Method for operating a particle beam system, particle beam system and computer program product

Abstract

A method for operating a particle beam system, the method comprising: repeating a sequence to guide a particle beam (7) over a surface (27) of an object (3), the object (3) having a region (25) on its surface (27) bounded by a virtual closed boundary line (29), the sequence comprising: guiding the particle beam (7) from an entry point (31-1 to 31-5) of the current sequence to an exit point (33-1 to 33-5) of the current sequence along a scan path (35-1 to 35-5), wherein the entry point (31-1 to 31-5) of the current sequence and the exit point (33-1 to 33-5) of the current sequence are on the boundary line (29) and wherein the scan path (35-1 to 35-5) is entirely within the region (25), and guiding the particle beam (7) from the exit point (33-1 to 33-5) of the current sequence to an entry point (31-2, 31-3, 31-4, 31-5, 31-1) of the next sequence along a return path (37-1 to 37-5),wherein the entry point (31-2, 31-3, 31-4, 31-5, 31-1) of the next sequence lies on the boundary line (29) and wherein the return path (37-1 to 37-5) lies completely outside the area (25).

Description

The present invention relates to a method for operating a particle beam system, in particular a particle beam microscope, as well as a particle beam system or a particle beam microscope configured to perform the method, and a computer program product. In conventional particle beam systems, the particle beam generated by the system is guided line by line across an area of ​​an object to be analyzed and / or processed. When the particle beam reaches the end of such a line, it must be recirculated, i.e., guided to the beginning of a new line. Typically, the particle beam is guided across the area during recirculation. If the particle beam collides with the object during recirculation from the end of one line to the beginning of the next, this can have negative effects on the object. For example, charge could be deposited or generated in the object, which could negatively affect the accuracy of the beam guidance in the next line. Furthermore, contamination or structural damage to the object could occur. To prevent these negative effects, so-called particle beam blankers can be used, which interrupt the particle beam so that it does not strike the object during recirculation. However, such particle beam blankers involve considerable control effort and are also associated with significant costs. DE 11 2008 000 170 T5 discloses such a particle beam system with particle beam blanker in the form of a scanning electron microscope with beam blanking unit. It is therefore the object of the present invention to provide a particle beam system, in particular a particle beam microscope, and a method for operating the particle beam system, which can avoid or at least reduce the above-mentioned negative effects generated when the particle beam is recirculated, using simple and cost-effective means. One aspect of the present invention relates to a method for operating a particle beam microscope, wherein the method comprises: repeating a sequence to guide a particle beam over a surface of an object which has a region on its surface bounded by a virtual closed boundary line, wherein the sequence comprises: guiding the particle beam from an entry point of the current sequence to an exit point of the current sequence along a scan path, wherein the entry point of the current sequence and the exit point of the current sequence are on the boundary line and wherein the scan path lies entirely within the region, and guiding the particle beam from the exit point of the current sequence to an entry point of the next sequence along a return path, wherein the entry point of the next sequence lies on the boundary line and wherein the return path lies entirely outside the region. According to this method, the particle beam generated by the particle beam microscope is guided across the surface of the object, meaning that the particle beam continuously, i.e., uninterruptedly, strikes the surface of the object during this process. Specifically, the particle beam is not interrupted by a particle beam blanker during this process. The particle beam can be composed of ions or electrons. Secondary particles are produced through the interaction of the particle beam with the object. These secondary particles can be, for example, secondary electrons, backscattered electrons, secondary ions, or backscattered ions. The term "secondary particle" can also refer to the particles of secondary radiation produced by the interaction of the particle beam with the object. Secondary radiation can include, for example, X-rays or cathodoluminescence. The area bounded by the closed boundary line is a region of the object that is to be analyzed and / or processed. For this purpose, the particle beam is directed onto this region. For example, an image of this region is to be taken. Alternatively, or furthermore, the object is to be processed by depositing material onto or removing it. The boundary line is a closed line that encloses the area. The boundary line is virtual, meaning that it is not a structural feature (of the surface) of the object. For example, if the area has a rectangular shape, the boundary line can have the shape of the edge of a rectangular shape. The procedure involves repeating a sequence. Each sequence comprises a first section and a second section. In the first section of each sequence, the particle beam is guided from the entry point of this sequence to the exit point of this sequence along a path that lies entirely within the region and is called the scan path. This means that the scan paths can also (partially) lie on the boundary line. In the second section of each sequence, which follows the first section, the particle beam is guided from the exit point of this sequence to the entry point of the next sequence, a process known as recirculation. To avoid negative effects on the region bounded by the closed boundary line, the particle beam is recirculated along a path that lies entirely outside the region and is called the recirculation path. Each sequence has exactly one entry point and exactly one exit point. The entry and exit points of all sequences lie on the boundary line and are generally different locations on the object's surface. The entry point is a location on the boundary line toward which the particle beam is directed at the beginning of a sequence. This sequence ends when the particle beam has been guided to the entry point of the next sequence. The secondary particles generated during the scanning process can be used to produce data that forms the basis for analyzing and / or processing the area. For example, the data represents an image of the area. The scan path, for example, is a "row", i.e., an essentially straight line. In contrast, the return path is usually not a straight line, since every return path at least partially circumvents the closed area. The sequence is repeated over time to gradually guide the particle beam, i.e., scan path by scan path, over the entire area to be analyzed and / or processed. According to one embodiment, the particle beam continuously strikes the object's surface for the duration of each sequence. Accordingly, the particle beam strikes the object's surface both while guiding it along the scan paths and while guiding it along the return paths. Therefore, the particle beam system does not require a particle beam blanker. According to a further embodiment, each of the sequence return paths has a return path segment that is included in all return paths. The length of the return path segment is, for example, at least 30% or at least 50% of the length of the shortest return path or at least 30% or at least 50% of the length of the shortest scan path of the sequences. In this embodiment, the particle beam is guided along the recirculation path segment in each sequence. This ensures that the particle beam strikes the object's surface as little as possible during recirculation. Thus, the negative effects caused by recirculation are limited to a small portion of the object's surface, which lies entirely outside the affected area. According to another embodiment, the area bounded by the closed boundary line is rectangular. However, the area can also have a different shape. Furthermore, the area can have a surface area of ​​at least 100 nm² or at least 1 µm². Accordingly, the area comprises a significantly large surface area of ​​the object. According to a further embodiment, the entry and exit points associated with a sequence (i.e., an entry point and an exit point of the same sequence) are separated by a distance of at least 50 nm, in particular at least 100 nm, and further, in particular, at least 200 nm. This effectively defines a minimum length for each scan path, which is at least 50 nm, in particular at least 100 nm, and further, in particular, at least 200 nm. According to a further embodiment, the distance between entry points that lie directly next to each other on the boundary line is at most 200 nm, in particular at most 100 nm, and further, in particular at most 10 nm. The smaller the distance between the entry points lying directly next to each other on the boundary line, the better the area can be analyzed and / or processed. According to a further embodiment, the distance between exit points that lie directly next to each other on the boundary line is at most 200 nm, in particular at most 100 nm, and further, in particular at most 10 nm. The smaller the distance between the exit points lying directly next to each other on the boundary line, the better the area can be analyzed and / or processed. According to another embodiment, the boundary line has a first uninterrupted section containing the entry points and a second uninterrupted section containing the exit points, the first and second uninterrupted sections not overlapping. Accordingly, the entry and exit points are collectively spaced apart. For example, the region is rectangular, and the boundary line therefore has two long sides and two short sides. For example, the first uninterrupted section is formed by one of the two long sides, and the second uninterrupted section is formed by the other of the two long sides. Accordingly, the first and second sections do not overlap. This corresponds, for example, to line-by-line beaming, where each line begins on the same side of the region. According to another exemplary embodiment, the scan paths are essentially straight lines. "Essentially straight" is a line that the particle beam system intends to execute as a straight line, but which, due to the finite precision of the particle beam system and external influences, is not executed as a perfectly straight line. The scan paths of each sequence can have the same shape, i.e., be essentially straight lines. However, the scan paths can also have a different shape. According to another embodiment, the mean length of the scan paths is smaller than the mean length of the feedback paths. According to an alternative embodiment, the mean length of the scan paths is larger than the mean length of the feedback paths. The mean value is, for example, the arithmetic mean or the median. According to a further embodiment, the method further comprises: defining the area; generating control signals for a deflector system of the particle beam system based on the defined area; whereby the guiding of the particle beam through the deflector system is effected. In practice, the area and its boundary line are defined by a user of the particle beam system. Defining the area specifies a section of the object's surface to be analyzed and / or processed by the particle beam system. Based on this defined area, the particle beam system's controller can generate control signals that operate the deflector system. The deflector system, in turn, deflects the particle beam according to these control signals, thus guiding the beam across the object's surface. According to a further embodiment, the method further comprises: detecting secondary particles generated by the interaction of the particle beam with the object; generating a detection signal representing the quantity and / or energy of the detected secondary particles as a function of time; and, in particular, generating data representing an image of the area based on the detection signal. The detection of the secondary particles and / or the generation of the detection signal can be performed for the duration of each sequence. In particular, only a portion of the detection signal is processed, namely that which is caused by secondary particles generated while the particle beam was striking the area bounded by the closed boundary line. In this embodiment, a detector of the particle beam system is configured to detect the secondary particles generated by the interaction of the particle beam with the object. The particles are detected for the duration of each sequence, i.e., continuously from the beginning to the end of the sequence. The detection signal is also generated for the duration of each sequence, i.e., continuously from the beginning to the end of the sequence. Accordingly, the detection signal is a continuous data stream representing the quantity and / or energy of the detected secondary particles as a function of time. Based on the detection signal, data can be generated that forms the basis for analysis and / or processing of the area. For example, the data represents an image of the area.To generate the data, the sections of the detection signal caused by secondary particles produced while the particle beam was moving along a scan path (rather than a return path) must be extracted. This can be done by the particle beam system's control unit. According to another embodiment, the particle beam, when guided along the scan paths, pauses at a multitude of dwell positions for a predetermined duration. This corresponds to a "scanning" of the area. Here, the particle beam is directed sequentially to a limited number of discrete positions on a scan path (dwell positions) and remains there for the predetermined duration. According to another embodiment, the particle beam is moved continuously as it is guided along the scan paths. In particular, the particle beam can be guided along the scan paths at a substantially constant speed. This principle is the counterpart to "scanning," since the particle beam is moved continuously at a substantially constant speed and does not remain in the same position for a predetermined dwell time. According to another embodiment, guiding the particle beam from the exit point of the current sequence to the entry point of the next sequence before reaching the entry point of the next sequence includes a waiting step, wherein the particle beam remains at substantially the same position for the duration of the waiting step. The electronic components used to guide the particle beam in a particle beam microscope can cause a damped oscillation at the point where the particle beam strikes the object. To ensure that this damped oscillation is sufficiently damped before the particle beam is guided along a scan path, the beam remains at essentially the same position during the return path for the duration of the waiting step. The point of impact varies primarily due to the damped oscillation. This position is typically located near the entry point of the next sequence. Embodiments of the invention are explained below with reference to the figures. Fig. 1 shows an exemplary particle beam system; Fig. 2 shows the guiding of a particle beam on the surface of an object; Fig. 3 shows a method for operating a particle beam system; Fig. 4 shows details of the spatial relationships when guiding a particle beam over the surface of an object; Fig. 5 shows another exemplary particle beam system, namely a scanning electron microscope; and Fig. 6 shows another exemplary particle beam system, namely a scanning electron microscope combined with an ion beam column. Fig. 1 shows an exemplary particle beam system 1, which is suitable for carrying out the procedures described herein, in particular for the analysis and / or processing of an object 3. The particle beam system 1 can, for example, be a particle beam microscope. The particle beam system 1 comprises a particle beam column 2. The particle beam column 2 includes a particle source 5, which is configured to generate a particle beam 7. The particle beam 7 is formed, for example, from electrons or ions. The particle beam column 2 further comprises a suppression electrode 9, which can be supplied with an electric potential such that only particles produced by the particle source 5 whose kinetic energy is sufficiently large can pass through an opening 11 in the suppression electrode 9. The particle beam column 2 further comprises an accelerating electrode 13, which is supplied with an electric potential in order to accelerate the particles passing through the opening 11 of the suppression electrode 9 to a predetermined kinetic energy. The particle beam column 2 further comprises a particle-optical lens 15, which is suitable for focusing the particle beam 7. The particle beam column 2 further comprises a deflector system 17, which is suitable for deflecting the particle beam 7 so that the particle beam 7 can be directed to different locations on the surface of the object 3. The deflector system 17 can be suitable for deflecting the particle beam 7 along two mutually perpendicular directions, each of which is in turn perpendicular to a principal axis 19 of the particle-optical lens 15. The particle beam system 1 further comprises a controller 21, which is suitable for controlling the particle beam column 2. The controller 21 is configured to control the particle source 5, the electric potential applied to the suppression electrode 9, the electric potential applied to the accelerating electrode 13, the deflector system 17, and the particle-optical lens 15. The particle beam system 1 further comprises a detector 23, which is suitable for detecting secondary particles 24 generated by the interaction of the particle beam 7 with the object 3. The detector 23 can be arranged outside or inside the particle beam column 2. Detector 23 is capable of outputting a detection signal representing the quantity and / or energy of the detected secondary particles as a function of time. The controller 21 can receive and process the detection signal from detector 23. With reference to Figures 2 and 3, an exemplary method for operating the particle beam system 1 is described below. Figure 2 shows how the particle beam 7 is guided on the surface 27 of the object 3. Figure 3 shows a flowchart of an exemplary method for operating the particle beam system 1. The aim of the method is to analyze and / or process a region 25 on the surface 27 of the object 3. The region 25 is bounded by a closed boundary line 29, which is shown as a dashed line in Figure 2. The procedure is based on a sequence that is repeated over time. In the example shown in Fig. 2, the procedure comprises five sequences, meaning the sequence is performed five times. This small number of sequences serves only to simplify the explanation of the procedure. In practice, the sequence is performed more frequently. The sequence comprises guiding the particle beam 7 from an entry point of the current sequence 31-1 to 31-5 to an exit point of the current sequence 33-1 to 33-5 along a scan path 35-1 to 35-5, wherein the entry point and the exit point are located on the boundary line 29 and wherein the scan path lies entirely within the region 25. The sequence further comprises guiding the particle beam 7 from the exit point of the current sequence 33-1 to 33-5 to an entry point of the next sequence 31-2 to 31-5, 31-1 along a return path 37-1 to 37-5, wherein the entry point of the next sequence lies on the boundary line 29 and wherein the return path lies completely outside the region 25. The first execution of the sequence, i.e., the first sequence, is assigned entry point 31-1 and exit point 33-1. The second execution of the sequence, i.e., the second sequence, is assigned entry point 31-2 and exit point 33-2. The third execution of the sequence, i.e., the third sequence, is assigned entry point 31-3 and exit point 33-3. The fourth execution of the sequence, i.e., the fourth sequence, is assigned entry point 31-4 and exit point 33-4. The fifth execution of the sequence, i.e., the fifth sequence, is assigned entry point 31-5 and exit point 33-5. Scan path 35-1 of the first sequence runs from entry point 31-1 of the first sequence to exit point 33-1 of the first sequence. Scan path 35-2 of the second sequence runs from entry point 31-2 of the second sequence to exit point 33-2 of the second sequence. Scan path 35-3 of the third sequence runs from entry point 31-3 of the third sequence to exit point 33-3 of the third sequence. Scan path 35-4 of the fourth sequence runs from entry point 31-4 of the fourth sequence to exit point 33-4 of the fourth sequence. Scan path 35-5 of the fifth sequence runs from entry point 31-5 of the fifth sequence to exit point 33-5 of the fifth sequence. The return path 37-1 of the first sequence runs from exit point 33-1 of the first sequence to entry point 31-2 of the second sequence. The return path 37-2 of the second sequence runs from exit point 33-2 of the second sequence to entry point 31-3 of the third sequence. The return path 37-3 of the third sequence runs from exit point 33-3 of the third sequence to entry point 31-4 of the fourth sequence. The return path 37-4 of the fourth sequence runs from exit point 33-4 of the fourth sequence to entry point 31-5 of the fifth sequence. The return path 37-5 of the fifth sequence runs from exit point 33-5 of the fifth sequence to entry point 31-1 of the first sequence. The first sequence begins by directing the particle beam 7 towards the entry point 31-1 of the first sequence. From entry point 31-1 of the first sequence, the particle beam 7 is guided along the scan path 35-1 of the first sequence to the exit point 33-1 of the first sequence, the first scan path lying entirely within the region 25 bounded by the boundary line 29. From exit point 33-1 of the first sequence, the particle beam 7 is guided to the entry point of the next sequence, i.e., entry point 31-2 of the second sequence, following the return path 37-1 of the first sequence, which lies entirely outside the region 25. The first sequence ends when the particle beam 7 reaches the entry point of the next sequence, i.e., entry point 31-2 of the second sequence. The second, third, and fourth sequences are performed analogously. The fifth sequence begins by directing the particle beam 7 towards the entry point 31-5 of the fifth sequence. From the entry point 31-5 of the fifth sequence, the particle beam 7 is guided along the scan path 35-5 of the fifth sequence to the exit point 33-5 of the fifth sequence, the fifth scan path lying entirely within the region 25 bounded by the boundary line 29. Starting from exit point 33-5 of the fifth sequence, the particle beam 7 is guided to the entry point of the next sequence, i.e., entry point 31-1 of the first sequence, with the particle beam 7 being guided along the return path 37-5 of the fifth sequence, which lies entirely outside the area 25. The fifth sequence ends when the particle beam 7 reaches the entry point of the next sequence, i.e., entry point 31-1 of the first sequence. Since the example of the method shown in Fig. 2 comprises only five executions of the sequence, the method ends after the fifth sequence. Alternatively, the method can be repeated, since the particle beam is already directed again to entry point 31-1 of the first sequence. In the example shown in Fig. 2, area 25 is scanned line by line, with no further scan paths between the scan paths of immediately consecutive sequences. This scan strategy serves only to illustrate the method, and numerous other scan strategies can be applied. Another scan strategy, for example, is the inter-line method, in which one or more scan paths lie between the scan paths of immediately consecutive sequences. Fig. 3 shows a flowchart for the procedure described in connection with Fig. 2, where the procedure has been generalized to N executions of the sequence, and N is a natural number. The generalized procedure begins in step S1 with the first execution of a sequence, i.e., the execution of the first sequence. In Fig. 3, the sequence counter “i” is used to indicate the i-th sequence, or the i-th execution of the sequence. In step S2, the particle beam 7 is guided from the i-th entry point (31-i) along the i-th scan path (35-i) to the i-th exit point (33-i), with the i-th scan path (35-i) lying completely within the region 25. In step S3, which follows step S2, the particle beam 7 is guided from the i-th exit point (33-i) along the i-th return path (37-i) to the (i+1)-th entry point (31-(i+1)), with the i-th return path (37-i) lying entirely outside region 25. This concludes the i-th sequence. If i equals N in step S3, the particle beam 7 is guided from the N-th exit point (33-N) along the N-th return path (37-N) to the first entry point (31-1). In step S4, which follows step S3, the sequence counter “i” is incremented by 1. In step S5, which follows step S4, it is determined whether all of the N sequences to be performed have been carried out. If all of the N sequences to be performed have been carried out (No), the procedure ends in step S6. Alternatively, the procedure can be repeated from the beginning, i.e., continued from step S1. If not all N sequences have yet been carried out (Yes), the procedure continues from step S2. In step S5, a different termination condition than the one described here as an example can be used. The methods described with reference to Figures 2 and 3 ensure that the particle beam 7 is systematically guided over the area 25. By detecting the secondary particles generated by the interaction of the particle beam 7 with the object 3, the area 25 can be analyzed and / or processed. Because the particle beam is guided along the return paths 37-1 to 37-5 and 37-i, which lie completely outside the area 25, to the beginning of the next scan path, it is prevented that the particle beam 7 strikes the area 25 during the return process, thus avoiding any negative effects. Therefore, it is not necessary to provide a particle beam blanker in the particle beam system 1 to prevent the particle beam from striking the object during the return process.This avoids the costs for the particle beam blanker, as its functionality is achieved through the methods described above. As shown in Fig. 2, each of the recirculation paths 37-1 to 37-5 can have a recirculation path section 39, which is included in all recirculation paths 37-1 to 37-5. In the example shown in Fig. 2, the recirculation path section 39 begins at position 41 and ends at position 43. In this way, the particle beam 7 is directed onto only a few parts of the object 3 during recirculation, thereby reducing negative effects. During the execution of the procedures described with reference to Figures 2 and 3, the secondary particles 24 generated by the interaction of the particle beam 7 with the object 3 can be detected. This means that the secondary particles 24 are detected for the duration of each sequence. Based on the detected secondary particles 24, a detection signal can be generated by the detector 23, where the detection signal represents the quantity and / or energy of the detected secondary particles as a function of time. This means that the detection signal is generated for the duration of each sequence. Based on the detection signal, data can be generated that form the basis for the analysis and / or processing of the area 25; for example, the data represent an image of the area 25.Time-limited segments can be extracted from the detection signal continuously emitted by detector 23. These time-limited segments are assigned to the secondary particles that were generated while the particle beam 7 was guided along a scan path 35-1 to 35-5. Accordingly, these segments do not contain any portions of the detection signal that are assigned to secondary particles that were generated while the particle beam 7 was guided along one of the return paths 37-1 to 37-5. With reference to Fig. 4, details concerning the entry points 31-1 to 31-5 of the sequences, the exit points 33-1 to 33-5 of the sequences and their spatial arrangement are explained. A double arrow 45 represents a distance between the entry point 31-1 of the first sequence and the exit point 33-1 of the same sequence. In the example of Fig. 4, the distance between the entry point of a particular sequence and the exit point of the same sequence is the same for each of the sequences. However, this distance need not be the same for all sequences. Thus, the distance can be different for different sequences. The distance represented by arrow 45 is, for example, at least 50 nm, in particular at least 100 nm, or further, in particular at least 200 nm, for at least one and at most all of the pairs of entry and exit points of the same sequence. In the example shown in Fig. 4, entry points 31-1 and 31-2 lie directly adjacent to each other on boundary line 29; entry points 31-2 and 31-3 lie directly adjacent to each other on boundary line 29; entry points 31-3 and 31-4 lie directly adjacent to each other on boundary line 29; and entry points 31-4 and 31-5 lie directly adjacent to each other on boundary line 29. The closer the entry points lying directly adjacent to each other on boundary line 29 are, the better the area 25 can be analyzed and / or processed. An arrow 47 represents a distance between entry points lying directly next to each other on the boundary line 29 (here between entry points 31-1 and 31-2). This distance is, for at least one and at most all of the pairs of entry points lying directly next to each other on the boundary line 29, for example, at most 200 nm, in particular at most 100 nm, or further, in particular at most 10 nm. In the example shown in Fig. 4, exit points 33-1 and 33-2 lie directly adjacent to each other on boundary line 29; exit points 33-2 and 33-3 lie directly adjacent to each other on boundary line 29; exit points 33-3 and 33-4 lie directly adjacent to each other on boundary line 29; and exit points 33-4 and 33-5 lie directly adjacent to each other on boundary line 29. The closer the exit points lying directly adjacent to each other on boundary line 29 are, the better the area 25 can be analyzed and / or processed. An arrow 49 represents a distance between exit points lying directly adjacent to each other on the boundary line 29 (here between exit points 33-1 and 33-2). This distance is, for at least one and at most all of the pairs of exit points lying directly adjacent to each other on the boundary line 29, for example, at most 200 nm, in particular at most 100 nm, or further, in particular at most 10 nm. In the example shown in Fig. 4, arrows 47 and 49 are of equal length. In general, the distances can be of different sizes. The boundary line 29 has a first continuous section 51, which is characterized by a thick line with diamonds at its ends. The first continuous section 51 contains all entry points 31-1 to 31-5. The boundary line 29 has a second continuous section 53, which is characterized by a thick line with triangles at its ends. The second continuous section 53 contains all exit points 33-1 to 33-5. The first section 51 and the second section 53 do not overlap. The methods described herein can also be carried out with the particle beam systems described with reference to Fig. 5 and Fig. 6. Fig. 5 shows in perspective and schematically simplified representation a particle beam system 101 which includes an electron microscopy system 103 with a principal axis 105. The electron microscopy system 103 is configured to generate a primary electron beam 119, which is emitted along the principal axis 105 of the electron microscopy system 103, and to direct the primary electron beam 119 towards an object 113. The electron microscopy system 103 comprises an electron source 121, schematically represented by a cathode 123 and a suppressor electrode 125, and an extractor electrode 126 arranged at a distance from it, for generating the primary electron beam 119. The electron microscopy system 103 further comprises an accelerator electrode 127, which transitions into a beam tube 129 and passes through a condenser assembly 131, schematically represented by a ring coil 133 and a yoke 135. After passing through the condenser assembly 131, the primary electron beam 119 passes through a pinhole 137 and a central hole 139 in a secondary electron detector 141, whereupon the primary electron beam 119 enters an objective lens 143 of the electron microscopy system 103. The objective lens 143 comprises a magnetic lens 145 and an electrostatic lens 147 for focusing the primary electron beam 119.In the schematic representation of Fig. 5, the magnetic lens 145 comprises a ring coil 149, an inner pole shoe 151, and an outer pole shoe 153. The electrostatic lens 147 is formed by a lower end 155 of the beam tube 129, the inner lower end of the outer pole shoe 153, and a ring electrode 159 that tapers conically towards the object 113. Although not shown in Fig. 5, the electron microscopy system 103 further comprises a deflector system for deflecting the primary electron beam 119 in directions orthogonal to the principal axis 105. The particle beam system 101 further comprises a control unit 177, which controls the operation of the particle beam system 101. In particular, the control unit 177 controls the operation of the electron microscopy system 103. Fig. 6 shows in perspective and schematically simplified representation a particle beam system 102, which includes an ion beam system 107 with a principal axis 109 and the electron microscopy system 103, which is described with reference to Fig. 5. The principal axes 105 and 109 of the electron microscopy system 103 and the ion beam system 107 intersect at a location 111 within a common working area at an angle α, which can have a value of, for example, 45° to 55° or approximately 90°, so that an object 113 to be analyzed and / or processed, with a surface 115, can be processed in a region of location 111 both with an ion beam 117 emitted along the principal axis 109 of the ion beam system 107 and analyzed with an electron beam 119 emitted along the principal axis 105 of the electron microscopy system 103. A schematically indicated holder 116 is provided for holding the object 113, which can adjust the object 113 with regard to its distance from and orientation to the electron microscopy system 103 and the ion beam system 107. The ion beam system 107 comprises an ion source 163 with an extraction electrode 165, a condenser 167, an aperture 169, deflector electrodes 171, and a focusing lens 173 for generating the ion beam 117 emerging from a housing 175 of the ion beam system 107. The longitudinal axis 109' of the support 116 is inclined at an angle to the vertical 105', which in this example corresponds to the angle α between the principal axes 105 and 109. However, the directions 105' and 109' need not coincide with the principal axes 105 and 109, and the angle they form need not coincide with the angle α between the principal axes 105 and 109. The particle beam system 102 further comprises a control unit 277, which controls the operation of the particle beam system 102. In particular, the control unit 277 controls the operation of the electron microscopy system 103, the ion beam system 107 and the camera 116.

Claims

A method for operating a particle beam system, the method comprising: repeating a sequence to guide a particle beam (7) over a surface (27) of an object (3), the object (3) having a region (25) on its surface (27) bounded by a virtual closed boundary line (29), the sequence comprising: guiding the particle beam (7) from an entry point (31-1 to 31-5) of the current sequence to an exit point (33-1 to 33-5) of the current sequence along a scan path (35-1 to 35-5), wherein the entry point (31-1 to 31-5) of the current sequence and the exit point (33-1 to 33-5) of the current sequence are on the boundary line (29) and wherein the scan path (35-1 to 35-5) is entirely within the region (25), and guiding the particle beam (7) from the exit point (33-1 to 33-5) of the current sequence to an entry point (31-2, 31-3, 31-4, 31-5, 31-1) of the next sequence along a return path (37-1 to 37-5),wherein the entry point (31-2, 31-3, 31-4, 31-5, 31-1) of the next sequence lies on the boundary line (29) and wherein the return path (37-1 to 37-5) lies completely outside the area (25). Method according to claim 1, wherein the particle beam (7) continuously strikes the surface (27) of the object (3) for the duration of each sequence. Method according to claim 1 or 2, wherein each of the recirculation paths (37-1 to 37-5) of the sequences has a recirculation path section (39) which is included in all recirculation paths (37-1 to 37-5). Method according to claim 3, wherein the length of the return path section (39) is at least 30%, in particular at least 50%, of the length of the shortest return path, or wherein the length of the return path section (39) is at least 30%, in particular at least 50%, of the length of the shortest scan path of the sequences. Method according to any one of claims 1 to 4, wherein the region (25) is rectangular; and / or wherein the region (25) has an area of ​​at least (100 nm)2 or at least (1 µm)2. Method according to one of claims 1 to 5, wherein the entry point of a sequence (31-1) of the sequences and the exit point of the same sequence (33-1) have a distance (45) from each other which is at least 50 nm, in particular at least 100 nm, and further in particular at least 200 nm. Method according to any one of claims 1 to 6, wherein the distance (47) between entry points that lie directly next to each other on the boundary line (31-1, 31-2) is at most 200 nm, in particular at most 100 nm, and further in particular at most 10 nm. Method according to any one of claims 1 to 7, wherein the distance (49) between exit points that lie directly next to each other on the boundary line (33-1, 33-2) is at most 200 nm, in particular at most 100 nm, and further in particular at most 10 nm. Method according to any one of claims 1 to 8, wherein the boundary line (29) has a first uninterrupted section (51) in which the entry points (31-1 to 31-5) are located, and a second uninterrupted section (53) in which the exit points (33-1 to 33-5) are located, wherein the first section (51) and the second section (53) do not overlap. Method according to any one of claims 1 to 9, wherein the scan paths (35-1 to 35-5) are essentially straight lines. Method according to any one of claims 1 to 10, wherein an average of the lengths of the scan paths (35-1 to 35-5) is smaller than an average of the lengths of the return paths (37-1 to 37-5). Method according to any one of claims 1 to 11, further comprising: defining the area (25); generating control signals for a deflector system (17) of the particle beam microscope based on the defined area (25); wherein the guiding of the particle beam (7) through the deflector system (17) is effected. Method according to any one of claims 1 to 12, further comprising: detecting secondary particles (24) generated by interaction of the particle beam (7) with the object (3); generating a detection signal which represents the quantity and / or energy of the detected secondary particles (24) as a function of time; and in particular generating data which represent an image of the area based on the detection signal. Method according to any one of claims 1 to 13, wherein the particle beam (7) is guided along the scan paths (35-1 to 35-5) and remains at a plurality of dwell positions for a predetermined dwell time; or wherein the particle beam is moved continuously along the scan paths (35-1 to 35-5). Particle beam system (1) configured to perform the method according to any one of claims 1 to 14. Computer program product comprising instructions which, when executed by a controller controlling a particle beam system, cause the controller to control the particle beam system such that the particle beam system performs the method according to any one of claims 1 to 14.

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