Charged particle ray device and optical axis adjustment method

Abstract

A charged particle ray device according to the present disclosure comprises: a charged particle optical system that irradiates a sample with a charged particle ray; one or more aligners that adjust the optical axis of the charged particle optical system; a detector that detects particles or electromagnetic waves generated by irradiating the sample with the charged particle ray; and a processing device that acquires an image by processing a detection signal acquired by the detector, the charged particle ray device being characterized in that the processing device: creates, for each of the aligners, a table storing optimum control values for a plurality of observation conditions and / or a formula for calculating said optimum control values; measures changes in the optimum control value for the aligner under one or more observation conditions, the number of said one or more observation conditions being smaller than the number of the plurality of observation conditions used for the creation of the table or the formula; and using the result of the measurement, converts the table and / or the formula in accordance with a conversion formula determined according to two-dimensional coordinate positional relationships in the charged particle optical system, thereby updating the table and / or the formula.

Description

Charged particle beam device and optical axis adjustment method

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

[0002] In charged particle beam devices such as scanning electron microscopes, a primary electron beam emitted from an electron gun is focused using several electromagnetic lenses and apertures. Images are obtained by detecting the particles generated by scanning or passing this primary electron beam over a sample. To obtain a clear image, the trajectory of the optical axis of the primary electron beam must be adjusted. Specifically, by adjusting the primary electron beam to pass through the center of the aperture, more primary electrons are allowed to pass through, resulting in a brighter, less noisy image. Furthermore, by adjusting the primary electron beam to pass near the center of the electromagnetic lens, the aberrations caused by the electromagnetic lens can be reduced, resulting in a clearer image with high resolution.

[0003] Optical axis adjustment (alignment) typically involves adjusting the position of the primary electron beam by deflecting it with an electromagnetic lens called an aligner. In scanning electron microscopes, the main optical axis adjustments performed are beam alignment, which aligns the primary electron beam to the center of the objective aperture; aperture alignment, which aligns the primary electron beam to the center of the objective lens; and stigma alignment, which aligns the primary electron beam to the center of the astigmatism corrector. Beam alignment uses the image obtained by scanning a charged particle beam across the aperture to adjust the primary electron beam to the scanning center. Aperture alignment and stigma alignment adjust the conditions to prevent image misalignment when the current or voltage of the objective lens or astigmatism corrector is changed. These alignments typically involve a wobbler, which periodically oscillates the current or voltage. The observer must adjust these optical axes during observation, and adjustments using a wobbler are particularly difficult. Depending on the observer's level of skill, adjustments can take a long time and the adjustment results can vary. For this reason, recent electron microscopes are equipped with automatic axis adjustment functions.

[0004] Patent Document 1 discloses a technology for automatic optical axis adjustment. Specifically, Patent Document 1 estimates optimal aligner control values ​​that do not cause misalignment for each aligner control value that performs optical axis adjustment, based on the amount and direction of misalignment that occurs when the current value of the objective lens or astigmatism corrector is changed. Because this optimal aligner control value depends on the observation conditions that change optical conditions such as the acceleration voltage and irradiation current value, the operator has traditionally performed optical axis adjustment manually or using the automatic axis adjustment function described above.

[0005] Japanese Patent Application Laid-Open No. 2003-022771

[0006] In recent years, there has been a growing demand for improved throughput in electron microscope observations and for the observation of a larger number of specimens. In electron microscope observations, optical axis adjustment is performed for each observation and each observation condition, and optical axis adjustment is often a bottleneck during observations. High-speed manual optical axis adjustment requires skilled operation techniques, but even experienced, advanced observers face limitations in improving the adjustment speed. Furthermore, there are few skilled advanced observers; most observers are beginners or intermediate level observers. Therefore, automatic optical axis adjustment methods have been devised to enable optical axis adjustment regardless of the observer's level of skill. However, even with automatic optical axis adjustment, there are limitations in improving the adjustment speed. In other words, the need for frequent optical axis adjustment for each observation and each observation condition, and the limited speed of optical axis adjustment, whether manual or automatic, are two main reasons for the inability to meet the required throughput. Therefore, a solution to this issue is needed that is different from simply increasing the speed of the optical axis adjustment itself.

[0007] One way to solve this problem is to store the optimal control values ​​of the aligner corresponding to the observation conditions in advance as a table or formula. However, the optimal control values ​​of the aligner change over time due to the influence of external disturbances, etc. In particular, the optimal control values ​​can change significantly due to factors such as replacing the electron gun, moving the objective aperture, and baking the lens barrel.

[0008] Therefore, the present disclosure provides a technique that enables optical axis adjustment in a short time in a charged particle beam device.

[0009] In order to solve the above problems, the charged particle beam device disclosed herein comprises a charged particle optical system that irradiates a sample with a charged particle beam, at least one aligner that adjusts the optical axis of the charged particle optical system, a detector that detects particles or electromagnetic waves generated when the sample is irradiated with the charged particle beam, and a processing device that processes the detection signal obtained by the detector to obtain an image, wherein the processing device creates at least one of a table that stores optimal control values ​​for multiple observation conditions for each aligner and a formula for calculating them, measures changes in the optimal control values ​​of the aligner under one or more observation conditions that are less than the number of the multiple observation conditions used to create the table or formula, and uses the results of the measurement to update at least one of the table and formula by converting them using a conversion formula calculated from the two-dimensional coordinate arrangement of the charged particle optical system.

[0010] Further features related to the present disclosure will become apparent from the description of this specification and the accompanying drawings. Also, aspects of the present disclosure 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 of the present disclosure in any way.

[0011] According to the technique of the present disclosure, the optical axis adjustment in the charged particle beam device can be performed in a short time. Problems, configurations, and effects other than those described above will become clear from the following description of the embodiment.

[0012] 1 is a schematic diagram of a scanning electron microscope. FIG. 1 is a flowchart of a method for adjusting an optical axis in a scanning electron microscope. FIG. 2 is a diagram showing an example of a correspondence table. FIG. 3 is a diagram showing an example of a two-dimensional display of the correspondence table in the control value plane. FIG. 4 is a schematic diagram of an electron optical system near the aperture of a scanning electron microscope. FIG. 5 is a flowchart of a method for updating optimal control values ​​for an aligner. FIG. 6 is a diagram for explaining the process of updating the correspondence table for aligner control values. FIG. 7 is a diagram showing a two-dimensional display of the process of updating the correspondence table in the control value plane. FIG. 8 is a diagram for explaining an example of a method for uniformly selecting observation conditions in the correspondence table in the control value plane. FIG. 9 is a diagram for explaining another example of a method for uniformly selecting observation conditions in the correspondence table in the control value plane. FIG. 10 is a diagram showing changes in the electron optical system that occur with updating the correspondence table for an aperture aligner. FIG. 11 is a diagram showing a process of reflecting the influence of updating the correspondence table for an upper aligner in the correspondence table for a lower aligner. FIG. 12 is a diagram showing a two-dimensional display of the reflection process in the control value plane. FIG. 13 is a diagram showing a display screen for updating an input correspondence table or correspondence formula. FIG. 14 is a diagram showing a display screen for a table related to the correspondence table or correspondence formula at the time of updating.

[0013] [First Embodiment] <Configuration of Scanning Electron Microscope> FIG. 1 is a schematic diagram of a scanning electron microscope 1 (charged particle beam device). The scanning electron microscope 1 includes a column 100 and a processing device 200. The column 100 contains an electron gun 101, a focusing lens 102, an aperture aligner 103, an aperture 104, a scan coil 105, an astigmatism corrector aligner 106, an astigmatism corrector 107, an objective lens aligner 108, an objective lens 109, a sample stage 112, and a detector 113. The processing device 200 is, for example, any computer device. The processing device 200 includes a processor, a memory, a storage device, an input device, an output device, and buses connecting these devices. The processing device 200 includes an image forming unit 115, a calculation processing unit 116, a storage unit 117, a control unit 118, and an input / display unit 119, which are functions realized by the processor executing programs stored in the memory.

[0014] The electron gun 101 irradiates a primary electron beam 110 (charged particle beam). The focusing lens 102 and objective lens 109 focus the primary electron beam 110. The aperture 104 adjusts the aperture angle of the primary electron beam 110. The scan coil 105 deflects and scans the primary electron beam 110. The detector 113 detects secondary particles 114 generated when the primary electron beam 110 irradiates a sample 111. The scanning electron microscope 1 has three types of aligners: an aperture aligner 103, an astigmatism corrector aligner 106, and an objective lens aligner 108, arranged from top to bottom. Since the aligners deflect the primary electron beam 110 three-dimensionally, each aligner is composed of two deflection coils that deflect the primary electron beam 110 in directions approximately perpendicular to each other on a plane approximately perpendicular to the primary electron beam. The optical axis is adjusted by adjusting the control values ​​of these two coils.

[0015] Other charged particle beams such as ions may be used as the primary electron beam 110. Secondary particles 114 are ions or X-rays (particles or waves) secondarily generated by irradiation with the primary electron beam 110, and are detected by a detector 113. An image forming unit 115 forms a charged particle beam image based on a signal from the detector 113, and transmits the formed image to a calculation processing unit 116 and an input display unit 119.

[0016] The calculation processing unit 116 processes images transmitted from the image forming unit 115 and performs calculations necessary for the operation of the scanning electron microscope 1. The storage unit 117 stores information such as values ​​related to the observation conditions of the scanning electron microscope 1 and values ​​related to electron optical conditions, such as aligner control values. The observation conditions include, for example, information such as acceleration voltage, current value, contrast, and number of accumulated images. The electron optical conditions are conditions related to the electromagnetic field that affects the primary electron beam 110 within the electron tube 100. The control unit 118 acquires, controls, and transmits values ​​related to the scanning electron microscope 1. The storage unit 117 stores values ​​transmitted from the control unit 118 and transmits these values ​​to the input / display unit 119. The input / display unit 119 displays images and values ​​transmitted from the image forming unit 115, calculation processing unit 116, storage unit 117, and control unit 118 on a display device, and also accepts values ​​related to the scanning electron microscope 1 input by the operator via an input device and transmits the values ​​to the control unit 118.

[0017] 2 is a flowchart of the optical axis adjustment method for the scanning electron microscope 1. The optical axis adjustment method of the present disclosure can be implemented by the processor of the processing device 200 executing a program. For the sake of simplicity, the following description may focus mainly on the functional units of the processing device 200.

[0018] (Step S201) The input display unit 119 accepts input of the observation conditions or range of observation conditions to be used for observation from the operator. For simplicity, in this embodiment, the acceleration voltage of the electron gun 101 is described as an example of an observation condition. However, in actual operation, multiple observation conditions, such as the probe current value and working distance, are combined. Furthermore, the observation conditions to be used in the table or formula (described later) that is actually created are selected from the input observation conditions only if they affect the electron optical conditions. In this embodiment, the acceleration voltage (kV) to be used is specified to be in the range of Vmin to Vmax (Vmax = Vmin + 9).

[0019] (Step S202) The calculation processing unit 116 checks, via the input / display unit 119 or the storage unit 117, whether there is a table or calculation formula (hereinafter referred to as a correspondence table or correspondence formula) storing optimal aligner control values ​​corresponding to the observation conditions of the scanning electron microscope 1 within the specified range of observation conditions. Because three types of aligners are arranged in the scanning electron microscope 1, the calculation processing unit 116 checks for correspondence tables or correspondence formulas for the three types of aligners. Note that, in this embodiment, the optimal aligner control values ​​refer to control values ​​when the primary electron beam 110 passes through the centers of the aperture 104, the astigmatism corrector 107, and the objective lens 109. If there is no correspondence table or correspondence formula for optimal aligner control values ​​(No), the process proceeds to step S203. If there is a correspondence table or correspondence formula (Yes), the process proceeds to step S204.

[0020] (Step S203) The calculation processing unit 116 creates a new correspondence table or correspondence formula and stores it in the storage unit 117. For example, a new correspondence table or correspondence formula is created before shipping the scanning electron microscope 1 or when observation is performed under a new range of observation conditions. A method for creating a correspondence table will be described below.

[0021] FIG. 3A is a diagram showing an example of a correspondence table 301. FIG. 3B is a diagram showing an example of a two-dimensional display 302 of the correspondence table on the control value plane. In creating the correspondence table, the operator first determines the observation conditions under which the optimal control values ​​for the aligner will be investigated. Specifically, the operator inputs the steps of the observation conditions and the number of investigation points via the input display unit 119. The calculation processing unit 116 determines the observation conditions to be investigated according to the observation range initially input. In this embodiment, the acceleration voltage is set to 1 kV in steps, and the optimal control values ​​for each aligner are investigated for 10 acceleration voltage conditions (No. 0 to 9).

[0022] In this embodiment, only one accelerating voltage condition is selected as the observation condition, but if this number increases to two or three conditions, the number of columns in the correspondence table will increase exponentially. Therefore, it is advisable to use a technique such as experimental design to reduce the number of observation conditions for investigating the optimal control value for each aligner. In addition, the operator may arbitrarily determine the observation conditions for investigating the optimal control value for the aligner.

[0023] Next, normal optical axis adjustment is performed under the determined observation conditions, and the optimal control value for each aligner is investigated. The calculation processing unit 116 stores the optimal control value in the column for the investigated observation condition in the correspondence table 301. Here, normal optical axis adjustment refers to the optical axis adjustment that has traditionally been performed manually or using an automatic optical axis adjustment function.

[0024] When adjusting the optical axis during observation with the scanning electron microscope 1, the control values ​​of the aligner are set by referring to this created correspondence table 301. If the desired observation conditions are not present in the correspondence table 301, the calculation processing unit 116 calculates and sets values ​​by interpolating or extrapolating the control values ​​stored in the correspondence table 301. For example, if the accelerating voltage of the observation conditions is Vmin+2.5 kV, the control values ​​of Vmin+2 kV and Vmin+3 kV are interpolated using a linear function. In other words, the control value at the midpoint between Vmin+2 kV and Vmin+3 kV in the two-dimensional display 302 of the control values ​​is adopted. The operator may freely select the interpolation or extrapolation function using the input display unit 119.

[0025] Furthermore, when obtaining the optimal control value for the aligner as a correspondence formula, normal optical axis adjustment is performed under several observation conditions to create the correspondence table 301 in the same manner as in the above-described correspondence table 301. The calculation processing unit 116 can obtain the correspondence formula by fitting the results of the correspondence table 301 using an equation such as a polynomial. Specifically, in the case of a linear function, the constants a, b, c, and d of the control value x = fitting b and the control value y = c × acceleration voltage + d are obtained by fitting.

[0026] (Step S204) The calculation processing unit 116 determines whether the optimal control value of the aligner has changed. If the optimal control value of the aligner has changed (Yes), the process proceeds to step S205. If the optimal control value of the aligner has not changed (No), the process proceeds to step S206. In observations immediately after creating the correspondence table 301 or the correspondence formula, there is almost no change in the correspondence table or the correspondence formula over time, so the aligner control value can be set by referring to the correspondence table 301 or the correspondence formula (step S206). However, if the electron-optical system is mechanically moved, the lens barrel is baked, or sufficient time has passed, the optimal control value of the aligner is likely to change. Therefore, it is necessary to update the created correspondence table 301 or the correspondence formula. To confirm whether the optimal control value of the aligner has changed, the observer can manually adjust the optical axis under certain observation conditions, or the observer can determine this based on the results of the automatic optical axis adjustment function.

[0027] (Step S205) If it is determined that the optimal control value of the aligner has changed, the calculation processing unit 116 updates the correspondence table or the correspondence formula. The method for updating the correspondence table or the correspondence formula will be described below. First, the operating principle of the aligner for adjusting the optical axis related to the updating method will be described. For simplicity, the explanation will be given in two dimensions rather than three dimensions.

[0028] FIG. 4 is a schematic diagram of the electron optical system near the aperture 104 of the scanning electron microscope 1. A primary electron beam 110 emitted by the electron gun 101 is first focused by a focusing lens 102. However, if the primary electron beam 110 continues on its current trajectory, it will reach the outside of the aperture of the aperture 104, as shown by the dashed line. Therefore, the aperture aligner 103 deflects the primary electron beam 110, adjusting it so that it passes through the center of the aperture 104, as shown by the solid line trajectory. Generally, an aligner controls the deflection angle using an electromagnetic field or an electrostatic field. In the case of an electromagnetic field, the deflection angle is controlled by the current value of the coil, and the deflection angle is proportional to the −0.5 power of the acceleration voltage. In the case of an electrostatic field, the deflection angle is controlled by the strength of the electric field, i.e., the voltage between the electrodes, and the deflection angle is proportional to the reciprocal of the acceleration voltage. In this embodiment, for ease of explanation, the actual deflection angle taking into account the acceleration voltage is used as the control value.

[0029] In FIG. 4 , a two-dimensional plane coordinate system (two-dimensional coordinate system) is set, with the horizontal direction being the x (y) axis and the vertical direction being the z axis. In an ideal electron optical system arrangement, the position of the electron gun 101 and the center of the aperture 104 are at x = 0, and the angle of incidence of the primary electron beam 110 is 0°. However, the arrangement of these electron optical systems can be mechanically misaligned, which is thought to be the main cause of changes in the optimal control value of the aligner. Therefore, the influence of the positional misalignment of the electron gun 101 in the x-axis direction is defined as xc, and the influence of the angular misalignment is defined as θc. The deviation of the center position of the aperture 104 in the x-axis direction is defined as xa. The difference between the aperture aligner 103 and the aperture 104 in the z-axis direction is defined as za. The difference between the focusing lens 102 and the aperture 104 in the z-axis direction is defined as zc. When the control value of the aligner is θ, the x-coordinate at which the primary electron beam 110 reaches the aperture 104 is expressed by the following equation (1):

[0030] xc+(zc-za)sinθc+zasin(θc+θ)...Formula (1)

[0031] In the scanning electron microscope 1, the values ​​of θc and θ are sufficiently small, so that the formula (1) can be approximately expressed by the following formula (2).

[0032] xc+(zc-za)θc+za(θc+θ)...Formula (2)

[0033] When the control value θ of the aligner is optimal, the value of formula (2) is xa. In other words, the optimal control value θ is expressed by formula (3).

[0034] θ=(xa-xc-zcθc) / za...Formula (3)

[0035] From equation (3), when xa, xc, zc, and θc change, the optimal control value θ changes by adding a constant such as θ+B. When za changes, the optimal control value θ changes by multiplying it by a constant such as Aθ. Both A and B are constants determined by xa, xc, zc, θc, and za. In other words, it can be seen that the change in the optimal control value θ can be expressed by a linear conversion formula, Aθ+B.

[0036] This can be expanded from two dimensions to three dimensions using complex numbers. If the optimal control value before the change is θ = θx + iθy and the optimal control value after the change is θ' = θx' + iθy', then θ' = Aθ + B can be expressed using the complex numbers A = Ax + iAy and B = Bx + iBy. Furthermore, because charged particle beams move in a spiral motion within an electromagnetic field, the effect of rotation must be taken into consideration. If the effect of this rotation is θr, then θ' = exp(iθr)(Aθ + B). Therefore, by examining the θ and θ' control values ​​of the aligner before and after the change under multiple observation conditions, the values ​​of θr, A, and B can be determined, and the following formula (4), which is a conversion formula for the optimal control value of the aligner, can be obtained.

[0037] F(θ)=exp(iθr)(Aθ+B)...Formula (4)

[0038] Although the aperture aligner 103 is shown as an example in FIG. 4, the same applies to the astigmatism corrector aligner 106 and the objective lens aligner 108.

[0039] (Step S206) The calculation processing unit 116 references the correspondence table or correspondence formula created in step S203 or the correspondence table or correspondence formula updated in step S205 to set control values ​​for each aligner that correspond to the observation conditions desired by the measurer. This completes the optical axis adjustment process. The control unit 118 controls each aligner in accordance with the set control values, and the sample 111 is observed.

[0040] <Method of Updating Correspondence Table or Correspondence Formula> Next, a specific procedure for updating the correspondence table or correspondence formula (step S205) will be described.

[0041] 5 is a flowchart of a method for updating the optimal control values ​​of the aligners. First, the updating is performed on the aligners in the lens barrel 100, starting from the top. In this embodiment, the order is the aperture aligner 103, the astigmatism corrector aligner 106, and the objective lens aligner 108. First, the updating of the topmost aperture aligner 103 is started.

[0042] (Step S501) Step S501 is a process in which the calculation processing unit 116 reflects the update of the control values ​​for the upper aligners. However, since the aperture aligner 103 is the topmost aligner, step S501 is not executed.

[0043] (Step S502) Next, the calculation processing unit 116 checks whether the correspondence table or the correspondence formula is updated. Fig. 6A is a diagram for explaining the process of updating the correspondence table 601 of the aligner's control values. Fig. 6B is a diagram showing a two-dimensional representation 602 of the process of updating the correspondence table on the control value plane. The update process will be explained using Figs. 6A and 6B.

[0044] First, in step S502, several observation conditions are selected within the range of the correspondence table to be updated, and optical axis adjustment is performed. In this embodiment, the range of acceleration voltage, which is an observation condition, is specified as Vmin to Vmax, so several observation conditions are selected from this range. The observation conditions to be investigated for updating can be selected directly by the operator from the two-dimensional plane of control values ​​displayed on the input display unit 119. Furthermore, to perform updates with greater precision, it is desirable to select observation conditions so that they are uniform across the two-dimensional plane of control values.

[0045] 7A and 7B are diagrams illustrating an example of a method for uniformly selecting viewing conditions in a correspondence table in two-dimensional displays 701 and 702 of a control value plane, respectively. First, the pre-update correspondence table or correspondence formula within the range of viewing conditions is referenced, and an arbitrary frame is set on the two-dimensional plane of control values ​​that surrounds the entire range to be updated. FIG. 7A shows an example in which the frame is a polygon simply formed by connecting the control values ​​in the correspondence table with straight lines. FIG. 7B shows an example in which the smallest rectangle that surrounds the control values ​​in the correspondence table is used as the frame.

[0046] Next, the observation conditions can be selected so that they are evenly spaced within the frame. The black dots in Figures 7A and 7B indicate the control values ​​of the observation conditions selected for update investigation. The white dots indicate the control values ​​in the correspondence table. In Figure 7A, when a polygon is used as the frame, selecting the observation conditions so that they are approximately evenly spaced along the frame line results in an even selection within the frame. In this case, control values ​​obtained by internally or externally interpolating the correspondence table may be used. When a rectangle is used as the frame, as in Figure 7B, the selection method is one that maximizes the uniformity between the vertices and the center of gravity (the black dots at the bases of the arrows), but no observation conditions corresponding to these exist within the range of the correspondence table. In this case, it is advisable to use the observation conditions closest to the control value plane within the range of the correspondence table or correspondence formula to be updated. In this case, control values ​​obtained by internally or externally interpolating the correspondence table may be used.

[0047] In this way, any desired frame line can be set automatically by the calculation processing unit 116 or manually by the operator via the input display unit 119, and the operator can specify the number of observation conditions to be selected via the input display unit 119, thereby recommending to the operator observation conditions for which updates are to be investigated via the input display unit 119. Note that the rules for calculating the arrangement of control values ​​so as to be uniform on a two-dimensional plane are not limited to the above example.

[0048] However, since the purpose is to determine the unknowns in the linear transformation equation, it is recommended to select six or more observation conditions. However, this is not always the case when some of the unknowns are known. In this embodiment, A = Ax + iAy, B = Bx + iBy, and θr are unknowns, and θr is a real number, so five observation conditions are selected.

[0049] Furthermore, for the sake of simplicity in this embodiment, Figures 6A and 6B show a state in which the operator has arbitrarily specified five observation conditions (No. 0, No. 3, No. 5, No. 7, and No. 9) that exclude internal and external interpolation from the specified range of the correspondence table.

[0050] Next, normal optical axis adjustment is performed under the selected observation conditions. As in the case where the correspondence table or correspondence formula is created (step S203), the optical axis may be adjusted manually or by using a conventional automatic optical axis adjustment function.

[0051] (Step S503) In Figures 6A and 6B, the results of optical axis adjustment under the selected observation conditions (No. 0, No. 3, No. 5, No. 7, No. 9) are plotted as triangles. The calculation processing unit 116 estimates the unknowns in Equation (4) using the results of optical axis adjustment under the selected observation conditions. If the number of observation conditions investigated for updating is the same as the unknowns, the calculation processing unit 116 solves the simultaneous equations. If the number of observation conditions investigated for updating is greater than the unknowns, the calculation processing unit 116 estimates the unknowns by fitting or the like. The linear transformation formula expressed by Equation (4) is obtained using these estimated unknowns.

[0052] (Step S504) The calculation processing unit 116 updates the correspondence table or correspondence formula within the specified range all at once using the linear conversion formula expressed by Equation (4). In the case of a correspondence formula, the correspondence formula is directly converted by linear conversion. The square plots in Figures 6A and 6B show the control values ​​when the correspondence table or correspondence formula is updated using the linear conversion formula of Equation (4).

[0053] Furthermore, if a conversion formula is provisionally determined during the update investigation, the control value at which the update investigation for the next observation condition is started may be the control value obtained by updating the control value in the correspondence table before the update with the provisional conversion formula. This allows the optical axis adjustment to be performed from a position close to the optimal control value, making it possible to complete the update investigation in a short time. This completes the update of the aperture aligner 103.

[0054] (Step S501) Next, the calculation processing unit 116 updates the correspondence table or correspondence formula for the astigmatism corrector aligner 106. First, returning to step S501, the calculation processing unit 116 reflects the results of updating the upper-stage aperture aligner 103. Since the upper-stage electron optical conditions have been updated, the calculation processing unit 116 corrects the resulting deviation of the astigmatism corrector aligner 106.

[0055] 8 is a diagram showing changes in the electron optical system that occur when the correspondence table of the aperture aligner 103 is updated. The dashed line shows the state before updating the correspondence table or correspondence formula of the upper aperture aligner 103, and the solid line shows the state after updating. As shown in FIG. 8, when the electron optical conditions of the aperture aligner 103 are changed by updating, it can be seen that the primary electron beam 110 no longer passes through the center of the lower astigmatism corrector 107. When the upper aperture aligner 103 is updated in this way, a positional shift and an angular shift of the primary electron beam 110 occur at the height of the aperture 104, and this shift is canceled out by reflecting it to the lower aligner.

[0056] A method for reflecting the deviation of the primary electron beam 110 to the aligner in the lower row will be described. The deviation of the primary electron beam 110 generated in the upper row can be estimated using Equation (4), which is the conversion equation used in updating the upper row. For simplicity, the description will be given using two-dimensional coordinates.

[0057] First, the deviation in the height direction of the aperture 104, i.e., in the z-axis direction, can be estimated from A because A is determined by za, which is the height of the aperture 104. If we consider that the height of the aligner is fixed and only the height of the aperture 104 is variable, zc can also be estimated at the same time. Next, we estimate the influence of xa, xc, and θc, but since B is determined by xa, xc, zc, θc, and za, the influence of xa, xc, and θc cannot be separated. Therefore, we consider the positional deviations occurring at xa and xc as an angular deviation approximately combined into θc. In other words, we only consider the angular deviation θc' = θc + (xc - xa) / zc.

[0058] Here, if the angular deviation of θc' is denoted as dθ, the effect of updating the optimal control value of the upper aligner (aperture aligner 103) can be reflected in the lower aligner based on the distance L1 between the aperture 104 and the astigmatism corrector aligner 106 and the distance L2 between the astigmatism corrector aligner 106 and the astigmatism corrector gap 107. If the optimal control value of the astigmatism corrector aligner 106 before the positional deviation and angular deviation around the aperture 104 in the upper aligner is denoted as θs and the angle of incidence of the primary electron beam 110 on the aperture 104 is denoted as θ0, then the following equation (5) is satisfied.

[0059] L1sinθ0=L2sin(θs-θ0)...Formula (5)

[0060] Furthermore, since θ0 and θs are sufficiently small in the scanning electron microscope 1, the formula (5) can be approximately expressed by the formula (6).

[0061] L1θ0=L2(θs-θ0)...Formula (6)

[0062] After updating the optimal control value of the upper aligner, as described above, a height deviation dza of the aperture 104 and an incident angle deviation dθ of the primary electron beam 110 occur. The variation value of za is used for the height deviation dza, and the variation value of θc' is used for the angle deviation dθ. At this time, the optimal control value θs' of the astigmatism corrector aligner 106 satisfies the following mathematical formula (7):

[0063] (L1+dza)(θ0+dθ)=L2(θs'-θ0-dθ)...Formula (7)

[0064] If θ0 is eliminated from the formulas (6) and (7), the following formula (8) is obtained.

[0065] θs'=(L1+L2+dz) {θs / (L1+L2)+dθ / L2}...Formula (8)

[0066] By using Equation (8), the influence of updating the control value of the upper aligner can be reflected to the lower aligner. When this is expanded from two-dimensional space to three-dimensional space using complex numbers, the reflection equation G becomes the following Equation (9).

[0067] G=(L1+L2+dz)exp(iθrs) {θs / (L1+L2)+dθ / L2}...Formula (9)

[0068] Here, θs = θxs + iθys, θs' = θxs' + iθys', and dθ = dθx + dθy are defined. dθx indicates the angular deviation in the x-axis direction. dθy indicates the angular deviation in the y-axis direction. θrs indicates the rotation angle of the spiral motion of the charged particle beam. Using reflection formula G in equation (9), the effect of updating the control values ​​of the upper aligner can be reflected all at once in the correspondence table or correspondence formula for the lower aligner.

[0069] 9A is a diagram showing a correspondence table 901 in the process of reflecting the influence of an update of the correspondence table of the upper aligner in the correspondence table of the lower aligner. FIG. 9B is a diagram showing a two-dimensional representation 902 of the update reflection process on the control value plane. The calculation processing unit 116 reflects the influence of the update of the upper row in the correspondence table or correspondence formula before reflection using the reflection formula G obtained in the previous procedure. In the case of the correspondence formula, the reflection formula G is directly applied to the correspondence formula.

[0070] Then, in steps S502 to S504, the calculation processing unit 116, starting from the control value of the updated correspondence table or correspondence formula, checks for updates to the astigmatism corrector aligner 106, similar to the case of the diaphragm aligner 103, finds the conversion formula F, and updates the correspondence table or correspondence formula using the conversion formula. By doing so, by reflecting the changes in the upper-stage aligner in the lower-stage, it is possible to check for updates while canceling out any deviations that occur as a result of the reflection. In other words, optical axis adjustment can be performed from a point closer to the optimal control value than before the reflection, which leads to a reduction in the time required for checking for updates. In particular, if there is almost no deviation around the astigmatism corrector 107, it is possible to update the correspondence table or correspondence formula simply by reflecting the deviations in the upper-stage without checking for updates.

[0071] The calculation processing unit 116 also performs steps S501 to S504 to update the remaining objective lens aligner 108 in the same manner as in the case of the astigmatism corrector 107, reflecting the updates in the upper row and updating the correspondence table or correspondence formula.

[0072] The above procedure completes the update of the correspondence table or correspondence formula that stores the optimal control values ​​for the aligner. Furthermore, in this embodiment, the conversion formula is a linear conversion, but a different conversion formula may be used depending on the arrangement of the lens barrel or the operating principle of the aligner. All calculations related to the above correspondence table or correspondence formula are performed by the calculation processing unit 116, and the calculation results are sent to the storage unit 117 as appropriate.

[0073] Summary of First Embodiment As described above, the scanning electron microscope 1 (charged particle beam device) according to the first embodiment includes a charged particle optical system including an electron gun 101 that irradiates a sample 111 with a primary electron beam 110 (charged particle beam), an aperture aligner 103 that adjusts the optical axis of the charged particle optical system, an astigmatism corrector aligner 106, and an objective lens aligner 108 (at least one aligner), a detector 113 that detects secondary particles 114 (particles or electromagnetic waves) generated by irradiating the sample 111 with the primary electron beam 110, and a processing device 200 that processes the detection signal acquired by the detector 113 to acquire an image. The processing device 200 creates at least one of a correspondence table that stores optimal control values ​​for multiple observation conditions for each aligner and a correspondence formula to calculate the optimal control values ​​(step S203). The processing device 200 measures changes in the optimal control values ​​for the aligner under one or more observation conditions that are less than the number of observation conditions used to create the correspondence table or the correspondence formula (steps S502 to S503). The processing device 200 updates at least one of the correspondence table and the correspondence formula using the measurement results of the change by converting it with a conversion formula obtained from the arrangement relationship of the two-dimensional coordinates of the charged particle optical system (steps S205, S504).

[0074] In this way, a correspondence table or correspondence formula for optimal aligner control values ​​corresponding to electron optical conditions is created in advance, and when the optimal control values ​​in this correspondence table or correspondence formula change, the optical axis is adjusted again under fewer observation conditions. This makes it possible to update the correspondence table or correspondence formula for optimal aligner control values ​​in a short time. With this configuration, by referencing the correspondence table or correspondence formula that stores the updated aligner control values ​​when observing the sample 111, it is no longer necessary to adjust the optical axis for each observation or observation condition, and it becomes possible to perform electron microscope observation in a short time.

[0075] Second Embodiment In the second embodiment, a scanning electron microscope having a function for checking whether the correspondence table or correspondence formula updated in the first embodiment has been properly updated will be described. The device configuration of the scanning electron microscope of this embodiment is the same as that of the first embodiment. First, the correspondence table or correspondence formula is created and updated according to the same flow as in the first embodiment (FIGS. 2 and 5).

[0076] Fig. 10A is a diagram showing a display screen 1001 for updating the correspondence table or correspondence formula displayed on the input display unit 119. The display screen 1001 includes a two-dimensional display 1002 of a table (table 1006 in Fig. 10B) relating to the correspondence table at the time of updating in the control value plane. Fig. 10B is a diagram showing a display screen 1005 of the table 1006 relating to the correspondence table or correspondence formula at the time of updating. The display screen 1001 in Fig. 10A and the display screen 1005 in Fig. 10B can be displayed simultaneously on the input display unit 119.

[0077] As described in the first embodiment, the transformation formula F used for updating is found by solving simultaneous equations or by fitting using the results of the update investigation. However, as shown in FIG. 10A , the results of the update investigation (triangular plot in FIG. 10A ) and the results of the conversion using the transformation formula (square plot in FIG. 10A ) may have different values. In this embodiment, the distance between the triangular plot and the square plot is called the "residue." If the update investigation is successful, the residual value will be small, but if it is unsuccessful, the residual value will be large. In other words, the quality of the results of the update investigation can be determined from the size of the residue.

[0078] To determine whether the results of the update inspection are satisfactory, first, the input display unit 119 displays the update process of the correspondence table or correspondence formula on a two-dimensional plane of control values. Based on the size of the residue, the operator selects the observation conditions under which the update inspection is thought to have failed from the two-dimensional display 1002 of table 1006 relating to the correspondence table at the time of update, or table 1006 relating to the correspondence table or correspondence formula at the time of creation and update, displayed on the input display unit 119. When the operator selects the observation conditions, the scanning electron microscope 1 switches to the selected observation conditions and transitions to a manual optical axis adjustment screen (not shown). The operator can switch the aligner control values ​​at this time by selecting the triangular and square plots on the two-dimensional display 1002, or by selecting the aligner control values ​​in table 1006.

[0079] The method for determining whether an update investigation based on the residue is acceptable is to determine, in descending order of residue, whether the updated control values ​​for the corresponding observation conditions are optimal on the optical axis adjustment screen. If they are determined to be optimal, it can be determined that the update investigation has been performed appropriately, and no corrections to the update investigation are made. On the other hand, if they are determined to be inappropriate, the optical axis is adjusted again, and the measurer selects a recalculation button 1003 on the display screen 1001 to recalculate the update conversion formula. This updates the two-dimensional display 1002 of the table 1006 related to the updated correspondence table and the table 1006 related to the correspondence table or correspondence formula. The pass / fail determination and corrections of the update investigation are repeated until the maximum residue falls within the allowable range. If the maximum residue exceeds the allowable range even after repeated update investigations, the range of observation conditions is changed to divide it, and each conversion formula is calculated for each divided observation range.

[0080] Next, a method for verifying whether the optimal control value of the updated aligner is appropriate under observation conditions where no update investigation has been performed will be described.

[0081] The operator selects an observation condition for which an update investigation has not been performed from the two-dimensional display 1002 of the table 1006 relating to the correspondence table at the time of update displayed on the input display unit 119, or the table 1006 relating to the correspondence table or correspondence formula. When the operator selects the observation condition, the scanning electron microscope 1 switches to the selected observation condition and transitions to a manual optical axis adjustment screen. The aligner control value at this time becomes the updated value indicated by the square plot. The operator refers to the optical axis adjustment screen to determine whether the updated control value is acceptable. If it is not acceptable, the operator makes minor corrections, adds these results to the update investigation results, and the conversion formula and updated control value are recalculated. The addition of the update investigation results is also reflected in the two-dimensional display 1002 of the table relating to the correspondence table at the time of update displayed on the input display unit 119. This determination and correction is repeated, and if the result is acceptable several times in a row, it is determined that the update has been performed appropriately.

[0082] If observation conditions that increase the amount of residue appear during this process, the pass / fail judgment of the renewal inspection described above may be performed under the observation conditions used for the renewal inspection, as appropriate.

[0083] Furthermore, if the operator wishes to check the updated results evenly across the entire table, the operator may press the test button 1004 on the display screen 1001 to automatically and evenly select the observation conditions that have not been subject to update investigation.

[0084] As described above, by repeatedly correcting the update investigation results that serve as learning data and confirming and correcting the update results using verification data, and illustrating this process on a two-dimensional plane of control values, the validity of the update results can be confirmed and corrected.

[0085] Summary of Second Embodiment As described above, the scanning electron microscope 1 according to the second embodiment shows the control values ​​to the operator by displaying them two-dimensionally on the input display unit 119. This allows the operator to check whether the optimum aligner control values ​​have been appropriately updated.

[0086] [Modifications] The present disclosure is not limited to the above-described embodiments and includes various modifications. For example, the above-described embodiments have been described in detail to clearly explain the present disclosure, and it is not necessary to include all of the described configurations. Furthermore, a part of one embodiment can be replaced with a configuration of another embodiment. Furthermore, a configuration of another embodiment can be added to a configuration of one embodiment. Furthermore, a part of the configuration of each embodiment can be added to, deleted from, or substituted for a part of the configuration of another embodiment.

[0087] Furthermore, the above-described configurations, functions, processing units, processing means, etc. may be realized in part or in whole as, for example, integrated circuits or other hardware. Furthermore, the above-described configurations, functions, etc. may be realized by a processor interpreting and executing a program that realizes each function. That is, they may be realized as software. Information such as programs, tables, and files that realize each function can be stored in storage devices such as memory, hard disks, and solid-state drives (SSDs), or storage media such as IC cards, SD cards, and DVDs.

[0088] Furthermore, the control lines and information lines are shown as those considered necessary for the explanation, but do not represent all the control lines and information lines necessary for the product. In reality, it can be considered that almost all components are interconnected.

[0089] DESCRIPTION OF SYMBOLS 1...Scanning electron microscope 100...Column 101...Electron gun 102...Converging lens 103...Aperture aligner 104...Aperture 105...Scan coil 106...Astigmatism corrector aligner 107...Astigmatism corrector 108...Objective lens aligner 109...Objective lens 110...Primary electron beam 111...Sample 112...Sample stage 113...Detector 114...Secondary particles 115...Image forming unit 116...Calculation processing unit 117...Storage unit 118...Control unit 119...Input display unit 200...Processing device

Claims

1. A charged particle beam device comprising: a charged particle optical system that irradiates a sample with a charged particle beam; at least one aligner that adjusts the optical axis of the charged particle optical system; a detector that detects particles or electromagnetic waves generated by irradiating the sample with the charged particle beam; and a processing device that processes the detection signal obtained by the detector to obtain an image, wherein the processing device creates, for each aligner, at least one of a table that stores optimal control values ​​for a plurality of observation conditions and a formula for calculating them, measures changes in the optimal control values ​​of the aligner under one or more observation conditions that are less than the number of the plurality of observation conditions used to create the table or formula, and uses the results of the measurement to update at least one of the table and formula by converting them using a conversion formula calculated from the arrangement of two-dimensional coordinates of the charged particle optical system.

2. A charged particle beam device according to claim 1, characterized in that the processing device reflects the influence of changes to the lower aligner due to the control value after the update of the upper aligner from the two-dimensional plane of the control value before the update of the lower aligner, and updates the control value of the lower aligner from that state.

3. A charged particle beam device according to claim 1, characterized in that the processing device, in measuring the change in the optimal control value, selects an observation condition within the range of the table, including internal and external interpolation, that is the control value closest to the control value in which the observation conditions are evenly distributed in accordance with a predetermined standard within any frame surrounding the range of the table, including internal and external interpolation.

4. A charged particle beam device according to claim 3, characterized in that the processing device uses a rectangle that surrounds the range of the table, including the internal and external interpolation, as the arbitrary frame, and selects control values ​​from the observation conditions for the range of the table, including the internal and external interpolation, that are closest to the vertices and center of gravity of the rectangle.

5. A charged particle beam device according to claim 1, characterized in that the processing device displays on a display device a two-dimensional plane of the optimum control value before and after the update and in measuring the change.

6. A method for adjusting an optical axis of a charged particle beam device comprising: a charged particle optical system that irradiates a sample with a charged particle beam; at least one aligner that adjusts the optical axis of the charged particle optical system; a detector that detects particles or electromagnetic waves generated by irradiating the sample with the charged particle beam; and a processing device that processes the detection signal acquired by the detector to obtain an image, the method comprising: creating, by the processing device, at least one of a table that stores optimal control values ​​for a plurality of observation conditions for each aligner and a formula for calculating them; measuring changes in the optimal control values ​​of the aligner under one or more observation conditions that are less than the number of the plurality of observation conditions used to create the table or the formula; and using the results of the measurement to update at least one of the table and the formula by converting them using a conversion formula calculated from the arrangement of two-dimensional coordinates of the charged particle optical system.

7. The optical axis adjustment method according to claim 6, further comprising the steps of: reflecting, by the processing device, the influence of the change on the lower aligner due to the control value after the update of the upper aligner from the two-dimensional plane of the control value of the lower aligner before the update; and updating the control value of the lower aligner from that state.

8. An optical axis adjustment method according to claim 6, characterized in that measuring the change in the optimal control value includes selecting an observation condition within the range of the table, including internal and external interpolation, that is the control value closest to the control value in which the observation conditions are evenly distributed in accordance with a predetermined standard within an arbitrary frame surrounding the range of the table, including internal and external interpolation.

9. An optical axis adjustment method according to claim 8, characterized in that selecting the observation conditions for the range of the table, including the internal and external interpolation, includes selecting control values ​​that are closest to the vertices and center of gravity of a rectangle that surrounds the range of the table, including the internal and external interpolation, as the arbitrary frame.

10. The optical axis adjustment method according to claim 6, further comprising displaying, on a display device, a two-dimensional plane of the optimum control value before and after the update and in measurement of the change, by the processing device.

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