JPS58218738A - Observation area display unit for scanning type electron microscope - Google Patents

Abstract

PURPOSE:To quickly detect an observation area and facilitate its setting by spacially differentiating the brightness distribution of the secondary electron image of a sample, taking out its characteristics as line pictures, and displaying them on a CRT display. CONSTITUTION:The electron beam 3 from an electron gun 2 controlled by an electron beam scanning circuit 1 is raster-scanned on a sample 4. Then the secondary electron 5 from the sample 4 is detected by a detector circuit 6 and the detection signal is differentiated twice by a differential circuit 8. Besides, a signal exceeding preset wave height is sent to a rectangular generator circuit 10 through a wave height discriminator circuit 9 and the output is displayed on a CRT display 17. Furthermore a display image can be stored in a memory circuit 12 through an arithmetic control circuit 11. As a result, since only the characteristic parts of the secondary electron image of the sample can be extracted as line pictures, the observation area can quickly be detected and its setting is facilitated.

Description

DETAILED DESCRIPTION OF THE INVENTION The present invention relates to a scanning electron microscope, and more particularly to an observation area display device suitable for quickly and easily setting an observation area.

In a conventional scanning electron microscope, the observation area is set nine times by moving the sample using a sample fine movement device while observing a secondary electron (hereinafter referred to as 8E) image on a CIt T display. However, this method has the disadvantage that it is difficult to identify which part of the sample the observation area corresponds to unless the contrast of the SE image on the CRT is strong. In addition, the conventional technology (% 1986-26
347. In JP-A-56-38755), since the amount of movement of the sample moving device is processed electrically, it depends on the accuracy of the sample moving device, and is therefore unsuitable for high-magnification observation.

SUMMARY OF THE INVENTION An object of the present invention is to provide an observation area display device for a scanning electron microscope that can quickly and accurately locate a portion of a sample to be observed and set an observation area.

The present invention achieves the above object by spatially differentiating the luminance distribution of the SE image, extracting and displaying the features of the SE image as a line drawing.

An embodiment of the present invention will be described below with reference to the drawings.

FIG. 1 is an outline of a conventional SE image display circuit.

An electron beam 3 from an electron gun 2 controlled by an electron beam λ scanning circuit 1 raster scans a sample 4. Secondary electrons 5 generated from the sample 4 are detected by a secondary electron detection circuit 6. Is this detection signal CI? , the normal SE image displayed on the T display 7.

FIG. 2 shows an overview of the embodiment.

In this embodiment, the secondary electron detection signal is divided into two by the differentiating circuit 8.
The signal is differentiated twice, and further passed through a wave height discrimination circuit 9, and a signal exceeding a set wave height is inputted into a rectangular wave generation circuit 1°, and the output signal is displayed on a CRT display 7. This display image can be stored in the memory circuit 12 via the arithmetic control circuit 11, and conversely, the contents stored in the memory circuit 12 can also be redisplayed on the CRT display 7.

Next, the operation of this embodiment will be explained using diagrams of display images and signal waveforms. FIG. 3 shows a normal 8'E image based on the signal from the secondary electron detection circuit 6. In Figure 3, scanning line a
When the screen is turned upward, the intensity of the secondary electron detection signal there, that is, the brightness intensity of the display, becomes as shown in FIG. The signal obtained by differentiating this signal once through the differentiating circuit 8 is shown in FIG.
, the signal differentiated twice is shown in FIG. When the discrimination level of the pulse height discrimination circuit 9 is set to b in FIG. 6, the output signal of this circuit becomes as shown in FIG. When this signal is input to the rectangular wave generating circuit 10, an output as shown in FIG. 8 is obtained. By performing the above signal processing on all scanning lines, the image shown in FIG. 9 is obtained. In this way, the features of the SE image can be displayed as line drawings. The degree of feature extraction can be changed by adjusting the time constant of the differentiation circuit 80 and the discrimination level of the pulse height valve circuit 9.

For example, if the discrimination level of the pulse height discrimination circuit 9 is set to C in FIG. 6, the obtained image will be as shown in FIG. 10. It is also possible to display line drawings and SE images in an overlapping manner, so an appropriate line drawing can be selected while checking the degree of feature extraction. This line drawing can be stored in the memory circuit 12 and displayed overlappingly when setting the observation area later, so that by matching the line drawings, it is possible to observe exactly the same area as the previous observation area.

As explained above, according to this embodiment, by adjusting the time constant of the differentiating circuit 8 and the discrimination level of the pulse height discrimination circuit 9, features can be extracted to any degree from the sample SE image and displayed as a line drawing. Therefore, it is possible to quickly find the observation area. In particular, when re-observing a past observation area, by displaying the line drawing of the past observation area stored in the storage circuit 12 over the current line drawing, the observation area can be accurately reset.

According to the present invention, only the characteristic portion of the sample SE image can be extracted as a line drawing, so it is possible to quickly find and set the observation area. Particularly when re-observing the same area as the past observation area, the area can be easily reset by superimposing the memorized line drawing on the display. The accuracy of resetting is independent of the magnitude of the magnification and depends on the line width of the line drawing on the CRT, so even when observing a deer at a high magnification of 104 times, resetting is possible with an accuracy of about 10-2 μm.

[Brief explanation of the drawing]

FIG. 1 shows a conventional SE image display circuit, and FIG. 2 shows an outline of an embodiment of the present invention. FIG. 3 is an example of a normal BE image. 4, 5, 6, 7 and 8 respectively show the secondary electron detection circuit 6.degree. differentiator circuit 7. This is an example of output signals of the wave height discrimination circuit 9 and the rectangular wave generation circuit 10. FIGS. 9 and 10 are examples of line drawings in which features of SE images obtained as a result of signal processing are extracted.

Claims (1)

[Claims] 1. A differentiating circuit that differentiates a signal obtained by detecting secondary electrons generated from a sample to be observed, a square wave generating circuit that generates a rectangular wave based on the output signal of this differentiating circuit, and the differentiating circuit. An observation area display device for a scanning electron microscope, comprising an output signal and a CRT display that displays the output signal of the rectangular wave generation circuit.