JPS5824901B2 - scanning electron microscope - Google Patents

Description

DETAILED DESCRIPTION OF THE INVENTION The present invention relates to an improvement in the means used for the sample movement operation of a scanning electron microscope.

In image observation using a scanning electron microscope, in order to obtain a desired field of view, it is necessary to move the sample to the center of the electron beam irradiation area using a sample moving mechanism.

At this time, in order to search for another field of view 1 while observing a medium-high magnification image, the magnification is usually lower than the value being observed and the specimen is moved after expanding the field of view, but the distance of field movement is long. It has been customary to lower the magnification and increase the operating speed of the sample moving mechanism.

In this way, the desired location on the sample is determined. The procedure used was to operate the sample moving mechanism so that the image was positioned at the center of the field of view, then increase the magnification again and observe the sample image.

An object of the present invention is to automatically switch the image magnification in the field of view selection operation described above, thereby facilitating the operation.

FIG. 1 is a schematic diagram showing the main parts of an apparatus according to an embodiment of the present invention.

In the figure, the irradiation position of an electron beam 2 that irradiates a sample 1 is scanned by a deflection coil 5 to which a deflection signal is supplied from a scanning signal generation circuit 3 via a magnification circuit 4.

A part of the output of the scanning signal generating circuit 3 is directly supplied to the deflection means of the image displaying cathode ray tube 6, and since the intensity of the cathode ray tube 6 is modulated by the signal detected from the sample, the sample image is not displayed on the cathode ray tube screen. is displayed.

The field of view of the sample image is defined by an X provided on the sample moving mechanism 7 on which the sample is placed.

The sample image is moved by operating a moving rod in the Y direction, and the magnification of the sample image is controlled by changing the amplification degree of the scanning signal in the magnification circuit 4.

The configuration described above is provided in a general scanning electron microscope, but in the apparatus of the present invention, the automatic magnification ff51J11 means 8 for controlling the magnification circuit 4 based on the output from the sample moving mechanism 7 is provided. It is provided.

The input section of the automatic magnification control means 8 is provided with a pulse conversion circuit 9 that detects the movement of the sample in the sample moving mechanism 7 and generates a constant pulse every time the sample moves by a certain amount. The counting circuit 10 is reset at regular intervals by a clock pulse A (FIG. 2a) from the clock pulse generating circuit 11.

The output pulse of the counting circuit 10 is sent to the up/down counting circuit 12.
is applied to the comparison circuit 13, which compares the output of the amplifier down counting circuit 12 and the output of the counting circuit 10, and if the output of the counting circuit 10 is larger, the output value is applied to the load gate circuit 14. Based on the clock pulse B (FIG. 2b) from the clock pulse generation circuit 15 which is input to the clock pulse A and has a slightly different phase from the clock pulse A, the up/down counting circuit 12 performs Read the output of the counting circuit 10.

Conversely, the up/down counting circuit 12 of the output of the counting circuit 10
If the output of the up/down counting circuit 12 is lower than the output of
Decrease steps.

A part of the output of the up-down counting circuit 12 is sent to the comparison circuit 17.
, the signal from the up-down counting circuit is compared with the output of the magnification setting circuit 18 that stores the count value corresponding to the magnification set in advance before the sample movement operation, and the signal from the up-down counting circuit is determined to have a lower magnification than the signal from the magnification setting circuit 18. Only when this is the case, the output of the up/down counter circuit is applied to the magnification circuit 4, and scanning is performed at a magnification lower than the set magnification.

Next, the operating principle of the embodiment shown in FIG. 1 will be explained using FIG. 2.

The horizontal direction of each signal waveform shown in FIG. 2 represents the time axis, waveforms a and b represent clock pulses A and B, respectively, and waveform C
represents the output signal of the pulse conversion circuit 9.

Assume now that the sample moving mechanism 7 is operated and the output of the pulse conversion circuit 9 becomes as shown in FIG. 2C.

This C pulse is counted by the counting circuit 10, but is reset by the clock pulse A, so its output signal is expressed as d.

The part d, which shows the highest value in the signal d, means that the sample moved most rapidly in this unit time. The entire field of view within the camera changes instantaneously, creating a major obstacle in visual field selection operations.

FIG. 2e shows the waveform of the up-down counting circuit 120. Since the value of the output d of the counting circuit 10 at each unit time of T1 p T2 t T3 is a higher value than the output e of the up-down counting circuit 12, The load gate circuit 14 is activated by the output of the comparison circuit 13, and the amplifier down counting circuit 12 reads the value of the output d of the counting circuit 100.

The larger the count value (step value) read in this way is, the lower the multiplication factor is, and it is always higher than the magnification setting value before the sample movement operation, which is represented by the baseline of waveform e. (Since it is a low multiplication, it is applied to the magnification circuit 4 via the comparison circuit 17, and a magnification lower than the magnification value stored in the magnification setting circuit 18 is obtained.

Therefore, movement of the field of view due to sudden sample movement operations can be suppressed.

Next, in each unit time from T4 to TIO, the output e of the up-down counting circuit 12 is higher than the output e of the counting circuit 100.
Since the output d has a lower value, the down gate circuit 16 operates to reduce the count value of the up/down counter circuit 12 by two steps per unit time.

By this operation, when the operation of the sample moving mechanism 7 is stopped or performed slowly, the magnification that has been changed to a low magnification is gradually returned to the set magnification before moving the sample.

As described below, in the device of the present invention, when searching the field of view during observation of medium-high magnification images, magnification operations are automatically performed, such as switching to low magnification, moving the sample, and switching again to medium-high magnification, as in the conventional method. This has a significant effect on improving the operability of scanning electron microscopes.

[Brief explanation of drawings]

FIG. 1 is a schematic diagram showing an apparatus according to an embodiment of the present invention, and FIG. 2 is a schematic diagram for explaining the operation of the apparatus shown in FIG. DESCRIPTION OF SYMBOLS 1... Sample, 3... Scanning signal generation circuit, 4... Magnification circuit, 7... Sample moving mechanism, 8... Magnification automatic control means, 9... Pulse conversion circuit, 10...・Counting circuit,
11゜15...Clock pulse generation circuit, 12...
Amplifier down counting circuit, 13, 17...-J:F! Circuit, 14... Load gate circuit, 16... Down gate circuit, 18... Magnification setting circuit.

Claims (1)

[Claims] 1. Pulse generating means that detects the movement of the sample by the sample moving mechanism and generates a pulse every time the sample moves for a certain period of time; means that counts the output pulses from the pulse generating means at fixed time intervals; If the count value is larger than the count value of the previous period, the magnification of the sample scan image is automatically lowered, and if the count value is smaller than the count value of the previous period, the magnification of the sample scan image is automatically increased. scanning electron microscope.