JPS5919622B2 - electronic microscope - Google Patents

Description

DETAILED DESCRIPTION OF THE INVENTION The present invention relates to an electron microscope that obtains a transmission electron microscope image by scanning an electron beam over a sample surface.

To photograph a transmission electron microscope image using a transmission electron microscope, an electron beam with a relatively large spot diameter (several to several + micrometers) is irradiated onto the sample, and the electron beam that has passed through the sample is focused through an objective lens, etc. An image lens system is used to form an enlarged image on the film.

On the other hand, a transmission electron microscope image is created by scanning the sample surface two-dimensionally with the electron beam focused to a minute diameter, and then magnifying and focusing the electron beam that has passed through the sample onto a film using a magnifying lens system. It is also well known to take pictures.

However, in such a method, when photographing a sample such as a thin metal film, if the thickness of the sample is not uniform or the diffraction conditions are different, uneven brightness of the image will occur within the photographic field of view.

Therefore, it is necessary to perform ``oiyaki'' at the printing stage to eliminate unevenness in brightness, and if the unevenness in brightness is large, it is necessary to take multiple photographs with different exposures for one field of view.

Therefore, it takes time to take a photograph and is very difficult to handle.

In addition, since the signal amount itself from the thick part of the sample becomes small, the S/N of the net signal part related to the fine structure of the sample becomes small, and unless the photograph is taken multiple times with different exposures, the sample It was not possible to fully understand the state of the microstructure.

The present invention aims to solve such inconveniences, and will be explained in detail below with reference to the drawings.

FIG. 1 is a schematic diagram showing an embodiment of the present invention, and 1 is a mirror body of a transmission electron microscope.

Reference numeral 2 denotes an electron gun placed above the mirror body 1, and the electron beam 3 generated by the electron gun is focused by a focusing lens 4 to a diameter of, for example, 0.
The sample 5 is irradiated with the beam being focused to a small diameter of about 1 to 0.2 μm.

A deflection coil 6 scans the electron beam 3 two-dimensionally over the sample 5 by being supplied with a scanning signal from a scanning power source 7 via a scanning speed control circuit 8 .

Reference numeral 9 denotes an imaging lens system consisting of an objective lens, a projection lens, etc., which is used to enlarge and image the electron beam that has passed through the sample 5.

Reference numeral 10 denotes a film placed on this imaging plane, and the film is moved from the unphotographed case 11 to the photographing position by an appropriate feeding mechanism, and from this position into the photographed case 12.

Now, when the irradiation electron beam 3 is deflected by the deflection coil 6 as shown by the solid line to irradiate a point P on the sample 5, the electrons transmitted from the point P are directed to a point P' on the film 10 by the imaging lens system 9. Form an image.

Further, when the deflection coil 6 is irradiating an electron beam to a point Y on the sample 5 as shown by a dotted line, the transmitted electrons from the point Y are imaged at a point Y/ on the film 10.

Therefore, when a scanning signal is supplied to the deflection coil 6 and a certain area on the sample 5 is scanned by the irradiated electron beam 3, the transmitted electrons from each point form an image according to the process described above, and the film 1 is
A transmission electron microscope image is exposed on the 0.

Furthermore, if a fluorescent plate 13 is set above the film 10, the transmission electron microscope image can be observed with the naked eye.

When the cassette 14 holding the film 10 is set at the photographing position, it is electrically isolated from the mirror body 1, so that transmitted electrons that have reached the film 10 can be detected.

The detected signal is amplified by an amplifier 15 and sent to a filter circuit 16.

The filter circuit 16 cuts high frequency components of the detection signal and passes only relatively low frequency components of, for example, several to several tens of Hz.

The low frequency component signal from the filter circuit 16 is sent to a differential amplifier 17 and compared with a reference voltage of a reference power supply 18.

The output signal from the differential amplifier 17 is sent to the scanning speed control circuit 8, which changes the slope of the scanning signal from the scanning power source 7, thereby changing the scanning speed of the electron beam on the sample 5.

In this configuration, the film cassette 14 detects electrons that have passed through each point of the sample as the irradiated electron beam scans, and the signals detected at this time contain information based on the structure or composition of the sample. and information based on the thickness of the sample.

Information based on the structure or composition of the sample has high frequency components, and there is no sudden change in the thickness of the sample, so if the scanning speed of the irradiated electron beam during normal imaging is used, the number of It has a relatively low frequency component of about 10 Hz.

Therefore, if the low frequency component is extracted from the filter circuit 16, it will become a signal corresponding to the thickness of the sample, and by comparing this signal with a preset reference value in a differential amplifier, if the sample is thick, the irradiated electron Lower the line scanning speed,
Conversely, if the sample is thin, the electron dose (electron current density x time product) at each point of the final image can be kept constant by increasing the scanning speed.

As a result, it is possible to automatically correct unevenness in brightness due to changes in the thickness of the sample, making it possible to shorten the imaging time and making handling extremely easy.

Furthermore, in the apparatus of the present invention, since the sample is thick,
When the extracted low-frequency component signal value is small, the scanning speed of the electron beam is controlled to be small, so the thick part of the sample is sufficiently irradiated with the electron beam to increase the S/N. Based on this signal, an image representing the fine structure of the sample can be obtained in one photographing operation.

It should be noted that the above-described embodiments are merely illustrative of the present invention, and many modifications may be made in implementing the present invention.

For example, the detection of electrons transmitted through a sample has been described above, but this is not limited to the detection of electrons flowing into a film cassette. The same effect as described above can be obtained by detecting the electron beam, or by detecting the electron beam flowing into the aperture (objective aperture, etc.) using an imaging lens system.

Furthermore, in the above explanation, the transmission electron microscope image was directly exposed to the film, but a fluorescent plate was installed on the electron beam path, and the transmitted electrons that reached this fluorescent plate were detected and sent to a filter circuit to determine the thickness of the sample. If the scanning speed of the irradiated electron beam is controlled by extracting a signal corresponding to , a transmission electron microscope image with uniform brightness can be observed with the naked eye.

Furthermore, we have described the case where the present invention is applied to a transmission electron microscope. As shown in FIG. A cathode ray tube 21 synchronized with the irradiated electron beam scanning via
The same method can be applied to a scanning electron microscope in which a scanning electron microscope is installed to obtain a scanning image.

That is, since the video signal detected by the detector 19 also contains information regarding the thickness of the sample 5, a portion of the video signal is sent to the filter circuit 16 in the same way as in FIG. If the scanning speed of the irradiated electron beam and the scanning speed of the electron beam of the cathode ray tube 21 are changed in accordance with the change in the thickness of the sample 5 by extracting a signal corresponding to the thickness of the sample, the cathode ray tube 21 can be brightened. A transmission scanning electron microscope image with no unevenness can be observed, or a photograph can be taken with the camera 23.

Note that the same numbers in Figure 2 as in Figure 1 indicate the same components;
2 is a deflection coil of the cathode ray tube.

[BRIEF DESCRIPTION OF THE DRAWINGS] Fig. 1 is a schematic diagram showing an embodiment of the present invention in a transmission electron microscope, and Fig. 2 is an embodiment of the invention in a scanning electron microscope. FIG. 1: mirror body, 2: electron gun, 3 two electron beams, 4: focusing lens,
5: Sample, 6: Deflection coil, 7: Scanning power supply, 82 Scanning speed control circuit, 92 Imaging lens system, 10: Film, 11
:Unphotographed case, 12:Photographed case, 132 fluorescent plates,
14: Cassette, 15 and 20: Amplifier, 16: Filter circuit, 17: Differential amplifier, 18 Two reference power supplies, 19:
Detector, 21: cathode ray tube, 22 two deflection coils.

Claims (1)

[Claims] 1. In an apparatus that obtains a transmission electron microscope image by irradiating a thin film sample with a narrowly focused electron beam and scanning the sample surface two-dimensionally with the electron beam, each point of the sample is A means for detecting transmitted electrons, a means for extracting a low frequency component from a signal detected by the means, and a means for controlling the scanning speed of the electron beam using an output signal from the means. Electron microscopic bird characterized by its small size