JP2007035386A - Electron beam apparatus and device manufacturing method using same - Google Patents

Abstract

<P>PROBLEM TO BE SOLVED: To provide an electron beam apparatus carrying out a sample at a high throughput, without problems of a fringe electromagnetic field, and with a throughput speed improved by correction of axial chromatic aberration and spherical aberration. <P>SOLUTION: In the electron beam apparatus scanning a sample S with a plurality of primary electron beams and detecting a plurality of secondary electron beams emitted from the sample S through an image projection optical system C, the image projection optical system C includes an axial chromatic aberration correction lens 20, which is to be placed on an image surface of a lens 19 of the image projection optical system C and is preferred to be a Wien filter having a quadrupole electrode as well as a quadrupole magnetic pole. <P>COPYRIGHT: (C)2007,JPO&INPIT

Description

  The present invention relates to an electron beam apparatus that improves performance by correcting aberrations and evaluates a substrate having a pattern with a minimum line width of 0.2 μm or less with high throughput.

  An electron beam apparatus for inspecting and evaluating a pattern defect on a substrate is well known. In the technical field of such an electron beam apparatus, a technique for constructing a scanning electron microscope (SEM) or a transmission electron microscope (TEM) having an ultrahigh resolution by using an axial chromatic aberration correction lens is known (Non-Patent Document 1). reference). A technique is also known in which a plurality of beams are formed to scan a sample, and secondary electrons emitted from the sample are detected by a plurality of detectors to obtain a sample image. As axial chromatic aberration correction lenses and spherical aberration correction lenses, lenses having quadrupole or dodecapole electrodes or magnetic poles are known.

  However, a known electron beam apparatus using a plurality of electron beams has a problem that if the resolution is reduced, a large beam current cannot be obtained due to aberration, and the throughput is extremely small. Further, in the conventional aberration correcting lens of the multipole type, there is a possibility that extra aberration may occur due to the fringe field. Moreover, it has not been reported that by correcting aberrations such as axial chromatic aberration and spherical aberration, an NA aperture member having a large aperture is used, the beam current is increased, or the space charge effect is reduced. It was.

  On the other hand, only a convex lens can be used as an axially symmetric lens system, whereas a non-axially symmetric multipole lens can produce a concave lens and generate negative axial chromatic aberration and negative spherical aberration. Multipole lenses have begun to be used in electron beam apparatuses having one optical system such as SEM and TEM.

Conventionally, such an axial chromatic aberration correction lens and a spherical aberration correction lens have been used only for reducing the resolution. However, when a semiconductor device is manufactured or evaluated using an electron beam apparatus, there is a case where it is desired to greatly improve the processing speed while the resolution remains several tens of nm rather than the limit resolution. However, the on-axis chromatic aberration correction lens or spherical aberration correction lens used in the electron beam apparatus increases the optical path length, which increases the space charge effect and prevents the processing speed from increasing. there were.
52nd Applied Physics Related Conference Lecture Proceedings (Spring 2005, Saitama University), pp. 812, 815

  The present invention has been proposed in view of the above problems, and an object of the present invention is to provide an electronic device capable of obtaining a very high throughput with a resolution of about 100 nm using a novel aberration correction technique. It is another object of the present invention to provide an electron beam apparatus using a Wien filter that evaluates a sample at a high throughput and does not cause a problem of an electromagnetic field of fringes. Another object of the present invention is to provide an electron beam apparatus in which a processing speed is improved by arranging a lens for correcting axial chromatic aberration or spherical aberration at an appropriate position.

To achieve the above objective,
The invention of claim 1
An electron beam apparatus that scans a sample with a plurality of primary electron beams and detects a plurality of secondary electron beams emitted from the sample via a mapping optical system,
An electron beam apparatus, wherein the mapping projection optical system comprises an axial chromatic aberration or spherical aberration correction lens;
I will provide a.

  According to a second aspect of the present invention, the on-axis chromatic aberration or spherical aberration correction lens has a multipole electrode and a multipole magnetic pole, and the bore diameter between the opposed electrodes continuously increases and decreases along the optical axis. It is a non-dispersive Wien filter having an area to be used.

The invention of claim 3
A sample is scanned by a plurality of primary electron beams through a first electron optical system, and a plurality of secondary electron beams emitted from the sample are imaged on a detector through a second electron optical system to form an image of the sample. An electron beam device for detecting an image,
The first electron optical system includes a first axial chromatic aberration correction lens, and the second electron optical system includes a second axial chromatic aberration correction lens;
An electron beam apparatus, wherein the first on-axis chromatic aberration correction lens and the second on-axis chromatic aberration correction lens are Wien filters having an even number of electromagnetic poles;
I will provide a.

The invention of claim 4
An electron optical system for irradiating the sample with a plurality of primary electron beams, an objective lens for focusing the plurality of secondary electron beams emitted from the sample, and axial chromatic aberration of the focused secondary electron beams are corrected. An electron beam apparatus comprising an aberration correction lens and an electron optical system for forming an image of the secondary electron beam whose axial chromatic aberration has been corrected on a detector,
An electron beam apparatus comprising an NA aperture member disposed between the objective lens and the aberration correction lens;
I will provide a.

The invention according to claim 5 is characterized in that the objective lens includes an electrode composed of a cylindrical electrode and a disk-shaped electrode plate.
The invention of claim 6
An electron beam apparatus that scans a sample with a primary electron beam, forms an image of a secondary electron beam emitted from the sample on a detector, and detects an image of the sample,
The primary electron beam is focused by a first objective lens to irradiate the sample;
The secondary electron beam is focused by the first objective lens and the second objective lens, and axial chromatic aberration of the secondary electron beam focused by the first objective lens and the second objective lens is reduced by an aberration correction lens. Correcting and axially correcting the secondary electron beam corrected for chromatic aberration on the detector,
An electron beam apparatus, wherein a beam separator for separating the primary electron beam and the secondary electron beam is disposed between the first objective lens and the second objective lens;
I will provide a.

The invention according to claim 7 is characterized in that the first objective lens includes a frustoconical electrode plate whose wall thickness continuously decreases toward the sample.
The invention of claim 8
A marker plate used when correcting either axial chromatic aberration or spherical aberration in the electron beam apparatus according to any one of claims 1 to 7, wherein the marker plate has a diameter different from that of a smooth surface having a large secondary electron beam emission coefficient. A marker plate, wherein a plurality of holes or dots are formed;
I will provide a.

  Hereinafter, embodiments of an electron beam apparatus according to the present invention will be described with reference to the accompanying drawings. Throughout the drawings, the same or similar components are designated by the same reference numerals or reference symbols.

  FIG. 1 schematically shows a first embodiment of an electron beam apparatus according to the present invention. In the figure, an electron beam apparatus irradiates a sample S with an electron gun G, an electron optical system A carrying a primary electron beam emitted from the electron gun G, and a primary electron beam sent from the electron optical system A. And an electron optical system B that separates the secondary electron beam emitted from the sample S from the primary electron beam, an electron optical system C that carries the separated secondary electron beam, and a secondary electron beam from the electron optical system C. And a detector D for receiving.

  The electron optical system A includes a multi-aperture member 1, a condenser lens 2, reduction lenses 3 and 4, an NA aperture member 5, an aberration correction lens 6, a first scanning deflector 7, and a beam separation pre-deflector 8. . The aberration correction lens 6 is composed of, for example, a two-stage correction lens, and each correction lens is composed of a Wien filter. The primary electron beam emitted from the electron gun G uniformly irradiates the multi-aperture of the multi-aperture member 1 having a plurality of apertures. Thereby, a plurality of primary electron beams are generated. The generated plurality of primary electron beams are focused by the condenser lens 2 and form an image of a light source created by a crossover, that is, an electron gun, before entering the reducing lens 3.

  The image of the multi-aperture 1 is reduced by the reduction lenses 3 and 4 to form a reduced image at the object point 9 of the aberration correction lens 6. The NA aperture member 5 is disposed in front of the reduction lens 4 and ensures the beam resolution of a plurality of primary electron beams that have passed through the reduction lens 3. The reduced image formed at the object point 9 forms an equal-magnification image at an intermediate point 10 of the aberration correction lens 6 and an image point 11 of the aberration correction lens 6. A plurality of primary electron beams focused on the image point 11 are focused again by an objective lens (described later) of the electron optical system B and imaged on the surface of the sample S.

  The first scanning deflector 7 deflects the traveling direction of the plurality of primary electron beams formed at the image point 11 in a predetermined direction with a predetermined amplitude, thereby scanning the surface of the sample S with the plurality of primary electron beams. Let Further, the traveling directions of the plurality of primary electron beams are deflected by the pre-deflector 8 so as to enter the center of the beam separator in the electron optical system B.

  The electron optical system B includes a beam separator 12, a second scanning deflector 13, an axially symmetric electrode 14, a first MOL (Moving Objective Lens) deflector 15, a second MOL deflector 16, and an objective lens 17. The objective lens 17 is, for example, an electromagnetic lens in which the magnetic gap 18 is located on the sample S side. Each of the plurality of primary electron beams deflected by the pre-deflector 8 passes through the beam separator 12 and is further deflected by the second scanning deflector 13. Are imaged at different positions on the surface of the sample S to scan the sample S. The deflection fulcrum at this time is set at a position where the sum of the deflection chromatic aberration and coma aberration generated in the objective lens is minimized.

  Both the first MOL deflector 15 and the second MOL deflector 16 are electromagnetic deflectors, and operate so as to further reduce the deflection aberration by setting a condition close to the MOL condition. The MOL condition is a condition for generating a deflection magnetic field proportional to the differential of the on-axis magnetic field distribution of the objective lens 17. In this case, the deflection fulcrum is located at −∞. That is, the principal rays of the plurality of primary electron beams are incident in parallel to the optical axis L of the electron optical system A. When the conditions close to the MOL condition are set, the deflection aberration is further reduced. By using such conditions, the lens axis can be moved to the beam position, and the lens axis can be adjusted even when the beam is deflected. Since the chief ray passes, the deflection aberration can be reduced.

  A plurality of primary electron beams that pass through the electron optical system B and are imaged on the surface of the sample S are subjected to axial chromatic aberration and spherical aberration by the objective lens 17. However, since the two-stage Wien filter 6 in the electron optical system A operates so as to produce negative axial chromatic aberration and negative spherical aberration, the axial chromatic aberration and spherical aberration produced by the objective lens 17 are two-stage. It is counteracted by negative axial chromatic aberration and negative spherical aberration produced by the Wien filter 6. Since aberrations are canceled out in this way, even if the NA aperture of the NA aperture member 5 is set to a large value, it is possible to narrow down a plurality of primary electron beams by the reduction lenses 3 and 4. The axially symmetric electrode 14 can adjust the degree of longitudinal chromatic aberration caused by the objective lens 17 by changing the voltage applied to the electrode.

  The first MOL deflector 15 and the second MOL deflector 16 operate so as to cancel the refractive action of the objective lens 17 with respect to the principal ray. For this reason, out of the plurality of secondary electron beams emitted from different positions on the surface of the sample S irradiated by the plurality of primary electron beams focused by the electron optical system B, it was emitted in the normal direction of the sample S. The principal rays of the plurality of secondary electron beams travel parallel to the optical axis L without being refracted by the objective lens 17 and are separated from the arrival direction of the primary electron beam by the beam separator 12 in FIG. And enters the electron optical system C. The pre-deflector 8 is an electrostatic deflector, and operates to cancel the deflection chromatic aberration generated in the plurality of primary electron beams in the beam separator 12.

  The electron optical system C is a mapping projection optical system including a secondary electron image forming lens 19, an aberration correction lens 20, a first magnifying lens 21, and a second magnifying lens 22. Since the aberration correction lens 20 only needs to correct axial chromatic aberration, it only needs to generate a quadrupole electric field and a quadrupole magnetic field, and may be a quadrupole Wien filter, for example. Instead, the aberration correction lens 20 may be a hexapole Wien filter to correct only spherical aberration.

  The plurality of secondary electron beams separated from the primary electron beam by the beam separator 12 forms an image on the object point 23 of the aberration correction lens 20 by the secondary electron image forming lens 19. That is, the aberration correction lens 20 is disposed on the image plane of the secondary electron image forming lens 19. The aberration correction lens 20 forms an image of the object point 23 at the point 24. The image created at the point 24 by the aberration correction lens 20 is magnified by the first magnifying lens 21 and the second magnifying lens 22, and an image corresponding to a plurality of secondary electron beams is created on the detector D. The detector D is a multi-detector and generates a signal corresponding to each incident secondary electron beam. A processing circuit (not shown) creates a two-dimensional image of the sample S using the signal thus generated.

  The aberration correction lens 6 of the electron optical system A is required to have a resolution of about 25 nm in the case of a 25 nm pixel size. Therefore, it is predicted that an aberration is generated due to the influence of the fringe electric field and the fringe magnetic field generated at the end where the primary electron beam enters the aberration correction lens 6 and the end where the primary electron beam exits from the aberration correction lens 6. Is done. In order to avoid the influence of the fringe field, it is preferable to use a Wien filter divided into two as the aberration correction lens 6 and to cancel the influence of the fringe field using the symmetry thereof. 1A and 1B are cross-sectional views showing an example of the configuration of the Wien filter in this case. FIG. 1A also shows the on-axis electric and magnetic field distribution of this filter.

  1A and 1B, the Wien filter 30 has a permalloy core 31 which is a cylinder having a thickness of 10 to 20 mm. The permalloy core 31 forms a magnetic circuit and is designed to be thick in order to increase the rigidity of the Wien filter 30. As shown in detail in the configuration of the Wien filter 30 in FIG. 1B, the space inside the permalloy core 31 has twelve electromagnetics centered on a bore 32 having a predetermined diameter for passing a primary electron beam. The poles (that is, the twelve electrodes and magnetic poles) 331, 332, 333,..., 3312 are respectively connected to the permalloy core 31 via insulating spacers 341, 342, 343,. Arranged at intervals.

  The thickness a (that is, the width in the radial direction) of each of the insulating spacers 341 to 3412 is selected to a minimum value so that the magnetic resistance is small and the required insulating property is maintained. On the other hand, the circumferential length b of each insulating spacer is set to a value that cannot be directly viewed from the optical axis L so that the insulating spacer is hidden behind the magnetic pole piece when viewed from the optical axis in FIG. 1B. However, the circumferential length b of the insulating spacer may be larger than the circumferential length of the pole piece to prevent discharge. These electromagnetic poles 331 to 3312 and the insulating spacer are attached to the permalloy core 31 at a plurality of required positions by appropriate fixing means 35. 1A and 1B show only one fixing means 35 for the sake of simplicity. When a fastening screw is used as the fixing means 35, a spacer 351 for insulating between the fastening screw and the permalloy core 31 is preferably provided.

  Each electromagnetic pole is divided into two stages along the optical axis L and has the same structure in which an excitation coil is wound around each electromagnetic pole. Thus, two electromagnetic poles facing each other, for example, the electromagnetic poles 331 and 337 will be described. The electromagnetic poles 331 and 337 include upper electromagnetic poles 331U arranged in two stages along the optical axis L, as shown in FIG. 337U and lower electromagnetic poles 331L and 337L, and the upper and lower electromagnetic poles have an integrated structure connected by connecting portions 331M and 337M. A magnetic field is placed around the electromagnetic poles 331 and 337 in a predetermined direction. Exciting coils 331C and 337C for forming are wound. Thereby, each opposing electromagnetic pole forms a magnetic field in a direction orthogonal to the optical axis L. The connection portions 331M and 337M have a bore diameter that does not substantially generate a magnetic field and an electric field, and have an integrated structure in which the upper electromagnetic poles 331U and 337U and the lower electromagnetic poles 331L and 337L are not misaligned.

  Furthermore, as shown to FIG. 1A, the cross-sectional shape in the surface containing the optical axis L of the upper side electromagnetic poles 331U and 337U and the lower side electromagnetic poles 331L and 337L is formed in a trapezoid. For this reason, the diameter of the central bore 32 varies from the minimum value h between the adjacent electromagnetic poles with the optical axis L in between to the maximum value k between the adjacent connection portions with the optical axis L in between. As a result, the strength of the on-axis magnetic field formed between the upper electromagnetic poles adjacent to each other across the optical axis L and between the lower electromagnetic poles adjacent to each other across the optical axis L is as shown on the right side of FIG. 1A. Furthermore, it changes between the minimum value and the maximum value in a shape close to a trapezoid twice in the direction of the optical axis L. In this way, the on-axis electric field is generated by the six electromagnetic poles along the optical axis L of the Wien filter 30 so that the magnetic field changing along the optical axis L of the Wien filter 30 cancels the Lorentz force exerted on the primary electron beam. Is formed. The distribution of this on-axis electric field also takes the form shown in FIG. 1A.

  Since the aberration correction lens 6 is divided into two stages in this way, a primary electron beam that diverges from the object point 9 and converges to the point 10, and a primary electron that diverges from the point 10 and converges to the image point 11. The symmetry with the line can be improved and the influence of the fringe field can be negated. Furthermore, since the cross-sectional shape of the upper and lower electromagnetic poles including the optical axis L is trapezoidal and the bore 32 changes monotonously, the fringe magnetic field and the fringe electric field at the upper and lower ends of the Wien filter are changed. The difference can be reduced, and since the upper side and the plate side are integrated, it is possible to prevent deterioration in manufacturing accuracy between the upper side and the lower side.

  FIG. 2 is a diagram schematically showing a second embodiment of the electron beam apparatus according to the present invention. Similarly to the first embodiment, the electron beam apparatus in this embodiment also includes an electron gun G, electron optical systems A, B, C, and a detector D, and the electron beam emitted from the electron gun is The sample S is irradiated through the electron optical systems A and B, and the secondary electron beam emitted from the sample S is guided by the electron optical system C and reaches the detector D.

  In FIG. 2, the electron optical system A includes an axis alignment deflector 41, a condenser lens 42, an axis alignment deflector 43, a molded aperture member 44 having a plurality of square openings, a condenser lens 45, an axis alignment deflector 46, A molded lens 47 and a primary electron beam trajectory adjusting deflector 48 are provided. Here, there are a plurality of openings of different sizes when the openings are dirty and when the pixel dimensions are changed, and only one is irradiated. The primary electron beam emitted from the electron gun G is deflected by the alignment deflector 41 so as to travel along the optical axis L, and then focused by the condenser lens 42 so that the square opening of the shaped aperture member 44 is uniformly formed. To form a primary electron beam having a square cross-sectional shape. The magnification of the primary electron beam having a square cross section is adjusted by the condenser lens 45 and the shaping lens 47, and the square primary electron beam is deviated from the optical axis L by the axis alignment deflector 46 and the trajectory adjustment deflector 48. The trajectory is corrected to a certain opening 501 and enters the electron optical system B. When the beam energy is high, the primary electron beam passes through the trajectory L1, and when the beam energy is low, the deflection angle by the beam separator 49 is large, so that the primary electron beam is controlled to pass through the trajectory L2.

  The electron optical system B includes a beam separator 49 that is, for example, an electromagnetic deflector, an NA aperture member 50, and an objective lens 51 having a plurality of (three in FIG. 2) electrodes. As shown in FIG. 2A, the NA opening member 50 has a square hole 501 and a ring-shaped hole 502 divided into four, and the square primary electron beam transmitted from the electron optical system A is a sample. The traveling direction is changed by the beam separator 49 so as to be incident on the optical axis position of the secondary optical system of S, and after passing through the square hole 501 of the NA aperture member 50, it is focused to a predetermined size by the objective lens 51. And focused on the surface of the sample S.

Of the three electrodes of the objective lens 51, the center electrode 511, as shown, has a circular plate portion 511 ₁ and the circular plate shape combining a vertical cylindrical portion 511 ₂ to the part. As a result, the electric field intensity on the sample surface is small, and the energy of the primary electron beam is high on the optical axis where the lens is located, so that low aberration is obtained. Further, by applying a lower potential to the electrode 512 closer to the sample S than the central electrode 511, the electric field in the vicinity of the sample surface can be set to a value that can avoid discharge, for example, 1.8 kV / mm or less. it can. Furthermore, since the surface on the 513 side of the central electrode 511 is a flat surface, the distance from the electrode 513 far from the sample S can be reduced, and a required focal length can be obtained only by applying a relatively small voltage to the electrode 513. Can be set.

  The secondary electron beam emitted from the sample S by the irradiation of the square primary electron beam is focused by the objective lens 51, passes through the four divided ring holes 502 of the NA opening member 50, and has a hollow cross section. It is said. As will be described later, since the axial chromatic aberration is corrected by the aberration correction lens of the electron optical system C, a hollow beam having a large aperture angle can be formed by the ring-shaped hole 502. For this reason, the blur due to the space charge effect is small. Further, since the primary electron beam passes through the hole 501 away from the ring-shaped hole 502, the amount of space charge caused by the primary electron beam causing the blur of the secondary electron beam is negligibly small. The secondary electron beam made into a hollow beam by the ring-shaped hole 502 is separated from the primary electron beam by the beam separator 49 and enters the electron optical system C.

  The electron optical system C includes an electrostatic deflector 52, an aberration correction lens 53, an auxiliary lens 54, a first magnifying lens 55, an auxiliary lens group 56, a second magnifying lens 57, and a deflector 58. The secondary electron beam separated by the beam separator 49 is deflected by the electrostatic deflector 52 so as to correct the deflection chromatic aberration generated by the beam separator 49, and the course is deflected so as to proceed in a direction perpendicular to the sample S. Then, a secondary electron image is formed at the object point 59 of the aberration correction lens 53.

The aberration correction lens 53 is, for example, a 12-pole Wien filter, and has a two-stage structure similar to that shown in FIGS. 1A and 1B, similar to the Wien filter 6 in the first embodiment. In order to correct axial chromatic aberration and spherical aberration, the dipole electromagnetic field is given to the aberration correction lens 53 so as to satisfy the Wien condition, and negative axial chromatic aberration is generated by the quadrupole electromagnetic field, and the hexapole electromagnetic field and 8 It is controlled to create a negative spherical aberration with the pole field. The aberration correction lens 53 focuses the secondary electron beam emanating from the object point 59 on the intermediate point 60 so as to be non-dispersive, and then forms a secondary electron image at the image point 61. The image point 61 is located on the main surface of the auxiliary lens 54. As shown in FIG. 2, the length of the aberration correction lens 53 in the traveling direction of the secondary electron beam is smaller than the distance between the object point 59 and the image point 61. The dimension d ₁ from the object point 59 to one end of the filter is equal to the distances d ₂ and d ₃ from the intermediate point 60 to the opposite end of the filter and the distance d ₄ from the other end of the filter to the image point 61.

  As described above, when a Wien filter is used as the aberration correction lens 53, the beam trajectory of the secondary electron beam is axially symmetric and has a wide field of view, so that even if the secondary electron image is wide, the whole has low aberration. Can be. In addition, since the field of view is wide, it is easy to align the aberration correction lens 53.

  The auxiliary lens 54 forms an image of the ring-shaped hole 502 of the NA aperture member 50 on the main surface of the first magnifying lens 55 without affecting the imaging condition of the secondary electron image. Therefore, the first magnifying lens 55 enlarges the image of the secondary electrons, and the enlarged image of the secondary electrons is formed on one of the auxiliary lens groups 56. Further, the secondary electron image is further magnified by the second magnifying lens 57 and formed on the detector D. Since the auxiliary lens group 56 is composed of a plurality of (three stages in the drawing) lenses, it is possible to handle even when the pixel dimensions are changed. When the pixel size is the smallest, the lens closest to the second magnifying lens 57 in the auxiliary lens group 56 is used, and the other lenses are not excited. The secondary electron image stored on the main surface of the lens is greatly magnified by the second magnifying lens 57, and a secondary electron image having the maximum magnification is formed on the detector D. Conversely, when the pixel size is the maximum, a secondary electron image is created on a lens far from the second magnifying lens 57 in the auxiliary lens group 56, and an enlarged image of the same size is created on the detector D.

  If the detector D has a configuration in which a plurality of CCD devices are arranged, it is possible to avoid unnecessary waiting time due to the fact that the CCD data read time is longer than the exposure time. For example, as shown in FIG. 2B, when the detector D has a configuration in which four CCD devices 62 to 65 are arranged on the same plane, the deflector 58 deflects the secondary electron beam emitted from the second magnifying lens 57. The secondary electron images magnified by the second magnifying lens 57 are sequentially formed on the four CCD devices 62 to 65. Thereby, even if the data reading time of the CCD device is four times the exposure time, the secondary electron image can be continuously detected without useless waiting time.

  Next, a third embodiment of the electron beam apparatus of the present invention will be schematically described with reference to FIG. The electron beam apparatus according to the third embodiment also includes an electron gun G, electron optical systems A, B, and C, and a detector D, as in the two embodiments described so far, and further includes control. Has system E. The electron beam emitted from the electron gun G passes through the electron optical systems A and B and irradiates the sample S, whereby the secondary electron beam emitted from the sample S is guided by the electron optical system C and is detected by the detector D. To. The control system E uses the output from the detector D to adjust the potential applied to the objective lens.

The electron optical system A includes two condenser lenses 71 and 72, an opening member 73 having a rectangular opening, two lenses 74 and 75, and a two-stage deflector 76 for adjusting the incident point. Electron gun G has a cathode, for example made of L _a B _6, an electron beam emitted from the cathode is focused by the condenser lens 71 and 72 of the two-stage, uniform irradiation intensity rectangular aperture of the aperture member 73 Irradiate with. The primary electron beam formed into a rectangular cross section by the opening is reduced or enlarged at a desired magnification by the two-stage lenses 74 and 75, and is further incident on a predetermined incident point of the electron optical system B by the deflector 76. The direction of travel is adjusted. This adjustment is necessary because the deflection angle at the beam separator 77 is large when the energy of the primary electron beam is small, so that the trajectory L3 is taken.

  The electron optical system B includes a beam separator 77 and a first objective lens 78 having three electrodes. The beam separator 77 is an electromagnetic deflector, for example. The primary electron beam whose traveling direction is adjusted by the deflector 76 is incident on a point away from the center of the beam separator 77 by a predetermined distance, for example, a point 4 mm away, and the beam separator 77 makes an angle β (<α ) Is deflected only. β is, for example, 23 degrees. As a result, the primary electron beam enters the first objective lens 78 at an angle α-β with respect to the sample S, and is focused by the first objective lens 78 and further slightly deflected to irradiate the sample S.

  The secondary electron beam emitted from the sample S by the irradiation of the primary electron beam is focused by the first objective lens 78, and then deflected away from the primary electron beam by the beam separator 77 to the electron optical system C. enter. The electron optical system C includes a beam trajectory correcting deflector 79, an NA aperture member 80, a second objective lens 81 having three electrodes, an aberration correcting lens 82, a first magnifying lens 83, an auxiliary lens group 84, and a second magnifying lens. 85.

  The secondary electron beam separated by the beam separator 77 is further deflected by the beam trajectory correcting deflector 79 and travels in a direction parallel to the normal direction of the sample S. The beam trajectory correcting deflector 79 is also an electromagnetic deflector, for example, and deflects the secondary electron beam by the same angle and in the opposite direction as the angle at which the beam separator 77 deflects the primary electron beam, that is, by −α. As a result, the chief ray of the secondary electron beam travels perpendicularly to the sample S, and the beam diverged from the sample becomes a parallel beam between the two stages of lenses, so that the deflection chromatic aberration can be removed. Note that astigmatism may occur due to deflection in the beam separator 77 and the beam trajectory correcting deflector 79. In order to remove this, it is desirable to superimpose astigmatism correction current on these beam separators. Further, by tilting the beam trajectory correcting deflector 79 with respect to the optical axis L ′ of the electron optical system C by an angle that is ½ of the deflection angle, no distortion occurs even if the beam separator has a small aperture. can do.

  The secondary electron beam deflected by the beam trajectory correcting deflector 79 is limited by the NA aperture member 80, and a secondary electron image slightly reduced by the second objective lens 81 is formed at the object point 86 of the aberration correction lens 82. . By adjusting the position of the NA aperture member 80 in the optical axis L ′ direction, coma aberration can be minimized and lateral chromatic aberration can be sufficiently reduced. Here, when the reduction ratio between the first objective lens 78 and the second objective lens 81 is increased, the secondary electron beam travels along the path indicated by the solid line 87, and the first objective lens 78 and the second objective lens 81 are reduced. When the rate is reduced, the secondary electron beam follows the path indicated by the dotted line 88.

  The configuration of the aberration correction lens 82 is the same as that of the aberration correction lens 6 shown in FIG. 1, and a description thereof is omitted here. The aberration correction lens 82 forms a secondary electron image at the object point 86 at the image point 89, and the secondary electron beam from the image point 89 is magnified by the first magnifying lens 83, the auxiliary lens group 84, and the second magnifying lens 85. An image that is adjusted and enlarged to a desired size so as to match the pixel pitch of the detector D is formed on the detector D.

  The output from the detector D is supplied to the CPU 90 of the control system E, and the CPU 90 generates a two-dimensional image signal of the sample surface using the output of the detector D. When the image displayed using the two-dimensional image signal includes an aberration, the control power supply 91 receives the command from the CPU 90 in order to correct the aberration, and the control power supply 91 controls the first objective lens 78 and the second objective lens 81. The voltage applied to each electrode is adjusted.

  Here, the first objective lens 78 and the second objective lens 81 will be described. First, the first objective lens 78 has electrodes 781, 782, and 783, and the center electrode 782 includes a truncated cone portion having an opening for passing an electron beam at the center and a disk portion around the same. By adopting such a shape, coma aberration can be reduced, and a desired focal length can be obtained with a relatively small positive voltage. By reducing the voltage applied to the electrode 783 closer to the sample S, the electric field strength on the sample surface can be reduced to avoid discharge. On the other hand, when the voltage applied to the electrode 783 is increased, the axial chromatic aberration coefficient of the objective lens 78 can be reduced, so that the axial chromatic aberration due to the first objective lens 78 and the second objective lens 81 is reduced by the aberration correction lens 82. It becomes easy to cancel by the longitudinal chromatic aberration. Further, by changing the voltage applied to the electrode 781 by, for example, about ± 100 V, it is possible to dynamically correct the focus shift due to the unevenness of the sample surface.

  The second objective lens 81 also has a plurality of (three in FIG. 3) electrodes. By adjusting the voltage applied to the center electrode, the secondary electron image can be generated without changing the imaging position 86 of the primary electron beam. The magnification can be adjusted. Using this result, the spherical aberration correction coefficient or the axial chromatic aberration correction coefficient of the first objective lens 78 and the second objective lens 81 can be finely adjusted.

  Here, marks used for beam adjustment in the electron beam apparatuses according to the first to third embodiments described so far will be described with reference to FIGS. 4A to 4E. FIG. 4A shows a marker plate 101 having three different diameter holes. That is, the marker plate 101 is formed such that a small marker hole 102 having the smallest diameter, a medium marker hole 103 having an intermediate diameter, and a large marker hole 104 having the largest diameter are arranged in the row direction. The areas other than the holes are coated on both sides with a conductive material having a large secondary electron emission rate. FIG. 4B shows the cross-sectional shape of the marker plate 101.

  The marker plate 101 is placed at the same height as the sample S, irradiated with a primary electron beam, and a two-dimensional image of the marker hole 102, 103 or 104 is detected by the detector D. Examples of images detected at this time are shown in FIGS. 4C, 4D, and 4E. When the alignment of the correction lens in the optical path of the electron beam from the electron gun G through the sample S to the detector D is not appropriate, coma aberration as shown in FIG. 4C is observed, and as shown in FIG. 4D. Axis alignment is required to obtain a circular image. Actually, as shown in FIG. 4E, since the marker hole 102 is small, the image has a very low contrast and it is difficult to detect aberration. On the other hand, the image of the marker hole 104 has a large and clear contrast, but the large marker hole also increases the blur of the image and may cause a risk of overlooking subtle aberrations. Therefore, an optimal hole diameter may be selected. Alternatively, as another marker, as shown in FIG. 4F, the marker plate 101 is made of a thin film having a small secondary electron emission rate, and a marker 105 made of heavy metal dots is formed on the Si thin film instead of the marker holes 102 to 104. It is also good to use what was done.

  Although several embodiments of the electron beam apparatus according to the present invention have been described above, the present invention is not limited to such embodiments, and various modifications and corrections are possible.

  As described above, it can be understood from the detailed description of some embodiments of the electron beam apparatus according to the present invention. Since the present invention corrects longitudinal chromatic aberration or spherical aberration in the secondary electron optical system, Even if the distance between the lines is reduced, a plurality of secondary electron beams can be detected sufficiently, and therefore a large number of primary electron beams can be arranged in the vicinity of the optical axis.

1 is a diagram schematically showing a first embodiment of an electron beam apparatus according to the present invention. FIG. 2 is a longitudinal sectional view of the aberration correction lens shown in FIG. 1, showing a cross section taken along line XX in FIG. 1B, and a graph showing the distribution of magnetic field strength and electric field strength in the aberration correction lens of FIG. It is. It is a cross-sectional view of the aberration correction lens shown in FIG. 1, and shows a cross section taken along line YY in FIG. 1A. It is a figure which shows schematically 2nd Embodiment of the electron beam apparatus which concerns on this invention. FIG. 3 is a plan view of the NA opening member shown in FIG. 2. It is a figure which shows the arrangement | sequence of the CCD detector of the detector shown in FIG. It is a figure which shows schematically 3rd Embodiment of the electron beam apparatus which concerns on this invention. It is a top view of the marker which can be used with the electron beam apparatus which concerns on this invention. It is sectional drawing which follows the line ZZ in FIG. 4A. It is a figure which shows the image of a marker hole in case axial alignment is inappropriate. It is a figure which shows the image of a marker hole in case axial alignment is appropriate. It is a figure which shows the image of an actual marker hole. FIG. 6 is a cross-sectional view of an alternative marker.

Explanation of symbols

G: electron gun, A, B, C: electron optical system, D: detector, E: control system, S: sample,
1: multi-aperture member, 2: condenser lens, 3, 4: reduction lens, 5: NA aperture member, 6: aberration correction lens, 7: first scanning deflector, 8: pre-deflector, 9: object point, 11: Image point 12, Beam separator 13: Second scanning deflector 14: Axisymmetric electrode 15: First MOL deflector 16: Second MOL deflector 17: Objective lens 19: Secondary electron image Forming lens, 20: aberration correction lens, 21, 22: magnifying lens,
30: Vienna filter, 31: Permalloy core, 32: Bore, 331-3312: Magnetic pole and electrode, 341-3412: Insulating spacer,
41: Axis alignment deflector, 42: Condenser lens, 43: Axis alignment deflector, 44: Molded aperture member, 45: Condenser lens, 46: Axis alignment deflector, 47: Molded lens, 48: Primary electron beam trajectory Deflector for adjustment, 49: Beam separator, 50: NA aperture member, 51: Objective lens, 52: Electrostatic deflector, 53: Aberration correction lens, 54: Auxiliary lens, 55, 57: Magnifying lens, 56: Auxiliary Lens group, 58: deflector,
501: Square hole 502: Ring-shaped hole 62-65: CCD device
71, 72: condenser lens, 73: aperture member, 74, 75: lens, 76: deflector, 77: beam separator, 78: first objective lens, 79: beam trajectory correcting deflector, 80: NA aperture member 81: second objective lens, 82: aberration correction lens, 83, 85: magnifying lens, 84: auxiliary lens group, 90: CPU, 91: control power supply,
101: Marker plate: 101: Small marker hole, 102: Medium marker hole, 103: Large marker hole, 105: Heavy metal dot

Claims (8)

An electron beam apparatus that scans a sample with a plurality of primary electron beams and detects a plurality of secondary electron beams emitted from the sample via a mapping optical system,
An electron beam apparatus, wherein the mapping projection optical system includes an axial chromatic aberration or spherical aberration correction lens.   An axial chromatic aberration or spherical aberration correction lens for use in the electron beam apparatus according to claim 1, wherein the lens has a multipole electrode and a multipole magnetic pole, and a bore diameter between the facing electrodes is light. An axial chromatic aberration correction lens, which is a non-dispersive Wien filter having an area that continuously increases or decreases along the axis. A sample is scanned by a plurality of primary electron beams through a first electron optical system, and a plurality of secondary electron beams emitted from the sample are imaged on a detector through a second electron optical system to form an image of the sample. An electron beam device for detecting an image,
The first electron optical system includes a first axial chromatic aberration correction lens, and the second electron optical system includes a second axial chromatic aberration correction lens;
The electron beam apparatus according to claim 1, wherein the first on-axis chromatic aberration correction lens and the second on-axis chromatic aberration correction lens are Wien filters having an even number of electromagnetic poles. An electron optical system for irradiating the sample with a plurality of primary electron beams, an objective lens for focusing the plurality of secondary electron beams emitted from the sample, and axial chromatic aberration of the focused secondary electron beams are corrected. An electron beam apparatus comprising an aberration correction lens and an electron optical system for forming an image of the secondary electron beam whose axial chromatic aberration has been corrected on a detector,
An electron beam apparatus comprising: an NA aperture member disposed between the objective lens and the aberration correction lens.   The electron beam apparatus according to claim 8, wherein the objective lens includes an electrode including a cylindrical electrode and a disk-shaped electrode plate. An electron beam apparatus that scans a sample with a primary electron beam, forms an image of a secondary electron beam emitted from the sample on a detector, and detects an image of the sample,
The primary electron beam is focused by a first objective lens to irradiate the sample;
The secondary electron beam is focused by the first objective lens and the second objective lens, and axial chromatic aberration of the secondary electron beam focused by the first objective lens and the second objective lens is reduced by an aberration correction lens. Correcting and axially correcting the secondary electron beam corrected for chromatic aberration on the detector,
An electron beam apparatus, wherein a beam separator for separating the primary electron beam and the secondary electron beam is disposed between the first objective lens and the second objective lens.   The electron beam apparatus according to claim 6, wherein the first objective lens includes a frustoconical electrode plate whose wall thickness continuously decreases toward the sample. A marker plate used when correcting either axial chromatic aberration or spherical aberration in the electron beam apparatus according to claim 1,
A marker plate, wherein a plurality of holes or dots having different diameters are formed on a smooth surface having a large secondary electron beam emission coefficient.

Images