JP2856518B2 - Ex-B type energy filter - Google Patents

Description

Description: TECHNICAL FIELD The present invention relates to an E × B type energy filter having a superposition field in which an electric field and a magnetic field are formed orthogonal to each other.

2. Description of the Related Art Conventionally, an E × B type energy filter (hereinafter simply referred to as an energy filter) that performs energy analysis by orthogonalizing an electric field and a magnetic field and advancing charged particles in a direction orthogonal to the superimposed field is known. Have been. Although various structures of such an energy filter have been proposed, an energy filter used by being connected or inserted into an optical axis of an electron microscope or the like is shown in FIGS.
Description will be made based on (c).

The energy filter shown in FIG. 4 (a) is provided with an electric field and a magnetic field that are orthogonal to the electron beam optical axis.
By deflecting the electron beam deflecting action by the electric field by the magnetic field deflecting action, only the electrons having a specific energy in the incident electron beam are made to go straight. Here, the distance between the pole pieces between the two pole pieces 1, 1 'and the distance between the electrodes between the two electrodes 2, 2' are substantially or preferably equal. 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 entrance and exit of the electron beam in the energy filter. That is, in the energy filter, the charged particles need to travel straight, and when the electric field is E, the magnetic field is B, and the speed of the charged particles is v, the Wien condition of E = v · B must be satisfied. However, E, B, and v are all vectors.

However, when a uniform electric and magnetic field is used for the electric and magnetic fields, the electron beam is converged in the direction of the electric field as shown in FIG. Therefore, even when a circular beam is incident on the energy filter, an arc-shaped beam is emitted. In order to make up for this drawback, a gradient magnetic field type filter as shown in FIG. 4 (b) and an arc-shaped electrode type filter as shown in FIG. 4 (c) have been proposed. These filters use an electric field
When Ex, magnetic field By, is expressed by the following expression Ex = E ₀ (1 + a ₁ x + a ₂ x ² + ...) expression By = B ₀ (1 + b ₁ y + b ₂ y ² + ...) expression, b ₁ term or a ₁ term is added to each of them, and this component delays the convergence in the x direction and y
Converging action of the direction is generated by a combination of suitable a ₁ Section or b ₁ wherein or both terms, as shown in FIG. 5 (b)
It is known that an image without astigmatism in which the trajectories in the x and y directions are matched can be obtained. Note that a ₁ that gives this astigmatic imaging
The value of the term or b ₁ term is determined by the filter length L.

[Problems to be Solved by the Invention] By examining the distribution of the electric field and the magnetic field produced by the energy filter as shown in FIG. 4 (b) in the Z-axis direction, the magnetic field is as shown in FIG. Changes slowly at the edge of the large pole, while the electric field shows a rapid change due to the narrow electrode gap.

As described above, when the gap between the magnetic pole and the gap between the electrodes is different, the manner of attenuation of both fields at the edge is different, the Wien condition is satisfied only at the center of the filter, and the incident electron beam is at the edge field. Is largely deflected in the filter, and travels in a direction away from the optical axis in an arbitrary direction in the filter. Therefore, it is a problem that the orbital result as predicted by the calculation cannot be obtained.

For achieving stigmatic imaging in Wien filter as described above, the configuration of a ₁ Section or b ₁ term is determined by the filter length L, in the range said value is spanning the edge field in practice Is also relevant, and it is difficult to ask for it clearly. The effective filter length also differs depending on the positional relationship between the object plane P and the filter on the image plane I, and the actual filter length L
Different from the mechanical length of For this reason, the energy filter that realizes the astigmatic imaging condition uses the pole piece with the least astigmatism by experimentally changing the inclination of the pole piece based on the electrode and pole shape obtained by simulation. This was realized by the method of selection.

An object of the present invention is to provide an E × B type energy filter having a function capable of always satisfying an astigmatic imaging condition even for an unknown effective filter length in consideration of the above-described problems. And

[Means for Solving the Problems] According to a first aspect of the present invention, there is provided an E × B type energy filter in which an electric field and a magnetic field are formed orthogonal to each other. It is characterized in that means for applying any positive or negative equal voltage to both are provided.

According to a second aspect of the present invention, in the first aspect, there is provided a power source for independently changing a voltage applied to each of the pair of electrodes forming the electric field with respect to a voltage applied to the pole piece pair. It is characterized by having been provided.

[Example] Hereinafter, an example of the present invention will be described with reference to the drawings. FIG. 1 is a block diagram for explaining one embodiment of the first invention, FIG. 2 is a diagram for explaining one embodiment of the second invention, and FIGS. FIG. 4 is a diagram for explaining an electric field distribution of an E × B type energy filter according to the present invention.

First, the first present invention will be described with reference to FIG. In FIG. 1, 1,1 'is a pole piece, 2,2' is an electrode,
Is a yoke, 4 and 5 are electrical insulators, 6 is an exciting coil, 7 is an electric field power supply, and 8 is a power supply between pole pieces.

The inclined pole pieces 1, 1 'are connected to a yoke 3 via an electrical insulator 4, and the pole pieces and the yoke are magnetically connected. Then, the voltage -V ₂ is applied from the power source 8 to the magnetic pole piece 1, 1 '. Here, operating voltages + V ₁ , −V ₁ are applied between the electrodes 2, 2 ′ from the power supply 7, and the applied voltage −V ₁ to the electrode 2 ′ has a relationship of −V ₁ > −V _2. if, quadrupole component of the electric field as shown in FIG. 3 (a) is generated, a ₁ term is obtained as shown in the formula. This pole piece
By adjusting the voltage applied to the 1,1 ', since it is possible to change from the outside the value of a ₁ Section be always satisfied stigmatic coupling conditions for unclear effective filter length it can.

Next, a second present invention will be described with reference to FIG. In FIG. 2, 1,1 'is a pole piece, 2,2' is an electrode,
7a and 7b are electric field power supplies.

Pole piece pair 1, 1 'are both grounded, is kept at a reference potential V _0. The power supply 7a 'in the pole pieces 1, 1' electrodes 2,2 is independently varied relative to the potential of the individual from 7b positive and negative voltages + V _1, -V ₁ is applied. In this way, by applying the voltages applied to the electrodes 2 and 2 'so that they can be independently adjusted with respect to the potentials applied to the pole pieces 1, 1', as shown in FIG. quadrupole component of the electric field is generated, a ₁ term is obtained as shown in the formula. By adjusting the voltage applied to the electrodes 2 and 2 'individually, it is possible to vary externally the value of a ₁ Section always stigmatic coupling conditions for unclear effective filter length Can be satisfied.

[Effects of the Invention] As is clear from the above description, according to the first aspect of the present invention, Ex × B in which an electric field and a magnetic field are formed orthogonal to each other.
In the type energy filter, by providing means for applying any positive or negative equal voltage to both of the pole piece pairs opposed to each other to form a magnetic field, externally changing the value of a1 term Can be satisfied, and the astigmatic imaging condition can always be satisfied for an unclear effective filter length.

According to a second aspect of the present invention, in the first aspect,
By providing a power supply for independently changing the voltage applied to each of the pair of electrodes forming the electric field with respect to the voltage applied to the pole piece pair, the value of a1 is externally changed. It is possible to always satisfy the astigmatism-free imaging condition for an unclear effective filter length.

[Brief description of the drawings]

FIG. 1 is a configuration diagram for explaining one embodiment of an E × B type energy filter according to the first invention. FIG. 2 is a block diagram for explaining one embodiment of the E × B energy filter according to the second invention, and FIGS. 3A and 3B are electric field distributions of the E × B energy filter according to the invention. FIGS. 4 (a) to 4 (c) are diagrams for explaining a conventional E × B type energy filter, and FIG. 5 is (a).
(B) A diagram showing the trajectories of electrons in the energy filter,
FIG. 6 is a diagram for explaining an electric field distribution and a magnetic field distribution in an edge field of the energy filter. 1,1 ': Pole piece 2,2': Electrode 3: Yoke 4,5: Electric insulator 6: Exciting coil 7: Electric field power supply 8: Power supply between pole pieces

Claims (2)

(57) [Claims] In an E × B type energy filter in which an electric field and a magnetic field are formed orthogonal to each other, an arbitrary positive or negative equal voltage is applied to both pairs of pole pieces arranged to face each other to form a magnetic field. An E × B-type energy filter, characterized in that a means for applying the energy is provided. 2. A power supply for changing the voltage applied to each of the pair of electrodes forming the electric field independently of the voltage applied to the pair of pole pieces. Item 7. An E × B type energy filter according to Item 1.