JPH10134745A - Method and apparatus for controlling current density of electron beam - Google Patents

Abstract

PROBLEM TO BE SOLVED: To control a current density of an electron beam with excellent reproducibility without varying a radiation range of the electron beam on a sample by disposing aperture means having a fine opening on an optical path of the electron beam to be emitted from an electronic gun. SOLUTION: An electron beam emitted from an electron gun 5 is projected on a fixed beam limiting 6, passes a fine opening 7 formed at the beam limiting 6, and then, is radiated on a sample via a focusing lens. In this case, the radiated position of the electronic beam on the beam limiting 6 and the position of the opening 7 are moved relatively to each other, so that a current density of the electron beam passing the opening 7 is controlled. Consequently, it is possible to eliminate an influence of hysteresis of the focusing lens and to control the current density of the electron beam with excellent reproducibility. the radiation range of the electron beam on the sample always becomes the same despite of variation of the current density since the size of the fine opening 7 is not varied. If a deflection quantity of the electron beam is increased, the current of the electron beam passing the fine opening 7 becomes zero, thereby enlarging a dynamic range of the current density control.

Description

DETAILED DESCRIPTION OF THE INVENTION

[0001]

The present invention relates to a method and an apparatus for controlling the current density of an electron beam for controlling the current density of an electron beam irradiated on a sample in an electron microscope or the like.

[0002]

2. Description of the Related Art For example, a sample is irradiated with an electron beam,
A transmission electron microscope for observing a projected image by enlarging electrons transmitted through a sample requires a function of changing the current density of an electron beam applied to the sample. In this case, the current density of the electron beam is changed by changing the excitation of the focusing lens system arranged in front of the sample and changing the degree of convergence of the electron beam on the variable diaphragm.

FIG. 1 is a diagram for explaining the principle of a system for controlling the current density of an electron beam by such a focusing lens, and 1 is a focusing lens. A variable stop 2 is arranged below the focusing lens 1. Here, from the state where the electron beam as shown by the solid line is focused by the focusing lens 1, the excitation of the focusing lens 1 is strengthened and the electron beam is focused as shown by the dotted line. Is spread, and the current density of the electron beam passing through the opening 3 is reduced.

Conversely, by weakening the excitation of the focusing lens 1 and changing the state of the electron beam from a solid line to a dashed line, the current density of the electron beam passing through the aperture 3 increases. In this method, not only the excitation of the focusing lens 1 can be varied, but also the current density can be changed by moving the diaphragm 2 and arranging apertures 4 of different sizes on the electron beam optical path.

[0005]

In the above-mentioned electron beam current density control method, even if the excitation of the focusing lens is changed under the influence of the asymmetric hysteresis of the focusing lens 1 and the original excitation is returned again, the focusing lens is not affected. The field strength according to 1 will not be the same as in the initial state. Therefore, the reproducibility of the position of the electron beam irradiated on the sample is deteriorated under the influence of the horizontal deflection magnetic field due to the asymmetric hysteresis.

Further, the current density of the electron beam is set to 0 (pA /
cm ² ), and there is a problem that the variable range of the current density is narrow. Furthermore, since the excitation of the focusing lens 1 is changed, the opening angle of the electron beam passing through the aperture 3 of the diaphragm 2 changes, and there is also a problem that the irradiation range of the electron beam on the sample varies depending on the current density.

Further, when the aperture 2 having different sizes is arranged on the optical path of the electron beam by mechanically moving the stop 2, the irradiation range of the electron beam on the sample changes. Therefore, a focusing lens must be further provided near the variable stop 2, and the excitation of the focusing lens must be controlled so that the irradiation range is constant.

SUMMARY OF THE INVENTION The present invention has been made in view of the above circumstances, and has as its object to control the current density of an electron beam without changing the irradiation range of the electron beam on a sample with good reproducibility. An object of the present invention is to realize a method and an apparatus for controlling the current density of an electron beam.

[0009]

According to a first aspect of the present invention, there is provided a method of controlling a current density of an electron beam, wherein a diaphragm having a minute aperture is arranged on an optical path of an electron beam from an electron gun.
The present invention is characterized in that the electron beam is irradiated onto the aperture means, and the irradiation position of the electron beam and the position of the opening are relatively moved to control the current density of the electron beam passing through the opening.

According to the first aspect of the present invention, the irradiation position of the electron beam on the aperture means having the minute opening is relatively moved between the position of the minute opening and the current density of the electron beam passing through the opening. Control.

According to a second aspect of the present invention, there is provided a method of controlling a current density of an electron beam according to the first aspect of the present invention, wherein an electron beam deflecting means is provided on an upper stage of the aperture means, and the electron beam deflecting means controls an electron beam irradiation position and an aperture. Is relatively moved with respect to the position.

According to the second aspect of the invention, the electron beam deflecting means relatively moves the irradiation position of the electron beam and the position of the aperture to control the current density of the electron beam. Claim 3
According to a second aspect of the present invention, there is provided a method for controlling a current density of an electron beam, wherein the deflecting means is a two-stage deflecting means.

According to the third aspect of the present invention, the irradiation position of the electron beam and the position of the opening are relatively moved by the two-stage electron beam deflecting means to control the current density of the electron beam. According to a fourth aspect of the present invention, there is provided a method of controlling a current density of an electron beam according to the first aspect of the present invention, wherein the stop means is mechanically moved to relatively move the electron beam irradiation position and the aperture position. It is characterized by doing.

According to the fourth aspect of the present invention, the current density of the electron beam is controlled by moving the stop means mechanically and relatively moving the irradiation position of the electron beam and the position of the aperture. According to a fifth aspect of the present invention, there is provided a method for controlling a current density of an electron beam.
The invention according to claim 1 is characterized in that the electron gun is tilted so that the irradiation position of the electron beam and the position of the opening are relatively moved.

In the present invention, the current density of the electron beam is controlled by relatively moving the irradiation position of the electron beam and the position of the aperture. According to a sixth aspect of the present invention, there is provided an electron beam current density control apparatus comprising: two-stage deflecting means for deflecting an electron beam from an electron gun; and a diaphragm means having an electron beam passage opening provided behind the deflecting means. A deflection controller for supplying a deflection signal to the two-stage deflection means, wherein the deflection controller adjusts the electron beam so that the electron beam is always deflected at the pseudo occurrence point by the two-stage deflection means. And a second adjuster for controlling the deflection angle of the electron beam.

According to a sixth aspect of the present invention, there is provided a first adjuster for adjusting the deflection angle of the electron beam so as to be always deflected at the pseudo-occurrence point by the two-stage deflection means, and a second adjuster for controlling the deflection angle of the electron beam. The current density of the electron beam is controlled by the deflection angle of the electron beam.

[0017]

Embodiments of the present invention will be described below in detail with reference to the drawings. FIG. 2 shows an example of a configuration for implementing the electron beam current density control method according to the present invention, and 5 is an electron gun. The electron beam EB generated from the electron gun 5 is projected on a fixed stop 6. Fixed aperture 6
The electron beam that has passed through the small aperture 7 provided in the aperture stop 10 is focused by the focusing lenses 8 and 9, and
The sample 12 is irradiated with the electron beam passing through the sample 1.

Between the electron gun 5 and the fixed stop 6, two-stage deflection coils 13 and 14 are arranged. FIG. 3 shows an example of a deflection controller 15 that supplies a deflection signal to the two-stage deflection coils 13 and 14.

In the deflection controller 15, a signal from a signal source 16 is supplied to a deflection balance adjuster 19 via an adder 17 and an amplifier 18. Deflection balance adjuster 1
9 is supplied to the deflection coil 13 via the amplifier 20.
Supplied to The other signal is supplied to the deflection coil 14 via the amplifier 21.

A signal from the current density adjuster 22 is supplied to the adder 17 via a changeover switch 23. The operation of such a configuration will now be described. The electron beam generated from the electron gun 5 is deflected by the deflection coils 13 and 14 and is projected on the fixed stop 6. The electron beam passing through the minute aperture 7 provided in the fixed stop 6 is
The electron beam focused by 9 and passed through the opening 11 of the variable aperture 10 irradiates the sample 12.

The electrons transmitted through the sample 12 are magnified by an objective lens, an intermediate lens, and a projection lens (not shown) and are projected on a fluorescent plate, so that a transmitted image of the sample is obtained on the fluorescent plate.

Here, the electron beam generated from the electron gun 5 is deflected by the deflecting coils 13 and 14, and this deflection is caused by A which is a pseudo source of the electron beam from the electron gun 5.
It is adjusted to be deflected at points. This adjustment is performed by adjusting the deflection balance adjuster 19 in a state where the changeover switch 23 of the deflection controller 15 is turned off.
14 by adjusting the balance of the signal intensities supplied to.

After the above adjustment, the changeover switch 23 is turned on.
Is connected to the current density adjuster 22, and the signal from the current density adjuster 22 is supplied to the adder 17. When the deflection coil 13, 14 responds to the signal, the electron beam starts at the point A. Is deflected as

FIG. 4 shows the state of deflection of the electron beam starting from point A (FIG. 4A) and the current density distribution of the electron beam generated from the electron gun 5 (FIG. 4B). Is shown. When the signal from the current density adjuster 22 is applied to the adder 17, the electron beam is deflected from the solid line state in FIG. 4A to the dotted line state.

The current density distribution of the electron beam generated from the electron gun 5 has a substantially Gaussian distribution as shown in FIG. The vertical axis of FIG. 4A indicates the current density. Therefore, if the electron beam having the maximum current density passes through the aperture 7 of the fixed stop 6 in the state of the solid line in FIG. 4A, the current density of the electron beam passing through the aperture 7 due to the deflection of the electron beam becomes When the electron beam gradually decreases and largely deflects the electron beam, the current amount of the electron beam passing through the opening 7 can be finally reduced to zero.

As described above, the two-stage deflection coils 13 and 14
The current density of the electron beam passing through the aperture of the aperture 6 can be continuously changed by changing the magnitude of the deflection signal supplied to the aperture and changing the deflection angle of the electron beam at the point A.

In this case, since the signal intensity from the current density adjuster 22 is merely changed, the current density of the electron beam can be controlled with good reproducibility without being affected by the hysteresis of the focusing lens. Since the size of the aperture 7 of the fixed stop 6 does not change, the irradiation range of the upper electron beam is always the same even when the current density is changed.

If the deflection amount of the electron beam is increased, the current amount of the electron beam passing through the opening 7 becomes zero,
The dynamic range of the control of the current density becomes wide. When the irradiation range of the electron beam on the sample 12 is changed, the variable stop 10 may be mechanically moved, and openings having different sizes may be arranged on the optical path of the electron beam.
In that case, there is no change in the current density of the electron beam applied to the sample 12.

In the example shown in FIG.
The electron beam is deflected to change the current density of the electron beam passing therethrough. However, if the position of the opening 7 and the irradiation position of the electron beam on the stop 6 are relatively moved, the current of the electron beam is similarly changed. Density can be changed. Therefore,
The fixed stop 6 may be moved mechanically without deflecting the electron beam. Of course, if the electron gun 5 is tilted, the emission direction of the electron beam is changed, and the same result can be obtained by deflecting the electron beam.

Although the embodiment of the present invention has been described in detail, the present invention is not limited to this embodiment. For example, the present invention has been described using the example of the transmission electron microscope, but the present invention can be applied to other electron beam devices such as a scanning electron microscope.

[0031]

According to the first aspect of the present invention, the irradiation position of the electron beam on the aperture means having a minute opening and the position of the minute opening are relatively moved, and the current of the electron beam passing through the opening is changed. Because the density is controlled, the current density of the electron beam can be controlled with good reproducibility without being affected by the hysteresis of the focusing lens, and the irradiation range of the electron beam on the sample is determined by the size of the aperture of the stop. Since there is no change in the current density, it is always equal even if the current density is changed. Further, if the deflection amount of the electron beam is increased, the current amount of the electron beam passing through the opening 7 becomes 0, and the dynamic range for controlling the current density becomes wider.

According to the second and third aspects of the present invention, the electron beam deflecting means relatively moves the irradiation position of the electron beam and the position of the aperture to control the current density of the electron beam. The same effect as that described above can be obtained, and since the control is not mechanical control, the current density of the electron beam can be easily and accurately controlled.

According to the fourth aspect of the present invention, the stop means is mechanically moved to relatively move the irradiation position of the electron beam and the position of the aperture to control the current density of the electron beam. The same effect as in the item 1 can be obtained.

According to the fifth aspect of the invention, the current density of the electron beam is controlled by relatively moving the irradiation position of the electron beam and the position of the aperture, so that the same effect as the first aspect can be obtained. .

According to the sixth aspect of the present invention, there is provided a first adjuster for adjusting the deflection so as to be always deflected at the pseudo-occurrence point by the two-stage deflection means, and a second adjuster for controlling the deflection angle of the electron beam. The current density of the electron beam is controlled by the deflection angle of the electron beam.
The same effect can be obtained.

[Brief description of the drawings]

FIG. 1 is a diagram for explaining the principle of a conventional electron beam current density control method.

FIG. 2 is a diagram showing an example of a configuration for implementing a current density control method according to the present invention.

FIG. 3 is a diagram showing a specific configuration of a deflection controller.

FIG. 4 is a diagram showing electron beam deflection and current density distribution.

[Explanation of symbols]

 Reference Signs List 5 Electron gun 6 Fixed aperture 7 Micro aperture 8, 9 Focusing lens 10 Variable aperture 11 Aperture 12 Sample 13, 14 Deflection coil 15 Deflection controller 16 Signal source 17 Adder 18, 20, 21 Amplifier 19 Deflection balance adjuster 22 Current density Regulator 23 switch

Claims (6)

[Claims] An aperture means having a minute aperture is arranged on the optical path of an electron beam from an electron gun. The aperture means is irradiated with an electron beam, and the irradiation position of the electron beam and the position of the aperture are determined. A current density control method for an electron beam, wherein the current density is controlled by relatively moving the electron beam through an aperture. 2. An electron beam current according to claim 1, wherein an electron beam deflecting means is provided at an upper stage of the diaphragm means, and the electron beam deflecting means relatively moves an electron beam irradiation position and an aperture position. Density control method. 3. The deflecting means is a two-stage deflecting means.
The method for controlling a current density of an electron beam according to the above. 4. The electron beam current density control method according to claim 1, wherein the aperture means is mechanically moved to relatively move the irradiation position of the electron beam and the position of the aperture. 5. The method for controlling the current density of an electron beam according to claim 1, wherein the electron gun is tilted to relatively move an electron beam irradiation position and an aperture position. 6. A two-stage deflecting unit for deflecting an electron beam from an electron gun, a diaphragm unit provided behind the deflecting unit with an electron beam passage opening, and a deflection signal supplied to the two-stage deflecting unit. A first controller for adjusting the electron beam so that the electron beam is always deflected at the quasi-occurrence point by the two-stage deflecting means, and a deflection controller for controlling the deflection angle of the electron beam. A current density control device for an electron beam, comprising a second regulator.