JPS5916705B2 - scanning transmission electron microscope - Google Patents

Description

DETAILED DESCRIPTION OF THE INVENTION The present invention relates to a scanning transmission electron microscope that displays a scanning transmission image based on a transmission electron detection signal obtained when an electron beam is scanned over a sample.

Contrast in a normal high-resolution transmission electron microscope depends greatly on phase contrast, and to obtain the highest contrast, shift the focus by a small amount △f from just focus to underfocus. It is also well known that it is necessary to shift.

However, depending on the magnitude of the defocus amount Δf, the resolution and image quality of the sample image differ significantly.

In normal cases, it is not possible to detect changes in image quality due to the amount of defocus by observing images on a fluorescent plate. The photograph is taken and the photograph with the best image quality, that is, the photograph with the optimum contrast, is selected.

Even in high-resolution scanning transmission electron microscopes, contrast (as in the case of ordinary transmission electron microscopes mentioned above), depends largely on phase contrast.

In such a scanning transmission electron microscope, since the image is directly displayed on the cathode ray tube, the amount of defocus can be set relatively easily, but the image quality and resolution are still affected by changes in the amount of defocus. The problem still exists that changes cannot be clearly seen until a series of many photographs are taken.

SUMMARY OF THE INVENTION The present invention aims to solve the above-mentioned problems and provide an apparatus that can easily obtain an image with optimal contrast. , a scanning power supply that generates a scanning signal for two-dimensionally scanning the electron beam on the sample, a transmission electron detector for detecting electrons transmitted through the sample, and a scanning signal ζ from the scanning power supply. a cathode ray tube for displaying a sample image based on a signal ζ from the detector; a control scanning signal generation circuit that generates a scanning signal for scanning the cathode ray tube based on the scanning signal so that transmission scanning images corresponding to each focus position are displayed side by side in independent areas on the screen; means for specifying an arbitrary position from among a plurality of focus positions; and scanning signals supplied to the cathode ray tube from the control scanning signal generation circuit in conjunction with the specification of the focus position by the specifying means. The present invention is characterized in that it includes means for checking to switch from the signal to the scanning signal from the scanning power source.

FIG. 1 is a block diagram showing an embodiment of the basic configuration of the present invention, and 1 indicates an electron gun.

The electron beam from this electron gun is transmitted through a focusing lens 2 and an objective lens 3.
is focused on the sample 4.

Two stages (or one stage may be sufficient) of deflection coils 5a and 5b are installed between the focusing lens 2 and the objective lens 3, and a scanning power supply 6 is provided.
Both horizontal and vertical sawtooth signals are supplied.

Therefore, the electron beam is scanned two-dimensionally over the sample 4.

From this scanning number, the electrons transmitted through each point of the sample are detected by the detector I.
The output signal is amplified by an amplifier 8 and then introduced into a brightness modulation grid of a cathode ray tube 9.

Horizontal and vertical sawtooth wave signals are introduced from the scanning power supply 6 to the deflection coil 10 of the cathode ray tube through an adder circuit 11, so that a transmitted scanning electron image of the sample 4 is displayed on the screen of the cathode ray tube. That will happen.

Reference numeral 12 denotes a DC power supply for the objective lens 3, which can continuously vary the excitation current, thereby changing the focus position of the electron beam.

Close to this objective lens, a ° auxiliary coil 13 is provided, which is supplied with a step signal for defocusing from a step wave generator 14, and which changes the focal length of the objective lens 3 and thus
The focus position of the electron beam is varied minutely.

This step generator is synchronized with the scanning power supply 6, and for example, a signal is sent to the circuit 14Il every horizontal scan, and the output is increased (decreased) in steps.

A part of the output of this step wave generating circuit is supplied to the adder circuit 1.
1 and is summed with the horizontal sawtooth signal from the scanning power supply mentioned above.

Incidentally, the vertical sawtooth wave signal is not added to the stepwise wave, but is arranged so that a signal having the same period as the signal supplied to the deflection coils 5a, 5b# is sent to the deflection coil 10# of the cathode ray tube 9. There is.

Further, the output signal of the step wave generator 14 is transmitted through a variable resistor 15.
It is possible to arbitrarily vary the defocus step amount by adjusting the defocus step amount.

Fig. 2 shows the output signals of each main circuit of the apparatus shown in Fig. 1 and the screen of the cathode tube 9. and the addition circuit 11 (this is sent.

Figure b shows the output signal of the staircase wave generator 14 that changes stepwise in synchronization with this horizontal sawtooth wave, and is repeated at a fixed number of steps (for example, five).

This signal is sent to the addition circuit 11 and also to the auxiliary coil 13 of the objective lens, and the focus is varied in a stepwise manner.

In FIG. 2C, the signals a and b are added at the output of the adder circuit 11, and as can be seen from the figure, a signal having a period five times that of FIG. 8 is converted into a signal.

Since this signal is supplied to the deflection coil of the cathode ray tube 9, the electron beam on the sample is horizontally scanned five times for one horizontal scan of the cathode ray tube 91.

Since the focus position is changed for each horizontal scan, when one vertical scan is completed, an image as shown in FIG. 2d is displayed on the cathode ray tube.

Each of the image areas A, B, C, D, and E in Fig. 2d is an image corresponding to a different focus position, and assuming that the dashed line in Fig. 2 is in just focus,
Area C is the image, A and B are underfocus images, and E is overfocus images.

By contrastively observing these images, the focus position that provides the optimum contrast can be determined.

FIG. 3 shows an embodiment of the present invention that allows an image at the optimal focus position to be instantaneously developed over the entire screen from the state shown in FIG. 2 d. The reference numerals indicate the same components, and the stepwise wave generating circuit 14 is shown in a more specific form.

The step wave generation circuit 14 includes an up counter (or down counter) 16, a count hold circuit 11, and a D-A
It is composed of a converter 18 and an amplifier 19.

The up counter 16 has a constant count value (for example, 5).
# When this is reached, something is used that resets the count and starts counting again.

The count hold circuit 17 is designated with a count value to hold by the designation circuit 20, for example, when 14'' is designated, the count hold circuit 17 continues to hold that value after the count value reaches that value.

The digital signal that came out through the hold circuit is D-A
It is converted into an analog signal by a converter 18, and two parts are sent to the adder circuit 11 via a switch S, and the other part is sent to an auxiliary coil 13ζ of the objective lens 3 via an amplifier 19.

On the other hand, the output of the scanning power supply 6 is sent to the deflection coils 5a, 5b, and also to the adder circuit 11 or the amplifier 21 via the changeover switch S2.

This amplifier 21 has a gain such that each horizontal scan covers a predetermined area (for example, the entire screen), and therefore, when a horizontal scanning signal is supplied to the deflection coil 10 through this amplifier, Only a single image appears on the cathode ray tube screen.

Therefore, if you want to obtain an image with the optimum contrast, first reset the designated circuit 20 (or set it to 0FF), then the counter 16 will not work because the count hold circuit will not work.
The count value is then converted into an analog signal by the DA converter 18, and a step signal is output.

In conjunction with the reset of the designated circuit, the switch S1 is connected, and the changeover switch S2 is connected to the addition circuit side.

As a result, the same circuit as shown in FIG. 1 is formed, and images as shown in FIG. 2d are obtained on both sides of the cathode ray tube 90.

While observing this image, adjust the variable resistor 15 to vary the amount of defocus A, B, and C.

Try to obtain the best image in either area D or E.

Now, assuming that region B is the best, I21 is designated by the designation circuit 20, and the hold circuit continues to hold the count value 121.

Therefore, the output of the DA converter 18 becomes a constant value corresponding to the count value 121, and the focus of the objective lens is fixed to the state ζ of the B area.

In conjunction with the designation by the designation circuit 20, the switch S
1 is turned off, and the selector switch S2 is switched to the amplifier 21 side.

As a result, the scanning power supply 6 is connected to the deflection coil 10 of the cathode ray tube 9.
The horizontal scanning signal from the sample is supplied as is, and only the sample image shown in B of FIG. 2d is displayed on the screen.

With the configuration detailed above, a plurality of scanned transmission images with minutely different focus positions can be contrastively displayed on a single cathode ray tube, making it extremely easy to obtain images with optimal contrast.
In addition to being able to know this, an image with the optimum contrast can be instantly expanded and observed on the entire screen, and operability can be greatly improved.

[Brief explanation of the drawing]

Fig. 1 is a diagram showing an embodiment of the basic configuration of the present invention, Fig. 2 is a diagram showing signals from each circuit, and Fig. 3 is a diagram showing an embodiment of the basic configuration of the present invention.
The figure is a diagram for showing one embodiment of the present invention. DESCRIPTION OF SYMBOLS 1... Electron gun, 2... Focusing lens, 3... Objective lens, 4... Sample, 5a, 5b and 10... Deflection coil, 6... Scanning power supply, 7... Detection Vessel, 9...
Cathode ray tube, 11...addition circuit, 13...auxiliary coil, 14...step wave generation circuit.

Claims (1)

[Claims] 1. A focusing lens for focusing the electron beam onto the sample, a scanning power source for generating a scanning signal for two-dimensionally scanning the electron beam on the sample, and a scanning power source for detecting the electrons that have passed through the test ISI. In an apparatus including a transmission electron detector and a cathode ray tube for scanning based on a scanning signal from the scanning power source and displaying a sample image based on the signal from the detector, the focus position of the focusing lens is determined. a switching means for repeatedly switching over multiple stages; and a scanning signal for scanning the cathode ray tube so that transmission scanning images corresponding to each focus position are displayed side by side in independent areas on the screen. a control scanning signal generation circuit that can be created based on the
A means for specifying an arbitrary position from among the plurality of focus positions, and a scanning signal to be supplied to the cathode ray tube from the control scanning signal generation circuit in conjunction with the specification of the focus position by the specifying means. A scanning transmission electron microscope characterized in that it comprises means for switching from a scanning signal from the scanning power supply to a scanning signal from the scanning power supply.