Method for operating an electron beam microscope and electron beam microscope

Abstract

A method for operating an electron beam microscope having an electron source and a beam tube comprises recording a first image of a sample and recording a second image of the sample. Recording comprises directing an electron beam from the electron source, propagating through an interior of the beam tube, onto the sample and generating a detection signal by means of a detector comprising a scintillator arranged in the interior of the beam tube for converting electrons emitted by the sample into light and a light detector for generating the detection signal based on the light generated by the scintillator. A first value and a second value of a beam tube voltage are selected such that a value of a backscattered electron-secondary electron contribution ratio when recording the first image is greater than a value of the backscattered electron-secondary electron contribution ratio when recording the second image, wherein the backscattered electron-secondary electron contribution ratio is indicative of a ratio of a contribution of backscattered electrons to the detection signal to a contribution of secondary electrons to the detection signal when recording a particular image.

Description

Technical Field

[0001] The present invention relates to a method for operating an electron beam microscope and an electron beam microscope. Background Technology

[0002] Electron beam microscopy can be used for sample analysis. For this purpose, for example, images of the sample can be recorded by sequentially pointing an electron beam at multiple different locations on the sample and detecting the interaction products of the interaction between the electron beam and the sample. Examples of such interaction products are secondary electrons and backscattered electrons.

[0003] Secondary electrons possess low kinetic energy (emission energy) when emitted from a sample. For example, the emission energy of secondary electrons ranges from 0 eV to approximately 100 eV. In this paper, secondary electron images represent images of a sample obtained by (almost exclusively or at least primarily) detecting secondary electrons.

[0004] Backscattered electrons are electrons from an electron beam that are essentially elastically scattered at the sample. Therefore, when emitted by the sample, a backscattered electron possesses a kinetic energy (emission energy) that deviates slightly from the landing energy. The landing energy represents the kinetic energy of the electrons from the electron beam incident on the sample. In this paper, backscattered electron images represent images of the sample obtained by (almost exclusively or at least primarily) detecting backscattered electrons.

[0005] Secondary electron images and backscattered electron images of the same sample can reveal different properties of the sample. Therefore, having both types of images simultaneously can be advantageous for sample analysis.

[0006] To provide both secondary electron and backscattered electron images of the same sample, conventional electron beam microscopy includes two separate detectors: one for detecting secondary electrons (almost exclusively or at least primarily), and another for detecting backscattered electrons (almost exclusively or at least primarily). Such a configuration with multiple detectors is complex and costly. Summary of the Invention

[0007] The purpose of this invention is to provide the possibility of recording secondary electron images and backscattered electron images using a simpler and more cost-effective means.

[0008] This objective is achieved by means of the invention described below. Advantageous developments of the invention are also defined below.

[0009] One aspect of the present invention relates to a method for operating an electron beam microscope comprising an electron source and a beam tube. The method includes: recording a first image of the sample while applying an accelerating voltage between the electron source and the sample and applying a beam tube voltage, which is a voltage between the beam tube and the sample, according to a first value; and recording a second image of the sample while applying an accelerating voltage between the electron source and the sample and applying a beam tube voltage, according to a second value. Recording the first and second images each includes: sequentially pointing an electron beam, provided by the electron source and propagating through the interior of the beam tube, to a plurality of different locations on the sample, and generating a detection signal by means of a detector comprising a scintillator and a photodetector, the scintillator being arranged inside the beam tube for converting electrons emitted by the sample into light, and the photodetector being used to generate the detection signal based on the light generated by the scintillator. The first and second values ​​of the beam tube voltage are different from each other and are selected such that the backscattered electron-secondary electron contribution ratio is greater when recording the first image than when recording the second image. The backscattered electron-secondary electron contribution ratio indicates the ratio of the contribution of backscattered electrons to the detection signal to the contribution of secondary electrons to the detection signal when recording a specific image. Secondary electrons are electrons emitted by the sample with energies of up to 100 eV. Backscattered electrons are electrons emitted by the sample with energies that differ from the product of the electron's charge and the accelerating voltage by up to 500 eV.

[0010] In one embodiment, the first and second values ​​of the beam tube voltage are selected such that the backscattered electron-secondary electron contribution ratio when recording the first image is at least 1.2 times the value of the backscattered electron-secondary electron contribution ratio when recording the second image.

[0011] In one embodiment, the first and second values ​​of the beam tube voltage are selected such that the conversion efficiency difference when recording the first image is greater than the conversion efficiency difference when recording the second image; the conversion efficiency difference indicates the difference between the conversion efficiency of the scintillator at a first energy and the conversion efficiency of the scintillator at a second energy; the first energy is the product of the electron element charge and the voltage between the beam tube and the electron source, and the second energy is the product of the electron element charge and the beam tube voltage.

[0012] In one embodiment, the first and second values ​​of the tube voltage are selected such that the conversion efficiency difference when recording the first image is at least 1.2 times the conversion efficiency difference when recording the second image.

[0013] In one embodiment, the first and second values ​​of the beam tube voltage are selected such that the conversion efficiency ratio when recording the first image is greater than the conversion efficiency ratio when recording the second image; the conversion efficiency ratio indicates the ratio of the conversion efficiency of the scintillator at a first energy to the conversion efficiency of the scintillator at a second energy; the first energy is the product of the electron element charge and the voltage between the beam tube and the electron source, and the second energy is the product of the electron element charge and the beam tube voltage.

[0014] In one embodiment, the first and second values ​​of the tube voltage are selected such that the conversion efficiency ratio when recording the first image is at least 1.5 times the conversion efficiency ratio when recording the second image.

[0015] In one embodiment, a first value of the tube voltage is selected such that the conversion efficiency ratio during recording of the first image is at least 1; the conversion efficiency ratio indicates the ratio of the conversion efficiency of the scintillator at a first energy to the conversion efficiency of the scintillator at a second energy; the first energy is the product of the electron charge and the voltage between the tube and the electron source, and the second energy is the product of the electron charge and the tube voltage.

[0016] In one embodiment, the conversion efficiency at a specific energy represents the average number of photons generated by the scintillator when an electron of that specific energy is incident on the scintillator.

[0017] In one embodiment, no electric or magnetic field is generated between the sample and the scintillator to repel the electrons emitted by the sample from the scintillator.

[0018] In one embodiment, recording the first image and recording the second image are performed directly and sequentially.

[0019] In one embodiment, recording the first image and recording the second image are part of a repetitive sequence.

[0020] In one embodiment, the method further includes: automatically setting the current supplied to the objective lens of the electron beam microscope based on the current value of the beam tube voltage.

[0021] In one embodiment, the accelerating voltage is selected such that the electron beam is accelerated to the sample, and a first value and a second value of the beam tube voltage are selected such that the electrons emitted by the sample are accelerated from the sample to the beam tube.

[0022] In one embodiment, the first and second values ​​of the tube bundle voltage are greater than 500 V.

[0023] In one embodiment, the accelerating voltage is greater than 500 V and less than 10 kV.

[0024] In one embodiment, the method further includes: using a display device to simultaneously display the first image and the second image side by side.

[0025] Another aspect of the invention relates to an electron beam microscope for recording images of a sample, the electron beam microscope comprising: an electron source configured to provide an electron beam; a beam tube surrounding an interior in which the electron beam propagates during operation; a deflection system configured to laterally deflect the electron beam relative to the direction of propagation of the electron beam; a detector comprising a scintillator and a photodetector, wherein the scintillator is disposed within the interior of the beam tube and configured to convert electrons emitted by the sample and incident on the scintillator into light, and wherein the photodetector is configured to detect the light generated by the scintillator; a driver system configured to apply an accelerating voltage between the electron source and the sample, and to apply a variably adjustable voltage between the beam tube and the sample; and a controller configured to perform the method according to the invention.

[0026] The accelerating voltage between the electron source and the sample accelerates the electron beam supplied to the sample by the electron source.

[0027] The beam tube voltage accelerates electrons emitted from the sample between the sample and the beam tube; these electrons include both secondary electrons and backscattered electrons (accelerated to varying degrees). Therefore, the incident energy of the electrons emitted from the sample at the scintillator (i.e., the kinetic energy of these electrons incident on the scintillator) is obtained as the sum of: the emission energy (i.e., the kinetic energy of the electrons emitted from the sample); and the energy absorbed as a result of acceleration in the electric field generated by the beam tube voltage between the sample and the beam tube. This means that the incident energy is directly affected by the voltage between the sample and the beam tube.

[0028] Scintillators have energy-dependent conversion efficiency. This means that the efficiency with which a scintillator converts incident electrons into light varies depending on the incident energy.

[0029] Therefore, by changing the beam tube voltage, the incident energy of electrons emitted from the sample on the scintillator can be adjusted so that the electrons are converted into light by the scintillator with a desired conversion efficiency. In particular, by changing the beam tube voltage, the conversion efficiency of the scintillator for converting backscattered electrons and the conversion efficiency of the scintillator for converting secondary electrons can be adjusted.

[0030] A photodetector detects the light generated by the scintillator and generates a detection signal based on the detected light. The detection signal represents, for example, the intensity of the light generated by the scintillator. For instance, the detection signal could represent the total intensity of the light detected by the photodetector during the recording of a single image. The detection signal depends on the conversion efficiency of the scintillator and the detection efficiency of the photodetector.

[0031] The detection signal generated by the detector during the recording of the first and second images consists essentially of two contributions: a first contribution from backscattered electrons and a second contribution from secondary electrons. The contribution of backscattered electrons to the detection signal lies in the light generated by backscattered electrons in the scintillator and detected by the photodetector. The contribution of secondary electrons to the detection signal lies in the light generated by secondary electrons in the scintillator and detected by the photodetector. The backscattered electron-secondary electron contribution ratio indicates the ratio of the contribution of backscattered electrons to the detection signal to the contribution of secondary electrons to the detection signal during the recording of a specific image.

[0032] The first and second values ​​of the beam tube voltage are selected such that the backscattered electron-secondary electron contribution ratio during the recording of the first image is greater than the backscattered electron-secondary electron contribution ratio during the recording of the second image. This means that the first image is based on the detection of backscattered electrons to a greater extent than the second image.

[0033] For example, the first value of the beam voltage is chosen such that the first image is a backscattered electron image. The difference of a backscattered electron image lies in the fact that it is primarily based on the detection of backscattered electrons, rather than primarily based on the detection of secondary electrons.

[0034] For example, a second value of the beam tube voltage is chosen such that the second image is a secondary electron image. The difference of a secondary electron image lies in the fact that it is primarily based on the detection of secondary electrons, rather than primarily based on the detection of backscattered electrons. Attached Figure Description

[0035] Embodiments of the present invention will now be explained in more detail with reference to the accompanying drawings, in which:

[0036] Figure 1 A schematic diagram of an electron beam microscope is shown;

[0037] Figure 2 A schematic diagram of the detector in an electron beam microscope is shown;

[0038] Figure 3 A flowchart is shown, illustrating a method for operating an electron beam microscope;

[0039] Figure 4 The energy-dependent conversion efficiency of the detector's scintillator and a first schematic diagram of the energy spectrum when electrons are incident on the scintillator using a beam tube voltage according to a first value are shown; and

[0040] Figure 5The energy-dependent conversion efficiency of the detector's scintillator and a second schematic diagram of the energy spectrum when electrons are incident on the scintillator using a bundle tube voltage according to a second value are shown. Detailed Implementation

[0041] Electron beam microscope

[0042] Figure 1 A schematic diagram of an electron beam microscope 1 is shown, which can be used to perform the method according to the invention. The electron beam microscope 1 is used to record images of a sample 4 arranged in the working area 6 of the electron beam microscope 1.

[0043] The electron beam microscope 1 includes an electron beam column 10. The electron beam column 10 includes an electron source 11 configured to provide an electron beam 3 (i.e., an electron beam). A potential can be applied to the electron source 11.

[0044] An electron source 11 is arranged in a first vacuum zone VB1, in which a first vacuum is created during operation. For example, the first vacuum is established by a first housing section 13, a second housing section 14, and a pump (not shown) that evacuates the vacuum zone VB1. The first housing section 13 is designed to be, for example, an electrical conductor, while the second housing section 14 is an electrical insulator.

[0045] The electron beam column 10 also includes a beam tube 15, which is arranged downstream of the electron source 11 along the propagation direction of the electron beam 3. In other words, the beam tube 15 is arranged between the electron source 11 and the working area 6. Figure 1 In the example shown, viewed along the central axis 2 of the electron beam column 10, the beam tube 15 extends from the housing section 14 into the interior of the objective lens 30. The beam tube 15 includes a tubular body having a first opening 15a at a first end and a second opening 15b at a second end. During operation, the electron beam 3 from the electron source 11 enters the interior 16 of the beam tube 15 through the first opening 15a, travels within the interior 16 of the beam tube 15 from the first opening 15a to the second opening 15b, and exits the interior 16 of the beam tube 15 through the second opening 15b.

[0046] An electric potential can be applied to the beam tube 15. During operation, the electric potential of the beam tube 15 and the electric potential of the electron source 11 are generated in such a way that an electric field is generated between the beam tube 15 and the electron source 11, which accelerates the electrons of the electron beam 3 from the electron source 11 to the beam tube 15.

[0047] During operation, the electron beam microscope 1 has a second vacuum region VB2 in the beam tube 15, in which a second vacuum is formed, which may be different from the first vacuum in the first vacuum region VB1. For example, the second vacuum region VB2 is established by the beam tube 15 and a pump (not shown) that evacuates the vacuum region VB2.

[0048] The electron beam column 10 also includes a focusing lens 21 configured to generate a magnetic field. The focusing lens 21 includes a magnetic core 22 for guiding the magnetic field and an excitation coil 23 for generating the magnetic field. During operation, current is supplied to the excitation coil 23, generating the magnetic field. The magnetic core 22 is designed to be substantially rotationally symmetric about the central axis 2. The magnetic core 22 is completely disposed outside the beam tube 15. The magnetic core 22 is disposed downstream of the first opening 15a of the beam tube 15 along the propagation direction of the electron beam 3. In other words, the magnetic core 22 is disposed between the electron source 11 and the objective lens 30.

[0049] During operation, the focusing lens 21 causes a change in the divergence angle of the electron beam 3 by focusing it. This allows the beam diameter of the electron beam 3 to be changed. In particular, the beam diameter of the electron beam 3 can be adapted to the effective range of the objective lens 30.

[0050] The electron beam column 10 also includes an objective lens 30, which is positioned downstream of the condenser lens 21 along the propagation direction of the electron beam 3. In other words, the objective lens 30 is positioned between the condenser lens 21 and the working region 6. The objective lens 30 is positioned at the second end of the beam tube 15. The objective lens 30 is configured to focus the electron beam 3 onto the working region 6. The sample 4 can be positioned in the working region 6, for example, on the sample holder 5. The working region 6 is located outside the electron beam column 10. Therefore, the objective lens 30 is configured to focus the electron beam 3 onto the sample 4.

[0051] although Figure 1 Not shown, but the electron beam microscope 1 also includes a vacuum chamber into which the electron beam 3 enters, and in which the sample 4 and the working area 6 are arranged.

[0052] For example, objective lens 30 includes a magnetic core 31 and an excitation coil 32. During operation, current is supplied to the excitation coil 32, thereby generating a magnetic field guided by the magnetic core 31. The magnetic field exits the magnetic core 31 through a gap 33 in the magnetic core 31 and is formed when properly excited, such that the magnetic field has a focusing effect on the electron beam 3.

[0053] The electron beam column 10 also includes a deflection system 35. The deflection system 35 is arranged along the central axis 2 and flush with the objective lens 30. The deflection system 35 is configured to deflect the electron beam 3 in the radial direction (i.e., laterally relative to the central axis 2) so as to direct the electron beam 3 to different positions in the working area 6, and therefore to different positions in the sample 4. Figure 1 In the example shown, the deflection system 35 includes two deflection units 36 and 37 formed by coils. Figure 1In the example shown, the coils of deflection units 36 and 37 are arranged between the beam tube 15 and the magnetic core 31 of the objective lens 30. The two deflection units 36 and 37 are arranged in a manner distributed along the central axis 2. During operation, current is supplied to the deflection units 36 and 37, thereby generating a magnetic field that deflects the electron beam 3 in the radial direction.

[0054] The electron beam column 10 also includes a terminal stop 38, which is arranged downstream of the beam tube 15 along the propagation direction of the electron beam 3 and has an aperture 39. In other words, the terminal stop 38 is arranged between the beam tube 15 and the working region 6. During operation, the electron beam 3 passes through the aperture 39 and enters the vacuum chamber. A potential can be applied to the terminal stop 38. During operation, the potential of the terminal stop 38 and the potential of the beam tube 15 are generated in such a way that an electric field acting on the electron beam 3 is generated between the terminal stop 38 and the beam tube 15. However, the terminal stop 38 and the beam tube 15 can alternatively have the same potential. Figure 1 In the example shown, the terminal stop 38 is formed by the magnetic core 31. However, this is merely an example. The terminal stop 38 may be discrete from and electrically insulated from the magnetic core 31.

[0055] The electron beam microscope 1 also includes a sample holder 5 on which the sample 4 can be positioned. A potential can be applied to the sample holder 5 or the sample 4. The application of a potential to the sample 4 is described herein as an example.

[0056] The voltage between the potential of sample 4 and the potential of electron source 11 (i.e., the voltage between sample 4 and electron source 11) is called the accelerating voltage U0. The accelerating voltage U0 (crucially) determines the kinetic energy of the electrons incident on sample 4 by electron beam 3. This kinetic energy is also called the landing energy LE and is calculated as LE = e·U0, where e is the absolute value of the electron elemental charge. During operation, the potentials of sample 4 and electron source 11, and therefore the accelerating voltage U0, are selected and set such that electron beam 3 is accelerated to sample 4.

[0057] The electron beam microscope 1 also includes a detector 41, which is configured to output a detection signal based on electrons incident on a detection region 42 of the detector 41. Figure 2 A schematic diagram of a portion of the electron beam column 10 and the detector 41 is shown. Figure 2As shown, detector 41 includes a scintillator 44, a light guide 45, and a photodetector 46. The detection region 42 of detector 41 is the surface of the scintillator 44. The detection region 42 of detector 41 is arranged within the interior 16 of the beam tube 15. The scintillator 44 is arranged (at least partially) within the interior 16 of the beam tube 15. The detection region 42 and the scintillator 44 are arranged along the propagation direction of the electron beam 3 between the first opening 15a and the second opening 15b of the beam tube 15. Specifically, the detection region 42 and the scintillator 44 are arranged along the central axis 2 of the electron beam column 10 between the first opening 15a of the beam tube 15 and the location of maximum intensity of the field generated by the objective lens 30. The detection region 42 at least partially surrounds (i.e., partially or completely surrounds) a gap 43 through which the electron beam 3 passes when the electron beam column 10 is in operation. The detection region 42 surrounds the gap 43 (partially or completely) in a circumferential direction about the central axis 2. For example, the gap 43 is formed by an opening extending through the detection region 42. Alternatively, the detection region 42 may have a rift, for example, achieved by a gap extending through the detection region 42 along the central axis 2.

[0058] The detection area 42 can face the working area 6. The detection area 42 of the detector 41 is arranged such that electrons (secondary electrons and backscattered electrons) emitted by the sample 4 can be incident on the detection area 42.

[0059] Scintillator 44 is configured to convert electrons 50 emitted by sample 4 and incident on detection region 42 or scintillator 44 into light 47. Light guide 45 is configured to guide light 47 to photodetector 46. In the example shown, light guide 45 penetrates the beam tube 15. Accordingly, light 47 emitted by scintillator 44 propagates from inside 16 to outside electron beam column 10 via light guide 45. Photodetector 46 is configured to detect the light 47 supplied to photodetector 46 by light guide 45. For this purpose, light guide 45 is connected to photodetector 46. However, this is merely an example. Detector 41 only needs to include scintillator 44 and photodetector 46. Further details related to detection will be described below.

[0060] The detection signal of detector 41 is generated by photodetector 46. The detection signal of detector 41 is transmitted through... Figure 1 The signal line 64, shown schematically, transmits to the controller 61.

[0061] Scintillator 44 has an energy-dependent conversion efficiency. This means that the conversion efficiency varies depending on the incident energy of the electron. For example, from a first energy value to a second energy value (which is at least 100 eV greater than the first energy value), the conversion efficiency of scintillator 44 is less than the first conversion efficiency value, and from a third energy value (which is at least 1 keV and at most 10 keV greater than the first energy value) to a fourth energy value (which is at least 1 keV greater than the third energy value), the conversion efficiency of the scintillator is greater than the second conversion efficiency value, which is at least 30% greater than the first conversion efficiency value. For example, the conversion efficiency of scintillator 44 varies by at least 30% over an energy range with a width of at least 5 keV.

[0062] No electric or magnetic field is generated between the sample 4 and the scintillator 44 of the detector 41 to repel electrons 50 emitted by the sample 4 from the scintillator 44. Specifically, the potentials of the sample 4, the beam tube 15, and the terminal aperture 38 are set such that electrons emitted by the sample 4 are not prevented from entering the second opening 15b of the beam tube 15. In particular, no gate electrode is arranged between the second end of the beam tube 15 and the scintillator 44 of the detector 41 to prevent electrons emitted by the sample 4 from propagating in the direction of the scintillator 44. Therefore, the difference between the incident energy of the electrons 50 emitted by the sample 4 when incident on the scintillator 44 and the emission energy of these electrons is essentially limited only by the voltage between the beam tube 15 and the sample 4.

[0063] like Figure 1 As shown, the electron beam microscope 1 also includes a driver system 62. The driver system 62 is configured to generate and supply the potentials, voltages, and currents required to operate the components of the electron beam microscope 1. Specifically, the driver system 62 generates potentials for the electron source 11, for the beam tube 15, for the terminal aperture 38, for the sample 4, and for the currents used to operate the objective lens 30, the condenser lens 21, and the deflection system 35. Therefore, the driver system 62 also generates an accelerating voltage U0 and a voltage between the beam tube 15 and the sample 4 (beam tube voltage).

[0064] For this purpose, the driver system 62 may include one or more voltage and current sources that generate the potential, voltage, and current required to operate the components of the electron beam microscope 1. Line 63 schematically represents all the electrical lines required to supply the potential, voltage, and current from the driver system 62 to the individual components of the electron beam microscope 1.

[0065] The electron beam microscope 1 also includes a controller 61 for controlling the electron beam microscope 1. The controller 61 controls the electron beam column 10, specifically via a control driver system 62. The controller 61 can thus set the individual potentials, voltages, and currents required to operate the components of the electron beam microscope 1 in a targeted manner, and therefore can control the operation and effects of the components of the electron beam microscope 1. The potentials, voltages, and currents intended to be generated by the driver system 62 can be represented in the controller 61 by corresponding operating parameters. For example, the values ​​of the operating parameters define the values ​​of the potentials, voltages, or currents.

[0066] The controller 61 can change the operation and effect of the components of the electron beam microscope 1 by changing the values ​​of the corresponding operating parameters. The values ​​of the operating parameters can be stored in the memory of the controller 61 and can be changed by the processor of the controller 61. A set of operating parameter values ​​sufficient to operate the electron beam microscope 1 defines the operating mode of the electron beam microscope 1. Multiple sets of operating parameter values ​​defining various different operating modes can be stored in the memory of the controller 61. The controller 61 can selectively operate the electron beam microscope 1 in one of multiple operating modes accordingly. For this purpose, the controller 61 loads the values ​​of the operating parameters for the selected operating mode from the memory and instructs the driver system 62 to generate the potential, voltage, and current required to operate the components of the electron beam microscope 1 according to the loaded operating parameter values. The user can change the values ​​of the operating parameters for the operating mode via the input device 65.

[0067] Controller 61 can be configured to perform the methods described herein.

[0068] The electron beam microscope 1 also includes at least one input device 65 and at least one output device 66. Examples of the input device 65 include a keyboard, mouse, etc. Examples of the output device 66 include a display device, speaker, etc. The input device 65 is connected to a controller 61 and configured to receive input from an operator or some other external device, and to transmit the received input to the controller 61. The output device 66 is connected to the controller 61 and configured to output data provided by the controller 61 to the operator or some other external device.

[0069] Methods for operating an electron beam microscope

[0070] The following text is for reference only. Figure 3 A method for operating an electron beam microscope 1 is described.

[0071] To record the first image (specifically the backscattered electron image) of sample 4, the method includes steps S1 and S2.

[0072] In step S1, the accelerating voltage U0 between the electron source 11 and the sample 4 is set to a value suitable for accelerating the electron beam 3 to the sample 4. In addition, the voltage (beam tube voltage) between the beam tube 15 and the sample 4 is set to a first value U1 suitable for accelerating the electrons 50 emitted by the sample 4 to the beam tube 15 (and thus to the scintillator 44).

[0073] In step S2, performed after step S1, a first image of sample 4 is recorded using electron beam microscope 1 with the settings taken in step S1. This means that the first image is recorded when a set accelerating voltage U0 is applied and a beam tube voltage is applied according to a first value U1. Recording the first image includes: sequentially pointing electron beam 3 to multiple different positions on sample 4; and generating a detection signal by means of detector 41. Controller 61 associates each position with the detection signal and stores this information, thereby obtaining the first image.

[0074] During the recording of the first image in step S2, sample 4 emits secondary electrons and backscattered electrons. These secondary electrons and backscattered electrons are accelerated by an electric field whose intensity is set by the beam tube voltage and enter the interior 16 of the beam tube 15 through the terminal aperture 38 and the second opening 15b of the beam tube 15. Inside the interior 16, the secondary electrons and backscattered electrons further propagate and incident on the detection region 42 of the detector 41, i.e., on the surface of the scintillator 44.

[0075] In the scintillator 44, incident secondary electrons and backscattered electrons are converted into light 47, and the generated light is detected by a photodetector 46, which generates a detection signal based on the detected light 47. The detection signal generated by the detector 41 during the recording of the first image consists essentially of two contributions: a first contribution generated by backscattered electrons and a second contribution generated by secondary electrons. The setting value of the beam tube voltage affects the value of the backscattered electron-secondary electron contribution ratio, i.e., the ratio of the first contribution to the second contribution. The value of the backscattered electron-secondary electron contribution ratio during the recording of the first image is referred to as V1.

[0076] To record a second image (specifically a secondary electron image) of sample 4, the method includes steps S3 and S4.

[0077] In step S3, performed after step S2, the accelerating voltage U0 is maintained and the beam tube voltage is set to a second value U2. The first value U1 and the second value U2 of the beam tube voltage are different from each other. To change the beam tube voltage, the potential of the beam tube 15 can be changed. The potential of the electron source 11 and the potential of the sample 4 can remain unchanged. Since the beam tube voltage is changed to value U2, the strength of the electric field between the beam tube 15 and the sample 4 is set to different values ​​suitable for accelerating the electrons 50 emitted by the sample 4 to the beam tube 15.

[0078] In step S4, performed after step S3, a second image of sample 4 is recorded using electron beam microscope 1 with the settings taken in step S3. This means that the second image is recorded when the set accelerating voltage U0 is applied and the beam tube voltage is applied according to the second value U2. Otherwise, the recording of the second image is performed in the same manner as the recording of the first image.

[0079] During the recording of the second image in step S4, sample 4 emits secondary electrons and backscattered electrons. These secondary electrons and backscattered electrons are accelerated by an electric field whose intensity is set by the beam tube voltage, and enter the interior 16 of the beam tube 15 through the terminal aperture 38 and the second opening 15b of the beam tube 15. Inside the interior 16, the secondary electrons and backscattered electrons further propagate and are incident on the detection region 42 of the detector 41.

[0080] Due to the difference between the first value U1 and the second value U2 of the beam tube voltage, a value V2, which is different from the value V1, is obtained for the backscattered electron-secondary electron contribution ratio. Therefore, the second image is generated based on the value V2 of the backscattered electron-secondary electron contribution ratio, which is different from the value V1 of the backscattered electron-secondary electron contribution ratio when the first image was recorded.

[0081] Specifically, the first value U1 and the second value U2 of the beam tube voltage are set such that the value V1 of the backscattered electron-secondary electron contribution ratio when recording the first image is greater than the second value V2 of the backscattered electron-secondary electron contribution ratio when recording the second image. For example, the first value U1 and the second value U2 of the beam tube voltage are selected such that the first value V1 is at least 1.2 times the second value V2, that is, V1 / V2 ≥ K, where the value of K is at least 1.2. However, this is only an example, and the value of K can be at least 1.5, at least 2, at least 5, or at least 10. Therefore, the first image can be referred to as a backscattered electron image, and the second image can be referred to as a secondary electron image.

[0082] In this example, the backscattered electron image (first image) is recorded before the secondary electron image (second image). However, this is just an example, and the secondary electron image can be recorded before the backscattered electron image.

[0083] Another embodiment of the method

[0084] According to one embodiment of the method, in steps S1 and S3, a first value U1 and a second value U2 of the bundle tube voltage are selected such that the conversion efficiency difference D1 when recording the first image is greater than the conversion efficiency difference D2 when recording the second image. (This reference...) Figure 4 and Figure 5 Let me explain in detail.

[0085] Figure 4An exemplary energy-dependent conversion efficiency W(E) and the energy spectrum of the incident energy of electron 50 on scintillator 44 when the first image is recorded in step S2 are shown. Figure 5 The energy-dependent conversion efficiency W(E) and the energy spectrum of the incident energy of electron 50 on scintillator 44 when the second image is recorded in step S4 are shown.

[0086] Regarding the energy-dependent conversion efficiency W, Figure 4 and Figure 5 The horizontal axis represents the incident energy, i.e., the kinetic energy of electron 50 when it is incident on scintillator 44. The vertical axis represents the conversion efficiency W of scintillator 44 as a function of incident energy. The conversion efficiency W of scintillator 44 at a specific energy represents the average number of photons generated by scintillator 44 when electron 50 with a specific energy is incident on scintillator 44. The conversion efficiency W can have values ​​between 0 and 1. High conversion efficiency means that a single electron is converted into a large number of photons. In contrast, low conversion efficiency means that a single electron is converted into a small number of photons.

[0087] like Figure 4 The energy spectrum of the incident energy of electrons 50 on scintillator 44 during the recording of the first image, as shown, comprises two components: the curve indicated by reference numeral SE represents the number of secondary electrons incident on scintillator 44 during the recording of the first image, the number of which varies depending on the incident energy of the secondary electrons on scintillator 44; the curve indicated by reference numeral RE represents the number of backscattered electrons incident on scintillator 44 during the recording of the first image, the number of which varies depending on the incident energy of the backscattered electrons on scintillator 44.

[0088] The incident energy of the secondary electron on the scintillator 44 is essentially the sum of the emission energy of the secondary electron (approximately 0 V to 100 V) and the energy absorbed as a result of acceleration in the electric field generated by the bundle tube voltage between the sample 4 and the bundle tube 15 (i.e., e·U1, where e is the absolute value of the elementary charge of the electron).

[0089] The incident energy of backscattered electrons on scintillator 44 is essentially the sum of the emission energy of the backscattered electrons (which is essentially equal to the landing energy of the electrons in electron beam 3 on sample 4 and essentially corresponds to e·U0) and the energy absorbed as a result of acceleration in the electric field generated by the beam tube voltage between sample 4 and beam tube 15 (i.e., e·U1, where e is the absolute value of the elementary charge of the electron). Therefore, the incident energy of backscattered electrons on scintillator 44 roughly corresponds to the product of the elementary charge of the electron and the voltage between beam tube 15 and electron source 11.

[0090] The conversion efficiency difference represents the difference between the conversion efficiency W(E1) of scintillator 44 at the first energy E1 and the conversion efficiency W(E2) of scintillator 44 at the second energy E2, i.e., W(E1) - W(E2). The first energy E1 is defined as the product of the electron element charge and the voltage between the beam tube 15 and the electron source 11. Therefore, the first energy is the typical incident energy of backscattered electrons on scintillator 44 during image recording. The second energy E2 is defined as the product of the electron element charge and the voltage between the beam tube 15 and the sample 4 (beam tube voltage). Therefore, the second energy is the typical incident energy of secondary electrons on scintillator 44 during image recording.

[0091] like Figure 4 As shown, the first energy E1 during the recording of the first image is e · (U0 + U1), and the second energy E2 during the recording of the first image is e · U1, where e is the absolute value of the elementary charge of the electron. The conversion efficiency difference during the recording of the first image is: .

[0092] like Figure 5 As shown, the first energy E1 when recording the second image is e · (U0 + U2), and the second energy E2 when recording the second image is e · U2, where e is the absolute value of the elementary charge of the electron. The value of the conversion efficiency difference when recording the second image is: .

[0093] As from Figure 4 and Figure 5 The comparison shows that the conversion efficiency difference D1 when recording the first image is greater than the conversion efficiency difference D2 when recording the second image. This means that, by appropriately selecting the beam tube voltage when recording the first image, the efficiency of backscattered electrons being converted into light by the scintillator 44 is higher than that of secondary electrons compared to the conversion when recording the second image. Therefore, the first image can be referred to as the backscattered electron image, and the second image can be referred to as the secondary electron image.

[0094] According to another embodiment, the first value U1 and the second value U2 of the tube voltage are selected such that the conversion efficiency difference D1 when recording the first image is at least 1.2 times the conversion efficiency difference D2 when recording the second image. This is merely an example. The value D1 can be at least 1.5 times, at least 2 times, or at least 3 times the value D2.

[0095] According to another embodiment, the first value U1 and the second value U2 of the beam tube voltage are selected such that the conversion efficiency ratio W1 when recording the first image is greater than the conversion efficiency ratio W2 when recording the second image. The conversion efficiency ratio represents the ratio of the conversion efficiency W(E1) at the first energy E1 to the conversion efficiency W(E2) at the second energy E2. Therefore, value W1 is the ratio of the conversion efficiency W(E1) at the first energy E1 when recording the first image to the conversion efficiency W(E2) at the second energy E2 when recording the first image; and value W2 is the ratio of the conversion efficiency at the first energy E1 when recording the second image to the conversion efficiency at the second energy E2 when recording the second image.

[0096] Specifically, the first value U1 and the second value U2 of the tube voltage are selected such that the conversion efficiency ratio W1 when recording the first image is at least 1.5 times, particularly at least 2 times or at least 5 times, the conversion efficiency ratio W2 when recording the second image.

[0097] exist Figure 4 In the example shown, the conversion efficiency W(E1) at the first energy E1 when recording the first image is approximately 80%, and the conversion efficiency W(E2) at the second energy E2 when recording the first image is approximately 5%. Therefore, the value W1 is approximately 80% / 5% = 16. Figure 5 In the example shown, the conversion efficiency W(E1) at the first energy E1 is approximately 90% when recording the second image, and the conversion efficiency W(E2) at the second energy E2 is approximately 70% when recording the second image. Therefore, the value W2 is approximately 90% / 70% ≈ 1.29. Figure 4 and Figure 5 In the example shown, the value W1 is therefore approximately (≈ 16 / 1.29) 12 times the value W2.

[0098] According to another embodiment, the first value U1 of the beam tube voltage is selected such that the conversion efficiency ratio W1 during recording of the first image is at least 1, preferably at least 1.5, more preferably at least 2 or at least 3. Therefore, the efficiency of backscattered electrons in converting into light is higher than that of secondary electrons.

[0099] According to another embodiment, recording the first image and recording the second image are performed directly and sequentially. This means that in Figure 3 In step S2, the first image is recorded and... Figure 3 The duration between recording the second image in step S4 is relatively short. For example, the duration is less than 2 minutes, especially less than 1 minute or less than 30 seconds.

[0100] According to another embodiment, recording the first image and recording the second image are performed repeatedly. Figure 3An arrow is shown from step S4 to step S1, indicating that the method can be repeated starting from step S1 after step S4. The time interval between recording the second image in step S4 and subsequently recording the first image in step S2 can be relatively short. For example, the duration is less than 2 minutes, particularly less than 1 minute or less than 30 seconds.

[0101] According to another embodiment, the accelerating voltage U0 is selected such that the electron beam 3 is accelerated to the sample 4, and the first value U1 and the second value U2 of the beam tube voltage are selected such that the electrons 50 emitted by the sample 4 are accelerated from the sample 4 to the beam tube 15. Therefore, the electrons of the electron beam 3 are incident on the sample 4, and thus the electrons 50 emitted by the sample 4 are accelerated from the sample 4 in the direction of the scintillator 44.

[0102] According to another embodiment, the first value U1 and the second value U2 of the beam tube voltage are greater than 500 V. This means that the accelerating voltage of the electrons 50 emitted by the sample 4 during the recording of the first and second images is at least 500 V in the direction of the scintillator 44.

[0103] According to another embodiment, the accelerating voltage U0 is greater than 500 V and less than 10 kV. This means that the landing energy of electrons from electron beam 3 onto sample 4 is at least 500 V and at most 10 keV.

[0104] According to another embodiment, the method further includes displaying the first image and the second image by means of a display device, particularly displaying them simultaneously and / or side by side. The display device is an example of an output device 65. Therefore, the operator can view the recorded first image and the recorded second image and compare them with each other.

[0105] According to another embodiment, the method further includes automatically setting the current supplied to the objective lens 30 by the driver system 62 based on the current value of the beam tube voltage. Therefore, in the event of a change in the beam tube voltage, the focusing of the electron beam 3 on the sample 4 is adapted such that the electron beam 3 remains focused on the sample 4.

[0106] List of reference numerals

[0107] 1. Electron Beam Microscope

[0108] 2. Central axis

[0109] 3 electron beam

[0110] 4 samples

[0111] 5 Sample Holders

[0112] 6 work areas

[0113] 10 electron beam column

[0114] 11 electronic sources

[0115] Shell sections 13 and 14

[0116] 15 bundled tubes

[0117] The first opening of the 15a bundle tube

[0118] The second opening of the 15b bundle tube

[0119] 16 Internal

[0120] 21 Converging Lens

[0121] 22 magnetic cores

[0122] 23 Excitation Coil

[0123] 30 objective lens

[0124] 31 magnetic core

[0125] 32 excitation coils

[0126] 33 gap

[0127] 35 deflection system

[0128] 36 and 37 deflection units

[0129] 38 terminal aperture

[0130] 39 aperture

[0131] 41 detectors

[0132] 42 detection areas

[0133] 43 gaps

[0134] 44 scintillators

[0135] 45 optical guide

[0136] 46 photodetectors

[0137] 47 light

[0138] 50 electrons emitted by the sample

[0139] 61 controller

[0140] 62 drive system

[0141] Lines 63 and 64

[0142] 65 Input Device

[0143] 66 Output device.

Claims

1. A method for operating an electron beam microscope (1) comprising an electron source (11) and a beam tube (15), in, The method includes: When an accelerating voltage (U0) is applied between the electron source (11) and the sample (4) and a bundle tube voltage, which is the voltage between the bundle tube (15) and the sample (4) is applied according to a first value (U1), a first image of the sample (4) is recorded; and When the accelerating voltage (U0) is applied between the electron source (11) and the sample (4) and the beam tube voltage is applied according to the second value (U2), a second image of the sample (4) is recorded; The recording of the first image and the second image, in their respective cases, includes: sequentially pointing an electron beam (3) provided by the electron source (11) and propagating through the interior (16) of the beam tube (15) to multiple different locations on the sample (4), and generating a detection signal by means of a detector comprising a scintillator (44) and a photodetector (46), the scintillator being arranged in the interior (16) of the beam tube (15) for converting electrons (50) emitted by the sample (4) into light (47), and the photodetector being used to generate the detection signal based on the light (47) generated by the scintillator (44); The first value (U1) and the second value (U2) of the beam tube voltage are different from each other and are selected such that the backscattered electron-secondary electron contribution ratio (V1) when recording the first image is greater than the backscattered electron-secondary electron contribution ratio (V2) when recording the second image. The backscattered electron-secondary electron contribution ratio indicates the ratio of the contribution of backscattered electrons to the detection signal to the contribution of secondary electrons to the detection signal when recording a specific image. The secondary electron is an electron emitted by the sample (4) with an energy of up to 100 eV, and the backscattered electron is an electron emitted by the sample (4) with an energy that differs from the product of the electron elemental charge and the accelerating voltage by up to 500 eV.

2. The method according to claim 1, wherein, The first value (U1) and the second value (U2) of the tube voltage are selected such that the value (V1) of the backscattered electron-secondary electron contribution ratio when recording the first image is at least 1.2 times the value (V2) of the backscattered electron-secondary electron contribution ratio when recording the second image.

3. The method according to claim 1 or 2, in, The first value (U1) and the second value (U2) of the tube voltage are selected such that the value of the conversion efficiency difference (D1) when recording the first image is greater than the value of the conversion efficiency difference (D2) when recording the second image. The conversion efficiency difference indicates the difference between the conversion efficiency (W) of the scintillator (44) at the first energy (E1) and the conversion efficiency (W) of the scintillator (44) at the second energy (E2). Wherein, the first energy (E1) is the product of the electron element charge and the voltage between the tube bundle (15) and the electron source (11), and the second energy (E2) is the product of the electron element charge and the tube bundle voltage.

4. The method according to claim 3, wherein, The first value (U1) and the second value (U2) of the tube voltage are selected such that the value of the conversion efficiency difference (D1) when recording the first image is at least 1.2 times the value of the conversion efficiency difference (D2) when recording the second image.

5. The method according to any one of claims 1 to 4, in, The first value (U1) and the second value (U2) of the tube voltage are selected such that the conversion efficiency ratio (W1) when recording the first image is greater than the conversion efficiency ratio (W2) when recording the second image. The conversion efficiency ratio indicates the ratio of the conversion efficiency (W) of the scintillator (44) at the first energy (E1) to the conversion efficiency (W) of the scintillator (44) at the second energy (E2). Wherein, the first energy (E1) is the product of the electron element charge and the voltage between the tube bundle (15) and the electron source (11), and the second energy (E2) is the product of the electron element charge and the tube bundle voltage.

6. The method according to claim 5, wherein, The first value (U1) and the second value (U2) of the tube voltage are selected such that the conversion efficiency ratio (W1) when recording the first image is at least 1.5 times the conversion efficiency ratio (W2) when recording the second image.

7. The method according to any one of claims 1 to 6, in, The first value (U1) of the tube voltage is selected such that the conversion efficiency ratio (W1) during recording of the first image is at least 1. The conversion efficiency ratio indicates the ratio of the conversion efficiency (W) of the scintillator (44) at the first energy (E1) to the conversion efficiency (W) of the scintillator (44) at the second energy (E2). Wherein, the first energy (E1) is the product of the electron element charge and the voltage between the tube bundle (15) and the electron source (11), and the second energy (E2) is the product of the electron element charge and the tube bundle voltage.

8. The method according to any one of claims 3 to 7, wherein, The conversion efficiency (W) at a specific energy represents the average number of photons generated by the scintillator (44) when an electron (50) of that specific energy is incident on the scintillator (44).

9. The method according to any one of claims 1 to 8, wherein, No electric or magnetic field is generated between the sample (4) and the scintillator (44) to repel the electrons (50) emitted by the sample (4) from the scintillator (44).

10. The method according to any one of claims 1 to 9, wherein, The recording of the first image and the recording of the second image are executed directly and sequentially.

11. The method according to any one of claims 1 to 10, in, Recording the first image and recording the second image are part of a sequence that is repeated.

12. The method according to any one of claims 1 to 11, further comprising: The current supplied to the objective lens (30) of the electron beam microscope (1) is automatically set based on the current value of the tube voltage.

13. The method according to any one of claims 1 to 12, in, The accelerating voltage (U0) is selected such that the electron beam (3) is accelerated to the sample (4), and The first value (U1) and the second value (U2) of the tube voltage are selected such that the electrons (50) emitted by the sample (4) are accelerated from the sample (4) to the tube (15).

14. The method according to any one of claims 1 to 13, wherein, The first value (U1) and the second value (U2) of the tube voltage are greater than 500 V.

15. The method according to any one of claims 1 to 14, wherein, The accelerating voltage (U0) is greater than 500 V and less than 10 kV.

16. The method according to any one of claims 1 to 15, further comprising: The first image and the second image are displayed side by side simultaneously by means of a display device (65).

17. An electron beam microscope (1) for recording images of a sample (4), comprising: An electron source (11) is configured to provide an electron beam (3); A beam tube (15) surrounds an interior (16) in which the electron beam (3) propagates during operation; A deflection system (35) is configured to deflect the electron beam (3) laterally relative to the propagation direction of the electron beam (3); The detector (41) includes a scintillator (44) and a photodetector (46), wherein the scintillator (44) is disposed inside (16) of the beam tube (15) and is configured to convert electrons (50) emitted by the sample (4) and incident on the scintillator (44) into light (47), and wherein the photodetector (46) is configured to detect the light (47) generated by the scintillator (44). A driver system (62) configured to apply an accelerating voltage (U0) between the electron source (11) and the sample (4) and to apply variablely adjustable voltages (U1, U2) between the beam tube (15) and the sample (4); and A controller (61) configured to perform the method according to any one of claims 1 to 16.

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