JPS5829571B2 - Sample moving device in electron microscope - Google Patents

Description

DETAILED DESCRIPTION OF THE INVENTION The present invention automatically corrects changes in the moving direction of a sample image on a fluorescent screen due to the rotation of the sample image that occurs when changing the excitation of the imaging lens system in an electron microscope. The present invention relates to a sample moving device that can always move in a fixed direction regardless of excitation changes in an imaging lens system.

In general, in an electron microscope using a magnetic field type electron lens, a sample image projected onto a fluorescent screen is rotated due to a change in magnification, focus current, etc. due to the rotation effect caused by the magnetic field of the electron beam.

Therefore, the moving direction of the sample image on the fluorescent screen when the sample is moved changes every time the magnification, etc. is changed, making it difficult for the operator to predict the direction and making the operation extremely troublesome.

The present invention aims to solve such inconveniences, and the principle of the present invention will be explained in detail below with reference to FIGS. 1a and 1b.

FIG. 1a shows the coordinates on the sample, which can be moved in the X-Y directions by the sample moving mechanism.

FIG. 1 also shows the locations x-y on the fluorescent screen.

Considering the case where both coordinates match at a certain reference magnification Mo, if the sample is moved, for example, by Xo in the X direction, the sample image on the fluorescent screen will be moved by MO-Xo in the X direction.

When the magnification is changed from Mo to Mo, the coordinates of the sample image become x/y/ rotated by θ on the fluorescent screen.

Therefore, when the sample is moved Xo in the X direction, the sample image is
'It will move in the force direction Ml·Xo.

At this time, in order to eliminate the shift in the moving direction of the sample image, the sample needs to be moved Xo in a direction rotated by 1θ, as shown by the dotted line P in FIG. 1A.

Here, the amount of movement Xo of the sample indicated by P is the amount of movement Xo-cosθ in the X direction and the amount of movement in the Y direction -Xo-31
It can be decomposed into nθ.

Therefore, operate the X-direction sample moving mechanism to move the sample in the
If the sample is moved by -Xo-5inθ in the Y direction via the Y direction sample moving mechanism in conjunction with the o-cosθ movement, the sample can be moved Xo in the direction rotated by 1θ.

Similarly, when the Y-direction sample moving mechanism is operated to move the sample in the Y direction by Yo-cos θ, the sample is also moved in the X-direction by Yo-31nθ.

FIG. 2 is a schematic diagram illustrating one embodiment of an apparatus based on the principles of the present invention.

In the figure, 1 is a mirror body of an electron microscope, and an electron gun 2 is provided above the mirror body.

The electron beam generated from the electron gun is narrowly focused by a focusing lens 3 and irradiated onto a sample 4, and the electron beam transmitted through the sample is enlarged and imaged by an imaging lens system consisting of an objective lens 5, a projection lens 6, etc. , a sample image is projected onto the fluorescent screen 7.

Reference numeral 8 denotes a lens control circuit for controlling excitation currents of the objective lens 5 and projection lens 6, respectively.

9 is a memory circuit for storing the magnitude and direction (polarity) of the rotation angle θ of the sample image at each magnification determined by the objective lens 5 and the projection lens 6, and a signal corresponding to the magnification to be observed from the lens control circuit 8; By introducing the rotation angle and direction, a signal corresponding to the rotation angle and direction is read out.

The direction stored at this time is the direction opposite to the rotation direction of the sample image rotating on the fluorescent screen 1.

Reference numeral 10 denotes a moving stage on which the sample 4 is placed, and the moving stage is movable along the X-axis by an X-direction drive pulse motor 11X, and is movable along the X-axis by a Y-direction drive pulse motor 11Y. It is configured to be movable along the Y axis orthogonal to the Y axis.

Both pulse motors are controlled by pulse signals from pulse conversion circuits 12X and 12Y.

13X and 13Y are potentiometers for specifying the positions in the X and Y directions, respectively, and one of the two potentiometers
The output from 3X is supplied to correction circuits 14X and 15Y,
The output from 13Y is also supplied to correction circuits 14Y and 15X.

In the correction circuits 14X and 14Y, the cosine of the rotation angle θ from the storage circuit 9 is taken and the potentiometer 1 is
perform multiplication with the respective output signals from 3X and 13Y;
In other words, Xo-cos θ and Yo-cos described in Fig. 1
In addition, in the correction circuits 15Y and 15X, the sine of the rotation angle θ from the storage circuit 9 is taken and multiplied by the respective output signals from the potentiometers 13X and 13Y, that is, -Xo- as described in FIG. 81nθ and Yo-81nθ
seek.

The output signals from the correction circuits 14X and 15X are introduced into the X-direction addition circuit 16X, where they are added together, and then sent to the arithmetic circuit 1.
Introduced in 7X.

Similarly, the output signals from the correction circuits 14Y and 15Y are introduced into the Y-direction adding circuit 16Y and added.
It is introduced into the arithmetic circuit 17Y.

The arithmetic circuits 17X and 17Y are adder circuits 16X and 16
It is used to detect changes in the output signal from Y, and has a memory function.

Signals corresponding to the changes detected by the arithmetic circuits 17X and 17Y are sent to the pulse conversion circuits 12X and 12Y via gates t-18X and 18Y, respectively, and are converted into the number of pulses corresponding to the changes.

The gates N8X and 18Y are opened and closed by signals from the detection circuit 19, and the potentiometers 13X and 13
It is configured to open only when a change in voltage occurs by operating either one of Y.

Furthermore, when changing the magnification, each correction circuit 14X, 14Y, 15
The rotation angle θ of X, 15Y changes, and the arithmetic circuits 17X, 1
7Y is detected, but if potentiometers 13X and 13Y are not operated at this time, gate 1 will be detected.
8X.

Since 18Y is kept closed, the sample does not move even if the sample image rotates by an angle θ.

The operation of such a device will be explained.

First, when the observation magnification of the sample is set to the reference magnification Mo, that is, the magnification such that the coordinates on the sample and the coordinates on the fluorescent screen match, the memory circuit 9 outputs the correction circuits 14X and 14Y.

A rotation angle signal corresponding to zero degrees is sent to 15X and 15Y.

Here, when the rotation angle θ is zero, the value of the sine is zero, so the signals from the correction circuits 15X and 15Y are zero.

At this time, the voltage is changed to X by operating the X-direction potentiometer 13X.

If the arithmetic circuit 17X is increased by
θ, that is, a change corresponding to Xo is detected, and the gate 18
The signal is introduced into the pulse conversion circuit 12X via X.

As a result, the pulse motor 11X is driven and the sample 4 or
Move by Xo in the direction.

Similarly, by operating the Y-direction potentiometer 13Y, the sample 4 moves in the Y-direction.

Next, when the lens control circuit 8 is operated to change the observation magnification from the reference magnification Mo to a certain magnification M, the rotation angle θ of the sample image at the magnification M1 and its polarity are introduced from the storage circuit 9.

At this time, the voltage of the X direction potentiometer 13X is changed to
When increased by o, the arithmetic circuit 17X becomes Xo-c.
A change corresponding to osθ is detected and the pulse drinking circuit 12
At the same time as being sent to X, -X is also sent to the arithmetic circuit 12Y.
A change corresponding to o - sin θ is detected and sent to the pulse conversion circuit 12Y.

Therefore, the sample 4 is connected to the pulse motor 11 as shown in FIG. 1a.
Since it moves by Xo-cos θ in the X direction by X and also moves by -Xo-sin θ in the Y direction by the pulse motor 11Y, the base is rotated by an angle -θ around the X axis as shown by P. Move by Xo in the direction.

As a result, the sample image projected onto the fluorescent screen 7 moves in the X direction already shown in FIG. 1, and there is no deviation in the moving direction due to a change in magnification.

Here, when the rotation angle θ of the sample image is, for example, 90 degrees, the value of the cosine in the correction circuits 14X, 14Y, 15X, and 15Y is zero, and the value of the sine is 1.

Therefore, when the X-direction potentiometer 13X is operated, a change of -Xo is detected only in the arithmetic circuit 17Y.
Move by -Xo in the direction.

Similarly, by operating the Y-direction potentiometer 13Y, the sample moves by Yo in the X direction, which is the direction that cancels the rotation of the sample image.

With the above configuration, the present invention can automatically correct the change in the moving direction of the sample image due to the rotation of the sample image, so even if the magnification is changed, the moving direction of the sample image is always constant. Field selection can be done very easily, etc.
It has great practical effects.

It should be noted that the above description is an illustration of the present invention, and many modifications can be made in implementing the invention.

For example, we have described the case where the rotation angle of the sample image at each magnification is stored as a previously measured value using a memory circuit, but for example, the magnetomotive force in the imaging lens system is measured using a Hall element etc. The rotation angle may be measured each time and the value may be sent to the correction circuit.

Further, although the case where analog control is used to specify the sample position in the X and Y directions is shown, digital control is also possible.

[Brief explanation of drawings]

FIGS. 1A and 1B are diagrams for explaining the present invention in detail, and FIG. 2 is a schematic structural diagram showing one embodiment of the present invention. In Fig. 2, 1 is a mirror body, 2 is an electron gun, 3 is a focusing lens, 4 is a sample, 5 and 6 are objective and projection lenses, 7 is a fluorescent screen, 8 is a lens control circuit, 9 is a storage circuit, and 10 is a movement 11X and 11Y are pulse motors, 12X and 12Y
is a pulse conversion circuit, 13X and 13Y are potentiometers, and 14X. 14Y, 15X and 15Y are correction circuits, 16X and 16
Y is an adder circuit, 1γX and 17Y are arithmetic circuits, 18X and 18Y are gates, and 19 is a detection circuit.

Claims (1)

[Claims] 1. A lens system that forms an image of the electron beam transmitted through the sample, and a sample moving means that moves the sample two-dimensionally in a plane substantially orthogonal to the electron beam optical axis, and the direction of movement of the sample by the sample moving means A sample moving device for an electron microscope, characterized in that the sample moving device for an electron microscope is provided with means for changing the excitation current according to a change in the excitation current of the imaging lens system.