A method and apparatus for correcting image errors when scanning a sample with a charged particle beam

Abstract

The present application relates to a method and an apparatus for correcting at least one image error when scanning a sample with a charged particle beam of a scanning particle microscope. The method includes: (a) dividing a scanning region of the charged particle beam into at least two sub-regions, each of the at least two sub-regions including at least one structural element; (b) for each of the at least two sub-regions, determining at least one correction value of at least one structural element with respect to a target position of the at least one structural element; and (c) using the determined correction value to correct the beam deflection of the charged particle beam for at least one of the at least two sub-regions.

Description

Technical Field

[0001] Cross-reference This patent application claims priority to German Patent Application DE 10 2022 207 930.2, filed with the German Patent and Trademark Office on August 1, 2022, entitled "Verfahren und Vorrichtung zum Korrigieren von Abbildungsfehlern beim Rastern eines geladenen Teilchenstrahls über eine Probe", the entire content of which is incorporated herein by reference.

[0002] The present invention relates to a method and apparatus for correcting image errors, particularly when scanning an electron beam over a photolithography mask, when scanning a charged particle beam over a sample. The present invention also relates to pre-correcting at least one image error when scanning a charged particle beam over a sample.

Background Art

[0003] Advances in nanotechnology have enabled the manufacture of components with increasingly miniaturized structural elements. To display and process the chip structures of microscale or nanoscale components, tools are needed that can image and correct these chip structures.

[0004] A microscope is a powerful tool for imaging nanostructures. In a microscope, a sample to be analyzed and / or processed typically interacts with a particle beam. A microscope that uses particles having mass, such as electrons, to scan a sample has a high diffraction-limited resolution when imaging nanostructures by scanning the particle beam over the sample because the de Broglie wavelength of the particles in the particle beam is short. As an example, an electron beam can currently be focused to a diameter within the range of single-digit nanometers. In addition, a microscope may include tools for processing the sample. The processing may include mechanical and / or chemical processing.

[0005] In the case of a non-conductive sample or a sample with low conductivity, typically including a quartz substrate, such as a photolithography mask, when an image is recorded using a charged particle beam, the sample surface may become charged. There are problems with the charging of the sample. As an example, when an electron beam scans, i.e., images, the sample, it produces forgery, so-called scanning artifacts, which can significantly inhibit the impression of the image, especially image processing by algorithms. As a result, important details may not be reproduced in the recorded image.

[0006] U.S. Patent No. 6,066,849 describes using the electron beam of a scanning electron microscope to scan the sample multiple times under various operating conditions to compensate for the charging of the sample while the sample is being imaged using the electron beam.

[0007] The sample is usually scanned two-dimensionally by guiding the charged particle beam of a particle beam microscope line by line over the sample. Various lines are usually scanned continuously in the horizontal direction. In the case of a sample having a linear structure, such as a photolithography mask, the imaging quality of the pattern elements depends on its alignment with respect to the scanning direction or the line direction of the scan. This is schematically shown in FIG. 100 of FIG. 1. In the exemplary sample 110 of FIG. 1, squares 130 having sides 140 are regularly arranged. In the example shown, as represented by the symbol of arrow 190, the particle beam scans horizontally over the square 130 or the pattern element 130. The side 160 of the pattern element 130 of the sample 110 is imaged with significantly lower contrast in the line direction 120 than the side 150 that extends perpendicular to the scanning direction 120 of the particle beam of the structure or pattern element 130. Furthermore, strip-shaped artifacts 170 with low intensity are generated in the scanning direction 120, and in FIG. 100, these appear darker than the remaining regions of the sample surface.

[0008] These difficulties are typically avoided by scanning the sample 110 obliquely with respect to its pattern elements 130. The scanning artifacts that still exist in this case can be further reduced by scanning the sample 110 multiple times in different directions. FIG. 2 shows an image 200 of an excerpt of the sample 110 of FIG. 1 obtained by overlaying data from two scans. The first scan 220 was performed at an angle of 45° with respect to the horizontal, and the second scan 230 was performed at an angle of 135° with respect to the horizontal. This is indicated by the symbol of arrow 290 in FIG. 2. The image 200 of the sample 110 reproduced in FIG. 2 is the result of the overlay of the data or image data of the first scan 220 and the second scan 230. Both the vertical side 250 and the horizontal side 260 of the structural element 130 are very clearly and distinctly bounded. This means that although the scanning artifacts 270 still exist, they can be significantly reduced by scanning the sample 110 twice in different directions 290, i.e., 220 and 230.

[0009] The pixels of the two scans 220, 230 or the scanning procedures 220, 230 must correspond to each other so that the scanning data of the first scan 220 and the second scan 230 or the images created from that data can be overlaid. This means that the pixels of the first scan 220 to which the pixels of the second scan 230 are overlaid must correspond to the same position on the sample 110. This assumes that the images of the first scan 220 and the second scan 230 are not shifted and / or distorted with respect to each other.

[0010] This requirement places high demands on the reproducibility when scanning a charged particle beam over a sample, i.e., on the linearity of the deflection functions x(t) = a·t and y(t) = b·t in the case of line-by-line horizontal scanning.

[0011] An electrostatic deflection system for scanning a sample 110 by scanning with a charged particle beam 120, 220, 230 usually has the linearity required due to its high bandwidth. Furthermore, the electrostatic deflection system generally does not exhibit any hysteresis.

[0012] For the purpose of scanning the sample 110 with a charged particle beam 120, 220, 230, a magnetic deflection system can be used as an alternative to the electrostatic deflection system. In contrast, a magnetic deflection system generally has a narrower bandwidth than the bandwidth of the electrostatic deflection system. In addition, the magnetic deflection system exhibits hysteresis. Furthermore, eddy currents induced in metal components in the vicinity of the magnetic deflection system can make it almost impossible to control the beam deflection component of the charged particle beam.

[0013] The combination of these effects can reduce the linearity of the deflection functions x M (t) and y M (t) for the magnetic deflection system compared to the electrostatic deflection system. This results in different pixels of different scanning procedures 220, 230 not scanning exactly the same positions on the sample 110. As a result, when the images of two scanning procedures 220, 230 of the sample 110 are superimposed, image errors, such as distortions appearing as ghost images or double images, may occur. This is shown by the image 300 in FIG. 3 where the data of two scans 220, 230 are combined. The left partial image 305 shows an image of a sample 310 with 81 squares 350 arranged as an example of a structural element 350, and this structural element 350 is produced by superimposing the data of two images of the sample 310, i.e., two scanning procedures 220 and 230 as indicated by the arrows 220 and 230 in FIG. 2.

[0014] The right partial image 395 reproduces the details 330 of the sample 310 after magnification. From this enlarged view, it is clear that the reproduction 360 of the structural element 350 of the first scan 220 does not coincide with the reproduction 380 of the structural element 350 of the second scan 230 in the superimposed image 300. Instead, the insufficient linearity of the individual scanning procedures 220, 230 results in image errors of the structural element 350 in the form of distortion of the individual reproductions 360, 380 of the structural elements 350 of the different scans 220, 230. As a result, the reproductions 360, 380 or representations 360, 380 of the structural element 350 cannot be properly superimposed from the data of the various scans 220, 230. Summary of the Invention Problems to be Solved by the Invention

[0015] Accordingly, the present invention addresses the problem of identifying a method and an apparatus that enable improvement of the imaging of a sample using a charged particle beam of a scanning particle microscope. Means for Solving the Problems

[0016] According to an exemplary embodiment of the present invention, this problem is at least partially solved by the subject matter of independent claims 1 and 17 of the present application. Representative embodiments are described in the dependent claims.

[0017] In one embodiment, a method for correcting at least one image error when scanning a sample with a charged particle beam of a scanning particle microscope includes: (a) dividing a scanning region of the charged particle beam into at least two sub-regions, each of the at least two sub-regions including at least one structural element; (b) for each of the at least two sub-regions, determining at least one correction value of at least one structural element with respect to a target position of the at least one structural element; and (c) using the determined correction value to correct the beam deflection of the charged particle beam for at least one of the at least two sub-regions.

[0018] As discussed above, when the linearity of the deflection system that scans the sample with a charged particle beam is not sufficient, one or more positioning errors of the charged particle beam may occur as compared with the intended position of the charged particle beam on the sample. The positioning error of the charged particle beam caused by the imperfect linearity of the deflection system may result in image errors in the form of distortion, for example, when the recorded data is represented as an image on a monitor. Usually, an ideal image of the sample cannot be obtained. Therefore, small distortions cannot be detected in a single recorded image.

[0019] However, when using a deflection system having a non-linear deflection function that causes, for example, a positioning error of the charged particle beam to scan the sample from a plurality of different directions and superimpose or overlap a plurality of different scans, image errors in the form of ghost images or double images may occur due to the distortion of each individual representation. Therefore, for example, the positioning error of the charged particle beam during scanning may cause image errors when the recorded data is represented on a monitor.

[0020] After performing the calibration process, the method according to the invention enables the correction of the non-linear deflection of the charged particle beam by correcting at least one of at least two sub-regions with time-dependent and / or position-dependent correction values. Preferably, all of the at least two sub-regions are corrected by invoking time-dependent and / or position-dependent correction values. By linearizing the beam deflection of the charged particle beam thus brought about, image errors such as distortion during imaging of the sample are almost avoided. It is possible to omit computationally intensive post-processing of the recorded image of the sample.

[0021] In particular, the method according to the invention can always be advantageously used when an image of the sample is created from data generated by two or more scanning procedures.

[0022] The sample may have a specific calibration structure for the purpose of performing a calibration process. One or more structural elements of the calibration structure may be adapted to the intended purpose. It is advantageous if one or more structural elements of the calibration structure extend over a majority of the scanning area of the charged particle beam. Ideally, one or more structural elements of the calibration structure cover the scanning area uniformly and completely. Preferably, the calibration structure is arranged in a part of the sample that the sample does not need to perform its function. As an example, the calibration structure may be arranged on the inactive area of a photolithography mask.

[0023] However, alternatively and / or additionally, the calibration process can also be performed on a part of the sample having a suitable number of preferably linear structural elements.

[0024] By selecting the size of the scanning area, i.e., the magnification, when the charged particle beam scans the sample, it is possible to set the accuracy in correcting the non-linear deflection of the charged particle beam in addition to the granularity of the partial area. Usually, the size of the scanning area (field of view, FOV) is specified by its application. Therefore, it may be advantageous to use different or dedicated calibrations for each size of the scanning area. Furthermore, it is advantageous to adapt the calibration structure used for this purpose to the size of the scanning area. The larger the FOV or the scanning area, the stronger the electric or magnetic field needs to be to deflect the charged particle beam. However, as a result, all the harmful effects on the linearity of beam deflection appear more strongly. The correction or linearization of beam deflection is particularly important when the scanning area of the charged particle beam of a scanning electron microscope is large.

[0025] Alternatively, a specially designed calibration element having one or more calibration structures can be used to perform the calibration process. The calibration element may comprise a calibration structure in which the structural elements are adapted to various settings of the scanning electron microscope, such as the size and / or magnification of the scanning area of the scanning electron microscope.

[0026] After performing a calibration process based on either a separate calibration element or a calibration structure present on the sample, the determined correction value can be used to linearize the deflection of the charged particle beam when inspecting a number of samples. As a result, only one sample out of a set of identical or similar samples requires the calibration structure.

[0027] The calibration process can be repeated after changing the settings of the scanning particle microscope. Furthermore, it is possible to repeat the calibration process at regular or irregular time intervals during the operation of the scanning particle microscope. This means that the correction value once determined can be used to correct the scanning procedure of various samples or the images determined therefrom.

[0028] The method according to the invention is preferably used to correct or linearize the magnetic deflection system of the charged particle beam. However, this defined method also enables the improvement of the linearity of the electrostatic deflection system, especially when the bandwidth is limited.

[0029] A sample to be inspected that has a lateral dimension exceeding the maximum scanning area of the charged particle beam of the scanning particle microscope, or a sample that has a small area with a high-resolution scanned field of view (FOV), can be scanned using the charged particle beam by dividing the sample into a plurality of scanning regions, generally N scanning regions, that are continuously scanned through appropriate displacement of the sample by the charged particle beam. To linearize the deflection of the charged particle beam when scanning each individual partial region of the sample to be analyzed, the correction value determined by invoking the calibration structure within the calibration process can be used for each scanning region of the sample to be inspected.

[0030] The division of the scanning region into at least two partial regions can be performed in an automated manner based on algorithmic image processing. As a result, the method according to the invention does not require interaction with a human.

[0031] At least two partial regions are 2 where n ≧ 2 nIt may include a plurality of sub-regions. The number of correction values determined within the scanning region of the charged particle beam is determined by the number of sub-regions into which the scanning region is divided. As a result, the number of discrete correction values used to correct the time-continuous deflection signal of the charged particle beam is thereby determined.

[0032] The sample may comprise any type of photolithography mask. The photolithography mask typically has a rectangular structural element. The charged particle beam may include an electron beam and / or an ion beam.

[0033] At least one structural element may include a change in the topography of the sample and / or a change in the material composition of the sample.

[0034] It is advantageous if at least one structural element has a change in topography aimed at creating a topographical difference in the image recorded by the charged particle beam and a change in material composition aimed at creating a material difference.

[0035] At least one structural element of the first sub-region of the scanning region may be identical to at least one second structural element of at least one second sub-region of the scanning region. However, the structural elements of the first sub-region may also be different from the structural elements of at least one second sub-region of the scanning region.

[0036] The determination of the correction value may include a first scan in which the charged particle beam scans at least one structural element in a first line direction over at least two sub-regions, and at least one second scan in which the charged particle beam scans at least two sub-regions in at least one second line direction, where at least one second line direction has an angle different from 0° with respect to the first line direction.

[0037] It may be advantageous to determine the correction value from two or more scanning procedures and to use these correction values when recording an image of the sample from the data of a single scanning process.

[0038] At least one structural element may have a linear structure, and the first line direction may have an angle of 45° with respect to at least one structural element.

[0039] In the oblique scanning of the linear structural element of the sample, the appearance of scanning artifacts is significantly reduced compared to the scanning of the rectangular or linear structural element parallel to one of the sides of the rectangular or linear structural element.

[0040] Determining the correction value may further include creating a superimposed image from the data from the first scan and from at least one second scan.

[0041] By scanning a sample having at least one structural element in two different directions and displaying the obtained data as an image, it is possible to visualize in the superimposed image the distortion caused because the deflection of the charged particle beam is not completely linear. The image error can be quantified by appropriately analyzing the various reproductions or representations of the structural element in the superimposed image. The deflection function over various sub-regions of the scanning region of the charged particle beam can be linearized by determining correction values for different sub-regions of the scanning region.

[0042] Determining the target position includes forming an average value of a first reproduction of at least one structural element and at least one second reproduction of at least one structural element in the superimposed image, and the target position of at least one structural element can be determined by this average value.

[0043] Determining the correction value may include determining a first deviation from the target position and determining at least one second deviation from the target position.

[0044] Determining a first deviation from a target position and determining at least one second deviation from the target position may include determining a difference between the target position of at least one structural element and a first reproduction of the at least one structural element in an image superimposed with the target position of the at least one structural element, and determining at least one second deviation from the target position may include determining a difference between the target position of at least one structural element and at least one second reproduction of the at least one structural element in an image superimposed with the target position of the at least one structural element.

[0045] The first deviation may include a first correction value used when performing a first scanning process. The at least one second deviation may include at least one second correction value used when performing at least one second scanning process. The first deviation and the at least one second deviation may form a two-dimensional vector within the sample plane.

[0046] Determining the correction value may include forming an average value from the absolute value of the first deviation and the absolute value of the at least one second deviation to determine the correction value.

[0047] When determining two correction values, it is possible to determine two correction values with the same absolute value for two directions, rather than correction values in the form of two vectors with different lengths or different absolute values.

[0048] The average value may include at least one element from the group consisting of arithmetic mean, geometric mean, harmonic mean, weighted arithmetic mean, weighted geometric mean, and weighted harmonic mean.

[0049] The second line direction may include an angle of 90° with respect to the first line direction.

[0050] The first scan of the rectangular structural element is at 45° with respect to one of the sides of the rectangular structural element, and in the second scan, it is preferable that the line direction is rotated 90° with respect to the line direction of the first scan within that range. The reason is that this minimizes scan artifacts while still imposing a limited outlay for the pictorial representation of the structural element.

[0051] At least one second scan may include two scanning procedures, and the two second line directions may include angles of 60° and 120° with respect to the first line direction, or at least one second scan may include three scanning procedures, and the three second line directions may include angles of 45°, 90°, and 135° with respect to the first line direction.

[0052] Determining the correction value may include determining the correction value based on a dynamic model from the scan parameters. The dynamic model describes the system behavior of the scanning particle microscope in the form of a mathematical function. As an example, the mathematical function may have the following form.

[0053]

Equation

[0054] The method may further include the step of interpolating between the correction values of adjacent sub-regions and / or extrapolating the correction value to a sub-region when the sub-region bounds one side of the scanning region of the charged particle beam. The interpolation may include linear interpolation, and the extrapolation may include linear extrapolation.

[0055] By interpolation and extrapolation of position-discrete correction values, and thus time-discrete correction values, it is possible to determine a time-continuous correction function for the scanning region of the charged particle beam, whereby the deflection signal of the charged particle beam is corrected or linearized.

[0056] Correction of the beam deflection of a charged particle beam using the determined correction value can be performed when scanning a sub-region of the scanning region and / or when reproducing an image of the scanned sub-region of the scanning region.

[0057] Correction of the non-linear deflection of a charged particle beam can be performed in advance within the range of scanning of the sample by adding the correction value for the currently scanned sub-region of the scanning region of the sample to the deflection signal of the charged particle beam. As a result, there is substantially no linearity error in the data recorded by the scanning. However, when expressing or reproducing the data on the visual display unit, the measurement data determined based on the scanning procedure can also be corrected by the correction value determined for each corresponding sub-region of the scanning region.

[0058] A computer program may comprise instructions that cause a computer system to perform the method steps of the aspects described herein when the computer program is executed by the computer system.

[0059] In one embodiment, an apparatus for correcting at least one image error when scanning a sample with a charged particle beam of a scanning electron microscope comprises: (a) means for dividing the scanning region of the charged particle beam into at least two sub-regions, each of the at least two sub-regions including at least one structural element; (b) means for determining, for each of the at least two sub-regions, at least one correction value for the at least one structural element with respect to the target position of the at least one structural element; and (c) means for correcting the beam deflection of the charged particle beam for at least one of the at least two sub-regions using the determined correction value.

[0060] The apparatus may be configured to perform the method steps described herein.

[0061] The means for determining the correction value may comprise a magnetic deflection system and / or an electrostatic deflection system for scanning the sample with a charged particle beam.

[0062] Means for dividing the scanning area into at least two partial areas and / or for correcting beam deflection for at least one or each of at least two partial areas of the scanning area may comprise an image processing program.

[0063] Means for correcting the beam deflection of a charged particle beam may comprise a computer system. The computer system may comprise a non-volatile memory for storing an image processing program.

[0064] The method according to the invention enables correction of the insufficient linearity when scanning a sample with a charged particle beam, preferably of a magnetic deflection system. As a result, most of the disadvantages of the magnetic deflection system with respect to the electrostatic deflection system can be compensated for.

[0065] Furthermore, the device may have at least one means for processing the sample. The at least one processing means may comprise a micromanipulator for processing the sample, in particular for removing particles and / or defects from the sample.

[0066] In the following detailed description, presently preferred exemplary embodiments of the invention will be described with reference to the following drawings.

Brief Description of the Drawings

[0067]

Figure 1

Figure 2

Figure 3

Figure 4

Figure 5

Figure 6

Figure 7

Figure 8

Mode for Carrying Out the Invention

[0068] The presently preferred embodiments of the apparatus and method according to the present invention will be described below. These will be described in detail using the example of a scanning electron microscope (SEM). However, the apparatus and method according to the present invention are not limited to the use of a beam of particles having a mass in the form of an electron beam. Rather, they can be used for any particle beam that uses particles in the form of bosons or fermions when scanning a sample with a particle beam for the purpose of imaging the sample. Further, the use of the apparatus and method according to the present invention will be described using the example of a photolithography mask. However, this too is not meant to represent any limitation. Rather, the apparatus and method according to the present invention can be used for imaging and processing any desired sample. By way of example, the methods and apparatus described in the present application can be used to image and modify chip structures or semiconductor structures, MEMS (microelectromechanical systems), NEMS (nanoelectromechanical systems), and / or PICs (photonic integrated circuits) on a wafer by means of a particle beam or by means of a mechanical processing process.

[0069] Regarding FIGS. 1 to 3 for explaining the prior art, these have already been considered in this specification.

[0070] FIG. 4 reproduces once again the details of the sample 310 of the left partial image 305 of FIG. 3. The details of the sample 310 represent an exemplary calibration structure 400. In the example described, the calibration structure 400 is part or a detail of the sample 310 to be inspected, for example a photolithography mask. By way of example, the calibration structure 400 may be arranged outside the active region of the photolithography mask. However, it is also possible to perform a calibration process for determining a correction value of the deflection signal of the charged particle beam on the pattern elements of the photolithography mask. Further, the calibration process can be carried out using a calibration element specially designed for this purpose, having a plurality of calibration structures adapted to various settings of the scanning particle microscope.

[0071] The calibration structure 400 serves to execute a calibration process for the purpose of determining a correction value, which is preferably used to improve the linearity when scanning the part of the sample 310 to be inspected with a charged electron beam.

[0072] It is obvious that the calibration structure 400 can also be designed as an independent calibration element having one or more calibration structures adapted to the scanning area of the electron beam and / or the settings of the scanning electron microscope without being part of the sample to be analyzed.

[0073] The calibration structure 400 comprises a scanning area 420 of a charged particle beam of a scanning electron microscope as an example of a scanning particle microscope. In the example shown in FIG. 4, the calibration structure 400 comprises 81 structural elements 450.

[0074] In a first step for determining a correction value for the deflection signal for scanning the scanning area 420 of the calibration structure 400 with a charged particle beam, the scanning area 420 is divided into sub-areas 410. Two sub-areas 410 are the minimum number of sub-areas 410 into which the scanning area 420 is divided. The maximum number of sub-areas 410 is determined by the number of pixels when the data of the scanning procedure is drawn on the monitor. The size of the sub-areas 410 determines the granularity when the correction value is determined within the scanning area 420. The larger the number of sub-areas 410, the more correction values are determined for the scanning area 420 of the charged particle beam, and the determined correction values can be used to better correct, i.e., linearize, the deflection of the charged particle beam. The price for this advantage is an increase in the amount of calculation for determining the correction value.

[0075] In order to divide the scanning area 420 of the charged particle beam into sub-areas 410, software, for example in the form of an image processing program, can be used.

[0076] The exemplary calibration structure 400 of FIG. 4 has a structural element 450 in the form of a square arranged in a square. This means that in the example shown in FIG. 4, each sub-region 410 of the scanning region 420 has one structural element 450. As already explained in the context of FIG. 3, the data of the two scans 220, 230 or the two scanning procedures are combined or superimposed in the image 300. The first scanning process 220 scans the sub-region 410 or the structural element 350 at an angle of 45° with respect to the horizontal. During the second scan 230, the line direction has an angle of 135° with respect to the horizontal direction, or an angle of 90° with respect to the line direction of the first scan 220.

[0077] As shown in the context of FIG. 3, the structural element 350 is not properly superimposed between the first scan 220 and the second scan 230. Instead, the structural element 350 is reproduced once as the square 360 and once as the square 380 in the superimposed image 395.

[0078] As explained in the context of FIG. 3, after scanning the calibration structure 400 twice, the target position of the structural element 450 of each sub-region 410 of the scanning region 420 can be determined in the superimposed image, that is, in the image where the data of the scans 220 and 230 are reproduced, by forming the average value of the positions of the structural element 450 of the calibration structure 400.

[0079] In the next step of determining the correction value, a first deviation 520 of the structural element 450 from the target position of the structural element 450 is obtained. This first deviation 520 from the target position of the structural element 450 is represented by the symbol of arrow 520 in FIG. 5. Arrow 520 presents the shift of the structural element 450 of the calibration structure 400 brought about by the first scan 220. Further, for each partial region 410 of the scan region 420, a second deviation 540 of the structural element 450 from the target position of the structural element 450 is obtained by subtraction. The second deviation 540 is reproduced by arrow 540 in FIG. 5. The first deviation 520 and the second deviation 540 are two-dimensional (2-D) vectors in the sample plane or in the plane of the calibration structure 400 and provide the correction value for one corresponding partial region 410 of the scan region 420. In the case of two scans 220, 230 performed at an angle of 90°, the absolute values, and thus the lengths, of the 2-D vectors 520, 540 are equal, but they are oriented in opposite directions.

[0080] When scanning the partial region 410 of the scan region 420 of the test sample 310, the first deviation 520 and the second deviation 540 can be used to correct the beam position of the charged particle beam during the scanning of the partial region 410 of the scan region 420.

[0081] The first deviation 520 and the second deviation 540 are correction values specific to the partial region, having constant values within the partial region 410 of the scan region 420. The absolute value of the deviation can be determined by forming an average value from the two deviations 520 and 540, or from three or more deviations if the overlaid image includes three or more scans. The resulting deviation is in the form of a 2-D vector and, in the general case, has different lengths and points in different directions.

[0082] By performing interpolation between various partial regions 410, a continuous-time two-dimensional correction function can be determined from the deviations 520 and 540 specific to the discrete partial regions. When a partial region 410 is located at the edge of the scanning region 420, the correction function can be extrapolated to the edge of the scanning region 420. In general, linear interpolation and extrapolation across the scanning region 420 of the charged particle beam result in good linearization of the scanning of the sample 310 by the charged particle beam. However, if necessary, higher-order polynomials can also be used for interpolation or extrapolation of the deviations 520 and 540 specific to the partial regions.

[0083] In FIG. 6, FIG. 600 exemplarily shows the x-component of the deflection signal 620 as a function of time with reference to the left vertical axis, and further shows the associated correction signal 640 with reference to the right vertical axis. The x-component of the continuous-time correction signal 640 has a value on the order of 1 percent of the deflection signal 620.

[0084] To each point (x, y) in the scanning region 420 of the charged particle beam, a correction vector (Δx, Δy) is assigned by a two-dimensional continuous-time function (Δx(t), Δy(t)). During each new scanning process of the sample 310, this correction value (Δx, Δy) is used to correct, i.e., make available, the beam position of the charged particle beam by the correction vector (Δx, Δy). This makes it possible to prevent the occurrence of image errors, and instead, when scanning the sample 310, the occurrence of image errors can be avoided in advance.

[0085] Alternatively and / or additionally, it is also naturally possible to store the data generated by scanning the structural element 350 of the sample 310 with a charged particle beam together with the associated correction values 520, 540 determined by a calibration process using the calibration structure 400. When displaying or reproducing the data or image data on a monitor, they can be corrected based on the associated correction values 520, 540.

[0086] FIG. 7 shows again the details of the sample 310 of the left partial image 305 of FIG. 3. However, in the case of the two scans 220 and 230 for recording data, as described above in this specification, the beam deflection of the charged particle beam was corrected during the scan. As indicated by reference numeral 750, the data 360, 380 recorded by the two scans 220, 230 can be properly superimposed, that is, without offset or distortion. Image errors caused by scan artifacts, such as the double image depicted in FIG. 3, no longer occur.

[0087] Finally, FIG. 8 presents a flowchart 800 that reproduces some important steps of the method according to the present invention for correcting image errors when scanning a sample 310 with a charged particle beam of a scanning electron microscope. The method starts at step 810. The scanning region 420 is divided into at least two sub-regions 410 in a first step 820, and each sub-region 410 comprises at least one structural element 450. Image processing software can be used to divide the scanning region 420 into two or more sub-regions 410. It is advantageous if one or more structural elements 450 are uniformly arranged across the scanning region 420 of the charged particle beam.

[0088] In the next step 830, for each of the at least two sub-regions, correction values 520, 540 of at least one structural element 450 with respect to the target position of at least one structural element 450 are determined. Determining the correction values 520, 540 includes scanning at least two sub-regions 410 at least twice in different line directions 220, 230 using a charged particle beam. Determining the correction values 520, 540 from the data of the at least two scans 220, 230 can be performed by a dedicated image processing program. For each sub-region 410 of the scanning region 420, the correction values 520, 540 comprise two-dimensional vectors in the sample plane.

[0089] In an optional step not depicted in flowchart 800, a time - continuous two - dimensional correction function (Δx(t), Δy(t)) can be derived from discrete correction values 520, 540 that are constant within sub - regions 410, by interpolation and extrapolation between various sub - regions 410 of the scanning region 420.

[0090] Then, in step 840, using the determined correction values 520, 540, the beam deflection of the charged particle beam is corrected for at least one of at least two sub - regions 410 of the scanning region 420. Preferably, the beam deflection for each of at least two sub - regions 410 of the scanning region 420 is corrected using the determined correction values 520, 540. This correction can be performed in two different ways. First, the correction values 520, 540 can be used in advance during the scanning of the charged particle beam on the sample 310 to linearize the beam deflection. Second, the determined correction values 520, 540 can be used to correct the deviation from the linearity of the beam deflection when expressing or reproducing the data generated by the scans 220, 230 as an image.

[0091] Finally, the method ends at step 850.

[0092] Further embodiments 1. A method for correcting at least one image error when scanning a sample with a charged particle beam of a scanning electron microscope, comprising: a. dividing a scanning region of the charged particle beam into at least two sub - regions, each of the at least two sub - regions including at least one structural element; b. determining, for each of the at least two sub - regions, at least one correction value for at least one structural element with respect to a target position of the at least one structural element; c. using the determined correction values to correct the beam deflection of the charged particle beam for at least one of the at least two sub - regions.

[0093] 2. The division of the scanning area into at least two partial areas is performed in an automated manner based on algorithmic image processing, the method according to aspect 1.

[0094] 3. The at least two partial areas comprise n partial areas with n ≥ 2, the method according to aspect 1 or 2. n 7. The determination of the correction value includes a first scan in which a charged particle beam scans over at least two partial areas in a first line direction with respect to at least one structural element, and at least one second scan in which the charged particle beam scans over at least two partial areas in at least one second line direction, wherein the at least one second line direction has an angle different from 0° with respect to the first line direction, the method according to any one of aspects 1 to 4.

[0095] 4. At least one structural element includes a change in the topography of the sample and / or a change in the material composition of the sample, the method according to any one of aspects 1 to 3.

[0096] 5. The determination of the correction value includes a first scan in which a charged particle beam scans over at least two partial areas in a first line direction with respect to at least one structural element, and at least one second scan in which the charged particle beam scans over at least two partial areas in at least one second line direction, wherein the at least one second line direction has an angle different from 0° with respect to the first line direction, the method according to any one of aspects 1 to 4.

[0097] 6. At least one structural element has a linear structure, and the first line direction has an angle of 45° with respect to at least one structural element, the method according to aspect 5.

[0098] 7. The determination of the correction value further includes creating a superimposed image from the data from the first scan and the data from at least one second scan, the method according to aspect 5 or 6.

[0099] 8. The determination of the target position includes forming an average value of a first reproduction of at least one structural element and at least one second reproduction of at least one structural element in the superimposed image, and the target position of at least one structural element is determined by the average value, the method according to any one of aspects 1 to 7.

[0100] 9. The method according to aspect 8, wherein determining the correction value includes determining a first deviation from the target position and determining at least one second deviation from the target position.

[0101] 10. Determining the first deviation from the target position and determining at least one second deviation from the target position includes determining the difference between the first reproduction of at least one structural element in the image superimposed with the target position of at least one structural element, and determining at least one second deviation from the target position includes determining the difference between at least one second reproduction of at least one structural element in the image superimposed with the target position of at least one structural element. The method according to aspect 9.

[0102] 11. The method according to aspect 10, wherein the first deviation includes a first correction value for performing a first scan, and the at least one second deviation includes at least one second correction value for performing at least one second scan.

[0103] 12. The method according to aspect 10, wherein determining the correction value includes forming an average value from the absolute values of the first deviation and the at least one second deviation in order to determine the correction value.

[0104] 13. The method according to any one of aspects 5 to 12, wherein the second line direction includes an angle of 90° with respect to the first line direction.

[0105] 14. The method according to any one of aspects 1 to 13, further including performing interpolation between the correction values of adjacent partial regions and / or extrapolating the correction value to a partial region when a certain partial region bounds one side of the region scanned by the charged particle beam.

[0106] 15. The method according to any one of aspects 1 to 14, wherein correction of the beam deflection of the charged particle beam using the determined correction value is performed when scanning a partial region of the scanning region and / or when reproducing an image of the scanned partial region of the scanning region.

[0107] 16. A computer program comprising instructions that, when the computer program is executed by a computer system, cause the computer system to perform the method steps described in Aspects 1 to 15.

[0108] 17. An apparatus for correcting at least one image error when scanning a sample with a charged particle beam of a scanning particle microscope, a. means for dividing the scanning region of the charged particle beam into at least two sub-regions, each of the at least two sub-regions containing at least one structural element; b. means for determining, for each of the at least two sub-regions, at least one correction value of at least one structural element with respect to the target position of the at least one structural element; c. means for correcting the beam deflection of the charged particle beam for at least one of the at least two sub-regions using the determined correction value.

[0109] 18. The apparatus according to aspect 17, configured to perform the method steps described in aspects 1 to 15.

[0110] 19. The apparatus according to aspect 17 or 18, wherein the means for determining the correction value comprises a magnetic deflection system and / or an electrostatic deflection system for scanning the sample with a charged particle beam.

[0111] 20. The apparatus according to any one of aspects 17 to 19, wherein the means for dividing the scanning region into sub-regions and / or for correcting the beam deflection for each of the at least two sub-regions comprises an image processing program.

Claims

1. A method for correcting at least one positioning error caused by a magnetic deflection system when scanning a sample with a charged particle beam of a scanning particle microscope, comprising: a. dividing a scanning region of the charged particle beam into at least two sub-regions, each of the at least two sub-regions including at least one structural element; b. for each of the at least two sub-regions, determining a correction value of the at least one structural element with respect to a target position of the at least one structural element; and c. using the determined correction value to correct a beam deflection of the charged particle beam caused by the magnetic deflection system for at least one of the at least two sub-regions.

2. The method according to claim 1, wherein the division of the scanning region into the at least two sub-regions is performed in an automated manner based on algorithmic image processing.

3. The at least two partial regions are two partial regions with n ≥ 2. n The method according to claim 1 or 2, comprising two partial regions with n ≥ 2.

4. The method according to any one of claims 1 to 3, wherein the at least one structural element includes a change in topography of the sample and / or a change in material composition of the sample.

5. The method according to any one of claims 1 to 4, wherein the determination of the correction value includes a first scan in which the charged particle beam scans over the at least two sub-regions in a first line direction with respect to the at least one structural element, and at least one second scan in which the charged particle beam scans over the at least two sub-regions in at least one second line direction, the at least one second line direction having an angle different from 0° with respect to the first line direction.

6. The method according to claim 5, wherein the at least one structural element has a linear structure and the first line direction has an angle of 45° with respect to the at least one structural element.

7. The method according to claim 5 or 6, wherein the determination of the correction value further includes creating an overlaid image from data from the first scan and data from the at least one second scan.

8. The determination of the target position includes forming an average value of a first reproduction of the at least one structural element in the superimposed image and at least one second reproduction of the at least one structural element, and the target position of the at least one structural element is determined by the average value. The method according to any one of claims 1 to 7.

9. The determination of the correction value includes determining a first deviation from the target position and determining at least one second deviation from the target position. The method according to claim 8.

10. The determination of the first deviation from the target position and the determination of the at least one second deviation from the target position include determining a difference between the target position of the at least one structural element and a first reproduction of the at least one structural element in the superimposed image. The determination of the at least one second deviation from the target position includes determining a difference between the target position of the at least one structural element and at least one second reproduction of the at least one structural element in the superimposed image. The method according to claim 9.

11. The first deviation includes a first correction value for performing the first scan using the magnetic deflection system, and the at least one second deviation includes at least one second correction value for performing the at least one second scan using the magnetic deflection system. The method according to claim 10.

12. The determination of the correction value includes forming an average value from the absolute values of the first deviation and the at least one second deviation to determine the correction value. The method according to claim 10.

13. The second line direction includes an angle of 90° with respect to the first line direction. The method according to any one of claims 5 to 12.

14. Further including performing interpolation between the correction values of adjacent partial regions and / or extrapolating the correction value to the partial region when a certain partial region bounds one side of the scanning region of the charged particle beam. The method according to any one of claims 1 to 13.

15. The correction of the beam deflection of the charged particle beam using the determined correction value is performed when scanning a partial region of the scanning region and / or when reproducing an image of the scanned partial region of the scanning region, according to any one of claims 1 to 14.

16. A computer program comprising instructions that, when the computer program is executed by a computer system, prompt the computer system to perform the method steps according to claims 1 to 15.

17. An apparatus for correcting at least one positioning error caused by a magnetic deflection system when scanning a sample with a charged particle beam of a scanning electron microscope, a. means for dividing the scanning region of the charged particle beam into at least two partial regions, each of the at least two partial regions including at least one structural element; b. means for determining, for each of the at least two partial regions, a correction value of the at least one structural element with respect to a target position of the at least one structural element; c. means for correcting the beam deflection of the charged particle beam caused by the magnetic deflection system for at least one of the at least two partial regions using the determined correction value.

18. The apparatus according to claim 17, configured to perform the method steps according to claims 1 to 15.

19. The apparatus according to claim 17 or 18, further comprising means for processing the sample.

20. The means for dividing the scanning region into partial regions and / or for correcting the beam deflection of the magnetic deflection system for each of the at least two partial regions comprises an image processing program, according to any one of claims 17 to 19.

Images