Charged particle beam device and aberration measurement method

Abstract

In an imaging unit 100, an aligner is caused to perform a two-dimensional sweep with a charged particle beam of a principal plane of a lens by a first modulation signal, and a deflector is caused to perform a two-dimensional sweep with the charged particle beam over a sample 112 by a second modulation signal synchronized with the first modulation signal. On the basis of an angle-scan image for beam-landing control, which is image data generated by a signal processing unit 103 by synchronously recording a detection signal of a detector 115 with the first modulation signal or the second modulation signal, geometric aberration coefficients of the lens at the surface position of the sample are calculated.

Description

Charged particle beam device and aberration measurement method

[0001] The present disclosure relates to a charged particle beam device and a method for measuring the aberration of a lens at the surface position of a sample.

[0002] Measurement of geometric aberration in electron microscopes is often performed by separating and quantifying each aberration component using the aperture angle dependence of aberration. For example, Patent Document 1 discloses a method (aberration diagram method) for acquiring multiple SEM images under different beam tilt conditions using a scanning electron microscope (SEM) and calculating aberration coefficients from field-of-view deviation information between the images. Because SEM images convolute sample information with beam information, it is difficult to directly determine the beam state from the SEM image. Therefore, it is necessary to estimate the beam state from indirect quantities such as field-of-view deviation and sharpness, or to extract only the beam information using image calculations. Patent Document 2 also discloses a method for obtaining beam profile information that blurs the sample information by dividing a defocused image by an in-focus image in frequency space.

[0003] International Publication No. 2011 / 152303 Japanese Patent Application Laid-Open No. 2005-183086

[0004] The technology disclosed in Patent Document 1 involves repeatedly tilting the beam under multiple different conditions and taking images, which requires a long measurement time. Furthermore, there are concerns about contamination of the sample due to the repeated imaging. Meanwhile, the technology disclosed in Patent Document 2 has the advantage of requiring fewer images for aberration measurement and a shorter measurement time. However, since it is a type of deconvolution processing, it is susceptible to noise during beam profile extraction. Furthermore, because it is a semi-empirical method that classifies each aberration component based on shape characteristics such as the beam profile width and brightness distribution, there are concerns about the accuracy of the results.

[0005] A charged particle beam device according to one embodiment of the present disclosure includes an imaging unit including a charged particle source, a sample stage for holding a sample, a lens for focusing a charged particle beam from the charged particle source onto the sample, an aligner for controlling a position at which the charged particle beam passes through a main surface of the lens, a deflector for scanning the charged particle beam over the sample, and a detector for detecting signal electrons emitted when the charged particle beam is irradiated onto the sample, a signal processing unit, and a computer system, wherein the computer system causes the aligner to two-dimensionally sweep the charged particle beam over the main surface of the lens in response to a first modulation signal, and causes the deflector to two-dimensionally sweep the charged particle beam over the sample in response to a second modulation signal synchronized with the first modulation signal, and calculates a geometric aberration coefficient of the lens at the surface position of the sample based on a beam landing control angle sweep image, which is image data generated by the signal processing unit by synchronously recording the detection signal of the detector with the first modulation signal or the second modulation signal.

[0006] The geometric aberration coefficient of a charged particle beam at the sample surface position can be measured more quickly and with higher accuracy. Other objects and novel features will become apparent from the description of this specification and the accompanying drawings.

[0007] 1 is a first hardware configuration example of a charged particle beam device; FIG. 2 is a second hardware configuration example of a charged particle beam device; FIG. 3 is a third hardware configuration example of a charged particle beam device; FIG. 4 is a fourth hardware configuration example of a charged particle beam device; FIG. 5 is a diagram for explaining the principle of the present disclosure; FIG. 6 is a diagram for explaining the principle of the present disclosure; FIG. 7 is a diagram for explaining a first calculation example of a geometric aberration coefficient; FIG. 8 is a diagram for explaining a first calculation example of a geometric aberration coefficient; FIG. 9 is a diagram for explaining a second calculation example of a geometric aberration coefficient; FIG. 10 is a diagram for explaining a third calculation example of a geometric aberration coefficient; FIG. 11 is a diagram for explaining a fourth calculation example of a geometric aberration coefficient; FIG. 12 is a diagram for explaining an example of a GUI; FIG. 13 is a diagram for explaining an example of a GUI; FIG. 14 is a diagram for explaining an example of a GUI;

[0008] Hereinafter, the present embodiment will be described with reference to the accompanying drawings. In the accompanying drawings, functionally identical elements may be designated by the same or corresponding numerals. Note that the accompanying drawings show embodiments and implementation examples according to the principles of the present disclosure, but these are for understanding the present disclosure and are not to be used to interpret the present disclosure in a limiting manner. The descriptions in this specification are merely typical examples and are not intended to limit the scope or application of the present disclosure in any way.

[0009] Although the present disclosure has been described in sufficient detail to enable those skilled in the art to practice the present disclosure, it should be understood that other implementations are possible, and that configurations, structures, and various element substitutions can be made without departing from the scope and spirit of the technical ideas of the present disclosure. Therefore, the following description should not be interpreted as being limited thereto.

[0010] The principle of the present disclosure will be described with reference to Figures 5A and 5B. Figure 5A shows the position (x) at which the electron beam 105 traveling on the optical axis 123 passes through the main surface 124 of the objective lens 111 under modulation control by the aligner 120. ｎ , y ｎ ) is two-dimensionally swept within the scanning region 125. If the objective lens 111 has no aberration, the electron beam 105 lands at a point O where the optical axis 123 intersects with the sample 112, regardless of the position where the electron beam 105 passes through the main surface 124. The set of the tilt angle θ and azimuth angle φ of the electron beam 105 from the optical axis 123 is called the beam landing control angle, and the beam landing control angle is determined by the position (x ｎ , y ｎ ) is uniquely determined by

[0011] Typically, when acquiring an SEM image, the electron beam 105 is controlled by the aligner 120 so as to pass through the intersection of the principal surface 124 of the objective lens 111 and the optical axis 123, and is two-dimensionally swept over the sample 112 by a deflector (not shown). At this time, if the objective lens 111 does not have aberration, even if the electron beam 105 does not pass through the intersection of the principal surface 124 of the objective lens 111 and the optical axis 123, the electron beam 105 will land at point O where the optical axis 123 and the sample 112 intersect, as described above, and no distortion will occur in the image. On the other hand, if the objective lens 111 has aberration, and the electron beam 105 passes through a point other than the intersection of the principal surface 124 of the objective lens 111 and the optical axis 123, the electron beam 105 will land at a position displaced from point O depending on the aberration, and distortion will occur in the image.

[0012] Therefore, in the present disclosure, an image (hereinafter referred to as a "beam landing control angle sweep image") is acquired by two-dimensionally sweeping the electron beam 105 on the main surface 124 of the objective lens 111 in synchronization with the two-dimensional sweep on the sample 112. Since the beam landing control angle sweep image synchronizes two two-dimensional sweeps, the following relationship exists between the scanning area 125 on the main surface 124 and the scanning area 135 on the sample 112 (corresponding to the field of view (FOV)) of the SEM:

[0013] As shown in FIG. 5B, the intersection (x ａ , y ａ The electron beam 105 passing through the center of the field of view (X ａ , Y ａ ) on the principal surface 124 of the objective lens 111. ｎ , y ｎ ) on the sample 112. ｎ , Y ｎ At this time, if there is no aberration in the objective lens 111, the landing position (X ｎ , Y ｎ ) when acquiring an SEM image (the electron beam 105 always intersects with the intersection (x ａ , y ａ )) at the landing position (Xｎ , Y ｎ ), the field of view of the SEM image and the field of view of the beam landing control angle sweep image coincide with each other. On the other hand, if the objective lens 111 has an aberration, the landing position (X ｎ , Y ｎ ) and the landing position (X ｎ , Y ｎ ) does not match. That is, the beam landing control angle sweep image contains distortion corresponding to the aberration of the objective lens 111 at the surface position of the sample 112. In the present disclosure, the geometric aberration coefficient of the objective lens 111 at the surface position of the sample 112 is calculated based on the distortion of the beam landing control angle sweep image.

[0014] Although the objective lens has been used as an example, the lens for which the geometric aberration coefficients are calculated is not limited to the objective lens. It is possible to calculate the geometric aberration coefficients for any lens or combination of lenses used in a charged particle beam device.

[0015] First, the hardware configuration of the charged particle beam device capable of measuring aberrations according to this embodiment will be described, focusing on elements related to aberration measurement. Although the description will be made using an SEM as an example, the present invention is not limited to this, and other charged particle beam devices such as a scanning transmission electron microscope (STEM) or a focused ion beam device can also be used.

[0016] 1 includes an imaging unit 100 (SEM main body), a computer system 101, a signal processing unit 103, an input / output unit 122, and a storage unit 102. The storage unit 102 also functions as a non-transitory recording medium that stores a computer program that controls the operation of this system. The computer system 101 is connected to the input / output unit 122. Upon receiving a command from the computer system 101, the input / output unit 122 controls the electron optical system by outputting a control signal to the electron optical system provided in the imaging unit 100.

[0017] The electron optical system of the imaging unit 100 includes an objective lens 111 that converges the electron beam 105 onto the sample 112, a deflector 110 that two-dimensionally sweeps the electron beam 105 over the sample 112, an aligner 120 that deflects the electron beam 105, and a driver 127 for the aligner 120. Although the aligner 120 is depicted here as having a single stage, this is not intended to limit the configuration, and it may also have, for example, a two-stage or more stage configuration.

[0018] The electron beam 105 that passes through the electron optical system of the imaging unit 100 is irradiated onto a sample 112. Signal electrons 114, such as secondary electrons (SE) and backscattered electrons (BSE), that are emitted from the sample 112 by irradiation with the electron beam 105 are detected by a detector 115 installed on the trajectory.

[0019] In the aberration measurement, in the imaging unit 100, a two-dimensional modulated current signal or a two-dimensional modulated voltage signal (128) output from a driver 127 is sent to the aligner 120, and the electron beam 105 is guided to a passing position (x ｎ , y ｎ ) is two-dimensionally swept. In addition, in synchronization with the two-dimensional modulation current (voltage) signal 128 given to the aligner 120, the electron beam 105 is swept by the deflector 110 to a landing position (X ｎ , Y ｎ ) is swept two-dimensionally.

[0020] After passing through the objective lens 111, the electron beam 105 is irradiated onto the sample 112, and signal electrons 114 emitted from the vicinity of the irradiation position are detected by the detector 115. The signal processing unit 103 synchronizes the detection signal of the detector 115 with the modulation signal of the aligner 120 or the deflector 110 and records it in a frame memory or the like to generate image data (beam landing control angle sweep image).

[0021] The signal processing unit 103 integrates image data obtained based on multiple two-dimensional sweeps of the field of view (FOV). Image integration is a method of repeatedly irradiating an observation area on the sample surface with the electron beam 105 by scanning the area multiple times with the primary electron beam, thereby increasing the number of times (number of frames) the observation area is scanned with the primary electron beam and integrating and combining images for each frame. This image integration reduces noise through the offset effect of integrating and combining multiple frame images, while increasing the amount of detected signal by simple integration as the number of frames increases, thereby improving the S / N ratio. In this embodiment, an example of image integration in FOV units will be described. However, this is not limited to this. For example, a composite image may be generated by selectively integrating image data of a specific region or region of interest (ROI) within the field of view.

[0022] The image data is recorded in the storage unit 102 by the computer system 101. The computer system 101 may perform image processing as appropriate.

[0023] (Second Hardware Configuration Example) The second hardware configuration example will be described with reference to Fig. 2, focusing on the differences from the first hardware configuration example, and overlapping explanations will be omitted. The electron optical system of the imaging unit 100 includes an aperture 108 between the electron source (not shown in the figure) and the aligner 120. The aperture 108 adjusts the aperture angle of the electron beam 105 on the sample 112. The smaller the aperture angle, the deeper the depth of focus of the image obtained.

[0024] (Third Hardware Configuration Example) The third hardware configuration example will be described with reference to Figure 3, focusing on the differences from the first or second hardware configuration example, and overlapping explanations will be omitted. The electron optical system of the imaging unit 100 includes an electron source 104 that emits an electron beam 105, an aperture 108 that adjusts the aperture angle of the electron beam 105 on the sample 112, and an aberration corrector 126 that corrects aberrations caused by the objective lens 111 between the aligner 120 and the objective lens 111. Here, the aligner 120 is depicted as having a two-stage configuration in order to cause the electron beam 105 to be incident on the aberration corrector 126 as a parallel beam, but this configuration is not limited thereto, and the aligner 120 may have, for example, two or more stages.

[0025] The visibility of the beam landing control angle sweep image can be improved by the aberration corrector 126. If necessary, the aperture of the stop 108 through which the optical axis 123 passes is switched.

[0026] (Fourth Hardware Configuration Example) The fourth hardware configuration example will be described with reference to FIG. 4, focusing on the differences from the first to third hardware configuration examples, and overlapping descriptions will be omitted.

[0027] The electron optical system of the imaging unit 100 includes an electron source 104 that emits an electron beam 105, a converging lens 129 that converges the electron beam 105, an aperture 108 that adjusts the aperture angle of the electron beam 105 on the sample 112, a converging lens 107 that further converges the electron beam 105 that has passed through the converging lens 129, and a converging lens 109 that further converges the electron beam 105 that has passed through the converging lens 107. The electron optical system also includes an aligner 106 that deflects the electron beam 105, a deflector 110, aligners 120 and 121, and an objective lens 111 that controls the height at which the electron beam 105 converges. Although the aligner and deflector are depicted here as having a single stage configuration, this configuration is not limited thereto, and they may be configured, for example, as two or more stages. Furthermore, both the aligner and the deflector have the function of deflecting the electron beam 105, but in this embodiment, to avoid confusion in the explanation, the one provided for the purpose of controlling the incident position with respect to the electron lens is called the aligner, and the one provided for the purpose of controlling the incident position with respect to the sample 112 is called the deflector. The deflector also includes an image shift deflector (not shown in the figure) that moves the field of view (FOV) of the SEM.

[0028] Furthermore, the electron optical system of the imaging unit 100 includes a blanking deflector 118 that limits the electron beam 105 from reaching the sample 112 by deflecting the electron beam 105 off the optical axis, and a blanking electrode 119 that receives the electron beam 105 deflected by the blanking deflector 118.

[0029] The electron beam 105 passing through the electron optical system of the imaging unit 100 is irradiated onto a sample 112 held on a sample stage 113. Signal electrons 114, such as SEs and BSEs, emitted from the sample 112 upon irradiation with the electron beam 105 are detected by a lower detector 115b and an upper detector 116 installed on the trajectory of the electron beam 105. An aperture provided in the upper detector 116 allows the electron beam 105 to pass through. By making this aperture sufficiently small, SEs emitted from the bottom of a deep hole or deep trench formed in the sample 112, passing near the center of the pattern, and escaping onto the sample surface can be detected. Furthermore, by deflecting the secondary electrons using an aligner 120 as needed, secondary electrons passing near the optical axis after escaping from a deep hole or the like can be guided to the detection surface of the lower detector 115b. Furthermore, the signal electrons 114 can be energy-discriminated by energy filtering using an energy filter 117a installed immediately before the detection surface of the upper detector 116 and an energy filter 117b installed immediately before the detection surface of the lower detector 115b.

[0030] In measuring the aberration, the imaging unit 100 synchronizes the deflector 110 with one of the aligners 106, 120, and 121 to perform two-dimensional sweeping, and signal electrons emitted from the vicinity of the irradiation position of the electron beam 105 are detected by the lower detector 115b or the upper detector 116. The signal processing unit 103 synchronizes the detection signals of the lower detector 115b and / or the upper detector 116 with the modulation signal and records them in a frame memory or the like to generate image data (beam landing control angle sweep image).

[0031] The sum of the geometric aberrations of the convergent lens 107, the convergent lens 109, and the objective lens 111 can be calculated from a beam landing control angle sweep image obtained when the passing position of the electron beam 105 on the principal surface of the convergent lens 107 is two-dimensionally swept by the aligner 106 in synchronization with the deflector 110. Similarly, the sum of the geometric aberrations of the convergent lens 109 and the objective lens 111 can be calculated from a beam landing control angle sweep image obtained when the passing position of the electron beam 105 on the principal surface of the convergent lens 109 is two-dimensionally swept by the aligner 121 in synchronization with the deflector 110. As a result, the geometric aberration of the convergent lens 107 can be obtained from the difference between the two.

[0032] Below, a method for calculating the geometric aberration coefficient from the beam landing control angle sweep image taken by these charged particle beam devices will be described.

[0033] (Calculation Example 1 of Aberration Coefficients) Referring to FIGS. 6A and 6B , an example of a method for calculating geometric aberration coefficients using a beam landing control angle sweep image acquired using an SEM having the configurations illustrated as the first to fourth hardware configuration examples will be described. Here, an example is shown in which a randomly distributed circular pattern is used to measure the geometric aberration coefficients. However, the present invention is not limited to this; for example, a periodic pattern or a pattern other than a circle can also be used. First, a beam landing control angle sweep image 203 is acquired for a sample FOV 201 with the field of view center A. Then, the sample is moved from the field of view center A to the field of view center B by using the image shift deflector of the imaging unit 100 or by moving the sample position using the sample stage. Then, a beam landing control angle sweep image 204 is acquired for a sample FOV 202 with the field of view center B.

[0034] A common pattern n (n=1 to N) is selected from both the image 203 and the image 204. The position information of the pattern may be, for example, the coordinates of the center of gravity of the pattern (X ｎ , Y ｎ By synchronizing the two-dimensional sweep on the lens principal surface and the two-dimensional sweep on the sample, the coordinates (X ｎ , Y ｎThe position (x) on the lens principal surface when the electron beam 105 irradiated onto the lens principal surface passes through the lens principal surface. ｎ , y ｎ As described above, the passing position (x ｎ , y ｎ ) uniquely determines the beam landing control angle.

[0035] Here, if a geometric aberration exists in the lens at the surface position of the sample 112, the beam displacement vector r ｎＡ , r ｎＢ and the movement vector R of the visual field center Ａ，Ｂ and have the relationship of (Equation 1).

[0036] FIG. 6B illustrates the vector relationship when pattern 3 (see FIG. 6A) is used as an example. The beam displacement vector is a vector whose starting point is the center of the field of view and whose end point is the coordinates of the pattern. In the beam landing control angle sweep image, even the same pattern is detected at different positions as viewed from the center of the field of view due to lens aberration. However, since it is the same pattern, it is at the same position on the FOV of the SEM image. Therefore, in FIG. 6B, the end points of the two beam displacement vectors are made to coincide, and the respective centers of the field of view that serve as starting points are shown as (A) and (B). Here, since the position of the center of the field of view in the beam landing control angle sweep image is not affected by geometric aberration, vector 205 whose starting point (A) and ending point (B) is a movement vector R on the FOV of the SEM image. Ａ，Ｂ This relationship is expressed mathematically in (Equation 1). The right side of (Equation 1) is the beam displacement vector r ｎＡ , r ｎＢ are functions of the geometric aberration coefficient and the beam landing control angle, respectively, and the geometric aberration coefficient can be calculated by solving this simultaneous equation.

[0037] The geometric aberration coefficient A exemplified in (Equation 1) １ , C １ , A ２ , B ２ , A ３ , C ３ , S ３and represent two-fold symmetric astigmatism, defocus, three-fold symmetric astigmatism, axial coma aberration, four-fold symmetric astigmatism, third-order spherical aberration, and star aberration, respectively. The geometric aberration coefficients to be calculated do not necessarily include all of the exemplified components. Furthermore, the geometric aberration coefficients to be calculated are not limited to the exemplified components, and higher-order geometric aberration coefficients can also be calculated. The geometric aberration coefficients can be calculated based on a number of relational expressions equal to or greater than the number of components of the geometric aberration coefficients contributing to the beam displacement to be considered. Therefore, patterns commonly appearing in the beam landing control angle sweep image 203 and the beam landing control angle sweep image 204 are extracted so that their number is equal to or greater than the number of components of the geometric aberration coefficients to be calculated. In this case, a beam landing control angle sweep image with the field of view center C can be separately captured, and the relational expression (Equation 1) can be created between the image 203 and the beam landing control angle sweep image with the field of view center C and / or between the image 204 and the beam landing control angle sweep image with the field of view center C.

[0038] (Aberration Coefficient Calculation Example 2) Referring to FIG. 7 , an example of a method for calculating geometric aberration coefficients using a beam landing control angle sweep image acquired using an SEM having any of the configurations illustrated as the first to fourth hardware configuration examples will be described. Here, an example is shown in which a randomly distributed circular pattern is used to measure the geometric aberration coefficients. However, the present invention is not limited to this, and it is also possible to use, for example, a periodic pattern or a pattern other than a circle. First, an SEM image is acquired for a predetermined FOV of the sample. Then, a beam landing control angle sweep image is acquired for the same field of view. FIG. 7 shows an SEM image 206 and a beam landing control angle sweep image 207 acquired in this manner. Note that as long as the same pattern is captured in both images, it does not matter if the fields of view at the time of acquisition are shifted between the SEM image 206 and the beam landing control angle sweep image 207.

[0039] A combination of the same pattern n (n=1 to N) included in both the image 206 and the image 207 is selected. As in the calculation example 1, the position information of the pattern is, for example, the coordinates of the center of gravity of the pattern (X ｎ , Y ｎBy synchronizing the two-dimensional sweep on the lens principal surface and the two-dimensional sweep on the sample, the coordinates (X ｎ , Y ｎ The position (x) on the lens principal surface when the electron beam 105 irradiated onto the lens principal surface passes through the lens principal surface. ｎ , y ｎ ) can be identified.

[0040] Here, when geometric aberration exists in the lens at the surface position of the sample 112, taking the combination of pattern i and pattern k as an example, the beam displacement vector r for each pattern affected by the geometric aberration is ｉ , r ｋ and the movement vector R between the two patterns on the sample. ｉ，ｋ and have the relationship of (Equation 2).

[0041] Figure 7 illustrates the vector relationship when i = 1 and k = 2 as an example. The beam displacement vector is a vector whose starting point is the center of the field of view 208 and whose end point is the coordinates of the pattern. In (Equation 2), the left side is the movement vector R of the two patterns on the sample. ｉ，ｋ which indicates that the difference is equal to the difference between the beam displacement vectors of the two patterns on the beam landing control angle sweep image, which is the right-hand side of the formula. This is because the starting point of the beam displacement vector is the center of the field of view 208, and therefore the beam landing control angle sweep image is not affected by the aberration of the lens.

[0042] When N patterns are extracted for the beam landing control angle sweep image, (Equation 2) includes as many equations as there are combinations of the N patterns. As in calculation example 1, the geometric aberration coefficient is calculated based on relational equations whose number is equal to or greater than the number of components of the geometric aberration coefficient that contribute to the beam displacement to be considered. For this reason, patterns appearing in the beam landing control angle sweep image 207 are extracted so that the number of combinations thereof is equal to or greater than the number of components of the geometric aberration coefficient to be calculated. At this time, it is also possible to separately capture an SEM image and a beam landing control angle sweep image having different field-of-view centers and create the relational equation of (Equation 2). Note that the maximum number of equations included in (Equation 2) is the number of combinations for extracting two from N identical patterns when N patterns are extracted. Ｎ C ２ and can be calculated as N! / [2! × (N-2)!].

[0043] In addition, the movement vector R between the patterns on the sample ｉ，ｋ Although an example in which an SEM image (scanned image) is used to acquire the image has been shown, the present invention is not limited to this, and images captured by, for example, a scanning ion microscope or an atomic force microscope may also be used.

[0044] 8A and 8B, an example of a method for calculating the geometric aberration coefficient using a beam landing control angle sweep image acquired using an SEM having the configurations exemplified as the first to fourth hardware configuration examples will be described. Here, an example is shown in which a periodically arranged circular pattern is used to measure the geometric aberration coefficient, but the present invention is not limited to this, and it is also possible to use a non-circular pattern such as a triangle or a square.

[0045] As shown in the SEM image 209, circular patterns are periodically arranged at intervals a in the X direction and at intervals b in the Y direction on the surface of the sample 112. The concept of calculating the geometric aberration coefficient in Calculation Example 3 is the same as in Calculation Example 2, but the use of periodically arranged patterns makes the calculation easier.

[0046] Two patterns m and n are selected from the circular patterns included in the beam landing control angle sweep image 210. As in the calculation examples 1 and 2, the position information of the patterns is, for example, the coordinates of the center of gravity of the patterns (X ｍ , Y ｍ ), (X ｎ , Y ｎ By synchronizing the two-dimensional sweep on the lens principal surface and the two-dimensional sweep on the sample, the coordinates (X ｍ , Y ｍ ), (X ｎ , Y ｎ ) on the lens principal surface when the electron beam 105 irradiated onto each of the lens principal surfaces passes through the lens principal surface. ｍ , y ｍ ), (x ｎ , y ｎ ) can be identified.

[0047] In addition, to serve as a reference for calculation, a pattern s is arbitrarily selected from the periodically arranged circular patterns, and the coordinates of the center of gravity of the pattern s are calculated as coordinates (X ｓ , Y ｓ ) where, if geometric aberration exists in the lens at the surface position of the sample 112, taking the combination of pattern m and pattern n as an example, the center of gravity position (X ｓ , Y ｓ ) based on the beam displacement vector l ｍ , l ｎ and the movement vector L between the two patterns ｍ，ｎ and have the relationship of (Equation 3).

[0048] The vector relationship of patterns m, n, and s is illustrated in Figure 8B. In Figure 8B, the beam displacement vector l ｍ , l ｎ In addition to the above, the beam displacement vector r ｍ , r ｎ , r ｓ Here, the movement vector L between pattern m and pattern n is ｍ，ｎ and the beam displacement vector r ｍ , rｎ As explained in Calculation Example 2, the relationship of (Equation 2) holds between

[0049] On the other hand, the beam displacement vector r ｍ is the beam displacement vector r ｓ and the beam displacement vector l ｍ and the beam displacement vector r ｎ is the beam displacement vector r ｓ and the beam displacement vector l ｎ Therefore, the beam displacement vector r ｍ and the beam displacement vector r ｎ The difference between these two is the beam displacement vector r ｓ are cancelled out, and the relationship in (Equation 3) holds.

[0050] Furthermore, the movement vector L on the left side of (Equation 3) ｍ，ｎ can be expressed as (-a, 3b) in the example of FIG. 9A based on the periodicity of the pattern. Since the intervals a and b are known values, the movement vector L ｍ，ｎ This eliminates the need to take the trouble of determining the value from an SEM image or the like.

[0051] The maximum number of expressions included in (Equation 3) is the number of combinations of extracting two patterns from N patterns arranged periodically, as in the second calculation example. Ｎ C ２ and can be calculated as N! / [2! × (N-2)!].

[0052] (Calculation Example 4 of Aberration Coefficients) An example of a method for calculating geometric aberration coefficients using a beam landing control angle sweep image acquired using an SEM having any of the configurations exemplified as the first to fourth hardware configuration examples will be described with reference to Figure 9. Here, an example is shown in which a rotationally symmetric isolated pattern such as that shown in an SEM image 214 is used to measure the geometric aberration coefficients. Here, a circular pattern is shown as an example, and a beam landing control angle sweep image 216 is captured by aligning the field of view center 217 with the rotation center 215 of the isolated pattern.

[0053] For an isolated pattern in the image 216, any coordinate on the boundary (X ｉ , Y ｉ) is selected, the two-dimensional sweep on the lens principal surface and the two-dimensional sweep on the sample are performed in synchronization, and the coordinates (X ｉ , Y ｉ The position (x) on the lens principal surface when the electron beam 105 irradiated onto the lens principal surface passes through the lens principal surface. ｉ , y ｉ ) can be identified.

[0054] For the image 216, a beam displacement vector r is defined, which starts from the center of the field of view 217 and ends at any coordinate on the boundary of the isolated pattern. ｉ The magnitude of the radius R of the circular pattern is equal to the magnitude of the radius R of the circular pattern. This establishes the relationship of (Equation 4).

[0055] The number of coordinates selected is equal to or greater than the number of components of the geometric aberration coefficient that contribute to the beam displacement to be considered, and the geometric aberration coefficient is calculated. Here, an example is shown in which the shape of the isolated pattern is circular, but it is also possible to use a pattern other than a circle, such as a polygon that is tangent to a circumscribing circle. In these cases, the relational expression shown in (Equation 4) can be constructed by focusing on the vertices of the polygon.

[0056] (GUI) A GUI (Graphical User Interface) provided in the charged particle beam device for performing the above-described aberration measurement will be described with reference to FIGS.

[0057] 10 shows an example of a GUI for setting the sample, pattern, and imaging position used in beam landing control angle sweep image acquisition. These imaging conditions are set in a sample selection tab 301 on an aberration measurement and correction tool screen 300. The input method can be selection from a menu or direct input by the user. The imaging position may also be specified from a microscope image 302. The microscope image 302 may be an optical microscope image or an electron microscope image (SEM image).

[0058] 11 shows an example of a GUI for setting the optical element (lens) or position on the optical path to be the target of aberration measurement, the range of geometric aberration coefficients to be measured, and the imaging conditions for the beam landing control angle sweep image, and then executing measurement of the geometric aberration coefficients. These imaging conditions are set in the aberration measurement tab 303 on the aberration measurement and correction tool screen 300, and the aberration measurement is started.

[0059] The target of aberration measurement may be a lens (for example, at least one of lenses 107, 109, and 111 (see FIG. 4)) included in the charged particle beam device. Instead of selecting a lens, a position (crossover) on the optical path where the beam is focused may be selected. For example, when specifying position O where the optical axis 123 shown in FIG. 5A intersects with the surface of the sample 112, this is equivalent to selecting the objective lens 111. By selecting any crossover on the optical path, one or more lenses for which aberrations are to be measured can be selected from the lenses included in the charged particle beam device.

[0060] The measurement range of the geometric aberration coefficients can be specified, for example, up to third-order aberrations, up to fifth-order aberrations, etc. In setting the imaging conditions, it is possible to specify the aligner used to sweep the beam landing control angle and its scanning area, and to specify the deflector that synchronously sweeps the irradiation position of the electron beam on the sample 112 and its scanning area.

[0061] Once the above settings are complete, the user presses the start button 304 to start the aberration measurement.

[0062] 12 shows an example of a GUI for displaying and saving the measurement results of the geometric aberration coefficients, or for calling and displaying past measurement results. This is performed on the results tab 311 of the aberration measurement and correction tool screen 300.

[0063] 13 shows an example of a GUI for setting conditions for performing aberration correction and controlling its execution based on measured geometric aberration coefficients. An aberration correction tab 312 on the aberration measurement and correction tool screen 300 allows the user to display and set aberration correction conditions, such as selecting automatic or manual aberration correction, displaying and specifying the name of the aberration to be corrected, displaying and specifying the residual aberration or beam diameter after aberration correction, and displaying and setting the upper limit of the number of repeated aberration corrections.

[0064] In automatic mode, the geometric aberration coefficients to be corrected for the target residual aberration or beam diameter are narrowed down based on the contribution of each geometric aberration coefficient to the beam diameter from the measurement results of the geometric aberration coefficient specifications (see FIG. 12 ), and can be recommended via the GUI. Aberration correction and aberration measurement are repeated until the target residual aberration or target beam diameter is achieved, as long as the upper limit of the number of repeated aberration corrections is not exceeded. Meanwhile, in manual mode, the user can select the geometric aberration coefficient to be corrected, the amount of correction, and the number of repeated corrections.

[0065] The above embodiments and modifications have been described in detail to make the present disclosure easier to understand, 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 embodiment or modification with the configuration of another embodiment or modification, and it is also possible to add the configuration of another embodiment or modification to the configuration of one embodiment or modification. Furthermore, it is possible to add, delete, or replace part of the configuration of each embodiment or modification with other configurations.

[0066] 100: imaging unit, 101: computer system, 102: memory unit, 103: signal processing unit, 104: electron source, 105: electron beam, 106, 120, 121: aligner, 107, 109, 129: converging lens, 108: aperture, 110: deflector, 111: objective lens, 112: sample, 113: sample stage, 114: signal electron, 115: detector, 115b: lower detector, 116: upper detector, 117a: energy filter, 117b: energy filter, 118: blanking deflector, 119: blanking electrode, 122: input / output unit, 123: optical axis , 124: Main surface, 125: Scanning area, 126: Aberration corrector, 127: Driver, 128: Two-dimensional modulation current (voltage) signal, 135: Scanning area, 201, 202: FOV, 203, 204, 207, 210, 216: Beam landing control angle sweep image, 205: Vector, 206, 209, 214: SEM image, 208, 212, 217: Center of field of view, 209: SEM image, 215: Rotation center, 300: Aberration measurement and correction tool screen, 301: Sample selection tab, 302: Microscope image, 303: Aberration measurement tab, 304: Start button, 311: Result tab, 312: Aberration correction tab.

Claims

1. A charged particle beam device comprising: an imaging unit including a charged particle source, a sample stage for holding a sample, a lens for focusing a charged particle beam from the charged particle source onto the sample, an aligner for controlling the position where the charged particle beam passes through a main surface of the lens, a deflector for scanning the charged particle beam over the sample, and a detector for detecting signal electrons emitted when the charged particle beam is irradiated onto the sample; a signal processing unit; and a computer system, wherein the computer system, in the imaging unit, causes the aligner to perform a two-dimensional sweep of the charged particle beam over the main surface of the lens using a first modulation signal, and causes the deflector to perform a two-dimensional sweep of the charged particle beam over the sample using a second modulation signal synchronized with the first modulation signal, and the computer system calculates the geometric aberration coefficient of the lens at the surface position of the sample based on a beam landing control angle sweep image, which is image data generated by the signal processing unit by synchronously recording the detection signal of the detector with the first modulation signal or the second modulation signal.

2. In claim 1, the sample has a plurality of patterns on its surface, the imaging unit is equipped with an image shift deflector and is configured so that the field of view can be moved by the sample stage or the image shift deflector, and the computer system acquires a first beam landing control angle sweep image at a first field of view center and a second beam landing control angle sweep image at a second field of view center different from the first field of view center, the computer system calculates a geometric aberration coefficient of the lens at a surface position of the sample for a common pattern that is included in both the first beam landing control angle sweep image and the second beam landing control angle sweep image and that is arbitrarily extracted from a plurality of patterns of the sample, based on a relational expression between a first beam displacement vector that has its start point at the center of the first field of view and its end point at the position of the common pattern in the first beam landing control angle sweep image, a second beam displacement vector that has its start point at the center of the second field of view and its end point at the position of the common pattern in the second beam landing control angle sweep image, and a movement vector that has its start point at the center of the first field of view and its end point at the center of the second field of view.

3. A charged particle beam device according to claim 2, wherein the first beam displacement vector is expressed by a function whose variables are the geometric aberration coefficient of the lens at the surface position of the sample and the position where the charged particle beam irradiated onto the common pattern passes through the main surface of the lens when the first beam landing control angle sweep image is acquired; the second beam displacement vector is expressed by a function whose variables are the geometric aberration coefficient of the lens at the surface position of the sample and the position where the charged particle beam irradiated onto the common pattern passes through the main surface of the lens when the second beam landing control angle sweep image is acquired; and the computer system extracts the common patterns in a number greater than or equal to the number of components of the geometric aberration coefficient of the lens to be calculated.

4. A charged particle beam device according to claim 1, wherein the sample has a plurality of patterns on its surface, and the computer system calculates the geometric aberration coefficient of the lens at a surface position of the sample for a first pattern and a second pattern arbitrarily extracted from the beam landing control angle sweep image, based on a relational expression between a first beam displacement vector having a start point at the center of the field of view in the beam landing control angle sweep image and an end point at the position of the first pattern, a second beam displacement vector having a start point at the center of the field of view in the beam landing control angle sweep image and an end point at the position of the second pattern, and a movement vector having a start point at the position of the first pattern on the sample and an end point at the position of the second pattern.

5. A charged particle beam device according to claim 4, wherein the first beam displacement vector is expressed by a function having variables of the geometric aberration coefficient of the lens at the surface position of the sample and the position where the charged particle beam irradiated onto the first pattern passes through the main surface of the lens when the beam landing control angle sweep image is acquired; the second beam displacement vector is expressed by a function having variables of the geometric aberration coefficient of the lens at the surface position of the sample and the position where the charged particle beam irradiated onto the second pattern passes through the main surface of the lens when the beam landing control angle sweep image is acquired; and the computer system extracts combinations of the first pattern and the second pattern in a number equal to or greater than the number of components of the geometric aberration coefficient of the lens to be calculated.

6. A charged particle beam device as claimed in claim 4, wherein the computer system, in the imaging unit, causes the aligner to pass the charged particle beam through the intersection of the principal plane of the lens and the optical axis, and causes the deflector to two-dimensionally sweep the charged particle beam over the sample, and the computer system determines the movement vector from a scanned image, which is image data generated by the signal processing unit by synchronously recording the detection signal of the detector with the modulation signal of the deflector.

7. A charged particle beam device according to claim 1, wherein the sample has a plurality of patterns periodically arranged on its surface, and the computer system calculates the geometric aberration coefficient of the lens at a surface position of the sample for a first pattern, a second pattern, and a reference pattern arbitrarily extracted from the beam landing control angle sweep image, based on a relational expression between a first beam displacement vector having a start point at the position of the reference pattern and an end point at the position of the first pattern, a second beam displacement vector having a start point at the position of the reference pattern and an end point at the position of the second pattern, and a movement vector having a start point at the position of the first pattern on the sample and an end point at the position of the second pattern.

8. A charged particle beam device according to claim 7, wherein the first beam displacement vector is expressed by a function having variables of the geometric aberration coefficient of the lens at the surface position of the sample and the position where the charged particle beam irradiated onto the first pattern passes through the main surface of the lens when the beam landing control angle sweep image is acquired; the second beam displacement vector is expressed by a function having variables of the geometric aberration coefficient of the lens at the surface position of the sample and the position where the charged particle beam irradiated onto the second pattern passes through the main surface of the lens when the beam landing control angle sweep image is acquired; and the computer system extracts combinations of the first pattern and the second pattern in a number equal to or greater than the number of components of the geometric aberration coefficient of the lens to be calculated.

9. A charged particle beam device according to claim 7, wherein the computer system determines the movement vector based on the periodicity of the plurality of patterns of the sample.

10. A charged particle beam device according to claim 1, wherein the sample has a rotationally symmetric isolated pattern on its surface, the shape of the isolated pattern being a circle or a polygon tangent to a circumscribing circle, and the computer system acquires the beam landing control angle sweep image using the imaging unit with the rotation center of the isolated pattern as the field of view center, and the computer system calculates the geometric aberration coefficient of the lens at the surface position of the sample based on a relational expression between the magnitude of a beam displacement vector that has the center of view of the beam landing control angle sweep image as its start point, a point on the circumference of the isolated pattern if the shape of the isolated pattern is a circle, or a vertex of the polygon of the isolated pattern if the shape of the isolated pattern is a polygon, and the radius of the circle or circumscribing circle of the isolated pattern.

11. A charged particle beam device according to claim 10, wherein the beam displacement vector is expressed as a function having variables of the geometric aberration coefficient of the lens at the surface position of the sample and the position where the charged particle beam, irradiated at the position to be the end point of the beam displacement vector when the beam landing control angle sweep image is acquired, passes through the main surface of the lens, and the computer system determines the number of beam displacement vectors equal to or greater than the number of components of the geometric aberration coefficient of the lens to be calculated.

12. A charged particle beam device according to claim 1, wherein the imaging unit includes an aperture between the charged particle source and the aligner.

13. A charged particle beam device according to claim 1, wherein the imaging unit is provided with an aberration corrector between the aligner and the lens for correcting aberration of the lens.

14. A charged particle beam device according to claim 13, wherein the computer system corrects the aberration of the lens using the aberration corrector based on the calculated geometric aberration coefficient of the lens.

15. A charged particle beam device according to claim 1, wherein the imaging unit has a plurality of combinations of the aligner and the lens, and the computer system is capable of selecting the lens for which the geometric aberration coefficient is calculated.

16. An aberration measurement method in which an imaging unit comprises a charged particle source, a sample stage for holding a sample, a lens for focusing a charged particle beam from the charged particle source onto the sample, an aligner for controlling the position at which the charged particle beam passes through a main surface of the lens, a deflector for scanning the charged particle beam over the sample, and a detector for detecting signal electrons emitted when the charged particle beam is irradiated onto the sample, wherein the imaging unit causes the aligner to two-dimensionally sweep the charged particle beam over the main surface of the lens using a first modulation signal, and causes the deflector to two-dimensionally sweep the charged particle beam over the sample using a second modulation signal synchronized with the first modulation signal, a signal processing unit synchronously records the detection signal of the detector with the first modulation signal or the second modulation signal to generate image data, and a computer system calculates the geometric aberration coefficient of the lens at the surface position of the sample based on the image data, that is, a beam landing control angle sweep image.

17. According to claim 16, the sample has a plurality of patterns on its surface, the imaging unit is capable of moving the field of view by the sample stage or an image shift deflector, and the computer system acquires a first beam landing control angle sweep image at a first field of view center and a second beam landing control angle sweep image at a second field of view center different from the first field of view center, the computer system calculates a geometric aberration coefficient of the lens at a surface position of the sample for a common pattern that is included in both the first beam landing control angle sweep image and the second beam landing control angle sweep image and that is arbitrarily extracted from a plurality of patterns of the sample, based on a relational expression between a first beam displacement vector that has its start point at the center of the first field of view and its end point at the position of the common pattern in the first beam landing control angle sweep image, a second beam displacement vector that has its start point at the center of the second field of view and its end point at the position of the common pattern in the second beam landing control angle sweep image, and a movement vector that has its start point at the center of the first field of view and its end point.

18. An aberration measurement method according to claim 16, wherein the sample has a plurality of patterns on its surface, and the computer system calculates the geometric aberration coefficient of the lens at a surface position of the sample for a first pattern and a second pattern arbitrarily extracted from the beam landing control angle sweep image, based on a relational expression between a first beam displacement vector having a start point at the center of the field of view in the beam landing control angle sweep image and an end point at the position of the first pattern, a second beam displacement vector having a start point at the center of the field of view in the beam landing control angle sweep image and an end point at the position of the second pattern, and a movement vector having a start point at the position of the first pattern on the sample and an end point at the position of the second pattern.

19. An aberration measurement method according to claim 16, wherein the sample has a plurality of patterns periodically arranged on its surface, and the computer system calculates the geometric aberration coefficient of the lens at a surface position of the sample for a first pattern, a second pattern, and a reference pattern arbitrarily extracted from the beam landing control angle sweep image, based on a relational expression between a first beam displacement vector having a start point at the position of the reference pattern and an end point at the position of the first pattern, a second beam displacement vector having a start point at the position of the reference pattern and an end point at the position of the second pattern, and a movement vector having a start point at the position of the first pattern on the sample and an end point at the position of the second pattern.

20. An aberration measurement method according to claim 16, wherein the sample has a rotationally symmetric isolated pattern on its surface, the shape of the isolated pattern being a circle or a polygon tangent to a circumscribing circle, and the computer system acquires the beam landing control angle sweep image using the imaging unit with the rotation center of the isolated pattern as the center of field of view, and the computer system calculates the geometric aberration coefficient of the lens at the surface position of the sample based on a relational expression between the magnitude of a beam displacement vector that has as its start point the center of field of view in the beam landing control angle sweep image, and if the shape of the isolated pattern is a circle, has as its end point a point on the circumference of the isolated pattern, or if the shape of the isolated pattern is a polygon, has as its end point a vertex of the polygon of the isolated pattern, and the radius of the circle or circumscribing circle of the isolated pattern.

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