JP2862330B2 - Retarding Wien filter - Google Patents

Description

Description: TECHNICAL FIELD The present invention relates to a Wien filter, and more particularly to a retarding energy filter having a deceleration field immediately before a Wien filter.

[Prior art] A Wien filter has long been used as an apparatus for analyzing the energy or mass of a charged particle beam. In particular, a Wien filter is provided with a deceleration field immediately before a Wien filter to realize high resolution. There is known a retarding Wien filter in which the speed of a charged particle beam transmitted through a filter is reduced and the speed of the charged particle beam is incident on a Wien filter.

An example of the configuration is shown in FIG. In FIG. 4, 1 is a filament, 2 is a sample, 3 is an electrode, 4 is a diaphragm, 5 is an electrode, 6 is a Wien filter, 7 is an electrode, and 8 is a detector.

In FIG. 4, a negative high voltage, for example, a voltage of about −100 kV is applied to the filament 1, and the electron beam emitted from the filament 1 passes through the sample 2 set at the set potential, the objective lens, the intermediate lens, and the like. After passing through a lens system (not shown) such as a lens, an image 12 is formed on the aperture of the diaphragm 4 placed near the electrode 3 set to the ground potential. A negative high voltage slightly higher than the filament 1, for example, −100 kV + 20 V is applied to the electrode 5 covering the Wien filter 6. Thereby, a deceleration field 9 for the electron beam is formed between the electrode 3 and the electrode 5. The image 12 formed on the stop 4 forms an image 13 at the entrance of the Wien filter 6 by the lens action of the deceleration field 9, and the image 13 is further formed as an image 14 at the exit by the lens action of the Wien filter 6. It is imaged. Further, the electron beam forming the image 14 is
An image 15 is formed on the detector 8 by the lens action of the acceleration field 10 formed between the electrode 5 and the electrode 7 at the ground potential.

With the above configuration, energy analysis or mass analysis can be performed with high resolution.

[Problems to be Solved by the Invention] By the way, the Wien filter has an electric field E _x orthogonal to each other in a plane orthogonal to an optical axis (hereinafter, referred to as a Z axis).
A magnetic field B _y was added, correct by the magnetic field bends the electric field of the beam, resulting in which is straight beam, E _x =
Only charged particles having a velocity v that satisfies vB _y (Vienna condition) go straight. The velocity v of the charged particles depends on the potential of the electric field. When the potential of the electric field is U, the charged amount of the charged particles is e, and the mass of the charged particles is m, v = (2Ue / m) ^{1 /} Represented by ² .

Then, the Vienna condition is not intended may be established only in the mere mechanical position electrodes and the magnetic poles are present, which must be satisfied in the entire area over which the electric field E _x and the magnetic field B _y Wien filter Therefore, the beam is bent and cannot go straight unless the Wien condition is satisfied, even at the edge field or at the edge of the electrode or magnetic pole called the fringe. In the past, Wien filters were often neglected in the design of Wien filters, ignoring the effects of these marginal fields, and thus the agreement between the theoretical calculations and the actual ones was extremely poor. In recent years, a filter shape that satisfies the Wien condition has been found in this marginal field, and this problem has been solved.

As described above, the velocity of the charged particles depends on the potential of the electric field, and this has revealed that there is a problem that the arrangement of the Wien filter is restricted.

That is, in FIG. 4, the voltage applied to the filament 1 is −U ₀ (U ₀ > 0), the voltage applied to the electrode 5 is −U ₀ + ΔU (ΔU> 0), and Filter 6
In When the electric field E _x and the magnetic field B _y is set to Wien condition is satisfied for the speed v _0, the deceleration field 9
, The potential in the Z-axis direction sharply changes from −U ₀ to −U ₀ +
△ rather than varying U, leads to, as shown in FIG. 5 gradually changes from -U ₀ -U ₀ + △ U. Since the intensity of the deceleration electric field in the Z-axis direction is proportional to the potential,
In the region indicated by 20 in FIG. 5, the intensity of the deceleration electric field is gradually changing. Therefore, the Wien filter is changed to the fifth
In the case of being arranged in the region of the deceleration electric field indicated by 20 in the figure, even if the shapes of the electrodes and the magnetic poles of the Wien filter are designed to satisfy the Wien condition including the edge field as described above, However, since the speed in the area 20 is different from v _{0, the} vehicle does not satisfy the Wien condition, and cannot travel straight.

Therefore, it is desired that the Wien filter 6 be disposed in a region where the potential in the Z-axis direction is uniform as shown by 21 in FIG. 5 and therefore the electric field intensity is uniform. However, in such a case, the distance between the electrode 3 and the electrode 5 must be increased, and the device becomes large. More importantly, as described above, since the lens action of the deceleration field contributes to the image transfer, when the distance of the deceleration field is increased, the image transfer is performed well. The possibility of getting lost.

The above is a discussion about the deceleration field, but the same applies to the acceleration field.

The present invention has been made to solve the above problems, and enables charged particles having a desired velocity to travel straight, image transfer is performed well, and retarding without increasing the size of the apparatus. It is intended to provide a Wien filter.

Means for Solving the Problems In order to achieve the above object, the retarding Wien filter according to claim 1 intersects when the deceleration electric field distribution and the electric field distribution or the magnetic field distribution of the Wien filter are drawn in an overlapping manner. In a region where the potential at the crossing position is sufficiently smaller than the accelerating voltage and the electric field strength and the magnetic field strength of the Wien filter are sufficiently smaller than the electric field strength and the magnetic field strength at the center thereof. It is characterized in that a filter is arranged.

The retarding Wien filter according to claim 2,
2. The retarding Wien filter according to claim 1, wherein the Wien filter has a potential in a region where the Wien filter is arranged, substantially equal to or less than five times a value at which a potential of a deceleration field is uniform. Are arranged in regions where the intensity of the edge fields of the electric field and the magnetic field is less than or equal to approximately one-tenth of the electric field intensity and the magnetic field intensity at the center of the Wien filter, respectively.

[Operation and Effect of the Invention] In both the first invention and the second invention of the present invention, the intensity of the decelerating electric field of the Wien filter is changed as well as the charged particles can be emitted from the Wien filter. Since the device can be arranged in the region, the device can be made compact, and furthermore, the Wien filter can be arranged in a device that can transfer an image satisfactorily by the lens action of the deceleration field.

Example An example will be described below.

As is clear from the above description, the condition for moving the charged particle beam straight is to satisfy the Wien condition including the edge field. Accordingly, when arranged in a region where the deceleration electric field as shown at 20 in Figure 5 the Wien filter is changed also, the electric field E _x and the magnetic field B _y of the Wien filter, including the edge field, the If the Wien condition is satisfied with respect to the velocity of the charged particles in the field, the charged particles can travel straight.

That is, the electric field E _x of the Wien filter, the magnetic field B _y is to satisfy the following two equations simultaneously, to be able to place the Wien filter to the region 20 of FIG. 5 can be seen.

_{E x = v 0 B y v} 0 = (2Ue / m) 1/2 where, U is the amount of charge in each potential deceleration field, e, m, v ₀ is a charged particle, mass, and speed.

Such conditions can be satisfied by selecting the shapes of the electrodes and magnetic poles of the Wien filter. That is, FIG. 1 is a sectional view of a Wien filter in a plane perpendicular to the Z-axis, as the applicant has been described in the application so far, the electric field E _x of the edge of the Wien filter distribution and the shape of the magnetic field B _y distribution pole 25,2
5 'inter-pole distance S _m and electrodes 27, 27' the distance between the electrodes S _e of
Is determined by the dimensions of Therefore, various values of S _m and
By simulating the trajectory of charged particles for S _e , an electrode of a Wien filter that allows charged particles to travel straight even when the Wien filter is placed in a region where the electric field strength of the deceleration field is not constant and changes The shape and pole shape can be determined.

Now, for ease of understanding, it is assumed that the electric field distribution 31 and the magnetic field distribution 33 of the Wien filter 30 have substantially the same shape as shown in FIG. This can be realized by setting S _m = S _{e in} FIG. Note that 35 in FIG.
Denotes an edge field at the entrance of the Wien filter 30, and 37 denotes an edge field at the exit.

When such a Wien filter 30 is arranged in a region where the deceleration electric field is changing, the distribution of the deceleration electric field and the electric field distribution or the magnetic field distribution of the Wien filter are superimposed as shown in FIG. In FIG. 3, reference numeral 40 denotes the potential distribution of the deceleration electric field, and -U ₀ denotes the filament 1
, And -U ₀ + ΔU is the fourth
The potential applied to the electrode 5 in the figure is shown. Further, 41 indicates an electric field distribution or magnetic field distribution of the Wien filter, respectively in the central part of the Wien filter E _x0, E _y0
It is the value.

In such a state, since the deceleration electric field is not constant at the edge field of the Wien filter, it can be concluded from the previous theory that the charged particles do not travel straight, but the deceleration electric field shown by P in FIG. in the position distribution 40 and the electric field distribution or magnetic field distribution of the Wien filter intersect, the potential of the decelerating field at point P when the U _P, as compared with the accelerating voltage -U ₀ to U _P is applied to the filament 1 Electric field strength E _xP of Wien filter at point P, small enough
When the magnetic field strength _ByP was sufficiently smaller than the central intensities _Ex0 , _By0 , it was found that charged particles could be emitted from the Wien filter. In fact, the diameter of the hole of the electrode covering the Wien filter shown by 5 in FIG.
In the case of, if satisfied all _{U P ≦ 5 × (-U 0} + △ U) E xP ≦ E x0 / 10 B yP ≦ B y0 / 10, was confirmed to emit the charged particles from the Wien filter Was.

How much U _P should actually be with respect to U ₀
E _xP and B _yP the E _x0, how to do I against B _y0 varies depending use state of the Wien filter, the number be greater the diameter of the hole of the electrode covering the Wien filter mm
In general, the above-mentioned conditions generally apply except for a special use state.

The above is a discussion about the deceleration field, but the same applies to the acceleration field.

[Brief description of the drawings]

FIG. 1 is a diagram for explaining a retarding Wien filter according to the present invention, showing an example of the shape of the electrodes and magnetic poles of the retarding Wien filter. FIG. 2 is a diagram showing the electric field distribution and magnetic field of the Wien filter in the Z-axis direction. FIG. 3 is a diagram showing a distribution, FIG. 3 is a diagram in which a potential distribution in a deceleration field is superimposed on an electric field distribution or a magnetic field distribution of a Wien filter, FIG. 4 is a diagram showing a configuration example of a retarding Wien filter, FIG. FIG. 4 is a diagram illustrating an example of a potential distribution of a deceleration field. 1 ... filament, 2 ... sample, 3 ... electrode, 4 ...
Aperture, 5 ... electrode, 6 ... Wien filter, 7 ... electrode, 8 ... detector.

Claims (2)

(57) [Claims] 1. A position where a deceleration electric field distribution and an electric field distribution or a magnetic field distribution of a Wien filter intersect when drawn in an overlapping manner, wherein the potential at the intersecting position is sufficiently smaller than an accelerating voltage, and A retarding Wien filter, wherein a Wien filter is arranged in a region where the electric field strength and the magnetic field strength of the filter are sufficiently smaller than the electric field strength and the magnetic field strength at the center thereof. 2. The Wien filter has a potential in a region where the Wien filter is arranged, substantially equal to or less than five times a value at which a potential of a deceleration field is uniform, and an edge of an electric field and a magnetic field of the Wien filter. 2. The retarding Wien filter according to claim 1, wherein the intensity of the end field is arranged in a region where the intensity of the electric field and the intensity of the magnetic field at the center of the Wien filter are each approximately 1/10 or less.