JPH0479138A - Exb-type energy filter - Google Patents

Abstract

PURPOSE:To satisfy imaging codition without astigmatism constantly for an unkown effective filter length by installing a means to apply either positive or negative optional voltage between magnetic poles. CONSTITUTION:Magnetic poles l, 1' which are tilted are connected with a yoke 3 through an electrical insulator 4 and the magnetic poles and the yoke are connected magnetically, and voltage -V2 from an electric power source is applied between the magnetic poles 1, 1'. Working voltage +V1, -V1 from an electric power source 7 is applied between electrodes 2, 2', and if the voltage -V1 applied to said electrode 2' satisfies -V1>-V2, quadrupole components of an electric field are generated and a1 term to obtain images without astigmatism in a Wien filter is obtained. The value of the a1 term is able to be altered from outside by adjusting the voltage to applied to the magnetic poles 1, 1'. The conditions for imaging without astigmatism for an unkown effective filter length are thus satisfied.

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 Various structures have been proposed for such energy filters, but the energy filters used by connecting or inserting them into the optical axis of an electron microscope, etc. are shown in Figures 4 (a) to (C).
The explanation will be based on.

The energy filter shown in Fig. 4(a) is provided with an electric field and a magnetic field that are orthogonal to each other with respect to the optical axis of the electron beam, and by canceling the deflection effect of the electron beam due to the electric field with the deflection effect due to the magnetic field, the energy filter It is constructed so that only electrons with a specific energy within the line travel straight. Here, the inter-pole distance between the two magnetic pole pieces 1, 1' and the inter-electrode distance between the two electrodes 2, 2' are preferably equal to or equal to each other. Note that Z is the optical axis of the energy filter, which coincides with the optical axis of the electron microscope.

According to the configuration shown in FIG. 4(a), the Wien condition can be satisfied not only inside the energy filter but also in the fringe field, that is, the electron beam entrance and exit portions of the energy filter. In other words, in an energy filter, charged particles must travel straight,
When the electric field is E1, the magnetic field is B, and the velocity of the charged particle is V,
The Vienna condition of Emv.B must be satisfied. However, both ESB and V are vectors.

However, when using electric and magnetic fields that are similar to the above, the electron beam is either focused in the direction of the electric field or has no focusing effect in the direction of the magnetic field, as shown in Figure 5(a). Because of the divergence, even if a circular beam is incident on the energy filter, an arc-shaped beam will be emitted. In order to compensate for this drawback, a gradient magnetic field type filter as shown in FIG. 4(b) and an arc electrode type filter as shown in FIG. 4(c) have been proposed. In these filters, the electric field E
x, magnetic field BY, using the following formula Ex-Eo (1+a, x+a2 x2+・) Formula ■
B 3/ -B o (1+b + '/ + b
2 y2+ -) When expressed by formula (■), the b1 term or the 81 term is added, and this component delays the convergence effect in the X direction, and also causes the convergence effect in the It is known that by using the term or the b1 term or a combination of both vertices, an image without astigmatism with matching trajectories in the x and X directions as shown in FIG. 5(b) can be obtained. 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 H Now, if we examine the distribution of the electric field and magnetic field created by the energy filter shown in Figure 4(b) in the Z-axis direction, we will see that the magnetic field is distributed between the magnetic poles as shown in Figure 6. The electric field changes slowly at the large pole edges, whereas the electric field changes quickly because the electrode gap is narrow.

In this way, when the magnetic pole gap and the electrode gap are different, the way the magnetic field is attenuated at the edges is different, and the Wien condition is satisfied only at the center of the filter, so that the incident electron beam is attenuated at the edges. The beam will be greatly deflected, and will proceed in an arbitrary direction within the filter in a portion away from the optical axis. Therefore, it is considered a problem that the orbit results cannot be obtained as predicted by calculation.

As mentioned above, the setting of the 81 term or the b1 term to achieve astigmatic imaging in the Wien filter is determined by the filter length, but this value is actually related to the range of the edge. However, it is difficult to determine clearly. Further, the effective filter length varies depending on the positional relationship between the filter on the object plane P and the image plane I, and differs from the mechanical length of the actual filter length. Therefore, the energy filter that realizes the astigmatism-free imaging condition is based on the electrode and magnetic pole shapes obtained through simulation, and experimentally changes the inclination of the magnetic pole pieces to find the magnetic pole pieces that have the least astigmatism. This was achieved through a selection method.

In consideration of the above-mentioned problems, the present invention provides an E×B type main energy filter that has a function that can always satisfy the astigmatism-free imaging condition even for an unknown effective filter length. The purpose is

[Means for Solving the Problems] The first invention is an E×B type energy filter in which an electric field and a magnetic field are formed orthogonally to each other, and an arbitrary positive or negative voltage is applied between the magnetic pole pieces. It is characterized by the provision of means.

A second aspect of the present invention is an E×B main energy filter in which an electric field and a magnetic field are formed orthogonally to each other, and the magnetic pole piece pair is maintained at a reference potential, and the voltage applied to the electrode is It is characterized by the provision of a power supply for independently changing the reference voltage.

[Example] Hereinafter, an example of the present invention will be described based on the drawings. 1st
The figure is a configuration diagram for explaining an embodiment of the first invention,
FIG. 2 is a diagram for explaining an embodiment of the second invention,
3(a) and 3(b) are diagrams for explaining the electric field distribution of the ExB type energy filter according to the present invention.

First, the first invention will be explained based on FIG. In Figure 1, 1.1- is a magnetic pole piece, 2.2' is an electrode, 3 is a yoke, 4 and 5 are electrical insulators, 6 is an excitation coil,
7 is an electric field power supply, and 8 is a power supply between magnetic pole pieces.

The tilted pole piece 1.1- is connected to the yoke 3 via an electrical insulator 4, and the pole piece and the yoke are magnetically connected. A voltage -2 is applied from a power source 8 to the magnetic pole pieces 1, 1-. Here, electrode 2,
Operating voltages +V, -V, are applied from the power source 7 between electrodes 2', and the voltage -1 applied to the electrodes 2' is -V, >
-V2, a quadrupolar acid component of the electric field as shown in FIG. 3(a) is generated, and the term a shown in the above equation 0 is obtained. By adjusting the voltage applied to these magnetic pole pieces 1 and 1', the value of term 81 can be changed externally, so that the astigmatic coupling condition is always satisfied for an uncertain effective filter length. I can do it.

Next, the second invention will be explained based on FIG. In FIG. 2, 1 and 1' are magnetic pole pieces, 2 and 2- are electrodes, and 7a and 7b are electric field power supplies.

The pair of magnetic pole pieces 1, 1' are both grounded and at a reference potential V. is maintained. Positive and negative voltage elements 1 and -Vl are respectively applied to the electrodes 2.2' from power sources 7a and 7b which are changed independently with respect to the potential of the magnetic pole piece 1.1'. In this way, by applying the voltages applied to the electrodes 2 and 2' so that they can be adjusted independently of the potential applied to the pole piece 1.1', a voltage as shown in FIG. 3(b) can be obtained. A quadrupolar acid component of the electric field is generated, and the 81 term shown in the above equation 0 is obtained. By adjusting the voltages applied to electrodes 2 and 2' individually, the value of term 81 can be changed externally, so the astigmatism-free coupling condition is always satisfied for uncertain effective filter lengths. I can do it.

[Effects of the Invention] As is clear from the above description, according to the first invention, in the E×B type energy filter in which the electric field and the magnetic field are formed orthogonally to each other, there is a positive or negative polarity between the magnetic pole pieces. By providing a means for applying an arbitrary voltage, it is now possible to change the value of the a□ term from the outside, and the astigmatism-free imaging condition is always satisfied for an uncertain effective filter length. be able to.

According to the second aspect of the present invention, in an E×B type energy filter in which an electric field and a magnetic field are formed orthogonally to each other, the pair of magnetic pole pieces is maintained at a reference potential, and the voltage applied to the electrodes is By providing a power supply to vary the value independently from the reference voltage, it is now possible to change the value of item 81 from the outside, and there is no stigma at all times for uncertain effective filter lengths. Imaging conditions can be satisfied.

[Brief explanation of the drawing]

FIG. 1 is a configuration diagram for explaining an embodiment of an E×B type energy filter according to the first invention. FIG. 2 is a configuration diagram for explaining an embodiment of the E×B type energy filter according to the second invention, and FIG. 3(a) (
b) is a diagram for explaining the electric field distribution of the E×B type energy filter according to the present invention, FIGS. 4(a) to (C) are diagrams for explaining the conventional E×B type energy filter,
5A and 5B are diagrams showing electron trajectories within the energy filter, and FIG. 6 is a diagram illustrating the electric field distribution and magnetic field distribution at the edge groups of the energy filter. 1.1 Two magnetic pole pieces 2.2-: Electrode yoke Electric insulator Excitation coil Electric field power supply Power supply between the magnetic pole pieces

Claims (2)

[Claims] (1) E× where the electric field and magnetic field are formed orthogonally to each other
An E×B type energy filter characterized in that the B type energy filter is provided with means for applying a positive or negative arbitrary voltage between the magnetic pole pieces. (2) E× where the electric field and magnetic field are formed orthogonally to each other
The B-type energy filter is characterized in that a power source is provided for maintaining the pair of magnetic pole pieces at a reference potential and for varying the voltage applied to the electrodes independently of the reference voltage. type energy filter.