement distance by which the position of the focus of the particle beam 5 in the depth direction 7 is offset between successive ablation unit steps, A indicates a length of a section of the particle beam 5 along the depth direction 7, in which a local strength of the particle beam 5 exceeds an ablation threshold of the sample 3, G indicates an ablation threshold from which further executions of the ablation unit step do not cause any further ablation.The parameters d 0, F n, F 0, f 0, A and G characterize the ablation unit step. Formula (1) takes into account the physical process of ablation based on theoretical knowledge about a focused particle beam and its local state. The trench depth D N after carrying out N removal unit steps is obtained from formula (2):Regression curve R (FIG. 4 ) contains points (n; D n) according to formula (2). The parameters d 0, F 0, f 0, A, and G in formula (1) are determined by a regression method (for example, least squares method) using the calibration data sets. Accordingly, only five calibration data sets are needed to determine all the parameters in formula (1). This number of calibration data sets, which is equal to the number of calibration measurements to be performed, is significantly smaller than in the conventional methods of the prior art.In many cases, for example, if the number of executions X is sufficiently small to achieve the desired trench setpoint depth D X (for example, less than 100), each removal unit step contributes significantly to the removal. In these cases, the removal threshold parameter G in formula (1) above can be neglected. Accordingly, formula (1) is simplified. In addition, the number of parameters to be determined decreases by one and thus the number of calibration measurements to be carried out also decreases by one. In the regression curve shown in FIG. 4, the parameter G of the ablation threshold was not taken into consideration. When taking into account the parameter G of the ablation threshold, the regression curve extends only horizontally from a specific execution number. In other cases, the user can specify a suitable value for the ablation threshold, for example 5% or 1%.In addition, the parameter f 0 can generally be set sufficiently accurately, such that the parameter f 0 can be understood as part of the particle beam system setting and is therefore predefined (by the operator). In this case, the number of parameters to be determined decreases by one and thus the number of calibration measurements to be carried out also decreases by one.In addition, the number of calibration measurements to be carried out can also be reduced if, during the focusing of the particle beam, the focus is set exactly on the surface to be ablated during the first execution of the ablation unit step, i.e. F 0= 0 can be assumed.The regression curve R contains the points (n; D n) according to formula (2) and interpolates / extrapolates between them, so that the regression curve R assigns a number of executions X to each arbitrary trench setpoint depth D X as is shown by way of example in FIG. 4.Step S 104 (FIG. 1 ) includes: setting the trench target depth D X for the sample 3. For example, an operator of the particle beam system 100 sets the trench target depth D X by an input input input to the controller 101 of the particle beam system 100 through the input device 102.Step S 105 performed after performing steps S 103 and S 104 includes: determining a performing number X based on the regression curve R (determined in step S 103) and the target trench depth D X. (determined in step S 104). Specifically, the execution number X indicating the number of executions of the single ablation step to be performed according to the particle beam system setting (set in step S 101) for creating a trench having the trench target depth D X is determined by: determining a value to which the regression curve R associates the trench target depth D X ; and rounding the determined value to the closest integer, thereby determining the execution number X (i.e., the rounded value corresponds to the execution number X). The integer closest to any value denotes that integer of all integers whose magnitude of the difference between the value and the number is the smallest. Step S 105 is performed by the particle beam system 100.Step S 106 performed after step S 105 includes: forming a trench 1 in the sample 3 using the particle beam system setting (determined in step S 101) and the execution number X (determined in step S 105). Forming the trench 1 in the sample 3 is performed by performing the ablation unit step corresponding to the execution number X, i.e., by performing the ablation unit step X times. The generation of the trench 1 according to step S 106 is described below with reference to FIG. 5 and corresponds to the procedure described with reference to FIG. 6.Step S 61 comprises: arranging the sample 3 in the working region 4 of the particle beam system 100 (analogous to FIG. 6, n=1, left side). Step S 61 is carried out, for example, by an operator of the particle beam system 100.Step S 62, which is performed after step S 61, comprises: performing the ablation unit step according to the particle beam system setting (analogous to FIG. 6, n=1, right side) (determined in step S 101). Step S 62 is carried out by the particle beam system 100.Step S 63 performed after step S 62 includes: checking whether the removal unit step has already been performed X times (i.e., corresponding to the execution number X determined in step S 105, i.e., as many times as indicated by the execution number X determined in step S 105). Step S 63 is carried out, for example, by the particle beam system 100. When it is determined in step S 63 that the removal unit step has not yet been performed according to the execution number X (no in step S 63), the process proceeds to step S 62 (FIG. 6, n=2, 3,... ). When it is determined in step S 63 that the removal unit step corresponding to the execution number X has been performed (Yes in step S 63), step S 106 is ended, whereby a sample 3 having a trench 1 has been produced.An example of a particle beam system 100 is described below with reference to FIG. 7. The particle beam system 100 comprises a controller 101 having a CPU 104 and a data memory 105, an input device 102, an output device 103, a vacuum chamber 106, a laser 107 configured to generate and direct a laser beam 108 onto a sample 3, 3K, a sample table 109, an electron beam column 110 configured to generate and direct an electron beam 111 onto the sample 3, 3K, and a detector 112. The laser 107, the electron beam column 110, and the detector 112 are communicatively coupled to the controller 101 to transmit and receive signals or data to and from the controller 101.In the example shown here, the laser 107 serves to ablate material from the sample 3, 3K according to the methods described herein, whereas the electron beam column 110 and the detector 112 in conjunction with data analysis in the controller 101 provide an apparatus for measuring the depth of a trench 1 in the sample 3, 3K. This configuration is merely exemplary. Generally, material ablation and trench depth measurement need not be provided by the same system and may instead be provided by different devices or different systems.The controller 101 receives instructions input to the input device 102 (e.g., keyboard, mouse, etc.) by an operator, and stores them in the data storage 105. The controller 101 controls the output device 103 (for example, monitor, etc.) to output information. The CPU 104 executes a computer program stored in the data memory 105 to control the other system components and process data.The laser 107 is configured to generate and focus the laser beam 108 into a working region 4 in which the sample 3, 3K can be arranged. Additionally, the laser 107 is configured to direct the focused laser beam 108 to a plurality of different raster locations, for example, by deflecting the laser beam 108.The electron beam column 110 is configured to generate and focus the electron beam 111 into the working region 4 (or another region) in which the sample 3, 3K can be arranged. In addition, the electron beam column 110 is configured to direct the focused electron beam 111 to a plurality of different grid locations, for example by deflecting the electron beam 111.The detector 112 is configured to detect particles emanating from the sample 3, 3K by interaction of the beams 108, 110 with the sample 3, 3K. Such particles are, for example, electrons, ions or photons.Second EmbodimentA second embodiment will be described below with reference to FIGS. 8 and 9. The method according to the second embodiment differs from the method according to the first embodiment in that the regression curve R is not determined by acquiring calibration data sets by means of measurement on a calibration sample and calculating the regression curve R from the measured calibration data sets (according to the first embodiment), but has already been determined and is stored in a data set in association with the particle beam system setting and the sample property of the calibration sample which were used for determining the regression curve R. The regression curve R suitable for a sample 3 is obtained from the database as a function of a predetermined sample property of the sample 3 and a predetermined particle beam system setting.FIG. 8 shows a flow diagram of a method according to the second embodiment for generating a trench 1 having a trench nominal depth D X in a sample 3 by removing material from the sample 3 by means of a particle beam generated by a particle beam system 100 and focused into a working region 4 of the particle beam system 100. The particle beam system 100 corresponds to that of the first embodiment, to the description of which reference is made.Step S 201 comprises: providing a database with a plurality of data sets, wherein each of the data sets comprises a particle beam system setting, which is a setting of the particle beam system 100 for carrying out an ablation unit step with the particle beam 5, a sample property, which is a property of a calibration sample 3K, and a regression curve R, wherein the regression curve is defined as a function of at least one parameter characterizing the ablation unit step. The data sets can be determined with steps S 101 to S 103 of the method shown in FIG. 1. FIG. 9 shows an exemplary content of the database. A data record in line #1 of the database comprises a particle beam system setting A 1, a sample property B 1 and a regression curve R 1. A data record in line #2 of the database comprises a particle beam system setting A2, the sample property B1and a regression curve R2. A data record in #3 of the database comprises the particle beam system setting A1, a sample property B2 and a regression curve R3. A data record in line #4 of the database comprises the particle beam system setting A2, the sample property B2 and a regression curve R4. The database is stored in the data memory 105, for example, or can be obtained from an external data memory.Step S 202 following step S 201 includes: selecting a first particle beam system setting and a first sample property included in one of the data sets of the database. The first sample property characterizes the sample 3 in which the trench 1 is to be produced. That is, in step S 202, a data set including a sample property of a calibration sample 3K equal to or similar to the sample property of the sample 3 is selected.For example, an operator selects from the database the particle beam system setting A 1 and the sample property B 1 of line #1 or the particle beam system setting A 2 and the sample property B 1 of line #2 when a trench is to be generated in a sample 3 having the sample property B 1. In the meantime, when a trench is to be formed in a sample 3 having the sample property B 2, the operator selects either the particle beam system setting A 1 and the sample property B 2 of the line #3 or the particle beam system setting A 2 and the sample property B 2 of the line #4.Step S 203 following step S 202 comprises: obtaining a first regression curve R from one of the data sets which contains the first particle beam system setting (selected in step S 202) and the first sample property (selected in step S 202). Step S 203 is carried out, for example, by the controller 101 of the particle beam system 100. When selecting the particle beam system setting A 1 and the sample property B 1 of the line #1 in step S 202, the regression curve R 1 of the line #1 is acquired from the database.Step S 204 corresponds to step S 104 to which description is made, and includes: setting a target trench depth D X.Step S 205 performed after performing steps S 203 and S 204 substantially corresponds to step S 105 to which description is directed, and includes: determining a performing number X based on the first regression curve R (obtained in step S 203) and the target trench depth D X. (determined in step S 204).Step S 206 performed after step S 205 substantially corresponds to step S 106 to which description is directed, and includes: forming a trench in the sample 3 by repeatedly performing the ablation unit step with the first particle beam system setting (selected in step S 202) corresponding to the performing number X determined (in step S 205).Third EmbodimentA third embodiment will be described below with reference to FIGS. 10 and 11. The method according to the third embodiment differs from the method according to the first embodiment in that the calibration data sets are not acquired by measurement on a calibration sample (corresponding to the first embodiment), but have already been acquired and are stored in a data set in a database in association with the particle beam system setting and the sample property of the calibration sample 3K that were used for acquiring the calibration data sets. The regression curve R is determined from calibration datasets of one of the datasets which contains the particle beam system setting and the sample property of the sample 3. That is, a data set including a sample property of a calibration sample 3K that is the same or similar to the sample property of the sample 3 is selected.FIG. 10 shows a flow diagram of a method according to the third embodiment for generating a trench 1 having a trench nominal depth D X in a sample 3 by removing material from the sample 3 by means of a particle beam generated by a particle beam system 100 and focused into a working region 4 of the particle beam system 100. The particle beam system 100 corresponds to that of the first embodiment, to the description of which reference is made.Step S 301 includes: providing a database including a plurality of data sets, each of the data sets including a particle beam system setting which is a setting of the particle beam system 100 for performing an ablation unit step on the particle beam, a sample property which is a property of a calibration sample 3K, and a plurality of calibration data sets, each of the calibration data sets including a predetermined execution number of the ablation unit step and a depth of a trench generated by performing the ablation unit step corresponding to the predetermined execution number. The data sets can be determined using steps S 101 and S 102 of the method shown in FIG. 1.FIG. 11 shows an exemplary content of a database according to the third embodiment. A data record in line #1 of the database comprises a particle beam system setting A1, a sample property B1 and calibration data records K1. A data record in line #2 of the database comprises a particle beam system setting A2, the sample property B1 and calibration data records K2. A data record in line #3 of the database comprises the particle beam system setting A1, a sample property B2 and calibration data records K3. A data record in line #4 of the database comprises the particle beam system setting A2, the sample property B2 and calibration data records K4. The database is stored in the data memory 105, for example, or can be obtained from an external data memory.Step S 302 following step S 301 substantially corresponds to step S 202 to which description is directed, and includes: selecting a first particle beam system setting and a first sample property included in one of the data sets of the database. For example, an operator selects from the database the particle beam system setting A 2 and the sample property B 2 of the line #4 if a trench is to be generated in a sample 3 having the sample property B 2.Step S 303 subsequent to step S 302 includes: acquiring first calibration data sets included in the data set including the first particle beam system setting (selected in step S 302) and the first sample property (selected in step S 302). Step S 303 is carried out, for example, by the controller 101 of the particle beam system 100. When selecting the particle beam system setting A 2 and the sample property B 2 of the line #4 in step S 302, the calibration datasets K 4 of the line #4 are obtained from the database.Step S 304 which follows step S 303 corresponds substantially to step S 103 and comprises: determining a regression curve R based on the first calibration datasets (obtained in step S 303), wherein the regression curve is defined as a function of at least one parameter characterizing the ablation unit step.Step S 305 corresponds to step S 104 to which description is made, and includes: setting a target trench depth D X.Step S 306 performed after performing steps S 304 and S 305 substantially corresponds to step S 105 to which description is directed, and includes: determining a performing number X based on the regression curve R (determined in step S 304) and the trench target depth D X. (determined in step S 305).Step S 307 performed after step S 306 substantially corresponds to step S 106 to which description is directed, and includes: forming a trench 1 in the sample 3 by repeatedly performing the ablation unit step with the first particle beam system setting (selected in step S 302) according to the execution number X determined (in step S 306).Fourth EmbodimentA fourth embodiment will be described below with reference to FIGS. 12 and 13. The method according to the fourth embodiment differs from the methods according to the first to third embodiments in that no particle beam system setting to which a matching regression curve is determined or obtained is specified. Instead, a particle beam system setting is determined such that a performance number of the ablation unit step for a trench target depth D X satisfies a predetermined condition, for example, that the performance number is a short distance from the closest integer (or is an integer).FIG. 12 shows a flow diagram of a method according to the fourth embodiment for generating a trench 1 having a trench nominal depth D X in a sample 3 by removing material from the sample 3 by means of a particle beam generated by a particle beam system 100 and focused into a working region 4 of the particle beam system 100. The particle beam system 100 corresponds to that of the first embodiment, to the description of which reference is made.Step S 401 comprises: providing a database with a plurality of data sets, wherein each of the data sets comprises a particle beam system setting, which is a setting of the particle beam system 100 for carrying out an ablation unit step with the particle beam 5, a sample property, which is a property of a calibration sample 3K, and a regression curve R, wherein the regression curve is defined as a function of at least one parameter characterizing the ablation unit step. Fig. 9 shows an example of such a database, to the description of which reference is made. The database is stored in the data memory 105, for example, or can be obtained from an external data memory.Step S 402 comprises: selecting a first sample property from one of the data records of the database. For example, an operator of the particle beam system 100 selects the first sample property by an input which is input into the controller 101 of the particle beam system 100 by the input device 102. That is, in step S 402, a data set including a sample property of a calibration sample 3K that is the same or similar to the (first) sample property of the sample 3 is selected.Step S 403 corresponds to step S 104 to which description is referred includes: setting a target trench depth D X.The first sample property identifies the sample 3 in which a trench 1 having the trench nominal depth D X is to be produced. As indicated in the example of FIG. 9, the database comprises a data record comprising a sample property B1 in line #1 and a further data record comprising the sample property B1 in line #2. FIG. 13 shows an exemplary representation of a plurality of different regression curves, namely the regression curve R 1 of the data set from line #1 which comprises the sample property B 1 and the regression curve R 2 of the data set from line #2 which also comprises the sample property B 1. The horizontal axis of FIG. 13 represents the execution number of the removal unit step, where a, b, and c indicate integers. The vertical axis of FIG. 13 represents trench depth. The regression curves associate a pass count with any trench depth (and vice versa).The regression curve R1 assigns a value X1 to the trench target depth D X determined in step S403, which lies between the integers a and b and whose magnitude is relatively large in relation to the difference from the nearest integer (integer "a" here). Rounding the value X1 to the nearest integer a may therefore result in a relatively large deviation between the target trench depth D X and an actual trench depth, which is obtained by performing the ablation unit step corresponding to the integer a.The regression curve R 2 assigns a value X 2 to the trench target depth D X determined in step S 403, which value is relatively close to the integer b and the amount of which is relatively small in relation to the difference from the closest integer (integer "b" here). Rounding the value X2 to the nearest integer b therefore leads to a relatively small deviation between the target trench depth D X and an actual trench depth, which is obtained by carrying out the ablation unit step corresponding to the integer b.According to the example, it is therefore advantageous with regard to the trench setpoint depth D X established in step S 403 to use that of the regression curves of the database which assigns the trench setpoint depth D X a value which is as integer as possible, that is to say fulfills a predetermined condition. This process is performed in step S404.Step S 404 includes: selecting one of the data sets including a first regression curve R that associates a value satisfying a predetermined condition with the trench target depth D X. For example, the predetermined condition is satisfied when an amount of a difference between the value and the integer closest to the value is less than a predetermined threshold value. Examples of the predetermined threshold are 0.3 or 0.2 or 0.1.Step S 405 following step S 404 includes: acquiring a first particle beam system setting included in the data set selected (in step S 404).Step S 406 subsequent to step S 404 or step S 405 includes: determining a execution number X based on the regression curve included in the data set selected (in step S 404) and the trench target depth D X.Step S 407 performed after step S 406 substantially corresponds to step S 106 to which description is directed, and includes: forming a trench 1 in the sample 3 by repeatedly performing the ablation unit step with the first particle beam system setting (acquired in step S 405) according to the execution number X determined (in step S 406).Combinations of EmbodimentsThe embodiments described herein may be combined with each other. For example, the fourth embodiment may be modified to acquire the data sets stored in the database by measurement on calibration samples as described in the first embodiment, instead of pre-setting the data set as given.

Claims

Method for generating a trench having a trench nominal depth (D X) in a sample (3) by removing material from the sample (3) by means of a particle beam generated by a particle beam system (100) and focused into a working region (4) of the particle beam system (100), comprising: defining a particle beam system setting which is a setting of the particle beam system (100) for carrying out an removal unit step with the particle beam; acquiring calibration data sets using the defined particle beam system setting on a calibration sample (3K); determining a regression curve (R) based on the acquired calibration data sets, wherein the regression curve is defined as a function of at least one parameter characterizing the removal unit step; determining a performance number (X) based on the determined regression curve (R) and the trench target depth (D X); and generating a trench in the sample ( 3) by repeatedly performing the ablation unit step with the determined particle beam system setting corresponding to the determined performance number (X).The method according to claim 1, wherein acquiring calibration data sets using the determined particle beam system setting on a calibration sample (3K) comprises: arranging the calibration sample (3K) in the working area (4) of the particle beam system (100); and repeating the following steps until a predetermined number of calibration data sets is acquired: repeatedly performing the ablation unit step with the determined particle beam system setting, thereby creating or deepening a trench in the calibration sample (3K); and after a predetermined number of performing the ablation unit step is reached, measuring a current depth of the trench in the calibration sample (3K) and storing a calibration data set comprising a current number of performing the ablation unit step and the measured current depth of the trench.The method according to claim 1 or 2, wherein the determining a performance number (X) based on the determined regression curve (R) and the trench target depth (D X) comprises: determining a value to which the regression curve (R) associates the trench target depth (D X) ; and rounding the determined value to the closest integer, thereby determining the performance number (X).The method according to any one of claims 1 to 3, wherein the generating a trench in the sample (3) by repeatedly performing the ablation unit step with the determined particle beam system setting corresponding to the determined execution number (X) comprises: disposing the sample (3) in the work area (4) of the particle beam system (100); and performing the ablation unit step with the determined particle beam system setting until the determined execution number (X) of executions of the ablation unit step is reached, thereby generating or recessing the trench (1) in the sample (3).Method according to one of claims 1 to 4, wherein each individual execution of the ablation unit step comprises: focusing the particle beam into a focus plane lying in the working region (4), wherein, during the first focusing of the particle beam, the focus plane is adjusted to a surface of the calibration sample (3K) to be ablated or to a surface of the sample (3) to be ablated and wherein, during the subsequent focusing of the particle beam, the focus plane is offset by a constant preset focus displacement distance (f 0) ; and directing the particle beam successively to a plurality of different locations of the focus plane according to the determined particle beam system adjustment.Method for generating a trench having a trench nominal depth (D X) in a sample (3) by removing material from the sample (3) by means of a particle beam generated by a particle beam system (100) and focused into a working region (4) of the particle beam system (100), comprising: providing a database with a plurality of data sets, wherein each of the data sets contains a particle beam system setting, which is a setting of the particle beam system (100) for carrying out an removal unit step with the particle beam, a sample property, which is a property of a calibration sample (3K), and a regression curve, wherein the regression curve is defined as a function of at least one parameter characterizing the removal unit step; selecting a first particle beam system setting and a first sample property, which are contained in one of the data sets; acquiring a first regression curve (R) from the dataset containing the first particle beam system setting and the first sample property; determining a performance number (X) based on the first regression curve (R) and the trench target depth (D X); and creating a trench in the sample ( 3) by repeatedly performing the ablation unit step with the first particle beam system setting corresponding to the determined performance number (X).A method for generating a trench having a trench nominal depth (D X) in a sample (3) by removing material from the sample (3) by means of a particle beam generated by a particle beam system (100) and focused into a working area (4) of the particle beam system (100), comprising: providing a database with a plurality of data sets, each of the data sets comprising a particle beam system setting which is a setting of the particle beam system (100) for performing an removal unit step with the particle beam, a sample property which is a property of a calibration sample (3K), and a plurality of calibration data sets, wherein each of the calibration data sets contains a predetermined number of executions of the removal unit step and a depth of a trench generated by performing the removal unit step according to the predetermined number of executions; selecting a first particle beam system setting and a first sample property which are contained in one of the data sets; obtaining first calibration data sets from the data set which contains the first particle beam system setting and the first sample property; determining a regression curve (R) based on the obtained first calibration data sets, wherein the regression curve is defined as a function of at least one parameter characterizing the ablation unit step; determining a performance number (X) based on the determined regression curve (R) and the trench target depth (D X); and generating a trench in the sample (3) by repeatedly performing the ablation unit step with the first particle beam system setting corresponding to the determined performance number (X).Method for generating a trench having a trench nominal depth (D X) in a sample (3) by removing material from the sample (3) by means of a particle beam generated by a particle beam system (100) and focused into a working region (4) of the particle beam system (100), comprising: providing a database with a plurality of data sets, wherein each of the data sets comprises a particle beam system setting, which is a setting of the particle beam system (100) for carrying out an removal unit step with the particle beam, a sample property, which is a property of a calibration sample (3K), and a regression curve, wherein the regression curve is defined as a function of at least one parameter characterizing the removal unit step; selecting a first sample property from one of the data sets; selecting one of the data sets including the selected first sample property and a first regression curve associating the trench target depth (D X) with a value satisfying a predetermined condition; acquiring a first particle beam system setting included in the selected data set; determining a first execution number (X) based on the regression curve included in the selected data set and the trench target depth D X; and generating a trench in the sample (3) by repeatedly performing the ablation unit step with the acquired first particle beam system setting corresponding to the determined first execution number (X).The method of claim 8, wherein the predetermined condition is satisfied when an amount of a difference between the value and the integer closest to the value is less than a predetermined threshold.Method according to one of Claims 1 to 9, wherein the particle beam system setting comprises at least one of the following settings: a setting of a strength of the particle beam; a setting of a pulse length and a pulse repetition rate of pulses of the particle beam; a setting of a dwell time of the particle beam at each raster location; a setting of a raster path; a setting of a raster speed; a setting of a focus displacement distance (f 0).The method according to any one of claims 1 to 10, wherein the regression curve (R) indicates a relation between a number of executions of the removal unit step and a trench depth.The method of claim 11, wherein the confluence is expressed by: d n = { d 0 [1 + ( D n - 1 - F n A ) 2 ] - 1 f u%0020̈ r [1 + ( D n - 1 - F n A ) 2 ] 0 else - 1 > G D N = ∑ n = 1 N d n with N ≥ 1, D 0= 0 and F n = { F 0 f u%0020̈ r n = 1 ( n - 1) ⋅ f 0 + F 0 f u%0020̈ r n > 1 wherein: N indicates a number of ablation unit steps, D N indicates an estimated trench depth after carrying out N ablation unit steps, d 0 indicates an ablation depth of a single ablation unit step in the case of ideal focusing, F n indicates a position of the focus of the particle beam in a depth direction (7) for the nth carrying out of the ablation unit step, F 0 indicates a deviation of the position of the focus of the particle beam in the depth direction (7) from a surface to be ablated in the first carrying out of the ablation unit step, f 0 indicates a focus displacement distance by which the position of the focus of the particle beam in the depth direction (7) is displaced between successive ablation unit steps, A indicates a length of a section of the particle beam along the depth direction (7), in which a local strength of the particle beam (5) exceeds an ablation threshold of the sample (3), and G indicates an ablation threshold from which further executions of the ablation unit step do not cause any further ablation.The method according to any one of claims 1 to 12, wherein the particle beam is a light beam, a laser beam, a continuous laser beam, a pulsed laser beam, an electron beam or an ion beam.A computer program product comprising a computer program having instructions controlling a particle beam system (100) to perform the method according to any one of claims 1 to 13.

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