JP2012003909A - Charged particle beam device - Google Patents

Abstract

PROBLEM TO BE SOLVED: To provide a charged particle beam device capable of obtaining a charged particle beam image in which shape contrast and shade contrast are emphasized while maintaining a high SN ratio.SOLUTION: The charged particle beam device includes a metal plate for generating a tertiary electron by impacting a secondary electron or a reflection electron against the metal plate, between an electron source and a specimen. The metal plate comprises divided regions in each of which a voltage can be applied independently. In addition, a primary beam through hole provided in the metal plate is provided at a place adequately far from an electron beam optical axis.

Description

  The present invention relates to an apparatus for detecting a charged particle signal generated secondarily by irradiating a sample with a charged particle beam, and in particular, a signal generated secondarily from a sample while scanning an electron beam on the sample. The present invention relates to a scanning electron microscope that detects electrons and performs imaging or composition analysis.

  There is a scanning electron microscope as an apparatus for performing sample image formation or sample analysis from a charged particle signal generated by irradiating a sample with a charged particle beam. In order to obtain a high-definition image, it is necessary to improve the ratio of signal amplitude to signal noise (SN ratio). If the time required for signal acquisition is lengthened, the accumulated signal amount increases and the SN ratio is improved. However, since the observation time becomes long, it becomes an application restriction. Further, if the electron dose to be irradiated is increased, the S / N ratio is improved, but the angle of taking in the electron beam from the electron beam source has to be increased, and the lens aberration is increased and the spatial resolution is deteriorated. Therefore, in order to improve the S / N ratio while maintaining the observation time and the spatial resolution, it is necessary to maximize the detection signal amount or minimize the amount of noise to be mixed. An example is shown in Patent Document 1.

  On the other hand, in order to be able to distinguish the shape, structure, or material of the sample on the image, there must be a sufficient difference in the amount of signal from parts having different characteristics. A state where there is a sufficient difference is called high contrast. The image contrast includes a shape contrast that represents the shape of the sample surface, a shadow contrast that emphasizes the unevenness, a potential contrast that corresponds to the potential distribution on the sample surface, and a material contrast that enhances the composition of the sample. For example, in order to enhance shadow contrast, signal electrons emitted in different directions are emitted as shown in the document L. Reimer, Scanning Electron Microscopy, 2nd Ed. (Springer Verlag, 1998), p. 191. A method of detecting with different detection efficiencies depending on the direction has been published. When performing detection in accordance with the signal emission direction, signal electrons in a specific direction are not detected, so that the total signal amount decreases, and therefore the SN ratio also decreases.

  In order to improve the shape contrast or the shadow contrast, methods disclosed in Patent Documents 2 to 7 are known as methods for detecting signal electrons according to the emission angle. Japanese Patent Application Laid-Open Nos. 8-27369, 2000-30654, and 2006-228999 disclose methods of arranging a plurality of detectors. In WO00 / 19482, JP2008-108592, and JP2008-186589, a single detector and a plurality of metal plates are provided, and high-speed components of signal electrons (reflected electrons or backscattered electrons). Among them, a method is disclosed in which the metal plates are arranged so that signal electrons having various emission angles are irradiated onto the different metal plates. According to this method, it is possible to control the discharge angle range that can be detected by varying the voltage applied to the metal plate.

  In the method disclosed in WO00 / 19482, since it is necessary to convert signal electrons to tertiary electrons with a metal plate, among the signal electrons, a high-speed component having sufficient kinetic energy to generate tertiary electrons. Only the object of angle discrimination. In the methods disclosed in Japanese Patent Application Laid-Open Nos. 2008-108592 and 2008-186689, since a negative high voltage is applied to the sample, it is a low-speed component (secondary electrons) of signal electrons. Also has high kinetic energy at the metal plate position. Accordingly, tertiary electrons can be generated from the metal plate. However, in these patent documents, only high-speed components of signal electrons whose trajectories do not change greatly even when accelerated by the high voltage are targeted for angle discrimination. On the other hand, the low-speed components of the signal electrons do not arrive at positions that are far enough to perform angle discrimination because the trajectories intersect due to the acceleration electric field and the objective lens magnetic field.

JP 2000-11939 A Japanese Patent Laid-Open No. 8-27369 JP 2000-30654 A JP 2006-228999 A WO00 / 19482 JP 2008-108592 A JP 2008-186689 A JP 2006-332038 A

L. Reimer, Scanning Electron Microscopy, 2nd Ed. (Springer Verlag, 1998), p. 191

  However, in the irradiation energy region (100 eV to 3000 eV) of the primary electron beam frequently used in the scanning electron microscope, the generated amount of the high speed component of the signal electrons is as small as 1/3 to 1/20 compared to the low speed component. It is known. Accordingly, the methods disclosed in WO 00/19482, JP 2008-108592 A, and JP 2008-186689 all have high contrast because angle discrimination is performed on high-speed components with a small total signal amount. However, the SN ratio is inevitable. Further, in the methods disclosed in Japanese Patent Application Laid-Open Nos. 8-27369, 2000-30654, and 2006-228999, detectors are required as many as the number of angular regions to be distinguished, and various samples are used. In order to optimize the detection angle, a very large number of detectors are required, and the manufacturing cost of the apparatus increases. Further, as in the method disclosed in Japanese Patent Application Laid-Open No. 2006-332038, in the method of deflecting the secondary signal by an electromagnetic field, a method of suppressing the optical axis bending of the primary electron beam (orthogonal electromagnetic field generator or ExB field generation) However, since the deflection chromatic aberration of the primary beam is increased, the spatial resolution is deteriorated.

  A first problem to be solved by the present invention is to provide a charged particle beam apparatus capable of obtaining a charged particle beam image in which shape contrast and shadow contrast are enhanced while maintaining a high S / N ratio. The second problem is to provide a method for solving the first problem while suppressing the manufacturing cost. A third problem is to solve the first and second problems while maintaining a high spatial resolution.

  In order to solve the first problem, a primary electron beam irradiation system that scans a sample with a primary electron beam emitted from an electron source, and an accelerating electric field in which secondary electrons generated from the sample are accelerated in the direction of the electron source. And a configuration including a metal plate divided into a plurality of portions between the electron source and the sample is used. The metal plate is connected to a power source and a power source control means for independently applying a voltage to the divided areas. Further, it is necessary to make a through hole in the metal plate as a passage for guiding the primary beam to the sample, but the most main part or center of the divided region is provided at a location sufficiently away from the through hole. It is characterized by. Furthermore, the said metal plate uses the structure which the said secondary electron collides and detects the tertiary electron which generate | occur | produced from the metal plate with a detector. By performing the division sufficiently finely, the low speed component of the signal electrons can be separated for each angle even in the presence of the acceleration electric field. Therefore, the SN ratio can be improved as compared with the discrimination by the high speed component. Furthermore, the generation of the tertiary electrons can be suppressed by applying a positive voltage by the power source and the power source control means to the portion of the divided metal plate where the angle component of the signal electrons that are not detected collides. Angle discrimination can be performed. The center of the low speed component of the signal electrons generated from the sample is provided with a deflecting means for deflecting the signal electrons so as to collide with the division center or other desired division part. Alternatively, the power supply control means controls the voltage arrangement of the divided metal plates so as to follow the center position of the low-speed component of the signal electrons.

  In order to solve the second problem, the number of detectors may be reduced as compared with the number of divided regions of the divided metal plate. Since the angle control is performed by the metal plate, images having different contrasts can be acquired by applying voltages to different divisions even if there is only one detector. Therefore, the number of detectors, amplifiers, signal processing circuits, etc. can be greatly reduced, resulting in cost reduction.

  The third problem is solved simultaneously with the first problem. This is because the signal discrimination of the present invention is performed on the tertiary electrons generated from the metal plate, and since the tertiary electrons do not have an accelerating field, the generation can be suppressed with an applied voltage of several tens of volts at most. . For this reason, the adverse effect (aberration increase and axial bending) on the primary electron beam having a kinetic energy of several keV can be ignored.

  According to the present invention, it is possible to obtain a charged particle beam image in which the shape contrast and the shadow contrast are enhanced while maintaining a high SN while maintaining a high spatial resolution while suppressing a manufacturing cost.

1 shows a configuration example of a scanning electron microscope to which the present invention is applied. Energy distribution of signal electrons. Release efficiency of TSE and BSE. 1 is an overall configuration diagram of a charged particle beam apparatus according to Embodiment 1. FIG. The conceptual explanatory drawing of the emission angle of a secondary electron. Explanatory drawing of a metal plate. The conceptual diagram which shows the relationship between the electric potential distribution which a divided electrode forms, and a tertiary electron. The adjustment flowchart of a secondary electron deflection | deviation means. The schematic diagram of an acquisition image. The secondary electron deflection amount adjustment flowchart. The schematic diagram of the standard sample used for adjustment of the amount of secondary electron deflection. FIG. 6 is a diagram illustrating the shape of a divided electrode according to Example 2. The conceptual diagram which shows the electric potential distribution which the division | segmentation electrode of Example 3 forms, and the relationship of a tertiary electron. FIG. 6 is an adjustment flowchart of secondary electron deflecting means according to the fourth embodiment. The schematic diagram which shows the grating | lattice for determining the amount of secondary electron deflection. FIG. 6 is a schematic diagram showing a divided electrode of Example 5. Explanatory drawing of the angle selection detection of a present Example.

  FIG. 1 shows a scanning electron microscope to which the present invention is applied. In particular, an electron for observing, measuring dimensions, measuring shapes, inspecting, and reviewing defects on a circuit pattern or a resist pattern formed on a semiconductor wafer or an exposure mask. 1 shows a line inspection apparatus. An electron emission source 101 is attached to the electron microscope column 1 and is controlled by an electron source control unit 201 to emit a primary electron beam 102. The diameter of the primary electron beam is optimized by one or more converging lenses 103 controlled by the lens control unit 202 and the current limiting diaphragm 104, and then the sample is sampled by the objective lens 105 controlled by the lens control unit 202. Focus on 106. The primary electron beam 102 is scanned on the sample 106 by the deflector 107 controlled by the deflection control unit 203, and as a result, the secondary electron beam 108 generated from the sample 106 is detected by the detector 109. The detection signal is amplified by the amplifier 204 and displayed on the display unit 205. The sample 106 is connected to a high voltage power source 206 that controls the irradiation energy on the sample by decelerating the primary electron beam. Each control unit is controlled by the central control unit 207 in an integrated manner. Control values and adjustment values are stored in the storage unit 208.

  FIG. 2 schematically shows the energy distribution of signal electrons. The low-speed component of the signal electron 108 is defined as a signal having a kinetic energy smaller than 50 eV, and is referred to as a true secondary electron (TSE). It is the signal of the area | region shown by 108a in FIG. TSE has a large peak in energy at several eV. Those having a kinetic energy higher than 50 eV are defined as high-speed components, and are called backscattered electrons (BSE). This is indicated by 108b in FIG. The energy distribution of BSE strongly depends on the average atomic number of the sample, and a sample having a large average atomic number (Z1) exhibits an elastic scattering distribution having a peak at an energy substantially equal to the incident energy of the primary electron beam 102. On the other hand, a sample having a small average atomic number (Z2) has a peak at an energy about half of the incident energy of the primary electron beam 102.

  FIG. 3 schematically shows the release efficiency of TSE and BSE. The emission efficiency of BSE increases as the average atomic number of the sample increases, and hardly depends on the incident energy of the primary electron beam. The size is about 0.1 to 0.2 for light elements such as carbon and silicon, and about 0.4 for heavy elements such as gold. On the other hand, TSE greatly depends on the incident energy of the primary electron beam, and TSE emission efficiency exceeds 1.0 in the range of several hundred eV to 3000 eV.

  In the best mode for carrying out the invention described here, a circuit pattern or resist pattern formed on a semiconductor wafer or an exposure mask is assumed to be the sample 106. However, when these materials are used, In general, incident energy of about several hundred eV to about 3000 eV is used for the purpose of avoiding sample charging. Further, these materials are often formed of light elements such as nitrogen and silicon. Therefore, as a conclusion derived from FIG. 3, it is possible to obtain a larger signal amount when TSE is the main component of the detection signal than when BSE is the main component, and a high S / N ratio can be realized. In the following, embodiments will be described in more detail.

Example 1
The first embodiment will be described with reference to FIGS. The electron source 101, the primary electron beam 102, the sample 106, and the deflector 107 have the same configuration as in FIG. A negative voltage is applied to the sample 106 by a high-voltage power source 206, and the primary electron beam is decelerated from 100 eV to 3000 eV and collides with the sample 106. The primary electron beam is scanned on the sample 106 by the deflector 107. As a result, TSE 108a and BSE 108b are emitted from the sample as signal electrons, but for the electrons between the negative voltage and the ground voltage of the mirror 1 Thus, the TSE 108a and the BSE 108b are accelerated from the sample toward the electron source. In the present embodiment, the case where a negative voltage is applied to the sample and the mirror is installed has been described. However, the electric field between the sample and the mirror only needs to form an accelerating electric field for the signal electrons. Even if the voltage arrangement is different from the voltage arrangement described, there is no difference in the effect of the present invention.

  The emitted TSE and BSE are emitted from the sample 106 with various emission angles. As shown in FIG. 5, when the electron emission direction θ measured from the direction parallel to the sample surface is defined as the elevation angle, the signal having a large elevation angle is emitted. As the signal electron flies in an orbit closer to the optical axis of the signal electron, the smaller the elevation angle, the more the signal electron flies in the orbit away from the optical axis. Further, a signal electron (BSE) having higher energy flies on a trajectory farther from the optical axis of the signal electron, and a signal electron (TSE) having lower energy flies on a trajectory farther from the optical axis of the signal electron.

  A divided metal plate 300 is disposed between the sample and the electron source. Further, a secondary electron deflection unit 112 controlled by the control unit 303 is provided between the metal plate and the sample in order to separate the secondary electron orbit from the primary electron orbit.

  The shape of the metal plate 300 is shown in FIG. The metal plate is divided coaxially with respect to the point A, and a hole serving as a passage for guiding the primary electron beam to the sample is provided at a point B different from the point A. The voltage sources 301a, 301b, 301c,... Are connected to the divided regions 300a, 300b, 300c,... Independently, and the output values are controlled by the power supply control means 302.

  As shown in FIG. 4, the TSE 108 a generated from the sample and accelerated is deaxiald by the secondary electron deflecting means 112 and collides with the metal plate 300. At this time, the secondary electron deflection means 112 is adjusted so that the center of the arrival position distribution of the TSE on the metal plate substantially coincides with the point A shown in FIG. This adjustment method will be described later in detail. By this adjustment, the TSE mainly concentrates and collides with the central division 300a of the metal plate 300, and a component having a large elevation angle selectively collides with the TSE. According to experiments, in order to selectively collide only the TSE component having an elevation angle larger than 60 ° with the division 300a, it is necessary to reduce the size of the divided area from about 1 mm to 2 mm in diameter. On the other hand, it is necessary to secure a hole diameter of about 1 mm for the hole through which the primary electron beam passes, from the viewpoint of easily adjusting the optical axis, and a configuration in which the above-described B point is away from the A point selects a TSE with a high elevation angle. It is essential for that.

  From each divided area of the metal plate, the tertiary electrons 113 are generated by the collision of TSE. Whether the tertiary electrons 113 can reach the detector 109 depends on the output values of the voltage sources 301a, 301b, 301c. Change. For example, when only the voltage source 301a connected to the central divided region is set to 0V and other voltages are set to positive potentials, the tertiary electrons generated from other than the divided 300a are potentials as shown in FIG. The barrier 109 cannot be overcome and the detector 109 cannot be reached. As a result, only TSE with a high elevation angle (actually, the number of tertiary electrons proportional to the number of TSE occurrences with a high elevation angle) is detected. Since TSE occurs more frequently than BSE, a high-contrast scanning electron microscope image depending on the emission angle can be obtained by the method described in this embodiment while maintaining a high signal SN. In addition, since most of the tertiary electrons generated from the metal plate are low-energy electrons of 50 eV or less, the voltage applied to the power supply 301b or the like may be several tens of volts or less, and in many cases, several volts or less, and the influence on the primary electron beam. Can be ignored. As a result, high spatial resolution can be maintained. The elevation angle region that is selectively detected is not limited to a high angle. For example, when only the voltage source 301b connected to the divided region 300b is set to 0V and the other voltages are set to positive potentials, the tertiary electrons generated from other than the divided 300b are potential barriers as shown in FIG. 7B. Cannot be overcome and the detector 109 cannot be reached. As a result, the number of tertiary electrons proportional to the amount of TSE emitted with a certain elevation angle range is detected.

  In this way, if the divided area is designed with an appropriate size and the center thereof is set apart from the passage hole for the primary electron beam, an image by TSE emitted in an arbitrary elevation angle range can be obtained. The method for determining the dimensions of the divided areas is easy. If the electromagnetic field in the space from the sample to the metal plate is calculated in advance using an electromagnetic field simulator, etc., the TSE trajectory in the electromagnetic field is calculated, and the position of the TSE with the emission elevation angle to be detected arrives on the metal plate. Good.

  The adjustment flow of the secondary electron deflecting means 112 will be described with reference to FIG. Hereinafter, a secondary electron deflecting unit having a configuration in which a deflection action by a magnetic field is exerted on secondary electrons will be described. The adjustment method is the same even in a configuration having a deflection action by an electric field or a configuration having both an electric field and a magnetic field. This adjustment work must be performed for each condition (acceleration voltage, probe current amount, etc.) of the primary electron optical system used for observation.

  First, in step 801, the adjustment sample is transported to the sample chamber. Next, in step 802, conditions for the primary electron optical system are set. Next, in step 803, only the voltage source 301a connected to the central divided region 300a is set to 0V, and the other voltages are set to a positive potential + 100V. In step 804, the image acquisition area (field of view) is set to 100 μm × 100 μm. In step 805, the deflection intensity (ΔX, ΔY) of the secondary electron deflection means 112 is set. The deflection intensity (ΔX, ΔY) to be set may be a value empirically obtained in advance, or may be set to (0, 0), that is, no secondary electron deflection if unknown. In step 806, an SEM image of the entire field of view is acquired. The field of view is sufficiently wider than the normal image observation area. Accordingly, the number of electrons, which are emitted from the sample, reach the divided region 300a regardless of the elevation angle, except for the specific portion of the visual field. Therefore, as shown in FIG. 9, the acquired image is an image in which only the portion has a strong (bright) region 901 with high signal intensity. In step 807, a distance ΔL between the center of the bright area 901 and the center 902 of the visual field is measured. If it is determined in step 808 that ΔL is smaller than the allowable value, it is determined that the secondary electron deflection amount is optimal, the deflection intensity (ΔX, ΔY) is stored in the storage means 208 (step 810), and adjustment work is performed. finish. If ΔL is larger than the allowable value in decision 808, the secondary electron deflection amount is changed to (ΔX + δx, ΔY + δy) in step 809, and steps 806 to 808 are repeated. After a plurality of repetitions, if ΔL is smaller than the allowable value in determination 808, it is determined that the amount of secondary electron deflection is optimal, and the deflection intensity is stored in storage means 208 (step 810) for adjustment. Finish the work.

  Note that the normal image acquisition area (field of view) is 5 μm × 5 μm or less, and the above-described brightness non-uniformity 901 in the image does not exist, and the image quality does not deteriorate. In addition, the above-mentioned visual field sizes of 100 μm × 100 μm and 5 μm × 5 μm are merely described as examples of the electron beam apparatus, and are values that vary greatly depending on the apparatus. These absolute values are not essential to the practice of the invention. If the value corresponding to the 100 μm × 100 μm field of view is sufficiently larger than the normal image acquisition area of the apparatus, there is no difference in the effect of the invention.

  By the way, the method for adjusting the amount of secondary electron deflection described above is effective only when both of the following two assumptions hold. One is a means for observing an area sufficiently wider than the normal observation area, and the second is that the metal plate 300 has the same emission angle as long as the electrons are emitted from different points in the area. To collide with different areas above. A method of adjusting the secondary electron deflection amount when these two assumptions are not satisfied will be described with reference to FIG.

  First, in step 1001, a sample in which cylindrical, spherical, or hemispherical protrusions shown in FIG. Next, in step 1002, conditions for the primary electron optical system are set. Next, in step 1003, only the voltage source 301a connected to the central divided region 300a is set to 0V, and other voltages are set to a positive potential + 100V. In step 1004, the deflection intensity (ΔX, ΔY) of the secondary electron deflection means 112 is set. The deflection intensity (ΔX, ΔY) to be set may be a value empirically obtained in advance, or may be set to (0, 0), that is, no secondary electron deflection if unknown. In step 1005, an SEM image of the protrusion on the sample is acquired. The brightness of the outer periphery of the protrusion in the image acquired in step 1006 is measured, and the brightness variation σ over the entire periphery is obtained. If it is determined in decision 1007 that σ is smaller than the allowable value, it is determined that the amount of secondary electron deflection is optimum, the deflection intensity (ΔX, ΔY) is stored in the storage means 208 (step 1008), and adjustment work is performed. finish. If it is determined in step 1507 that σ is larger than the allowable value, the secondary electron deflection amount is changed to (ΔX + δx, ΔY + δy) in step 1009 and steps 1005 to 1007 are repeated. After multiple iterations, if it is determined in decision 1007 that ΔL is smaller than the allowable value, it is determined that the amount of secondary electron deflection is optimum, and the deflection intensity is stored in the storage means 208 (step 1008) for adjustment. Finish the work.

(Example 2)
A second embodiment will be described with reference to FIG. The difference from the first embodiment is the method for dividing the metal plate 300. Description of other common parts is omitted. FIG. 12 shows a method for dividing the metal plate 300. The feature is that the division is performed radially from the center point A, and the colliding metal plates are designed differently according to the emission azimuth angle φ of the TSE. Here too, the passage hole for the primary electron beam is provided at point B sufficiently away from point A. A region 1201 indicated by a dotted line indicates a range where the TSE reaches. The point B is arranged outside the region 1201. From the experiment conducted, the spread on the metal plate 300 was as small as about 3 mm in diameter even when the total elevation angle component of TSE was detected. Therefore, if the points A and B are not separated by a distance of 1.5 mm or more, the detection efficiency of TSE having a specific azimuth angle component is lowered, leading to a decrease in contrast. Therefore, the configuration in which the point B is moved away from the point A is essential for selecting the TSE corresponding to the azimuth angle.

(Example 3)
A third embodiment will be described with reference to FIG. This embodiment describes a method for avoiding inconveniences that may occur in the first and second embodiments. As shown in FIGS. 7A and 7B, the signal selection according to the angle of TSE is realized by the potential distribution formed by the voltages applied to the metal plates 300a, 300b. When the divided metal plate is large, as shown in FIG. 13A, the tertiary electrons from the divided regions 1301 and 1302 to which a positive voltage is applied are prevented from being detected, and the tertiary is distributed over the entire divided region 1303 where 0V is set. Electrons are detected with high efficiency. On the other hand, since the spread of TSE is small, the division dimension of the metal plate may be 1 mm or less. At this time, as shown in FIG. 13B, the electric field distribution formed by the divided regions 1301 and 1302 protrudes to a part or the whole of the divided region 1303, and the detection efficiency of the tertiary electron signal generated from the divided region 1303 decreases. There was a thing. Therefore, as shown in FIG. 13C, by arranging a porous metal mesh 1304 to which 0 V is applied on the sample side of the divided metal plates 300a, 300b,..., The protrusion of the electric field distribution can be suppressed. it can. Further, with this configuration, the electric field strength in the vicinity of point B that adversely affects the primary electrons can be reduced, and the deterioration of the spatial resolution can be further reduced.

(Example 4)
A fourth embodiment will be described with reference to FIG. 4 again. The amount of deflection of the secondary electron deflecting means 112 described in the first embodiment is uniquely determined if the electron optical conditions are determined according to the procedure shown in FIGS. However, when the image shift deflector 110 is disposed between the metal plate 300 and the sample 106, if the image shift deflector 110 is used to move the observation region, the trajectory of not only the primary electron beam but also the signal electron beam. Therefore, it is necessary to reset the deflection amount of the secondary electron deflecting means 112. FIG. 14 is a flow chart for adjusting the secondary electron deflecting means 112 so that angle discrimination detection can be performed correctly when an image shift deflector is used.

  First, in step 1401, the adjustment sample is transferred to the sample chamber. Next, in step 1402, conditions for the primary electron optical system are set. In step 1403, the usage amount of the image shift deflector is set to (0, 0). Here, the numerical values in parentheses are coefficients by which the unit visual field movement amount δI in the x and y directions is multiplied. Next, in step 1404, a secondary electron deflection amount with respect to the image shift usage amount is determined. The contents of this step are the same as steps 803 to 810 in FIG. 8 or steps 1003 to 1009 in FIG. Next, in step 1405, the usage amount (the coefficient) of the image shift deflector is changed to (1, 0), and step 1404 is repeated. This operation is repeated for 25 points (n = 1 to n = 25) shown in FIG. The correspondence relationship between the image shift deflection amount and the secondary electron deflection intensity obtained as a result is stored in the storage means 208 as a numerical table (step 1406), and the adjustment operation is terminated.

  A correct secondary electron deflection amount for each image shift amount can be obtained. Further, the image shift movement amount other than the 25 points is also calculated by interpolating the results of the 25 points.

  Similarly, it is possible to cause the primary beam deflector 107 to follow the amount of secondary electron deflection. If the sensitivity ratio between the usage amount of the image shift deflector 110 and the usage amount of the deflector 107 is obtained in advance, the optimum secondary electron deflection amount is obtained for each usage amount of the deflector based on the data obtained in the flow of FIG. be able to.

(Example 5)
A fifth embodiment will be described with reference to FIG. In the fifth embodiment, one mode that compensates for the following drawbacks which are concerned in the first to fourth embodiments will be described. That is, in the first to fourth embodiments, the trajectory of the signal electrons, particularly TSE, flying between the metal plates 300 divided from the sample is changed by the secondary electron deflection means. Depending on the arrangement and configuration of the secondary electron deflection means, the influence on the primary electron beam may become large, which causes deterioration of the spatial resolution of the image. In order to compensate for this drawback, the configuration shown in FIG. That is, an assembly 400 of minute metal plates having a sufficiently smaller size than the divided metal plates shown in FIGS. 6 and 12 is arranged instead of the metal plate 300. The metal plates 400a, 400b, 400c,... Constituting the metal plate 400 are connected to voltage application means 501a, 501b, 501c,..., Respectively. Be controlled. In the first to fourth embodiments, the usage amount of the secondary electron deflecting means 112 is adjusted in accordance with the flow of FIGS. 8, 10, and 14 so as to guide the trajectory of the signal electrons onto the predetermined metal plate 300. . In the present embodiment, instead of deflecting the secondary electrons, a method of moving the output distribution of the voltage applying means 501a, 501b, 501c,... According to the arrival position of the secondary electrons on the metal plate assembly 400. Take.

  FIG. 17 shows a case where angle selection detection corresponding to FIG. 7A is performed in this embodiment. The division filled in black is maintained at 0 V, and the tertiary electrons generated from the division are detected by the detector 109. On the other hand, a positive voltage is applied to the white-painted division, which does not contribute to the detection signal. When the center distribution of signal electrons collides with the upper left of the aggregate 400 (FIG. 17A), when colliding with the center (FIG. 17B), when colliding with the lower right (FIG. 17C). The voltage arrangement applied to the division is different. If this voltage arrangement is determined by the same procedure as the case where the secondary electron deflection intensity is obtained in the flow chart of FIG. 8, FIG. 10, or FIG. 14, the secondary electrons are not deflected, that is, the primary electron beam. An image with enhanced contrast can be acquired without adversely affecting the image.

Claims (8)

In a charged particle beam apparatus for obtaining a microscopic image of the sample by detecting a secondary charged particle beam obtained by irradiating the sample with a primary charged particle beam,
A metal plate disposed between the charged particle beam source and the sample and divided into two or more;
Voltage applying means capable of independently applying a voltage to each of the divided metal plates,
The charged particle beam apparatus, wherein the secondary charged particle beam collides with the divided metal plate. The charged particle beam apparatus according to claim 1,
The divided metal plate is divided into concentric circles, and the center thereof does not coincide with the optical axis of the primary charged particle beam. The charged particle beam apparatus according to claim 1,
The divided metal plate is divided radially, and the center thereof does not coincide with the optical axis of the primary charged particle beam. In the charged particle beam device according to any one of claims 1 to 3,
The charged particle beam apparatus according to claim 1, wherein the sample is held on a sample stage, and a voltage for accelerating the secondary charged particle beam from the sample toward the metal plate is applied to the sample stage. In the charged particle beam device according to any one of claims 1 to 4,
A charged particle beam apparatus, wherein an electric field is applied between the sample and the metal plate for the purpose of accelerating the secondary charged particle beam to collide with the metal plate. In the charged particle beam device according to any one of claims 1 to 5,
The charged particle beam apparatus, wherein the secondary charged particle beam is an electron beam. In the charged particle beam device according to any one of claims 1 to 5,
The charged particle beam apparatus, wherein both the primary charged particle beam and the secondary charged particle beam are electron beams. In the charged particle beam device according to any one of claims 1 to 7,
A charged particle beam apparatus comprising means for deflecting a secondary charged particle beam between the divided metal plate and the sample.

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