Charged particle beam device, and method of adjusting charged particle beam device

Abstract

In order to provide a charged particle beam device with which EELS and energy filter imaging functions are both achieved by means of a simple slit mechanism, and a method for adjusting the charged particle beam device, there is provided a charged particle beam device that comprises: a spectroscope that performs energy spectroscopy on a charged particle beam that has passed through a sample; a first lens group that focuses the dispersed charged particle beam; and a slit with which the focused charged particle beam is formed as a color dispersion surface and through which a part of the energy passes, wherein the first lens group is controlled so that the color dispersion surface of the charged particle beam is variable in an X direction and a Y direction when the direction of color dispersion on the slit surface is the X direction and the direction perpendicular to the X direction is the Y direction. There is also provided a method for adjusting the charged particle beam device.

Description

Charged particle beam device and method for adjusting charged particle beam device

[0001] The present invention relates to a charged particle beam device and a method for adjusting a charged particle beam device.

[0002] In a transmission electron microscope (TEM), a charged particle beam is transmitted through a sample and the transmitted charged particle beam is observed. When the charged particle beam passes through the sample, the energy of inelastically scattered electrons that lose energy due to excitation of inner-shell electrons of specific elements is analyzed by spectroscopic analysis, allowing qualitative and quantitative analysis of the elements in the sample and analysis of the chemical bonding state.

[0003] There are two main analysis methods: EELS (Electron Energy Loss Spectroscopy): Obtaining the energy loss at a specific position in the sample as a spectrum. Energy Filter Imaging (hereinafter sometimes referred to as EF imaging): Obtaining an image of the sample (EF image) that contains only a specific loss energy.

[0004] Such an apparatus that realizes electron beam energy loss spectroscopy in combination with a TEM is called an energy filter optical system, and in particular, one that is placed after the TEM housing is called a post-column energy filter.

[0005] Since the EELS spectrum and the EF image are complementary, it is desirable that the same charged particle beam device be equipped with an optical system that can perform both spectrum acquisition and imaging.

[0006] Patent Document 1 discloses a technique for changing the optical conditions at the slit plane for spectrum acquisition and EF image acquisition in a post-column energy filter optical system that can achieve both spectrum acquisition and imaging, in order to acquire EELS spectra over a wider energy range.

[0007] Japanese Patent Application Laid-Open No. 2017-092025

[0008] In energy filter imaging, the electron beam that has passed through the sample is deflected by a prism and then focused on a slit plane to form a color-dispersed spot on the slit plane at a different position for each energy. A slit with an opening perpendicular to the color dispersion is used to selectively pass only specific energies, and only the electrons that have passed through the slit are used to form an image again on the detection plane, obtaining an EF image formed by transmitted electrons with only a specific loss energy range.

[0009] In the charged particle beam device described in Patent Document 1, the chromatic dispersion spot width on the slit plane is fixed, and the passing energy width is selected by adjusting the slit opening width. This method requires precise control of the slit opening and closing, which can lead to a complex slit mechanism, a decrease in throughput when conditions are changed, and a corresponding decrease in usability.

[0010] An object of the present invention is to provide a charged particle beam device that is capable of performing highly accurate energy filter imaging using a simple slit mechanism, and a method for adjusting a charged particle beam device.

[0011] The present invention has the following configuration to achieve the above object. a first lens group that converges the dispersed charged particle beam; a slit through which the converged charged particle beam is formed as a chromatic dispersion plane and through which a portion of the energy of the beam passes; a second lens group that diverges the passed charged particle beam; a detector that forms an image of the diverged charged particle beam and detects the formed image; and a controller that controls at least one of the charged particle source, the electromagnetic lens group, the spectrometer, the first lens group, the slit, the second lens group, and the detector, wherein the controller controls the first lens group so that the charged particle beam changes the chromatic dispersion plane in the X direction and the Y direction when the direction of chromatic dispersion at the slit plane is the X direction and the direction perpendicular to the X direction is the Y direction.

[0012] According to the present invention, it is possible to provide a charged particle beam device that is capable of performing highly accurate energy filter imaging using a simple slit mechanism, and a method for adjusting a charged particle beam device.

[0013] Schematic diagram of the main parts of an electron beam energy spectroscopy instrument. A diagram explaining the principles of spectrum acquisition and EF imaging. A schematic explanatory diagram of the electron optical system of an electron beam energy spectroscopy instrument. A diagram explaining a method of selectively passing only specific energies. A diagram showing the change in aberration when measured using an instrument in which only the amount of chromatic dispersion of the spot is adjusted. A diagram explaining a study of changing the focus condition at the slit plane. A diagram showing the results when defocused in the Y direction. A diagram showing an example of controlling the Y direction width with respect to the selected energy width. A diagram showing the configuration of an embodiment using a transmission electron microscope and an energy filter. A flowchart for acquiring an EF image using Y direction width adjustment. A flowchart for acquiring an EF image including correction according to the Y direction width amount. A flowchart for correcting the parameters of control equation (1).

[0014] Hereinafter, an embodiment of the present invention will be described with reference to the drawings.

[0015] The following describes an example of an apparatus that uses an electron beam as a charged particle beam. The present invention can also be applied to an apparatus that uses charged particles such as ions as the charged particle beam and observes and analyzes a sample. FIG. 1 is a schematic diagram of the main components of an electron beam energy spectroscopy apparatus according to an embodiment of the present invention. A charged particle beam (the dashed dot in the figure indicates the optical axis of the charged particle beam) emitted from a charged particle beam source 10 is subjected to an energy dispersion effect by a spectrometer 15, and then a charged particle beam energy loss spectrum is formed on an energy-selecting slit 19 (sometimes simply referred to as a "slit").

[0016] Two electromagnetic lens groups 12 and 13 are arranged upstream of the spectrometer 15, and a first lens group 14 is arranged between the spectrometer 15 and an energy-selecting slit 19. The electron beam is energy-dispersed on the energy-selecting slit 19 by the spectrometer 15, and an electron beam energy loss spectrum is formed on the energy-selecting slit 19 by the quadrupole lens action of the first lens group 14. The energy-selecting slit 19 has the role of selecting only the electron beam within a desired energy width and allowing the electron beam to pass through a second lens group 20 arranged downstream of the energy-selecting slit 19.

[0017] The detector 16 generally uses a two-dimensional sensor such as a CCD or C-MOS to obtain both a charged particle beam image and a spectral image, but a sensor for obtaining a spectrum may also be provided separately. For example, a one-dimensional sensor consisting of 1024 channels can be used to detect the intensity of the electron beam incident on each channel, thereby obtaining an electron beam energy loss spectrum.

[0018] Here, the principle of obtaining a spectrum of energy loss of electrons transmitted through a sample and imaging using a TEM will be explained with reference to FIG.

[0019] 2(a) shows a case where energy loss at a specific position in a sample is acquired as a spectrum. While viewing the two-dimensional TEM image detected by the detector 16, the electromagnetic lens group 12 (converging lens) and the electromagnetic lens group 13 (imaging lens) are adjusted so that the region (site) of interest in the sample is focused. The charged particle beam that passes through the region of interest is energy dispersed by a spectrometer (prism) according to its energy level (magnitude), and then focused by a first lens group 14 (a multipole lens such as a quadrupole lens) 14 so as to be focused on the energy-selecting slit 19. The charged particle beam that passes through the energy-selecting slit position is again focused by a second lens group 20 (a multipole lens such as a quadrupole lens) so as to be focused at the detector 16. Note that when acquiring energy loss as a spectrum, the energy-selecting slit 19 is not used. In the detector 16, the charged particle beam that has passed through the charged particle beam irradiation position on the sample is detected at positions aligned by energy, so by plotting energy (energy loss: Energy Loss (eV)) on the horizontal axis and the number of counts on the vertical axis, the energy loss due to substances contained in the observed portion can be visualized. In the example of Figure 2(a), peaks derived from carbon (C), sulfur (S), and nitrogen (N) are observed, which indicates that the observed sample region contains at least carbon, sulfur, and nitrogen.

[0020] Next, energy-filtered imaging will be described using FIG. 2( b). The electromagnetic lens group 12 is adjusted so that the charged particle beam is irradiated onto the observation field, or the observation region, in the sample where energy-filtered imaging is desired. The charged particle beam that has passed through the area where energy-filtered imaging is desired is converged to focus on the energy-selecting slit 19 surface, as in FIG. 2( a). Unlike in FIG. 2( a), an energy-selecting slit 19 is disposed on the energy-selecting slit 19 surface, and the opening position and width of the energy-selecting slit 19 are adjusted to allow only the energy to be observed to pass. The second lens group 20 is controlled so that the charged particle beam that has passed through the slit forms a transmission image of the sample on the detection surface of the detector 16. This allows only the area having the selected energy to be illuminated.

[0021] For example, by adjusting the opening position and width of the energy-selecting slit 19 so that the energy peak positions of carbon (C), sulfur (S), and nitrogen (N) found in FIG. 2(a) are transmitted, it is possible to switch and display the locations of carbon, sulfur, and nitrogen in the sample image detected by the detector 16. In the right diagram of FIG. 2(b), C, S, and N indicate the locations where carbon, sulfur, and nitrogen are contained, respectively. The lower right of the right diagram of FIG. 2(b) shows a transmitted electron beam image. By comparing this transmitted electron beam image with the image, it is possible to determine which elements are abundant in which structure.

[0022] Next, the principle of energy filter imaging will be explained using Figure 3. Figure 3 is a diagram illustrating the trajectory of an electron beam during imaging. An electron beam that has passed through a sample is deflected by a prism and then focused onto a slit plane. This forms chromatic dispersion spots (different energies, i.e., different frequencies, of the charged particle beam) at different positions on the slit plane for each energy. A slit with an opening perpendicular to the chromatic dispersion is used to selectively pass only specific energies. Only electrons that have passed through the slit are used to form an image again on the detection plane of the detector 16. This makes it possible to obtain an EF image formed by transmitted electrons with only a specific loss energy range.

[0023] A method for selectively passing only specific energies and controlling the energy width to be passed will be described using Figure 4. Figure 4(a) shows a conventional method. The electron beam transmitted through the sample during imaging is controlled so that it has a shape that has chromatic dispersion in the slit opening direction at the slit plane. Note that the wavelength of an actual charged particle beam is not in the visible light range and therefore cannot be perceived as a "color" by humans. However, in Figure 4 and Figure 6 (described later), the chromatic dispersion, with red (long wavelength, i.e., low energy) at the left end and purple (short wavelength, i.e., high energy) at the right end, is represented by different densities of hatched dots.

[0024] The width of the chromatic dispersion spot on the slit surface is fixed, and the passing energy width is controlled by adjusting the slit opening width. The narrower the slit width, the smaller the passing area of ​​the spot in the chromatic dispersion direction, so the energy width passing through the slit (selected energy width) becomes narrower, and by widening the slit width, a wider energy band can be passed. This method is called the chromatic dispersion fixed method.

[0025] The fixed chromatic dispersion method requires precise control of the slit opening and closing. For example, the positional change in the chromatic dispersion direction on the slit due to energy differences is typically on the order of a few μm per 1 eV. Since filtering images require control of the passing energy in increments of at most 1 eV, and preferably in increments of 0.1 eV or less, the slit opening width must also be controlled with precision of less than a μm. Constructing a slit that meets these specifications requires a complex mechanism, which can increase costs and even reduce usability due to poor maintenance. Furthermore, there is often a trade-off between precise controllability of the opening width and drive speed, raising concerns about reduced observation throughput when conditions change.

[0026] In contrast, Figure 4(b) shows the fixed slit width method adopted by the present invention. This method fixes the slit opening width on the slit plane and selects the passing energy width by adjusting the amount of chromatic dispersion of the spot. This method allows for a simplification of the slit mechanism compared to conventional techniques. In addition, since there is no mechanical driving part, conditions can be changed very quickly. However, there is a concern that the trajectory of the electron beam changes as chromatic dispersion is adjusted, which may have adverse effects due to increased aberration (chromatic aberration: the focal position varies depending on the wavelength of the electron beam).

[0027] We confirmed the change in aberration when measuring with an apparatus that simply adjusted the amount of chromatic dispersion of the spot. Figure 5(a) shows the optical system used for the confirmation. The electron beam was focused at the slit plane in both the X- and Y-direction trajectories. The chromatic dispersion at the slit plane in this optical system was compared by calculating isochromaticity, an index that represents the energy shift of the EF image due to aberration. The results are shown in Figure 5(b). It can be seen that as the chromatic dispersion at the slit plane increases, the aberration increases and the isochromaticity deteriorates.

[0028] Conventionally, focusing in the Y direction on the slit plane was required as a constraint, which limited the electron trajectories that could be taken, and this is thought to be the reason why a significant change in the amount of chromatic dispersion on the slit plane inevitably resulted in a trajectory that increased aberrations.

[0029] In response to this, in the present invention, we considered changing the focus conditions at the slit plane to reduce this aberration. Specifically, by defocusing in the Y direction at the slit plane (shifting the focal position from the slit plane to make the focus softer), we achieved different electron trajectories incident on the prism and in each multipole lens group according to the desired amount of chromatic dispersion. We estimated the change in chromatic dispersion using this method and understood the impact of aberrations, and searched for optimal conditions. Figure 6(a) is a conceptual diagram of the trajectory of an electron beam in a pre-slit optical system according to an embodiment of the present invention. By adjusting the multipole lenses, the electron beam emitted from the spectrometer was focused in the X direction (the vertical direction in the upper diagram of Figure 6(a)) at the slit plane, and defocused only in the Y direction (the vertical direction in the lower diagram of Figure 6(a)).

[0030] FIG. 6( b) is a conceptual diagram comparing the electron beam spot shape on the slit plane under these conditions with that under conventional conditions. The left image in FIG. 6( b) is a conventional charged particle beam image on the slit plane. The image is also in focus in the Y direction (the vertical direction on the page), forming a thin spot. Ideally, the spot width in the Y direction on the slit plane under conventional focusing is close to zero, at most a few μm. In contrast, the right image shows the spot shape in this embodiment. By adjusting the quadrupole lens corresponding to the first lens group, the focus in the Y direction is loosened (defocused), and the spot width in the Y direction is controlled to be significantly larger.

[0031] We investigated the characteristics when the focus was shifted in the Y direction (also referred to as defocusing). Figure 7 shows the results of a comparison of the deviation in color isochromaticity between a conventional method and Y defocus control. When electronic trajectory control is performed to defocus the spot in the Y direction as in this embodiment, so as to reduce aberration, it is possible to suppress changes in color isochromaticity (vertical axis) relative to the amount of chromatic dispersion (horizontal axis) at the slit surface, and it can be seen that color isochromaticity is significantly improved compared to the conventional method, especially under conditions where color dispersion is large.

[0032] To improve this color matching, it is important to appropriately control the Y-direction width of the spot on the slit plane. To determine a trajectory with reduced aberration, it is necessary to change the Y-direction width of the spot according to the selected energy width, which is proportional to the reciprocal of the chromatic dispersion on the slit plane.

[0033] Ideally, the Y-direction width (Wy) is preferably controlled in accordance with the selected energy width (Ew), for example, by changing it in accordance with the following control formula (1).

[0034]

[0035] where dslit is the slit opening width, C ０ ~C ３ is a coefficient. Coefficient C ０ The coefficient C is equal to the energy width selected in the optimal trajectory when controlling with the conventional chromatic dispersion fixing method. １ ~C ３ is a proportionality coefficient for the order of the selected energy width Ew.

[0036] It is desirable to determine the coefficients of this control equation in advance by electron optical simulation. More preferably, it is desirable to obtain the optimum values ​​of the coefficients by performing additional measurements on an actual device. For example, by measuring the Y-direction width at the slit plane and correlating this with the aberration and chromatic isochromaticity measured under the same conditions, it becomes possible to precisely determine the coefficients of the control equation. Furthermore, the control equation may be a simple linear equation for the selected energy width Ew, as needed, or a control equation that takes higher orders into account may also be used.

[0037] For example, an example of controlling the Y-direction width relative to the selective energy width according to control formula (1) assuming a slit opening width of 10 μm is shown in FIG. 8 . To sufficiently reduce aberrations, it is necessary to vary the spot Y-direction width to a size on the order of millimeters. For example, in the selective energy range of 2 to 20 eV as shown in FIG. 8( a), the Y-direction width is controlled in the range of 0 to 10 mm. Since reducing aberrations in regions where the selective energy range is small is particularly important, if observation is desired over a selective energy range of at least 5 eV or less, the Y-direction width is controlled in the range of 1 mm or more, preferably 2 mm or more.

[0038] Furthermore, it is not necessary to control the Y-direction width in full accordance with the above formula, and a control method in which the Y-direction width is changed partially and stepwise according to the selected energy width may be used. For example, the range of the selected energy width may be divided into stages, and the Y-direction width may be controlled at a constant value in each stage. Figure 8(b) shows stepwise control of the Y-direction width when the slit opening width is 10 μm.

[0039] The range of the selective energy width is divided into sections of 2.5 eV or less, 2.5 to 5 eV, 5 to 10 eV, and 10 eV or more, and the average value of the Y-direction width obtained by the control formula is used to control the Y-direction width at a constant value within each section. In this case, it is desirable to divide the selective energy width section finer as the selective energy width becomes smaller. This is because regions with a smaller selective energy width are more sensitive to aberrations and have a larger amount of change in the optimal Y-direction width relative to the selective energy width.

[0040] The Y-direction width of these spots is controlled using multipole lenses placed before and after the prism in the energy filter optical system. In particular, it is desirable to control the trajectory using a quadrupole lens placed between the prism and the slit. This is because the incident trajectory onto the prism has a significant effect on aberrations in the optical system, and controlling the Y-direction width of the spot on the slit plane while keeping the incident trajectory onto the prism fixed makes it easier to control aberrations. However, this does not necessarily mean that adjustments cannot be made using the lens system in front of the prism, and changing the incident trajectory onto the prism as needed is permitted.

[0041] The above results can be summarized as follows: During EF imaging with TEM-EELS, by adjusting the electron beam spot on the slit to a shape that is defocused in the direction perpendicular to the direction of chromatic dispersion and controlling the filtering energy width, it is possible to reduce aberrations associated with changes in chromatic dispersion on the slit, which are a problem when controlling the filtering energy width by changing the electron trajectory, and it becomes possible to acquire high-quality EFTEM images even under conditions where the slit plane chromatic dispersion is large (i.e., the passing energy width is narrow). This makes it possible to reduce aberrations, especially under conditions where the slit plane chromatic dispersion is large (i.e., the passing energy width is narrow).

[0042] FIG. 9 shows the configuration of an embodiment in which the present invention is applied to a transmission electron microscope. The main components are described below. An electron beam (the dotted line in the figure indicates the optical axis of the electron beam) generated by an electron beam source 1 is converged by an objective lens 4 and irradiated onto a sample 5. The electron beam transmitted through the sample 5 is incident on an electron beam energy spectrometer (sometimes abbreviated as "spectrometer") 15 via an electromagnetic lens group 13. The energy of the electron beam is analyzed by an energy filter optical system including the electron beam energy spectrometer 15, and electron beam energy loss spectra are measured, element distribution images are observed, and so on. The energy filter optical system is composed of a multipole lens 40 located upstream of the spectrometer 15, a first lens group 14 and a second lens group 20 located downstream of the spectrometer 15, an electron beam detector (hereinafter sometimes abbreviated as "detector") 16 for detecting the energy-dispersed electron beam, and an energy-selecting slit (slit) 19.

[0043] The control device 21 includes a control unit 30 that controls the position of the electron beam on the sample, scans and moves the electron beam, controls the electron energy analysis conditions of the electron energy spectrometer 15, such as the excitation conditions, and the focusing conditions, magnification conditions, and aberration correction conditions of the electron energy loss spectrum, and calculates the electron energy loss spectrum detected by the electron detector 16. The control device 21 also includes a memory unit 27 that stores a database of elements to be measured and control parameters for various lenses such as the multipole lens 40, the electromagnetic lens group 13, and the first lens group 14, an input unit 31 through which the operator inputs elements to be measured, and an output unit 25 that displays the electron energy loss spectrum and element distribution image.

[0044] The operation of the control device 21 during spectrum measurement will be described below.

[0045] When the operator inputs the element to be observed using the input unit 31, the control unit 30 retrieves the corresponding element information from the database and controls various lenses, such as the multipole lens 40, the electromagnetic lens group 13, the first lens group 14, and the spectrometer 15, in accordance with the element-specific measurement conditions contained in the element information, causing an electron beam within an energy range including the element-specific energy to be incident on the electron beam detector 16. The electron beam intensity signal from each channel of the electron beam detector 16 becomes an electron beam energy loss spectrum. The electron beam intensity signal from the electron beam detector 16 undergoes spectral background correction, electron beam detector gain correction, and the like. The calculated spectrum is stored in the memory unit 27 and displayed on the output unit 25. Through this series of processes, the operator can obtain a spectrum and an element distribution image.

[0046] Next, the flow for acquiring an EF image using Y-direction width adjustment will be described with reference to FIG. 10. Following the start of the flow (S101), the irradiation conditions for the charged particle beam are set (S102). Next, the energy width to be filtered for observation in the EF image is set (S103). Next, the amount of chromatic dispersion at the slit plane for passing the desired selected energy width at the current slit opening width is calculated and determined (S104).

[0047] Next, the optimum electron trajectory conditions for observation are calculated based on the set irradiation conditions and selected energy width (S105). The optimum conditions may be calculated by referring to the results of a previously performed electron trajectory simulation, or by sequentially recalculating the simulation to calculate the optimum conditions. Alternatively, an adjustment experiment may be performed in advance using the same device, and the simulation results may be corrected.

[0048] Next, based on the calculated optical trajectory conditions and the selected energy width, an optimal Y-direction width of the color dispersion spot formed on the slit plane is determined (S106). The Y-direction width is determined, for example, by creating a control formula for calculating an optimal value corresponding to the selected energy width and referring to the control formula. The control formula may be created by simulation, or some parameters of the control formula may be determined by experiments using an actual device.

[0049] Next, the electron trajectory is adjusted using a multipole lens (S107). The trajectory of the optical system is adjusted mainly using a quadrupole lens so that an EF image can be formed on the final detection plane in response to the trajectory change in the pre-slit optical system that accompanies the change in the spot on the slit surface. Additionally, if necessary, a hexapole, octopole, decapole, or dodecapole lens is used to finely adjust the electron trajectory and correct the aberration of the EF image. The adjustment amount of these multipole lenses may be an adjustment amount corresponding to the difference in the change in the spot shape on the slit surface.

[0050] An EF image is taken at the adjusted electron trajectory (S108), and the flow ends (S109).

[0051] In this way, controlling the Y-direction width of the color dispersion spot on the slit plane according to the filtering energy width makes it possible to acquire EF images under optimal conditions. The EF image acquisition flow presented in Figure 10 illustrates an example of EF image acquisition for a single filtering energy width, but it can also be applied to imaging with continuously changing filtering energy widths. In particular, as mentioned above, the present invention achieves changes in the filtering energy width by changing the spot shape on the slit plane, enabling high-quality image acquisition without the need for mechanically opening and closing the slit. Therefore, another feature is the ability to achieve measurements with freely changing filtering energy widths at high speed. For example, from images obtained by continuously changing the filtering energy width, it is possible to quickly search for an energy width that clearly shows the contrast of a target portion of the sample.

[0052] Next, the EF image acquisition flow including correction according to the Y-direction width amount will be described with reference to Fig. 11. After the flow starts (S111), desired measurement conditions for acquiring an EF image are set (S112). Then, an energy width to be filtered according to the observation target is set (S113).

[0053] Next, the amount of chromatic dispersion that must be satisfied at the slit plane for the desired selective energy width to pass through at the current slit opening width is determined (S114). Next, the optimum electron trajectory conditions for observation are calculated based on the set irradiation conditions and selective energy width (S115). The optimum Y-direction width of the chromatic dispersion spot formed at the slit plane is determined based on the calculated optical trajectory conditions and selective energy width (S116).

[0054] Next, the electron trajectory of the pre-slit optical system using a multipole lens is adjusted so that the determined chromatic dispersion spot shape is formed on the slit plane (S117). At this time, a step of measuring the spot shape and Y-direction width on the slit plane may be added. Measuring the spot shape allows for more precise adjustment.

[0055] Next, it is determined whether the change in the Y-direction width is equal to or less than a set value (S118). If it is equal to or less than the set value, the electron trajectory of the post-slit optical system is adjusted using a multipole lens so that an EF image is formed on the detector (S119). At the same time, aberration correction in the post-slit optical system is performed using a multipole lens. Then, an EF image is captured (S120), and the flow ends (S124). If the change in the Y-direction width is greater than the set value in S118, additional aberration correction conditions are determined (S121).

[0056] The additional correction conditions are determined, for example, so that the amount of aberration correction increases in proportion to the change in the Y-direction width. Next, the electron trajectory of the post-slit optical system is adjusted so that an EF image is formed on the detector using a multipole lens (S122). At this time, aberration correction using a multipole lens at the conventional intensity is simultaneously performed. Then, based on the added aberration correction conditions, further detailed aberration correction is performed using a multipole lens (S123). If the correction amount using the conventional multipole lens is insufficient, for example, a supplementary aberration correction multipole lens may be added to the optical system, and the added lens may be used to compensate for the necessary correction amount. After the adjustment is complete, an EF image is captured (S120), and the flow ends (S124).

[0057] For example, a flow for correcting the parameters of control formula (1) may be as shown in Figure 12. After the flow starts (S131), basic observation conditions such as acceleration voltage and field of view size are set according to the intended observation target (S132). Next, a filtering energy width for which the control formula is to be corrected is set (S133).

[0058] Next, based on the set energy width, the initial condition of the optimal Y-direction spot width on the slit plane is set using the control formula before correction (S134). Next, the electron trajectory is adjusted using a multipole lens to achieve the set spot shape (S135). Once the spot on the slit plane has been adjusted to the desired shape, color isochromaticity is measured (S136). Color isochromaticity can be measured, for example, by recording the brightness change at each position of the EF image on the detection plane when the acceleration voltage or prism excitation current is changed, and analyzing the relationship between the brightness change and the energy passing through the slit. The energy passing through the slit can be estimated from the change in acceleration voltage or prism excitation current.

[0059] Next, it is determined whether the measured color matching is better than a reference value (S137). The reference value is set to a value that is sufficiently good for the quality of the EF image to be ultimately acquired. If the color matching is not better than the reference value, the spot shape on the slit plane is adjusted (S138). At this time, the electron trajectory is adjusted using a multipole lens to change the Y-direction width while maintaining the chromatic dispersion amount of the spot on the slit plane in the X-direction. After adjusting the spot shape, the color matching is measured again, and the adjustment step is repeated until the obtained color matching is better than the reference value. Next, the adjusted spot shape is acquired, and the Y-direction width is measured (S139). For example, the Y-direction width may be measured by adjusting the multipole lens of the post-slit optical system so that the spot on the slit plane is imaged onto the detection plane, and then measuring the spot shape on the detection plane to determine the Y-direction width of the spot on the slit plane. Alternatively, a deflector arranged upstream from the slit may be used to scan the chromatic dispersion spot on the slit in the Y-direction, and the Y-direction width may be estimated from the intensity change detected by the detector during this process.

[0060] Next, the coefficients of the control formula are corrected by matching the measured Y-direction width with the set filtering energy width (S140), and the flow ends (S141). This control formula correction flow may be executed only for important filtering energy widths that the user uses for EF image measurement, or multiple adjustments may be made for any multiple filtering energy widths to perform more detailed correction of the control formula.

[0061] 1: electron beam source, 4: objective lens, 5: sample, 10: charged particle beam source, 12: electromagnetic lens group, 13: electromagnetic lens group, 14: first lens group, 15: electron beam energy spectrometer, 16: electron beam detector, 16: detector, 19: energy-selecting slit, 20: second lens group, 21: control device, 25: output section, 27: memory section, 30: control section, 31: input section, 40: multipole lens.

Claims

1. A charged particle beam device comprising: a charged particle source that emits a charged particle beam; a plurality of electromagnetic lens groups that adjust the charged particle beam; a sample holding stage that holds a sample to be irradiated with the charged particle beam; a spectrometer that energy-splits the charged particle beam that has passed through the sample; a first lens group that converges the dispersed charged particle beam; a slit on which the converged charged particle beam is formed as a chromatic dispersion surface and that allows a portion of the energy to pass; a second lens group that diverges the charged particle beam that has passed through the slit; a detector that forms an image of the charged particle beam diverged by the second lens group and detects the formed image; and a controller that controls at least one of the charged particle source, the electromagnetic lens group, the spectrometer, the first lens group, the slit, the second lens group, and the detector, wherein, when a direction of chromatic dispersion on a slit plane of the slit is defined as an X direction and a direction perpendicular to the X direction is defined as a Y direction, the controller controls the first lens group so that the charged particle beam can change the chromatic dispersion plane in the X direction and the Y direction.

2. A charged particle beam device according to claim 1, wherein the controller controls the first lens group so that a spot formed by the charged particle beam at the slit plane converges in the X direction and diverges in the Y direction to a predetermined Y direction width (Wy).

3. A charged particle beam device according to claim 2, characterized in that the controller controls the Y-direction width (Wy) of the spot on the slit plane based on a selective energy width (Ew), which is an energy width that selectively passes through the slit.

4. A charged particle beam device according to claim 3, characterized in that the controller controls the Y-direction width (Wy) of the spot on the slit plane based on a linear equation for the selected energy width (Ew).

5. In the charged particle beam device according to claim 3, the controller controls the Y-direction width (Wy) of the spot on the slit plane relative to a selected energy width (Ew) according to the following control formula (1): (where dslit is the slit opening width, C ０ ~C ３ is a coefficient).

6. A charged particle beam device according to claim 3, wherein the controller controls the Y-direction width (Wy) within a range of 0 to 10 mm when the selected energy width (Ew) is 2 to 20 eV.

7. A charged particle beam device according to claim 3, wherein the controller controls the Y-direction width (Wy) to be 1 mm or more when the selected energy width (Ew) is smaller than 5 eV.

8. A charged particle beam device according to claim 3, characterized in that the controller changes the aberration correction conditions using the first lens group and the second lens group based on the Y-direction width (Wy) of the spot on the slit plane.

9. A charged particle beam device according to claim 3, wherein the controller adjusts the second lens group so as to image the spot on the slit plane onto the detection plane of the detector, and measures the Y-direction width (Wy) of the spot on the detection plane, thereby measuring the Y-direction width (Wy) of the spot on the slit plane.

10. A charged particle beam device according to claim 3, wherein the controller uses a group of multiple electromagnetic lenses that adjust the charged particle beam to scan the spot on the slit surface of the slit in the Y direction, and measures the Y-direction width (Wy) of the spot on the slit surface based on the change in intensity detected by the detector during scanning.

11. A charged particle beam device according to claim 5, wherein the controller calculates a coefficient C in the control formula (1) based on the Y-direction width (Wy) of the spot on the slit plane. ０ ~C ３ and correcting the above.

12. In the charged particle beam device according to claim 5, the controller performs an aberration evaluation based on the relationship between the amount of change in brightness at each position of the image formed on the detection surface of the detector when the excitation current of the plurality of electromagnetic lenses that adjust the charged particle beam and the spectrometer is changed and the energy passing through the slit, and calculates a coefficient C in the control formula (1) based on the aberration evaluation. ０ ~C ３ and correcting the above.

13. A charged particle beam device according to claim 2, characterized in that the controller controls the Y-direction width (Wy) of the spot on the slit plane to be continuously changed by changing a selective energy width (Ew), which is the energy width selectively passed through the slit, and thereby controls the image formed on the detector to be acquired.

14. A method for adjusting a charged particle beam apparatus comprising: a charged particle source that emits a charged particle beam; a sample holding stage that holds a sample to be irradiated with the charged particle beam emitted from the charged particle source; a spectrometer that energy-disperses the charged particle beam that has passed through the sample; a first lens group that converges the charged particle beam energy-dispersed by the spectrometer; a slit on which the charged particle beam converged by the first lens group is formed as a color dispersion surface and that selectively passes only charged particle beams having a predetermined energy from the color-dispersed charged particle beams; a second lens group that diverges or converges the charged particle beam that has passed through the slit; and a detector that forms an image of the charged particle beam diverged or converged by the second lens group and detects the formed image, the method comprising controlling the first lens group to diverge the charged particle beam in a direction perpendicular to the direction of color dispersion on the color dispersion surface of the slit.

15. A method for adjusting a charged particle beam device according to claim 14, characterized in that the control of the first lens group controls the amount of divergence of the charged particle beam in a direction perpendicular to the direction of chromatic dispersion on the chromatic dispersion plane of the slit, based on a predetermined energy width for selectively passing through the slit.

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