JPS6333472Y2 - - Google Patents

Description

[Detailed Description of the Invention] (1) Field of Application of the Invention The present invention relates to improvement of an optical device for electron beam holography.

(2) Prior Art An electron beam hologram of a sample is created using an optical device for electron beam holography. This hologram records all the information of the electron beam after it passes through the sample, so by shining a laser beam onto this hologram, the image of the sample can be reproduced as a light wavefront on an optical bench. . Therefore, it becomes possible to observe interference microscopic images, phase microscopic images, etc. that cannot be obtained with an electron microscope.

FIG. 1 is an example of a conventional method for creating an electron beam hologram. The electron beam emitted from the electron gun 1 has its irradiation conditions adjusted by a condenser lens 2 and irradiates the sample 3. An electron beam prism 8 is provided between the objective lens 4 and the intermediate lens 5, and is composed of a parallel plate electrode 6 at ground potential and a thin core wire 7 stretched at the center thereof. When a positive voltage is applied to the core wire 7, the electron beams passing on both sides of the core wire are bent toward the core wire and overlap with each other below. At this time, sample 3 is placed on one side of the core wire.
When the electron beam that has passed through the sample is passed through the other side, and the electron beam that has passed through the part where there is no sample is passed through the other side, the two electron beams overlap at the bottom and an interference pattern 9 is formed. This is further magnified by the lower intermediate lens 5, projection lens 10, etc. and recorded on the film 11. This becomes a hologram.

The size of the sample area that can be recorded in the hologram can be adjusted by adjusting the voltage applied to the electron beam prism. However, by increasing the prism voltage, it is not possible to increase the overlapping area without limit. Increasing the prism voltage not only increases the overlapping area but also decreases the stripe spacing of the fundamental periodic fringes of the hologram. For this reason, first, the interference region of the irradiated electron beam (R=λ/2β: λ is the wavelength of the irradiated electron beam,
β is the aperture angle) must be increased, and in order to record finer fundamental periodic fringes on the film, the hologram magnification must be increased. For these reasons, there is an upper limit to the size of a hologram that makes maximum use of the interference area, and that value depends on the position of the electron beam prism. FIG. 2 shows the relationship between the position l of the electron beam prism and the maximum recordable sample area size (W _0nax ). In Figure 2, W ₀ is the size of the sample area recorded in the hologram, m ₀ is the magnification of the objective lens, L and l are the distances from the objective lens rear focus to the hologram surface and the electron beam prism, respectively, and λ is the electron wavelength of the line, d ₁
is the resolution of the film, ρ is the charge density required for the film to be exposed, B is the brightness of the irradiated electron beam, t
is the exposure time.

FIG. 2 shows that the closer the electron beam prism is to the back focal point of the objective lens, that is, the smaller the prism position l, the wider the sample area hologram can be created. However, generally, due to equipment limitations, the electron beam prism is provided close to the hologram surface, and it is difficult to move it in the optical axis direction. Therefore, with this method, it is not possible to create a hologram over a wide sample area. On the other hand, if the electron beam prism is placed close to the back focal point of the objective lens, the spacing between the interference fringes in the hologram will be larger than if it is placed close to the hologram surface, making it impossible to obtain a high-resolution hologram. .

In other words, in order to obtain both a wide field of view hologram and a high resolution hologram using conventional equipment,
A mechanism must be provided that can change the position of the electron beam prism from near the back focus of the objective lens to near the hologram surface. This is extremely difficult due to implementation constraints.

(3) Purpose of the invention The present invention provides an optical device for electron beam holography that allows the size of a sample area to be recorded in a hologram to be freely and easily changed.

An embodiment of the present invention will be described below with reference to FIG. Field emission type electron gun 12 and condenser lens 2
In the optical device, the electron beam prism 8 is provided between the intermediate lens 5 and the projection lens 10. The structure is such that two electron lenses are arranged between the sample 3 and the electron beam prism 8. According to this embodiment, the magnification of the sample image on the hologram surface 13 directly below the electron beam prism 8 can be easily and widely changed from reduction to enlargement by simply adjusting the excitation current of the objective lens 4 and intermediate lens 5. becomes possible. FIG. 3 shows an optical path diagram when the objective lens and intermediate lens are operated in the reduction mode. Changing the magnification of the sample image in this way is equivalent to changing m ₀ on the vertical axis in Figure 2, so according to this example, it is possible to record in a hologram even when the position of the electron beam prism is fixed. The size of the sample area can be freely selected.

According to the present invention, even when the electron beam prism position is fixed, by adjusting the excitation current of the electron lens placed between the sample and the electron beam prism,
It becomes possible to easily and widely select the size of the sample area that can be recorded in the hologram. In the embodiment, an example was explained in which two electron lenses were arranged between the sample and the electron beam prism, but the same effect can be obtained even if three or more electron lenses are arranged.

[Brief explanation of drawings]

Fig. 1 shows an example of a conventional optical device for electron beam holography, and Fig. 2 shows the relationship between the position of the electron beam prism and the size of the sample area that can be recorded in a hologram in an example of the conventional device. FIG. 3 is a diagram showing an embodiment of the present invention. 12... Field emission electron gun, 2... Condenser lens, 3... Sample, 4... Objective lens, 5...
Intermediate lens, 8...electron beam prism, 10...projection lens, 11...film.

Claims (1)

[Scope of utility model registration request] an electron beam irradiation system section having an electron gun 12 and a condenser lens system 2; a sample 3 to be irradiated with an electron beam by the electron beam irradiation system section; In an electron optical device composed of lenses 4, 5, 10 and a magnifying system section having an electron beam prism 8, two or more electron lenses 4, 5 are arranged between the sample 3 and the electron beam prism 8. An optical device for electron beam holography characterized by the following.