Charged particle beam system and optical axis adjustment method

Abstract

In order to realize an optical axis adjustment process that does not depend on charged particles (having a diameter smaller than an aperture diameter) generated from a specimen, the present invention proposes a charged particle beam system that executes: a process for scanning a plurality of aperture elements with a charged particle beam by controlling a charged particle beam deflector; a process for generating adjustment data indicating a relationship between centroid positions of the plurality of aperture elements and a position of the charged particle beam, on the basis of (i-1) an input signal to the charged particle beam deflector and (i-2) an output of a current measuring instrument and a signal detected by a detector, or on the basis of (ii-1) an input signal to the charged particle beam deflector and (ii-2) each output value of at least one current measuring instrument; and a process for adjusting positions of a plurality of optical elements with respect to the charged particle beam or a position of the charged particle beam with respect to the plurality of optical elements, on the basis of the adjustment data (see fig. 1).

Description

Charged particle beam system and optical axis adjustment method

[0001] The present invention relates to a charged particle beam system and an optical axis adjustment method.

[0002] In charged particle beam devices such as electron microscopes, a charged particle beam focused by electrostatic or electromagnetic lenses is irradiated onto a sample and scanned to obtain an image of the sample and information about the elements present in the sample. In such charged particle beam devices, the resolution of the image obtained is limited by the beam diameter at the sample surface. To achieve high spatial resolution, distortion must also be extremely small, requiring alignment of each optical element.

[0003] The optical axis adjustment to the aperture, which is one of the optical elements, is performed by scanning the charged particle beam across the aperture, and the passing beam strikes the sample and detects the charged particles emitted from the sample. This identifies the positional relationship between the charged particle beam and the aperture, and then a process (optical axis adjustment process) is performed to align their centers.

[0004] As a method for facilitating optical axis adjustment, for example, Patent Document 1 discloses automatic adjustment of the center of a charged particle beam and an aperture. More specifically, the charged particle beam is scanned over the aperture, and charged particles generated from the sample when the charged particle beam is blocked by the aperture and when it passes through are converted into signal intensity, thereby detecting the edge position of the aperture. From the detected position, the amount of shift of the charged particle beam is calculated, and the optical axis is automatically adjusted so that the charged particle beam passes through the center of the aperture.

[0005] Furthermore, Patent Document 2 discloses a hollow aperture having a doughnut-shaped opening, and adjusts the optical axis thereof without using a signal from a sample. More specifically, by irradiating the hollow aperture with a charged particle beam and adjusting the position of the charged particle beam so as to maximize the absorbed current, it becomes possible to align the center of the hollow aperture with the center of the charged particle beam.

[0006] Patent Document 3 discloses that, as an optical element mounted in a charged particle beam device, a deceleration type energy filter has an electrode shape with an axially symmetric space sandwiched between two apertures, thereby improving the energy resolution.

[0007] JP-T-2005-521990 A JP-A-2001-203150 A International Publication No. 2022 / 018782

[0008] In charged particle beam devices, the optical conditions of the focusing lens installed on the optical path are changed depending on the situation, such as when high resolution is required or when high probe current is required for high throughput. When the optical conditions are changed, the trajectory of the electron beam changes, causing optical axis misalignment for each optical element, so optical axis adjustment is necessary.

[0009] In recent years, charged particle beam devices have been proposed that include multiple optical elements, each with an aperture function. One example of such a device is a charged particle beam device with multiple differential pumping apertures. Apertures are necessary to limit the amount of electron beam energy, and because differential pumping is performed using a separate aperture, multiple apertures are often installed. Here, differential pumping allows a charged particle beam source, which needs to be maintained at a high vacuum, to be separated from the area near the sample, where a high vacuum is not required, by a small aperture, thereby ensuring a passage for the charged particles while maintaining a high vacuum near the charged particle beam source.

[0010] In this regard, even in a charged particle beam device having a plurality of apertures, it is important to perform the above-described optical axis adjustment.

[0011] However, when using the technology disclosed in Patent Document 1 to adjust the optical axis of a charged particle beam device having multiple apertures, such as that disclosed in Patent Document 3, it is difficult to pass all of the apertures from the charged particle beam source to the sample, making it difficult to detect the positional relationship using the detection signal of the charged particles emitted from the sample. To address this issue, it is possible to adjust the optical axis by moving downstream optical elements so as not to block the electron beam, and then adjusting the optical axis one by one, starting with the upstream optical elements. However, frequently moving optical elements can lead to mistakes, such as forgetting to return them, and can also cause misalignment.

[0012] On the other hand, the technology disclosed in Patent Document 2 allows optical axis adjustment to be performed regardless of the charged particles emitted from the sample. By applying this technology to an aperture upstream of the optical system, optical axis adjustment can be performed regardless of the position of the downstream aperture. However, in the case of an aperture with a normal round opening, under optical conditions where the diameter of the charged particle beam (electron beam) is equal to or smaller than the aperture diameter, the charged particle beam passes through all of the apertures, so no current is detected at the apertures, and it is not possible to perform processing to align the center of the charged particle beam with the center of the aperture.

[0013] In view of this situation, the present invention proposes a technology that facilitates optical axis adjustment to align the center of a charged particle beam with the center of the aperture when multiple apertures are provided and a charged particle beam with a diameter smaller than the opening diameter of the apertures is used.

[0014] In order to achieve the above object, the present invention provides, as an example, a charged particle beam system for irradiating a sample with a charged particle beam to acquire an image of the sample, the system comprising: a charged particle beam source for generating the charged particle beam; a charged particle beam deflector for deflecting the charged particle beam; a plurality of optical elements provided in an irradiation path of the charged particle beam to the sample and including an aperture for performing a diaphragm function for the charged particle beam; at least one current measuring device connected to at least one of the plurality of optical elements; a detector for detecting a signal generated when the sample is irradiated with the charged particle beam; and a computer for performing an optical axis adjustment process for aligning a center of the charged particle beam with a center of the plurality of optical elements, wherein, in the optical axis adjustment process, the computer performs a process of controlling the charged particle beam deflector to scan the plurality of optical elements with the charged particle beam when a diameter of the charged particle beam is smaller than a diameter of the apertures of the plurality of optical elements; We propose a charged particle beam system that performs the following steps: (i-1) generating adjustment data indicating the relationship between the center of gravity positions of the multiple optical elements and the position of the charged particle beam from an input signal to the charged particle beam deflector and (i-2) the output of the current measuring device and the signal detected by the detector, or from (ii-1) the input signal to the charged particle beam deflector and (ii-2) each output value of the at least one current measuring device; and (ii-2) adjusting the positions of the multiple optical elements relative to the charged particle beam, or the position of the charged particle beam relative to the multiple optical elements, based on the adjustment data.

[0015] Further features related to the present invention will become apparent from the description of this specification and the accompanying drawings. Also, aspects of the present invention are achieved and realized by the elements and combinations of various elements and the aspects of the following detailed description and the appended claims. The description of this specification is merely exemplary and does not limit the scope or application of the claims in any way.

[0016] According to the present invention, when a plurality of apertures are present in an optical system, it becomes easy to correct the optical axis deviation of a charged particle beam relative to the apertures.

[0017] 6 is a diagram showing a schematic configuration example of a scanning electron microscope (SEM) system 1 according to a first embodiment, which is equipped with a DAL (Double Aperture Lens) that is an energy filter having an aperture function in its optical system and is connected to a mechanism for detecting an absorbed current value generated when an electron beam is irradiated onto the aperture. FIG. 7 is a diagram for explaining an operation for detecting the positional relationship between the center of the electron beam and the center of the aperture from a current value generated when an electron beam is irradiated onto the aperture. FIG. 8 is a diagram showing a current value detected from the aperture (DAL) 105 when a charged particle beam is scanned across the aperture 105 during optical axis adjustment. FIG. 9 is a diagram showing a schematic configuration example of a circular image obtained by converting a current generated in the aperture. FIG. 10 is a diagram showing a state (image) in which each of two apertures is shifted from the center of the electron beam. FIG. 11 is a flowchart for explaining an optical axis adjustment process for a plurality of apertures using the circular images shown in FIG. 4 and FIG. 5 according to a first embodiment. FIG. 12 is a diagram showing a schematic configuration example of an SEM system 1′ according to a second embodiment.

[0018] The present invention relates to a charged particle beam system, and to an optical axis adjustment process for a charged particle beam aperture (including an optical member having an aperture function) that does not depend on the detection of electrons emitted from a sample.

[0019] The present invention can be implemented by a charged particle beam system. Hereinafter, features of the present invention will be described using a scanning electron microscope (SEM) system as an example of one aspect of a charged particle beam system. However, the present invention is not limited to SEMs and can also be applied to, for example, ion microscopes that irradiate hydrogen ions, helium ions, or liquid metals such as gallium, focused ion beam devices (FIBs), scanning transmission electron microscopes (STEMs), and the like. In all of the following figures, parts having the same functions are designated by the same reference numerals, and repeated explanations may be omitted.

[0020] <Configuration Example of Scanning Electron Microscope> FIG. 1 is a diagram showing a schematic configuration example of a scanning electron microscope (SEM) system 1 according to Example 1, which is equipped with a DAL (Double Aperture Lens), which is an energy filter having an aperture function in the optical system, and to which a mechanism for detecting an absorbed current value generated when an electron beam is irradiated onto the aperture is connected.

[0021] The SEM system 1 includes an electron beam source 101 that emits a primary electron beam to be irradiated onto a sample 112, a first alignment deflector 102 (a first X alignment deflector 102a and a first Y alignment deflector 102b) that adjusts the position of the electron beam relative to the energy filter, a first scan deflector 103 that scans the electron beam on the energy filter, a first focusing lens 104 that focuses the electron beam onto the center of the DAL 105, a DAL 105, an objective movable aperture 109 that limits the amount of electron beam irradiated onto the sample 112, and a second alignment deflector 106 (a second X alignment deflector 106a and a second Y alignment deflector 106b) that adjusts the position of the electron beam relative to the objective movable aperture 109. 6a and a second Y-alignment deflector 106b), a second scan deflector 107 that scans the electron beam on an objective movable aperture 109, a second focusing lens 108 that controls the probe current, a third focusing lens 110 that adjusts the aperture angle of the charged particle beam relative to the sample 112, an objective lens 111 that focuses the electron beam on the sample 112, a stage 113 on which the sample 112 is placed, an electron detector 114 that detects the electron beam emitted from the sample 112, an amplifier 115 that amplifies the signal, an ammeter 116 that detects the current generated in the aperture (DAL 105), and an integrated computer 117 that controls the entire apparatus. Each component is controlled by an electron beam source control circuit 118, a first alignment deflector control circuit 119, a first focusing lens control circuit 120, a second alignment deflector control circuit 121, a second focusing lens control circuit 122, a third focusing lens control circuit 123, an objective lens control circuit 124, a signal control circuit 125, and a stage control circuit 126.

[0022] The integrated computer 117 controls the operation of the entire SEM system 1 and constructs images based on control signals for each optical element and signals detected by the detector. The integrated computer 117 is connected to a controller 127 (keyboard, mouse, etc.) and an image display device 128. An operator can input instructions and parameters from the controller 127 to control the observation conditions and each control circuit, and display a control screen and observed image on the image display device 128.

[0023] In order to achieve high-resolution observation of the sample 112 in the SEM system 1, it is necessary to obtain a probe current that was set during the design of the device and to align the aperture center (which is the "center" if the aperture hole is circular, but the "center of gravity (a concept that includes the center)" if the aperture hole is not circular; the same applies below) with the center of the primary electron beam. Furthermore, when using the DAL 105, it is necessary to accurately direct the electron beam near the central axis of the DAL 105. For this reason, it is necessary to appropriately adjust the aperture position or the electron beam position.

[0024] When adjusting the electron beam position to the center of the aperture, the first alignment deflector control circuit 119 and the second alignment deflector control circuit 121 adjust the electron beam position by controlling the first alignment deflector 102 and the second alignment deflector 106. With the direction along the optical axis being the Z direction and the plane perpendicular to the Z axis being the XY plane, the first alignment deflector control circuit 119 and the second alignment deflector control circuit 121 can deflect the electron beam in the X-axis direction and the Y-axis direction on the XY plane using the first X alignment deflector 102 a and the second X alignment deflector 106 a and the first Y alignment deflector 102 b and the second Y alignment deflector 106 b, thereby adjusting the electron beam position two-dimensionally.

[0025] On the other hand, when adjusting the aperture position to the center of the electron beam, it is possible to adjust the aperture position using a movable mechanism (not shown) that can move the aperture position in the X-axis and Y-axis directions. The movable mechanism may be manual, or may be equipped with an electric unit operated by a motor.

[0026] When adjusting the optical axis relative to the aperture, the primary electron beam is scanned across the aperture by the first scanning deflector 103 and the second scanning deflector 107. The first alignment deflector 102 and the second alignment deflector 106 can be adjusted based on an image of the input signal to the first scanning deflector 103 and the second scanning deflector 107 and the signal from the electron detector 114 obtained when the electron beam passes through the aperture.

[0027] <Operation for Detecting the Positional Relationship Between the Center of the Electron Beam and the Center of the Aperture> FIG. 2 is a diagram for explaining the operation for detecting the positional relationship between the center of the electron beam and the center of the aperture from the current value generated when the aperture is irradiated with the electron beam.

[0028] The electron beam is deflected by the first X-alignment deflector 102a and / or the first Y-alignment deflector 102b, and the electron beam is scanned across the aperture 105 by the first scanning deflector 103, whereby the current value is measured by an ammeter 116 connected to the aperture (DAL) 105. At this time, a spectrum such as that shown in FIG. 3 is obtained depending on the amount of deflection of the electron beam.

[0029] FIG. 3 is a diagram showing current values ​​detected from the aperture (DAL) 105 when the charged particle beam scans the aperture 105 during optical axis adjustment. In FIG. 3 , the horizontal axis represents the signal (amount of current flowing through the deflection coil: unit: A) input to the first scanning deflector 103, and the vertical axis represents the measured current value. When the electron beam is blocked by the aperture 105, a current flows through the aperture 105. On the other hand, when the electron beam passes through the aperture 105, no current flows. Therefore, it can be said that the current change points 301 a and 301 b represent the edges of the aperture 105. By detecting the edges in two different scanning directions (not only directions perpendicular to each other, such as the X-axis direction and the Y-axis direction, but also directions of two straight lines passing through the center of the aperture 105 and forming an arbitrary angle), the positional relationship between the center of the aperture 105 and the center of the electron beam can be grasped (calculated).

[0030] Fig. 4 is a diagram schematically showing a circular image obtained by converting the current generated in the aperture 105. As shown in Fig. 4, an electron beam is scanned on the XY plane, and the magnitude of the obtained current value is converted into brightness, allowing the relationship with the deflection amount to be visualized and displayed. The center 401 of the circular image represents the center of the aperture (DAL 105), the entire image represents the scanning range of the electron beam by the first scanning deflector 103, and the center of the entire image represents the electron beam center 402. In other words, the image shown in Fig. 4 makes it possible to visualize the positional relationship between the aperture center (circular image center 401) and the electron beam center 402 before optical axis adjustment.

[0031] 5 is a diagram showing a state (image) in which each of two apertures (e.g., the DAL 105 and the objective movable aperture 109) is displaced from the center of the electron beam. As shown in Fig. 5, by controlling the first alignment deflector 102 and simultaneously displaying a circular image (image 501 due to a current generated when the electron beam is irradiated onto the aperture) obtained by imaging a current generated by irradiating and scanning the aperture (DAL) 105 with an electron beam and a circular image (image 502 due to a signal from the electron detector 114) obtained by imaging a signal from the electron detector 114, it is possible to visualize the positional relationship of multiple apertures (the DAL 105 and the objective movable aperture 109) with respect to the electron beam.

[0032] <Optical Axis Adjustment Processing> FIG. 6 is a flowchart for explaining the optical axis adjustment processing of a plurality of apertures using the circular images shown in FIGS. 4 and 5 according to the first embodiment.

[0033] (i) Step S61 When an operator (user) inputs an instruction to perform optical axis adjustment processing to the integrated computer 117 via the controller 127, the integrated computer 117 controls the first scanning deflector 103 via the first focusing lens control circuit 120 to scan the primary electron beam on the aperture (energy filter DAL) 105.

[0034] (ii) Step S62: When the electron beam is irradiated onto the energy filter DAL (aperture) 105, a current is generated. When the current is measured by the ammeter 116, the integrated computer 117 visualizes the relationship between the input signal to the first scanning deflector 103 and the measured current value (FIGS. 3 and 4 / 5). Here, the integrated computer 117 may detect the amount of deviation (amount of optical axis deviation: distance and direction) between the center of the electron beam and the center of the DAL 105 from the visualized data.

[0035] (iii) Step S63 When the operator inputs an instruction to execute an optical axis adjustment process for aligning the center of the DAL (aperture) 105 (center 401 of the circular image) with the center of the entire screen (center 402 of the electron beam) via the controller 127, the integrated computer 117 controls the first alignment deflector 102 via the first alignment deflector control circuit 119 based on the distance and direction between the center of the DAL (aperture) 105 (center 401 of the circular image) and the center of the entire screen (center 402 of the electron beam) so that they coincide with each other (optical axis adjustment). Here, the integrated computer 117 calculates the amount and direction of optical axis deviation, but the operator may input the adjustment amount (amount and direction of optical axis deviation) via the controller 127.

[0036] (iv) Step S64 After the optical axis adjustment by the first alignment deflector 102 is completed, the operator issues an instruction to start adjusting the second alignment deflector 106 to the integrated computer 117 via the controller 127. Then, the integrated computer 117 controls the second scanning deflector 107 to scan the primary electron beam on the objective movable diaphragm 109.

[0037] (v) Step S65: The primary electron beam that has passed through the objective aperture 109 is irradiated onto the sample 112, and secondary electrons generated from the sample 112 are detected by the electron detector 114. Then, the integrated computer 117 visualizes the relationship between the signal detected by the electron detector 114 and the input signal to the second scan deflector 107 (image 502 in FIG. 5 ). Here, the integrated computer 117 may detect the amount of deviation (amount of optical axis deviation) between the center of the electron beam and the center of the objective aperture 109 (center of the image 502) from the visualized data.

[0038] (vi) Step S66: When the operator inputs an instruction to execute an optical axis adjustment process via the controller 127 to align the center of the circular image (the center of the image 502 showing the objective variable aperture 109) with the center of the entire screen (the electron beam center 402), the integrated computer 117 controls the second alignment deflector 106 via the second alignment deflector control circuit 121 based on the distance and direction between the center of the circular image (the center of the objective variable aperture 109 (the center of the image 502)) and the center of the entire screen (the electron beam center 402) so that they coincide with each other (optical axis adjustment). Here, the integrated computer 117 calculates the amount and direction of optical axis deviation, but the operator may input the adjustment amount (amount and direction of optical axis deviation) via the controller 127.

[0039] The optical axis adjustment process is completed through the above steps. Note that it is desirable to perform the optical axis adjustment of each diaphragm after the optical axis adjustment of the other optical elements. Note that for diaphragms whose position can be changed (when a driving unit is attached to the objective movable diaphragm 109 or the DAL 105), the diaphragm center and the electron beam center may be aligned by changing the diaphragm position rather than controlling the irradiation position of the primary electron beam.

[0040] While the optical axis adjustment process when a movable diaphragm is provided has been described in Example 1, the optical axis adjustment process when a fixed diaphragm is provided will be described in Example 2. An example of a fixed diaphragm is a differential exhaust diaphragm for providing a difference in the degree of vacuum inside an SEM system.

[0041] 7 is a diagram showing a schematic configuration example of an SEM system 1' according to embodiment 2. In addition to the objective variable aperture 109, the SEM system 1' includes as its components a first differential pumping aperture 701, a second differential pumping aperture 702, an ammeter 116a connected to the first differential pumping aperture 701, and an ammeter 116b connected to the second differential pumping aperture 702. Note that since similar elements as those of a control circuit and an integrated computer are included in the configuration shown in FIG. 1, they are omitted from FIG. 7.

[0042] In the SEM system 1′, if the electron beam is blocked by the first differential pumping diaphragm 701 or the second differential pumping diaphragm 702, it will lead to a decrease in probe current and the occurrence of contamination. For this reason, it is necessary to adjust the optical axis so that the electron beam does not hit the first differential pumping diaphragm 701 or the second differential pumping diaphragm 702.

[0043] However, when performing the optical axis adjustment, the first differential pumping diaphragm 701 and the second differential pumping diaphragm 702 cannot be moved because they are fixedly disposed in the SEM system 1'. Therefore, the second embodiment proposes adjusting the position of the electron beam source 101 to align the center of the electron beam with the centers of the first differential pumping diaphragm 701 and the second differential pumping diaphragm 702.

[0044] First, when the electron beam is scanned with the objective variable diaphragm 109 removed, an SEM image is generated in a state in which the electron beam reaching the sample 112 is restricted by the first differential pumping diaphragm 701 and / or the second differential pumping diaphragm 702. Therefore, while observing this SEM image, the position of the electron beam source 101 is adjusted so that the center of the first differential pumping diaphragm 701 and the second differential pumping diaphragm 702 coincides with the center of the electron beam. By reducing the diameters of the first differential pumping diaphragm 701 and the second differential pumping diaphragm 702, it is possible to improve the differential pumping capacity.

[0045] On the other hand, if the diameter is reduced, the electron beam is more likely to be blocked due to misalignment with other apertures. In this case, the first alignment deflector 102 and the first scan deflector 103 are arranged upstream of the optical system of the first differential pumping aperture 701, and the second alignment deflector 106 and the second scan deflector 107 are arranged upstream of the optical system of the second differential pumping aperture 702. It is effective to connect an ammeter 116a as a current detection means to the first differential pumping aperture 701 and an ammeter 116b to the second differential pumping aperture 702. This makes it possible to visualize the positional relationship between the center of each differential pumping aperture and the center of the electron beam (by visualizing the relationship between the input signal to each scan deflector and the measured current value, as described above), and to align the center of the electron beam with the center of each differential pumping aperture with high precision.

[0046] The optical axis adjustment process of the objective variable aperture 109 (processing for aligning the center of the objective variable aperture 109 with the center of the electron beam) is performed in the same manner as in Example 1. That is, the integrated computer 117 visualizes the relationship between the signal detected by the electron detector 114 and the input signal to the second scan deflector 107 (image 502 in FIG. 5 ). Then, based on the distance and direction between the center of the circular image (the center of the objective variable aperture 109 (center of image 502)) and the center of the entire screen (center 402 of the electron beam), the integrated computer 117 controls the second alignment deflector 106 via the second alignment deflector control circuit 121 or adjusts the position of the objective variable aperture 109 (optical axis adjustment) so that the two are aligned.

[0047] Furthermore, the SEM system 1′ does not necessarily need to include the objective variable diaphragm 109. In this case, the optical axis adjustment process is performed using only the relationship (image) between the current values ​​measured by the ammeters 116 a and 116 b connected to the first differential pumping diaphragm 701 and the second differential pumping diaphragm 702 and the input signals to the scan deflectors. others

[0048] (i) The present invention is not limited to Examples 1 and 2, and includes various modifications. For example, Examples 1 and 2 have been described in detail to clearly explain the present invention, and are not necessarily limited to those including all of the described configurations. Furthermore, it is possible to replace part of the configuration of one Example with the configuration of another Example, and it is also possible to add the configuration of another Example to the configuration of one Example. Furthermore, it is possible to add, delete, or replace part of the configuration of each Example with each other.

[0049] (ii) The functions of this embodiment and each example can also be realized by software program code. In this case, a storage medium on which the program code is recorded is provided to a system or device, and the computer (or CPU or MPU) of that system or device reads the program code stored in the storage medium. In this case, the program code itself read from the storage medium realizes the functions of the above-mentioned embodiments, and the program code itself and the storage medium on which it is stored constitute the present disclosure. Examples of storage media for providing such program code include flexible disks, CD-ROMs, DVD-ROMs, hard disks, optical disks, magneto-optical disks, CD-Rs, magnetic tape, non-volatile memory cards, and ROMs.

[0050] Furthermore, an operating system (OS) running on a computer may perform some or all of the actual processing based on instructions in the program code, and the functions of the above-described embodiments may be realized by this processing.Furthermore, after the program code is read from a storage medium and written to memory on the computer, a CPU of the computer may perform some or all of the actual processing based on instructions in the program code, and the functions of the above-described embodiments may be realized by this processing.

[0051] Furthermore, the program code of the software that realizes the functions of the embodiments and each example may be distributed via a network and stored in a storage means such as a hard disk or memory of the system or device, or in a storage medium such as a CD-RW or CD-R, so that when used, the computer (or CPU or MPU) of the system or device reads and executes the program code stored in the storage means or storage medium.

[0052] Although specific examples are described in this disclosure, they are in all respects for the purpose of explanation (understanding the technology of the present disclosure) and not for the purpose of limitation. Those skilled in the art will recognize that there are many combinations of hardware, software, and firmware suitable for implementing the technology of the present disclosure. For example, the software described can be implemented in a wide variety of programming or scripting languages, such as assembler, C / C++, Perl, Shell, PHP, Java (registered trademark), etc.

[0053] Furthermore, in the above-described embodiment, the control lines and information lines are those that are considered necessary for the explanation, and not all control lines and information lines in the product are necessarily shown. All components may be interconnected.

[0054] In addition, other implementations of the present disclosure will be apparent to those skilled in the art from consideration of the present embodiments and examples. The specification and examples are exemplary only, with the scope and spirit of the present technology being indicated by the following claims.

[0055] 1, 1' Charged particle beam system 101 Electron beam source 102 First alignment deflector 102a First X alignment deflector 102b First Y alignment deflector 103 First scan deflector 104 First focusing lens 105 DAL 106 Second alignment deflector 106a Second X alignment deflector 106b Second Y alignment deflector 107 Second scan deflector 108 Second focusing lens 109 Objective adjustable aperture 110 Third focusing lens 111 Objective lens 112 Sample 113 Stage 114 Electron detector 115 Amplifier 116 Ammeter 116a Ammeter 116b Ammeter 117 Integrated computer 118 Electron beam source control circuit 119 First alignment deflector control circuit 120 First focusing lens control circuit 121 Second alignment deflector control circuit 122 Second focusing lens control circuit 123 Third focusing lens control circuit 124 Objective lens control circuit 125 Signal control circuit 126 Stage control circuit 127 Controller 128 Image display device 301a Current value change point 301b Current value change point 401 Circular image center 402 Electron beam center 501 Image due to current generated when electron beam is irradiated onto aperture 502 Image due to signal from electron detector 701 First differential pumping aperture 702 Second differential pumping aperture

Claims

1. A charged particle beam system for irradiating a sample with a charged particle beam to acquire an image of the sample, comprising: a charged particle beam source for generating the charged particle beam; a charged particle beam deflector for deflecting the charged particle beam; a plurality of optical elements provided in an irradiation path of the charged particle beam to the sample and including an aperture that performs a diaphragm function for the charged particle beam; at least one current measuring device connected to at least one of the plurality of optical elements; a detector for detecting a signal generated when the charged particle beam is irradiated onto the sample; and a computer for performing an optical axis adjustment process to align the center of the charged particle beam with the centers of the plurality of optical elements, wherein the computer performs the following optical axis adjustment process: when the diameter of the charged particle beam is smaller than the diameter of the apertures of the plurality of optical elements, control the charged particle beam deflector to scan the plurality of optical elements with the charged particle beam; A charged particle beam system that performs the following steps: (i-1) generating adjustment data indicating the relationship between the center of gravity positions of the plurality of optical elements and the position of the charged particle beam from an input signal to the charged particle beam deflector and (i-2) the output of the current measuring device and the signal detected by the detector, or from (ii-1) the input signal to the charged particle beam deflector and (ii-2) each output value of the at least one current measuring device; and (ii-2) adjusting the positions of the plurality of optical elements relative to the charged particle beam or the position of the charged particle beam relative to the plurality of optical elements based on the adjustment data.

2. A charged particle beam system according to claim 1, wherein the plurality of optical elements include a DAL and an objective movable aperture, the DAL being positioned closer to the charged particle beam source than the objective movable aperture and functioning not only as an aperture but also as an energy filter.

3. A charged particle beam system according to claim 1, wherein the plurality of optical elements include an objective variable aperture, and the computer generates the adjustment data for the optical elements other than the objective variable aperture from the output of the current measuring device and an input signal to the charged particle beam deflector, and generates the adjustment data for the objective variable aperture from the output of the detector and an input signal to the charged particle beam deflector.

4. A charged particle beam system as claimed in claim 3, wherein the computer converts the output value of the current measuring device into brightness, generates an image showing the relationship between the amount of deflection by the charged particle beam deflector and the brightness, and generates the adjustment data showing the relationship between the center of gravity positions of the multiple optical elements and the position of the charged particle beam from the image.

5. A charged particle beam system as claimed in claim 4, wherein the computer calculates the amount of deviation between the center of gravity position of the plurality of optical elements and the position of the charged particle beam from the relationship between the center of gravity position of the plurality of optical elements and the position of the charged particle beam, and adjusts the positions of the plurality of optical elements relative to the charged particle beam or the position of the charged particle beam relative to the plurality of optical elements based on the amount of deviation.

6. A charged particle beam system as set forth in claim 1, wherein the plurality of optical elements include a plurality of differential pumping diaphragms and a movable objective diaphragm, and the computer generates the adjustment data for the plurality of differential pumping diaphragms from the output of the current measuring device connected to each differential pumping diaphragm and an input signal to the charged particle beam deflector, and generates the adjustment data for the movable objective diaphragm from the output of the detector and an input signal to the charged particle beam deflector.

7. An optical axis adjustment method for adjusting the position of the center of a charged particle beam and the center of gravity of a plurality of optical elements including apertures that exhibit an aperture function in a charged particle beam system using a computer, comprising: emitting the charged particle beam from a charged particle beam source, the charged particle beam having a diameter smaller than the diameter of the apertures of the plurality of optical elements; controlling a charged particle beam deflector to scan the plurality of optical elements with the charged particle beam; measuring, using a current measuring device, a current generated in at least one of the plurality of optical elements by scanning the charged particle beam; and detecting, using a detector, a signal generated by irradiating a sample with the charged particle beam. an optical axis adjustment method comprising: generating adjustment data indicating a relationship between the center of gravity positions of the plurality of optical elements and the position of the charged particle beam from (i-1) an input signal to the charged particle beam deflector and (i-2) an output of the current measuring device and the signal detected by the detector, or from (ii-1) an input signal to the charged particle beam deflector and (ii-2) each output value of the at least one current measuring device; and adjusting the positions of the plurality of optical elements relative to the charged particle beam or the position of the charged particle beam relative to the plurality of optical elements based on the adjustment data.

8. An optical axis adjustment method according to claim 7, wherein the plurality of optical elements include a DAL and an objective movable diaphragm, and the DAL is positioned closer to the charged particle beam source than the objective movable diaphragm, and functions not only as a diaphragm but also as an energy filter.

9. An optical axis adjustment method according to claim 7, wherein the plurality of optical elements include an objective movable aperture, and generating the adjustment data includes: for the optical elements other than the objective movable aperture, generating the adjustment data from the output of the current measuring device and an input signal to the charged particle beam deflector; and for the objective movable aperture, generating the adjustment data from the output of the detector and an input signal to the charged particle beam deflector.

10. An optical axis adjustment method according to claim 9, wherein generating the adjustment data from the output of the current measuring device and the input signal to the charged particle beam deflector includes: converting the output value of the current measuring device to brightness and generating an image showing the relationship between the amount of deflection by the charged particle beam deflector and the brightness; and generating the adjustment data showing the relationship between the center of gravity positions of the multiple optical elements and the position of the charged particle beam from the image.

11. An optical axis adjustment method according to claim 10, wherein adjusting the positions of the plurality of optical elements relative to the charged particle beam, or the position of the charged particle beam relative to the plurality of optical elements, based on the adjustment data, includes: calculating the amount of deviation between the center of gravity position of the plurality of optical elements and the charged particle beam from the relationship between the center of gravity position of the plurality of optical elements and the position of the charged particle beam; and adjusting the positions of the plurality of optical elements relative to the charged particle beam, or the position of the charged particle beam relative to the plurality of optical elements, based on the amount of deviation.

12. An optical axis adjustment method as set forth in claim 7, wherein the plurality of optical elements include a plurality of differential pumping diaphragms and a movable objective diaphragm, and generating the adjustment data includes: for the plurality of differential pumping diaphragms, generating the adjustment data from the output of the current measuring device connected to each differential pumping diaphragm and an input signal to the charged particle beam deflector; and for the movable objective diaphragm, generating the adjustment data from the output of the detector and an input signal to the charged particle beam deflector.

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