JPH04336B2 - - Google Patents

Description

DETAILED DESCRIPTION OF THE INVENTION [Industrial Field of Application] The present invention relates to an electron diffraction apparatus for observing electron diffraction patterns.

[Prior Art] Fig. 1 is for explaining a conventional electron diffraction apparatus for observing an electron diffraction pattern. In the figure, 1 is an electron gun, and 2 and 3 are first and second
It is a converging lens. 4a and 4b are objective lenses 4
front and rear magnetic field lenses, and a sample 5 is placed between these lenses 4a and 4b. 6
is a cylindrical part for cutting off electron beams that are far away from the optical axis C out of the electron beams that have passed through the sample 5. When performing selected area observation at the center of this cylindrical part 6, a selected area diaphragm ( (not shown) is inserted. A lens system 7 consisting of an intermediate lens and a projection lens is arranged at the rear of the cylindrical portion 6, and a fluorescent plate 8 is arranged at the rear of the lens system 7.

Now, using such a device, the image of the electron gun 1 is formed onto the sample 5 by the first and second converging lenses 2 and 3 and the front magnetic field lens 4a, and as a result, the image of the electron gun 1 is made incident on the sample. The electron beam diffracted at step 5 is imaged at the position A by the backward magnetic field lens 4b, and the object plane position of the intermediate lens is made to coincide with the position A, and finally the image at the position A is formed by the projection lens. If the diffraction image formed at the position is projected onto the fluorescent plate 8, an electron beam diffraction pattern as shown in FIG. 2 will be obtained. When observing such a diffraction pattern, there are cases where it is desired to observe the patterns within the diffraction spots indicated by A, B, etc. in the figure. In order to easily observe the pattern in such a case, it is desirable to project the spots onto the fluorescent plate 8 as large as possible without overlapping the spots. To change the size of the spot,
It is sufficient to change the convergence angle indicated by 2α in the figure.
At this time, since the distance between the spots varies depending on the type of sample and which crystal plane the diffraction image is based on, it is necessary to be able to adjust the convergence angle 2α continuously. Therefore, conventionally, the adjustment of the convergence angle 2α is performed by adjusting the position of the sample 5 in the optical axis direction,
That is, this was done by shifting the z-coordinate.
Therefore, the z-coordinate of the sample deviates from the standard z-position in the Eucentric goniometer.
By the way, a eucentric goniometer can only maintain the same observation field of view even if the tilt angle of the sample is changed only when the sample is at the standard z position. Otherwise, when the sample is tilted, the electron beam irradiation position on the sample will shift. Therefore, even if a crystal-perfect region is initially set as an electron beam irradiation region, the irradiation region cannot be maintained and a desired diffraction image cannot be observed.

Furthermore, when the z-position of the sample 5 is moved, the lens action of the rear magnetic field lens 4b of the objective lens also changes, so that the diffracted electron beam no longer crosses over to the center of the cylindrical portion 6, and is therefore projected onto the fluorescent plate 8. The visual field radius r of the diffraction image obtained may become small, and the spot of interest may be cut off.

[Object of the Invention] The present invention solves these conventional drawbacks, allows the convergence angle 2α to be changed arbitrarily, and even when 2α is changed, the electron beam irradiation position and irradiation diameter on the sample are completely unchanged. The field diameter r of the diffraction pattern remains unchanged.
The object of the present invention is to provide an electron beam diffraction device whose size does not change.

[Structure of the Invention] Therefore, the present invention provides an electron gun, first and second converging lenses for converging the electron beam from the electron gun, a front magnetic field lens of an objective lens, and an electron beam that is largely off-axis. In an electron beam diffraction device equipped with a cylindrical part or selected area diaphragm for cutting the beam, and an intermediate and projection lens, the electron beam is irradiated onto the sample while keeping the spot diameter of the electron beam irradiated on the sample constant. a control means for automatically interlocking and changing excitation currents supplied to the objective lens and the first and second converging lenses so as to arbitrarily vary the opening angle of the line; an auxiliary lens disposed between the objective lens and the objective lens in order to cause the electron beam passing through the auxiliary lens to always cross over to the center of the cylindrical portion or selected area diaphragm regardless of changes in the excitation intensity of the objective lens; The present invention is characterized by comprising means for changing the excitation intensity of the auxiliary lens in conjunction with changes in the excitation intensity.

[Example] Hereinafter, an example of the present invention will be described in detail based on the drawings.

In FIG. 3 showing one embodiment of the present invention, the first
Components that are the same as those in the figures are numbered the same. In the same figure, 9 and 10 are the first,
This is the power source for the second converging lens. 11 is an excitation power source for the objective lens 4. The excitation current from the excitation power source 11 can be adjusted by a regulator 12. The excitation currents of the excitation power supplies 9 and 10 are controlled by converters 13 and 1, respectively, by transmitting control signals from the regulator 12.
It is controlled based on the signal converted in step 4. These converters 13 and 14 are arranged so that when the excitation intensity of the objective lens is changed by changing the output signal of the adjuster 12, the image of the electron gun (or its crossover) remains on the sample 5 despite this change. This is for changing the excitation intensities of the first and second converging lenses 2 and 3 in conjunction so that an image having the same spot diameter is formed on the converging lens, and these converters 13,
14 converts the control signal from the adjuster 12 into a control signal for exciting the first and second converging lenses 2 and 3 as necessary. These converters 13,1
4 each consists of a memory and its reading mechanism. The stored contents of the memory in each of these converters are how the front magnetic field lens 4a changes its position (the amount of change δ) when the output signal of the adjuster 12 is changed in various ways, and how it changes its position. Investigate in advance how the magnification changes (the amount of change ΔM), and theoretically or experimentally determine how much it is necessary to excite the first and second converging lenses 2 and 3 in accordance with this change. The control signal values that provide the required excitation intensity are stored at addresses corresponding to each value of the regulator 12. Further, an auxiliary lens 15 is provided between the objective lens 4 and the cylindrical portion 6. The excitation current of the excitation power source 16 for this auxiliary lens 15 is also converted into a signal from the adjuster 12 to a converter 17.
It is controlled based on the signal converted by . converter 1
7 also consists of a memory and its readout mechanism, and when the output signal of the adjuster 12 is changed to change the excitation intensity of the objective lens 4, this memory always reads the diffracted electron beam as described above regardless of this change. Cylindrical part 6
Power supply 1 required for crossover at the center of
6 control signal values are stored. Note that K is a converging lens aperture.

In such a configuration, when the output signal of the adjuster 12 is changed, the front magnetic field lens 4a of the objective lens changes in accordance with this change, but the adjuster 1
The control signals from the converters 13 and 14 that convert the output signals of the first and second converging lenses 2 and 3 change in conjunction with this change and are supplied to the excitation power supplies 9 and 10, respectively. The excitation intensity is such that the image of the electron gun (or its crossover) is subsequently imaged onto the specimen 5 at the same magnification. Therefore,
With this change, the object point position of the lens 4a moves as shown in FIG. 3, so that the convergence angle 2α can be changed. Therefore, while observing the diffraction spots of the diffraction pattern on the fluorescent plate 8, the operator adjusts the output of the adjuster 12 so that the spots are as large as possible without overlapping.
Furthermore, as the output signal of the adjuster 12 changes, the position and magnification of the rear magnetic field lens 4b also change.
Since a control signal is supplied to the excitation power source 16, the auxiliary lens 15 continues to act to cause the diffracted electron beam to cross over at the center. Therefore, the amount of cutoff of the diffracted electron beam does not increase with adjustment of the convergence angle 2α.

[Effect] As described above, according to the electron beam diffraction apparatus based on the present invention, it is possible to vary the aperture angle of the electron beam irradiated to the sample while maintaining the diameter of the electron beam irradiated to the sample at a constant value. can. Therefore, when observing diffraction spots in focused electron beam diffraction, once the electron beam irradiation area on the sample is set so that the electron beam is irradiated only on the area where the crystal is perfect, this irradiation area By adjusting the aperture angle while maintaining the diffraction spots within this set range, the size of the diffraction spots can be finely adjusted to the maximum size within a range where the diffraction spots do not overlap. As a result, as the irradiation diameter changes as the aperture angle is adjusted, new crystal defects are not added to the electron beam irradiation area, making it possible to observe high-quality diffraction images over minute areas. Become.

Furthermore, even if the convergence angle is adjusted, the amount of cutoff of the diffracted electron beam does not increase, and the visual field diameter r of the diffraction pattern image can be maintained at the maximum.

[Brief explanation of drawings]

FIG. 1 is a diagram for explaining a conventional device, and FIG. 2 is a diagram for explaining the diameter of a diffraction spot and field of view of a diffraction pattern projected onto a fluorescent plate.
FIG. 3 is a diagram showing one embodiment of the present invention. 1: Electron gun, 2, 3: Converging lens, 4a: Front magnetic field lens, 4b: Back magnetic field lens, 5: Sample,
6: Cylindrical part, 7: Lens system, 8: Fluorescent plate, 9, 1
0, 11, 16: Excitation power supply, 12: Regulator, 1
3, 14, 17: converter, 15: auxiliary lens,
C: Optical axis, K: Aperture.

Claims (1)

[Claims] 1. An electron gun, first and second converging lenses for converging the electron beam from the electron gun, a front magnetic field lens of the objective lens, and a cylindrical part for cutting off the electron beam that deviates significantly from the axis. Alternatively, in an electron beam diffraction apparatus equipped with a selected area diaphragm and an intermediate and projection lens, the aperture angle of the electron beam irradiated onto the sample can be arbitrarily varied while the spot diameter of the electron beam irradiated onto the sample is held constant. control means for automatically interlocking and changing excitation currents supplied to the objective lens and the first and second converging lenses so as to
An auxiliary lens disposed between the objective lens and the intermediate lens, and for making the electron beam that has passed through the auxiliary lens always cross over to the center of the cylindrical portion or selected area diaphragm regardless of changes in the excitation intensity of the objective lens. An electron beam diffraction apparatus comprising: means for changing the excitation intensity of the auxiliary lens in conjunction with changes in the excitation intensity of the objective lens.