Method for operating particle beam microscope

Abstract

For a given object direction, a method for operating a particle beam microscope comprises the measures of successively directing a particle beam to a plurality of incident positions within an elongated region of an object oriented in the given object direction, detecting the particle and determining a value representative of a measure of image sharpness, and varying an excitation of an anastigmator based on the value, the objective is to improve image definition. The method further comprises performing these measures for a first given object direction; and performing these measures for a second given object direction oriented crosswise to the first given object direction.

Description

Technical Field

[0001] The invention relates to a method for operating a particle beam microscope. Background Art

[0002] A conventional particle beam microscope comprises: a particle beam source for generating a particle beam; an objective lens for focusing the particle beam on an object; a scanning deflector for shifting the incident position of the particle beam on the object; and a detector for detecting particles generated by the particle beam at the object. By actuating the scanning deflector, the particle beam can be successively directed to a plurality of incident positions on the object, while the intensity of the particles generated by the particle beam at the object is detected using the detector for each incident position. Values ​​representing the detected intensities and values ​​representing the incident positions of the particle beam assigned to these detected intensities can be stored as data records representing a particle microscopic image of the object.

[0003] The particle beam microscope must be appropriately set up so that the image represented by the collected data record has the desired quality, for example in terms of resolution, image sharpness, contrast, etc. For example, a high-resolution particle beam microscopic image can be obtained when the spot exposed by the particle beam on the object is as small as possible. Furthermore, the particle beam should have as small as possible astigmatic distortion when incident on the object. Furthermore, for objects that are not planar but three-dimensionally structured, it is desirable that the generated particle beam microscopic image exhibits a sufficient depth of field.

[0004] In order to make the desired adjustment of the particle beam microscope, the latter also includes further particle optical elements, such as an stigmator, which is used to influence the particle beam astigmatically; an adjustment deflector, which is used to deflect the particle beam so that its position relative to the objective is modified; and a condenser, the excitation of which is variable in order to modify the numerical aperture of the particle beam when it is incident on the object.

[0005] The excitation of the elements in a particle beam microscope is modified within the scope of finding suitable settings, with the aim of improving the image sharpness of the recorded images. For this purpose, a number of test images of the object are usually recorded with the modified excitation of these elements in an optimization method, wherein the images are analyzed and compared with one another in order to find the optimal settings for the excitation. Subsequently, the desired particle beam microscopy image of the object can be obtained using the optimally found settings for the excitation.

[0006] While the desired image recorded with the optimized settings typically contains a large number of pixels, the test image recorded to find the optimized settings may have relatively few pixels. However, even a particle microscopy test image with a reduced number of pixels requires that the particle beam be directed to a plurality of incident positions on the object corresponding to these pixels, and a statistically representative number of particles need to be detected for the respective incident positions. This means that each test image in the optimization process requires a non-negligible recording time, and the optimization process as a whole takes a considerable period of time. This period of time is generally considered to be too long. Summary of the invention

[0007] It is therefore an object of the present invention to propose a method for operating a particle beam microscope which shortens the time taken for the process of setting up the particle beam microscope.

[0008] According to the present invention, the method for operating a particle beam microscope is applied to a particle beam microscope, which comprises: a particle beam source for generating a particle beam; an objective lens for focusing the particle beam on an object; a scanning deflector for deflecting the particle beam so that the incident position of the particle beam on the object can be shifted; and a detector for detecting particles generated by the particle beam at the object. The particle beam can be an electron beam or an ion beam.

[0009] According to an embodiment, the method comprises directing a particle beam in a plurality of directions successively using a scanning deflector so that the particle beam is incident successively on a plurality of incidence positions in the region of the object, detecting the particles using a detector, and generating data records representing the detected particles assigned to the respective directions. For different excitation settings of an element in a particle beam microscope, different data records are obtained, which are analyzed and possibly compared with one another in order to obtain values ​​forming the basis for a decision related to a change in the excitation of a particle optical element in the particle beam microscope.

[0010] In this case, the region of the object where the plurality of incident positions are located is a region that is elongated in a certain direction, for example, the extent of the region in the certain direction is more than ten times or more than fifty times the extent in the orthogonal direction.

[0011] In conventional methods for setting up a particle beam microscope, test images are obtained, each of which is obtained by scanning a rectangular area with an aspect ratio of, for example, 1 to 2, are analyzed and compared with one another.

[0012] The inventors have realized that with respect to finding the settings for the excitation of a specific element in a particle beam microscope, the recorded images representing data suitable for finding suitable settings for the excitation of an element in a particle beam microscope are not necessarily large. With respect to finding suitable settings for the excitation of a specific element in a particle beam microscope, the inventors have also realized that sufficient data required for this can be obtained by scanning the elongated area on the object, provided that the elongated area has a suitable orientation, i.e. the corresponding direction of the extent of the elongated area has been selected in a suitable manner.

[0013] According to an exemplary embodiment, the positions of incidence of the particle beam on the object in the elongated region are located on one or more straight lines extending on the object in a determined direction. In this case, data providing a basis for finding an optimized setting can be obtained particularly quickly by guiding the particle beam to, for example, 100 or 1000 positions of incidence located on a straight line. Assuming that the orientation of the lines is chosen appropriately, the data obtained can be used to improve the settings of the particle microscope, while within the scope of conventional methods, images containing 100×100 or 1000×1000 pixels would be obtained for this purpose. Due to the reduction in the number of positions of incidence required to obtain a data record, this data record can be obtained relatively quickly and the method for setting a particle microscope can be performed correspondingly quickly.

[0014] According to an exemplary embodiment, the particle beam microscope comprises an stigmator configured to affect the particle beam astigmatically, and for a given object direction, the method comprises the following measures: guiding the particle beam in a plurality of directions successively with a scanning deflector so that the particle beam is incident successively on the object at a plurality of incidence positions within an elongated region of the object oriented in the given object direction, detecting the particles using a detector and generating a data record representing the detected particles assigned to the respective deflections, evaluating the data record and determining at least one value representing a measure of image sharpness, and changing the excitation of the stigmator based on the at least one value, with the aim of improving the image sharpness. In this case, the method further comprises performing these measures for a first given object direction and performing these measures for a second given object direction oriented crosswise to the first given object direction. In the present disclosure, two directions are considered to be crosswise oriented to each other if they are not parallel to each other and the angle between the two directions is different from 0° and 180°. For example, the angle between the two directions is greater than 10° and less than 170°.

[0015] According to embodiments herein, the smaller angle formed between the two directions is between 10° and 80°, in particular between 20° and 70°, in particular between 30° and 60°.

[0016] The stigmator can be configured to collimate the particle beam in two mutually orthogonal collimation directions in a mutually independent manner, wherein the orientations of the two collimation directions can be freely set. For example, the stigmator comprises eight coils which are arranged in a circumferential direction so as to be distributed around the particle beam passing through the stigmator and are used to generate a quadrupole field whose strength and orientation around the particle beam need to be set.

[0017] According to an exemplary embodiment, the method further comprises repeatedly performing the measures for a first given object direction and performing the measures for a second given object direction a plurality of times.

[0018] According to an exemplary embodiment herein, the method further comprises changing the excitation of the objective lens based on at least one value determined when performing the measures for a first given object direction and / or when performing the measures for a second given object direction, with the aim of improving at least one measure of image sharpness.

[0019] According to an exemplary embodiment, the particle beam microscope comprises an adjustment deflector, which is arranged on the beam path of the particle beam between the particle beam source and the objective lens, and is configured to deflect the particle beam and change its position relative to the objective lens. In the method for setting the particle beam microscope, the excitation of the adjustment deflector is set so that the particle beam passes through the focusing field of the objective lens as centrally as possible, resulting in avoiding errors when focusing the particle beam, which are increasingly generated when the particle beam passes through the objective lens at an increased distance from the main axis of the objective lens.

[0020] According to an exemplary embodiment, a method for operating a particle beam microscope includes guiding a particle beam in multiple directions using a scanning deflector so that the particle beam is successively incident on the object at multiple incident positions within an elongated region of the object oriented in a given object direction, detecting particles generated by the particle beam at the object during the process, and generating a first data record representing the detected particles assigned to the corresponding direction, then changing the focus of the particle beam on the object, and then redirecting the particle beam in multiple directions so that the particle beam is successively incident on the object at multiple incident positions within a region oriented in a given direction, detecting particles and generating a second data record representing the detected particles assigned to the corresponding direction. The method then also includes evaluating the first data record and the second data record and determining at least one value representing a measure of the displacement, and changing the excitation of the adjustment deflector based on the value representing the displacement, with the aim of reducing the displacement.

[0021] For example, the particle beam focusing can be changed by changing the excitation of the object lens, wherein the increase of the excitation of the object lens makes the focusing of the particle beam stronger, so that the distance between the focus of the particle beam and the object lens is reduced. The focusing of the particle beam can also be realized by changing the kinetic energy of the particle passing through the object lens, wherein the reduction of the kinetic energy makes the focusing of the particle beam stronger, and therefore causes the distance between the focus and the object lens to reduce equally. For example, the kinetic energy of the particle in the particle beam passing through the object lens can be obtained by changing the accelerating voltage during utilizing the particle beam source to produce the particle beam.

[0022] Thus, the first data record and the second data record are obtained with different settings of the focus. If the particle beam passes through the objective lens centrally along the main axis of the objective lens, the focus of the particle beam is also located on the main axis and the same elongated area of ​​the object is scanned when the first data record and the second data record are obtained, and thus a zero shift is determined during the evaluation of the data records.

[0023] If the particle beam passes through the objective lens at a distance from the main axis of the objective lens, the focus also occurs at a position arranged at a distance from the main axis, wherein this distance changes with focusing. Therefore, the elongated areas of the object scanned when obtaining the first data record and the second data record are different due to being offset from each other. The value representing this displacement is then used as the basis for changing the excitation of the adjustment deflector, with the aim of reducing the displacement. This method can be repeatedly performed until the displacement is small enough and the particle beam therefore passes through the objective lens essentially centered.

[0024] According to an exemplary embodiment, when the main axis of the objective lens extends in the z-direction, the adjustment deflector can deflect the particle beam in two mutually independent directions, for example in the x-direction and the y-direction. The change of the deflection of the adjustment deflector in the two independent directions leads to a displacement of the region of the object scanned when obtaining the data record in corresponding different directions. It is for this reason that the method is performed for two different elongated regions of the object, which are oriented differently on the object, so that the excitation of the adjustment deflector can be changed for two different directions.

[0025] According to an exemplary embodiment, the first object direction and the second object direction are oriented orthogonally to each other.

[0026] According to an exemplary embodiment, the particle beam microscope also includes a condenser, which is arranged on the beam path of the particle beam between the particle beam source and the object lens, and is configured to collimate the particle beam. Like the object lens, the condenser also provides a magnetic field and / or an electric field with a focusing effect on the particle beam, and the result is that the condenser and the object lens focus the particle beam on the object together. In particular, the condenser and the object lens can image the emitter of the particle beam source on the surface of the object in a particle optical mode.

[0027] The condenser is located further from the object than the objective lens, with the result that when only the condenser has a focusing effect on the particle beam, the particle beam is incident on the object with the smallest possible convergence angle or the smallest possible numerical aperture. Conversely, if the focusing effect is only produced by the objective lens, the particle beam is incident on the object with the largest possible numerical aperture. By varying the ratio between the excitation of the condenser and the objective lens, the convergence or the numerical aperture of the particle beam on the object can thus be set.

[0028] The numerical aperture of the particle beam when incident on the object affects the maximum obtainable resolution and its depth of field of the image obtained by the particle beam simultaneously. The higher numerical aperture of the particle beam produces higher obtainable resolution and lower depth of field, and vice versa. For the structured object with scope in the direction of the particle beam, it is desirable to set the depth of field so that all regions of the extended object are imaged to have acceptable clarity. This can be achieved by the target setting of the excitation of the condenser and therefore the object lens.

[0029] In some cases, the goal includes producing an image of a substantially planar object arranged in front of the objective at a certain inclination, as a result of which the surface normal of a major surface of the object makes an angle, for example greater than 10° and less than 80°, with the direction of the particle beam incident on the surface.

[0030] According to an exemplary embodiment, a method for operating a particle beam microscope in such a situation comprises determining an object direction on a main surface of an object so that the object direction is cross-oriented with a direction on the main surface of the object that is oriented orthogonally to the particle beam direction. The method then further comprises determining an elongated region of the object so that it is oriented in the determined object direction, directing the particle beam to a plurality of incident positions within the determined region of the object, detecting particles and generating data records representing the detected particles assigned to the respective incident positions, evaluating the data records and determining at least one value representing a measure of image sharpness, and changing the excitation of a condenser and an objective lens based on the at least one value, in order to improve the image sharpness.

[0031] This method can be repeated several times until the desired image sharpness is obtained for the entire elongated area. In particular, a plurality of values ​​representing a measure of image sharpness can be determined from the data record. For example, values ​​representing a corresponding measure of image sharpness in a portion can be determined for a plurality of portions of the elongated area. The excitation of the concentrator can then be varied based on the plurality of values ​​so that a value derived from the plurality of values ​​(e.g. equal to an average of these values) becomes a maximum.

[0032] Once the above-mentioned settings have been made, i.e. the excitation of the elements influencing the particle beam, such as the excitation of the stigmator, the adjustment deflector or the condenser, has been set, a particle microscopic image can be recorded using a particle beam microscope with a largely optimized setting. According to an exemplary embodiment, this includes guiding the particle beam to a plurality of incident positions within an image area of ​​the object, detecting particles and generating a data record representing the detected particles assigned to the respective incident positions, wherein the image area on the object has a first extent in a first direction and a second extent in a second direction orthogonal to the first direction, and wherein the ratio between the first extent and the second extent is greater than 0.5 and less than 2.0. The data record represents a particle beam microscopic image of an image area that is not elongated but has a significant extent in both directions.

[0033] The present invention also provides a computer program product, which represents instructions, when these instructions are loaded onto a control computer of a particle beam microscope, causing the control computer to operate the particle beam microscope according to one of the methods described in the aforementioned embodiments. The computer program product may include a data carrier, such as an optical disk or a solid-state memory, wherein the instructions are represented by magnetic states, optical states or electrical states. The computer program product may also include a signal sequence, which may be transmitted, for example, via a network, a data line, a wireless communication path, etc., wherein the signal sequence encodes information representing the instructions. BRIEF DESCRIPTION OF THE DRAWINGS

[0034] The following is a detailed explanation of the embodiments of the present invention with reference to the accompanying drawings.

[0035] Figure 1 A schematic cross-sectional view of a particle beam microscope is shown;

[0036] Figure 2 The method for operating according to the first embodiment is shown. Figure 1 A flow chart of a method of particle beam microscopy;

[0037] Figure 3 Shows Figure 2 Schematic diagram of the object region used in the method;

[0038] Figure 4 Shown in Figure 2 Graphical representation of the data obtained by the method;

[0039] Figure 5 The method for operating according to the second embodiment is shown. Figure 1 A flow chart of a method of particle beam microscopy;

[0040] Figure 6 Shown in Figure 5 Graphical representation of the data obtained by the method;

[0041] Figure 7 The method for operating according to the third embodiment is shown. Figure 1 A flow chart of a method of particle beam microscopy; and

[0042] Figure 8 Shown in Figure 7 Graphical representation of the data obtained in the method. DETAILED DESCRIPTION

[0043] Figure 1 is a schematic cross-sectional view of a particle beam microscope 1 for obtaining a particle beam microscopic image of an object 3. The particle beam microscope 1 comprises a particle beam source 5, which is configured to generate a particle beam 7. The particle beam 7 may be an ion beam, with the result that the particle beam microscope 1 is an ion microscope. In the example described here, the particle beam 7 is an electron beam, and the particle beam microscope 1 is an electron microscope. The particle beam source 5 comprises an electron emitter 9 and an anode 11, between which a voltage is applied, so that electrons emitted from the electron emitter 9 are accelerated toward the anode 11 and enter the beam tube 13 through the anode. Before being incident on the surface of the object 3, the particle beam 7 is Figure 1 The electric field between the lower end of the beam tube 13 and the object 3 or between possible further electrodes arranged between the lower end of the beam tube 13 and the object 3 can be used to decelerate the particles in the particle beam before the particle beam impinges on the surface of the object 3 and to set the kinetic energy of the particles when impinging on the object 3.

[0044] The particle beam 7 emitted divergently from the electron emitter 9 is collimated by the collimator 15 and focused on the surface of the object 3 by the objective lens 17, wherein the electrostatic field between the lower end of the beam tube 13 and the surface of the object 3 and the possible additional electrodes can also have a focusing effect on the particle beam 7. The particles in the particle beam 7 focused on the surface of the object 3 are incident on the surface of the object 3 in a convergent manner. Figure 1 In FIG. 7 , the convergence angle of the focused particle beam 7 is schematically indicated as angle α.

[0045] In the example described here, the collimator 15 and the objective lens 17 are magnetic lenses that provide a magnetic field that focuses the particle beam 7, and for this purpose both include an energized coil 19 or 21 and a yoke 23 or 25 with an extreme point 27 or 29. By setting the current flowing through the coil 19, the excitation of the condenser 15 can be set. Therefore, by setting the current flowing through the coil 21, the excitation of the objective lens 17 can be set. Here, while maintaining the particle beam 7 focused on the surface of the object 3, the ratio of the collimator 15 and the objective lens 17 to the focusing of the particle beam 7 can be changed. If the collimator 15 is excited to a lesser extent and the objective lens 17 is excited to a greater extent, the convergence angle α is greater than the case where the collimator 15 is excited to a greater extent and the objective lens 17 is correspondingly excited to a lesser extent. This means that changing the excitation of the collimator 15 and correspondingly adapting the excitation of the objective lens 17 so that the particle beam 7 remains focused on the surface of the object 3 allows the convergence angle α to be set within a specific range.

[0046] The particle beam microscope 1 further comprises a scanning deflector 31 which is configured to deflect the particle beam in order to displace the position of incidence of the particle beam 7 on the surface of the object 3. The excitation of the scanning deflector 31 can be set in order to set a deflection angle in two mutually independent directions by which the particle beam 7 is deflected when passing through the scanning deflector 31. A change in the deflection angle of the scanning deflector 31 causes a corresponding change in the position of incidence of the particle beam 7 on the surface of the object 3.

[0047] The particle beam microscope 1 further comprises an stigmator 33, which is configured to generate a quadrupole field having an astigmatic effect on the particle beam 7. For example, the stigmator 33 comprises eight coils or electrodes, which are arranged in a circumferential direction in a manner distributed around the particle beam so as to generate a quadrupole electric field or a quadrupole magnetic field. The excitation of the elements of the stigmator 33 can be set in order to set the intensity and orientation of the quadrupole field. The stigmator 33 serves to compensate for the adverse astigmatic effects of other particle optical components, such as the condenser 15 or the objective lens 17, with the result that the particle beam 7 focused on the surface of the object 3 can illuminate a small, essentially circular spot there.

[0048] The particle beam microscope 1 further comprises an adjustment deflector 35 which is arranged in the beam path of the particle beam 7 between the particle source 5 and the objective lens 17. The excitation of the adjustment deflector 35 can be set in order to deflect the particle beam 7 so that the position of the particle beam changes relative to the objective lens 17. The excitation of the adjustment deflector 35 is set in such a way that the particle beam 7 passes through the objective lens 17 as centrally as possible, i.e. along the main axis of the objective lens 17. In this case, a smaller and better focusing of the particle beam 7 on the surface of the object 3 can be obtained compared to a situation in which the particle beam 7 passes through the objective lens at a distance from the main axis of the objective lens.

[0049] The particle beam microscope 1 further comprises a detector 37 for detecting particles generated on the object 3 as a result of the incidence of particles from the particle beam 7. These particles are, for example, electrons, such as so-called backscattered electrons (these electrons are emitted from the object 3 with a kinetic energy equal to or slightly less than the kinetic energy of the electrons from the particle beam 7 incident on the object) or so-called secondary electrons (these electrons are emitted from the object 3 with a kinetic energy of about 50 eV or less).

[0050] In order to obtain a particle microscopy image of the object 3, the particle beam 7 is successively directed to a plurality of incident positions within the image region of the object 3 by actuating the scanning deflector 31, the detector 37 is used to detect the particles generated in the process, and a data record representing the detection electrons assigned to the excitations of the scanning deflector 31 and thus to the incident positions is generated. This data record represents the particle microscopy image of the object and can be displayed on a display, for example, by virtue of the number of particles assigned to the incident positions in the image being represented by brightness and the incident positions being represented by position.

[0051] The image region scanned during recording of the particle microscopy image has a significant extent on the surface of the object in two mutually independent directions (e.g. in the x-direction and the y-direction). For example, the aspect ratio of the image region (i.e. the ratio between the extent of the image region in the x-direction and the extent of the image region in the y-direction) is 1:1 or 2:1, etc.

[0052] The following is based on Figures 2 to 4 A method for setting the excitation of the stigmator 33 is described. In this case, Figure 2 A flow chart showing the method is shown, Figure 3 shows a schematic diagram of the object region used during this method, and Figure 4 A graphical representation of the data obtained using this method is shown.

[0053] exist Figure 2In an embodiment of the method, elongated object regions 41 and 43 on a surface 45 of an object 3 are scanned. In this case, the object region 41 has an elongated extent in an object direction specified by an arrow 46 (e.g., the x-direction), while the object region 43 has an elongated extent in an object direction depicted by an arrow 47. The two object directions are not parallel to each other. In particular, the smaller angle between the two object directions is greater than 10° and less than 80°, in particular greater than 20° and less than 70°, further in particular greater than 30° and less than 60°. The two object directions 46 and 47 are preferably oriented at an angle β of 45° relative to each other, other orientations being possible. In the object direction 46, the elongated object region 41 has a length l1, which is more than 10 times or more than 100 times the width b1 of the surface region 41 as measured orthogonally to the object direction 46. The elongated surface region 41 contains incident positions 49, to which the particle beam is directed successively during the scanning of the elongated surface region 41. In Figure 3 In the embodiment, the incident positions 49 are arranged in three rows adjacent to each other in the direction 46 and in a direction orthogonal thereto, in each case with approximately the same spacing. The incident positions 49 in the elongated surface area 41 can be scanned row by row or column by column in a zigzag manner or in a random sequence in any desired sequence.

[0054] In some embodiments, region 41 includes only incident positions located on a single straight line 48 extending in the object direction 46, with the result that the elongated region 41 also has an extent l1 in the object direction 46, while its width b1 in a direction orthogonal to the object direction 47 is infinitely small or reduced to the diameter of the beam focus at the incident position 49.

[0055] In a corresponding manner, the surface area 43 is elongated in the object direction 47 by virtue of a length l2 in the object direction 47 being a multiple (e.g. 10 or 100 times) of a width b2 in a direction orthogonal to the direction 47. Three rows of incident positions 49 oriented in the object direction 47 are also depicted in the elongated surface area 43. In some embodiments, there is only one row of incident positions 49, which are located on a straight line 44 extending in the object direction 47.

[0056] Figure 2 The method shown is used to optimize the settings of the stigmator 33. Once the method has started, the excitation of the objective 17 is set in a step 51 using conventional methods, so that the particle beam microscope 1 can already be used to record images, although the quality is still unsatisfactory because the optimal settings of the stigmator 35 have not yet been found. Figure 3 The enlarged image part I1 in FIG. 5 shows a beam spot 53 at an incident position 49 irradiated on the surface 45 of the object 3 if the focusing of the particle beam 7 has astigmatism disturbance. Obviously, the beam spot 53 has an elliptical shape stretched in the object direction 46. Figure 3The enlarged portion I2 in FIG. 1 shows the beam spot 54 without astigmatism distortion; it has the form of a small circle.

[0057] In the upper part, Figure 4 It is shown that, assuming that a checkerboard pattern has been applied to the object 3 and the beam spot 54 has Figure 3 In the optimized form shown in the enlarged portion I2 in FIG. 4 , the graph of the intensity I detected by the detector 37 as a function of the position when the line 48 is scanned in the object direction 46 is specified by the line 57. Scanning this structure in the object direction 46 results in the alternating detection of increased and decreased intensities, wherein the transitions between these intensities have sharp edges and are steep. Figure 4 The lower graph in FIG. 5 is a representation corresponding to the upper graph and shows the detected intensity I when scanning in the object direction 46 by line 59, wherein the beam spot has Figure 3 The form of the astigmatic elliptical distortion shown in the image portion I1 in the middle. Due to the large range of the beam spot 53 in the object direction 46, when scanning the chessboard-like structure, the intensity changes do not have such clear edges and are not as sharp as Figure 4 If the particle beam 7 producing the beam spot 53 shown in the image portion I1 is scanned in the object direction 47, the curve representing the detected intensity will tend to have the shape of the sharp and steep edge of the curve 57 rather than the shape of the curve 59, because the range of the beam spot 53 in the object direction 47 is significantly smaller than the range in the object direction 46.

[0058] It is therefore clear that the shape of the curves 57, 59 allows conclusions to be drawn as to whether the focus of the particle beam has an astigmatic distortion and as to the direction of said distortion when the structure is scanned in the object directions 46 and 47. From this, it is possible to determine the excitations or changes in the excitation of the elements in the stigmator 33 which reduce the astigmatic distortion of the particle beam at the surface 45 of the object 3.

[0059] The smaller the range of the beam spots 53, 54 in the object directions 46, 47 extending in the scanning areas 41, 43, the more clearly the structures of the object are discernible in the detected intensity. Conversely, as the range of the beam spots 53, 54 increases in the scanning object directions 46, 47, the structures in the detected intensity are less clear, more rounded or more blurred. There are conventional methods in the field of image processing that allow values ​​to be derived from curves (such as curves 57 and 59), which represent a measure of image clarity and are suitable for forming the basis of an optimization method for setting the stigmator 33. For example, the curves 57, 59 can be Fourier transformed to obtain a spectrum, and the value of the highest frequency present in the spectrum can be used as a value representing image clarity. Obviously, this value of curve 57 will be higher than this value of curve 59.

[0060] exist Figure 2 In the method, the first setting in step 51 is followed by step 61, in which the particle beam 7 is scanned along a line 48 oriented in the object direction 46 by actuating the scanning deflector 31; the detector 37 is used to detect the corresponding particles generated during the scanning, and a first data record 63 representing the detected particles assigned to the corresponding incidence position is generated. This data record can be depicted graphically, for example as Figure 4 57 and 59 in FIG. 6 are identical. In step 65, the data record 63 is evaluated in order to determine an image sharpness value 67. For example, the image sharpness value 67 may be the above-mentioned highest frequency in the spectrum of the depicted line. Subsequently, steps 61, 65 and 69 are performed for the second orientation by scanning the particle beam 7 along the straight line 44 in the object direction 47 in step 71, detecting the intensity and generating a data record 73, which is evaluated in step 75 in order to further determine a corresponding image sharpness 77. Next, in step 79, based on the determined image sharpness value 67 for the first orientation and the image sharpness value 77 for the second orientation, the excitation of the elements in the stigmator 31 is changed, precisely with the aim of improving the image sharpness. Thus, if the two image sharpness values ​​66 and 67 are identical but can still be improved by changing the focus of the objective lens 17, the excitation of the objective lens 17 may also be slightly modified in step 81 based on the image sharpness values ​​67 and 77.

[0061] Once a satisfactory setting has been found, i.e. the image sharpness values ​​67 and 77 have reached the desired magnitude, the stigmator 33 of the particle beam microscope 1 is set to a sufficient degree and the desired particle microscopy image can be recorded in step 83. If a satisfactory setting has not yet been found, the method can continue with step 61 after step 81 so that steps 61 to 81 are repeated.

[0062] The changes in the excitation of the stigmator 33 in steps 69 and 79 and the change in the excitation of the objective lens 17 in step 81 are both carried out with the aim of improving the image sharpness. As is conventional for optimization methods, the results in this context may temporarily deteriorate when scanning the parameter space and, for example, the method is led into a local minimum.

[0063] The following is based on Figure 5 and Figure 6 A method for setting and adjusting the deflector 35 is described. In this case, Figure 5 A flow chart of the method is shown, and Figure 6 A graphical representation of the data obtained during the method is shown.

[0064] Figure 5The method shown is for setting and adjusting the deflector 35 so that the particle beam 7 passes through the objective lens 17 substantially centrally. To this end, in step 85, the focus is initially set to such an extent that, for example, a particle microscopic image can be recorded, but still with suboptimal quality. Further, for example, the object direction 46 is initially selected as a first orientation. Then, in step 87, the particle beam 7 is set to a position similar to that of the first orientation. Figure 2 Scan line 48 in the manner of step 61 in step 61; detect particles and generate a first data record 89 representing the detected particles assigned to the corresponding incident position. This data record 89 can be represented graphically, for example according to Figure 4 To express. Figure 6 The upper part of shows an exemplary representation of data record 89 via line 91 .

[0065] Subsequently, the focus is slightly changed in step 93. This can be achieved, for example, by changing the excitation of the objective lens 17 by changing the current flowing through the coil 21 or by changing the kinetic energy of the particles in the particle beam 7 passing through the objective lens 17 by changing the voltage between the electron emitter 9 and the anode 11.

[0066] After the focus is changed in step 93, the particle beam 7 is rescanned along the line 48 in step 95 by means of the excitation using the same scanning deflector as in step 87, in order to direct the particle beam 7 to a separate incident position. Therefore, in steps 87 and 95, the particle beam 7 is also deflected by the same angle and in the same direction. Further, in step 95, the particles generated for different deflection directions or incident positions are detected and a second data record 97 is generated thereby. An example of data record 97 is shown by Figure 6 91 and 99. Line 99 in the lower part of the curve is depicted. It is obvious from the comparison between lines 91 and 99 that lines 91 and 99 have an offset d relative to each other. This offset d can be traced back to the following fact: particle beam 7 does not pass through the object lens 17 in the center, and therefore particle beam is not only focused by the object lens 17, but also slightly deflected by this object lens. By changing the focusing in step 93, the size of this deflection is modified, thereby causing the offset d between two curves 91 and 99. On the contrary, the offset d determined from the comparison of two data records 89 and 97 can be used to modify the excitation of the adjustment deflector 35, and the purpose is to reduce this offset d.

[0067] Therefore, data record 89 and data record 97 are compared with one another in step 99 in order to determine a shift 101 which corresponds to the offset d.

[0068] In step 103, the excitation of the adjustment deflector 35 is changed based on the displacement 101, more precisely the deflection direction of the adjustment deflector 35 is changed, which deflection direction corresponds to the object direction oriented by the line scanned in steps 87 and 95. The purpose of this change of the excitation of the adjustment deflector 35 is to reduce the displacement 101.

[0069] Next, in step 105, the orientation used in steps 87 to 103 is changed, i.e., if the orientation used in steps 87 to 103 is a first orientation in object direction 46, the orientation is changed to a second orientation oriented in an object direction preferably orthogonal to object direction 46, other object directions being possible. Conversely, if the orientation used in the step is a second orientation, the orientation is changed to the first orientation. Here, based on Figure 6 In the described method, two non-parallel object directions are used. In particular, the smaller angle between the two object directions may be greater than 60°, in particular greater than 70°, in particular greater than 80°. Preferably, Figure 3 The two object directions 46 and 47 depicted in are oriented orthogonally to one another here.

[0070] Next, the method continues to step 87, and steps 87 to 103 are performed with the respective other orientation in order to also improve the excitation of the adjustment deflector 35 for the respective other orientation. If after step 105 it turns out that the displacement 101 determined for the two different orientations is sufficiently small, the optimization of the adjustment deflector 35 is complete and the desired particle microscopy image can be recorded with high quality in step 107. Otherwise, the method continues again in step 87.

[0071] The following is based on Figure 7 and Figure 8 A method for setting the convergence angle α is described. In this case, Figure 7 A flow chart of the method is shown, and Figure 8 A graphical representation of the data obtained during the method is shown.

[0072] This method can be used advantageously if the object to be imaged with particle microscopy comprises structures having a significant extent in the direction of the particle beam. An example of such an object is object 3', which has a Figure 1 3 and includes a planar main surface 45' which is inclined relative to the main surface 45 of the object 3 which is depicted with a solid line. In particular, the main surface 45' has a surface normal 111 which makes an angle α of, for example, 20° with the direction of the particle beam 7. Obviously, the Figure 1 The incident position on the surface 45' of the object 3' in the left image field in the illustration is arranged significantly closer to the objective lens 17 than the incident position in the right image field. Therefore, it is desired that the generated particle microscopic image has a sufficient depth of field so that the entire imaging area of ​​the image field presents sufficient image clarity in the generated image.

[0073] exist Figure 7In the method, the object is tilted accordingly as required in an initial step 113, so that the angle γ between the surface normal 111 of the main surface 45' and the direction of the particle beam 7 when incident on the object 3' is greater than, for example, 10°. In step 115, the focus of the particle beam microscope 1 is set so that an image of the object 3' can be produced, but the setting of the particle beam microscope 1 is still suboptimal with respect to image sharpness and depth of field.

[0074] Subsequently, in step 117 , the orientation of the subsequent line scan is determined as follows: On the main surface 45 ′ there is a straight line which extends through the position of incidence of the particle beam 7 on the main surface 45 ′ and is oriented orthogonally to the direction of the particle beam 7 . Figure 1 In the illustration of , this straight line extends orthogonally to the drawing plane. The direction determined in step 117 is oriented crosswise to the direction of this straight line. In particular, this direction can be oriented orthogonally to this straight line.

[0075] In step 119 , a line 48 oriented in a determined direction is scanned; particles occurring during the scanning of this line 48 are detected, and a data record 121 representing the detected particles assigned to the respective impact position is generated.

[0076] An exemplary graphical representation of data record 121 is provided by Figure 8 Here, it is assumed that the checkerboard pattern is scanned again, which results in a dependence of the detected particle intensity I on the position x, which is similar to Figure 3 and Figure 6 Due to the significant distance of the object 3' in the direction of the particle beam 7 and the limited depth of field, the image sharpness is not the same along the entire length of the line 48. On the contrary, Figure 8 The example shown has a central region 123 where image sharpness is higher (as evident from the relatively sharp edges of curve 122 in this region), and a left region 125 and a right region 127 where image sharpness is lower, as shown by the rounded curve 122 .

[0077] In step 129, values ​​of the image sharpness are determined for a plurality of regions along this line. For example, corresponding image sharpness values ​​are determined for three different regions along line 48, resulting in, for example, three values ​​131 representing the image sharpness being determined. In step 133, the actuation of the condenser and the objective is varied, more precisely with the aim of increasing the value of the image sharpness 131. This can be implemented, for example, by optimizing the sum of the values ​​representing the image sharpness of the individual regions.

[0078] Subsequently, steps 119 , 129 and 133 may be repeatedly performed until sufficient image clarity is obtained for all regions along line 48 , whereby the desired particle microscopic image may be recorded with high quality in step 135 .

Claims

1. A method for operating a particle beam microscope, wherein: The particle beam microscope includes: a particle beam source configured to generate a particle beam; an objective lens configured to focus the particle beam onto an object; a stigmator configured to affect the particle beam astigmatically; a scanning deflector configured to deflect the particle beam so as to shift an incident position of the particle beam on the object; and a detector configured to detect particles generated by the particle beam at the object; Among them, for a given object direction, the method includes the following measures: directing the particle beam in a plurality of directions successively by actuating the scanning deflector so that the particle beam is incident successively on the object at a plurality of incidence positions within an elongated region of the object oriented in the given object direction, detecting particles using the detector, and generating data records representing the detected particles assigned to the respective directions; evaluating the data record and determining at least one value representing a measure of image sharpness; and varying the excitation of the stigmator based on the at least one value in order to improve the image sharpness; and wherein the region of the object that is elongated in the given object direction has an extent in the given object direction that is at least ten times greater than an extent in a direction oriented orthogonally to the given object direction; Wherein, the method further comprises: performing the measures for a first given object direction; and These measures are performed for a second given object direction oriented crosswise to the first given object direction.

2. The method according to claim 1, in, The stigmator is configured to generate, as a result of its excitation, a quadrupole field with adjustable intensity and orientation, Therein, the smaller angle (β) between the first given object direction and the second given object direction is between 10° and 80°, in particular between 20° and 70°, in particular between 30° and 60°.

3. The method according to claim 1 or 2, Further comprising repeatedly performing the measures for the first given object direction and performing the measures for the second given object direction.

4. The method according to any one of claims 1 to 3, Further comprising changing the excitation of the objective lens based on the at least one value determined when performing the measures for the first given object direction and / or when performing the measures for the second given object direction, with the aim of improving the at least one measure of the image sharpness.

5. A method for operating a particle beam microscope, wherein: The particle beam microscope includes: a particle beam source configured to generate a particle beam; an objective lens configured to focus the particle beam onto an object; a scanning deflector configured to deflect the particle beam so as to shift an incident position of the particle beam on the object; an adjustment deflector configured to deflect the particle beam so as to change a position of the particle beam relative to the objective lens; a detector configured to detect particles generated by the particle beam at the object; Among them, for a given object direction, the method includes the following measures: by actuating the scanning deflector to direct the particle beam successively in a plurality of directions so that the particle beam successively impinges on the object at a plurality of incident positions within an elongated region of the object oriented in the given object direction, detecting particles using the detector and generating a first data record representing the detected particles assigned to the respective directions; then changing the focus of the particle beam on the object; and then directing the particle beam in a plurality of directions successively by actuating the scanning deflector so that the particle beam is incident successively on the object at a plurality of incidence positions within an elongated region of the object oriented in the given object direction, detecting particles using the detector, and generating a second data record representing the detected particles assigned to the respective directions; evaluating the first data record and the second data record and determining at least one value representing a measure of a shift; and varying the activation of the adjustment deflector based on the value representing the displacement in order to reduce the displacement; and wherein the region of the object that is elongated in the given object direction has an extent in the given object direction that is at least ten times greater than an extent in a direction oriented orthogonally to the given object direction; Wherein, the method further comprises: performing the measures for a first given object direction; and These measures are performed for a second given object direction oriented crosswise to the first given direction.

6. The method according to claim 5, in, The change of the focus comprises changing the kinetic energy of particles of the particle beam passing through the objective lens and / or changing the excitation of the objective lens.

7. The method according to any one of claims 1 to 6, in, The smaller angle (β) between the first given object direction and the second given object direction is larger than 60°, in particular larger than 70°, in particular larger than 80°.

8. A method for operating a particle beam microscope, wherein: The particle beam microscope includes: a particle beam source configured to generate a particle beam; an objective lens configured to focus the particle beam onto an object; a condenser, which is arranged on a beam path of the particle beam between the particle beam source and the objective lens and is configured to collimate the particle beam; a scanning deflector configured to deflect the particle beam so as to shift an incident position of the particle beam on the object; and a detector configured to detect particles generated by the particle beam at the object; Wherein, the method further comprises: Arranging the object so that a surface normal of a major surface of the object makes an angle (γ) greater than 10° and less than 80° with the direction of the particle beam incident on the surface; determining an object direction in a plane of a major surface of the object so that the object direction is cross-oriented with a direction in the plane of the major surface of the object oriented orthogonally to a direction of a particle beam incident on the object; directing the particle beam in a plurality of directions successively by actuating the scanning deflector so that the particle beam is incident successively on the object at a plurality of incidence locations within a region of the object oriented in the given object direction, detecting particles using the detector, and generating data records representing the detected particles assigned to the respective directions; evaluating the data record and determining at least one value representing a measure of image sharpness; and varying the excitation of the concentrator based on the at least one value in order to improve the image sharpness; Therein, the region of the object which is elongated in the given object direction has an extent in the given object direction which is at least ten times greater than its extent in a direction oriented orthogonally to the given object direction.

9. The method according to claim 8, Further comprising repeating multiple times directing the particle beam to the multiple incident positions, detecting particles, generating the data record, evaluating the data record and determining the at least one value representing a measure of the image sharpness, and changing the excitation of the concentrator based on the at least one value, in order to improve the image sharpness.

10. The method according to claim 8 or 9, Further comprising changing the excitation of the objective lens based on the at least one value in order to improve the image sharpness.

11. The method according to any one of claims 1 to 10, in, The plurality of incident positions within the region of the object are located on a straight line.

12. The method according to any one of claims 1 to 11, in, After the change of the stimulus, the method comprises: directing the particle beam to a plurality of incidence positions within an image region of the object by actuating the scanning deflector, detecting particles using the detector and generating a first data record representing the detected particles assigned to the respective incidence positions; wherein the image area has a first range in a first direction and a second range in a second direction orthogonal to the first direction, and Wherein, a ratio between the first range and the second range is greater than 0.5 and less than 2.

0.

13. A computer program product comprising instructions which, when loaded onto a control computer of a particle beam microscope, cause the control computer to operate the particle beam microscope according to the method according to any one of claims 1 to 12.

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