JPS5834679Y2 - Scanning electron microscope - Google Patents

Description

[Detailed Description of the Invention] The present invention relates to a scanning electron microscope that can always take images of a sample with accurate exposure.

When photographing a sample image using a scanning electron microscope, a cathode ray tube (C
It is necessary to adjust the brightness of the CRT (RT); conventionally, the brightness signal is filtered by operating the contrast knob and brightness knob while looking at two meters that indicate the amplitude and center level of the brightness signal supplied to the CRT; Accordingly, adjustments are made to fit within a predetermined shooting range.

However, this kind of operation is not necessarily accurate because it requires human power.

In addition, conventional methods have focused only on the luminance signal and not on the amount of light actually generated from the CRT screen. Therefore, if the luminance of the screen decreases due to changes in the fluorescent surface of the CRT over time, etc.
Even if a luminance signal of the same intensity is sent to the CRT, the amount of light generated from the screen decreases, which tends to result in underexposure during photographing.

The present invention has been made to improve such conventional disadvantages, and the present invention will be explained in detail below with reference to the drawings.

FIG. 1 is a block diagram showing one implementation of the present invention, and in the figure, numeral 1 represents an electron beam generated from an electron gun (not shown).

The electron beam 1 is narrowly focused onto a sample 3 by a focusing lens 2, and is two-dimensionally scanned over the sample 3 by a deflection coil 5 to which a scanning signal is supplied from a scanning circuit 4.

Information such as secondary electrons 5 and reflected electrons generated from the sample 3 by electron beam scanning on the sample is detected by the detector 6, and the resulting detection signal is amplified by the amplifier 7, and then sent to the adjustment circuit 8 and the switching It is supplied to the CRTIO via the circuit 9 as a luminance signal.

The adjustment circuit 8 includes a contrast knob 11 for adjusting the amplitude of the detection signal, a contrast knob 11 for displaying "D", a brightness knob 13 for changing the DC level of the detection signal, and a brightness knob for displaying the DC level. It is equipped with a meter 14.

Also, one word output from the adjustment circuit 8 is sent via the average brightness detection circuit 15 to the switching circuit 9.\\.

The average brightness detection circuit 15 includes a peak hold circuit 16.
17 and an average value detection circuit 18.

The deflection coil 19 of the CRTIO is supplied with a scanning signal generated from the scanning circuit 4 and synchronized with electron beam scanning on the sample via a shift circuit 20.

Also, the sample image displayed on the CRTIO screen above is the hood 2
1. The image is photographed by a camera 23 equipped with an aperture 22.

24 is a photodetector provided to detect light generated from a small area of the CRTIO screen;
The output signal of 4 is sent to a control circuit 25 that controls the throttle 22.

In such a configuration, the operator first moves the switching circuit 9 toward the adjustment circuit 8 side and adjusts the knob 11.13 while observing the sample image displayed on the CRT lo and the meter 12.14, thereby adjusting the detection signal sent to the CRT. The amplitude and level of the image can be kept within a predetermined shooting range.

However, such a conventional operation causes the above-mentioned inconveniences.

Therefore, in the present invention, the average brightness of the detection signal is displayed on the CRT screen, the brightness is detected by the photodetector 24, and the amount of light reaching the photographic film is controlled based on the obtained detection signal.

That is, as shown in FIG. 2, a sample image display area a and an average brightness display area are preset on the CRTIO screen, and when the shift circuit 20 is not operated, the electron beam in the CRTIO operates in area a. The device is configured so that the area can be scanned when the image is moved.

Further, the peak hold circuits 16 and 17 hold the maximum and minimum values of the detection signal obtained from the detector 6 for each screen (one frame), and the average value detection circuit 18 holds the average value of the maximum and minimum values. By this calculation, the center level (average brightness) of the detection signal is detected.

Therefore, by operating the shift circuit 20 and moving the switching circuit 9 toward the average brightness detection circuit 15, a raster having the average brightness of the sample image to be photographed will be displayed on the area of the CRT screen.

Since the light generated from the area is detected by the photodetector 24, a detection signal indicating the amount of light generated from the area is obtained from the detector 24.

Furthermore, the control circuit 25 compares the detection signal with a reference signal corresponding to a predetermined amount of light depending on the film, and if the amount of light generated from the area is smaller than the predetermined amount of light, the control circuit 25 changes the direction in which the aperture 22 is opened. control to increase the amount of light reaching the photographic film inside the camera 23, and when the amount of light generated from the other area is larger than a predetermined amount of light, the diaphragm 22 is controlled to close to increase the amount of light that reaches the photographic film inside the camera 23. This reduces the amount of light that reaches the photographic film.

Therefore, if the operation of the shift circuit 20 is then stopped and the switching circuit 9 is turned to the adjustment circuit 8 side, even if there is some error in the result of the adjustment made by the operator using the adjustment circuit 8,
Furthermore, even if there is a lack of brightness due to changes in the CRT over time, the aperture 22 operates to cancel this out, so the average brightness of the image reaching the photographic film is always kept constant. can be photographed.

Note that since areas a and b set on the CRT screen have different areas, when displaying the average brightness in each area, it is necessary to correct the brightness signal in the average brightness detection circuit 15 according to the area ratio. Needless to say.

Furthermore, in the embodiment described above, the aperture 2 is controlled by the output of the control circuit 25.
2, but the invention is not limited to this, and it is sufficient to control any means that can change the amount of light that reaches the film. For example, the control circuit 8
It may be possible to control the

[Brief explanation of the drawing]

FIG. 1 is a block diagram showing an embodiment of the present invention, and FIG. 2 is a diagram for explaining its operation. 4: Scanning circuit, 6: Detector, 8: Adjustment circuit, 9: Switching circuit, 10: CRT, 15: Average brightness detection circuit, 1
6.17: Peak hold circuit, 18: Average value detection circuit, 19: Deflection coil, 20: Shift circuit, 22: Aperture, 23: Camera, 24: Photodetector, 25: Control circuit.

Claims (1)

[Scope of utility model registration request] An electron beam is scanned two-dimensionally over a sample, information generated from the sample is detected by the scanning, and the obtained detection signal is introduced into a cathode ray tube display device synchronized with the electron beam scanning on the sample. A scanning electron microscope configured to obtain an image, comprising: a camera for photographing the sample image; a means for controlling the amount of light incident on the camera; means for determining the average brightness using the detection signal; switching means for switching the obtained average brightness signal with the detection signal and sending it to the cathode ray tube; and when the average brightness signal is being supplied to the cathode ray tube by the switching means, A photodetector is provided opposite to the cathode ray tube screen to detect light generated from the screen, and a comparison circuit compares the output signal of the photodetector with a reference signal, and the output signal of the comparison circuit is A scanning electron microscope characterized in that the scanning electron microscope is configured to send the light to a means for controlling the amount of light incident on the camera.