JPH0955178A - Electron microscope - Google Patents

Abstract

PROBLEM TO BE SOLVED: To perform alignment in the X and Y directions even when wobbler switches in the X and Y directions are concurrently turned on by switching the tilted signal wave-forms in the X and Y directions, and outputting them in turn. SOLUTION: When one or both of wobbler switches(WS) 32, 33 in the X and Y directions are turned on, a signal is outputted from a WS-on detecting NOR circuit 31 to actuate an oscillation circuit 10, and a wobbler wave-form signal is outputted. A WS-state detecting NAND circuit 23 is set to H when only one of the WS 32, 33 is turned on, and it is set to L when both of them are turned on. The output signal of the oscillation circuit 10 enters a signal generating circuit 22 through a frequency dividing circuit 21, and the wobbler signal wave-form in response to the state of the WS-state enters an adder circuit 37 through switching circuits 24, 25 via switching circuits 26, 27 of the rear stage. When both WS 32, 33 are concurrently turned on, the output of the NAND circuit 23 becomes L, the wobbler signals in the X and Y directions are outputted in turn, and alignment can be separately conducted.

Description

Detailed Description of the Invention

[0001]

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to an electron microscope capable of automatically tilting an electron beam during focusing in alternating X and Y directions.

[0002]

2. Description of the Related Art Conventionally, for focusing in an electron microscope, for example, an image wobbler method is used to search for a focal point by overlapping images when a sample is irradiated with a beam having a negative tilt and a beam having a positive tilt. FIG. 4 is a diagram for explaining focusing by the image wobbler method.
When a wobbler switch (not shown) is turned on, a beam tilt signal is added to the condenser lens alignment (CLA) 3 and 4, and the electron beam 2 emitted from the electron gun 1 is alternately swung to minus θ and plus θ to make a sample. 5 is irradiated onto the fluorescent plate 7 by the objective lens 6.
Focusing is performed by forming an image on the upper surface and changing the excitation of the objective lens so that both images coincide with each other while observing this image. This focusing is performed two-dimensionally by turning on the wobbler switch in the X and Y directions.

[0003]

In the current image wobbler method, when the wobbler switches in the X and Y directions are turned on, tilt signals in the X and Y directions are simultaneously generated, and both signals are added. Since the beam is tilted in a curved shape, it is not clear which direction is offset and the wobbler cannot be aligned. The present invention is for solving the above-mentioned problems. Even when the wobbler switches in the X and Y directions are simultaneously turned on, the X direction,
The purpose is to enable axis alignment in the Y direction.

[0004]

According to the present invention, there is provided an oscillation circuit for outputting a wobbler waveform signal when at least one of the wobbler switches in the X direction and the Y direction is turned on, a wobbler waveform output switching circuit, and an axis adjusting volume. The wobbler waveform output switching circuit alternately outputs beam tilt signals when the wobbler switches in the X and Y directions are simultaneously turned on, and axis alignment in each direction can be performed separately. .

[0005]

BEST MODE FOR CARRYING OUT THE INVENTION Embodiments of the present invention will be described below. FIG. 1 is a diagram showing the configuration of a wobbler signal generation circuit used in the electron microscope of the present invention, and FIG. 2 is a waveform diagram for explaining the operation thereof. The wobbler signal generation circuit includes an oscillation circuit 10, a wobbler waveform output switching circuit 20, a comparator 30, a NOR circuit 31 for detecting a wobbler switch ON, X-direction and Y-direction wobbler switches 32, 33, and axis adjusting volumes 34, 35. , Adding circuits 36 and 37, and switches 38 and 39. In addition, the wobbler waveform output switching circuit 20 is set to 1
It is composed of a 1/2 divider circuit 21, a signal generating circuit 22, a wobbler switch state detecting NAND circuit 23, and switching circuits 24 to 27.

When one or both of the X direction wobbler switch 32 and the Y direction wobbler switch 33 are turned on,
A signal is output from the NOR circuit 31 for detecting the wobbler switch ON, the oscillation circuit 10 operates, and the wobbler waveform signal is output (point A signal waveform in FIG. 2A). The NAND circuit 23 for detecting the wobbler switch state becomes "HIGH" when only one of the wobbler switches is turned on, and becomes "LOW" when both of them are turned on (signal waveform at point C in FIG. 2). The output signal of the oscillator circuit 10 (the signal at point A) is 1
The frequency is divided by the 1/2 frequency dividing circuit 21 and added to the signal generating circuit 22. The signal generating circuit 22 outputs a DC level signal or a repetitive pulse signal which is inverted with respect to each other according to the state of the wobbler switch (point D and point E signal waveforms in FIG. 2) and is applied to the switching circuits 24 and 25. . On the other hand, the wobbler waveform output from the oscillation circuit 10 that is shaped into ± 5 V by the comparator 30 (point signal waveform in FIG. 2F)
Is switched by the switching circuits 24 and 25 and added to the switching circuits 26 and 27 in the subsequent stage.

When the wobbler switches 32 and 33 are turned on, the switching circuits 26 and 27 are turned on to output the outputs from the preceding switching circuits 24 and 25 to the adder circuits 36 and 37, respectively. This is for setting the output level applied to the adder circuits 36 and 37 to 0 when 32 and 33 are turned off. For example, when only the X-direction wobbler switch 32 is turned on (period T1 in FIG. 2T), the signal generation circuit 22 outputs the signal from the NAND circuit 23 (potential at point C) is “HIGH”.
The DC level is output from the
At this time, the G point becomes "LOW", but since the wobbler switch 33 is OFF, the H point becomes "HIGH".
Therefore, the relay of the switching circuit 27 is turned off, the relay of the switching circuit 26 is turned on, and the wobbler signal waveform is added only to the adding circuit 36 (period T1 in FIG. 2T).
2I signal waveform in FIG. Further, when only the Y-direction wobbler switch 33 is turned on (period T2 in FIG. 2T), the output of the NAND circuit 23 (potential at the point C) is “H”.
Since the DC level is output from the signal generation circuit 22 because of "IGH", both the D point and the E point become "HIGH" and the H point becomes "LOW", but the wobbler switch 32 is turned off.
Therefore, point G is "HIGH", and switching circuit 2
The relay of 6 is turned off, the relay of the switching circuit 27 is turned on, and the wobbler signal waveform is added only to the addition circuit 37 (the signal waveform of point J in FIG. 2T in the period T2).

On the other hand, when the X-direction and Y-direction wobbler switches 32 and 33 are simultaneously turned on (period T3 in FIG. 2T), the output of the NAND circuit 23 (potential at the point C) is "LOW". The signal generating circuit 22 outputs repetitive pulses which are inverted to each other (point D and point E in FIG. 2), and as a result, the relays of the switching circuits 24 and 25 are alternately turned on.
N / OFF to alternately output the wobbler waveform signal at the F point, and since the G point and the H point both become "LOW", the relays of the switching circuits 26 and 27 are turned on, and as a result, the switching circuits 24 and 25 are turned on. The wobbler waveform signal alternately output from is added to the adding circuits 36 and 37 (point I and point J signal waveforms in FIG. 2T in the period T3). The lens drive voltages are applied to the adder circuits 36 and 37 from the X-direction and Y-direction axis adjustment volumes 34 and 35, respectively, and the signal obtained by adding the wobbler signal thereto is applied to the CLA coil through the switches 38 and 39. , The volume is adjusted and the axis is adjusted. When the X-direction and Y-direction wobbler switches are turned off in the focused state, the wobbler signal is not applied to the adding circuits 36 and 37, and only the volume-adjusted lens drive voltage is applied to the CLA coil. The switches 38 and 39 are turned on.
It is supposed to close with.

The X-direction and Y-direction axis-alignment signals thus output are respectively X-axis-dependent as shown in FIG. 3 (a).
In addition to CLA coil and YCLA coil, Fig. 3 (b)
Tilt the beam as shown in. At this time, even when the X-direction and Y-direction wobbler switches are turned on at the same time, since the X-direction and Y-direction wobbler signals are alternately output, the axes can be adjusted separately.
It should be noted that the axis alignment may be performed by a manual adjustment method in which the volume is manually adjusted while observing the image. Alternatively, for example, a minus tilt image signal and a plus tilt image signal at the time of beam tilt are detected and subtracted from each other. It is possible to use any of the automatic adjustment methods in which the shift amount is obtained and the volume is adjusted so that the shift amount is eliminated.

[0010]

As described above, according to the present invention, the gradient signal waveform is switched in the X direction and the Y direction and alternately output. Therefore, the wobbler switches in the X direction and the Y direction are simultaneously turned on. Even in this case, the axes of the beams can be separately adjusted.

[Brief description of drawings]

FIG. 1 is a diagram showing a configuration of a wobbler signal generation circuit used in an electron microscope of the present invention.

FIG. 2 is a waveform diagram for explaining the operation.

FIG. 3 is an explanatory diagram of application of a beam tilt signal.

FIG. 4 is an explanatory diagram of an image wobbler method.

[Explanation of symbols]

10 ... Oscillation circuit, 20 ... Wobbler waveform output switching circuit, 21 ... Dividing circuit, 22 ... Signal generating circuit, 23 ... NA
ND circuit, 24-27 ... Switching circuit, 30 ... Comparator, 31 ... NOR circuit, 32 ... X-direction wobbler switch, 33 ... Y-direction wobbler switch, 34 ... X
Direction axis adjusting volume, 35 ... Y direction axis adjusting volume, 36, 37 ... Adder circuit, 38, 39 ... Switch.

Claims (1)

[Claims] 1. An electron microscope equipped with X-direction and Y-direction wobbler switches, wherein the wobbler switch is turned on to generate a beam tilt signal for axis alignment, and an X-direction and Y-direction wobbler switch is provided. Are ON at the same time
An electron microscope comprising a wobbler waveform output switching circuit that alternately outputs a beam tilt signal when the above is performed.