JPS6161221B2 - - Google Patents

Description

DETAILED DESCRIPTION OF THE INVENTION The present invention relates to a novel drift correction device for an electron microscope.

It is well known that sample drift poses a major obstacle to high-resolution observation in electron microscopes. This drift is caused by the temperature and mechanical imbalance of structures near the sample, and is caused by changes in temperature during sample exchange, etc., and it may take several hours to reach an equilibrium state. This poses a major hindrance to observation.

Research has been carried out to reduce sample drift, but there has been no device with a simple structure that can correct drift with high precision.

SUMMARY OF THE INVENTION An object of the present invention is to provide a drift correction device for an electron microscope that can correct the drift with high precision using a device with a simple configuration and solves the above conventional drawbacks.

Therefore, the present invention includes means for forming an electron microscope image on a display screen, and in each of the two orthogonal X and Y directions along the display screen, the specified image area of the electron microscope image is focused in the said direction. a converting means for converting into an electric signal that changes over time, a means for binarizing the electric signal, and the display based on a signal synchronized with the conversion into each of the electric signals by the converting means. A circuit for creating a rising pulse signal and a falling pulse signal with a specific position in the direction on the screen as a boundary, an AND circuit output of the electrical signal and the rising pulse signal, and an output of the electrical signal and the falling pulse. A circuit for creating a counting signal representing the difference or ratio of the pulse width between the signal and the AND circuit output, and means for deflecting and moving the electron microscope image so that the counting signal output from the circuit is constant. It is characterized by

Embodiments of the present invention will be described in detail below based on the drawings.

FIG. 1 is a block diagram showing an embodiment of the present invention, in which 1 is an objective lens, 2 is an intermediate lens, and 3 is a projection lens. The electron beam transmitted through the sample 4 is imaged and magnified by the objective lens 1, and is further expanded by the intermediate lens 2,
It is magnified by a projection lens 3 to form a final image 5. A fluorescent screen 6 (second
) is placed, and the electronic image can be observed as a visible image. For example, a solid-state imaging plate 7 is attached to an appropriate location on the upper surface of the fluorescent screen, and is capable of converting an electron microscope image into an electrical signal that changes over time in two orthogonal directions (X and Y directions). Reference numeral 8 denotes a horizontal (X direction) synchronizing signal generation circuit, which generates pulse signals at regular intervals as shown in FIG. A video signal (FIG. 3b) having a temporal change that is scanned is obtained and sent to a binarization circuit 10 via an amplifier 9. In this binarization circuit, signals above a certain level E ₁ (see figure b) are converted to "1", and signals below that are converted to "0" signals (see figure 3 c), and the two AND gates 1
1a and 11b. On the other hand, the signal from the synchronization signal generation circuit 8 is transmitted to the sawtooth wave signal generation circuit 12.
and generates a sawtooth wave as shown in Figure d.
This signal is sent to a comparison circuit 13, where it is compared with a slice signal _E2 having a level approximately at the center, and when this level is exceeded, a signal is generated (FIG. 3e) which is sent to the AND gate 11a. The comparison circuit 13
A part of the signal from the inverting circuit 14 becomes the signal shown in FIG. 3f, and is sent to the AND gate 11b. A clock pulse of a constant period is sent to both AND gates 11a and 11b from a clock pulse oscillator 15, so the outputs of both gates are as shown in FIG. 3g and h, respectively. The time t ₁ at which this clock pulse appears is the length l ₁ to the right of the slice position of the image portion 5a showing the value "1" as shown in FIG.
, and t ₂ corresponds to the length l ₂ on the left side of the figure. Therefore, the slice position is at level E ₂ in Figure 3 d.
is set at a fixed position, so if image part 5
If a moves (drifts) to the left or right, the difference or ratio between l ₁ and l ₂ changes, and the values of t ₁ and t ₂ change accordingly. This time duration is converted into a number of clock pulses, each pulse being counted by a counter 16a, 16b. The counted values of both counters are sent to an arithmetic circuit 17, and the difference or ratio between them is determined.

The output from the arithmetic circuit is converted into an analog signal by the DA converter 18, and the output is converted into an analog signal by the DC amplifier 1.
Deflection system 20 placed in the imaging lens system via 9
A feedback system is constructed so that the difference determined by the arithmetic circuit is zero or a constant value, or the ratio is a constant value. Deflection system 20
The deflection coil need not be placed below the projection lens, but a deflection coil placed inside the objective lens as shown at 21 may also be used.

The above circuit system is related to the X direction, but
Although not shown, a similar circuit system is constructed in a direction perpendicular to this, that is, in the Y direction. in this case,
The slice position and scan position in FIG. 4 are opposite.

In the above configuration, the slice level E ₂ of the comparator circuit 13 is set appropriately (in the center), the specific image portion 5a is positioned in the center on the fixed image pickup plate 7,
The binarization circuit 10 is adjusted so that only the image portion has a "1" signal. Since the signals and clock pulses shown in FIG. 3c and e are introduced into the AND gate 11a, the counter 16a counts the number of clock pulses corresponding to _l1 in FIG. 4 (FIG. 3g). On the other hand, the signals c and f in FIG. 4 and the clock pulse are sent to the AND gate 11b.
As shown in FIG. 3h, a number of clock pulses corresponding to FIG. 4 _l2 are taken out and counted by counter 16b. Both counts are sent to the arithmetic circuit 17,
For example, the difference is required. Now, for example, if the slice position is exactly in the center of the image portion 5a, l ₁ = l ₂
In this case, no output signal is generated from the arithmetic circuit 17. If the image portion 5a moves to the right due to sample drift from this state, l ₁ > l ₂ and t ₁ in Fig. 3g
is larger than t ₂ , and the difference is calculated by the calculation circuit 1.
7, and a deflection voltage such that the difference becomes zero is applied to the deflection system 20. As a result, 5a moves to the left, and the drift of the sample is corrected.

Note that a normal image pickup tube may be used in place of the solid-state image pickup plate 7, and a minute electron beam passage hole 6a may be provided at a suitable location (for example, in the center) of the fluorescent plate 6 as shown in FIG.
2b, place an electron beam detector 22 such as a Faraday cage under it, and scan the electron beam in the X and Y directions using the deflection system 20 or another deflection system. It is also possible to obtain a video signal that changes as follows. Also, the counter 1
If an up-down counter is used in place of 6a, 16b and the arithmetic circuit, the AND gates 11a and 1
The difference in output pulses from 1b can be determined directly.

As is clear from the above description, according to the present invention, a specific position on the display screen in each direction is set as a boundary based on a signal synchronized with the conversion of a specific portion of an image into an electrical signal. A circuit for creating a rising pulse signal and a falling pulse signal creates a reference signal for detecting the position of the specific image area, and outputs an AND circuit of the electrical signal and the rising pulse signal; Since the position of the specific image area is detected with high precision by a circuit that creates a count signal representing the difference or ratio of the pulse width between the electric signal and the AND circuit output of the falling pulse signal, Image drift can be corrected with high precision using a device with a relatively simple structure.

[Brief explanation of the drawing]

FIG. 1 is a block diagram showing one embodiment of the present invention;
FIG. 2 is an enlarged view of a part thereof, FIGS. 3 and 4 are explanatory diagrams of the operation, and FIG. 5 is a diagram showing another example in place of the part shown in FIG. 1: Objective lens, 2: Intermediate lens, 3: Projection lens, 4: Sample, 5: Final image, 6: Fluorescent screen, 7: Solid-state image pickup plate, 8: Synchronization signal generation circuit,
9: Amplifier, 10: Binarization circuit, 11a and 11
b: AND gate, 12: Sawtooth wave generation circuit, 1
3: Comparison circuit, 14: Inversion circuit, 15: Clock pulse generation circuit, 16a and 16b: Counter, 17: Arithmetic circuit, 18: D-A converter, 1
9: DC amplifier, 20: Deflection system.

Claims (1)

[Scope of Claims] 1. A means for forming an electron microscope image on a display screen, and forming a specified image area of the electron microscope image in each of two orthogonal X and Y directions along the display screen. a converting means for converting into an electrical signal that changes over time in the direction, a means for binarizing the electrical signal, and a signal synchronized with the conversion into each of the electrical signals by the converting means. a circuit for creating a rising pulse signal and a falling pulse signal with a specific position in the direction on the display screen as a boundary; an AND circuit output of the electrical signal and the rising pulse signal; and an AND circuit output of the electrical signal and the rising pulse signal; a circuit for creating a counting signal representing the difference or ratio of the pulse width between the falling pulse signal and the AND circuit output; and a circuit for deflecting and moving the electron microscope image so that the counting signal output from the circuit is constant. A drift correction device for an electron microscope, comprising means.