Method for operating a particle beam microscope

Abstract

A method for operating a particle beam microscope 1 comprises generating a beam 5 of particles; directing the beam of particles to a location 7 on an object; generating electrons at the location of the object with the particles of the beam directed to the location; directing the generated electrons onto a detector 13 having a plurality of detector pixels; detecting detector events, each triggered by the electrons directed onto the detector striking detector pixels of the detector; generating a detection signal 44 for each detector event detected by a detector pixel with the detector pixel by encoding a value representing a quantity of charge carriers generated in the detector pixel during the detector event; and processing the detection signals based on the values ​​encoded in the detection signals representing the quantity of charge carriers.

Description

The present invention relates to methods for operating particle beam microscopes.In particular, the invention relates to methods for operating particle beam microscopes in which particle microscopic images of an object are generated by directing a particle beam successively onto different locations of an object, electrons generated by the particle beam on the object are detected and a particle microscopic image of the object is generated by assigning the detected electrons to locations of the particle microscopic image that correspond to the locations of the object to which the particle beam was directed during the generation of the detected electrons.Here, deflectors for the particle beam are usually excited in a time scheme such that the particle beam is scanned, for example, line by line over a region of the object. In this case, the assignment between the locations in the particle microscopic image and the locations on the object is possible in a simple manner by using the time-dependent excitations of the deflectors in, for example, an x-direction or horizontal direction and a y-direction or vertical direction in order to determine pixel positions within the particle microscopic image, for example, as indices (i, j).Moreover, in a particle microscope, detectors may be arranged at a plurality of different locations within the particle microscope, such that electrons emerging from the object with different energies strike different detectors, such that different types of electrons may be detected with the different detectors and correspondingly different images of the same object may be generated, which represent different properties of the object. For example, secondary electron images of objects obtained by detecting so-called secondary electrons emerging from the object are usually recorded, and for example, backscattered electron images obtained by detecting so-called backscattered electrons emerging from the object are recorded. Secondary electrons are usually referred to as electrons that exit the object with kinetic energies of less than 50 eV, and backscattered electrons are usually referred to as electrons that exit the object with kinetic energies that are significantly greater than 50 eV.It is an object of the present invention to extend the options for operating particle beam microscopes and to find new options for their operation, if appropriate.According to the invention, a method for operating a particle beam microscope comprises generating a beam of particles, directing the beam of particles onto at least one location on an object, generating electrons at the location of the object with the particles of the beam of particles directed onto the location, directing the generated electrons onto a detector, detecting detector events which are each triggered by an impingement of the electrons directed onto the detector on the detector, generating a detection signal for each detector event detected by the detector and processing the detection signals in order to generate, for example, a particle microscopic image of the object.The particles of the beam may be electrons or ions, such as helium ions or gallium ions.According to exemplary embodiments, the detector comprises a plurality of detector pixels, wherein detector events are each detected by a detector pixel and a detection signal is generated with the detector pixel for each detector event detected by the detector pixel, wherein the generation of the detection signal comprises encoding a value representing a quantity of charge carriers generated in the detector pixel at the detector event. The detection signals are then processed on the basis of the sets of charge carriers encoded in the detection signals.An electron striking detection material of the detector pixel leads to a detector event, in which the electron generates charge carriers in the detection material, which are detected and analyzed by an electronic circuit of the detector pixel. In the analysis, a value is determined which represents the amount of charge carriers generated in the detector pixel at the detector event. This value representing the quantity of charge carriers is encoded by the electronic circuit of the detector pixel into the digital detection signal generated for the detector event, so that the detection signal contains the value representing the quantity of charge carriers. In addition to the value representing the quantity of charge carriers, further values can also be encoded in the detection signal. An example of such another value is a value that identifies the detector pixel that generated the detection signal within the plurality of detector pixels. This value may be, for example, an address of the detector pixel within an array of detector pixels, which indicates the position of the detector pixel within the array by its column number and row number or the like. The additional value encoded in the detection signal may also represent a time of triggering the detector event.The amount of charge carriers generated in the detector pixel during a detector event depends on the kinetic energy with which the generated electron triggering the detector event impinges on the detector. By each generated detection signal also comprising an encoded value representing the amount of charge carriers generated in the detector pixel at the detector event, each detection signal also represents the kinetic energy with which the electron triggering the detector event is struck on the detector. Furthermore, electrons generated at the object that exit the object with higher kinetic energies also strike the detector with higher kinetic energies, and conversely, generated electrons that exit the object with lower kinetic energies also strike the detector with lower kinetic energies. It is thus possible to selectively process the detection signals for detection signals whose coded values for the quantity of charge carriers are in certain ranges corresponding to selected ranges of kinetic energies at which the generated electrons exit the object. For example, for a specific processing of the detection signals, only detection signals are taken into account whose value representing the quantity of charge carriers corresponds to a predetermined criterion. The predetermined criterion can be given, for example, by a threshold value which must be exceeded or undershot in order for the criterion to be fulfilled.If, for example, the object is to be examined with backscattered electrons, a lower threshold value for the value representing the quantity of charge carriers can be selected as a predetermined criterion for the detection signals which are processed such that only detection signals which are generated by backscattered electrons generated on the object and which emerge from the object with kinetic energies of significantly more than 50 eV meet the criterion.If, for example, the object is to be examined with secondary electrons, an upper threshold value for the value representing the quantity of charge carriers can be selected as a predetermined criterion for the detection signals which are processed such that only detection signals which are generated by secondary electrons generated on the object and which emerge from the object with kinetic energies of less than 50 eV meet the criterion.Whereas in conventional methods for operating particle beam microscopes for detecting back-scattered electrons and secondary electrons different separate detectors are used, which are arranged at different positions of the particle beam microscope, a single detector can be used with the method described here, since the generated detection signals allow a distinction to be made via the values representing the quantity of charge carriers encoded therein as to whether the detector event leading to the detection signal was triggered by back-scattered electrons or a secondary electron. Here, the distinction between back-scattering electron and secondary electron is merely exemplary. Any ranges can be defined for the values of the detection signals representing the quantity of charge carriers, which meet the predetermined criterion.According to example embodiments, the particles of the beam of particles are successively directed to different locations within a region of the object. According to exemplary embodiments herein, the method further comprises generating a particle microscopic image of the region of the object, wherein the image comprises a plurality of image pixels and wherein values of the image pixels of the image are determined based on a number of detection signals generated for detector events while the beam of particles was directed at an environment of the object associated with the image pixel. For example, the value of the image pixel of the image may represent a brightness of the image pixel in the image.As described above, only detection signals whose value representing the quantity of charge carriers corresponds to a predetermined criterion can be used for this purpose. Thus, it is possible to generate particle microscopic images, which are, for example, backscattered electron images or secondary electron images. Moreover, it is possible to provide two or more different criteria to which different colors are assigned. In a particle microscopic image generated thereby, detection signals that meet one of these criteria can then be displayed with the color assigned to this criterion. If detection signals meet a plurality of these criteria, it is possible to define priorities between the different criteria and to display the detection event with the colour which is associated with the criterion with the highest priority among the criteria fulfilled. Alternatively, the detection event can also be represented with a color which arises from a mixture or transparent superposition of the colors assigned to the fulfilled criteria.According to exemplary embodiments, the method comprises increasing the kinetic energies of the generated electrons, wherein the generated electrons are directed onto the detector with increased kinetic energies. In this way, it can be achieved, for example, that even electrons generated on the object that emerge from the object with very low kinetic energies strike the detector with kinetic energies increased to such an extent that they trigger detector events in the detector pixels of the detector with a sufficient number of generated charge carriers for detection. For example, the kinetic energies of the generated electrons are increased by at least 3 keV and in particular by at least 6 keV.Increasing the kinetic energies of the generated electrons may entail conversely lowering the kinetic energies of the particles of the beam of particles directed onto the object before striking the object. For this reason, the method may further comprise increasing the kinetic energies of the particles of the generated beam before decreasing the kinetic energies of the particles of the beam of particles having the increased kinetic energies before encountering the location on the object.According to further exemplary embodiments, the detector comprises a plurality of detector pixels, wherein detector events are each detected by a detector pixel and a detection signal is generated with the detector pixel for each detector event detected by the detector pixel, wherein the generation of the detection signal comprises encoding a value representing a time of triggering the detector event. The detection signals are then processed on the basis of the values representing the time of the triggering of the detector event.In the analysis of the detector event by the electronic circuit of the detector pixel, for example, the value representing time may be determined as a number provided by a clock of the detector at the time of the analysis of the detector event and incremented by the clock at the clock of the clock.According to exemplary embodiments, the method comprises directing the particles of the beam of particles successively to different locations within a region of the object and generating a particle microscopic image of the region of the object. In this case, the image has a multiplicity of image pixels, and the detection signals are each assigned to at least one of the image pixels of the image. The image pixel to which a given detection signal is assigned is determined based on the value of the detection signal representing the time of triggering the detector event. Since the location to which the particles of the beam are directed changes with time according to a known time scheme, the location on the object to which the particle beam was directed can be determined when the detector event was triggered by the value representing the time of triggering the detector event. From this location on the object, the location in the image corresponding thereto and the image pixel of the image belonging to this location in the image, which is associated with the location on the object, can in turn be determined. Thus, the image information contained in the processed detection signal can be added to the image based solely on the value representing the time of triggering the detector event without having to use the conventionally used excitation of the deflectors.According to exemplary embodiments, the method further comprises providing a deflector in a beam path of the electrons generated at the location of the object between the object and the detector and in a beam path of the beam of particles in front of the object, and further deflecting the generated electrons and the particles of the beam of particles such that the detector is arranged next to the beam of particles.Furthermore, a computer program product is proposed which comprises instructions which, when loaded into a control computer of a particle beam microscope, cause the latter to operate the particle beam microscope in accordance with the method explained above. The computer program product may comprise a data carrier, such as a compact disk or a solid state memory, in which the instructions are represented by magnetic, optical, electrical or other states. The computer program product can furthermore comprise a signal sequence which can be transmitted, for example, via a network, a data line, a wireless communication link or the like, wherein information representing the instructions is encoded in the signal sequence.Embodiments of the invention are explained in more detail below with reference to figures. The following shows: FIG. 1 shows a schematic illustration of a particle beam microscope, FIG. 2 shows a schematic illustration of a part of a detector of the particle beam microscope of FIG. 1, FIG. 3 is a schematic illustration with graphs for explaining the mode of operation of the detector of the particle beam microscope of FIG. 1 , FIG. 4 shows a schematic illustration of a detection signal generated with the detector of the particle beam microscope of FIG. 1, FIG. 5 shows a schematic illustration of a time scheme for scanning a region of an object with a particle beam of the particle beam microscope, FIGS. 6A and 6B are graphs representing the excitation of deflectors of the particle beam microscope of FIG. 1 for generating the time scheme of FIG. 5 ; and FIG. 7 shows a schematic illustration for assigning detection signals obtained with the time diagram of FIG. 5 to image pixels of a generated particle microscopic image.FIG. 1 is a schematic illustration of a particle beam microscope 1. the particle beam microscope 1 comprises a particle beam source 3 for generating a beam 5 of charged particles which are emitted by the particle source 3. The beam 5 of particles is directed to a location 7 of an object 9. At the location 7, the particles of the beam 5 directed onto the location 7 generate electrons which emerge from the object 9. A portion of these electrons emerging from the object 9 is focused to form an electron beam 11 which is directed onto a detector 13 for detecting these electrons.The particle source 3 is supplied with operating current by a controller 15 of the particle beam microscope 1 via a supply line 17 and is maintained at an electrical potential U 1. The object 9 is mounted on a sample holder 19 and is held at an electrical potential U2 by the controller 15 via a supply line 20. In the example explained here, the particles generated by the particle source 3 are electrons, and the voltage difference U 1-U 2 determines the kinetic energy with which the electrons of the beam 5 impinge on the object 9 at the location 7. However, the particles of the beam 5 generated by the particle source 3 can also be particles different from electrons, namely ions, such as helium ions or gallium ions, in order to carry out the method explained below.After being generated by the particle source 3, the electrons of the beam 5 enter the beam tube 22 at a first end 21 of a beam tube 22, pass through the beam tube and exit the beam tube 22 at a second end 23 of the beam tube before they strike the object 9. The beam tube 22 is held by the controller 15 via a supply line 25 at an electrical potential U 3 which is greater than the electrical potential U 1 of the particle source 3 and greater than the electrical potential U 2 of the object 9. For example, U3-U2is equal to 3 kV or 6 kV. The electrons of the beam 5 are thus accelerated from the particle source 3 into the beam tube 22, and they are decelerated again on their path towards the object 9 after they exit at the second end 23 of the beam tube 22.The beam 5 of electrons is furthermore focused by an objective lens 25, so that a spot illuminated with the electrons of the beam 5 at the location 7 of the object 9 is as small as possible, so that the particle beam microscope 1 can provide a high spatial resolution. The objective lens 5 is a magnetic objective lens which has at least one magnetic coil 27, the turns of which encompass the beam 5 of electrons. An excitation current is supplied from the controller 15 via a line 28 to the at least one magnetic coil 27 in order to generate a magnetic field which is guided in a yoke 29 annularly surrounding the beam 5 of electrons and which exits at pole ends 30 of the yoke 29 into a gap between the pole ends 30 close to the beam 5 of particles and provides a focusing magnetic field for the beam 5. An electric potential U4 is supplied from the controller 15 to the yoke 29 of the objective lens 25 via a line 33, which electric potential is for example the ground potential or is for example equal to the electric potential U2 of the object 9, so that an electric field is produced between the second end 23 of the beam tube 22 and the pole end 30 of the yoke 29 close to the object 9, which electric field can likewise have a focusing effect on the beam 5 of electrons.The electrons generated at the location 7 of the object 9 by the impinging electrons of the beam 5 are accelerated toward the beam tube 22 due to the difference between the electrical potential U 2 of the object 9 and the electrical potential U 3 of the beam tube 23 and enter the beam tube 22 at the second end 23 thereof. These electrons are also acted upon by the focusing magnetic and electric fields provided by the objective lens 25 so that these electrons are converged by these fields into the beam 112 and move in the beam tube 22 toward the first end 21 thereof. In this case, they pass through a deflector 37 which is supplied with excitations by the controller 15 via a line 38 in order to provide a deflection field for the electrons of the beam 11 so that these are conducted to the detector 13. In the illustration of FIG. 1, the deflector 37 acts in such a way that the electrons of the beam 11 conducted upward in the figure and toward the detector 13 are deflected to the right. However, the electrons of the beam 5, which move from the particle source 3 downwards towards the object 9 in the illustration of FIG. 1, also pass through this deflector 37 and are likewise deflected to the right by this deflector.In order to enable the beam 5 generated by the particle source 3 and directed downwards in the illustration of FIG. 1 to continue to run vertically downwards after deflection to the right by the deflector 37, two further deflectors 39 and 41 are provided which are supplied with excitations by the controller 15 via lines 40 and 42 in such a way that the deflector 39 initially deflects the electrons of the beam 5 to the right and the deflector 41 then deflects the electron beams 5 to the left, so that the beam path illustrated in FIG. 1 results for the beam 5 of electrons. This also achieves the effect that the detector 13 is arranged next to the beam 5 of electrons, with the result that the electrons of the beam 5 can strike the object 9 unimpeded by the detector 13, while the electrons of the beam 11 strike the detector.The electrons of the beam 11 incident on the detector 13 trigger detector events in the detector 13 which are detected by electronic circuits in the detector 13. A read-out circuit 43 of the detector 13 generates detection signals for the detected detector events, which detection signals are transmitted via a line 44 to the controller 15 and are processed by the controller 15.The particle beam microscope 1 further comprises a deflector 45 which is supplied with excitations by the controller 15 via a line 46 in order to deflect the beam 5 of electrons directed onto the object 9 so that it can strike different locations within a region 47 of the object in succession. Thus, the region 47 of the object 9 can be scanned with the beam 5 of electrons according to a predetermined time scheme, while the electrons generated on the object 9 in this case are continuously conducted to the detector 13 and trigger detection events for which detection signals are generated. By processing these detection signals, the controller 15 can then generate, for example, a particle microscopic image of the region 7 of the object 9 and display this particle microscopic image, for example, on a screen 49 of a computer 50 or store it in a database 51.FIG. 2 is a schematic illustration of a portion of the detector 13. the detector 13 includes a plurality of detector pixels 23 arranged in an array 51 of rows 52 and columns 54. Each detector pixel 53 comprises a semiconductor detector material in which the impinging electrons trigger the detector events that result in a number of mobile charge carriers that are detected and evaluated by an electronic circuit 55 comprising each detector pixel 53. For each detected detector event in a detector pixel 53, the electronic circuit 55 generates a detection signal which is passed on within the lines 52 and thus reaches the readout circuit 43, which transmits the detection signals obtained from the lines 52 via the line 44 to the controller 15. The line 44 can comprise an optical fiber line, or another signal transmission technique can be used, which is capable of transmitting signals from the detector, which is at the electrical potential U 3 of the beam tube 22, to the outside of the particle beam microscope 1, i.e. to ground potential. For example, optocouplers can be used here.FIG. 3 is a schematic diagram with graphs for explaining the detection of a detector event with the electronic circuit 55 of a detector pixel 53.In an upper first graph of FIG. 3, a line 61 represents a voltage profile at detection electrodes of the electronic circuit 55 caused by the charge carriers generated during the detector event, wherein the detector event is generated at a time t 1. In a time period following the time t1, the voltage rises until it reaches a maximum at a time t2, whereupon it returns to its original value at a later time t5. At a time t 3 lying between the times t 1 and t 2, the voltage 61 exceeds a threshold value 63 and at a time t 4 lying between the times t 2 and t 5, the voltage 61 falls below the threshold value 63 again. In the time period between the times t 3 and t 4, the voltage 61 is thus above the threshold value 63.A second graph of FIG. 3 shows a clock signal 65 having a clock frequency of, for example, 40 MHz. The periods of the clock signal 65 may be counted and a number indicating the period may also be output by the clock providing the clock signal 65, as exemplarily shown by a number row 67 in a third graph of FIG. 3.At time t3, at which the voltage 61 exceeds the threshold value 63, a counter is started which counts the periods of a further clock signal 69 at a frequency of 640 MHz until the next rising edge of the clock signal 65 appears at time t6. This further clock signal is schematically illustrated in a third graph of FIG. 3.Thus, the number (here, 16383) of the number row 67 belonging to the rising edge of the signal 65 at the time t6 and the number of counted clocks of the clock signal 69 between the time t3 and the time t6 represent the time at which the voltage 61 has exceeded the threshold 63. This time is also approximately equal to the time t1when the detector event was triggered.Furthermore, periods of the clock signal 65 are counted for evaluating the detector event, namely beginning with the time t3 at which the voltage 61 exceeds the threshold value 63 and ending with the full period of the clock signal 65 after the voltage 61 falls below the threshold value 63, as is illustrated in a fourth graph of FIG. 3 with the counted clocks by a line 71. In the example illustrated, these are four periods. This number (here: four) determined in this way is a value which represents the time duration t4-t3during which the signal 61 lies above the threshold value 63. This time duration is the greater the more charge carriers have been generated in the detector material during the detector event, since a greater maximum of the voltage is then reached at a later time and it also takes longer for the voltage to fall below the threshold value 63 again after reaching the maximum. The number of charge carriers is again the greater with the greater kinetic energy that the electron triggering the detector event has penetrated into the detector material. Thus, this number (here: four) is also a value representing the kinetic energy with which the electron triggering the detector event has penetrated into the detector material.For each detector event detected by the detector pixel 53, the electronic circuit 55 generates a digital detection signal in which the values explained above evaluated for the detector event are encoded. FIG. 4 shows an example of the coding of such a generated detection signal 77. the detection signal 77 comprises a head 79 for identifying the beginning of the signal 77, this head having four data bits. The detection signal 77 further comprises a coding of an address 81 of the detector pixel 53 in the field 51 which has detected the detector event. The address 81 is coded by 16 bits, namely 8 bits for the index of the row 52 of the image pixel 53 and 8 bits for the index of the column 54 of the image pixel 53. The signal 77 further comprises a coding of the value 83 of the number 67 of the period of the clock signal 65 at the time t6 (here: 16383), which approximately indicates the time t3. The clock signal 77 further includes encoding a value 85 indicative of the counted number of periods of the clock signal 69 between times t3 and t6. The values 83 and 85 together represent the time t3 with a time resolution of approximately 1.6 ns corresponding to the frequency of the clock signal 69. For the coding of this value 83, 14 bits are used, and for the coding of the value 85, 4 bits are used. The detection signal 77 then further comprises the coding of a value 78, which specifies the counted periods 71 of the clock signal 65 between the times t 3 and t 4 and thus the amount of charge carriers which are generated during the detector event or the kinetic energy with which the electron triggering the detector event is struck on the detector pixel. 4 bits are used for the coding of the value 87.The detector 13 thus generates for each detector event a detector signal 77, in which values are encoded, which represent the time of the triggering of the detector event and the quantity of charge carriers which are generated in the detector pixel during the detector event. An example of the realization of a detector enabling this is the detector referred to as "Timepix3", which is described in T. Poikela et al., "Timepix3: a 65K channel hybrid pixel reading chip with simultaneous ToA / ToT and sparse reading", Journal of Instrumentation 9.5 (2014), pages 1-8.FIG. 5 is a schematic illustration of a time diagram after which the location of incidence 7 is moved over the region 47 of the object 9 by excitation of the deflector 45. In the example shown here, the location 7 at which the beam 5 of electrons impinges on the object 9 is moved line by line over the object. In this case, the location is displaced continuously in the x-direction along a straight line 91 1 starting from the left edge of the region 47 in a first row until the right edge of the region 47 is reached, whereupon the point of impingement returns to the left edge of the region 47 in a next row, whereupon the location is displaced continuously in the x-direction to the right along a next straight line 91 2 etc.FIG. 6A is a graph representing the excitation generated by the controller 15 to deflect the beam 5 with the deflector 45 in the x-direction, and FIG. 6B is a graph representing the excitation of the deflector 45 to deflect the beam 5 in the y-direction, in order to obtain the time scheme illustrated in FIG. 5.From the predetermined time dependence of the excitations of the deflector 45 shown in FIGS. 6A and 6B, the location within the region 47 of the object 9 on which the beam 5 of electrons is directed is thus known for each point in time. The electrons generated at specific times by the beam 5 of electrons at the object 9 require a negligible time in order to reach the detector 13 and trigger a detector event there in a detector pixel. The detection signals generated for each detected detector event each include a value representing the time at which the detector event was triggered such that each detection signal can be associated with a determinable location within the region 47 of the object 9.The time diagram for the line-by-line scanning of the region 47 explained with reference to FIG. 5 is merely an example. Any other schemes may be used. For example, the beam may be directed one after the other to locations whose values are determined on the basis of a random series. In a particle microscopic image generated from the detection signals, locations within the image are assigned to locations within the imaged region 47 of the object 9. If the generated image has a plurality of image pixels, each image pixel is assigned to an environment within the region 47 of the object 9 due to the extent of the image pixel. Accordingly, to generate the image, detection signals generated while the beam 5 of electrons is directed to locations within a vicinity of the region 47 of the object 9 associated with a particular image pixel must be associated with that image pixel. FIG. 7 is a schematic diagram for explaining the assignment of detection signals 77 to image pixels 101 of a particle microscopic image 103. Depending on material properties of the object 9 at the location 7 to which the beam 5 of electrons is directed at a certain time, a larger or smaller current of electrons is generated at this location, which are directed to the detector 13. In FIG. 7, within the image 103, the detection signals 77 are shown at locations whose coordinates in the x direction and y direction correspond to the excitations of the deflector 45 in the x direction and y direction at the times at which the respective detector events were triggered, which are encoded in the values of the detection signals 77. Due to the extension of the image pixels 101, a plurality of detection signals 77 is assigned to a respective image pixel 101 with a pixel index i, j. In this case, it is also possible for a detection signal 77 to be assigned to one part of an image pixel i, j and to be assigned to another part of an adjacent image pixel i+1, j. The number of detection signals 77 assigned to a specific image pixel i, jrepresents the brightness of this image pixel i, jin the particle microscopic image 103.Furthermore, it is possible to take into account the value 87 contained in each detection signal 77, which value represents the number of charge carriers generated in the detector event, in the generation of the particle microscopic image 103 from the detection signals 77. For example, it is possible to set a criterion that must satisfy this value in order to take the detection signal 77 into account for the generation of the particle microscopic image. Thus, for example, a suitable threshold value can be established for this value representing the quantity of charge carriers, wherein only detection signals whose value representing the quantity of charge carriers falls below the threshold value are used for generating a first particle microscopic image. Furthermore, only detection signals whose value representing the quantity of charge carriers exceeds the threshold value can be used to generate a second particle microscopic image. With the threshold value appropriately selected, the first particle microscopic image may be referred to as a secondary electron image and the second particle microscopic image may be referred to as a backscattered electron image.

Claims

A method of operating a particle beam microscope, comprising: generating a beam of particles; directing the beam of particles onto a location on an object; generating electrons at the location of the object with the particles of the beam directed onto the location; directing the generated electrons onto a detector having a plurality of detector pixels; detecting detector events, each triggered by an impact of the electrons directed onto the detector onto detector pixels of the detector; generating a detection signal for each detector event detected by a detector pixel with the detector pixel by encoding a value representing an amount of charge carriers generated in the detector pixel at the detector event; and processing the detection signals based on the values representing the amount of charge carriers encoded in the detection signals.The method of claim 1, further comprising: increasing the kinetic energies of the generated electrons, wherein the generated electrons are directed to the detector with increased kinetic energies.Method according to claim 2, wherein the kinetic energies of the generated electrons are increased by at least 3 keV and in particular by at least 6 keV.The method of claim 2 or 3, further comprising: increasing the kinetic energies of the particles of the generated jet; and decreasing the kinetic energies of the particles of the jet of particles of increased kinetic energies, wherein the particles with decreased kinetic energies are directed to the location on the object.The method of any one of claims 1 to 4, wherein the particles of the beam of particles are successively directed to different locations within a region of the object.The method of claim 5, further comprising generating a particle microscopic image of the region of the object; wherein the image has a plurality of image pixels; and wherein values of the image pixels of the image are determined based on a number of detection signals generated for detector events while the beam of particles was directed at an environment of the object associated with the image pixel.The method of claim 5, further comprising generating a particle microscopic image of the region of the object; wherein the image has a plurality of image pixels; and wherein values of the image pixels of the image are determined based on a number of detection signals generated for detector events while the beam of particles was directed to an environment of the object associated with the image pixel, and whose value representing the amount of charge carriers corresponds to a predetermined criterion.Method according to claim 7, wherein the detection signals correspond to the predetermined criterion if their value representing the quantity of charge carriers exceeds a lower threshold value.The method according to claim 7 or 8, wherein the generated particle microscopic image of the region of the object is a backscattered electron image, the image information of which is substantially due to electrons generated on the object, which exit the object with kinetic energies of more than 50 eV.Method according to Claim 7, wherein the detection signals correspond to the predetermined criterion if their value representing the quantity of charge carriers falls below an upper threshold value.The method according to claim 7 or 10, wherein the generated particle microscopic image of the region of the object is a secondary electron image, the image information of which is substantially due to electrons generated on the object, which exit the object with kinetic energies of less than 100 eV.A method for operating a particle beam microscope, in particular in combination with the method according to any one of claims 1 to 11, wherein the method comprises: generating a beam of particles; directing the beam of particles onto a location on an object; generating electrons at the location of the object with the particles of the beam directed onto the location; directing the generated electrons onto a detector having a plurality of detector pixels; detecting detector events, which are each triggered by an incidence of the electrons directed onto the detector onto detector pixels of the detector; generating a detection signal for each detector event detected by a detector pixel with the detector pixel by encoding a value representing a time of triggering the detector event; and processing the detection signals based on the values encoded in the detection signals representing the time of triggering the detector event.The method of claim 12, wherein the particles of the beam of particles are successively directed to different locations within a region of the object.The method of claim 13, further comprising: generating a particle microscopic image of the region of the object; wherein the image has a plurality of image pixels; wherein the detection signals are each associated with at least one of the image pixels; wherein the at least one image pixel to which a given detection signal is associated is determined based on the value of the given detection signal that was generated for the detector event representing the time of triggering the detector event.The method of claim 14, wherein associating the detection signal with the at least one image pixel comprises increasing a value of the at least one image pixel.Method for operating a particle beam microscope, in particular in combination with the method according to one of Claims 1 to 15, wherein the method comprises: generating a beam of particles; directing the beam of particles onto a location on an object; generating electrons at the location of the object with the particles of the beam directed onto the location; directing the generated electrons onto a detector having a plurality of detector pixels; detecting detector events which are each triggered by an impingement of the electrons directed onto the detector on detector pixels of the detector; generating a detection signal for each detector event detected by a detector pixel with the detector pixel by encoding a value representing a time of triggering the detector event and by encoding a value representing a quantity of charge carriers generated in the detector pixel at the detector event; and processing the detection signals based on the values representing the quantity of charge carriers encoded in the detection signals and the values representing the time of triggering the detector event encoded in the detection signals.The method of any of claims 1 to 16, wherein generating the detection signal further comprises encoding a value identifying the detector pixel within the plurality of detector pixels.The method of any one of claims 1 to 17, further comprising: providing a first deflector in an optical path of the electrons generated at the location of the object between the object and the detector and in an optical path of the beam of particles in front of the object; and deflecting the generated electrons and the particles of the beam of particles such that the detector is disposed adjacent to the beam of particles.A particle beam microscope configured to carry out the method of any one of claims 1 to 18.A computer program product comprising instructions which, when loaded into a control computer of a particle beam microscope, cause the particle beam microscope to operate according to the method of any one of claims 1 to 19.

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