Patent Application
20080197282
1. Field of the Invention
The present invention relates to a transmission charged particle beam device, and, more particularly, to a scanning transmission charged particle beam device for generating a transmission scanning image.
2. Description of the Related Art
Referring to
When a bright-field STEM image is observed, an annular diaphragm 55 for a bright-field is arranged under a sample 52, and an electron detector for a bright-field image 56 is arranged thereunder as shown in
Japanese Patent Publication No. 3776887 has disclosed a method for changing the scattering-angle range of transmission electrons to be detected by way of a configuration such that the position of a transmission electron detector may be changed. Moreover, Japanese Patent Publication No. 3776887 also has disclosed a method for securing an appropriate signal-to-noise ratio and a proper contrast by arranging a deflecting coil, a bright-field diaphragm, and an electron detector for a bright-field image under an electron detector for a dark-field image, and by leading transmission electrons to a diaphragm with an appropriate hole diameter through the deflecting coil.
Japanese Patent Application Laid-Open No. 2004-253369 has disclosed a method for separating transmission electrons (electrons of a bright-field image) from transmission scattering electrons (electrons of a dark-field image) by providing a transmission signal conversion member for emitting secondary electrons by collision with transmission electrons.
Generally, the discharging range of electrons of a bright-field image and that of electrons of a dark-field image are also changed when the scanning range of electron beams on a sample is changed. Thereby, the hole diameter of a bright-field diaphragm and the outside diameter of a dark-field diaphragm are required to be changed, corresponding to changes in the seaming range of electron beams, in order to clearly separate electrons of a bright-field image and electrons of a dark-field image. When the diameter of the diaphragm is not changed even under a state in which the scanning range of electron beams is changed, the electrons of a bright-field image and the electrons of a dark-field image are not sufficiently separated. Thereby, detection amount by an electron detector for a bright-field image, and that by an electron detector for a dark field image are reduced to cause resolution reduction in a bright-field image and that in a dark-field image. For example, when a STEM image with a low magnification is acquired, an enlarged diaphragm-diameter is required. In this case, a contrast and a S/N (signal to noise ratio) for a STEM image is reduced because non-separation between the electrons of a bright-field image and the electrons of a dark-field image becomes large.
According to conventional methods shown in
An object of the present invention is to provide a scanning transmission charged particle beam device by which charged particles of a bright-field image and charged particles of a dark-field image may be clearly separated, and bright-field images and dark-field images with high accuracy may be obtained even in a state in which a scanning range on a sample is changed.
According to the present invention, a deflecting coil is provided below a sample, and a signal detector for a dark-field image with an opening is provided below the deflecting coil. A signal detector for a bright-field image is provided below the above opening. By the deflecting coil below the sample, a charged particle beam of a bright-field image is configured to be synchronized with the scanning of a particle beam and to be deflected in an opposite direction to the deflected direction of the particle beam. Thereby, a charged particle beam of a bright field image passes through the opening of the signal detector for a dark-field image, and is detected by the signal detector for a bright-field image.
According to the present invention, the signal detector for a dark-field image has an effective detection region around the opening, and the region has a concentric configuration with the opening. Non-elastically scattered charged particles are detected by the effective detection region.
According to the present invention, charged particles of a bright-field image and charged particles of a dark-field image may be clearly separated, and bright-field images and dark-field images with high accuracy may be obtained even in a state in which the scanning range of charged particle beams on a sample is changed.
An example of a scanning transmission electron microscope according to the present invention will be explained referring to
Electron beams 4 are generated from the electron source 1 by the extraction electrode 2. The electron beam 4 is accelerated, for example, to about 30 keV by the accelerating electrode 3. The accelerated electron beam 4 is focused on an optical axis by the focusing lens 5, and is focused again by the objective lens 8 for irradiation on the sample 9. There is performed two-dimensional scanning of the electron bean) 4 on the sample 9 with a deflection fulcrum 7 as a fulcrum by the electron beam deflecting coil 6.
Electrons of a bright field image 11 and electrons of a dark field image 12 are irradiated from the undersurface of the sample 9. The electrons of a bright-field image 11 are chiefly electrons which have transmitted the sample, and have a small scattering angle, and large energy. The electrons of a dark field image 12 are chiefly electrons scattered in the sample, and have a large scattering angle and small energy.
The transmission electron deflecting coil 10 is arranged below the sample 9. By the transmission electron deflecting coil 10, electrons of a bright-field image 11 are configured to be synchronized with the electron beam deflecting coil 6 and to be deflected in an opposite direction to the deflected direction by the electron beam deflecting coil 6. The electrons of a bright-field image 11 are deflected by the transmission electron deflecting coil 10, and are always focused at a focusing point of electrons of a bright-field image 14 on the electron detector for a dark-field image 15. The focusing point of electrons of a bright-field image 14 may be on an optical axis 13. The electrons of a bright-field image 11 are focused to pass through the opening 15a in the electron detector for a dark-field image 15, and are irradiated onto the electron detector for a bright-field image 16. Thus, the present example has a configuration such that, even under a state in which an electron beam 4 is deflected by the electron beam deflecting coil 6, the electrons of a bright-field image 11 from the sample always pass through the opening 15a in the electron detector for a dark-field image 15 to be detected by the electron detector for a bright-field image 16.
On the other hand, the electrons of a dark-field image 12 are detected by the electron detector for a dark-field image 15. All the electrons of a bright-field image 11 are led to the opening 15a in the electron detector for a dark-field image 15 by the transmission electron deflecting coil 10. Accordingly, only the electrons of a dark-field image 12 are irradiated onto the electron detector for a dark-field image 15.
The scattering angle and the energy of the electrons of a dark-field image 12 and those of the electrons of a bright-field image 11 are different from each other. Even when the electrons of a bright-field image 11 are deflected by the transmission electron deflecting coil 10, the electrons of a dark-field image 12 are not deflected in a manner similar to that of the electrons of a bright-field image 11. The electrons of a dark-field image 12 do not pass through the opening 15a of the electron detector for a dark-field image 15. On the other hand, almost all the electrons of a dark-field image 12 may be detected when the effective detection region of the electron detector for a dark-field image 15 is set enough large. Thus, the electrons of a dark-field image 12 and the electrons of a bright-field image 11 may be clearly separated in the present example.
Even when the scanning region of the electron beam 4 on the sample is changed, the deflection by the transmission electron deflecting coil 10 is controlled, corresponding to the changes, according to the present invention. Accordingly, the electrons of a dark-field image 12 and the electrons of a bright-field image 11 may be completely separated even when the scanning region of the electron beam 4 is changed. Furthermore, a bright-field image may be obtained by the electron detector for a bright-field image 16, and, at the same time, a dark-field image may be obtained by the electron detector for a dark-field image 15 according to the present invention. That is, the bright-field image and the dark-field image may be obtained at the same time without exchange of the detector.
The diameter of the opening 15a in the electron detector for a dark-field image 15 is required to be determined in such a way that the focused electrons of a bright-field image 11 may pass through the opening 15a, but the diameter is preferably as small as possible. However, too small diameter causes difficult processing. The diameter of the opening 15a is, preferably, smaller than 5 mm, and larger than 0.01 mm, and, more preferably, 1 mm or less.
In the present example, the effective detection region of the electron detector for a bright-field image 16 may be slightly larger than the diameter of the opening 15a. For example, when the diameter of the opening 15a is 1 mm, the diameter of the effective detection region for the electron detector for a bright-field image 16 may be 1.1 mm through 2 mm.
The configuration of the signal detection portion in the electron detector for a dark-field image 15, and that of the signal detection portion in the electron detector for a bright-field image 16 are well-known. For example, a CCD (charge coupled device), or a scintillator may be used for the signal detection portion.
Though there has been explained here a case in which the magnetic field by the transmission electron deflecting coil 10 is used, a focusing lens, instead of the transmission electron deflecting coil 10 may be used. That is, the electrons of a bright-field image are not deflected, but are focused. In the case of a focusing lens, stronger excitation is required in comparison with that of a deflecting coil. Thereby, it is difficult to focus the electrons of a bright-field image when the scanning range of electron beams is large. Then, it is required to limit the scanning range of the electron beam. Alternatively, the converging efficiency may be increased by a configuration such that there are provided two or more stages of focusing lenses.
The electrons of a dark-field image will be explained in detail referring to
The electrons of a dark-field image 24 includes a non-elastically scattered electron 24A which is non-elastically scattered within the sample, and an elastically scattered electron 24B which is elastically scattered within the sample. The scattering angle of the non-elastically scattered electron 24A is about several ten mrad, and the energy is about 90% of that of the irradiation electron beam. On the other hand, the scattering angle of the elastically scattered electron 24B is about several 100 mrad, and the energy is equal to that of an irradiation electron beam. Here,
The energy of the non-elastically scattered electron 24A depends on the scattering angle. A larger scattering angle of the non-elastically scattered electron 24A causes the energy to become smaller. Accordingly, a non-elastically scattered electron of specific energy may be detected by selectively detecting a non-elastically scattered electron with a specific scattering angle. As described above, useful information for a structural analysis of a sample is obtained by detecting the non-elastically scattered electron of specific energy, and by obtaining a transmission electron image. Hereinafter, there will be explained an example of a non-elastically scattered electron detector, by which a non-elastically scattered electron with a specific energy is detected.
Other examples of the scanning transmission electron microscope according to the present invention will be explained referring to
The detailed structure of the non-elastically scattered electron detector 17 will be explained referring to
In the non-elastically scattered electron detector 17 shown in
As shown in
Non-elastically scattered electrons with a broader range of energies may be detected, for example, by increasing the width of the effective detection region 171. On the other hand, non-elastically scattered electrons with a narrower range of energies may be detected by reducing the width of the effective detection region 171. That is, it may be said that the width of the effective detection region 171 is corresponding to the energy width of detected non-elastically scattered electrons. Accordingly, the width of the effective detection region 171 is acceptably reduced when non-elastically scattered electrons with an extremely-narrow specific range of energies are detected.
On the other hand, non-elastically scattered electrons with larger energies may be detected when the diameter of the effective detection region 171 is reduced. On the other hand, non-elastically scattered electrons with smaller energies may be detected when the diameter of the effective detection region 171 is increased. That is, it may be said that the diameter of the effective detection region 171 is corresponding to the size of the energies of the non-elastically scattered electrons to be detected. Accordingly, the diameter and the width of the effective detection region 171 are acceptably reduced when non-elastically scattered electrons with an extremely large energy are detected.
The scattering angle of non-elastically scattered electrons depends on the structure, the composition, and the thickness of a sample, and the like, and, moreover, on the energy of the irradiation electrons. Accordingly, a voltage (acceleration voltage) applied to the accelerating electrode 3 is adjusted, and, thereby, the scattering angle may be adjusted by adjusting the energy of the irradiation electrons. For example, the voltage applied to the accelerating electrode 3 may be configured to be changed by about 1 V. In the examples shown in
In order to keep the resolution of the sample, a negative voltage is acceptably applied to the sample in a state in which an acceleration voltage is kept high. Here, a positive voltage may be applied to the sample. Thereby, the energy of irradiation electrons is increased, and the energy of non-elastically scattered electrons is increased.
Examples according to the present invention have been explained as described above, but it will be easily appreciated by persons skilled in the art that the present invention is not limited to the above-described examples, and various modifications may be made within the scope of the invention described in claims.
Examples of scanning transmission electron microscopes have been explained in
The present invention may be applied not only to a scanning transmission electron microscope detecting transmission scanning electrons, but also to a scanning transmission charged particle beam device irradiating charged particles to a sample.
| Number | Date | Country | Kind |
|---|---|---|---|
| 2007-036399 | Feb 2007 | JP | national |
