JPH0479139A - Exb-type energy filter - Google Patents

Abstract

PURPOSE:To prevent the disorder of electric field distribution owing to the presence of magnetic poles made of a metal magnetic material by putting magnetic poles divided by planes rectangular to an electric field in the electric field rectangularly and applying electric voltage controllably to the magnetic poles with the same polarity as the voltage applied to the electrodes of the electric field nearest each of the divided magnetic poles and lower than that applied to the electric field electrodes. CONSTITUTION:Magnetic poles 1a, 1b and magnetic poles 2a, 2b divided by planes rectangular to an (x) direction of an electric field are put in the opposite each other rectangularly to the electric field. Voltage +Va, -Va with the same polarity of voltage +V or -V applied to the electrodes 3 or 3' of an electric field nearest each of the magnetic poles and at highest one second of voltage applied to the electrodes of the electric field is applied to each of the divided magnetic poles from electric power sources 8a, 8b for magnetic poles. Consequently, the electric field distribution formed by the voltage +V and -V applied to the electrodes 3, 3' of the electric field can be corrected by voltage value +Va, -Va applied to the magnetic poles la, 2a and the magnetic poles 1b, 2b and parallel degree to the x-axis is improved and uniform electric field distribution is obtained.

Description

DETAILED DESCRIPTION OF THE INVENTION [Field of Industrial Application] The present invention relates to an E×B type energy filter having a superimposed field in which an electric field and a magnetic field are formed orthogonally to each other.

[Prior Art] Conventionally, an E×B type energy filter (hereinafter simply referred to as an energy filter) is known, which performs energy analysis by orthogonalizing an electric field and a magnetic field and causing charged particles to travel straight in a direction perpendicular to this superimposed field. It is being Although various structures of such energy filters have been proposed, an energy filter used by being connected or inserted into the optical axis of an electron microscope, etc. will be explained based on FIGS. 3(a) to (c). . In Fig. 3, 10.10- is a magnetic pole piece,
11.11- is an electric field electrode.

The energy filter shown in Fig. 3(a) applies an electric field and a magnetic field perpendicular to each other to the optical axis 2 of the charged particle beam, cancels the deflection of the charged particles due to the electric field with the deflection due to the magnetic field, and absorbs the incident charged particle beam. It is configured so that particles with a certain energy are selectively moved straight.

According to the configuration shown in FIG. 3(a), the Wien condition can be satisfied not only inside the energy filter but also in the fringe field, that is, the entrance and exit parts of the electron beam in the energy filter. In other words, in an energy filter, charged particles must travel straight,
When the electric field is E, the magnetic field is 85, and the velocity of the charged particle is V,
The Vienna condition of Emv.B must be satisfied. However, both E and BSV are vectors.

However, when a charged particle beam, for example an electron beam, is incident on an energy filter using an electric field and a magnetic field similar to the electric field and magnetic field as shown in FIG. is converged, but diverges without having a convergence effect in the direction of the magnetic field, so even if an electron beam with a circular cross section is incident on an energy filter, an arc-shaped electron beam, that is, an electron beam with astigmatism will be emitted. It will be done. In order to compensate for this drawback, a gradient magnetic field type filter as shown in FIG. 3(b) and an arc electrode type filter as shown in FIG. 3(c) have been proposed. In these filters, the electric field Ex and the magnetic field By are expressed as follows: Ex = E o (1+
a , x 10a 2 x 2+-) Formula ■By-B
o (1+b, y+b2y2+-) When expressed by formula (■), the b1 term or the 81st term is added, and this component delays the convergence effect in the X direction, and also causes the convergence effect in the X direction, It is known that by using an appropriate 31 term or b1 term or a combination of both vertices, it is possible to obtain an image without astigmatism with matching trajectories in the x and X directions as shown in FIG. 4(b). Note that the value of the 81 term or the b1 term that provides this astigmatic imaging is determined by the filter length.

[Problem to be solved by the invention] In the energy filter as described above, normally only the above-mentioned terms 82 and b1 are taken into consideration when designing, but the magnetic pole piece made of a metal magnetic material such as iron and copper When determining an example of each of the above coefficients for an energy filter consisting of electrodes made of non-magnetic metal materials such as 83 terms and b1 terms, a, =0.005 mm-', b
z -0,275 mm-', whereas the 82nd term and b2 term are a2-0.039 mm-', b2--
It is 0.0022 mm-'. Here, if we pay attention to the values (absolute values) of the 82nd term and the b2 term, we can see that the value of the 82nd term is one or more orders of magnitude larger than the b2 term. In this way, when the 82 term has a large value, the electric field distribution inside the filter differs in magnitude between the center of the magnetic pole and the periphery, as shown by the broken line in Figure 5, and the electron beam is slightly deviated from the optical axis. However, if the electrons are incident at a different position, the electron trajectory within the filter will be disturbed, making it impossible to selectively pass electrons with the desired energy along the optical axis.

The reason for the non-uniformity of the electric field distribution is that, first, by tilting the magnetic pole pieces, the surface area of one electrode becomes smaller. Second, although the formation of a magnetic field contributes only to the opposing magnetic pole pieces, the formation of an electric field is caused by the fact that, in addition to the electrodes to which voltage is applied, the magnetic pole pieces at ground potential are placed approximately parallel to the electric field. It is thought that the situation is disrupted in a negative way.

The present invention has been made in consideration of the above-mentioned problems, and an object of the present invention is to provide an E×B type energy filter that can reduce disturbances in electric field distribution due to the presence of magnetic pole pieces made of metal magnetic material.

[Means for Solving the Problems] The present invention provides an E×B type energy filter in which an electric field and a magnetic field are formed orthogonal to each other, in which magnetic pole pieces divided by a plane orthogonal to the electric field are arranged orthogonal to the electric field. At the same time, a voltage having the same polarity as the voltage applied to the electric field electrode closest to each magnetic pole piece and lower than the voltage applied to the electric field electrode is applied to each of the divided magnetic pole pieces in an adjustable manner. It is characterized by what it did.

[Embodiments] Hereinafter, embodiments of the present invention will be described based on the drawings. 1st
The figure is a block diagram of an E×B type energy filter according to an embodiment of the present invention, and FIG. 2 is a diagram for explaining a method of applying voltage to each electrode and a magnetic pole piece.

1 and 2, 1alb, 2a, 2b are magnetic pole pieces, 3.3' are electrodes, 4a, 4b are yokes, 5, 6
7 is an excitation coil, 7 is an electric field power supply, and 8a and 8b are power supplies for between magnetic pole pieces.

A magnetic pole piece 1a divided by a plane perpendicular to the electric field direction
, lb and the magnetic pole pieces 2a, 2b are arranged facing each other orthogonally to the electric field. The magnetic pole pieces 1a and 2a are the yoke 4a
The magnetic pole pieces 1b and 2b are connected to both ends of the yoke 4.
The magnetic pole pieces 1a and 1b are excited by the excitation coil 5 to generate an S pole, and the magnetic pole pieces 2a and 2b are excited by the excitation coil 6 to generate an N pole. Here, the excitation coil 5°6 is electrically insulated from the yokes 4a and 4b. Each of the divided magnetic pole pieces is applied with a voltage +
Voltages +Va and -Va, which have the same polarity as V or =■ and are less than half of the voltage applied to the electric field electrodes, are applied from the power supplies 8a and 8b for between the pole pieces.

Note that the angle of inclination of the tilted magnetic pole pieces 1a, lb, and 2a2b is related only to the value of the third term in equation (2), and can be treated independently from the derivation of the 82nd term and the b2 term. In FIG. 2, the method of applying voltage to each electrode and pole piece is explained based on a simplified diagram of the structure of the electrode and pole piece, ignoring the inclination of the pole piece.

In the case of an energy filter with the configuration shown in Figure 2 1
．． The electric field electrode has a six-pole configuration. Therefore, electric field electrode 3.
The distribution of the electric field formed by the voltage +V and V applied to the pole piece 1a.

2a and the voltage value +Va applied to the magnetic pole pieces 1b, 2b
, -Va, and the parallelism with respect to the X axis is improved as shown by the solid line in FIG.

In this way, even if there is a magnetic pole piece made of a metallic magnetic material, disturbances in the electric field distribution can be corrected from the outside, so the value of the above-mentioned equation 82 can be made extremely small.

Note that the embodiment described above is only one embodiment of the present invention, and the present invention can be implemented with various modifications. For example, in the embodiment described above, the excitation coils 5 and 6 are passed between the yokes 4a and 4b to excite the divided magnetic pole pieces, or the magnetic pole piece 1 connected to the yoke 4a is
a, 2a and magnetic pole pieces 1b, 2 connected to the yoke 4b.
Coils that individually excite b may be provided on the yoke 4a side and the yoke 4b side.

Further, in the above-described embodiment, the electric field electrodes 33' are configured as a pair of electrodes facing each other, but the electrodes may be configured as two pairs of divided electrodes. in this case,
The voltage applied to each electrode is adjusted independently.

[Effects of the Invention] As is clear from the above description, the present invention provides an E×B type energy filter in which an electric field and a magnetic field are formed orthogonally to each other, in which magnetic pole pieces are divided by a plane orthogonal to the electric field. A voltage that is arranged perpendicular to the electric field and has the same polarity as the voltage applied to the electric field electrode closest to each of the divided magnetic pole pieces, and is lower than the voltage applied to the electric field electrode. By adjusting the application of 8
The value of the second term can now be changed externally, and a uniform electric field distribution can be obtained.

[Brief explanation of the drawing]

Fig. 1 is a configuration diagram of an E×B type energy filter according to an embodiment of the present invention, Fig. 2 is a diagram for explaining the method of applying voltage to each electrode and magnetic pole piece, and Fig. 3 (a) ~(c
) is a diagram for explaining the conventional E×B type energy filter, Figures 4(a) and (b) are diagrams showing the trajectory of electrons within the energy filter, and Figure 5 is a diagram showing the electric field distribution within the energy filter. It is a figure for explaining. la, lb, 2a, 2b: magnetic pole piece 3.3-: electrode 4a 4b: yoke 5.6: excitation coil 7; electric field power source 8a, 8b: power source between magnetic pole pieces

Claims (1)

[Claims] In an E×B type energy filter in which an electric field and a magnetic field are formed orthogonally to each other, magnetic pole pieces divided by a plane perpendicular to the electric field are arranged perpendicular to the electric field, and each divided magnetic pole piece has An E×B type energy filter characterized in that a voltage having the same polarity as the voltage applied to the electric field electrode closest to each magnetic pole piece and lower than the voltage applied to the electric field electrode is applied in an adjustable manner.