JPH0696710A - Electron microscope provided with automatic focusing function - Google Patents

Abstract

PURPOSE:To provide an electron microscope provided with an automatic focusing function in which any complicated control is made unnecessary by obtaining the correlation between an image signal and a wobbler signal. CONSTITUTION:The focus is adjusted with an image formed in an image formation part 9 by an object lens 6 with a wobbler signal being applied to a first and a second deflection lens 4, 5 for deflecting an electron beam 7 emitted from an electron gun 3. This device is provided with a power supply 10 for the first deflection lens 4, a power supply 11 for the second deflection lens 5, a wobbler signal generator means 14 for applying a wobbler signal to the power supply 10 for the first deflection lens 4 and the power supply 11 for the second deflection lens 5, a detector means 13 for detecting the image signal of an image formed in the image formation part 9, a correlation means 15 for obtaining the correlation between the detected image signal and the wobbler signal and a power supply 12 for an object lens for adjusting the object lens current so that the output of the correlation means 15 is minimized. With this arrangement, a correlation signal which is different in magnitude can be obtained between the focused state and the defocused state, and the focusing can be automatically performed with such a simple operation that only a wobbler image function is turned on.

Description

Detailed Description of the Invention

[0001]

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention applies a wobbler signal to a first deflecting lens and a second deflecting lens for deflecting an electron beam emitted from an electron gun to focus from an image formed on an image forming portion by an objective lens. The present invention relates to an electron microscope having an automatic focusing function configured to perform focusing.

[0002]

2. Description of the Related Art For focusing and astigmatism operation of an electron microscope, a switch for turning on / off a wobbler image function and an objective lens current adjusting knob are provided for coarse adjustment of an objective lens current. There is.
Then, when performing coarse adjustment of the objective lens current, operating this switch to turn on the wobbler image function,
A wobbler signal is applied to the first and second deflection coils,
The current changes periodically. When the focal point is out of focus with respect to this periodic change in current, the image vibrates in the X direction when the X wobbler signal is turned on, and the image when the Y wobbler signal is turned on. It seems to vibrate in the Y direction.
Therefore, at each time, the adjustment knob is operated to adjust the objective lens current to stop the vibration of the image and perform the rough adjustment.

[0003]

However, in the above-mentioned conventional method, the switch for turning on / off the wobbler image function is operated, and the adjustment knob is operated while observing the vibration state of the image to operate the objective lens current. To adjust
There is a problem that the operation becomes complicated. Further, since the adjustment operation relies on intuition, it is difficult to know the relationship between the image vibration state and the adjustment direction of the objective lens current, and there is a problem that extra time is spent for adjustment.

SUMMARY OF THE INVENTION The present invention is to solve the above problems, and an object of the present invention is to provide an electron microscope having an automatic focusing function that correlates a video signal and a wobbler signal and does not require a complicated operation. It is what

[0005]

To this end, according to the present invention, a wobbler signal is applied to a first deflection lens and a second deflection lens for deflecting an electron beam emitted from an electron gun, and the wobble signal is applied to an image forming section by an objective lens. In an electron microscope configured to perform focusing from the image, a power source for the first deflecting lens, a power source for the second deflecting lens, and a wobbler signal for applying a wobbler signal to the power source for the first deflecting lens and the power source for the second deflecting lens. The generating means, the detecting means for detecting the video signal of the image formed on the image forming section, the correlating means for correlating the detected video signal with the wobbler signal, and the objective lens current so as to minimize the output of the correlating means. It is characterized in that a power source for the objective lens for adjustment is provided.

[0006]

In the electron microscope having the automatic focusing function of the present invention, since the correlating means for correlating the detected video signal and the wobbler signal is provided, it is possible to adjust the size depending on whether the image is in focus or not. Different correlation outputs can be obtained, and by adjusting the objective lens current with the power supply of the objective lens so that this correlation output becomes the minimum, the focus can be automatically adjusted by simply turning on the wobbler image function. Matching can be done.

[0007]

Embodiments of the present invention will be described below with reference to the drawings. FIG. 1 is a view showing an embodiment of an electron microscope of the present invention, 1 is an electron microscope, 2 is an electron optical column, 3 is an electron gun, 4 is a first deflection lens, 5 is a second deflection lens, and 6 is Objective lens, 7 is electron beam, 8 is sample, 9 is imaging section,
Reference numeral 10 is a power supply for the first deflection lens, 11 is a power supply for the second deflection lens, 12 is a power supply for the objective lens, 13 is a video signal detector, 14 is a wobbler signal generator, 15 is a correlation circuit, 16
Indicates a fluorescent plate.

In FIG. 1, a first deflecting lens 4 and a second deflecting lens 5 are for deflecting an electron beam emitted from an electron gun 3, and a power source 1 for the first deflecting lens 1 respectively.
0, driven by the power supply 11 of the second deflection lens. The wobbler signal generator 14 applies a wobbler signal to the power source 10 of the first deflecting lens and the power source 11 of the second deflecting lens when the rough adjustment of the objective lens current is performed. The power supply 12 for the objective lens drives the objective lens 6 arranged below the sample 8. The image signal detector 13 places a fluorescent plate 16 on the image forming section 9 and detects the brightness of the image as an image signal. The light shielding plate blocks light from outside the image forming section 9. The correlation circuit 15 controls the power supply 12 of the objective lens by the correlation output by correlating the wobbler signal and the video signal, and this correlation output is the minimum when the focus is achieved.

Next, the operation will be described. FIG. 2 is a diagram showing an image in a focused state and an image in a defocused state, and FIG.
Is a diagram showing a wobbler signal and a video signal, and FIG. 4 is a diagram for explaining output characteristics of the correlation circuit.

First, when the mode is set to the coarse adjustment mode of the objective lens current, the wobbler signal is applied from the wobbler signal generator 14 to the power source 10 of the first deflecting lens and the power source 11 of the second deflecting lens. Therefore, the electron beam 7 emitted from the electron gun 3 receives the first deflection lens 4 and the second deflection lens 5.
The sample 8 is deflected by the wobbler signal applied to the sample 8. The electron beam transmitted through the sample 8 forms an image on the image forming unit 9 by the objective lens 6. At this time, FIG. 2A shows the in-focus state, and in this case, an image is formed at the same position with respect to the deflected electron beam 7 shown by the solid line and the dotted line. However, in the non-focused state, as shown in FIG. 2B, the deflected electron beam 7 shown by the solid line and the dotted line is different in the same image forming unit 9 as in FIG. 2A. Connect the image to the position. Therefore, when the solid-line and dotted-line electron beams are created alternately by the wobbler signal, the image appears to be vibrating in the case of no focus. In this state, if the electric current of the objective lens 6 is adjusted to focus on the image forming unit 9, the image appears to be stationary at the same position.
Even when the sample is removed, the same phenomenon occurs as a spot image of the electron beam.

Therefore, in the electron microscope having the automatic focusing function of the present invention, when a wobbler signal is applied to the power source 10 of the first deflecting lens and the power source 11 of the second deflecting lens to oscillate the image, FIG. As shown in, the signal synchronized with the wobbler signal appears in the video signal detector 13, so that, for example, 18
The wobbler signal and the video signal are correlated with a phase difference of 0 °, and the objective lens current is adjusted by this correlation output for focusing.

As shown in FIG. 4, the correlation output of the correlation circuit 15 is minimum when the object is in focus and has a large value when the object is not in focus. The power is supplied to the objective lens 12, and the objective lens power source 12 adjusts the objective lens current so that the correlation output becomes small, thereby performing focusing.

The present invention is not limited to the above embodiment, but various modifications can be made. For example, in the above-described embodiment, the fluorescent plate is placed on the image forming unit 9 and the image signal of the brightness is detected, but the current amount of the small fluorescent plate for detecting the total light amount of the limited area such as the central portion of the fluorescent plate is measured. Alternatively, a mechanism for extracting only the current in a predetermined area of the fluorescent plate may be provided. Alternatively, the signal of the television camera in the image forming unit 9 may be used.

[0014]

As is apparent from the above description, according to the present invention, the wobbler signal is applied and the video signal of the image formed on the image forming portion by the objective lens is correlated with the wobbler signal. Correlation outputs of different sizes can be obtained depending on whether or not they match, and automatic focusing can be performed by a simple operation of turning on the wobbler image function. Moreover, since the objective lens current is automatically adjusted so that the correlation output signal is minimized, a complicated operation is not required and operability can be improved.

[Brief description of drawings]

FIG. 1 is a diagram showing an embodiment of an electron microscope of the present invention.

FIG. 2 is a diagram showing an image in a focused state and an image in a non-focused state.

FIG. 3 is a diagram showing a wobbler signal and a video signal.

FIG. 4 is a diagram for explaining output characteristics of a correlation circuit.

[Explanation of symbols]

1 ... Electron microscope, 2 ... Electron optical column, 3 ... Electron gun, 4
... first deflection lens, 5 ... second deflection lens, 6 ... objective lens, 7 ... electron beam, 8 ... sample, 9 ... imaging unit, 10 ... first deflection lens power supply, 11 ... second deflection lens power supply 1
2 ... Power supply for objective lens, 13 ... Video signal detector, 14 ...
Wobbler signal generator, 15 ... Correlation circuit, 16 is fluorescent plate

Claims (1)

[Claims] 1. A structure for applying a wobbler signal to a first deflecting lens and a second deflecting lens for deflecting an electron beam emitted from an electron gun to perform focusing from an image formed on an image forming portion by an objective lens. The first electron microscope
Deflection lens power supply, second deflection lens power supply, wobbler signal generating means for applying a wobbler signal to the first deflection lens power supply and second deflection lens power supply, and detection for detecting a video signal of an image formed on the image forming unit. Means, a correlating means for correlating the detected video signal and the wobbler signal, and an objective lens power supply for adjusting the objective lens current so that the output of the correlating means is minimized. An electron microscope with functions.