JP2005108545A - Electron/secondary ion microscope device - Google Patents

Abstract

<P>PROBLEM TO BE SOLVED: To provide an electron/secondary ion microscope device (for instance, a photoelectron microscope) capable of removing a spherical aberration and a chromatic aberration of an imaging optics in order to obtain a high-resolution observation image. <P>SOLUTION: This electron/secondary ion microscope device is provided with: an imaging optics for photoelectrons, secondary electrons or secondary ions emitted into vacuum from a surface of a substance used as an observation object by using short-wavelength electromagnetic waves including light waves as an excitation light source; a control mechanism for rapidly changing the focal position of the imaging optics; an image detection means for integrating and storing an image on an imaging surface while changing the focal position; and an upper spatial frequency emphasizing filtering mechanism for image information obtained from an image detector; and used for removing influence of the spherical aberration and the chromatic aberration of the imaging optics. By virtue of the electron/secondary ion microscope device, the spherical aberration and the like in the electron/secondary ion microscope device can be removed, and a high-resolution aberration-free observation image can be provided. <P>COPYRIGHT: (C)2005,JPO&NCIPI

Description

  The present invention relates to photoelectrons, secondary electrons (including Auger electrons), or secondary ions emitted from a sample by irradiating the observation sample with a short wavelength electromagnetic wave including light waves, an electron beam or a charged particle beam as an excitation light source. The present invention relates to an electron / secondary ion microscope apparatus (for example, a photoelectron microscope) that observes an observation sample through an imaging optical system, and more specifically, a high-resolution that eliminates spherical aberration and chromatic aberration of the imaging optical system. The present invention relates to an electron / secondary ion microscope capable of acquiring an observation image.

  In recent years, various microscopes and analysis methods have been developed for surface nano-characterization for observing a very fine form of a sample. As typical examples thereof, for example, as shown in FIG. 7, a scanning electron microscope (SEM) and a scanning probe microscope (SPM) mainly used for observing, evaluating and analyzing the form of a sample, Scanning Auger electron microscope (AEM), secondary ion mass spectrometry (SIMS) and analytical electron microscope, mainly used for elemental analysis, transmission electron microscope (TEM), mainly used for crystal structure analysis, and Examples thereof include X-ray photoelectron spectroscopy (XPS), a scanning photoelectron microscope, and a synchrotron radiation photoelectron microscope that are used for analyzing the electronic state of a substance. Scanning photoelectron microscopes, synchrotron radiation photoelectron microscopes, and the like are one type of electron / secondary ion microscope.

  The analysis scale (resolution) of these microscopes and the like is about several nm for SEM and about 1 nm to 0.1 nm for SPM, as shown on the horizontal axis of FIG. Further, it is about several tens to 10 nm for AEM and SIMS, and several nm for an analytical electron microscope. Moreover, TEM is about several nm like SEM and an analytical electron microscope.

  However, the resolution of an XPS analysis scale is usually around 10 μm, a scanning photoelectron microscope is several hundred nm, and a synchrotron photoelectron microscope is several tens of nm. Compared to the electron microscope, it clearly falls. On the other hand, since the photoelectron microscope has high surface sensitivity, it is extremely useful for observing the electronic state of the nanomaterial.

Here, it is conventionally known that the resolution of the imaging optical device can be increased, that is, the resolution can be increased by removing the spherical aberration and chromatic aberration of the imaging optical system. For example, in Patent Document 1 and Non-Patent Documents 1 and 2, a high-resolution observation image having no spherical aberration or chromatic aberration is acquired using a real-time focal position modulation spherical aberration removal method (real-time spherical aberration correction method). An imaging optical device is disclosed. According to this, it is possible to develop an electron microscope or the like that can remove the influence of spherical aberration (rotation invariant wavefront aberration) and chromatic aberration included in the imaging optical system and reproduce an image with high resolving power. As a result, it has succeeded in observing an aberration-free electron microscope image and obtaining an atomic image from which artifacts due to spherical aberration are removed.
JP 2003-131138 (Publication date: May 8, 2003) T.A. Ikuta: J. E1 Electron Microsc. 38, 415 (1989). Y. Takai et. a1. : J. E1 Electron Microsc. 48, 879 (1999).

  However, a normal electron microscope is a coherent imaging system that forms an image of a diffracted electron beam, whereas an electron / secondary ion microscope is a short wavelength electromagnetic wave including a high-intensity light wave, an electron beam / charged particle beam, or the like. Is an incoherent imaging system that forms an image of photoelectrons, secondary electrons, and secondary ions emitted from the observation object as a result. For this reason, it can be said that the imaging mechanism of a normal electron microscope and an electron secondary ion microscope (for example, a photoelectron microscope) is clearly different. The same applies when imaging secondary ions emitted by irradiation of excitation light instead of photoelectrons. That is, the same can be said for the secondary electron / secondary ion microscope.

  Therefore, even if the real-time focal position modulation spherical aberration removing method described in Patent Document 1 and the like applied to a conventional electron microscope is applied to an electron / secondary ion microscope (for example, a photoelectron microscope) as it is, it is sufficient. However, spherical aberration and the like cannot be removed, and a photoelectron microscope that acquires a high-resolution observation image cannot be developed.

  As described above, since an electron / secondary ion microscope (for example, a photoelectron microscope) can measure a spatial distribution of an electronic state, real-time observation of a nanoscale solid sample local surface, element distribution, chemical state, While it is a very excellent device that can directly observe the magnetic state and the like, there is a problem that the resolution is limited. Furthermore, no specific method has been developed for achieving high resolution for the electron / secondary ion microscope. Therefore, in order to obtain a high-resolution observation image, there has been a strong demand for development of a specific method for removing spherical aberration and the like of the imaging optical system in the electron / secondary ion microscope.

  The present invention has been made in view of the above-described problems, and an object of the present invention is to obtain an electron 2 that can remove spherical aberration and chromatic aberration of an imaging optical system in order to obtain an observation image with high resolution. A secondary ion microscope apparatus (for example, a photoelectron microscope) is provided.

  As a result of intensive studies in view of the above-mentioned problems, the present inventors have obtained a photoelectron microscope or an excitation obtained by fusing X-ray photoelectron spectroscopy (XPS), which obtains photoelectrons of a specific energy and obtains information on the bonding state, and an electron microscope. In a secondary ion / secondary electron microscope using a secondary ion as an image code source, a method for rapidly changing (modulating) a focal position by using chromatic aberration of an imaging optical system by wavelength modulation of emitted light, and a lens system We have uniquely found that spherical aberration can be removed by the method of changing (modulating) the sample at a high speed and the method of changing (modulating) the sample position at high speed. The removed photoelectron microscope capable of obtaining remarkably higher resolution than before has been developed, and the present invention has been completed. That is, as shown in FIG. 7, an electron / secondary ion microscope (for example, a photoelectron microscope) capable of analyzing an electronic state with a high resolution of about 2 nm to 10 nm has been developed.

  That is, the present invention includes the following 1) to 6) as industrially useful products or methods.

  1) (a) An imaging optical system for photoelectrons, secondary electrons, or secondary ions emitted from a surface of a substance to be observed in a vacuum using a short wavelength electromagnetic wave including a light wave as an excitation light source; A control mechanism for changing the focal position of the imaging optical system at high speed; (c) an image detecting means for accumulating and accumulating images on the imaging plane while changing the focal position; and (d) obtained from the image detector. (E) an electron / secondary ion microscope apparatus that removes the influence of spherical aberration and chromatic aberration of the imaging optical system.

  2) The control mechanism that changes the focal position of the imaging optical system at high speed (b) includes objective lens changing means that changes the magnetic field or electric field of the objective lens at high speed. Ion microscope device.

  3) The control mechanism that changes the focal position of the imaging optical system at high speed (b) includes an object changing unit that mechanically changes the position of the observation object itself. Next ion microscope device.

  4) The electron / secondary ion microscope apparatus according to 1), wherein the control mechanism that changes the focal position of the imaging optical system at high speed includes light source changing means that changes the wavelength of the excitation light source.

  5) The excitation light source is radiated light or an equivalent high-intensity light source, and the light source changing means is configured to irradiate the observation object with short-wavelength incident light (particularly radiated light) emitted from the excitation light source 4. The electron / secondary ion microscope apparatus according to 4), further comprising a spectroscope angle changing unit that changes the angle of the spectroscope in contact with the incident light.

  6) The electron / secondary ion microscope apparatus according to any one of 1) to 5), wherein the excitation light source is replaced with an electron beam or a charged particle beam.

  According to the configuration of 1) to 4) of the electron / secondary ion microscope apparatus according to the present invention, for example, the focal position of the imaging optical system is changed in the electron / secondary ion microscope apparatus such as a photoelectron microscope. The spherical aberration of the imaging optical system in the electron / secondary ion microscope apparatus can be removed by the accumulative image detecting means and the middle / high frequency spatial frequency enhancement filter for the image information obtained from the accumulating image detecting means. Further, chromatic aberration can be removed at the same time. Therefore, according to this method, it is possible to provide a photoelectron microscope in which both aberrations are removed and resolution is improved. The “object changing means” is a moving mechanism that mechanically changes the distance between the observation object and the objective lens.

  In addition, according to the configuration of the electron / secondary ion microscope apparatus 5) according to the present invention, the wavelength of the emitted light is reliably changed (modulated) by changing (modulating) the angle of the spectroscope in real time. Can be made. Therefore, the focal position of the electron / secondary ion microscope apparatus can be reliably changed (modulated), and the aberration of the imaging optical system of the electron / secondary ion microscope apparatus combined with powerful radiation light can be reliably removed. There is an effect that can be.

  Also, it is possible to provide an electron / secondary ion microscope apparatus that can be used in various fields including nanotechnology, by combining an electron / secondary ion microscope apparatus with high resolution and powerful synchrotron radiation. There is an effect that can be done.

  The present invention provides a specific technique that enables aberration-free high-resolution observation in an electron / secondary ion microscope apparatus (for example, a photoelectron microscope) that uses electromagnetic waves (for example, light, particularly radiated light) as excitation light, The present invention also provides an electron / secondary ion microscope apparatus that realizes aberration-free high-resolution observation using this technique. By using the present invention, it is considered that research, development, and evaluation in extremely wide fields such as engineering, medicine, biology, and astronomy can be remarkably made efficient, and a lot of new knowledge can be obtained thereby. Therefore, it can be said that the present invention is very useful and has a strong social impact.

  Accordingly, the basic concept of the “focal position modulation spherical aberration elimination method” that is the basis of the present invention will be briefly described below, and then the focal position changing method of the photoelectron microscope and the photoelectron microscope according to the present invention will be described. . Needless to say, the present invention is not limited to this.

<Basic concept of “focal position modulation spherical aberration removal method”>
First, the “focal position modulation spherical aberration removal method”, which is the principle underlying the present invention, will be described with reference to FIGS. In the “focal position modulation spherical aberration removal method”, first, the influence of main and higher order spherical aberration having a rotation invariant wavefront aberration function is removed. For this purpose, the Heusler-type focal depth expansion method is used. In the following, the principle of depth-of-focus expansion by the moving average method of defocus amount and the extraction of aberration-free information will be described from an optical standpoint.

  First, imaging of a self-luminous body (including photoelectrons) and the influence of spherical aberration will be shown. FIG. 8 shows a state in which a light wave or electron wave emitted from one point on the sample 1 and a substance wave for ions reach the rear focal plane (imaging plane) 3 through the imaging optical system drawn by the convex lens 2. Is shown from both geometrical and wavefront optics.

  As described above, light waves emitted from different points on the sample 1 do not interfere. Only light waves emitted from the same point contribute to interference. In wavefront optics, spherical waves emitted from a point sample are regarded as a collection of plane waves traveling in each direction. The imaging optical system changes the direction of these plane waves incident on the pupil (entrance pupil) and collects them at the rear focal position.

  In the aberration-free optical system shown in FIG. 9, the phases of these plane waves coincide with each other at the rear focal position 4, and a small spot is formed. On the other hand, in the optical system with spherical aberration shown in FIG. 10, the phase of the plane wave changes (the wavefront moves) in proportion to the fourth power of the angle formed by the optical axis and the plane wave traveling direction. As a result, the phase of these plane waves does not match at the rear focal position 4, resulting in a large spot.

  The above situation will be limited to a set of two plane waves with different traveling directions. Real-time imaging can be described by a collection of interference fringes caused by these different sets of plane waves.

  FIG. 11 shows a three-dimensional interference fringe 7 generated around a rear focal position (focal plane) 6 by a two-plane wave emitted from a point sample and passing through the imaging optical system 5. Note that the wavefront moves at the speed of light, but the three-dimensional interference fringes 7 do not move. When the traveling directions of the two plane waves are at the same angle with respect to the optical axis 8, the three-dimensional interference fringes 7 are parallel to the optical axis 8 as shown in FIG. 11.

  On the other hand, FIG. 12 shows a case where the traveling directions of the two plane waves are the same with respect to the optical axis 8 and have a larger angle. As described above, the interference fringe interval viewed from the focal plane 6 is almost inversely proportional to the angle formed by the traveling directions of the two plane waves.

  As shown in FIGS. 11 and 12, if there is no spherical aberration, one of the peaks of interference fringes (high intensity) is located at the origin position of the rear focal point. When the traveling directions of the two plane waves are the same angle with respect to the optical axis, the observed interference fringes do not move when the focal position is changed.

  On the other hand, as shown in FIG. 13, when the angle between the optical axis 8 and the traveling direction of the two plane waves is different, the interference fringes are observed to move when the focal position 6 is changed. Thus, even if the focal position 6 is changed only when the angles formed by the traveling directions of the two plane waves are equal, the observed interference fringes do not move.

  When there is spherical aberration, the phase of the two plane waves changes in proportion to the fourth power of the angle formed by the optical axis 8 and the plane wave traveling direction, as shown in FIG. Along with this, the three-dimensional interference fringes 7 also move in proportion to the difference in phase shift between these two plane waves. As a result, the peak of the interference fringe (strong intensity) deviates from the origin position of the rear focal point.

  However, as shown in FIG. 15, when the angles formed by the traveling directions of the two plane waves are equal, the difference between the phase shifts of the two plane waves becomes zero. Is located at the origin position of the rear focal point. At this time, even if the focal position 6 is changed, the interference fringes are observed to be stationary. All the three-dimensional interference fringes 7 parallel to the optical axis 8 are not affected by the spherical aberration. Conversely, if only the interference fringes that are observed to remain stationary even when the focal position 6 is changed, that is, only the interference fringes with an increased focal depth are extracted, an aberration imaging that is not affected by the spherical aberration is obtained. realizable. This is the principle of the aberration-free imaging method based on the expansion of the focal depth.

  Next, the depth of focus expansion method performed by Heusler will be described. First, the observed positions are continuously changed and the observed images are integrated (focus moving average method). As a result, most of the interference fringes (three-dimensional interference fringes not parallel to the optical axis) that move due to the change of the focal position are removed, and an image with a deep focal depth is obtained. According to the principle of the present method, this makes it possible to realize aberration-free imaging. However, since the interference fringes that move with the change of the focal position are removed, it is indispensable to emphasize the middle and high frequencies to compensate for their contribution. When the spherical aberration coefficient is large, the focal distance required for non-aberration imaging increases. Also, a larger mid / high frequency enhancement process is required.

  On the other hand, in terms of chromatic aberration included in the imaging optical system, this essentially has the same effect as the focal moving average. In this non-aberration imaging method, it is possible to incorporate chromatic aberration into the process of focal moving average, and the chromatic aberration can be substantially removed and ignored. If the focal movement range due to chromatic aberration is close to or exceeds the focal movement distance required for aberration-free imaging, the focal moving average is completely unnecessary.

  The features and advantages of this spherical aberration removal method can be realized by an extremely simple operation of (a) focal moving average, and real-time processing is possible. (B) There is no need to know the spherical aberration coefficient. (C) Chromatic aberration important in an electron optical system or the like can be substantially removed and ignored. (D) Light waves (electromagnetic waves), electrons, charged particle beams, and sound waves are transmitted to transmission / reflection microscopes and dark field illumination microscopes under incoherent illumination that exhibit the same imaging characteristics as those of self-luminous materials (including fluorescence). It is applicable regardless. Etc.

  Although this method uses the Heusler-type method of expanding the depth of focus, it is intended only for processing spherical and chromatic aberrations of the imaging optical system, and collects the depth direction information of the observation sample. The direction of application is completely different from the depth-of-focus processing to be shown and belongs to a different application field.

  An electron microscope that realizes high aberration-free resolution using the “focal position modulation spherical aberration elimination method” as described above has been developed (see, for example, Patent Document 1). An electron microscope to which this focal position modulation spherical aberration removing method is applied has an advantage that the spherical aberration can be removed even if the aperture diameter inside the electron microscope is large to some extent, so that the resolution can be increased. However, as described above, since the imaging mechanism is different between the conventional electron microscope and the photoelectron microscope, this method cannot be applied as it is. Accordingly, the present inventors have developed a specific method of the focal position changing method applicable to the photoelectron microscope based on the basic concept of the focal position modulation spherical aberration removing method.

<Electron / secondary ion microscope apparatus according to the present invention>
In the present embodiment, a photoelectron microscope will be described as an example among electron / secondary ion microscope apparatuses. A general photoelectron microscope will be briefly described with reference to FIG. As shown in FIG. 1, the photoelectron microscope is a fusion of X-ray photoelectron spectroscopy (XPS) and an electron microscope.

  Here, XPS is a method in which a sample is irradiated with electromagnetic waves (light, X-rays, etc.), photoelectrons are excited from the sample, and information on the photoelectrons is analyzed to check the electronic state of the sample. Since the excited photoelectrons reflect the information of the inner shell level in the sample material, by analyzing this photoelectron information, information on the bonding state of the material (for example, information on chemical bonds), that is, Know the electronic state information. On the other hand, an electron microscope is a microscope that uses an electron beam instead of a light beam and an electron lens instead of a glass lens, and magnifies and observes a fine substance or the like to obtain an enlarged microscope image.

  It can be said that the photoelectron microscope is intended to observe an enlarged image of a substance reflecting information on an electronic state by fusing the XPS and the electron microscope.

  A general configuration of a photoelectron microscope is shown in FIG. When the excitation light 31 is irradiated onto the sample 1, photoelectrons are emitted. The photoelectrons are imaged by the objective lens 10. In general, not all photoelectrons that have passed through the objective lens 10 are imaged, and the contract aperture 211 limits the capture angle. Thereafter, an image is formed once at the entrance of the energy filter 213 by the intermediate lens 212, the energy is selected by the energy filter 213, and enlarged and projected by the projection lens 214 to form a photoelectron image on the screen 215. The photoelectron image on the screen 215 is photographed by a camera or the like and observed on the monitor 12.

  The important factors that determine the resolution in this photoelectron microscope are spherical aberration, chromatic aberration, and the like, as in the above-described electron microscope. Therefore, as shown in FIG. 2, in the photoelectron microscope, in principle, as in the above-described electron microscope, by changing the focal position, it is possible to remove these aberrations and improve the resolution. However, as described above, since the same aberration removal method as that of the conventional electron microscope cannot be applied to the photoelectron microscope as it is, the present inventors have developed a specific focal position changing method applicable to the photoelectron microscope.

  As a specific method of focus position modulation in the photoelectron microscope, first, a method of changing the focus position of the imaging optical system by changing (modulating) the objective lens of the photoelectron microscope can be cited. As the objective lens of the photoelectron microscope, there are a magnetic field type and an electric field type objective lens. In this method, both types of objective lenses are targeted.

  When the electric field type objective lens is changed (modulated), for example, the objective lens is configured as shown on the left side of FIG. 3A, and the electric field type objective lens 10 that can change (modulate) the electric field. This can be realized by manufacturing. When changing (modulating) the magnetic field type objective lens, for example, the objective lens is configured as shown in the right side of FIG. 3A to change (modulate) the magnetic field objective. This can be realized by manufacturing the lens 10. Note that the method for changing (modulating) the objective lens is not limited to these, and the present invention also includes a method for changing (modulating) the objective lens by appropriately using other conventionally known methods. It is.

  By changing (modulating) the objective lens of the photoelectron microscope in this manner, images with different focal positions can be acquired at high speed, and as a result, the focal position of the imaging optical system can be changed.

  As another specific method for changing the focal position (modulation) in the photoelectron microscope, a method for changing the focal position of the imaging optical system by changing (modulating) the position of the observation object (sample) in the photoelectron microscope. Can be mentioned. As a specific method for changing (modulating) the position of the sample, for example, as shown in FIG. 3B, the distance between the sample 1 and the objective lens 10 irradiated with the excitation light (here, radiated light) 31 is used. Can be changed (modulated), that is, a method of moving the position of the sample 1 in a direction in which the distance between the sample 1 and the objective lens 10 becomes longer or shorter (a double-headed arrow in the figure). The method for changing (modulating) the sample position is not limited to this, and the present invention also includes a method for changing (modulating) the sample position by appropriately using other conventionally known methods. It is.

  By changing (modulating) the sample position in the photoelectron microscope in this way, images with different focal positions can be acquired in real time, and as a result, the focal position of the imaging optical system can be changed.

  In addition, as another specific method of focus position modulation in the photoelectron microscope, a method of changing the focus position of the imaging optical system by changing the wavelength of the excitation light can be mentioned. In addition, it is preferable that excitation light here is very powerful light like radiation light. Examples of the “radiation light” include, but are not limited to, radiation light obtained from the beam line of the synchrotron radiation facility SPring-8.

  As a specific method for changing (modulating) the wavelength of the excitation light (for example, radiation light), for example, as shown in FIG. Before being performed, a method of once irradiating the incident beam 31 to the spectrometer 21 and changing (modulating) the wavelength of the incident beam 31 by changing (modulating) the angle of the spectrometer in real time is given. be able to. Note that the method of changing the wavelength of the excitation light is not limited to this, and the present invention also includes a method capable of changing the wavelength of the excitation light by appropriately using other conventionally known methods.

  In this way, by changing the wavelength of the excitation light in the photoelectron microscope, images with different focal positions can be acquired at high speed, and as a result, the focal position of the imaging optical system can be changed.

  By changing (modulating) the focal position by any one of the above methods, the spherical aberration and chromatic aberration of the imaging optical system in the photoelectron microscope can be simultaneously removed. Therefore, a photoelectron microscope with improved resolution can be obtained. The term “modulation” is used in the present invention as a term synonymous with change or change.

  FIG. 4 schematically shows an example of the configuration of a photoelectron microscope that embodies a specific method for changing the focal position in the photoelectron microscope described above.

  As shown in FIG. 4, the photoelectron microscope 100 according to the present embodiment includes three monitors 12, 14, 14 ′, an image storage / processing device 13, two focal position modulation control devices 15, 15 ′, and a CCD controller 16. A CCD camera 17, an electro-optical device 18, a modulation signal generating device 19, a focal position modulating device 20, an electro-optical system control device 21, and a spectrometer 22. The photoelectron microscope 100 uses the emitted light 31 as the excitation light. The emitted light 31 enters the electron optical device 18 via the spectroscope 22.

  The CCD controller 16 controls the operation of the CCD camera 17. The three monitors 12, 14, and 14 'are for observing the operation statuses of the image storage / processing device 13 and the two focus position modulation control devices 15 and 15' from the outside. The electron optical system control device 21 operates the electron optical device 18. The electron optical device 18 has a sample setting member having a sample therein, and the photoelectrons excited from the sample 1 are captured by irradiating the sample on the sample setting member with the radiated light 31. A photoelectron image is formed.

  In addition, the monitor 12 and the image storage / processing device 13 integrate and store the images from the CCD camera 17 and have a middle / high-frequency spatial frequency enhancement filtering function for the obtained image information. Thereby, in the photoelectron microscope 100, a high-resolution observation image from which spherical aberration is removed is obtained. The image storage / processing device 13 also has a function of transmitting a modulation signal to the focal position modulation control devices 15 and 15 ′ via the modulation signal generating device 19.

  The monitor 14, the focal position modulation control device 15, the modulation signal generating device 19, and the focal position modulation device 20 form a focal position modulation system. This focal position modulation system controls the change (modulation) of an objective lens (not shown) of the electron optical device 18 and also controls the modulation of the position of the sample (not shown). Specifically, the focal position modulation control device 15 changes (modulates) the electric field or magnetic field of the objective lens in synchronization with the signal from the modulation signal generation device 19 via the focal position modulation device 20. Change (modulate) the objective lens. Further, the focal position modulation control device 15 changes (modulates) the distance between the sample in the electron optical device 18 and the objective lens in synchronization with the signal from the modulation signal generation device 19 via the focal position modulation device 20. Thus, the sample position is changed (modulated). Thereby, the objective lens or the sample position in the electron optical device 18 is changed (modulated), and the focal position in the photoelectron microscope 100 is changed (modulated). Therefore, the focal position modulation system functions as an objective lens changing unit that changes an electric field or a magnetic field of the objective lens, and also functions as an object changing unit (a mechanical moving unit of the observation target).

  The monitor 14 ′, the focal position modulation control device 15 ′, the modulation signal generation device 19, and the spectroscope 22 form a wavelength modulation system. This wavelength modulation system changes the wavelength of the emitted light 31 by changing (modulating) the angle of the spectroscope 22 at high speed. That is, the modulation signal is transmitted from the focal position modulation control device 15 ′ to the spectroscope 22 in synchronization with the signal from the modulation signal generator 19, and the angle of the spectroscope 22 is changed (modulated) at high speed. As a result, the wavelength of the radiation 31 incident on the electron optical device 18 is changed (modulated), and the focal position in the photoelectron microscope 100 is changed (modulated). Therefore, the wavelength modulation system changes the angle of the spectroscope 22 in contact with the radiation light 31 (excitation light) before the radiation light 31 (excitation light) is irradiated onto the sample 1 (observation object). It functions as a device angle changing means (light source changing means).

  That is, the photoelectron microscope 100 is designed and manufactured so that the above-described three specific focal position changing methods can be applied. The basic experimental results of trying to remove aberrations using the photoelectron microscope 100 capable of realizing this focal position changing method are shown below.

  Specifically, as shown in FIG. 5A, using the photoelectron microscope 100, a focal position modulation signal for changing (modulating) the focal position by changing (modulating) the magnetic field or electric field of the objective lens; A low-energy photoelectron image of Pb / Si (111) as a sample was obtained by synchronizing the moving focal image. Since radiant light cannot be used as a light source, a low energy photoelectron image was obtained using a mercury lamp.

  The results are shown in FIGS. In addition, a bright spot shows the nanostructure of lead (Pb). FIG. 5B is an original image obtained without aberration correction, and FIG. 5C is an aberration-removed image obtained by carrying out the focal position changing method and removing aberrations. As is clear from these figures, the chromatic aberration mainly works in the low energy region, so the effect of correcting the spherical aberration is not sufficient, but the aberration is also reduced, and a clear image of the nanostructure is clearly obtained. I understand that. Therefore, it has been clarified that the spherical aberration can be removed by implementing the focal position changing method, and as a result, the resolution in the photoelectron microscope can be improved.

  In addition, a preliminary experiment was conducted on a method of changing (modulating) the focal position by moving the position of the sample up and down using an optical microscope. Specifically, as shown in FIG. A. = 0.6, λ = 0.65 μm The distance between the optical microscope and the sample was changed (modulated) in the range of 20 μm, and the focal position was changed (modulated) to obtain an image. The results are shown in FIGS. 6 (b) and 6 (c).

  FIG. 6B is an original image obtained without aberration correction, and FIG. 6C is an aberration-removed image obtained by carrying out the focal position changing method and removing aberrations. From these figures, it is clear that the focal position of the imaging optical system can be changed and spherical aberration can be removed by changing (modulating) the sample position in the optical microscope. As a result, it was found that the resolution of the aberration-removed image can be improved as compared with a normal observation image. This method seems to be applicable to a photoelectron microscope.

  The present invention is not limited to the above-described embodiments, and various modifications can be made within the scope of the claims, and embodiments obtained by appropriately combining the respective technical means disclosed are also included in the present invention. Included in the technical scope.

  As described above, according to the focal position changing method according to the present invention and the photoelectron microscope that realizes the focal position changing method, spherical aberration and chromatic aberration can be simultaneously removed, and resolution can be improved. it can.

  For this reason, not only can it be used for research, development and evaluation in a wide range of industrial fields such as engineering (especially materials and semiconductors), medicine and biology, but it can also contribute to new fields such as nanotechnology. it can.

It is a figure which shows the principle of a photoelectron microscope typically. It is a figure which shows typically the principle of the focus position change method in the photoelectron microscope which concerns on this invention. It is a figure which shows typically the specific method of the focus position change method in the photoelectron microscope which concerns on this invention, (a) is a figure which shows typically the method of changing the electric field or magnetic field of an objective lens, (b ) Is a diagram schematically showing a method of changing the sample position, and (c) is a diagram schematically showing a method of changing the wavelength of the emitted light. It is a figure which shows typically an example of the principal part structure of the photoelectron microscope which concerns on embodiment of this invention. (A) is a figure which shows typically the basic experiment conducted using the photoelectron microscope which concerns on embodiment of this invention, (b) is the original image which has not carried out the aberration correction obtained as a result of (a). (C) is the figure of the aberration removal image obtained by implementing a focus position change method and performing aberration removal. (A) is a figure which shows typically the preliminary experiment conducted using the optical microscope in embodiment of this invention, (b) is the original image which does not carry out the aberration correction obtained as a result of (a). (C) is the figure of the aberration removal image obtained by implementing a focus position change method and performing aberration removal. It is a figure which shows the relationship between the electron microscope and analysis method which have been developed so far for surface nano-characterization, and the photoelectron microscope which concerns on this invention. It is a figure which shows the geometric optical interpretation and wave optical interpretation regarding the image formation of a self-light-emitting body (a photoelectron is included). It is a figure which shows the wave front and intensity distribution which are synthesize | combined by the back side focal plane through a non-aberration imaging system from a point light emitter. It is a figure which shows the wave front and intensity distribution with which a back focal plane is synthesize | combined through a non-aberration imaging system with spherical aberration from a point light emitter. It is the figure which showed the three-dimensional interference fringe which the 2 plane wave which emitted from the point-like sample and passed the non-aberration imaging optical system makes around a back focal position. It is the figure which showed the three-dimensional interference fringe in case the advancing direction of two plane waves is the same with respect to an optical axis, and becomes a larger angle than the case of FIG. FIG. 3 is a diagram showing a three-dimensional interference fringe generated around a rear focal position by a two-plane wave emitted from a point-like sample and passed through a non-aberration imaging optical system when the angle between the optical axis and the two-plane wave traveling direction is different. is there. A three-dimensional interference fringe generated around a rear focal point by a two-plane wave that is emitted from a pointed sample and passed through an imaging optical system having spherical aberration is shown when the angle between the optical axis and the traveling direction of the two-plane wave is different. FIG. A three-dimensional interference fringe generated around a rear focal point by a two-plane wave emitted from a pointed sample and passed through an imaging optical system having spherical aberration is shown for the case where the angle between the optical axis and the two-plane wave traveling direction is equal. FIG.

Explanation of symbols

1 Sample (observation object)
2 Convex lens 3 Rear focal plane (imaging plane)
4 Rear focal position 5 Imaging optical system 6 Rear focal position (focal plane)
7 Three-dimensional interference fringes 8 Optical axis 10 Objective lens 12 Monitor 13 Image storage / processing device 14 Monitor 14 'Monitor 15 Focus position modulation control device (objective lens changing means, object changing means)
15 'focus position modulation control device (light source changing means, spectrometer angle changing means)
16 CCD controller 17 CCD camera 18 Electro-optical device 19 Modulation signal generator 20 Focus position modulator (objective lens changing means, object changing means)
21 Electron optical system controller 22 Spectrometer 31 Excitation light (radiated light)
100 Photoelectron microscope 211 Contrast aperture 212 Intermediate lens 213 Energy filter 214 Projection lens 215 Sclone

Claims (6)

(A) an imaging optical system for photoelectrons, secondary electrons, or secondary ions emitted from the surface of a substance to be observed into a vacuum using a short-wave electromagnetic wave including a light wave as an excitation light source;
(B) a control mechanism that changes the focal position of the imaging optical system at high speed;
(C) image detecting means for accumulating and accumulating images on the imaging plane while changing the focal position;
(D) a medium / high frequency spatial frequency enhancement filtering mechanism for image information obtained from the image detector;
(E) An electron / secondary ion microscope apparatus that removes the influence of spherical aberration and chromatic aberration of the imaging optical system.   2. The control mechanism according to claim 1, wherein the control mechanism that changes the focal position of the imaging optical system at high speed includes objective lens changing means that changes the magnetic field or electric field of the objective lens at high speed. Electron / secondary ion microscope device.   2. The control mechanism according to claim 1, wherein the control mechanism that changes the focal position of the imaging optical system at high speed includes object changing means that mechanically changes the position of the observation object itself. Electron / secondary ion microscope equipment.   2. The electron / secondary ion according to claim 1, wherein the control mechanism (b) that changes the focal position of the imaging optical system at high speed includes light source changing means for changing the wavelength of the excitation light source. Microscope device. The excitation light source is radiant light or an equivalent high brightness light source,
The light source changing means includes a spectroscope angle changing means for changing the angle of the spectroscope contacting the incident light when the short wavelength incident light irradiated from the excitation light source is irradiated to the observation object. The electron secondary ion microscope apparatus according to claim 4.   6. The electron / secondary ion microscope apparatus according to claim 1, wherein the excitation light source is replaced with an electron beam or a charged particle beam.

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