JPH0395841A - Electron microscope - Google Patents

Abstract

PURPOSE:To allow smooth adjustment of a focal point and an axis while shifting a magnification in observation into a high level by keeping the shift of an image constant, regardless of any magnification, in observation on a displaying means when signals are supplied to lens means or a deflecting means. CONSTITUTION:In a memory attached to a CPU 13, data are stored which show magnification in observation and the amplitude of wobbling signals. The wobbling signals which are produced by the CPU 13 through the read-out of the data have different amplitude values corresponding to a magnification in observation. The amplitude values of the signals are set so that the shift of an image on a display device can be kept constant regardless of any magnification. On this account, in case of adjusting a diaphragm axis using a wobbler while shifting a magnification in observation into a high level, the shift of the image is kept always constant to allow smooth adjustment of the axis.

Description

DETAILED DESCRIPTION OF THE INVENTION Field of the Invention The present invention relates to electron microscopes, and more particularly to electron microscopes with wobblers for focusing or axial alignment.

[Prior Art] Conventionally, when focusing an electron microscope, a wobbler that periodically changes the excitation current of an objective lens is used to slightly move an electron microscope image displayed on a cathode ray tube or fluorescent screen. The objective lens excitation current value that minimizes the amount of image movement is found. Also, when aligning the electron beam axis, a wobbler is used to periodically change the excitation current of the objective lens to slightly move the formed electron microscope image, causing the image to change concentrically. The axis is aligned so that In addition, there is a type of wobbler that uses a deflector to periodically change the incident angle of the electron beam that enters the sample, and in this case, the objective is Focusing is performed by changing the excitation current of the lens.

[The problem that the invention seeks to solve.] XJ] When the wobbling signal for adjustment as described above is supplied to the objective lens or deflector at a constant amplitude regardless of the observation magnification, as the image magnification is increased to a higher magnification, the signal on the cathode ray tube or fluorescent Since the amount of movement of the image on the plate increases, the moved image comes off the cathode ray tube or fluorescent screen, making it difficult for the observer to perform focusing and axis alignment while viewing the image.

The present invention takes the above-mentioned problems into consideration and aims to provide an electron microscope equipped with a focusing or axis alignment device that can adjust the wobbler signal to an optimal value depending on the observation magnification of the electron microscope. .

[Means for Solving the Problems] The present invention provides an electron gun, a lens means and a deflection means for irradiating a sample with an electron beam emitted from the electron gun, and a means for displaying an image of the sample. an electron microscope comprising: signal generating means for supplying a periodically changing excitation signal or deflection signal to the lens means or deflection means; In an electron microscope in which focusing or axis alignment is performed by a wobbler that monitors the amount of movement of an image displayed on the display means, means for changing the amplitude of the signal in conjunction with the observation magnification of the electron microscope. The present invention is characterized in that the amount of movement of the image observed on the display means when the signal is supplied to the lens means or the deflection means is substantially constant regardless of the magnification.

[Example] Hereinafter, an example of the present invention will be described based on the drawings. 1st
The figure is an apparatus configuration diagram for explaining one embodiment of the present invention.

In FIG. 1, reference numeral 1 denotes an electron gun, and an electron beam emitted from the electron gun is focused by a focusing lens 2 and then irradiated onto a sample 5 by an objective lens 3. 6x, 6y
are horizontal and vertical deflection lenses for horizontally and vertically scanning the electron beam on the sample 5, and the lens 6x
, 6y are supplied with horizontal and vertical apparatus signals from a scanning signal generating circuit 7 via a magnification setting circuit 13. The horizontal and vertical device signals from the scanning signal generating circuit 7 are also supplied to the horizontal and vertical deflection coils 9x and 9y of the cathode ray tube 8. Secondary electrons generated by irradiating the sample 5 with the electron beam are detected by a secondary electron detector 10. The detector 1
After the output signal from 0 is amplified by the amplifier 11,
It is supplied to the grid G of the cathode ray tube 8. Moreover, the CPU 1 is connected to the objective lens 3 via a DA converter 15.
A lens power supply 4 is connected to the lens power supply 3, and the power supply 4 is configured to change the excitation value of the objective lens based on a control signal from the CPU 13.

Now, when the observation magnification of the electron microscope is set on the CPU 3 by an operation terminal (not shown), a control signal is supplied from the CPU to the magnification setting circuit 12.

Based on the magnification control signal, the scanning signal supplied from the scanning signal generation circuit 7 to the magnification setting circuit 12 is converted into a scanning signal corresponding to the set magnification, and then supplied to the deflection lens. Here, the CPU is controlled by an operation terminal (not shown).
For example, by using a wobbler in I3, the objective lens aperture 14
When an operation command is issued to align the axis of C.
The PU 13 outputs a positive focus value f. as shown in FIG. 2(a).
, positive and negative binary values f. 10Δfl. fo−△f. A wobbling signal that periodically changes between the two directions is generated, and the wobbling signal is supplied to the objective lens 3. At this time, if the objective lens aperture 14 is not placed at an appropriate position, the image displayed on the cathode ray tube 8 will move in synchronization with the wobbling signal. Therefore, the axis of the aperture is aligned so that the movement of the image changes concentrically. Here, the positive focus value f as shown in FIG. 2(a) is used. When a wobbling signal that periodically changes between positive and negative binary values (fo+fl, fo-Δft) is supplied to the objective lens, the magnification of the electron microscope image changes discretely.

The memory attached to CP013 stores data representing the observation magnification and the amplitude of the wobbling signal. This data is read out, and the wobbling signal generated by the CPU 1B based on the data has an amplitude value that differs depending on the observation magnification.

For example, the signal shown in FIG. 2(b) shows a wobbling signal when the observation magnification is higher than the observation magnification at which the wobbling signal shown in FIG. 2(a) is used, and the amplitude value of the signal is The magnification is also set so that the amount of movement of the image on the display device is approximately constant. Therefore, when adjusting the aperture axis using a wobbler while changing the observation magnification to a high magnification, the amount of movement of the image is always kept constant, so the axis alignment can be performed smoothly.

Note that the above-described embodiment is only one embodiment of the present invention, and the present invention can be implemented with various modifications.

For example, in the embodiments described above, an axis alignment device for a scanning electron microscope has been described, but the present invention can also be implemented in an axis alignment device for a transmission electron microscope. In addition, in the case of a transmission electron microscope, in addition to supplying a wobbling signal to the objective lens, the angle of incidence of the electron beam that enters the sample is periodically changed to minimize the amount of movement of the formed electron microscope image. The present invention can also be practiced when focusing is performed by changing the excitation current of the objective lens.

In addition, in the embodiment described above, positive and negative 2
Although the wobbling signal that periodically changes between two values is formed as a square wave, the wobbling signal may be a sawtooth wave or a step wave that changes positive or negative around the positive focus value.

Further, in the above embodiment, the amplitude of the wobbling signal is changed according to the magnification based on the stored data, but the amplitude may be controlled to a value determined by calculation.

[Effects of the Invention] As is clear from the above description, according to the present invention, an electron gun, a lens means and a deflection means for irradiating a sample with an electron beam emitted from the electron gun, and a means for displaying an image; signal generating means for supplying a periodically changing excitation signal or deflection signal to the lens means or deflection means; In an electron microscope, focusing or axis alignment is performed by a wobbler that monitors the amount of movement of an image displayed on the display means when the deflection means is supplied, the signal is adjusted in conjunction with the observation magnification of the electron microscope. means for changing the amplitude of the signal, so that when the signal is supplied to the lens means or the deflection means, the amount of movement of the image observed on the display means is approximately constant regardless of the magnification. Therefore, the amount of movement of the image does not change as the image magnification changes, and when performing focusing and axis alignment while changing the observation magnification to a high magnification, adjustment work can be performed smoothly.

[Brief explanation of drawings]

FIG. 1 is an apparatus configuration diagram for explaining an embodiment of the present invention, and FIG. 2 is a diagram for explaining a wobbling signal. 1: Electron gun 2: Focusing lens 3: Objective lens 4: Lens power supply 5: Sample 6x, 6y dual deflection lens 7: Scanning signal generation circuit 8: Cathode ray tube 9x, 9y: Deflection coil 10: Secondary electron detector 11: Amplifier 13: CPU 12: Magnification setting circuit 14: Objective lens aperture

Claims (1)

[Claims] (1) An electron microscope comprising an electron gun, lens means and deflection means for irradiating a sample with an electron beam emitted from the electron gun, and means for displaying the sample image, signal generating means for supplying a periodically changing excitation signal or deflection signal to the lens means or deflection means; and a signal generating means for supplying a periodically changing excitation signal or a deflection signal to the lens means or deflection means; In an electron microscope in which focusing or axis alignment is performed by a wobbler that monitors the amount of movement, means is provided for changing the amplitude of the signal in conjunction with the observation magnification of the electron microscope, and the signal is detected by the lens means or An electron microscope characterized in that the amount of movement of an image observed on the display means when supplied to the deflection means is substantially constant regardless of the magnification.